WO2010013839A1 - Battery pack and electric tool - Google Patents

Battery pack and electric tool Download PDF

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Publication number
WO2010013839A1
WO2010013839A1 PCT/JP2009/063897 JP2009063897W WO2010013839A1 WO 2010013839 A1 WO2010013839 A1 WO 2010013839A1 JP 2009063897 W JP2009063897 W JP 2009063897W WO 2010013839 A1 WO2010013839 A1 WO 2010013839A1
Authority
WO
WIPO (PCT)
Prior art keywords
secondary battery
battery cells
battery pack
cells
capacity
Prior art date
Application number
PCT/JP2009/063897
Other languages
French (fr)
Inventor
Takao Aradachi
Fumio Tashimo
Eiji Nakayama
Original Assignee
Hitachi Koki Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Koki Co., Ltd. filed Critical Hitachi Koki Co., Ltd.
Publication of WO2010013839A1 publication Critical patent/WO2010013839A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/64—Heating or cooling; Temperature control characterised by the shape of the cells
    • H01M10/643—Cylindrical cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/61—Types of temperature control
    • H01M10/613—Cooling or keeping cold
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/62—Heating or cooling; Temperature control specially adapted for specific applications
    • H01M10/623—Portable devices, e.g. mobile telephones, cameras or pacemakers
    • H01M10/6235—Power tools
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/65—Means for temperature control structurally associated with the cells
    • H01M10/651—Means for temperature control structurally associated with the cells characterised by parameters specified by a numeric value or mathematical formula, e.g. ratios, sizes or concentrations
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H01M50/207—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape
    • H01M50/213—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape adapted for cells having curved cross-section, e.g. round or elliptic
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/267—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders having means for adapting to batteries or cells of different types or different sizes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a battery pack that houses a plurality of lithium-ion secondary batteries (secondary battery cells) while holding them in electrical connection, and particularly to a battery pack with a secondary battery cell housing structure that can improve the effect of cooling a plurality of lithium-ion secondary batteries housed in the battery pack and the charge-discharge cycle life of the battery pack without upsizing the battery pack.
  • Battery packs of lithium-ion secondary batteries are beginning to be used in cordless electric tools as their drive power supply.
  • lithium-ion battery packs can have a higher nominal voltage and a higher power density than battery packs of nickel-cadmium batteries or nickel-metal-hydride batteries can. This can make lithium-ion battery packs small and light.
  • lithium-ion battery packs have excellent discharge efficiency in that they can discharge in a relatively low-temperature atmosphere, allowing a stable voltage to be applied at temperatures of a wide range.
  • lithium-ion battery packs are being expected as a power supply for electric tools, which can add to saving the weight and size of the electric tools and improving their working efficiency.
  • Patent Literature 1 proposes a technique of equipping a battery charger with a cooling fan. This technique enables a battery pack to be charged in a short time with a relatively large charging current while suppressing internal temperature rise in the battery pack.
  • Patent Literature 1 Unexamined Japanese Patent Application KOKAI Publication No. 2000-312440
  • the battery charger according to the conventional art described above has its cooling fan cool secondary battery cells in a battery pack.
  • some adjoining battery cells that are arranged more closely to each other than other adjoining cells are affected by heat produced by each other when charged, being left less cooled than secondary battery cells arranged at other positions in the battery pack. Therefore, a plurality of secondary battery cells housed in a battery pack are at a risk of causing local temperature rise.
  • a battery pack that is charged while a plurality of secondary battery cells housed therein are cooled to reduce heat production will have a severer shortening of the charge-discharge cycle life occur at a place where secondary battery cells develop a larger local temperature rise. That is, secondary battery cells that are arranged at a place in the battery pack where a lower cooling effect is obtained will sustain for a shorter charge-discharge cycle life than secondary battery cells arranged at a place where a higher cooling effect is obtained.
  • a battery pack whose constituent plurality of secondary battery cells are lithium-ion batteries is more dependent on temperature in terms of its charge-discharge cycle life.
  • Lithium-ion secondary batteries might let a copper foil liquate on their anode when they have over discharge. If the secondary batteries are charged in this state, the liquated copper might precipitate on the anode as a dendrite (dendritic precipitate) and penetrate the separators of the batteries, bringing about a risk of causing an internal short-circuit.
  • battery packs that house a plurality of lithium-ion secondary batteries (a plurality of secondary battery cells) are equipped therein with a protection IC or a microcomputer for preventing over discharge or overcharge. While a battery pack 2 discharges, such a protection circuit monitors the battery voltage of the plurality of secondary battery cells housed in the battery pack cell by each cell. The protection circuit is configured to stop the battery pack from discharging, when at least one of the plurality of secondary battery cells falls to or below a predetermined discharge voltage, determining that the at least one secondary battery cell is having over discharge. Further, while the battery pack 2 is charged, the protection circuit monitors each cell so as not to allow the battery voltage of the cell to exceed a predetermined charge voltage to suppress degradation of the battery pack due to overcharge. [0010]
  • Figs. 5 and Figs. 6 show secondary battery cell housing structures of a battery pack for electric tools according to the conventional art, wherein eight lithium-ion secondary battery cells 3a and four lithium-ion secondary battery cells 3b are housed respectively.
  • Fig. 5A and Fig. 6A show an electric tool body 1 , which is constituted by a body housing 1 a, a handle housing Ib, a head tool (e.g., a driver bit) Ic, and an electric motor Id housed in the body housing Ia.
  • FIG. 6B show a battery pack 2 that can easily be mounted to the handle housing Ib of the electric tool body.
  • the battery pack 2 houses a protection circuit board 4 and the lithium-ion secondary battery cells 3a or the lithium-ion secondary battery cells 3b.
  • Fig. 5C and Fig. 6C show the size of cylindrical lithium-ion secondary battery cells 3a and 3b in general use.
  • Fig. 5D and Fig. 6D show the states of electrical connection among the eight lithium-ion secondary battery cells 3a and the four lithium-ion secondary battery cells 3b respectively.
  • Fig. 5E and Fig. 6E show the arrangements of the eight lithium-ion secondary battery cells 3a and the four lithium-ion secondary battery cells 3b in the battery pack 2 respectively.
  • Each secondary battery cell 3a among the eight cylindrical secondary battery cells 3a shown in Fig. 5E has a size of 180 mm in diameter and 650 mm in length, and has a capacity of 1.5Ah.
  • Each two (each pair) of the secondary battery cells 3a that are electrically connected to each other in parallel constitute one battery group, and four battery groups or four pairs of secondary batteries are electrically connected to one another in series.
  • the battery pack 2 houses the protection circuit board (protection IC) 4, which prevents overcharge and over discharge.
  • the battery pack 2 shown in Figs. 6 has a nominal voltage of 14.4V and a nominal capacity of 3.0 Ah/battery cell as well as the battery pack 2 shown in Figs. 5.
  • the battery pack 2 shown in Figs. 6 houses four cylindrical secondary battery cells 3b in series electrical connection, which are different from the secondary battery cells 3a shown in Figs. 5 in the size (e.g., 260 mm in diameter x 650 mm in length) but have a capacity of 3.0Ah.
  • the battery pack 2 shown in Figs. 6 allows a larger space to be formed between the battery cells 3b and the housing 2a of the battery pack 2.
  • an object of the present invention is to provide a battery pack that can overcome the problems of the conventional art described above by having a secondary battery cell housing structure that can improve the effect of cooling secondary battery cells housed in the battery pack without upsizing the battery pack 2.
  • Another object of the present invention is to provide a battery pack that can achieve a compact secondary battery cell housing structure.
  • a battery pack houses a plurality of cylindrical secondary battery cells while holding them in electrical connection
  • the plurality of secondary battery cells include, as secondary battery cells with two kinds of larger and smaller diameters, a plurality of first secondary battery cells that have a smaller diameter and a plurality of second secondary battery cells that have a larger diameter
  • the plurality of first secondary battery cells and the plurality of second secondary battery cells are arranged in the same rows respectively, with the center axes of the first secondary battery cells and of the second secondary battery cells extending in parallel
  • the plurality of secondary battery cells are arranged in a staggered formation as a whole, when seen from the direction to which their center axes extend.
  • the plurality of first secondary battery cells are electrically connected in parallel.
  • the first secondary battery cells have an equal capacity to each other.
  • the plurality of second secondary battery cells are electrically connected in series.
  • the second secondary battery cells have an equal capacity to each other.
  • the total capacity of the plurality of first secondary battery cells that are electrically connected in parallel is equal to the capacity of each second secondary battery cell.
  • the second secondary battery cells are arranged in a row with their outer wall in contact, and the first secondary battery cells are arranged in a row, each first secondary battery cell being located between a pair of adjoining second secondary battery cells with its outer wall in contact with the outer wall of each of the pair of second secondary battery cells and with an interval equal to the diameter of the second secondary battery cell secured between the center axes of the first secondary battery cells.
  • the first secondary battery cells are arranged in a row with their outer wall in contact
  • the second secondary battery cells are arranged in a row, each second secondary battery cell being located between a pair of adjoining first secondary battery cells with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells and with an interval equal to double the diameter of the first secondary battery cell secured between the center axes of the second secondary battery cells.
  • an electric tool in another aspect of the present invention, includes the battery pack according to claim 1, which is detachably mounted in a handle housing of the electric tool.
  • the present invention makes size-varied lithium-ion secondary batteries (secondary battery cells) in electrical connection be housed in a battery pack, enabling a large space to be provided between adjoining lithium-ion secondary batteries, with some degree of arbitrariness in the arrangement of the lithium-ion secondary batteries in the battery pack.
  • This can provide a battery pack with an improved effect of cooling lithium-ion secondary batteries, without enlarging the volume of occupation of the lithium-ion secondary batteries.
  • Figs. IA to IE are configuration diagrams showing a battery pack according to one embodiment of the present invention.
  • Figs. 2A to 2E are configuration diagrams showing a battery pack according to another embodiment of the present invention.
  • Figs. 3 A to 3E are configuration diagrams showing generalized forms of the structures for housing secondary battery cells and generalized states of electrical connection among secondary battery cells of the battery pack according to the embodiments of the present invention.
  • Fig. 4 is a configuration diagram showing an example state of electrical connection among secondary battery cells in the battery pack according to one embodiment of the present invention.
  • Figs. 5A to 5E are configuration diagrams showing an example battery pack according to a conventional art.
  • Figs. 6A to 6E are configuration diagrams showing another example battery pack according to the conventional art.
  • Figs. 1 show a structure of a battery pack according to one embodiment of the present invention for housing lithium-ion secondary battery cells (hereinafter, simply referred to as "secondary battery cell").
  • second battery cell lithium-ion secondary battery cells
  • Fig. IA shows an electric tool body 1, which is constituted by a body housing Ia, a handle housing Ib, a head tool (e.g., a driver bit) Ic, and an electric motor Id housed in the body housing Ia.
  • Fig. IB shows a battery pack 2, which is detachably mounted in the handle housing Ib of the electric tool body.
  • the battery pack 2 houses a protection circuit board 4 and two kinds of cylindrical first and second secondary battery cells 3a and 3b having different diameters.
  • Fig. 1C shows the two kinds of cylindrical first and second secondary battery cells 3a and 3b having different diameters and capacities.
  • Fig. IA shows an electric tool body 1, which is constituted by a body housing Ia, a handle housing Ib, a head tool (e.g., a driver bit) Ic, and an electric motor Id housed in the body housing Ia.
  • Fig. IB shows a battery pack 2, which is detachably mounted in the handle housing Ib of the electric
  • Fig. IE shows the arrangement of the two first secondary battery cells 3a and the three second secondary battery cells 3b in the battery pack 2.
  • the battery pack 2 houses two kinds of first and second secondary battery cells 3a and 3b that have different diameters between the different kinds and an equal capacity within the same kind.
  • three second secondary battery cells 3b each of which has a size of 260 mm in diameter x 650 mm in length and a capacity of 3.0Ah, are electrically connected in series, and some sets of first secondary battery cells 3a, each set including two first secondary battery cells 3a, each of which has a size of 180 mm in diameter x 650 mm in length and a capacity of 1.5Ah, are electrically connected in parallel with each other in each set.
  • Such a set of two first secondary battery cells 3a that are electrically connected in parallel with each other constitute one battery group.
  • the three second secondary battery cells 3b and one battery group are housed in a housing 2a of the battery pack 2 in series electrical connection.
  • these three second secondary battery cells 3b and two (one group of) first secondary battery cells 3a are arranged in the same rows (an upper row and a lower row) respectively, with the center axis of each cell 3b and 3a extending in parallel.
  • These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends.
  • the second secondary battery cells 3b are arranged in a row with their outer wall in contact, while the first secondary battery cells 3a are arranged in a row, each first secondary battery cell 3a being located between a pair of adjoining second secondary battery cells 3b with its outer wall in contact with the outer wall of each of the pair of second secondary battery cells 3b and with an interval equal to the diameter of one second secondary battery cell 3b secured between the centers of the cells 3a.
  • these first and second secondary battery cells 3a and 3b are housed compactly in the housing 2a of the battery pack 2 with a high housing efficiency, with a large space 2b provided between the adjoining first secondary battery cells 3a to provide a higher effect of cooling inside the battery pack 2.
  • the two (or a plurality of) first secondary battery cells 3a that are in parallel electrical connection have an equal capacity to each other (one another). Further, in the present embodiment, with a higher effect of cooling provided inside the battery pack 2, the first secondary battery cells 3a will undergo degradation at the same pace. Hence, in the present embodiment, when the battery pack 2 discharges, it is possible to prevent an electric current from flowing into at least one of two first secondary battery cells 3a that are in parallel electrical connection from the others of first secondary battery cells 3a that are in parallel electrical connection.
  • two first secondary battery cells 3a in parallel electrical connection have a total capacity that is equal to the capacity of each of the second secondary battery cells 3b that are in series electrical connection.
  • the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves undergo degradation at the same pace, as described above.
  • the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge as the two (or a plurality of) first secondary battery cells 3a in parallel electrical connection and at least one of the three (or a plurality of) second secondary battery cells 3b in series electrical connection fall down to or below a predetermined discharge voltage.
  • the battery pack 2 when the battery pack 2 is charged, the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves are charged at the same pace, preventing the battery pack 2 from being overcharged as one battery pair consisting of the two first secondary battery cells 3a in parallel electrical connection and at least one of the three second secondary battery cells 3b in series electrical connection rise to or above their respective predetermined charge voltages . [0039] In this way, the battery pack 2 according to the present embodiment can suppress its degradation and prolong its duration of life.
  • the battery pack 2 can obtain a sufficient cooling effect, when it is internally cooled inside the housing 2a of the battery pack 2 by a cooling fan or the like provided on a battery charger, purging the warm air caused by heat production by the first secondary battery cells 3a and second secondary battery cells 3b from the inside of the housing 2a.
  • the battery pack 2 can be small, housing the first and second secondary battery cells 3a and 3b in an arrangement that allows a large space 2b to be formed between the adjoining first secondary battery cells 3a in the battery pack 2.
  • the battery pack 2 can suppress its temperature rise when the head tool Ic induces over discharge, without requiring the battery capacity to be changed or the capacity for housing the secondary batteries (i.e., the size of the battery pack 2) to be expanded.
  • This can eliminate temperature unevenness between the first secondary battery cells 3a and among the second secondary battery cells 3 b that are housed in the battery pack 2.
  • This can inhibit imbalanced deepening of degradation on some part of the first secondary battery cells 3a and of the second secondary battery cells 3b when they charge or discharge, improving the charge-discharge cycle life of the battery pack 2.
  • Figs. 2 show a secondary battery cell housing structure of a battery pack according to another embodiment of the present invention.
  • the battery pack 2 houses two kinds of first and second secondary battery cells 3a and 3b that have different diameters between the different kinds and the same capacity within the same kind.
  • two second secondary battery cells 3b each of which has a size of 260 mm in diameter x 650 mm in length and a capacity of 3.0Ah, are electrically connected in series
  • two sets of first secondary battery cells 3a each set including two first secondary battery cells 3a, each of which has a size of 180 mm in diameter x 650 mm in length and a capacity of 1.5Ah, are electrically connected in parallel with each other in each set.
  • Such a set of two first secondary battery cells 3a that are electrically connected in parallel with each other constitute one battery group.
  • the two second secondary battery cells 3b and two battery groups are housed in the housing 2a of the battery pack 2 in series electrical connection.
  • these two second secondary battery cells 3b and four (two groups of) first secondary battery cells 3a are arranged in the same rows (a lower row and an upper row) respectively, with the center axis of all the cells 3b and 3a extending in parallel.
  • These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends.
  • first secondary battery cells 3a are arranged in a row with their outer wall in contact, while the second secondary battery cells 3b are arranged in a row, each second secondary battery cell 3b being located between a pair of adjoining first secondary battery cells 3a with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells 3a and with an interval equal to double the diameter of one first secondary battery cell 3a secured between the centers of the cells 3b.
  • first secondary battery cells 3a are arranged in a row with their outer wall in contact
  • second secondary battery cells 3b are arranged in a row, each second secondary battery cell 3b being located between a pair of adjoining first secondary battery cells 3a with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells 3a and with an interval equal to double the diameter of one first secondary battery cell 3a secured between the centers of the cells 3b.
  • each first secondary battery cell 3a of the two (or a plurality of) first secondary battery cells 3a that are in parallel electrical connection have an equal capacity to each other (one another). Further, in the present embodiment, the first secondary battery cells 3a. will undergo degradation at the same pace as described above.
  • the battery pack 2 when the battery pack 2 discharges, it is possible to prevent an electric current from flowing into at least one of the first secondary battery cells 3a that are in parallel electrical connection from another first secondary battery cells 3a that are in parallel electrical connection. Further, in the present embodiment, when the battery pack 2 is charged, it is possible to prevent a first secondary battery cells 3a in parallel electrical connection and with a smaller capacity from being overcharged along with another first secondary battery cells 3a in parallel electrical connection and with a larger capacity being charged to the full capacity. [0045]
  • two first secondary battery cells 3a in parallel electrical connection have a total capacity that is equal to the capacity of each of the second secondary battery cells 3b that are in series electrical connection. Further, in the present embodiment, with no temperature unevenness, the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves undergo degradation at the same pace. Accordingly, in the present embodiment, when the battery pack 2 discharges, the first secondary battery cells 3a and the second secondary battery cells 3b discharge at the same pace within themselves respectively.
  • the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge as the two (or a plurality of) first secondary battery cells 3a in parallel electrical connection in each of the two battery groups and at least one of the two (or a plurality of) second secondary battery cells 3b in series electrical connection fall down to or below a predetermined discharge voltage.
  • the battery pack 2 when the battery pack 2 charges, the first secondary battery cells 3a and the second secondary battery cells 3b charge at the same pace within themselves respectively, which prevents the battery pack 2 from causing over discharge as the two (or a plurality of) first secondary battery cells 3a in parallel electrical connection in each of the two battery groups and at least one of the two second secondary battery cells 3b in series electrical connection rise to or above a predetermined charge voltage.
  • the battery pack 2 according to the present embodiment can suppress its degradation.
  • the battery pack 2 can have a battery capacity and a capacity for housing the secondary battery cells (i.e., the size of the battery pack 2) that is comparable to those of the battery pack 2 according to the conventional art as well as the embodiment shown in Figs. 1 , still can have thereinside a larger space 2b between the adjoining second secondary battery cells 3b.
  • the battery pack 2 can obtain a sufficient cooling effect, when it is internally cooled by a cooling fan or the like provided on a battery charger, purging the warm air caused by heat production by the first secondary battery cells 3a and second secondary battery cells 3b outside the housing 2a of the battery pack 2 from the inside of the housing 2a.
  • the battery pack 2 can be small, housing the first and second secondary battery cells 3a and 3b in an arrangement that allows a large space 2b between the adjoining second secondary battery cells 3b in the battery pack 2.
  • the battery pack 2 can suppress its temperature rise when the head tool Ic induces over discharge, without requiring the battery capacity to be changed or the capacity for housing the secondary batteries (i.e., the size of the battery pack 2) to be expanded. This can eliminate temperature unevenness between the first secondary battery cells 3a and between the second secondary battery cells 3b that are housed in the battery pack 2.
  • Figs. 3 show generalized forms of the secondary battery cell housing structures of the battery pack according to the embodiments of the present invention and generalized states of electrical connection among secondary battery cells.
  • Fig. 3A shows a generalized form of the secondary battery cell housing structure of the battery pack according to the conventional art shown in Figs. 5.
  • Fig. 3B and Fig. 3C show a generalized form of the secondary battery cell housing structures of the battery pack shown in Figs. 1 and Figs. 2 respectively.
  • Fig. 3A shows a generalized form of the secondary battery cell housing structure of the battery pack according to the conventional art shown in Figs. 5.
  • Fig. 3B and Fig. 3C show a generalized form of the secondary battery cell housing structures of the battery pack shown in Figs. 1 and Figs. 2 respectively.
  • FIG. 3D shows a state of electrical connection among "a” number of second secondary battery cells 3 b and "b" number of first secondary battery cells 3 a.
  • Fig. 3 E shows a state of electrical connection among "c" number of first secondary battery cells 3a and "d” number of second secondary battery cells 3b.
  • the battery pack 2 houses 2n first secondary battery cells 3a ("n" being a natural number) in the upper and lower rows each in the housing 2a.
  • n being a natural number
  • these plurality of second secondary battery cells 3b and plurality of (plural groups of) first secondary battery cells 3a are arranged in the same rows (an upper row and a lower row) respectively, with the center axis of all the cells 3b and 3a extending in parallel.
  • These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends.
  • the second secondary battery cells 3b are arranged in a row with their outer wall in contact.
  • the first secondary battery cells 3a are arranged in a row, each first secondary battery cell 3a being located between a pair of adjoining second secondary battery cells 3b with its outer wall in contact with the outer wall of each of the pair of second secondary battery cells 3b and with an interval equal to the diameter of one second secondary battery cell 3b secured between the centers of the cells 3a.
  • these first and second secondary battery cells 3a and 3b are housed in the housing 2a of the battery pack 2 with a high housing efficiency to make the battery pack 2 small, as well as the conventional art shown in Fig. 3A.
  • d a natural number indicating the total number of second secondary battery cells 3b, which constitute a plurality of second secondary battery cells 3b in series electrical connection
  • these plurality of second secondary battery cells 3b and plurality of (plural groups of) first secondary battery cells 3a are arranged in the same rows (a lower row and an upper row) respectively, with the center axis of all the cells 3b and 3a extending in parallel.
  • These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends.
  • first secondary battery cells 3a are arranged in a row with their outer wall in contact, while the second secondary battery cells 3b are arranged in a row, each second secondary battery cell 3b being located between a pair of adjoining first secondary battery cells 3a with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells 3a and with an interval equal to double the diameter of one first secondary battery cell 3a secured between the centers of the cells 3b.
  • these first and second secondary battery cells 3a and 3b are housed in the housing 2a of the battery pack 2 with a high housing efficiency to make the battery pack 2 small, as well as the conventional art shown in Fig. 3A.
  • the space in the battery pack 2 between adjoining first secondary battery cells 3a is small. Therefore, heat conduction between adjoining first secondary battery cells 3a is very influential. Further, in the secondary battery cell housing structure shown in Fig. 3A, the space between the first secondary battery cells 3a and the housing 2a of the battery pack 2 is small. Accordingly, even if the battery pack 2 is internally cooled by a cooling fan or the like provided on a battery charger, the air warmed by heat produced by the first secondary battery cells 3a remains inside the housing 2a of the battery pack 2, resulting in a poor cooling effect. [0057]
  • the secondary battery cell housing structure of the battery pack (or the arrangement of the secondary battery cells in the battery pack) shown in Figs. 3B and 3D can provide a large space 2b in the battery pack 2 between adjoining first secondary battery cells 3a, without making the capacity for housing secondary battery cells (i.e., the size of the battery pack 2) much larger than that of the battery pack 2 shown in Fig. 3A (note that the battery pack 2 shown in Figs. 1 has substantially the same housing capacity as the battery pack 2 shown in Figs. 5).
  • the secondary battery cell housing structure of the battery pack (or the arrangement of the secondary battery cells in the battery pack) shown in Figs. 3C and 3E provides the battery pack with a capacity for housing secondary battery cells that is comparable to that of the battery pack 2 shown in Fig. 3A. That is, the battery pack 2 shown in Figs.
  • the secondary battery cell housing structure of the battery pack shown in Figs. 3C and 3E can provide a larger space 2b between adjoining secondary battery cells 3b. This structure will not confine the air warmed by heat produced by the first secondary battery cells 3a and second secondary battery cells 3b in the housing 2a of the battery pack 2 when the battery pack 2 is internally cooled by a cooling fan or the like provided on a battery charger, achieving a sufficient cooling effect. Hence, this secondary battery cell housing structure of the battery pack is excellent in the cooling effect. [0059]
  • Fig. 4 shows a state of electrical connection among secondary battery cells in a battery pack according to one embodiment of the present invention.
  • one group of first secondary battery cells 3a' in parallel electrical connection may not necessarily consist of two (a pair of) first secondary battery cells 3a', but three or more first secondary battery cells 3a' in parallel electrical connection. Not all second secondary battery cells 3b in series electrical connection may be connected continuously. The total capacity of some first secondary battery cells 3a' in parallel electrical connection is equal to the capacity of each second secondary battery cell 3b in series electrical connection.
  • first secondary battery cells 3a' and second secondary battery cells 3b can also provide a large space 2b between adjoining first secondary battery cells 3a', by housing first secondary battery cells 3a' and second secondary battery cells 3b in the battery pack 2 by arranging the first and second secondary battery cells 3a' and 3b in the same rows (a lower row and an upper row) respectively while making the center axis of the cells 3a' and 3b extend in parallel and in a manner that the cells 3a' and 3b make a staggered formation as a whole when seen from the direction to which their center axis extends.
  • This can provide temperature uniformity among the first secondary battery cells 3a' and among the second secondary battery cells 3b respectively, subjecting them to equal-paced degradation.
  • the structure shown in Fig. 4 can prevent a first secondary battery cells 3a' in parallel electrical connection and with a smaller capacity from being overcharged along with another first secondary battery cells 3a' in parallel electrical connection and with a larger capacity being charged to the full capacity.
  • the total capacity of two first secondary battery cells 3a' in parallel electrical connection is equal to the capacity of each second secondary battery cell 3 b in series electrical connection. Accordingly, when the battery pack 2 discharges, the first secondary battery cells 3a' within themselves and the second secondary battery cells 3b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge.
  • the first secondary battery cells 3a' within themselves and the second secondary battery cells 3 b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge as a plurality of first secondary battery cells 3a in parallel electrical connection in each of the two battery groups and at least one of a plurality of second secondary battery cells 3b in series electrical connection fall down to or below a predetermined discharge voltage.
  • the structure shown in Fig. 4 can also improve the charge-discharge cycle life of the battery pack 2.
  • the battery pack according to the embodiments of the present invention is constituted by secondary battery cells, which include at least two kinds of smaller and larger first and second secondary battery cells 3a and 3b.
  • the first and second secondary battery cells 3a and 3b are arranged in the same rows respectively with the center axis of the cells 3a and 3b extending in parallel and to make a staggered formation as a whole when seen from the direction to which their center axis extends.
  • This arrangement can make the battery pack 2 small, by allowing the first and second secondary battery cells 3a and 3b to be housed in a way to provide a large space 2b in the battery pack 2 between adjoining first secondary battery cells 3a or between adjoining second secondary battery cells 3b.
  • this arrangement can improve the effect of cooling the interior of the battery pack 2, without enlarging the capacity for housing secondary battery cells, i.e., the size of the battery pack.
  • This feature of the present invention can eliminate temperature unevenness among first secondary battery cells 3a and among second secondary battery cells 3b respectively, to make them undergo degradation at the same pace.
  • the battery pack 2 can improve its charge-discharge cycle life.
  • the embodiments described above have been examples wherein the battery pack 2 is used in an electric tool. Not being limited to these embodiments, the battery pack according to the technical idea of the present invention will also be effective when embodied as a battery pack for other electric appliances such as personal computers.
  • the embodiments described above have been examples wherein the constituent secondary battery cells are lithium-ion secondary batteries, whose charge-discharge cycle life is temperature-dependent.
  • the battery pack according to the technical idea of the present invention may use other kinds of secondary batteries such as nickel-cadmium batteries and nickel-metal-hydride batteries.

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Abstract

Provided is a battery pack having a housing structure that can improve the effect of cooling lithium-ion secondary battery cells housed. A plurality of cylindrical secondary battery cells (3a, 3b) include a plurality of first secondary battery cells (3a) with a smaller diameter and a plurality of second secondary battery cells (3b) with a larger diameter. The plurality of first secondary battery cells and the plurality of second secondary battery cells are arranged in the same rows respectively, with the center axis of the cells and cells extending in parallel. The plurality of secondary battery cells are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends. This arrangement can increase the effect of heat dissipation from the lithium-ion secondary battery cells, without enlarging the capacity of a battery pack (2) for housing secondary battery cells.

Description

DESCRIPTION
Title of the Invention
BATTERY PACK AND ELECTRIC TOOL
Technical Field [0001]
The present invention relates to a battery pack that houses a plurality of lithium-ion secondary batteries (secondary battery cells) while holding them in electrical connection, and particularly to a battery pack with a secondary battery cell housing structure that can improve the effect of cooling a plurality of lithium-ion secondary batteries housed in the battery pack and the charge-discharge cycle life of the battery pack without upsizing the battery pack.
Background Art [0002]
Battery packs of lithium-ion secondary batteries are beginning to be used in cordless electric tools as their drive power supply. In cordless electric tools, lithium-ion battery packs can have a higher nominal voltage and a higher power density than battery packs of nickel-cadmium batteries or nickel-metal-hydride batteries can. This can make lithium-ion battery packs small and light. Further, lithium-ion battery packs have excellent discharge efficiency in that they can discharge in a relatively low-temperature atmosphere, allowing a stable voltage to be applied at temperatures of a wide range. Hence, lithium-ion battery packs are being expected as a power supply for electric tools, which can add to saving the weight and size of the electric tools and improving their working efficiency. [0003]
Battery packs of nickel-cadmium batteries or nickel-metal-hydride batteries or the like described above can be charged in a short time, if charged with a relatively large charging current. Meanwhile, in battery packs of these kinds, the secondary battery cells as the lithium-ion secondary batteries in the battery pack produce considerable heat when they are charged. The produced heat becomes one of the factors that shortens the charge-discharge cycle life of the secondary battery cells. Hence, in order to allow a battery pack to be charged in a short time with a large charging current, Patent Literature 1 identified below proposes a technique of equipping a battery charger with a cooling fan. This technique enables a battery pack to be charged in a short time with a relatively large charging current while suppressing internal temperature rise in the battery pack. [0004]
Patent Literature 1 : Unexamined Japanese Patent Application KOKAI Publication No. 2000-312440
Summary of Invention [0005] The battery charger according to the conventional art described above has its cooling fan cool secondary battery cells in a battery pack. In some arrangements of secondary battery cells in a battery pack, however, some adjoining battery cells that are arranged more closely to each other than other adjoining cells are affected by heat produced by each other when charged, being left less cooled than secondary battery cells arranged at other positions in the battery pack. Therefore, a plurality of secondary battery cells housed in a battery pack are at a risk of causing local temperature rise. [0006]
Hence, a battery pack that is charged while a plurality of secondary battery cells housed therein are cooled to reduce heat production will have a severer shortening of the charge-discharge cycle life occur at a place where secondary battery cells develop a larger local temperature rise. That is, secondary battery cells that are arranged at a place in the battery pack where a lower cooling effect is obtained will sustain for a shorter charge-discharge cycle life than secondary battery cells arranged at a place where a higher cooling effect is obtained.
[0007]
Especially, a battery pack whose constituent plurality of secondary battery cells are lithium-ion batteries is more dependent on temperature in terms of its charge-discharge cycle life. Lithium-ion secondary batteries might let a copper foil liquate on their anode when they have over discharge. If the secondary batteries are charged in this state, the liquated copper might precipitate on the anode as a dendrite (dendritic precipitate) and penetrate the separators of the batteries, bringing about a risk of causing an internal short-circuit. [0008]
In a battery pack that includes a plurality of secondary battery cells that are in different degrees of degradation, secondary battery cells in a higher degree of degradation will have a larger voltage drop applied when they discharge than the other secondary battery cells in a medium or a lower degree of degradation. [0009]
Generally, battery packs that house a plurality of lithium-ion secondary batteries (a plurality of secondary battery cells) are equipped therein with a protection IC or a microcomputer for preventing over discharge or overcharge. While a battery pack 2 discharges, such a protection circuit monitors the battery voltage of the plurality of secondary battery cells housed in the battery pack cell by each cell. The protection circuit is configured to stop the battery pack from discharging, when at least one of the plurality of secondary battery cells falls to or below a predetermined discharge voltage, determining that the at least one secondary battery cell is having over discharge. Further, while the battery pack 2 is charged, the protection circuit monitors each cell so as not to allow the battery voltage of the cell to exceed a predetermined charge voltage to suppress degradation of the battery pack due to overcharge. [0010]
Again, in a battery pack that includes more than one secondary battery cells that are in different degrees of degradation, secondary battery cells in a higher degree of degradation will have a voltage drop applied earlier than the others when they discharge. Accordingly, such secondary battery cells will fall to the predetermined discharge voltage described above in a shorter time. As a result, these secondary battery cells will stop discharging in a shorter time. In this way, unevenness among the secondary battery cells in the degree of being cooled will reduce the discharge capacity or the charge capacity of the battery pack on the whole, which will lead to a shorter charge-discharge cycle life of the battery pack. [0011]
This problem will be explained with a specific example of a battery pack for electric tools according to a conventional art shown in Figs. 5 and Figs. 6. Figs. 5 and Figs. 6 show secondary battery cell housing structures of a battery pack for electric tools according to the conventional art, wherein eight lithium-ion secondary battery cells 3a and four lithium-ion secondary battery cells 3b are housed respectively. Fig. 5A and Fig. 6A show an electric tool body 1 , which is constituted by a body housing 1 a, a handle housing Ib, a head tool (e.g., a driver bit) Ic, and an electric motor Id housed in the body housing Ia. Fig. 5B and Fig. 6B show a battery pack 2 that can easily be mounted to the handle housing Ib of the electric tool body. The battery pack 2 houses a protection circuit board 4 and the lithium-ion secondary battery cells 3a or the lithium-ion secondary battery cells 3b. Fig. 5C and Fig. 6C show the size of cylindrical lithium-ion secondary battery cells 3a and 3b in general use. Fig. 5D and Fig. 6D show the states of electrical connection among the eight lithium-ion secondary battery cells 3a and the four lithium-ion secondary battery cells 3b respectively. Fig. 5E and Fig. 6E show the arrangements of the eight lithium-ion secondary battery cells 3a and the four lithium-ion secondary battery cells 3b in the battery pack 2 respectively. [0012]
Each secondary battery cell 3a among the eight cylindrical secondary battery cells 3a shown in Fig. 5E has a size of 180 mm in diameter and 650 mm in length, and has a capacity of 1.5Ah. Each two (each pair) of the secondary battery cells 3a that are electrically connected to each other in parallel constitute one battery group, and four battery groups or four pairs of secondary batteries are electrically connected to one another in series. The battery pack 2 houses the protection circuit board (protection IC) 4, which prevents overcharge and over discharge. In this conventional art, the lithium-ion batteries have a nominal voltage of 14.4V (3.6V/group x four groups), and a nominal capacity of 3.0Ah /group (1.5Ah x two cells = 3.0Ah). [0013]
In the arrangement of the secondary battery cells 3a in the battery pack 2 shown in Figs. 5B and 5E, adjoining secondary battery cells 3a have a small space between them to make heat conduction between them very influential. In the arrangement of the first secondary battery cells 3a in the battery pack 2 shown in Figs. 5B and 5E, there is a small space formed between the battery cells 3a and a housing 2a of the battery pack 2. Accordingly, with this arrangement of the first secondary battery cells 3a, even if a cooling fan or the like provided on a battery charger cools the interior of the battery pack 2, it is structurally impossible to obtain a sufficient cooling effect because the air that is warmed by heat produced by the first secondary battery cells 3a stays inside the housing 2a of the battery pack 2. [0014]
Meanwhile, the battery pack 2 shown in Figs. 6 has a nominal voltage of 14.4V and a nominal capacity of 3.0 Ah/battery cell as well as the battery pack 2 shown in Figs. 5. The battery pack 2 shown in Figs. 6 houses four cylindrical secondary battery cells 3b in series electrical connection, which are different from the secondary battery cells 3a shown in Figs. 5 in the size (e.g., 260 mm in diameter x 650 mm in length) but have a capacity of 3.0Ah. As compared with the example of the conventional art shown in Figs. 5, the battery pack 2 shown in Figs. 6 allows a larger space to be formed between the battery cells 3b and the housing 2a of the battery pack 2. This structure makes it easier for air to flow between adjoining battery cells 3b, providing a higher cooling effect. However, the problem is, the battery pack 2 shown in Figs. 6 itself has a larger size because it has a larger space for housing the secondary battery cells 3b therein. [0015]
Accordingly, an object of the present invention is to provide a battery pack that can overcome the problems of the conventional art described above by having a secondary battery cell housing structure that can improve the effect of cooling secondary battery cells housed in the battery pack without upsizing the battery pack 2. [0016]
Another object of the present invention is to provide a battery pack that can achieve a compact secondary battery cell housing structure. [0017]
The present invention disclosed for solving the problems described above has the following typical aspects. [0018]
In one aspect of the present invention, a battery pack houses a plurality of cylindrical secondary battery cells while holding them in electrical connection, where the plurality of secondary battery cells include, as secondary battery cells with two kinds of larger and smaller diameters, a plurality of first secondary battery cells that have a smaller diameter and a plurality of second secondary battery cells that have a larger diameter, the plurality of first secondary battery cells and the plurality of second secondary battery cells are arranged in the same rows respectively, with the center axes of the first secondary battery cells and of the second secondary battery cells extending in parallel, and the plurality of secondary battery cells are arranged in a staggered formation as a whole, when seen from the direction to which their center axes extend. [0019] In another aspect of the present invention, the plurality of first secondary battery cells are electrically connected in parallel. [0020]
In another aspect of the present invention, the first secondary battery cells have an equal capacity to each other. [0021]
In another aspect of the present invention, the plurality of second secondary battery cells are electrically connected in series. [0022]
In another aspect of the present invention, the second secondary battery cells have an equal capacity to each other. [0023]
In another aspect of the present invention, the total capacity of the plurality of first secondary battery cells that are electrically connected in parallel is equal to the capacity of each second secondary battery cell. [0024]
In another aspect of the present invention, the first secondary battery cells and the second secondary battery cells satisfy a relationship of a=b+l, where "b" is a natural number indicating the number of the first secondary battery cells and "a" is a natural number indicating the number of the second secondary battery cells, and where a=(4n+l)/3 and b=l/3χ(4n-2), where "n" is a natural number. [0025]
In another aspect of the present invention, the second secondary battery cells are arranged in a row with their outer wall in contact, and the first secondary battery cells are arranged in a row, each first secondary battery cell being located between a pair of adjoining second secondary battery cells with its outer wall in contact with the outer wall of each of the pair of second secondary battery cells and with an interval equal to the diameter of the second secondary battery cell secured between the center axes of the first secondary battery cells. [0026]
In another aspect of the present invention, the first secondary battery cells and the second secondary battery cells satisfy a relationship of c=2d, where "c" is a natural number indicating the number of the first secondary battery cells and "d" is a natural number indicating the number of the second secondary battery cells, and where c=2n and d=n, where "n" is a natural number. [0027]
In another aspect of the present invention, the first secondary battery cells are arranged in a row with their outer wall in contact, and the second secondary battery cells are arranged in a row, each second secondary battery cell being located between a pair of adjoining first secondary battery cells with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells and with an interval equal to double the diameter of the first secondary battery cell secured between the center axes of the second secondary battery cells. [0028]
In another aspect of the present invention, an electric tool includes the battery pack according to claim 1, which is detachably mounted in a handle housing of the electric tool. [0029]
As described above, the present invention makes size-varied lithium-ion secondary batteries (secondary battery cells) in electrical connection be housed in a battery pack, enabling a large space to be provided between adjoining lithium-ion secondary batteries, with some degree of arbitrariness in the arrangement of the lithium-ion secondary batteries in the battery pack. This can provide a battery pack with an improved effect of cooling lithium-ion secondary batteries, without enlarging the volume of occupation of the lithium-ion secondary batteries.
These objects and other objects and advantages of the present invention will become more apparent upon reading of the following detailed description and the accompanying drawings.
Brief Description of Drawings [0030]
Figs. IA to IE are configuration diagrams showing a battery pack according to one embodiment of the present invention.
Figs. 2A to 2E are configuration diagrams showing a battery pack according to another embodiment of the present invention. Figs. 3 A to 3E are configuration diagrams showing generalized forms of the structures for housing secondary battery cells and generalized states of electrical connection among secondary battery cells of the battery pack according to the embodiments of the present invention.
Fig. 4 is a configuration diagram showing an example state of electrical connection among secondary battery cells in the battery pack according to one embodiment of the present invention.
Figs. 5A to 5E are configuration diagrams showing an example battery pack according to a conventional art.
Figs. 6A to 6E are configuration diagrams showing another example battery pack according to the conventional art.
Best Mode for Carrying Out the Invention [0031]
Embodiments of a battery pack according to the present invention will now be explained below with reference to Figs. 1 and Figs. 2. Note that any members that have the same function in Figs. 1 to Fig. 4 explaining the embodiments and in Figs. 5 and Figs. 6 related to the conventional art described above may be denoted by the same reference numeral to avoid repetitive explanation. [0032]
Figs. 1 show a structure of a battery pack according to one embodiment of the present invention for housing lithium-ion secondary battery cells (hereinafter, simply referred to as "secondary battery cell"). The present embodiment to be described below and other embodiments of the present invention are all examples wherein a battery pack that houses secondary battery cells is used for an electric tool. [0033]
Among Figs. 1 for explaining a battery pack, Fig. IA shows an electric tool body 1, which is constituted by a body housing Ia, a handle housing Ib, a head tool (e.g., a driver bit) Ic, and an electric motor Id housed in the body housing Ia. Fig. IB shows a battery pack 2, which is detachably mounted in the handle housing Ib of the electric tool body. The battery pack 2 houses a protection circuit board 4 and two kinds of cylindrical first and second secondary battery cells 3a and 3b having different diameters. Fig. 1C shows the two kinds of cylindrical first and second secondary battery cells 3a and 3b having different diameters and capacities. Fig. ID shows a state of electrical connection between/among two (or a plurality of) first secondary battery cells 3a and three (or a plurality of) second secondary battery cells 3b. Fig. IE shows the arrangement of the two first secondary battery cells 3a and the three second secondary battery cells 3b in the battery pack 2. [0034]
As shown in Fig. 1C and Fig. ID, the battery pack 2 according to the present embodiment houses two kinds of first and second secondary battery cells 3a and 3b that have different diameters between the different kinds and an equal capacity within the same kind. Here, three second secondary battery cells 3b, each of which has a size of 260 mm in diameter x 650 mm in length and a capacity of 3.0Ah, are electrically connected in series, and some sets of first secondary battery cells 3a, each set including two first secondary battery cells 3a, each of which has a size of 180 mm in diameter x 650 mm in length and a capacity of 1.5Ah, are electrically connected in parallel with each other in each set. Such a set of two first secondary battery cells 3a that are electrically connected in parallel with each other constitute one battery group. Hence, each such battery group has a capacity of 3.0A (1.5Ah x two cells = 3.0Ah). In the present embodiment, the three second secondary battery cells 3b and one battery group (each group including two first secondary battery cells 3a) are housed in a housing 2a of the battery pack 2 in series electrical connection. [0035] As shown in Fig. IE, these three second secondary battery cells 3b and two (one group of) first secondary battery cells 3a are arranged in the same rows (an upper row and a lower row) respectively, with the center axis of each cell 3b and 3a extending in parallel. These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends. [0036]
More specifically, the second secondary battery cells 3b are arranged in a row with their outer wall in contact, while the first secondary battery cells 3a are arranged in a row, each first secondary battery cell 3a being located between a pair of adjoining second secondary battery cells 3b with its outer wall in contact with the outer wall of each of the pair of second secondary battery cells 3b and with an interval equal to the diameter of one second secondary battery cell 3b secured between the centers of the cells 3a. Hence, as shown in Fig. IB, these first and second secondary battery cells 3a and 3b are housed compactly in the housing 2a of the battery pack 2 with a high housing efficiency, with a large space 2b provided between the adjoining first secondary battery cells 3a to provide a higher effect of cooling inside the battery pack 2. [0037] In the present embodiment, the two (or a plurality of) first secondary battery cells 3a that are in parallel electrical connection have an equal capacity to each other (one another). Further, in the present embodiment, with a higher effect of cooling provided inside the battery pack 2, the first secondary battery cells 3a will undergo degradation at the same pace. Hence, in the present embodiment, when the battery pack 2 discharges, it is possible to prevent an electric current from flowing into at least one of two first secondary battery cells 3a that are in parallel electrical connection from the others of first secondary battery cells 3a that are in parallel electrical connection. Further, in the present embodiment, when the battery pack 2 is charged, it is possible to prevent one of first secondary battery cells 3a in parallel electrical connection and with a smaller capacity from being overcharged along with other of first secondary battery cells 3a in parallel electrical connection and with a larger capacity being charged to the full capacity. [0038]
Moreover, in the present embodiment, two first secondary battery cells 3a in parallel electrical connection have a total capacity that is equal to the capacity of each of the second secondary battery cells 3b that are in series electrical connection. Further, in the present embodiment, the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves undergo degradation at the same pace, as described above. Accordingly, in the present embodiment, when the battery pack 2 discharges, the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge as the two (or a plurality of) first secondary battery cells 3a in parallel electrical connection and at least one of the three (or a plurality of) second secondary battery cells 3b in series electrical connection fall down to or below a predetermined discharge voltage. Further, in the present embodiment, when the battery pack 2 is charged, the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves are charged at the same pace, preventing the battery pack 2 from being overcharged as one battery pair consisting of the two first secondary battery cells 3a in parallel electrical connection and at least one of the three second secondary battery cells 3b in series electrical connection rise to or above their respective predetermined charge voltages . [0039] In this way, the battery pack 2 according to the present embodiment can suppress its degradation and prolong its duration of life.
The battery pack 2 according to the present embodiment can have the same capacity (3.0Ah x four groups =12. OAh) as the conventional art shown in Figs. 5 (i.e., a battery pack 2 constituted by series electrical connection of four battery groups, each including two first secondary battery cells 3a that are in parallel electrical connection and that each have a size of 180 mm in diameter x 650 mm in length). Further, the battery pack 2 according to the present embodiment can have a capacity for housing the secondary battery cells (i.e., the size of the battery pack 2) that is comparable to that of the battery pack 2 according to the conventional art and still can have thereinside a larger space 2b between the adjoining first secondary battery cells 3a. Hence, structurally, the battery pack 2 can obtain a sufficient cooling effect, when it is internally cooled inside the housing 2a of the battery pack 2 by a cooling fan or the like provided on a battery charger, purging the warm air caused by heat production by the first secondary battery cells 3a and second secondary battery cells 3b from the inside of the housing 2a. [0040]
Accordingly, the battery pack 2 according to the present embodiment can be small, housing the first and second secondary battery cells 3a and 3b in an arrangement that allows a large space 2b to be formed between the adjoining first secondary battery cells 3a in the battery pack 2. When mounted in the electric tool body 1, the battery pack 2 can suppress its temperature rise when the head tool Ic induces over discharge, without requiring the battery capacity to be changed or the capacity for housing the secondary batteries (i.e., the size of the battery pack 2) to be expanded. This can eliminate temperature unevenness between the first secondary battery cells 3a and among the second secondary battery cells 3 b that are housed in the battery pack 2. This can inhibit imbalanced deepening of degradation on some part of the first secondary battery cells 3a and of the second secondary battery cells 3b when they charge or discharge, improving the charge-discharge cycle life of the battery pack 2. [0041]
Figs. 2 show a secondary battery cell housing structure of a battery pack according to another embodiment of the present invention.
As shown in Fig. 2C and Fig. 2D, the battery pack 2 according to the present embodiment houses two kinds of first and second secondary battery cells 3a and 3b that have different diameters between the different kinds and the same capacity within the same kind. Here, two second secondary battery cells 3b, each of which has a size of 260 mm in diameter x 650 mm in length and a capacity of 3.0Ah, are electrically connected in series, and two sets of first secondary battery cells 3a, each set including two first secondary battery cells 3a, each of which has a size of 180 mm in diameter x 650 mm in length and a capacity of 1.5Ah, are electrically connected in parallel with each other in each set. Such a set of two first secondary battery cells 3a that are electrically connected in parallel with each other constitute one battery group. Hence, each such battery group has a capacity of 3.0A (1.5Ah x two cells = 3.0Ah). In the present embodiment, the two second secondary battery cells 3b and two battery groups (each group including two first secondary battery cells 3a) are housed in the housing 2a of the battery pack 2 in series electrical connection. [0042]
As shown in Fig. 2E, these two second secondary battery cells 3b and four (two groups of) first secondary battery cells 3a are arranged in the same rows (a lower row and an upper row) respectively, with the center axis of all the cells 3b and 3a extending in parallel. These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends. [0043]
More specifically, the first secondary battery cells 3a are arranged in a row with their outer wall in contact, while the second secondary battery cells 3b are arranged in a row, each second secondary battery cell 3b being located between a pair of adjoining first secondary battery cells 3a with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells 3a and with an interval equal to double the diameter of one first secondary battery cell 3a secured between the centers of the cells 3b. Hence, as shown in Fig. 2B, these first and second secondary battery cells 3a and 3b are housed in the housing 2a of the battery pack 2 with a high housing efficiency to make the battery pack 2 small, with a large space 2b provided between the adjoining second secondary battery cells 3b to provide a higher effect of cooling inside the battery pack 2. [0044] In the present embodiment, each first secondary battery cell 3a of the two (or a plurality of) first secondary battery cells 3a that are in parallel electrical connection have an equal capacity to each other (one another). Further, in the present embodiment, the first secondary battery cells 3a. will undergo degradation at the same pace as described above. Hence, in the present embodiment, when the battery pack 2 discharges, it is possible to prevent an electric current from flowing into at least one of the first secondary battery cells 3a that are in parallel electrical connection from another first secondary battery cells 3a that are in parallel electrical connection. Further, in the present embodiment, when the battery pack 2 is charged, it is possible to prevent a first secondary battery cells 3a in parallel electrical connection and with a smaller capacity from being overcharged along with another first secondary battery cells 3a in parallel electrical connection and with a larger capacity being charged to the full capacity. [0045]
In the present embodiment, two first secondary battery cells 3a in parallel electrical connection have a total capacity that is equal to the capacity of each of the second secondary battery cells 3b that are in series electrical connection. Further, in the present embodiment, with no temperature unevenness, the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves undergo degradation at the same pace. Accordingly, in the present embodiment, when the battery pack 2 discharges, the first secondary battery cells 3a and the second secondary battery cells 3b discharge at the same pace within themselves respectively. Hence, in the present embodiment, when the battery pack 2 discharges, the first secondary battery cells 3a within themselves and the second secondary battery cells 3b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge as the two (or a plurality of) first secondary battery cells 3a in parallel electrical connection in each of the two battery groups and at least one of the two (or a plurality of) second secondary battery cells 3b in series electrical connection fall down to or below a predetermined discharge voltage. Further, in the present embodiment, when the battery pack 2 charges, the first secondary battery cells 3a and the second secondary battery cells 3b charge at the same pace within themselves respectively, which prevents the battery pack 2 from causing over discharge as the two (or a plurality of) first secondary battery cells 3a in parallel electrical connection in each of the two battery groups and at least one of the two second secondary battery cells 3b in series electrical connection rise to or above a predetermined charge voltage. Hence, the battery pack 2 according to the present embodiment can suppress its degradation. [0046]
The battery pack 2 according to the present embodiment can have a battery capacity and a capacity for housing the secondary battery cells (i.e., the size of the battery pack 2) that is comparable to those of the battery pack 2 according to the conventional art as well as the embodiment shown in Figs. 1 , still can have thereinside a larger space 2b between the adjoining second secondary battery cells 3b. Hence, structurally, the battery pack 2 can obtain a sufficient cooling effect, when it is internally cooled by a cooling fan or the like provided on a battery charger, purging the warm air caused by heat production by the first secondary battery cells 3a and second secondary battery cells 3b outside the housing 2a of the battery pack 2 from the inside of the housing 2a. [0047]
Accordingly, the battery pack 2 according to the present embodiment can be small, housing the first and second secondary battery cells 3a and 3b in an arrangement that allows a large space 2b between the adjoining second secondary battery cells 3b in the battery pack 2. When mounted in the electric tool body 1, the battery pack 2 can suppress its temperature rise when the head tool Ic induces over discharge, without requiring the battery capacity to be changed or the capacity for housing the secondary batteries (i.e., the size of the battery pack 2) to be expanded. This can eliminate temperature unevenness between the first secondary battery cells 3a and between the second secondary battery cells 3b that are housed in the battery pack 2. This can inhibit imbalanced deepening of degradation on some part of the first secondary battery cells 3a and of the second secondary battery cells 3b when they charge or discharge, improving the charge-discharge cycle life of the battery pack 2. [0048] Figs. 3 show generalized forms of the secondary battery cell housing structures of the battery pack according to the embodiments of the present invention and generalized states of electrical connection among secondary battery cells. Fig. 3A shows a generalized form of the secondary battery cell housing structure of the battery pack according to the conventional art shown in Figs. 5. Fig. 3B and Fig. 3C show a generalized form of the secondary battery cell housing structures of the battery pack shown in Figs. 1 and Figs. 2 respectively. Fig. 3D shows a state of electrical connection among "a" number of second secondary battery cells 3 b and "b" number of first secondary battery cells 3 a. Fig. 3 E shows a state of electrical connection among "c" number of first secondary battery cells 3a and "d" number of second secondary battery cells 3b. [0049] In the arrangement of the secondary battery cells in the battery pack 2 shown in Fig.
3A, the battery pack 2 houses 2n first secondary battery cells 3a ("n" being a natural number) in the upper and lower rows each in the housing 2a. Note that the secondary battery cell housing structure of the battery pack shown in Figs. 5 is an example wherein n=2 is defined in Fig. 3A. [0050]
The form shown in Figs 3B and 3D satisfies the relationship of a=b+l, where "b" is a natural number indicating the total number of first secondary battery cells 3a, which constitute some battery groups each including two first secondary battery cells 3a in parallel electrical connection, and "a" is a natural number indicating the total number of second secondary battery cells 3b, which constitute a plurality of second secondary battery cells 3b in series electrical connection, and where a=(4n+l)/3 and b=l/3χ(4n-2) where "n" is a natural number. Note that the secondary battery cell housing structure of the battery pack shown in Figs. 1 is an example wherein n=2 is defined in Figs. 3 B and 3D. [0051]
As shown in Fig. 3B, these plurality of second secondary battery cells 3b and plurality of (plural groups of) first secondary battery cells 3a are arranged in the same rows (an upper row and a lower row) respectively, with the center axis of all the cells 3b and 3a extending in parallel. These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends. [0052]
More specifically, the second secondary battery cells 3b are arranged in a row with their outer wall in contact. The first secondary battery cells 3a are arranged in a row, each first secondary battery cell 3a being located between a pair of adjoining second secondary battery cells 3b with its outer wall in contact with the outer wall of each of the pair of second secondary battery cells 3b and with an interval equal to the diameter of one second secondary battery cell 3b secured between the centers of the cells 3a. Hence, as shown in Fig. 3B, these first and second secondary battery cells 3a and 3b are housed in the housing 2a of the battery pack 2 with a high housing efficiency to make the battery pack 2 small, as well as the conventional art shown in Fig. 3A. [0053]
The form shown in Figs 3C and 3E satisfies the relationship of c=2d, where "c" is a natural number indicating the total number of first secondary battery cells 3a, which constitute some battery groups each including a pair of first secondary battery cells 3a in parallel electrical connection, and "d" is a natural number indicating the total number of second secondary battery cells 3b, which constitute a plurality of second secondary battery cells 3b in series electrical connection, and where c=2n and d=n where "n" is a natural number. Note that the secondary battery cell housing structure of the battery pack for electric tools shown in Figs. 2 is an example wherein n=2 is defined in Figs. 3C and 3 E. [0054]
As shown in Fig. 3C, these plurality of second secondary battery cells 3b and plurality of (plural groups of) first secondary battery cells 3a are arranged in the same rows (a lower row and an upper row) respectively, with the center axis of all the cells 3b and 3a extending in parallel. These first and second secondary battery cells 3a and 3b are arranged in a staggered formation as a whole, when seen from the direction to which their center axis extends. [0055]
More specifically, the first secondary battery cells 3a are arranged in a row with their outer wall in contact, while the second secondary battery cells 3b are arranged in a row, each second secondary battery cell 3b being located between a pair of adjoining first secondary battery cells 3a with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells 3a and with an interval equal to double the diameter of one first secondary battery cell 3a secured between the centers of the cells 3b. Hence, as shown in Fig. 3C, these first and second secondary battery cells 3a and 3b are housed in the housing 2a of the battery pack 2 with a high housing efficiency to make the battery pack 2 small, as well as the conventional art shown in Fig. 3A. [0056]
As can be seen from the above, all of the secondary battery cell housing structures of the battery packs shown in Figs. 1, Figs. 2, and Figs. 5 are examples wherein n=2 is defined in Figs. 3.
In the secondary battery cell housing structure of the conventional battery pack shown in Fig. 3A, the space in the battery pack 2 between adjoining first secondary battery cells 3a is small. Therefore, heat conduction between adjoining first secondary battery cells 3a is very influential. Further, in the secondary battery cell housing structure shown in Fig. 3A, the space between the first secondary battery cells 3a and the housing 2a of the battery pack 2 is small. Accordingly, even if the battery pack 2 is internally cooled by a cooling fan or the like provided on a battery charger, the air warmed by heat produced by the first secondary battery cells 3a remains inside the housing 2a of the battery pack 2, resulting in a poor cooling effect. [0057]
In contrast, the secondary battery cell housing structure of the battery pack (or the arrangement of the secondary battery cells in the battery pack) shown in Figs. 3B and 3D can provide a large space 2b in the battery pack 2 between adjoining first secondary battery cells 3a, without making the capacity for housing secondary battery cells (i.e., the size of the battery pack 2) much larger than that of the battery pack 2 shown in Fig. 3A (note that the battery pack 2 shown in Figs. 1 has substantially the same housing capacity as the battery pack 2 shown in Figs. 5). This structure will not confine the air warmed by heat produced by the first secondary battery cells 3a and second secondary battery cells 3b in the housing 2a of the battery pack 2 when the battery pack 2 is internally cooled by a cooling fan or the like provided on a battery charger, achieving a sufficient cooling effect. Hence, this secondary battery cell housing structure of the battery pack is excellent in the cooling effect. [0058] The secondary battery cell housing structure of the battery pack (or the arrangement of the secondary battery cells in the battery pack) shown in Figs. 3C and 3E provides the battery pack with a capacity for housing secondary battery cells that is comparable to that of the battery pack 2 shown in Fig. 3A. That is, the battery pack 2 shown in Figs. 3C and 3E has a length that is substantially 2n times the diameter of one secondary battery cell 3a, as well as the battery pack 2 shown in Fig. 3A. Nonetheless, the secondary battery cell housing structure of the battery pack shown in Figs. 3C and 3E can provide a larger space 2b between adjoining secondary battery cells 3b. This structure will not confine the air warmed by heat produced by the first secondary battery cells 3a and second secondary battery cells 3b in the housing 2a of the battery pack 2 when the battery pack 2 is internally cooled by a cooling fan or the like provided on a battery charger, achieving a sufficient cooling effect. Hence, this secondary battery cell housing structure of the battery pack is excellent in the cooling effect. [0059]
Fig. 4 shows a state of electrical connection among secondary battery cells in a battery pack according to one embodiment of the present invention. As shown in the drawing, one group of first secondary battery cells 3a' in parallel electrical connection may not necessarily consist of two (a pair of) first secondary battery cells 3a', but three or more first secondary battery cells 3a' in parallel electrical connection. Not all second secondary battery cells 3b in series electrical connection may be connected continuously. The total capacity of some first secondary battery cells 3a' in parallel electrical connection is equal to the capacity of each second secondary battery cell 3b in series electrical connection. The structure shown in Fig. 4 can also provide a large space 2b between adjoining first secondary battery cells 3a', by housing first secondary battery cells 3a' and second secondary battery cells 3b in the battery pack 2 by arranging the first and second secondary battery cells 3a' and 3b in the same rows (a lower row and an upper row) respectively while making the center axis of the cells 3a' and 3b extend in parallel and in a manner that the cells 3a' and 3b make a staggered formation as a whole when seen from the direction to which their center axis extends. This can provide temperature uniformity among the first secondary battery cells 3a' and among the second secondary battery cells 3b respectively, subjecting them to equal-paced degradation. [0060] Accordingly, the structure shown in Fig. 4 can also prevent an electric current from flowing into at least one of a plurality of first secondary battery cells 3a' in parallel electrical connection from another first secondary battery cells 3a' in parallel electric connection in the same group when the battery pack 2 discharges. Further, when the battery pack 2 is charged, the structure shown in Fig. 4 can prevent a first secondary battery cells 3a' in parallel electrical connection and with a smaller capacity from being overcharged along with another first secondary battery cells 3a' in parallel electrical connection and with a larger capacity being charged to the full capacity. [0061]
In the structure shown in Fig. 4, the total capacity of two first secondary battery cells 3a' in parallel electrical connection is equal to the capacity of each second secondary battery cell 3 b in series electrical connection. Accordingly, when the battery pack 2 discharges, the first secondary battery cells 3a' within themselves and the second secondary battery cells 3b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge. Hence, when the battery pack 2 discharges, the first secondary battery cells 3a' within themselves and the second secondary battery cells 3 b within themselves discharge at the same pace, which prevents the battery pack 2 from causing over discharge as a plurality of first secondary battery cells 3a in parallel electrical connection in each of the two battery groups and at least one of a plurality of second secondary battery cells 3b in series electrical connection fall down to or below a predetermined discharge voltage. Further, in the structure shown in Fig. 4, when the battery pack 2 charges, the first secondary battery cells 3a' within themselves and the second secondary battery cells 3b within themselves charge at the same pace, preventing the battery pack 2 from causing overcharge, as a plurality of first secondary battery cells 3a' in parallel electrical connection in each of the two battery groups and at least one of the two second secondary battery cells 3b in series electrical connection rise to or above a predetermined charge voltage. [0062]
Hence, the structure shown in Fig. 4 can also improve the charge-discharge cycle life of the battery pack 2.
As obvious from the foregoing description, the battery pack according to the embodiments of the present invention is constituted by secondary battery cells, which include at least two kinds of smaller and larger first and second secondary battery cells 3a and 3b. The first and second secondary battery cells 3a and 3b are arranged in the same rows respectively with the center axis of the cells 3a and 3b extending in parallel and to make a staggered formation as a whole when seen from the direction to which their center axis extends. This arrangement can make the battery pack 2 small, by allowing the first and second secondary battery cells 3a and 3b to be housed in a way to provide a large space 2b in the battery pack 2 between adjoining first secondary battery cells 3a or between adjoining second secondary battery cells 3b. Further, this arrangement can improve the effect of cooling the interior of the battery pack 2, without enlarging the capacity for housing secondary battery cells, i.e., the size of the battery pack. This feature of the present invention can eliminate temperature unevenness among first secondary battery cells 3a and among second secondary battery cells 3b respectively, to make them undergo degradation at the same pace. Hence, with the first secondary battery cells 3a and the second secondary battery cells 3b placed in predetermined states of electrical connection respectively, the battery pack 2 can improve its charge-discharge cycle life. [0063] Though having been described specifically by way of embodiments, the invention of the present inventor is not limited to the embodiments described above but may be modified in various respects within the scope of the spirit of the invention. [0064]
For example, the embodiments described above have been examples wherein the battery pack 2 is used in an electric tool. Not being limited to these embodiments, the battery pack according to the technical idea of the present invention will also be effective when embodied as a battery pack for other electric appliances such as personal computers. [0065] Further, for example, the embodiments described above have been examples wherein the constituent secondary battery cells are lithium-ion secondary batteries, whose charge-discharge cycle life is temperature-dependent. Not being limited to these embodiments, the battery pack according to the technical idea of the present invention may use other kinds of secondary batteries such as nickel-cadmium batteries and nickel-metal-hydride batteries.
[0066] Various embodiments and changes may be made thereunto without departing from the broad spirit and scope of the invention. The above-described embodiments are intended to illustrate the present invention, not to limit the scope of the present invention.
The scope of the present invention is shown by the attached claims rather than the embodiments. Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention.
[0067]
This application is based on Japanese Patent Application No. 2008-199129 filed on
August 1, 2008 and including specification, claims, drawings and summary. The disclosure of the above Japanese Patent Application is incorporated herein by reference in its entirety.

Claims

Claim 1. A battery pack that houses a plurality of cylindrical secondary battery cells while holding them in electrical connection, characterized in that the plurality of secondary battery cells comprise a plurality of first secondary battery cells that have a smaller diameter and a plurality of second secondary battery cells that have a larger diameter, the plurality of first secondary battery cells and the plurality of second secondary battery cells are arranged in same rows respectively, with center axes of the first secondary battery cells and of the second secondary battery cells extending in parallel, and the plurality of secondary battery cells are arranged in a staggered formation as a whole, when seen from a direction to which their center axes extend.
Claim 2. The battery pack according to claim 1 , characterized in that the plurality of first secondary battery cells are electrically connected in parallel.
Claim 3. The battery pack according to claim 2, characterized in that the first secondary battery cells have an equal capacity to each other.
Claim 4. The battery pack according to claim 3, characterized in that the plurality of second secondary battery cells are electrically connected in series.
Claim 5. The battery pack according to claim 4, characterized in that in the second secondary battery cells have an equal capacity to each other.
Claim 6. The battery pack according to claim 5, characterized in that a total capacity of the plurality of first secondary battery cells that are electrically connected in parallel is equal to the capacity of each second secondary battery cell.
Claim 7. The battery pack according to claim 6, characterized in that the first secondary battery cells and the second secondary battery cells satisfy a relationship of a=b+l, where "b" is a natural number indicating a number of the first secondary battery cells and "a" is a natural number indicating a number of the second secondary battery cells, and where a = (4n+l)/3 and b=l/3χ(4n-2), where "n" is a natural number.
Claim 8. The battery pack according to claim 7, characterized in that the second secondary battery cells are arranged in a row with their outer wall in contact, and the first secondary battery cells are arranged in a row, each first secondary battery cell being located between a pair of adjoining second secondary battery cells with its outer wall in contact with the outer wall of each of the pair of second secondary battery cells and with an interval equal to the diameter of the second secondary battery cell (secured between the center axes of the first secondary battery cells.
Claim 9. The battery pack according to claim 6, characterized in that the first secondary battery cells and the second secondary battery cells satisfy a relationship of c=2d, where "c" is a natural number indicating a number of the first secondary battery cells and "d" is a natural number indicating a number of the second secondary battery cells, and where c=2n and d=n, where "n" is a natural number.
Claim 10. The battery pack according to claim 9, characterized in that the first secondary battery cells are arranged in a row with their outer wall in contact, and the second secondary battery cells are arranged in a row, each second secondary battery cell being located between a pair of adjoining first secondary battery cells with its outer wall in contact with the outer wall of each of the pair of first secondary battery cells and with an interval equal to double the diameter of the first secondary battery cell secured between the center axes of the second secondary battery cells.
Claim 1 1. An electric tool, comprising the battery pack according to claim 1 , the battery pack being detachably mounted in a handle housing of the electric tool.
PCT/JP2009/063897 2008-08-01 2009-07-30 Battery pack and electric tool WO2010013839A1 (en)

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JP2008199129A JP2010040226A (en) 2008-08-01 2008-08-01 Battery pack for electric tools

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US11382475B2 (en) 2017-06-19 2022-07-12 Tti (Macao Commercial Offshore) Limited Surface cleaning apparatus
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