WO2016046868A1 - Positive active material for lithium ion secondary battery, positive electrode material, and lithium ion secondary battery - Google Patents

Positive active material for lithium ion secondary battery, positive electrode material, and lithium ion secondary battery Download PDF

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WO2016046868A1
WO2016046868A1 PCT/JP2014/074986 JP2014074986W WO2016046868A1 WO 2016046868 A1 WO2016046868 A1 WO 2016046868A1 JP 2014074986 W JP2014074986 W JP 2014074986W WO 2016046868 A1 WO2016046868 A1 WO 2016046868A1
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positive electrode
active material
lithium ion
ion secondary
secondary battery
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PCT/JP2014/074986
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French (fr)
Japanese (ja)
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小西　宏明
所　久人
秀一 高野
崇 中林
心 高橋
小林　満
章 軍司
達哉 遠山
孝亮 馮
翔 古月
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株式会社日立製作所
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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 positive electrode active material for a lithium ion secondary battery, a positive electrode material, and a lithium ion secondary battery including the same.
  • the problem with electric vehicles is that the energy density of the drive battery is low and the distance traveled by one charge is short. Therefore, there is a need for a secondary battery that is inexpensive and has a high energy density.
  • Lithium ion secondary batteries have a higher energy density per weight than secondary batteries such as nickel metal hydride batteries and lead batteries. Therefore, application to electric vehicles and power storage systems is expected. However, in order to meet the demands of electric vehicles, it is necessary to further increase the energy density. In order to realize high energy density, it is necessary to increase the energy density of the positive electrode and the negative electrode.
  • a layered solid solution compound represented by Li 2 MO 3 —LiM′O 2 is expected.
  • the layered solid solution compound is a solution that dissolves electrochemically inactive Li 2 MO 3 and electrochemically active LiM′O 2 in a solid solution and draws out a high capacity while utilizing high activity properties.
  • the layered solid solution compound can also be represented by the composition formula Li 1 + x M 1-x O 2 .
  • Patent Document 1 discloses a solid solution formed by combining a plurality of solid solution compounds having different median diameters in a solid solution positive electrode material using a solid solution compound of Li [Li 1/3 M 1 2/3 ] O 2 and LiM 2 O 2. It has been reported that the tap density is improved by the positive electrode material (M 1 is one or more metal elements and the average valence is tetravalent, and M 2 is one or more metal elements and is an average. The valence is trivalent.)
  • the positive electrode material disclosed in Patent Document 1 has a problem that although a high energy density is obtained at a low rate, the energy density at a high rate is poor. Furthermore, this material has hysteresis in the open circuit voltage (OCV: Open circuit voltage) during the charging process and discharging process. That is, the OCV differs depending on the charging process and the discharging process, and there are two OCVs in the same SOC. For this reason, there is a problem that it is difficult to detect the state of charge (SOC) of the battery from the voltage. If the state of charge cannot be accurately grasped, it is necessary to allow a surplus in the remaining capacity of the battery, and the capacity of the battery that can be used decreases.
  • SOC state of charge
  • an object of the present invention is to provide a lithium ion secondary battery having a high energy density at a high rate and a small OCV hysteresis in the charging process and the discharging process.
  • another positive electrode material for a lithium ion secondary battery uses the positive electrode active material as a first positive electrode active material, has a similar composition range, and has a specific surface area of 3 m 2 / g or more. It contains the 2nd positive electrode active material, It is characterized by the above-mentioned.
  • the present invention it is possible to provide a lithium ion secondary battery having a high energy density even in a high rate discharge and having a small OCV hysteresis.
  • ⁇ Positive electrode material> When a lithium ion secondary battery is employed in an electric vehicle, it is expected that a high energy density can be obtained even in a large current discharge, and that SOC can be detected with high accuracy from the battery voltage. In order to increase the travel distance per charge, the battery is required to have a high energy density.
  • a lithium ion secondary battery using a layered solid solution compound as a positive electrode active material can be expected to have a high energy density at a low rate, but the energy density at a high rate is low, and it is difficult to detect the SOC of the battery from the battery voltage. There are issues such as.
  • the SOC is detected from the battery voltage.
  • the hysteresis in the OCV in the charging process and the OCV in the discharging process means that the OCV in the charging process is different from the OCV in the discharging process in the same SOC. That is, there are two SOCs corresponding to the same potential.
  • the difference between the two SOCs at the same potential is large, a large error occurs when the SOC is detected from the OCV, so that it is difficult to detect the SOC from the battery voltage. Therefore, in order to detect the SOC with high accuracy, it is necessary to suppress the hysteresis of the OCV.
  • the positive electrode active material (first positive electrode active material) having a specific surface area of 2.5 m 2 / g or less has a high energy density at a high rate, and can reduce OCV hysteresis in the charging and discharging processes. .
  • the energy density at a high rate can be further improved by mixing a positive electrode active material (second positive electrode active material) having a similar composition range and a specific surface area of 3 m 2 / g or more. I found out.
  • the positive electrode material having this feature it is possible to provide a positive electrode material having a high energy density even in a high rate discharge and having a small OCV hysteresis.
  • x represents the proportion of Li in Li x Ni a Mn b M c O 2 .
  • x represents the proportion of Li in Li x Ni a Mn b M c O 2 .
  • A represents the proportion of Ni.
  • Ni mainly involved in the charge / discharge reaction decreases, and the capacity decreases.
  • a 0.42 or more, the oxygen activation reaction in the initial charging process is unlikely to occur, and thus the capacity decreases.
  • B represents the ratio of Mn.
  • b is 0.42 or less, the activation reaction of oxygen hardly occurs, and thus the capacity decreases.
  • b is 0.63 or more, the amount of Ni that contributes to the reaction is reduced, so the capacity is reduced.
  • C represents the ratio of M (M is at least one element such as V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu).
  • M is at least one element such as V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu.
  • the filling rate of the positive electrode active material is improved, so that the density can be increased and a high volume energy density can be achieved.
  • the energy density per unit volume can be improved by mixing the present material with a second positive electrode active material having the same composition and a specific surface area of 3 m 2 / g or more.
  • the second positive electrode active material may have the same composition as the first positive electrode active material or a different composition as long as the composition range is satisfied.
  • the ratio of the second positive electrode active material to the total amount with the first positive electrode active material is preferably 40% or less by mass ratio.
  • a lithium ion secondary battery according to the present invention includes the above positive electrode material.
  • the lithium ion secondary battery according to the present invention can be preferably used for an electric vehicle.
  • a lithium ion secondary battery includes a positive electrode including a positive electrode material, a negative electrode including a negative electrode material, a separator, an electrolytic solution, an electrolyte, and the like.
  • the negative electrode material is not particularly limited as long as it is a substance that can occlude and release lithium ions.
  • Substances generally used in lithium ion secondary batteries can be used as the negative electrode material.
  • graphite, a lithium alloy, etc. can be illustrated.
  • separator those generally used in lithium ion secondary batteries can be used.
  • examples thereof include polyolefin microporous films and nonwoven fabrics such as polypropylene, polyethylene, and a copolymer of propylene and ethylene.
  • electrolytic solution and the electrolyte those generally used in lithium ion secondary batteries can be used.
  • diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, methyl acetate, ethyl methyl carbonate, methyl propyl carbonate, dimethoxyethane and the like can be exemplified as the electrolytic solution.
  • the lithium ion secondary battery 10 includes an electrode group having a positive electrode 1 in which a positive electrode material is applied on both sides of a current collector, a negative electrode 2 in which a negative electrode material is applied on both sides of the current collector, and a separator 3.
  • the positive electrode 1 and the negative electrode 2 are wound through a separator 3 to form a wound electrode group. This wound body is inserted into the battery can 4.
  • the negative electrode 2 is electrically connected to the battery can 4 via the negative electrode lead piece 6.
  • a sealing lid 7 is attached to the battery can 4 via a packing 5.
  • the positive electrode 1 is electrically connected to the sealing lid 7 via the positive electrode lead piece 8.
  • the wound body is insulated by the insulating plate 9.
  • the electrode group may not be the wound body shown in FIG. 1, but may be a laminated body in which the positive electrode 1 and the negative electrode 2 are laminated via the separator 3.
  • Preparation of first positive electrode active material (specific surface area 2.5 m 2 / g or less)> Lithium carbonate, nickel carbonate, and manganese carbonate were mixed at a predetermined ratio by a ball mill to obtain a precursor. The obtained precursor was calcined in the atmosphere at 500 ° C. for 12 hours to obtain a lithium transition metal oxide. After pelletizing the obtained lithium transition metal oxide, it was baked at 1000 ° C. or higher for 12 hours in the air. The fired pellets were pulverized in an agate mortar.
  • Second positive electrode active material (specific surface area of 3 m 2 / g or more)> Lithium carbonate, nickel carbonate, and manganese carbonate were mixed at a predetermined ratio by a ball mill to obtain a precursor. The obtained precursor was calcined in the atmosphere at 500 ° C. for 12 hours to obtain a lithium transition metal oxide. The obtained lithium transition metal oxide was pelletized and then calcined at 950 ° C. or lower for 12 hours in the air. The fired pellets were pulverized in an agate mortar.
  • the composition ratio of the first and second positive electrode active materials is the same, the first active material having a large particle size and the second active material having a small particle size are mixed, and each Example 1 ⁇ 6 / Positive electrode materials of Comparative Examples 1-5.
  • Table 1 shows the composition of the produced positive electrode material, the particle diameter and specific surface area of each positive electrode active material.
  • a positive electrode slurry was prepared by uniformly mixing a positive electrode material, a conductive agent, and a binder.
  • the positive electrode slurry was applied onto an aluminum current collector foil having a thickness of 20 ⁇ m, dried at 120 ° C., and pressed at 40 MPa to obtain an electrode plate. Thereafter, the electrode plate was punched into a disk shape having a diameter of 15 mm to produce a positive electrode.
  • the negative electrode was produced using metallic lithium.
  • a solution obtained by dissolving LiPF 6 at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 2 was used.
  • ⁇ Charge / discharge test> a charge / discharge test was performed on 11 types of prototype batteries produced as described above.
  • the charging was constant current constant voltage charging (CC-CV mode), and the upper limit voltage was 4.6V.
  • the discharge was constant current discharge (CC mode), and the lower limit voltage was 2.5V.
  • the charge / discharge current was 0.05 C, and the charge cutoff current was 0.005 C.
  • the discharge capacity at the second cycle was defined as the rated capacity.
  • the voltage after 5 hours was defined as OCV.
  • the voltage after charging from full discharge to 50% of rated capacity (SOC 50%) and waiting for 5 hours is the OCV during charging, discharging from full charge to 50% of rated capacity and waiting for 5 hours
  • the voltage after the discharge was defined as the OCV of the discharge process.
  • the difference between the OCV in the charging process and the OCV in the discharging process was calculated, and the value divided by the difference between the OCV in the charging process and the OCV in the discharging process in Comparative Example 1 was defined as the OCV ratio. The results are shown in Table 1.
  • Example 1 is an example in which the specific surface area was reduced with respect to Comparative Example 1 while maintaining the same composition.
  • the energy density at 5C was improved, and the OCV ratio could be lowered.
  • the specific surface area decreased, contributing to improvement of rate characteristics and reduction of OCV hysteresis.
  • the energy density ratio increased with an increase in the amount of the second active material added.
  • the OCV ratio also tended to increase. Therefore, the amount of the second active material having a small particle size is preferably 40% or less.
  • Example 3 and Comparative Example 2 are examples in which the amount of Li was decreased without changing the ratio of Ni and Mn to Example 2, and Examples 4 and Comparative Example 3 were examples in which Li was similarly increased.
  • Comparative Example 2 where the Li composition ratio is as small as 1.09
  • Comparative Example 3 where the Li composition ratio is as large as 1.20
  • the discharge capacity is lowered and the volume energy density at a high rate is lowered.
  • the OCV ratio tends to increase and the hysteresis tends to increase. Therefore, the composition ratio of Li needs to be in the range of 1.09 to 1.20.
  • the ratio of Li to the metal element M (Li / M) is preferably in the range of 1.2 to 1.4.
  • Example 6 and Comparative Examples 4 and 5 are examples in which the ratio of Ni contained in the metal element (Ni / Ni + Mn) was changed.
  • the discharge capacity decreased in both the case where the amount of Ni was small and the case where the amount of Ni was large.
  • the reaction in which Ni contributes to reduction can be followed even in high-rate discharge, but the reaction in which oxygen contributes to reduction cannot follow. Therefore, when the amount of Ni decreases, the energy density at a high rate decreases.
  • the amount of Ni is too large, the ratio of Li 2 MO 3 that contributes to higher energy density of the layered solid solution is relatively reduced, and a sufficient energy density cannot be obtained.
  • the OCV ratio increased as the proportion of Mn increased.
  • the ratio of Ni in the entire transition metal element (Ni / transition metal element M) is preferably 0.35 or more.
  • Example 2 the energy density ratio was higher than that in Example 1. This is because the second positive electrode active material having a specific surface area of 3 m 2 / g or more is included.
  • the second layered solid solution compound having a large specific surface area can achieve a high volumetric energy density, for example, by obtaining a high capacity and by improving the electrode density by mixing two materials having different specific surface areas.
  • Comparative Examples 2 to 5 were unable to achieve both a higher discharge capacity and a smaller OCV ratio than Comparative Example 1.
  • the composition formula Li x Ni a Mn b M c O 2 (1.09 ⁇ x ⁇ 1.20,0.21 ⁇ a ⁇ 0.42,0.42 ⁇ b ⁇ 0.63,0 ⁇ c ⁇ 0.02, x + a + b + c 2.0, M is represented by V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc.) and has a specific surface area of 2.5 m
  • the positive electrode active material of 2 / g or less obtained a high energy density even at a high rate, and resulted in a small OCV hysteresis during the charging and discharging processes.
  • composition formula Li x ′ Ni a ′ Mn b ′ M c ′ O 2 (1.09 ⁇ x ′ ⁇ 1.20, 0.21 ⁇ a ′ ⁇ 0.42, 0.42 ⁇ b ′ ⁇ 0. 63, 0 ⁇ c ′ ⁇ 0.02, x ′ + a ′ + b ′ + c ′ 2.0, M is at least one of V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc.
  • the volume energy density at the time of high rate can be further improved by mixing the second positive electrode active material represented by the above element) and having a specific surface area of 3 m 2 / g or more.

Abstract

The present invention addresses the problem of providing a lithium ion secondary battery which has a high capacity in both low-rate and high-rate discharges and is reduced in open circuit voltage (OCV) hysteresis arising between the charge and the discharge. The problem can be solved with a positive electrode material comprising: a first positive active material which is a positive active material represented by the empirical formula LixNiaMnbMcO2 (wherein 1.09<x<1.20, 0.21<a<0.42, 0.42<b<0.63, 0≤c≤0.02, x+a+b+c=2.0, and M is at least one element selected from among V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc.) and which has a specific surface area of 2.5 m2/g or less; and a second positive active material which has a similar composition and has a specific surface area of 3 m2/g or greater.

Description

リチウムイオン二次電池用正極活物質、正極材料及びリチウムイオン二次電池Positive electrode active material for lithium ion secondary battery, positive electrode material, and lithium ion secondary battery
　本発明は、リチウムイオン二次電池用の正極活物質、正極材料、及びそれを含むリチウムイオン二次電池に関する。 The present invention relates to a positive electrode active material for a lithium ion secondary battery, a positive electrode material, and a lithium ion secondary battery including the same.
　電気自動車の課題は、駆動用電池のエネルギー密度が低く、一充電での走行距離が短いことである。そこで、安価で高エネルギー密度をもつ二次電池が求められている。 The problem with electric vehicles is that the energy density of the drive battery is low and the distance traveled by one charge is short. Therefore, there is a need for a secondary battery that is inexpensive and has a high energy density.
　リチウムイオン二次電池は、ニッケル水素電池や鉛電池等の二次電池に比べて重量当たりのエネルギー密度が高い。そのため、電気自動車や電力貯蔵システムへの応用が期待されている。しかし、電気自動車の要請に応えるためには、さらなる高エネルギー密度化が必要である。高エネルギー密度化を実現するためには、正極及び負極のエネルギー密度を高める必要がある。 Lithium ion secondary batteries have a higher energy density per weight than secondary batteries such as nickel metal hydride batteries and lead batteries. Therefore, application to electric vehicles and power storage systems is expected. However, in order to meet the demands of electric vehicles, it is necessary to further increase the energy density. In order to realize high energy density, it is necessary to increase the energy density of the positive electrode and the negative electrode.
　高エネルギー密度の正極活物質として、Ｌｉ2ＭＯ3－ＬｉＭ′Ｏ2で表される層状固溶体化合物が期待されている。層状固溶体化合物は、電気化学的に不活性なＬｉ2ＭＯ3と、電気化学的に活性なＬｉＭ′Ｏ2とを固溶させ、高容量を引き出しつつ、高活性な性質を利用するものである。層状固溶体化合物は、組成式Ｌｉ1+xＭ1-xＯ2で表すこともできる。 As a high energy density positive electrode active material, a layered solid solution compound represented by Li 2 MO 3 —LiM′O 2 is expected. The layered solid solution compound is a solution that dissolves electrochemically inactive Li 2 MO 3 and electrochemically active LiM′O 2 in a solid solution and draws out a high capacity while utilizing high activity properties. . The layered solid solution compound can also be represented by the composition formula Li 1 + x M 1-x O 2 .
　特許文献１には、Ｌｉ［Ｌｉ1/3Ｍ1 2/3］Ｏ2とＬｉＭ2Ｏ2との固溶体化合物を用いた固溶体正極材料において、メディアン径の異なる複数の固溶体化合物を組み合わせてなる固溶体正極材料により、タップ密度が改善することが報告されている（Ｍ1は１種以上の金属元素であって平均価数が４価であり、Ｍ2は１種以上の金属元素であって平均価数が３価である。）。 Patent Document 1 discloses a solid solution formed by combining a plurality of solid solution compounds having different median diameters in a solid solution positive electrode material using a solid solution compound of Li [Li 1/3 M 1 2/3 ] O 2 and LiM 2 O 2. It has been reported that the tap density is improved by the positive electrode material (M 1 is one or more metal elements and the average valence is tetravalent, and M 2 is one or more metal elements and is an average. The valence is trivalent.)
特開２０１２－０５９５２８号公報JP 2012-059528 A
　特許文献１に示されている正極材料は、低レートでは高いエネルギー密度が得られるものの、高レートでのエネルギー密度が悪いという課題がある。さらに本材料は、充電過程と放電過程の開回路電圧（ＯＣＶ：Ｏｐｅｎ　ｃｉｒｃｕｉｔ　ｖｏｌｔａｇｅ）にヒステリシスが存在する。つまり、充電過程と放電過程によってＯＣＶが異なり、同一のＳＯＣにおけるＯＣＶが二つ存在する。そのため、電圧から電池の充電状態（ＳＯＣ：Ｓｔａｔｅ　ｏｆ　ｃｈａｒｇｅ）を検知することが困難であるという課題がある。充電状態を正確に把握できないと、電池の残存容量に余裕を見る必要があり、使用できる電池の容量が減少する。 The positive electrode material disclosed in Patent Document 1 has a problem that although a high energy density is obtained at a low rate, the energy density at a high rate is poor. Furthermore, this material has hysteresis in the open circuit voltage (OCV: Open circuit voltage) during the charging process and discharging process. That is, the OCV differs depending on the charging process and the discharging process, and there are two OCVs in the same SOC. For this reason, there is a problem that it is difficult to detect the state of charge (SOC) of the battery from the voltage. If the state of charge cannot be accurately grasped, it is necessary to allow a surplus in the remaining capacity of the battery, and the capacity of the battery that can be used decreases.
　そこで、本発明は、高レートにおいて高いエネルギー密度を有し、充電過程と放電過程のＯＣＶヒステリシスが小さいリチウムイオン二次電池を提供することを目的とする。 Therefore, an object of the present invention is to provide a lithium ion secondary battery having a high energy density at a high rate and a small OCV hysteresis in the charging process and the discharging process.
　本発明に係るリチウムイオン二次電池用正極材料は、組成式ＬｉxＮｉaＭｎbＭcＯ2（１．０９＜ｘ＜１．２０、０．２１＜ａ＜０．４２、０．４２＜ｂ＜０．６３、０≦ｃ≦０．０２、ｘ＋ａ＋ｂ＋ｃ＝２．０、ＭはＶ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｃｕ等の少なくともいずれかの元素）で表され、比表面積が２．５ｍ2／ｇ以下である正極活物質を含むことを特徴とする。 Positive electrode material for a lithium ion secondary battery according to the present invention, the composition formula Li x Ni a Mn b M c O 2 (1.09 <x <1.20,0.21 <a <0.42,0.42 <B <0.63, 0 ≦ c ≦ 0.02, x + a + b + c = 2.0, M is at least one element of V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc.) And a positive electrode active material having a specific surface area of 2.5 m 2 / g or less.
　また、他の本発明に係るリチウムイオン二次電池用正極材料は、上記の正極活物質を第一の正極活物質とし、同様の組成範囲を有し、比表面積が３ｍ2／ｇ以上である第二の正極活物質を含むことを特徴とする。 Further, another positive electrode material for a lithium ion secondary battery according to the present invention uses the positive electrode active material as a first positive electrode active material, has a similar composition range, and has a specific surface area of 3 m 2 / g or more. It contains the 2nd positive electrode active material, It is characterized by the above-mentioned.
　本発明によれば、高レートの放電においても高いエネルギー密度が得られ、ＯＣＶヒステリシスの小さいリチウムイオン二次電池を提供することができる。 According to the present invention, it is possible to provide a lithium ion secondary battery having a high energy density even in a high rate discharge and having a small OCV hysteresis.
リチウムイオン二次電池の構造を模式的に示す断面図である。It is sectional drawing which shows the structure of a lithium ion secondary battery typically.
　＜正極材料＞
　リチウムイオン二次電池を電気自動車に採用する場合、大電流の放電においても高いエネルギー密度が得られること、電池電圧からＳＯＣを高い精度で検知できることが期待される。一充電当たりの走行距離を長くするために、電池には、高エネルギー密度であることが要求される。正極活物質として層状固溶体化合物を用いたリチウムイオン二次電池は、低レートでは高いエネルギー密度が期待できるが、高レートでのエネルギー密度が低いこと、電池電圧から電池のＳＯＣを検知することが困難であるなどの課題がある。 <Positive electrode material>
When a lithium ion secondary battery is employed in an electric vehicle, it is expected that a high energy density can be obtained even in a large current discharge, and that SOC can be detected with high accuracy from the battery voltage. In order to increase the travel distance per charge, the battery is required to have a high energy density. A lithium ion secondary battery using a layered solid solution compound as a positive electrode active material can be expected to have a high energy density at a low rate, but the energy density at a high rate is low, and it is difficult to detect the SOC of the battery from the battery voltage. There are issues such as.
　リチウムイオン電池では、電池電圧からＳＯＣを検知している。充電過程のＯＣＶ、放電過程のＯＣＶにヒステリシスがあるということは、同一のＳＯＣにおいて、充電過程のＯＣＶと放電過程のＯＣＶが異なるということである。つまり、同一の電位に対応するＳＯＣが二つある。同一の電位における二つのＳＯＣの差が大きい場合、ＯＣＶからＳＯＣを検知する際に大きな誤差が生じてしまうため、電池電圧からＳＯＣを検知することが困難である。したがって、ＳＯＣを高精度で検知するためには、ＯＣＶのヒステリシスを抑制する必要がある。 In the lithium ion battery, the SOC is detected from the battery voltage. The hysteresis in the OCV in the charging process and the OCV in the discharging process means that the OCV in the charging process is different from the OCV in the discharging process in the same SOC. That is, there are two SOCs corresponding to the same potential. When the difference between the two SOCs at the same potential is large, a large error occurs when the SOC is detected from the OCV, so that it is difficult to detect the SOC from the battery voltage. Therefore, in order to detect the SOC with high accuracy, it is necessary to suppress the hysteresis of the OCV.
　発明者らが鋭意検討した結果、層状固溶体化合物における組成式ＬｉxＮｉaＭｎbＭcＯ2（１．０９＜ｘ＜１．２０、０．２１＜ａ＜０．４２、０．４２＜ｂ＜０．６３、０≦ｃ≦０．０２、ｘ＋ａ＋ｂ＋ｃ＝２．０、ＭはＶ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｃｕ等の少なくともいずれかの元素）とし、比表面積が２．５ｍ2／ｇ以下である正極活物質（第一の正極活物質）で、高レートでのエネルギー密度が高く、充電過程と放電過程のＯＣＶヒステリシスを低減出来ることを見出した。また、同様の組成範囲を有し、比表面積が３ｍ2／ｇ以上である正極活物質（第二の正極活物質）を混合することで、高レートでのエネルギー密度をさらに向上させることが出来ることを見出した。 Results inventors studied intensively, composition formula in the layered solid solution compound Li x Ni a Mn b M c O 2 (1.09 <x <1.20,0.21 <a <0.42,0.42 < b <0.63, 0 ≦ c ≦ 0.02, x + a + b + c = 2.0, M is at least one element of V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc.) The positive electrode active material (first positive electrode active material) having a specific surface area of 2.5 m 2 / g or less has a high energy density at a high rate, and can reduce OCV hysteresis in the charging and discharging processes. . Moreover, the energy density at a high rate can be further improved by mixing a positive electrode active material (second positive electrode active material) having a similar composition range and a specific surface area of 3 m 2 / g or more. I found out.
　本特徴を有する正極材料とすることで、高レートの放電においても高いエネルギー密度が得られ、かつＯＣＶヒステリシスの小さい正極材料を提供することができる。 By using the positive electrode material having this feature, it is possible to provide a positive electrode material having a high energy density even in a high rate discharge and having a small OCV hysteresis.
　第一の正極活物質において、ｘは、ＬｉxＮｉaＭｎbＭcＯ2におけるＬｉの割合を示す。ｘが１．０９以下であると、反応に寄与するＬｉの量が減り高容量が得られない。一方、ｘが１．２以上であると、結晶格子が不安定になり放電容量が低下する。 In the first positive electrode active material, x represents the proportion of Li in Li x Ni a Mn b M c O 2 . When x is 1.09 or less, the amount of Li contributing to the reaction is reduced, and a high capacity cannot be obtained. On the other hand, if x is 1.2 or more, the crystal lattice becomes unstable, and the discharge capacity decreases.
　ａはＮｉの割合を示す。ａが０．２１以下であると、主に充放電反応に関与するＮｉが少なくなり、容量が低下する。一方、ａが０．４２以上であると、初充電過程における酸素の活性化反応が起こりにくいため、容量が低下する。 A represents the proportion of Ni. When a is 0.21 or less, Ni mainly involved in the charge / discharge reaction decreases, and the capacity decreases. On the other hand, if a is 0.42 or more, the oxygen activation reaction in the initial charging process is unlikely to occur, and thus the capacity decreases.
　ｂはＭｎの割合を示す。ｂが０．４２以下であると、酸素の活性化反応が起こりにくいため、容量が低下する。一方、ｂが０．６３以上であると、反応に寄与するＮｉの量が低下するため、容量が低下する。 B represents the ratio of Mn. When b is 0.42 or less, the activation reaction of oxygen hardly occurs, and thus the capacity decreases. On the other hand, if b is 0.63 or more, the amount of Ni that contributes to the reaction is reduced, so the capacity is reduced.
　ｃはＭ（ＭはＶ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｃｕ等の少なくともいずれかの元素）の割合を示す。ｃが０．０２より大きいと反応に寄与する元素の割合が低下するため、放電容量が低下する。 C represents the ratio of M (M is at least one element such as V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu). When c is larger than 0.02, the ratio of the elements contributing to the reaction is lowered, so that the discharge capacity is lowered.
　上記の組成であり、比表面積が２．５ｍ2／ｇ以下にすることで、正極活物質の充填率が向上するため、高密度化し、高い体積エネルギー密度を達成できる。 When the specific surface area is 2.5 m 2 / g or less with the above composition, the filling rate of the positive electrode active material is improved, so that the density can be increased and a high volume energy density can be achieved.
　一方、組成式Ｌｉ1.2Ｎｉ0.2Ｍｎ0.6Ｏ2で表される層状固溶体化合物に代表されるようなＮｉが２価、Ｍｎが４価の状態の化合物では、比表面積を小さくすると、電極密度は高くなるものの、高レートでの容量が急激に低下するため、高い電極密度と高レートでの高い容量を両立することは出来ない。二つの特性を両立するためには、上に示した組成とする必要がある。 On the other hand, in a compound in which Ni is divalent and Mn is tetravalent as represented by the layered solid solution compound represented by the composition formula Li 1.2 Ni 0.2 Mn 0.6 O 2 , the electrode density increases when the specific surface area is reduced. However, since the capacity at a high rate rapidly decreases, it is impossible to achieve both a high electrode density and a high capacity at a high rate. In order to achieve both characteristics, it is necessary to have the composition shown above.
　さらに、本材料に対し、同様の組成を有し、比表面積が３ｍ2／ｇ以上の第二の正極活物質を混合することで、単位体積あたりのエネルギー密度を向上できる。第二の正極活物質は、上記組成範囲であれば、第一の正極活物質と同じ組成であってもよく、異なる組成のものとしてもよい。第二の正極活物質は、第一の正極活物質との合計量に占める割合が質量比で４０％以下が好ましい。 Furthermore, the energy density per unit volume can be improved by mixing the present material with a second positive electrode active material having the same composition and a specific surface area of 3 m 2 / g or more. The second positive electrode active material may have the same composition as the first positive electrode active material or a different composition as long as the composition range is satisfied. The ratio of the second positive electrode active material to the total amount with the first positive electrode active material is preferably 40% or less by mass ratio.
　＜リチウムイオン二次電池＞
　本発明に係るリチウムイオン二次電池は、上記の正極材料を含むことを特徴とする。上記の正極材料を正極に使用することにより、高レートの放電において、高いエネルギー密度が得られ、かつＯＣＶヒステリシスが小さい。本発明に係るリチウムイオン二次電池は、電気自動車に対して好ましく使用することができる。 <Lithium ion secondary battery>
A lithium ion secondary battery according to the present invention includes the above positive electrode material. By using the above positive electrode material for the positive electrode, a high energy density can be obtained and the OCV hysteresis is small in a high rate discharge. The lithium ion secondary battery according to the present invention can be preferably used for an electric vehicle.
　リチウムイオン二次電池は、正極材料を含む正極、負極材料を含む負極、セパレータ、電解液、電解質等から構成される。 A lithium ion secondary battery includes a positive electrode including a positive electrode material, a negative electrode including a negative electrode material, a separator, an electrolytic solution, an electrolyte, and the like.
　負極材料は、リチウムイオンを吸蔵放出することができる物質であれば特に限定されない。リチウムイオン二次電池において一般的に使用されている物質を負極材料として使用することができる。例えば、黒鉛、リチウム合金等を例示することができる。 The negative electrode material is not particularly limited as long as it is a substance that can occlude and release lithium ions. Substances generally used in lithium ion secondary batteries can be used as the negative electrode material. For example, graphite, a lithium alloy, etc. can be illustrated.
　セパレータとしては、リチウムイオン二次電池において一般的に使用されているものを使用することができる。例えば、ポリプロピレン、ポリエチレン、プロピレンとエチレンとの共重合体等のポリオレフィン製の微孔性フィルムや不織布等を例示することができる。 As the separator, those generally used in lithium ion secondary batteries can be used. Examples thereof include polyolefin microporous films and nonwoven fabrics such as polypropylene, polyethylene, and a copolymer of propylene and ethylene.
　電解液及び電解質としては、リチウムイオン二次電池において一般的に使用されているものを使用することができる。例えば、電解液として、ジエチルカーボネート、ジメチルカーボネート、エチレンカーボネート、プロピレンカーボネート、ビニレンカーボネート、メチルアセテート、エチルメチルカーボネート、メチルプロピルカーボネート、ジメトキシエタン等を例示することができる。また、電解質として、ＬｉＣｌＯ4、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＳｂＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＣ4Ｆ9ＳＯ3、ＬｉＣＦ3ＣＯ2、Ｌｉ2Ｃ2Ｆ4（ＳＯ3）2、ＬｉＮ（ＣＦ3ＳＯ2）2、ＬｉＣ（ＣＦ3ＳＯ2）3等を例示することができる。 As the electrolytic solution and the electrolyte, those generally used in lithium ion secondary batteries can be used. For example, diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, methyl acetate, ethyl methyl carbonate, methyl propyl carbonate, dimethoxyethane and the like can be exemplified as the electrolytic solution. Further, as the electrolyte, LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiN Examples thereof include (CF 3 SO 2 ) 2 and LiC (CF 3 SO 2 ) 3 .
　本発明に係るリチウムイオン二次電池の構造の一実施形態を、図１を用いて説明する。リチウムイオン二次電池１０は、集電体の両面に正極材料を塗布した正極１と、集電体の両面に負極材料を塗布した負極２と、セパレータ３とを有する電極群を備える。正極１及び負極２は、セパレータ３を介して捲回され、捲回体の電極群を形成している。この捲回体は電池缶４に挿入される。 An embodiment of the structure of a lithium ion secondary battery according to the present invention will be described with reference to FIG. The lithium ion secondary battery 10 includes an electrode group having a positive electrode 1 in which a positive electrode material is applied on both sides of a current collector, a negative electrode 2 in which a negative electrode material is applied on both sides of the current collector, and a separator 3. The positive electrode 1 and the negative electrode 2 are wound through a separator 3 to form a wound electrode group. This wound body is inserted into the battery can 4.
　負極２は、負極リード片６を介して、電池缶４に電気的に接続される。電池缶４には、パッキン５を介して、密閉蓋７が取り付けられる。正極１は、正極リード片８を介して、密閉蓋７に電気的に接続される。捲回体は、絶縁板９によって絶縁される。 The negative electrode 2 is electrically connected to the battery can 4 via the negative electrode lead piece 6. A sealing lid 7 is attached to the battery can 4 via a packing 5. The positive electrode 1 is electrically connected to the sealing lid 7 via the positive electrode lead piece 8. The wound body is insulated by the insulating plate 9.
　なお、電極群は、図１に示す捲回体でなくてもよく、セパレータ３を介して正極１と負極２とを積層した積層体でもよい。 The electrode group may not be the wound body shown in FIG. 1, but may be a laminated body in which the positive electrode 1 and the negative electrode 2 are laminated via the separator 3.
　以下、実施例及び比較例を用いて本発明をより詳細に説明するが、本発明の技術的範囲はこれに限定されるものではない。 Hereinafter, the present invention will be described in more detail using examples and comparative examples, but the technical scope of the present invention is not limited thereto.
　＜第一の正極活物質（比表面積２．５ｍ2／ｇ以下）の作製＞
　炭酸リチウム、炭酸ニッケル、及び炭酸マンガンを所定の比率でボールミルで混合し、前駆体を得た。得られた前駆体を大気中において５００℃で１２時間焼成し、リチウム遷移金属酸化物を得た。得られたリチウム遷移金属酸化物をペレット化した後、大気中において１０００℃以上で１２時間焼成した。焼成したペレットをメノウ乳鉢で粉砕した。 <Preparation of first positive electrode active material (specific surface area 2.5 m 2 / g or less)>
Lithium carbonate, nickel carbonate, and manganese carbonate were mixed at a predetermined ratio by a ball mill to obtain a precursor. The obtained precursor was calcined in the atmosphere at 500 ° C. for 12 hours to obtain a lithium transition metal oxide. After pelletizing the obtained lithium transition metal oxide, it was baked at 1000 ° C. or higher for 12 hours in the air. The fired pellets were pulverized in an agate mortar.
　＜第二の正極活物質（比表面積が３ｍ2／ｇ以上）の作製＞
　炭酸リチウム、炭酸ニッケル、及び炭酸マンガンを所定の比率でボールミルで混合し、前駆体を得た。得られた前駆体を大気中において５００℃で１２時間焼成し、リチウム遷移金属酸化物を得た。得られたリチウム遷移金属酸化物をペレット化した後、大気中において９５０℃以下で１２時間焼成した。焼成したペレットをメノウ乳鉢で粉砕した。 <Production of second positive electrode active material (specific surface area of 3 m 2 / g or more)>
Lithium carbonate, nickel carbonate, and manganese carbonate were mixed at a predetermined ratio by a ball mill to obtain a precursor. The obtained precursor was calcined in the atmosphere at 500 ° C. for 12 hours to obtain a lithium transition metal oxide. The obtained lithium transition metal oxide was pelletized and then calcined at 950 ° C. or lower for 12 hours in the air. The fired pellets were pulverized in an agate mortar.
　本実施の形態では、第一、第二の正極活物質の組成比は同じとし、大粒径の第一の活物質と小粒径の第二の活物質とを混合し、各実施例１～６/比較例１～５の正極材料とした。作製した正極材料の組成および、各正極活物質の粒子径、比表面積を表１に示す。 In the present embodiment, the composition ratio of the first and second positive electrode active materials is the same, the first active material having a large particle size and the second active material having a small particle size are mixed, and each Example 1 ~ 6 / Positive electrode materials of Comparative Examples 1-5. Table 1 shows the composition of the produced positive electrode material, the particle diameter and specific surface area of each positive electrode active material.
　＜試作電池の作製＞
　各実施例及び比較例では、上述のように作製した正極材料を用いて正極を作製し、１１種類の試作電池を作製した。 <Production of prototype battery>
In each example and comparative example, a positive electrode was produced using the positive electrode material produced as described above, and 11 types of prototype batteries were produced.
　正極材料と導電剤とバインダとを均一に混合して正極スラリーを作製した。正極スラリーを厚み２０μｍのアルミ集電体箔上に塗布し、１２０℃で乾燥した後、４０ＭＰａでプレスして電極板を得た。その後、電極板を直径１５ｍｍの円盤状に打ち抜き、正極を作製した。 A positive electrode slurry was prepared by uniformly mixing a positive electrode material, a conductive agent, and a binder. The positive electrode slurry was applied onto an aluminum current collector foil having a thickness of 20 μm, dried at 120 ° C., and pressed at 40 MPa to obtain an electrode plate. Thereafter, the electrode plate was punched into a disk shape having a diameter of 15 mm to produce a positive electrode.
　負極は金属リチウムを用いて作製した。非水電解液としては、体積比１：２のエチレンカーボネートとジメチルカーボネートとの混合溶媒に、ＬｉＰＦ6を１．０ｍｏｌ／Ｌの濃度で溶解させたものを用いた。 The negative electrode was produced using metallic lithium. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF 6 at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 2 was used.
　＜充放電試験＞
　各実施例及び比較例では、上述のように作製した１１種類の試作電池に対して、充放電試験を行った。充電は定電流定電圧充電（ＣＣ－ＣＶモード）とし、上限電圧は４．６Ｖとした。放電は定電流放電（ＣＣモード）とし、下限電圧は２．５Ｖとした。充放電の電流は０．０５Ｃ相当とし、充電のカットオフ電流は０．００５Ｃ相当とした。各実施例及び比較例において、上記の条件で２サイクルさせた後、２サイクル目の放電容量を定格容量とした。 <Charge / discharge test>
In each example and comparative example, a charge / discharge test was performed on 11 types of prototype batteries produced as described above. The charging was constant current constant voltage charging (CC-CV mode), and the upper limit voltage was 4.6V. The discharge was constant current discharge (CC mode), and the lower limit voltage was 2.5V. The charge / discharge current was 0.05 C, and the charge cutoff current was 0.005 C. In each example and comparative example, after two cycles were performed under the above conditions, the discharge capacity at the second cycle was defined as the rated capacity.
　＜体積エネルギー密度比（５Ｃ）測定＞
　充放電試験と同一の条件で４．６Ｖまで充電し、５C相当の電流で２．５Ｖまで放電した際の体積エネルギー密度を測定した。各実施例及び比較例の体積エネルギー密度を、比較例１の値で除した値を体積エネルギー密度比として表１に示す。 <Volume energy density ratio (5C) measurement>
The volume energy density was measured when the battery was charged to 4.6V under the same conditions as the charge / discharge test and discharged to 2.5V with a current corresponding to 5C. Table 1 shows the volume energy density ratio obtained by dividing the volume energy density of each example and comparative example by the value of comparative example 1.
　＜ＯＣＶ比の測定＞
　各実施例及び比較例では、上述のように作製した１１種類の試作電池に対して、充電過程のＯＣＶと放電過程のＯＣＶの差を求めた。 <Measurement of OCV ratio>
In each of the examples and comparative examples, the difference between the OCV in the charging process and the OCV in the discharging process was determined for the 11 types of prototype batteries manufactured as described above.
　０．０５Ｃ相当の電流で定格容量の１０％を充電し、５時間待機するという試験を１０回繰り返し、定格容量が１００％になるまで行った。その後、０．０５Ｃ相当の電流で定格容量の１０％定格容量の１０％を放電し、５時間待機するという試験を１０回繰り返し、満放電状態まで繰り返した。 The test of charging 10% of the rated capacity with a current equivalent to 0.05 C and waiting for 5 hours was repeated 10 times until the rated capacity reached 100%. Thereafter, a test of discharging 10% of the rated capacity at a current equivalent to 0.05 C and 10% of the rated capacity and waiting for 5 hours was repeated 10 times until the fully discharged state.
　このとき、５時間後の電圧をＯＣＶと定義した。本試験において、満放電状態から定格容量の５０％（ＳＯＣ５０％）まで充電して５時間待機した後の電圧を充電過程のＯＣＶ、満充電状態から定格容量の５０％まで放電して５時間待機した後の電圧を放電過程のＯＣＶと定義した。各実施例及び比較例において、充電過程のＯＣＶと放電過程のＯＣＶの差を算出し、比較例１の充電過程のＯＣＶと放電過程のＯＣＶの差で除した値をＯＣＶ比とした。結果を表１に示す。 At this time, the voltage after 5 hours was defined as OCV. In this test, the voltage after charging from full discharge to 50% of rated capacity (SOC 50%) and waiting for 5 hours is the OCV during charging, discharging from full charge to 50% of rated capacity and waiting for 5 hours The voltage after the discharge was defined as the OCV of the discharge process. In each example and comparative example, the difference between the OCV in the charging process and the OCV in the discharging process was calculated, and the value divided by the difference between the OCV in the charging process and the OCV in the discharging process in Comparative Example 1 was defined as the OCV ratio. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　実施例１は、比較例１に対し、同一組成のまま比表面積を小さくした例である。５Ｃでのエネルギー密度が向上するとともに、ＯＣＶ比を低下させることが可能となった。焼成温度を上げ、結晶性を高めることで、比表面積が低下し、レート特性向上、ＯＣＶヒステリシス低減に寄与したと推察される。 Example 1 is an example in which the specific surface area was reduced with respect to Comparative Example 1 while maintaining the same composition. The energy density at 5C was improved, and the OCV ratio could be lowered. By raising the firing temperature and increasing the crystallinity, it is speculated that the specific surface area decreased, contributing to improvement of rate characteristics and reduction of OCV hysteresis.
　さらに、同一組成かつ比表面積の大きい、小粒径の第二の活物質を混合した実施例２、５では、第二の活物質の添加量の増加とともにエネルギー密度比が大きくなった。一方、ＯＣＶ比も大きくなる傾向にあった。従って、小粒径の第二の活物質の添加量は４０％以下とすることが好ましい。 Furthermore, in Examples 2 and 5 in which a second active material having the same composition and a large specific surface area and a small particle diameter was mixed, the energy density ratio increased with an increase in the amount of the second active material added. On the other hand, the OCV ratio also tended to increase. Therefore, the amount of the second active material having a small particle size is preferably 40% or less.
　実施例３、比較例２は、実施例２とＮｉ、Ｍｎの比を変えずにＬｉの量を減少させた例、実施例４、比較例３は同様にＬｉを増加させた例である。Ｌｉの組成比が１．０９と小さい比較例２、Ｌｉの組成比が１．２０と多い比較例３のいずれの場合であっても放電容量が低下し、高レートでの体積エネルギー密度が低下するとともに、ＯＣＶ比が高くなり、ヒステリシスが大きくなる傾向にあった。従って、Ｌｉの組成比は１．０９～１．２０の範囲内とする必要がある。Ｌｉと金属元素Ｍの比（Ｌｉ/Ｍ）は、１．２～１．４の範囲とすることが好ましい。 Example 3 and Comparative Example 2 are examples in which the amount of Li was decreased without changing the ratio of Ni and Mn to Example 2, and Examples 4 and Comparative Example 3 were examples in which Li was similarly increased. In either case of Comparative Example 2 where the Li composition ratio is as small as 1.09 and Comparative Example 3 where the Li composition ratio is as large as 1.20, the discharge capacity is lowered and the volume energy density at a high rate is lowered. In addition, the OCV ratio tends to increase and the hysteresis tends to increase. Therefore, the composition ratio of Li needs to be in the range of 1.09 to 1.20. The ratio of Li to the metal element M (Li / M) is preferably in the range of 1.2 to 1.4.
　実施例６、比較例４および５は、金属元素に含まれるＮｉの比（Ｎｉ/Ｎｉ＋Ｍｎ）を変更した例である。Ｎｉの量が少ない例、多い例ともに放電容量が低下した。Ｎｉが還元に寄与した反応は、高レートの放電においても追従できるが、酸素が還元に寄与した反応は追従できない。そこで、Ｎｉ量が低下すると、高レートでのエネルギー密度が低下する。一方、Ｎｉ量が多くなりすぎると、相対的に層状固溶体の高エネルギー密度化に寄与するＬｉ2ＭＯ3の比が少なくなり、十分なエネルギー密度が得られない。さらに、Ｍｎの占める割合が多くなるほど、ＯＣＶ比が大きくなった。高いエネルギー密度を維持し、かつＯＣＶ比を低減するためには、遷移金属元素全体に占めるＮｉの割合（Ｎｉ/遷移金属元素Ｍ）は０．３５以上であることが好ましい。 Example 6 and Comparative Examples 4 and 5 are examples in which the ratio of Ni contained in the metal element (Ni / Ni + Mn) was changed. The discharge capacity decreased in both the case where the amount of Ni was small and the case where the amount of Ni was large. The reaction in which Ni contributes to reduction can be followed even in high-rate discharge, but the reaction in which oxygen contributes to reduction cannot follow. Therefore, when the amount of Ni decreases, the energy density at a high rate decreases. On the other hand, if the amount of Ni is too large, the ratio of Li 2 MO 3 that contributes to higher energy density of the layered solid solution is relatively reduced, and a sufficient energy density cannot be obtained. Furthermore, the OCV ratio increased as the proportion of Mn increased. In order to maintain a high energy density and reduce the OCV ratio, the ratio of Ni in the entire transition metal element (Ni / transition metal element M) is preferably 0.35 or more.
　上述の通り、実施例２～６では、実施例１に比べエネルギー密度比が高い値を示した。これは、比表面積が３ｍ2／ｇ以上の第二の正極活物質を含んでいるためである。比表面積の大きい第二の層状固溶体化合物は高容量が得られること、および比表面積の異なる二つの材料を混合することで電極密度を向上できることなどにより、高い体積エネルギー密度を達成できた。一方、比較例２～５では、比較例１より高い放電容量と、小さいＯＣＶ比を両立することが出来なかった。 As described above, in Examples 2 to 6, the energy density ratio was higher than that in Example 1. This is because the second positive electrode active material having a specific surface area of 3 m 2 / g or more is included. The second layered solid solution compound having a large specific surface area can achieve a high volumetric energy density, for example, by obtaining a high capacity and by improving the electrode density by mixing two materials having different specific surface areas. On the other hand, Comparative Examples 2 to 5 were unable to achieve both a higher discharge capacity and a smaller OCV ratio than Comparative Example 1.
　以上の通り、組成式ＬｉxＮｉaＭｎbＭcＯ2（１．０９＜ｘ＜１．２０、０．２１＜ａ＜０．４２、０．４２＜ｂ＜０．６３、０≦ｃ≦０．０２、ｘ＋ａ＋ｂ＋ｃ＝２．０、ＭはＶ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｃｕ等の少なくともいずれかの元素）で表され、比表面積が２．５ｍ2／ｇ以下の正極活物質は、高レートにおいても高いエネルギー密度が得られ、かつ充電過程と放電過程のＯＣＶヒステリシスの小さい結果となった。さらに、組成式Ｌｉx’Ｎｉa’Ｍｎb’Ｍc’Ｏ2（１．０９＜ｘ’＜１．２０、０．２１＜ａ’＜０．４２、０．４２＜ｂ’＜０．６３、０≦ｃ’≦０．０２、ｘ’＋ａ’＋ｂ’＋ｃ’＝２．０、ＭはＶ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｃｕ等の少なくともいずれかの元素）で表され、比表面積が３ｍ2／ｇ以上である第二の正極活物質を混合することで、高レート時の体積エネルギー密度をさらに向上させることが可能となった。 As described above, the composition formula Li x Ni a Mn b M c O 2 (1.09 <x <1.20,0.21 <a <0.42,0.42 <b <0.63,0 ≦ c ≦ 0.02, x + a + b + c = 2.0, M is represented by V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc.) and has a specific surface area of 2.5 m The positive electrode active material of 2 / g or less obtained a high energy density even at a high rate, and resulted in a small OCV hysteresis during the charging and discharging processes. Further, the composition formula Li x ′ Ni a ′ Mn b ′ M c ′ O 2 (1.09 <x ′ <1.20, 0.21 <a ′ <0.42, 0.42 <b ′ <0. 63, 0 ≦ c ′ ≦ 0.02, x ′ + a ′ + b ′ + c ′ = 2.0, M is at least one of V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc. The volume energy density at the time of high rate can be further improved by mixing the second positive electrode active material represented by the above element) and having a specific surface area of 3 m 2 / g or more.
　１　正極
　２　負極
　３　セパレータ
　４　電池缶
　５　パッキン
　６　負極リード片
　７　密閉蓋
　８　正極リード片
　９　絶縁板
　１０　リチウムイオン二次電池 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery can 5 Packing 6 Negative electrode lead piece 7 Sealing lid 8 Positive electrode lead piece 9 Insulation board 10 Lithium ion secondary battery

Claims (6)

  1. 　組成式ＬｉxＮｉaＭｎbＭcＯ2（１．０９＜ｘ＜１．２０、０．２１＜ａ＜０．４２、０．４２＜ｂ＜０．６３、０≦ｃ≦０．０２、ｘ＋ａ＋ｂ＋ｃ＝２．０、ＭはＶ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｃｕ等の少なくともいずれかの元素）で表される正極活物質であり、比表面積が２．５ｍ2／ｇ以下であることを特徴とするリチウムイオン二次電池用正極活物質。 The composition formula Li x Ni a Mn b M c O 2 (1.09 <x <1.20,0.21 <a <0.42,0.42 <b <0.63,0 ≦ c ≦ 0.02 X + a + b + c = 2.0, M is a positive electrode active material represented by V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg, Cu, etc.), and has a specific surface area of 2 A positive electrode active material for a lithium ion secondary battery, wherein the positive electrode active material is 0.5 m 2 / g or less.
  2. 　請求項１に記載のリチウムイオン二次電池用正極活物質であって、
    　０．３２＜ａ＜０．４２、かつ０．４０＜ｂ＜０．５３であることを特徴とする正極活物質。     The positive electrode active material for a lithium ion secondary battery according to claim 1,
    A positive electrode active material, wherein 0.32 <a <0.42 and 0.40 <b <0.53.
  3. 　リチウムイオン二次電池用正極材料であって、
    　第一の正極活物質と第二の正極活物質とを含み、
    　前記第一の正極活物質は、請求項１で記載された正極活物質であり、
    　前記第二の正極活物質は、組成式Ｌｉx’Ｎｉa’Ｍｎb’Ｍc’Ｏ2（１．０９＜ｘ’＜１．２０、０．２１＜ａ’＜０．４２、０．４２＜ｂ’＜０．６３、０≦ｃ’≦０．０２、ｘ’＋ａ’＋ｂ’＋ｃ’＝２．０、ＭはＶ、Ｍｏ、Ｗ、Ｚｒ、Ｎｂ、Ｔｉ、Ａｌ、Ｆｅ、Ｍｇ、Ｃｕ等の少なくともいずれかの元素）で表され、比表面積が３ｍ2／ｇ以上であることを特徴とする正極材料。     A positive electrode material for a lithium ion secondary battery,
    Including a first positive electrode active material and a second positive electrode active material,
    The first positive electrode active material is the positive electrode active material described in claim 1,
    The second positive electrode active material has a composition formula Li x ′ Ni a ′ Mn b ′ Mc ′ O 2 (1.09 <x ′ <1.20, 0.21 <a ′ <0.42, 0. 42 <b ′ <0.63, 0 ≦ c ′ ≦ 0.02, x ′ + a ′ + b ′ + c ′ = 2.0, M is V, Mo, W, Zr, Nb, Ti, Al, Fe, Mg And a specific surface area of 3 m 2 / g or more.
  4. 　請求項３に記載のリチウムイオン二次電池用正極材料であって、
    　前記第二の正極活物質は、前記第一及び第二の正極活物質の合計量に対し、４０質量％以下の割合で含まれることを特徴とする正極材料。     The positive electrode material for a lithium ion secondary battery according to claim 3,
    Said 2nd positive electrode active material is contained in the ratio of 40 mass% or less with respect to the total amount of said 1st and 2nd positive electrode active material, The positive electrode material characterized by the above-mentioned.
  5. 　請求項４に記載された正極材料であって、
    　前記第一及び第二の正極活物質は同一の組成よりなり、
    　前記第二の正極活物質は、前記第一及び第二の正極活物質の合計量に対し、２０質量％以下の割合で含まれることを特徴とする正極材料。     The positive electrode material according to claim 4,
    The first and second positive electrode active materials have the same composition,
    Said 2nd positive electrode active material is contained in the ratio of 20 mass% or less with respect to the total amount of said 1st and 2nd positive electrode active material, The positive electrode material characterized by the above-mentioned.
  6. 　請求項３ないし５のいずれか一項に記載の正極材料を使用したことを特徴とするリチウムイオン二次電池. A lithium ion secondary battery using the positive electrode material according to any one of claims 3 to 5.
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CN112557919A (en) * 2019-09-25 2021-03-26 郑州深澜动力科技有限公司 Method for testing open-circuit voltage of battery
EP3944362A4 (en) * 2019-03-18 2022-05-04 Panasonic Intellectual Property Management Co., Ltd. Secondary cell

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JP2002338250A (en) * 2001-05-17 2002-11-27 Mitsubishi Chemicals Corp Method for producing layered lithium-nickel-manganese composite oxide
JP2012134023A (en) * 2010-12-22 2012-07-12 Hitachi Vehicle Energy Ltd Lithium ion secondary battery
JP2014086282A (en) * 2012-10-24 2014-05-12 Kri Inc Material for nonaqueous power storage device and nonaqueous power storage device using the same

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JP2002338250A (en) * 2001-05-17 2002-11-27 Mitsubishi Chemicals Corp Method for producing layered lithium-nickel-manganese composite oxide
JP2012134023A (en) * 2010-12-22 2012-07-12 Hitachi Vehicle Energy Ltd Lithium ion secondary battery
JP2014086282A (en) * 2012-10-24 2014-05-12 Kri Inc Material for nonaqueous power storage device and nonaqueous power storage device using the same

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3944362A4 (en) * 2019-03-18 2022-05-04 Panasonic Intellectual Property Management Co., Ltd. Secondary cell
CN112557919A (en) * 2019-09-25 2021-03-26 郑州深澜动力科技有限公司 Method for testing open-circuit voltage of battery

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