WO2022205658A1 - 负极材料及包含其的电化学装置和电子设备 - Google Patents

负极材料及包含其的电化学装置和电子设备 Download PDF

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WO2022205658A1
WO2022205658A1 PCT/CN2021/104653 CN2021104653W WO2022205658A1 WO 2022205658 A1 WO2022205658 A1 WO 2022205658A1 CN 2021104653 W CN2021104653 W CN 2021104653W WO 2022205658 A1 WO2022205658 A1 WO 2022205658A1
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negative electrode
active material
carbonaceous
pores
particles
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PCT/CN2021/104653
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French (fr)
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金文博
董佳丽
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宁德新能源科技有限公司
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Priority to EP21934306.8A priority Critical patent/EP4318673A1/en
Publication of WO2022205658A1 publication Critical patent/WO2022205658A1/zh
Priority to US18/374,731 priority patent/US20240030439A1/en

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    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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    • C01B2204/32—Size or surface area
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    • C01P2006/16—Pore diameter
    • C—CHEMISTRY; METALLURGY
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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 application relates to the technical field of energy storage, and more particularly, to a negative electrode material and an electrochemical device and electronic device including the same.
  • the performance requirements for batteries have been continuously improved.
  • the batteries are required to be lightweight, but also the batteries are required to have good low-temperature charge-discharge performance.
  • the batteries used in them need to have good low-temperature discharge performance and low Charging also needs to meet the requirements of charging at higher rates without precipitation of lithium.
  • the combination of the two can make lithium-ion batteries work more efficiently under low temperature conditions. Therefore, in order to meet the market demand, it is necessary to develop anode materials with excellent kinetics to improve or enhance the ability of lithium-ion batteries to work under low temperature conditions.
  • the purpose of improving or improving the kinetics of the negative electrode material is achieved by reducing the graphite particle size to shorten the lithium intercalation path of lithium ions, or by directly coating the negative electrode material.
  • these two methods will cause a loss in the energy density of the anode material, including the compaction density, gram capacity, etc., and the cost is high.
  • the embodiments of the present application provide a negative electrode material, which at least to some extent solves at least one problem existing in the related art.
  • Embodiments of the present application also provide electrochemical devices and electronic devices using the negative electrode material.
  • the negative electrode materials of the embodiments of the present application have high low-temperature discharge rate performance and low-temperature charging capability, so that the low-temperature working performance of the electrochemical device can be improved.
  • the carbonaceous active material includes carbonaceous particles with pores; the The negative electrode material satisfies the following conditions; the longest direction of the hole is the maximum diameter Y of the hole, and the hole satisfies the following conditions (A) or (B): (A) The range of the maximum diameter Y of the single carbonaceous particle hole satisfies 0.3 ⁇ m ⁇ Y ⁇ 2.0 ⁇ m, and the average value X of the maximum pore diameter of the carbonaceous particles satisfies 0.6 ⁇ m ⁇ X ⁇ 1.5 ⁇ m; (B) The number of carbonaceous particles containing the number of pores N ⁇ 2 accounts for the carbonaceous particles in the region The proportion of the total number is ⁇ 60%, and the proportion of the number of carbonaceous particles containing the number of pores 3 ⁇ N ⁇ 5 to the total number of carbonaceous particles
  • the pores present in the carbonaceous particles satisfy the above condition (A) or (B), the condition (A) is satisfied, the pores of the particles have a larger size, and the condition (B) is satisfied, the pores of the particles are have a larger number.
  • the characteristics of the particles meet the above conditions (A) or (B), which can significantly improve the rate performance of the electrochemical device and the low-temperature charge-discharge performance of the negative electrode material, which can effectively improve the low-temperature lithium precipitation and the electrolysis of the negative electrode sheet. Fluid wettability is also improved.
  • the median diameter Dv50 of the carbonaceous particles with pores and the Y satisfy the following relationship: Dv50 ⁇ 5Y, wherein the unit of Dv50 is ⁇ m.
  • the volume of the pores accounts for the size of the entire particle is limited to a suitable range, which can reduce or avoid the formation of large cavities in the particles because the pores are too large relative to the particles, and reduce the mechanical strength of the particles. Cracks when cold pressed.
  • the maximum diameter Y of the pores and the average value X of the maximum diameters of the pores satisfy the following relationship: Y-X ⁇ 1.0 ⁇ m; in some embodiments of the present application, a single carbonaceous particle with pores , the distance L between two adjacent holes L ⁇ 8.0 ⁇ m.
  • the pore diameter difference of the carbonaceous particles satisfies the above range, which can ensure good pore size consistency, which is beneficial to the deintercalation of lithium ions.
  • the spacing between adjacent holes satisfies the above range, which can ensure that the holes are uniformly distributed in the carbonaceous particles, improve the wetting performance of the pole piece, and improve the kinetics of the negative electrode material.
  • the holes include at least one of through holes or blind holes.
  • the compacted density of the carbonaceous active material at a pressure of 5t is CD g/cm 3 , CD ⁇ 1.85, and a lower compacted powder density means that the pore structure of porous graphite is not easily affected by
  • the gram capacity of the carbonaceous active material is Cap mAh/g, Cap ⁇ 340, so The value of the compacted density CD g/ cm3 of the Cap and the carbonaceous active material under a pressure of 5t satisfies Cap ⁇ 350-50 ⁇ (1.90-CD), which can ensure the gram capacity of the porous material and the compacted density.
  • the particle size distribution of the carbonaceous active material satisfies Dv99 ⁇ 3.5 ⁇ Dv50, This can ensure that the particle size of the porous material is moderate and the particle distribution is narrow, so as to avoid too many large particles affecting the processing of the pole piece.
  • the parameters of the carbonaceous active material meet the above range, which is beneficial to improve the kinetics of the material and the low-temperature charge-discharge performance of the battery, while ensuring the energy density of the battery.
  • the graphitization degree G of the carbonaceous active material is 90% to 95.5%, and a lower graphitization degree can ensure that the graphite layer spacing of the porous material is larger, which is conducive to the rapid growth of lithium ions De-intercalation improves kinetics, and at the same time, in order to ensure battery energy density, the degree of graphitization should not be too low; in some embodiments of the present application, the specific surface area of the carbonaceous active material BET ⁇ 3.0m 2 /g, the porous material is The existence of the pore structure generally has a larger specific surface area, but an excessively large specific surface area will affect the storage and cycling performance of the battery. The specific surface area BET of the active material is at a low level; in some embodiments of the present application, the carbonaceous active material includes at least one of artificial graphite, natural graphite, or mesocarbon microspheres.
  • a suitable range of graphitization degree can take into account the material dynamics and energy density, and ensure the performance of the battery.
  • the specific surface area BET of the carbonaceous active material is in this range, which can ensure the electrochemical performance of the electrochemical device such as storage.
  • an electrochemical device comprising a negative electrode including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer Including the negative electrode material as described above.
  • the electrochemical device further includes a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.
  • the electrolyte includes fluoroethylene carbonate and 1,3-propane sultone.
  • the compaction density PD g/cm 3 of the negative electrode satisfies: 1.45 ⁇ PD ⁇ 1.75, the negative electrode of the porous material should not have too high compaction density, otherwise the pore structure of the material will be destroyed, and the high The compaction density will deteriorate the charging ability of the battery, and the compaction density of the negative electrode of the porous material is too low, which will cause the active material to fall from the pole piece and affect the stability of the battery, so it is limited to a certain range; in some implementations of this application In the example, the porosity ⁇ of the negative electrode satisfies: ⁇ 20%.
  • the porous material itself has more pore structures, when the negative electrode is formed, the higher the porosity of the negative electrode plate, the developed pore structure, and the electrolyte solution.
  • the wettability of the battery is good, and the kinetic performance of the battery is better.
  • the electrochemical device satisfying this negative electrode condition is excellent in low-temperature discharge performance and low-temperature charging capability.
  • the capacity retention rate decreases by less than or equal to 20%.
  • the fluoroethylene carbonate and 1,3-propane sultone in the electrolyte interact with the negative electrode material to effectively improve its contact interface, thereby improving cycling.
  • an electronic device comprising the electrochemical device according to the above-mentioned embodiments of the present application.
  • the negative electrode material provided by the embodiments of the present application includes carbonaceous particles with pores, and the pores are large in size and many in number, the contact surface between the negative electrode material and the electrolyte is significantly increased, the kinetic performance of the negative electrode material is improved, and the Low-temperature discharge rate performance and low-temperature charging capability of anode materials. Therefore, when the electrochemical device works under low temperature conditions, the use of the negative electrode material of the present application can effectively improve the low-temperature charge-discharge performance of the electrochemical device. Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part through the implementation of the embodiments of the present application in the subsequent description.
  • FIG. 1 is a scanning electron microscope (SEM) image of a negative electrode material provided by an exemplary embodiment of the present application.
  • a term may refer to a range of variation less than or equal to ⁇ 10% of the numerical value, such as less than or equal to ⁇ 5%, less than or equal to ⁇ 4%, less than or equal to ⁇ 3%, Less than or equal to ⁇ 2%, less than or equal to ⁇ 1%, less than or equal to ⁇ 0.5%, less than or equal to ⁇ 0.1%, or less than or equal to ⁇ 0.05%.
  • a list of items joined by the terms "at least one of,” “at least one of,” “at least one of,” or other similar terms may mean the listed items any combination of .
  • the phrase "at least one of A, B” means A only; B only; or A and B.
  • the phrase "at least one of A, B, C” means A only; or B only; C only; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.
  • Item A may contain a single element or multiple elements.
  • Item B can contain a single element or multiple elements.
  • Item C may contain a single element or multiple elements.
  • item A or B is listed, it means A only; B only; or A and B.
  • Dv99 means the particle size at which the material reaches 99% of the volume cumulatively from the small particle size side in the volume-based particle size distribution, ie, the volume of material smaller than this particle size accounts for 99% of the total volume of the material.
  • Dv50 is also referred to as “median particle size” and refers to the particle size at which the material reaches 50% of the cumulative volume from the small particle size side in the particle size distribution on a volume basis, ie, material smaller than this particle size The volume of the material accounts for 50% of the total volume of the material.
  • the Dv50 and Dv99 of the material can be measured by methods known in the art, for example, by a laser particle size analyzer (eg, a Malvern particle size tester).
  • a laser particle size analyzer eg, a Malvern particle size tester
  • the maximum diameter Y of the pores and the average value X of the maximum diameters of the pores, and the number of pores can be measured or calculated according to methods known in the art, such as scanning electron microscopy (SEM) detection on the sample, according to the obtained SEM.
  • SEM scanning electron microscopy
  • the map is visually obtained or calculated to obtain the length and number of pores in the sample.
  • the number of holes included is ⁇ 1, and the maximum diameter Y satisfies 0.3 ⁇ m ⁇ Y ⁇ 2.0 ⁇ m.
  • the present application provides a negative electrode material, the negative electrode material includes a carbonaceous active material, and the carbonaceous active material has a region (the size of the region can be, for example, 80 ⁇ m ⁇ 100 ⁇ m), which includes a Porous carbonaceous particles;
  • the direction with the longest length of the hole is the maximum diameter Y of the hole, and the hole satisfies:
  • the pores existing in the carbonaceous particles satisfy the above condition (A) or (B), the condition (A) is satisfied, the pores of the particles have a larger size, and the condition (B) is satisfied, the The holes have a greater number.
  • the characteristics of the particles meet the above conditions (A) or (B), which can significantly improve the rate performance of the electrochemical device and the low-temperature charge-discharge performance of the negative electrode material, which can effectively improve the low-temperature lithium precipitation and the electrolysis of the negative electrode sheet. Fluid wettability is also improved.
  • the carbonaceous particles there is at least one hole in the carbonaceous particles, and at least one hole has the largest diameter in the longest direction of the length (maximum circumscribed circle diameter), namely Y, the average maximum diameter of the holes of the plurality of particles is X, and the size of the hole
  • the range of Y and the range of X as defined above need to be satisfied.
  • the pores may be micron or sub-micron sized pores.
  • the cross-sectional shape of the hole can be arbitrary, such as any regular or irregular shape, and is not particularly limited; that is, although the maximum diameter of the hole is defined, the shape of the hole is not necessarily a circular hole.
  • the above Y may have different expressions.
  • the above Y can be used as the diameter of the hole, that is, the diameter of the hole; for example, when the cross-sectional shape of the hole is a rectangle, the above Y can be used as the diagonal distance of the rectangle.
  • the elongated slits do not belong to the holes described in the embodiments of the present application.
  • FIG. 1 shows a scanning electron microscope (SEM) picture of the negative electrode material provided by the embodiment of the present application.
  • the carbonaceous active material of the embodiment of the present application includes carbonaceous particles with pores, and the particles have a porous structure. And the size of the pores is relatively large, and their distribution is relatively uniform, and the pores can satisfy the above conditions (A) or (B).
  • the negative electrode material containing the carbonaceous particles with pores has a porous structure, and the pore size is large and the number is large, so the contact surface between the active material and the electrolyte is significantly increased.
  • Y can be listed as about 0.3 ⁇ m, about 0.4 ⁇ m, about 0.5 ⁇ m, about 0.6 ⁇ m, about 0.7 ⁇ m, about 0.8 ⁇ m, about 0.9 ⁇ m, about 1.0 ⁇ m, about 1.3 ⁇ m, about 1.5 ⁇ m, About 1.6 ⁇ m, about 1.7 ⁇ m, about 19 ⁇ m, about 2.0 ⁇ m, or a range of any two of these values.
  • X can be listed as about 0.6 ⁇ m, about 0.7 ⁇ m, about 0.8 ⁇ m, about 0.9 ⁇ m, about 1.0 ⁇ m, about 1.1 ⁇ m, about 1.2 ⁇ m, about 1.3 ⁇ m, about 1.4 ⁇ m, about 1.5 ⁇ m, or any two of these values range of composition.
  • the number of carbonaceous particles containing the number of pores N ⁇ 2 accounts for 5% to 60% of the total number of carbonaceous particles in the region, and the number of carbonaceous particles containing the number of pores 3 ⁇ N ⁇ 5 The proportion of the total number of carbonaceous particles is 2% to 30%. In some embodiments, the number of carbonaceous particles containing the number of pores N ⁇ 2 accounts for 10% to 60% of the total number of carbonaceous particles in the region, and the number of carbonaceous particles containing the number of pores 3 ⁇ N ⁇ 5 The proportion of the total carbonaceous particles is 5% to 30%.
  • the proportion of the carbonaceous particles comprising the number of pores N ⁇ 2 to the total number of carbonaceous particles in the region is about 10%, about 15%, about 20%, about 25%, about 30%, About 35%, about 40%, about 45%, about 50%, about 55%, about 60%, or a range of any two of these values; the number of carbonaceous particles comprising a pore number of 3 ⁇ N ⁇ 5 accounted for The proportion of the total number of carbonaceous particles in the region is about 5%, about 8%, about 10%, about 15%, about 18%, about 20%, about 22%, about 25%, about 28%, about 30% or A range consisting of any two of these values.
  • the median diameter Dv50 of the carbonaceous particles with pores and the Y satisfy the following relationship: Dv50 ⁇ 5Y. In some embodiments, the median diameter Dv50 of the carbonaceous particles with pores and the Y satisfy the following relationship: Dv50>5Y. In some embodiments, the median diameter Dv50 of the carbonaceous particles with pores and the Y satisfy the following relationship: Dv50>5Y, and Dv50 ⁇ 10Y.
  • the particle Dv50 in order to ensure that the negative electrode material has a certain mechanical strength and prevent the particles from breaking when the pole piece is cold pressed, the particle Dv50 is limited to satisfy: Dv50 ⁇ 5Y, under this condition, the volume of the pores accounts for the size of the entire particle is limited In a suitable range, the formation of large cavities in the particles due to the pores being too large relative to the particles is reduced or avoided, and the cracking of the particles during cold pressing due to excessive mechanical strength is reduced.
  • the carbonaceous particles with pores satisfy, (a) the maximum diameter Y of the pores and the average value X of the maximum diameters of the pores satisfy the following relationship: Y-X ⁇ 1.0 ⁇ m; (b) a single carbon with pores In the particle, the distance L between two adjacent holes L ⁇ 8.0 ⁇ m.
  • the difference between the maximum diameter Y of the pores and the average maximum diameter X satisfies Y-X ⁇ 1.0 ⁇ m. Therefore, when a single carbonaceous particle has multiple pores, the pore size consistency is good, which is beneficial to the deintercalation of lithium ions.
  • the distance L when the number of the pores N ⁇ 2 exists in a single carbonaceous particle with pores, the distance L ⁇ 8.0 ⁇ m between two adjacent pores. In some embodiments, when the number of pores N ⁇ 2 exists in a single carbonaceous particle with pores, the distance between two adjacent pores is 0.1 ⁇ m ⁇ L ⁇ 8.0 ⁇ m. In some embodiments, L can be listed as about 8.0 ⁇ m, about 7.5 ⁇ m, about 7.0 ⁇ m, about 6.6 ⁇ m, about 6.2 ⁇ m, about 6.0 ⁇ m, about 5.0 ⁇ m, about 4.0 ⁇ m, about 3.0 ⁇ m, about 2.5 ⁇ m, about 2.0 ⁇ m, etc.
  • the distance between two adjacent pores is L ⁇ 8.0 ⁇ m, so that It can ensure that the pores are evenly distributed in the particles, improve the wettability of the pole piece, and improve the kinetics of the negative electrode material.
  • the holes comprise at least one of through holes or blind holes. That is, in some embodiments, the existing form of the hole can be a through hole; or in other embodiments, the existing form of the hole can be a blind hole; or in other embodiments, the existing form of the hole can be both Through and blind vias.
  • the particle size distribution of the carbonaceous active material satisfies Dv99 ⁇ 3.5 ⁇ Dv50. In some embodiments, the particle size distribution of the carbonaceous active material satisfies Dv99 ⁇ 3.5 ⁇ Dv50.
  • the excessive particle size will lead to an increase in the extraction path of lithium ions and reduce the material kinetics. Too small particle size will affect the compaction of the pole piece and reduce the storage performance. Therefore, by making the particle size distribution of the active material satisfy Dv99 ⁇ 3.5 ⁇ Dv50, the kinetics of the material can be improved, which is beneficial to improve the low-temperature charge-discharge performance of the electrochemical device.
  • the compacted density of the carbonaceous active material under a pressure of 5t is CD g/cm 3 , CD ⁇ 1.85. In some embodiments, the compacted density of the carbonaceous active material under a pressure of 5t is CD g/cm 3 , CD ⁇ 1.84. In some embodiments, the carbonaceous active material has a compacted density CD g/cm 3 at a pressure of 5t, CD of about 1.85, about 1.84, about 1.82, about 1.80, about 1.79, about 1.78, about 1.76, about 1.75 etc. In order to ensure the energy density of the battery, the powder compaction density of the active material is limited, and the compaction density of the active material is positively correlated with the compaction density of the negative electrode sheet. Therefore, a suitable powder compaction density of the active material is beneficial to improve the battery Energy Density.
  • the gram capacity of the carbonaceous active material is Cap mAh/g, Cap ⁇ 340, and the value of Cap and the value of the compaction density CD of the carbonaceous active material under 5t pressure satisfy Cap ⁇ 350-50 ⁇ (1.90-CD). In some embodiments, the gram capacity of the carbonaceous active material Cap ⁇ 340mAh/g, and the value of the Cap and the value of the compaction density CD of the carbonaceous active material under 5t pressure satisfy Cap ⁇ 350-50 x (1.85-CD).
  • the carbonaceous active material has a gram capacity Cap mAh/g of about 340 mAh/g, about 341 mAh/g, about 342 mAh/g, about 343 mAh/g, about 344 mAh/g, about 345 mAh/g, About 346mAh/g, about 347mAh/g, about 348mAh/g, about 349mAh/g, about 350mAh/g, etc.
  • the gram capacity of the active material is limited to Cap mAh/g, Cap ⁇ 340, and at the same time, in order to ensure the balance between the gram capacity and the compaction density of the material, it has a high capacity under high capacity.
  • the compaction density of so as to obtain a higher battery energy density, so the satisfying condition of the active material is limited: Cap ⁇ 350-50 ⁇ (1.90-CD).
  • the graphitization degree G of the carbonaceous active material is 90% to 95.5%. In some embodiments, the graphitization degree G of the carbonaceous active material is 90.5% to 94.0%. In some embodiments, the graphitization degree G of the carbonaceous active material is about 90%, about 90.5%, about 90.8%, about 91%, about 91.5%, about 92%, about 92.1%, about 92.5%, About 93.0%, about 93.5%, about 94.0%, about 94.5%, about 95.0%, about 95.2%, about 95.5%, or a range of any two of these values.
  • the degree of graphitization is an important parameter that affects the gram capacity of graphite, and it is also a key parameter that affects the kinetics of the material.
  • the lower the degree of graphitization the larger the graphite layer spacing is, which is conducive to the rapid de-intercalation of lithium ions, and the kinetics is better.
  • the gram capacity of graphite is lower, and the compaction density is also lower, which affects the energy density of the battery. Therefore, in the embodiment of the present invention, the graphitization degree G of the active material satisfies 90% ⁇ G ⁇ 95.5%, so that the graphitization degree in the appropriate range can take into account both kinetics and energy density, and ensure the performance of the battery.
  • the carbonaceous active material has a specific surface area BET ⁇ 3.0 m 2 /g. In some embodiments, the carbonaceous active material has a specific surface area BET ⁇ 2.5 m 2 /g. In some embodiments, the negative electrode active particles have a specific surface area BET of about 3.0 m 2 /g, about 2.7 m 2 /g, about 2.5 m 2 /g, about 2.3 m 2 /g, about 2.0 m 2 /g , about 1.9 m 2 /g, about 1.6 m 2 /g, about 1.5 m 2 /g, about 1.3 m 2 /g, about 1.0 m 2 /g, about 0.8 m 2 /g, etc.
  • the specific surface area BET of a material can be determined by methods well known in the art, such as with a specific surface area analyzer (eg, a TriStar II specific surface analyzer).
  • the specific surface area BET of the active material is limited to satisfy BET ⁇ 3.0m 2 /g.
  • the specific surface area of the active material will affect the storage performance of the battery. The larger the specific surface area, the more violent the reaction with the electrolyte, and the gas is easily generated during high temperature storage, which reduces the battery performance. Therefore, the specific surface area of the active material is limited. within the range.
  • the carbonaceous active material includes at least one of artificial graphite, natural graphite, or mesocarbon microspheres.
  • the carbonaceous active material may include graphite, in which case, low temperature discharge rate performance and low temperature charging performance may be improved when the carbonaceous active material is used.
  • the carbonaceous particles with pores can be obtained by the following method: selecting some petroleum coke or needle coke with relatively high volatile content as the raw material, and in the process of converting it into graphite through special heat treatment, The volatilized gas volatilizes, thereby forming a pore structure in the particles, and finally obtaining a porous type of carbonaceous active particles, which is described here by taking petroleum coke as an example.
  • the precursor petroleum coke for preparing graphite does not choose high volatile petroleum coke. Direct heat treatment of high volatile petroleum coke is difficult, easy to damage the heating equipment and has the risk of fire. Generally, a low temperature heat treatment is performed first to remove a part of the volatilization.
  • High-volatile petroleum coke has more hydrocarbon compounds, which will decompose and overflow during the heating process of petroleum coke, but the conventional slow heating method will slowly decompose and overflow the hydrocarbon compounds, and the heating expansion of the particles and the small pores of the particles are sufficient.
  • the gas is slowly overflowed, and macropores of micron level will not be formed. Therefore, the embodiment of the present application adopts the method of rapid heating and heating, and the hydrocarbon compound is violently decomposed into gas overflow during the rapid heating process, and its short-term gas production is large, and it is difficult to grow from small to small. Exhaust from the micropores will change the small micropores into micrometer-level macropores by the expansion force of the gas.
  • the particle size of the pulverized raw coke should not be too small. If the particle size is too small, the specific surface area will be too large, and the gas will not be able to accumulate, and it will easily overflow from the small particles, which will not cause the expansion and opening of the small pores.
  • the embodiment of this application requires that the pulverized petroleum coke has a larger size, and the particle size Dv50 of the pulverized raw coke particles should be above 8 ⁇ m. It should not be too large, and the particle size Dv50 of the raw coke particles should be limited to less than 20 ⁇ m.
  • the embodiment of the present application can effectively ensure the smooth removal of gas by adding vents or active exhaust and other devices, without causing damage to the equipment, and will not be flammable. The accumulation of gas can cause problems such as fire.
  • the heating rate is higher than 30 °C/min (higher than the conventional heating rate of graphitization), which can quickly volatilize and decompose the volatile components of petroleum coke into gas, so as to meet the above pore-forming conditions.
  • the heating rate is slowed down, so as to ensure the sufficient and uniform heating of the petroleum coke transformation process, avoid the deformation and cracking of the particles due to uneven heating during the graphitization process, and ensure the stability and reliability of the graphitization process.
  • the heat preservation treatment is started, and the graphitization transformation is basically completed after the heat preservation for about 36 hours.
  • the graphitization degree of the graphite can reach more than 90%.
  • ball milling and shaping the particles can change the surface state of the particles and ensure that the specific surface area BET of the particles is in a suitable range.
  • the graphite defects on the surface layer will increase, which is conducive to improving the dynamics of the graphite material. Powder compaction also will improve.
  • the preparation method of the carbonaceous particles with pores is not limited to this, but can also be prepared by other methods well known in the art.
  • the carbonaceous particles with pores are prepared by the following method: selecting a raw material of petroleum coke or needle coke with high volatile content, the volatile content needs to reach more than 11%, and pulverizing the raw material to a certain particle size diameter range, the particle size Dv50 of the pulverized petroleum coke or needle coke raw material is controlled at 8 ⁇ m to 20 ⁇ m; then the pulverized petroleum coke or needle coke raw material is heat-treated alone, or mixed with a part of natural graphite or mesophase carbon microparticles.
  • the balls are heat treated together; the heat treatment includes firstly heating up from normal temperature to 1300°C, the heating rate is ⁇ 30°C/min, and then slowly heating up to 2850°C at a rate of 10 ⁇ 3°C/min and holding the temperature at 2850 ⁇ 30°C for 36 ⁇ 5 hours, make it undergo graphitization transformation, and finally cool down and cool, carry out ball milling and shaping, and then carry out sieving and demagnetization to obtain the negative electrode material.
  • the present application provides an electrochemical device comprising a negative electrode, a positive electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode.
  • the electrochemical device of the present application may be a lithium ion battery, or may be any other suitable electrochemical device.
  • the electrochemical device in the embodiments of the present application includes any device that undergoes an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, and solar cells. or capacitors.
  • the electrochemical device is a lithium secondary battery including, but not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.
  • the electrochemical device of the present application is an electrochemical device including a positive electrode having a positive electrode active material capable of occluding and releasing metal ions, and a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions. of any of the above negative electrode materials.
  • the negative electrode material used in the electrochemical device of the present application is any of the above negative electrode materials of the present application.
  • the negative electrode material used in the electrochemical device of the present application may further include other negative electrode materials within the scope of not departing from the gist of the present application.
  • the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the aforementioned negative electrode material.
  • the compaction density PD g/cm 3 of the negative electrode satisfies: 1.45 ⁇ PD ⁇ 1.75. In some embodiments, the compaction density PD g/cm 3 of the negative electrode satisfies: 1.50 ⁇ PD ⁇ 1.68.
  • the negative electrode has a compacted density PD g/cm 3 of about 1.45 g/cm 3 , about 1.50 g/cm 3 , about 1.52 g/cm 3 , about 1.56 g/cm 3 , about 1.58 g /cm 3 , about 1.60 g/cm 3 , about 1.62 g/cm 3 , about 1.65 g/cm 3 , about 1.67 g/cm 3 , about 1.68 g/cm 3 , about 1.70 g/cm 3 , about 1.75 g/cm 3 cm3 or a range of any two of these values. If the compaction density of the negative electrode is too high, the low-temperature kinetics will be reduced and the discharge rate will be affected. If the compaction density of the negative electrode is too low, the active material will fall from the pole piece and affect the battery stability.
  • the porosity ⁇ of the negative electrode satisfies: ⁇ 20%. In some embodiments, the porosity ⁇ of the negative electrode satisfies: ⁇ 22%. In some embodiments, the porosity ⁇ of the negative electrode satisfies: ⁇ 25%. From the perspective of the negative pole piece, the larger the porosity of the negative pole piece, the more developed its pore structure, the better the wettability of the electrolyte, and the higher the liquid phase conduction velocity of active ions. Therefore, the greater the porosity of the negative pole piece is , the better the kinetic performance of the battery; however, the greater the porosity of the negative pole piece, the energy density of the battery will also have a significant negative impact. Therefore, it is necessary to make the porosity of the negative electrode within the above-mentioned suitable range.
  • the capacity retention rate decreases by less than or equal to 20%.
  • Porous materials are conducive to the infiltration and circulation of the electrolyte. During the cycle, with the consumption of the electrolyte, the amount of the electrolyte decreases. When the material structure is dense and non-porous, the interface will affect the performance, forming purplish spots and other defects, reducing the cycle. The porous material electrolyte infiltration is better, which will greatly delay the occurrence of adverse events such as purpura, thereby improving the cycle and slowing down the capacity decay of the battery.
  • the electrochemical The device has excellent low-temperature discharge performance and low-temperature charging capability.
  • the negative electrode disassembled from the fresh battery and the negative electrode disassembled after cycling still meet the above-mentioned range of compaction density and porosity, and the negative electrode material stripped and extracted from it still meets the characteristics of the negative electrode material described in any of the above embodiments.
  • Electrochemical devices such as lithium ion batteries, which are composed of this negative electrode and positive electrode, electrolyte and separator, have excellent low-temperature discharge performance and low-temperature charging ability, and meet the discharge ratio at 0°C ⁇ 80%, and charge at 0°C and 0.3C. Does not precipitate lithium.
  • the negative active material layer further includes a binder.
  • the binder may include various binder polymers such as polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyfluoro Ethylene, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene Rubber, epoxy resin, nylon, etc.
  • the negative electrode active material layer further includes a conductive agent to improve electrode conductivity.
  • a conductive agent to improve electrode conductivity.
  • Any conductive material can be used as the conductive material as long as it does not cause chemical change.
  • conductive agents include, but are not limited to: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.; metal-based materials such as metals including copper, nickel, aluminum, silver, etc. Powder or metal fibers; conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof.
  • the negative current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, conductive metal clad polymer substrates, and any combination thereof. In some embodiments, the negative electrode current collector is copper foil.
  • the structure of the negative electrode is a negative electrode plate structure known in the art that can be used in an electrochemical device.
  • the preparation method of the negative electrode is known in the art and can be used for the preparation of the negative electrode of the electrochemical device.
  • the negative electrode can be obtained by mixing the active material, the conductive agent and the binder in a solvent, and heating the thickening agent as needed to prepare the active material composition, and coating the active material composition with the active material composition. overlaid on the current collector.
  • the solvent may include, but is not limited to, water, N-methylpyrrolidone.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the negative electrode current collector, the positive electrode active material layer including a positive electrode active material.
  • the specific types of the positive electrode active materials are not specifically limited, and can be selected according to requirements.
  • the positive active material includes a compound that reversibly intercalates and deintercalates lithium ions (ie, a lithiated intercalation compound).
  • the positive electrode active material may include a lithium transition metal composite oxide.
  • the lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.
  • the positive active material is selected from at least one of the following: lithium cobalt oxide (LiCoO 2 ), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn 2 O 4 ), nickel Lithium manganate (LiNi 0.5 Mn 1.5 O 4 ), lithium iron phosphate (LiFePO 4 ).
  • the positive active material layer further includes a binder, and optionally a conductive material.
  • the binder can improve the bonding of the positive electrode active material particles to each other, and can improve the bonding of the positive electrode active material and the positive electrode current collector.
  • the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl Ethoxylated polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy Resin and nylon, etc.
  • the positive active material layer includes a conductive material to impart electrical conductivity to the electrode.
  • the conductive material may include any conductive material as long as it does not cause chemical changes.
  • Non-limiting examples of conductive materials include carbon-based materials (eg, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, etc.), metal-based materials (eg, metal powders, metal fibers, etc., including such as copper, nickel, aluminum, silver, etc.), conductive polymers (eg, polyphenylene derivatives), and mixtures thereof.
  • the positive electrode current collector is a metal, such as, but not limited to, aluminum foil.
  • the structure of the positive electrode is a positive electrode plate structure known in the art that can be used in an electrochemical device.
  • the method of making the positive electrode is known to those skilled in the art as a method of making a positive electrode that can be used in an electrochemical device.
  • the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector.
  • the solvent may include water, N-methylpyrrolidone, etc., but is not limited thereto.
  • the electrolyte that can be used in the embodiments of the present application may be an electrolyte known in the prior art. Electrolytes can be divided into aqueous electrolytes and non-aqueous electrolytes. Compared with aqueous electrolytes, electrochemical devices using non-aqueous electrolytes can work in a wider voltage window, thereby achieving higher energy density.
  • the non-aqueous electrolyte includes an organic solvent, an electrolyte, and additives.
  • Electrolytes that can be used in the electrolyte of the embodiments of the present application include, but are not limited to: inorganic lithium salts, such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiSbF 6 , LiSO 3 F, LiN(FSO 2 ) 2 , etc.; Fluorine-containing organolithium salts such as LiCF 3 SO 3 , LiN(FSO 2 )(CF 3 SO 2 ), LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , cyclic 1,3- Lithium hexafluoropropanedisulfonimide, cyclic lithium 1,2-tetrafluoroethanedisulfonimide, LiPF 4 (CF 3 ) 2 , LiN(CF 3 SO 2 )(C4F 9 SO 2 ), LiC (CF 3 SO 2 ) 3 , LiPF 4 (CF 3 SO 2 ) 2 , Li
  • the said electrolyte may be used individually by 1 type, and may use 2 or more types together.
  • the electrolyte includes a combination of LiPF 6 and LiBF 4 .
  • the electrolyte includes LiPF 6 .
  • the concentration of the electrolyte is in the range of 0.8 mol/L to 3 mol/L, such as in the range of 0.8 mol/L to 2.5 mol/L, 0.8 mol/L to 2 mol/L, 1 mol/L In the range of L to 2 mol/L, another example is 1 mol/L, 1.15 mol/L, 1.2 mol/L, 1.5 mol/L, 2 mol/L or 2.5 mol/L.
  • the additives that can be used in the electrolyte of the embodiments of the present application can be additives known in the art that can be used to improve the electrochemical performance of batteries.
  • the additives include, but are not limited to, polynitrile compounds, sulfur-containing additives, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4 butane sulfonate at least one of lactones.
  • the organic solvent that can be used in the electrolyte in the embodiments of the present application can be any organic solvent known in the prior art.
  • organic solvents include, but are not limited to, carbonate compounds, ester-based compounds, ether-based compounds, ketone-based compounds, alcohol-based compounds, aprotic solvents, or combinations thereof.
  • examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
  • the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate , at least one of methyl acetate or ethyl propionate.
  • EC ethylene carbonate
  • PC propylene carbonate
  • DEC diethyl carbonate
  • EMC ethyl methyl carbonate
  • DMC dimethyl carbonate
  • propylene carbonate at least one of methyl acetate or ethyl propionate.
  • the preparation method of the electrolyte in the embodiments of the present application is not limited, and can be prepared in the manner of a conventional electrolyte.
  • the electrolytes of the present application may be prepared by mixing the components.
  • a separator is provided between the positive electrode and the negative electrode to prevent short circuits.
  • the material and shape of the separator are not particularly limited, and may be any of those disclosed in the prior art.
  • the separator includes a polymer or inorganic or the like formed from a material that is stable to the electrolyte of the present application.
  • the release film includes a substrate layer.
  • the base material layer is a non-woven fabric, membrane or composite membrane with a porous structure.
  • the material of the substrate layer may be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • the material of the substrate layer can be selected from polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane.
  • the present application provides an electronic device comprising the aforementioned electrochemical device.
  • the low-temperature discharge performance and low-temperature charging performance of the electrochemical device can be improved, so that the electrochemical device manufactured therefrom is suitable for electronic equipment in various fields, especially suitable for working under low temperature conditions. electronic equipment required.
  • the use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the art.
  • the electronic devices include, but are not limited to, notebook computers, pen-type computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphone headsets, video recorders, LCD televisions , portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys , game consoles, clocks, power tools, flashes, cameras, large household batteries and lithium-ion capacitors, etc.
  • the electrochemical device of the present application is applicable not only to the electronic devices exemplified above, but also to energy storage power stations, marine vehicles, and air vehicles.
  • Airborne vehicles include airborne vehicles within the atmosphere and airborne vehicles outside the atmosphere.
  • the negative electrode material graphite, additive (conductive agent), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) are fully stirred in solvent deionized water in a weight ratio of 95.7:1.5:1.8:1 Mix to form a homogeneous anode slurry.
  • the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, dried, and cold pressed to form a negative electrode active material layer, and then the negative electrode is obtained by cutting and welding the tabs.
  • the difference in the preparation of the negative electrode mainly lies in the difference of the negative electrode material used.
  • the positive active material lithium iron phosphate (LiFePO 4 ), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed in the solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.3:2.2:1.5, in The mixture is fully stirred under a vacuum mixer to obtain a positive electrode slurry.
  • NMP N-methylpyrrolidone
  • the positive electrode material is coated on the aluminum foil of the positive electrode current collector, dried, and cold-pressed to form a positive electrode active material layer, and then the positive electrode is obtained by cutting pieces and welding tabs.
  • the concentration of LiPF 6 is 1 mol/L.
  • a polyethylene (PE) porous polymer film was used as the separator.
  • the obtained positive electrode, separator and negative electrode are stacked in sequence, so that the separator is placed between the positive electrode and the negative electrode to isolate the positive electrode and the negative electrode, and then the bare cell is obtained by winding;
  • the electrolyte is obtained through the process of vacuum packaging, standing, and chemical formation to obtain a lithium-ion battery.
  • the low-temperature discharge ratio test process of lithium-ion batteries is as follows:
  • the discharge ratio at 0°C of the lithium ion battery (0°C discharge capacity/25°C discharge capacity) ⁇ 100%, and the discharge rate is 1C discharge.
  • the low-temperature charging performance test process of lithium-ion batteries is as follows:
  • the test standard for powder compaction refers to GB/T24533-2009 "Graphite Anode Materials for Lithium Ion Batteries”.
  • the specific test method is as follows: Weigh 1.0000 ⁇ 0.0500g of the sample and place it in the test mold (CARVER#3619 (13mm), then place the sample in the test equipment, the test equipment is Sansi Zongheng UTM7305, the test tonnage is 0.3t, 0.5t, 0.75t, 1.0t, 1.5t, 2.0t, 2.5t, 3.0t, 4.0t, 5.0t, the boost rate is 10mm/min, the boost hold time is 30s, the pressure relief rate is 30mm/min, the pressure relief hold The time is 10s, and the powder compaction density described in the text is the compaction density measured when 5t is released.
  • the compaction density of the negative electrode the mass of the negative electrode active material layer/the volume of the negative electrode active material layer.
  • Scanning Electron Microscope (SEM) test hereinafter referred to as Scanning Electron Microscope (SEM) test, the principle is to use the secondary electron signal imaging generated by the interaction between the focused electron beam and the sample to test the sample, which is often used to test the microscopic appearance of the sample. appearance.
  • the scanning electron microscope used in this application is JSM-6360LV of JEOL company and its supporting X-ray energy spectrometer to analyze the morphology and structure of the sample. In the process of use, the prepared samples were evenly coated on the conductive tape, and the samples were dipped on the sample stage and placed in the electron microscope for testing.
  • the specific test steps are as follows:
  • the active material if the active material is in powder form, it can be directly and evenly coated on the conductive tape. If the active material has been coated on the copper foil (it can be understood that the active material is combined with the copper foil to form an anode sheet), place the combined pole piece in a muffle furnace at 400°C for 40 ⁇ 5min, then cool down to room temperature and take it out, then peel off the active material on the surface of the copper foil, gently grind and disperse it and then apply it on the conductive On the tape, ready for the next observation;
  • the range of the selected area for SEM observation of particle morphology is 80 ⁇ m ⁇ 100 ⁇ m. On the basis of this range, it is necessary to ensure that the number of active particles in this area is greater than 30. If these two conditions are met, the selected area can be considered as an effective area. area;
  • the particle structure can be observed one by one in the region, and the number of particles in the effective region, the number of particles with pores and the number of pores in a single particle can be counted.
  • Table 1 shows the relevant performance parameters of the negative electrode materials in Examples 1 to 16 and Comparative Examples 1 to 3 and the performance of the corresponding batteries.
  • Examples 1 to 16 satisfy 0.3 ⁇ m ⁇ Y ⁇ 2.0 ⁇ m, 0.6 ⁇ m ⁇ X ⁇ 1.5 ⁇ m; or the ratio of the number of carbonaceous particles containing the number of pores N ⁇ 2 to the total number of carbonaceous particles ( In Table 1, it is abbreviated as N ⁇ 2 /N total ) ⁇ 60%, and the proportion of the number of carbonaceous particles containing pores with a number of 3 ⁇ N ⁇ 5 to the total number of carbonaceous particles (abbreviated as N 3-5 /N in Table 1 total ) ⁇ 30%, while the negative electrode materials of Comparative Examples 1 to 3 did not satisfy the above conditions.
  • the negative electrode materials of Examples 1 to 16 have porous structures and satisfy 0.3 ⁇ m ⁇ Y ⁇ 2.0 ⁇ m, 0.6 ⁇ m ⁇ X ⁇ 1.5 ⁇ m; or N ⁇ 2 / Ntotal ⁇ 60 %, N
  • the size of the pores is suitable and the distribution is uniform, so that the battery has good low-temperature discharge ratio performance and low-temperature charging capability.
  • Example 1-10 when the active material simultaneously satisfies 0.3 ⁇ m ⁇ Y ⁇ 2.0 ⁇ m, 0.6 ⁇ m ⁇ X ⁇ 1.5 ⁇ m and N ⁇ 2 /N total ⁇ 60 %, N 3-5 /N total ⁇ 30 %
  • the low temperature performance of the battery is significantly improved, because the size of the pores is suitable and the number distribution is uniform, which can not only ensure the wettability of the electrolyte to the active material but also the mechanical strength of the particles, because the low temperature improvement effect is the best.
  • Example 11-13 when the active material satisfies 0.3 ⁇ m ⁇ Y ⁇ 2.0 ⁇ m, 0.6 ⁇ m ⁇ X ⁇ 1.5 ⁇ m and does not satisfy N ⁇ 2 / Ntotal ⁇ 60 %, N3-5 / Ntotal ⁇ 30 % , the low temperature performance is improved to a certain extent.
  • the pore size of the active material satisfying 0.3 ⁇ m ⁇ Y ⁇ 2.0 ⁇ m and 0.6 ⁇ m ⁇ X ⁇ 1.5 ⁇ m is larger, which can improve the wettability of the electrolyte to the active material and improve the low temperature performance of the battery.
  • N ⁇ 2 /N total ⁇ 60%, and N 3-5 /N total ⁇ 30% the number of pores is too large, which will lead to a decrease in the mechanical strength of the active material, and the active material particles are easily broken after the pole piece is cold pressed Crack, destroy part of the pore structure and generate a new unfilmed graphite interface, and the re-film formation will continue to consume the electrolyte, which will lose part of the low-temperature performance of the battery.
  • Comparative Examples 1-3 are the battery performance when the negative electrode materials do not meet the above conditions (A) and (B), it can be found that when the pore size is too small or too large and the number of pores of the active material particles is too large, the low temperature performance of the battery Obvious reduction. This is because when the pores in the active material are too small, it is not only insufficient to significantly increase the contact area between the active material and the electrolyte, but also increases the side reactions between the active material and the electrolyte, reducing the low-temperature performance of the battery.
  • the active material needs to meet the appropriate pore size and number distribution to achieve the most ideal low-temperature performance improvement effect.
  • Table 2 shows the relevant performance parameters of the negative electrode materials of Examples 17 to 24 and the performance of the corresponding batteries. Table 2 continues to improve the battery performance on the basis of Example 6. In order to ensure that the active material has a certain mechanical strength while having a porous structure, the relationship between Dv50 and 5Y is defined.
  • Table 3 shows the relevant performance parameters of the negative electrode materials of Examples 25 to 28 and the performance of the corresponding batteries. Table 3 continues to improve the low-temperature charge-discharge performance of the battery on the basis of Example 20.
  • the range of distance L defines the maximum diameter Y of pores in a certain area (such as the aforementioned 80 ⁇ m ⁇ 100 ⁇ m area), X is the average maximum diameter X of particles with pores in this area, and the difference range of Y-X.
  • Example 20 It can be found from Table 3 that when Y-X ⁇ 1.0 ⁇ m and L ⁇ 8.0 ⁇ m are satisfied, compared with Example 20, the 0°C discharge ratio of Example 25 to Example 28 is improved; this is because the pores are in the active material When the particles are uniformly distributed and have good size consistency, the electrolyte wettability of the negative electrode sheet will be significantly improved, which will promote the deintercalation speed of lithium ions in the active particles and reduce the deintercalation path length, thereby improving the battery performance. Low temperature discharge performance.
  • Y is the maximum diameter Y of the pores in a selected area (such as the aforementioned 80 ⁇ m ⁇ 100 ⁇ m area)
  • X is the average maximum diameter X of the particles with pores in this area
  • Y-X can be used to characterize the consistency of the pore size, the difference The larger the value, the worse the consistency of the pore size, which is not conducive to the uniformity of the infiltration of the electrolyte, affects the infiltration of the electrolyte, and reduces the battery performance. Therefore, by making Y-X satisfy Y-X ⁇ 1.0 ⁇ m, the size of the pores of the negative electrode material can be guaranteed. consistency.
  • the uniformity of the pore distribution can be ensured, so that the pores are evenly distributed on the active material particles, the infiltration of the electrolyte is improved, and the low temperature performance of the battery is effectively improved. Therefore, after defining the uniformity of pore size and the uniformity of pore distribution, the low temperature discharge ratio of the battery is significantly improved.
  • Table 4 shows the relevant performance parameters of the negative electrode materials of Examples 29 to 33 and the performance of the corresponding batteries. Table 4 continues to improve the low-temperature charge-discharge performance of the battery on the basis of Example 26.
  • the compaction density CD g/cm 3 In order to ensure the processing performance of the negative electrode material and other related properties, the compaction density CD g/cm 3 , the gram capacity Cap mAh/g, and the gram capacity Cap mAh/ The relationship between g and the compaction density CD g/cm 3 and the relationship between Dv99 and Dv50 are within suitable ranges.
  • Example 26 the 0°C discharge ratio of Example 29 to Example 33 is improved, which indicates that by limiting the particle size, compaction, gram capacity of the active material and their combined relationship, it can be guaranteed that The processability and electrical properties of the active materials are fully exploited, effectively improving the low-temperature performance of the battery.
  • the particle size distribution of the active material by making the particle size distribution of the active material satisfy Dv99 ⁇ 3.5 ⁇ Dv50, it can ensure that the particle size of the active material is moderate and the particle distribution is narrow, so as to avoid too many large particles affecting the processing of the pole piece, and at the same time, to avoid excessive particle size and lead to lithium
  • the de-intercalation path of the ions increases, reduces the material kinetics, and avoids that the particle size is too small, which will affect the compaction of the pole piece and reduce the storage performance.
  • the energy density of the battery can be guaranteed, and at the same time, in order to balance the gram capacity and the compaction density, it has a high compaction density under high capacity, so as to obtain more High battery energy density makes the active material satisfy Cap ⁇ 350-50 ⁇ (1.90-CD).
  • Table 5 shows the relevant performance parameters of the negative electrode materials of Examples 34 to 40 and the performance of the corresponding batteries. Table 5 continues to improve the low-temperature charge-discharge performance of the battery on the basis of Example 32. In order to ensure the electrochemical performance of the material such as kinetics and energy density, the specific surface area BET and the degree of graphitization G of the active material are limited within an appropriate range.
  • Example 34 the 0°C discharge ratio of Example 34 to Example 40 is better than that of Example 32, indicating that a suitable range of graphitization degree and specific surface area can improve the performance of the battery.
  • the degree of graphitization is an important parameter affecting the gram capacity of graphite, and it is also a key parameter affecting the kinetics of the material. The lower the degree of graphitization, the larger the graphite layer spacing is, which is conducive to the rapid de-intercalation of lithium ions and has better kinetics.
  • the graphite gram capacity is lower at a lower degree of graphitization, and the compaction density is also lower, which affects the energy density of the battery. Therefore, if the degree of graphitization needs to be in an appropriate range, both kinetics and energy density can be taken into account.
  • the specific surface area of the active material will affect the storage performance of the battery. The larger the specific surface area, the more violent the reaction with the electrolyte, which is easy to generate gas during high temperature storage, reducing the battery performance. Therefore, by making the graphitization degree G of the active material satisfy 90% ⁇ G ⁇ 95.5% and the specific surface area BET ⁇ 3.0 m 2 /g, it is beneficial to optimize the performance of the battery.
  • Table 6 shows the relevant performance parameters of the negative electrode materials of Examples 41 to 46 and the performance of the corresponding batteries. Table 6 continues to improve the low-temperature charge-discharge performance of the battery on the basis of Example 36. By making the compaction density PD g/cm 3 of the negative electrode and the porosity ⁇ of the negative electrode within an appropriate range, the low-temperature discharge performance of the battery can be improved.
  • Example 41 to Example 46 is better than that of Example 36, indicating that the appropriate compaction density and porosity of the negative electrode plate can improve the performance of the battery.
  • the range can take into account the cohesion of the negative electrode and the non-breakage of the particles. The higher porosity ensures the wettability of the electrolyte to the negative electrode, which can effectively improve the low-temperature performance of the battery.
  • the compaction density PD g/ cm3 of the negative electrode satisfy 1.45 ⁇ PD ⁇ 1.75, it can be ensured that the cohesive force of the negative electrode pole piece and the active material particles will not be crushed during cold pressing; if the compaction density of the pole piece is Too low, the cohesion of the pole piece is low, the active material is easy to fall from the negative pole piece, and the performance of the battery is reduced. Reduce battery performance.
  • the porosity ⁇ of the negative electrode satisfy ⁇ 20%, the infiltration performance of the battery can be ensured. If the porosity of the negative electrode is too low, the electrolyte infiltration of the negative electrode will be poor, and the low temperature performance of the battery will be reduced.

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Abstract

一种负极材料，所述负极材料包含碳质活性材料，通过观察SEM图像，在80μm×100μm区域，所述碳质活性材料包括具有孔的碳质颗粒；所述负极材料满足以下条件(A)或(B)：(A)所述孔的长度最长的方向为孔的最大直径Y，单个碳质颗粒孔最大直径Y的范围满足0.3μm≤Y≤2.0μm，且碳质颗粒的孔最大直径平均值X满足0.6μm≤X≤1.5μm；(B)包含孔数量N≤2的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为≤60％，包含孔数量3≤N≤5的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为≤30％；包括该负极材料的电化学装置。

Description

负极材料及包含其的电化学装置和电子设备
本申请要求于2021年03月30日提交中国专利局，申请号为202110340794.6、申请名称为“负极材料及包含其的电化学装置和电子设备”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及储能技术领域，更具体地，涉及一种负极材料及包含其的电化学装置和电子设备。
背景技术
随着电化学装置比如锂离子电池动力市场的不断扩大，对电池的性能要求也一直不断提升，比如不仅要求电池轻便，而且还要求电池具有良好的低温充放电性能。以电动车或电动工具为例，其应用场景非常广泛，使得其使用工况也复杂多样，在低温条件下工作是难以避免的，因而需要其所使用的电池具有良好的低温放电性能，且低温充电也需要满足较高倍率下充电不析锂，这两者结合起来可使锂离子电池在低温工况下更有效的工作。因此，为了满足市场需求，需要开发出动力学优异的负极材料，以改善或提升锂离子电池在低温条件下工作的能力。
通常，通过采用减小石墨粒度来缩短锂离子的嵌锂路径的方式，或通过对负极材料进行直接包覆处理的方式，来达到改善或提高负极材料动力学的目的。然而，这两种方式会对负极材料的能量密度造成损失，包括压实密度，克容量等，且成本较高。
申请内容
本申请实施例提供了一种负极材料，在至少某种程度上解决至少一种存在于相关领域中的问题。本申请实施例还提供了使用该负极材料的电化学装置和电子设备。本申请实施例的负极材料具有较高的低温放电倍率性能与低温充电能力，从而可以改善电化学装置的低温工作性能。
根据本申请的第一方面，提供一种负极材料，通过观察SEM图像，在80μm×100μm区域，该区域可以通过SEM观察后选取，所述碳质活性材料包括具有孔的碳质颗粒；所述负极材料满足以下条件；所述孔的长度最长的方向为孔的最大直径Y，所述孔满足以下条件(A)或(B)：(A)单个碳质颗粒孔最大直径Y的范围满足0.3μm≤Y≤2.0μm，且碳质颗粒的孔最大直径平均值X满足0.6μm≤X≤1.5μm；(B)包含孔数量N≤2的碳 质颗粒的数量占所述区域碳质颗粒总数量的比例为≤60％，包含孔数量3≤N≤5的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为≤30％。
在上述方案中，通过使存在于碳质颗粒中的孔满足上述条件(A)或(B)，满足条件(A)，颗粒的孔具有较大的尺寸，满足条件(B)，颗粒的孔具有较多的数量。颗粒的特征满足上述条件(A)或(B)，可以使负极材料对电化学装置的倍率性能有明显改善，对低温充放电性能也有显著提高，可以有效改善低温析锂，负极极片的电解液浸润性也会有所改善。
在本申请的一些实施例中，所述具有孔的碳质颗粒的中值粒径Dv50与所述Y满足以下关系：Dv50≥5Y，其中Dv50的单位为μm。
在上述方案中，孔的体积占整个颗粒的尺寸被限定在合适的范围，可以减少或避免因为孔相对于颗粒太大而在颗粒中形成大空腔，减小了因机械强度过大而导致颗粒冷压时破裂。
在本申请的一些实施例中，所述孔的最大直径Y与所述孔最大直径平均值X满足以下关系：Y-X≤1.0μm；在本申请的一些实施例中，单个具有孔的碳质颗粒中，相邻两个所述孔之间的距离L≤8.0μm。
在上述方案中，碳质颗粒的孔直径差满足上述范围，可以保证孔大小一致性较好，有利于锂离子的脱嵌。并且相邻孔的间距满足上述范围，可以保证孔在碳质颗粒中均匀分布，提高极片浸润性能，改善负极材料的动力学。
在本申请的一些实施例中，所述孔包括通孔或盲孔中的至少一种。
在本申请的一些实施例中，所述碳质活性材料在5t压力下的压实密度CD g/cm 3,CD≤1.85，较低的粉末压实密度意味着多孔石墨的孔结构不容易被破坏，在较大的压力下仍能保证孔结构的完整，不至于被压碎；在本申请的一些实施例中，所述碳质活性材料的克容量Cap mAh/g，Cap≥340，所述Cap与所述碳质活性材料在5t压力下的压实密度CD g/cm 3的数值满足Cap≤350-50×(1.90-CD)，这样可以保证多孔材料的克容量与压实密度的平衡，使其在高容量下具有高的压实密度，从而获得更高的电池能量密度；在本申请的一些实施例中，所述碳质活性材料的粒径分布满足Dv99≤3.5×Dv50，这样可以保证多孔材料粒度大小适中且颗粒分布较窄，避免出现太多的大颗粒影响极片加工。
在上述方案中，碳质活性材料参数满足上述范围，有利于提升材料的动力学及电池的低温充放电性能，同时保证电池的能量密度，
在本申请的一些实施例中，所述碳质活性材料的石墨化度G为90％至95.5％，较 低的石墨化度可以保证多孔材料的石墨层间距较大，有利于锂离子的快速脱嵌，提升动力学，同时为了保证电池能量密度，石墨化度不宜过低；在本申请的一些实施例中，所述碳质活性材料的比表面积BET≤3.0m 2/g，多孔材料因为孔结构的存在，比表面积一般较大，但是过大的比表面积会影响到电池的存储与循环性能，比表面积越大，其与电解液反应越剧烈，恶化电池的存储与循环性能，因此控制活性材料的比表面积BET处于较低水平；在本申请的一些实施例中，所述碳质活性材料包括人造石墨、天然石墨或中间相碳微球中的至少一种。
在上述方案中，合适范围的石墨化度可以兼顾材料动力学与能量密度，保证电池的性能。并且，碳质活性材料的比表面积BET在此范围，可以保证电化学装置的存储等电化学性能。
根据本申请的第二方面，提供一种电化学装置，包括负极，所述负极包括负极集流体和设置在所述负极集流体至少一个表面上的负极活性物质层，其中所述负极活性物质层包括如前述的负极材料。
所述电化学装置还包括正极、设置于所述正极和所述负极之间的隔离膜以及电解液。所述电解液包括氟代碳酸乙烯酯和1,3-丙烷磺内酯。
在本申请的一些实施例中，所述负极的压实密度PD g/cm 3满足：1.45≤PD≤1.75，多孔材料的负极不宜压实密度太高，不然会破坏材料的孔结构，而且高的压实密度会恶化电池的充电能力，多孔材料的负极压实密度过低，会导致活性材料从极片掉落，影响电池稳定性，因此限定其在一定的范围；在本申请的一些实施例中，所述负极的孔隙率Φ满足：Φ≥20％，多孔材料因为其本身具有较多的孔结构，其在构成负极时，负极极片的孔隙率越高，孔道结构发达，电解液的浸润性好，电池的动力学性能较好。
在上述方案中，满足此负极条件的电化学装置的低温放电性能及低温充电能力优异。
在本申请的一些实施例中，25℃条件下，经过循环500次循环后，容量保持率降低小于或等于20％。电解液中的氟代碳酸乙烯酯和1,3-丙烷磺内酯与负极材料相互作用，有效的改善其接触界面，从而改善循环。
根据本申请的第三方面，提供一种电子设备，其包括根据本申请上述实施例所述的电化学装置。
本申请实施例提供的负极材料包括具有孔的碳质颗粒，且该孔的尺寸较大，数量较多，负极材料与电解液的接触面明显增加，提高了负极材料的动力学性能，改善了负极材料的低温放电倍率性能与低温充电能力。因此，当电化学装置在低温条件下工 作时，使用本申请的负极材料能有效改善该电化学装置的低温充放电性能。本申请实施例的额外层面及优点将部分地在后续说明中描述、显示、或是经由本申请实施例的实施而阐释。
附图说明
在下文中将简要地说明为了描述本申请实施例或现有技术所必要的附图以便于描述本申请的实施例。显而易见地，下文描述中的附图仅只是本申请中的部分实施例。对本领域技术人员而言，依然可以根据这些附图中所例示的结构来获得其他实施例的附图。
图1为本申请示例性的一种实施方式提供的负极材料的扫描电子显微镜(SEM)图。
具体实施方式
本申请的实施例将会被详细的描示在下文中。本申请的实施例不应该被解释为对本申请的限制。
如本文中所使用，术语“约”、“大致”或“大体上”用以描述及说明小的变化。当与事件或情形结合使用时，所述术语可指代其中事件或情形精确发生的例子以及其中事件或情形极近似地发生的例子。举例来说，当结合数值使用时，术语可指代小于或等于所述数值的±10％的变化范围，例如小于或等于±5％、小于或等于±4％、小于或等于±3％、小于或等于±2％、小于或等于±1％、小于或等于±0.5％、小于或等于±0.1％、或小于或等于±0.05％。
另外，有时在本文中以范围格式呈现量、比率和其它数值。应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于所述范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围一般。
在具体实施方式及权利要求书中，由术语“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A、B，那么短语“A、B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B、C，那么短语“A、B、C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元 件。项目C可包含单个元件或多个元件。在具体实施方式及权利要求书中，如果列出项目A或B，意味着仅A；仅B；或A及B。
如本文中所使用，“Dv99”表示材料在体积基准的粒度分布中从小粒径侧起达到体积累计99％的粒径，即，小于此粒径的材料的体积占材料总体积的99％。
如本文中所使用，“Dv50”也称为“中值粒径”，表示材料在体积基准的粒度分布中从小粒径侧起达到体积累计50％的粒径，即，小于此粒径的材料的体积占材料总体积的50％。
负极材料中，材料的Dv50、Dv99可以用本领域公知的方法进行测定，例如用激光粒度分析仪(例如，马尔文粒度测试仪)测定。
负极材料中，孔的最大直径Y与孔最大直径平均值X，及孔的数量可以按本领域公知的方法进行测定或计算，例如对样品进行扫描电子显微镜(SEM)检测，根据所得到的SEM图谱直观地得到或计算得到样品中孔的长度和孔的数量。如本申请实施例中，存在一SEM区域内至少存在30个颗粒(80μm×100μm)，可以得知这30个以上的颗粒中有一部分颗粒具有孔，具有孔的颗粒中至少存在一个颗粒，其包含的孔数量≥1个，且最大直径Y满足0.3μm≤Y≤2.0μm。对具有孔的碳质颗粒孔的最大直径Y计算平均值，即为碳质颗粒孔的最大直径Y的平均值X，即这部分具有孔的颗粒还满足孔的最大直径Y的平均值X满足范围0.6μm≤X≤1.5μm。
一、负极材料
在一些实施例中，本申请提供了一种负极材料，所述负极材料包含碳质活性材料，所述碳质活性材料存在一区域(该区域的尺寸如可以为80μm×100μm)，其包括具有孔的碳质颗粒；
所述孔的长度最长的方向为孔的最大直径Y，所述孔满足：
(A)单个碳质颗粒孔的最大直径Y的范围满足0.3μm≤Y≤2.0μm，且碳质颗粒的孔最大直径平均值X满足0.6μm≤X≤1.5μm；(B)包含孔数量N≤2的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为≤60％，包含孔数量3≤N≤5的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为≤30％。
根据本申请实施例，通过使存在于碳质颗粒中的孔满足上述条件(A)或(B)，满足条件(A)，颗粒的孔具有较大的尺寸，满足条件(B)，颗粒的孔具有较多的数量。颗粒的特征满足上述条件(A)或(B)，可以使负极材料对电化学装置的倍率性能有明显改善，对低温充放电性能也有显著提高，可以有效改善低温析锂，负极极片的电解液浸润性也会有所改善。
可以理解，碳质颗粒中存在至少一个孔，且至少一个孔具有长度最长方向上的最大直径(最大外接圆直径)也即Y，多个颗粒的孔最大直径平均值为X，孔的尺寸需要满足如上所限定的Y的范围和X的范围。孔可以是微米级别或亚微米级别的孔。孔的截面形状可以是任意的，如任何规则或不规则的形状，是无特殊限制的；也即，虽然限定了孔的最大直径，但孔的形状并不一定是圆孔。对于不同的孔的截面形状，上述Y可以具有不同的表述。举例说明，比如当孔的截面形状为圆形时，上述Y可以作为孔的直径即孔径；再如当孔的截面形状为长方形时，上述Y可以作为长方形的对角线距离。但值得注意的是，细长的缝隙不属于本申请实施例中所述的孔。
图1显示了本申请实施例提供的负极材料的扫描电子显微镜(SEM)图片，如图1所示，本申请实施例的碳质活性材料包括具有孔的碳质颗粒，该颗粒具有多孔结构，且孔的尺寸较大，其分布也比较均匀，孔可以满足上述条件(A)或(B)。由此，使得包含上述具有孔的碳质颗粒的负极材料为多孔结构，且孔径较大，数量较多，因此使得活性材料与电解液的接触面明显增加，此外，由于孔的存在，金属离子如锂离子的嵌锂通道增加，其嵌锂路径也减小，这样更有利于锂离子的快速脱嵌，提高了负极材料的动力学，进而改善了低温放电倍率性能与低温充电能力。
在一些实施例中，0.5μm≤Y≤1.5μm，0.8μm≤X≤1.2μm。在一些实施例中，Y可以列举为约0.3μm、约0.4μm、约0.5μm、约0.6μm、约0.7μm、约0.8μm、约0.9μm、约1.0μm、约1.3μm、约1.5μm、约1.6μm、约1.7μm、约19μm、约2.0μm或者这些数值中任意两者组成的范围。X可以列举为约0.6μm、约0.7μm、约0.8μm、约0.9μm、约1.0μm、约1.1μm、约1.2μm、约1.3μm、约1.4μm、约1.5μm或者这些数值中任意两者组成的范围。
在一些实施例中，包含孔数量N≤2的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为5％至60％，包含孔数量3≤N≤5的碳质颗粒的数量占总碳质颗粒数量的比例2％至30％。在一些实施例中，包含孔数量N≤2的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为10％至60％，包含孔数量3≤N≤5的碳质颗粒的数量占总碳质颗粒数量的比例5％至30％。在一些实施例中，包含孔数量N≤2的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为约10％、约15％、约20％、约25％、约30％、约35％、约40％、约45％、约50％、约55％、约60％或者这些数值中任意两者组成的范围；包含孔数量3≤N≤5的碳质颗粒的数量占所述区域碳质颗粒总数量的比例为约5％、约8％、约10％、约15％、约18％、约20％、约22％、约25％、约28％、约30％或者这些数值中任意两者组成的范围。
在一些实施例中，所述具有孔的碳质颗粒的中值粒径Dv50与所述Y满足以下关系：Dv50≥5Y。在一些实施例中，所述具有孔的碳质颗粒的中值粒径Dv50与所述Y满足以下关系：Dv50＞5Y。在一些实施例中，所述具有孔的碳质颗粒的中值粒径Dv50与所述Y满足以下关系：Dv50＞5Y，且Dv50＜10Y。
根据本申请实施例，为了保证负极材料具有一定的机械强度，避免极片冷压的时候颗粒破裂，限定颗粒Dv50满足：Dv50≥5Y，在此条件下，孔的体积占整个颗粒的尺寸被限定在合适的范围，减少或避免因为孔相对于颗粒太大而在颗粒中形成大空腔，减小了因机械强度过大而导致颗粒冷压时破裂。
在一些实施例中，具有孔的碳质颗粒满足，(a)所述孔的最大直径Y与所述孔最大直径平均值X满足以下关系：Y-X≤1.0μm；(b)单个具有孔的碳质颗粒中，相邻两个所述孔之间的距离L≤8.0μm。
根据本申请实施例，为了保证负极材料孔大小的均匀性，限定单个碳质颗粒存在两个或两个以上的孔时，其孔的最大直径Y与最大直径平均值X的差异满足Y-X≤1.0μm。因此单个碳质颗粒具有多个孔时，孔大小一致性较好，有利于锂离子的脱嵌。
在一些实施例中，单个所述具有孔的碳质颗粒存在的所述孔的数量N≥2时，相邻两个所述孔之间的距离L≤8.0μm。在一些实施例中，单个所述具有孔的碳质颗粒存在的所述孔的数量N≥2时，相邻两个所述孔之间的距离0.1μm＜L≤8.0μm。在一些实施例中，L可以列举为约8.0μm、约7.5μm、约7.0μm、约6.6μm、约6.2μm、约6.0μm、约5.0μm、约4.0μm、约3.0μm、约2.5μm、约2.0μm等。
根据本申请实施例，为了保证负极材料的孔在颗粒中分布的均匀性，限定负极材料颗粒存在两个或两个以上的孔时，其相邻两个孔之间距离L≤8.0μm，这样可以保证孔在颗粒中均匀分布，提高极片浸润性能，改善负极材料的动力学。
在一些实施例中，所述孔包括通孔或盲孔中的至少一种。也即，在一些实施例中，孔的存在形式可以为通孔；或在另一些实施例中，孔的存在形式可以为盲孔；或在另一些实施例中，孔的存在形式可以同时为通孔和盲孔。
在一些实施例中，所述碳质活性材料的粒径分布满足Dv99≤3.5×Dv50。在一些实施例中，所述碳质活性材料的粒径分布满足Dv99＜3.5×Dv50。根据本申请实施例，为了保证负极材料粒度大小适中且颗粒分布较窄，避免出现太多的大颗粒影响极片加工，同时，粒度过大会导致锂离子的脱嵌路径增加，降低材料动力学，粒度过小会影响极片压实以及降低存储性能。因此通过使活性材料的粒径分布满足Dv99≤3.5×Dv50可以 提升材料的动力学，利于提升电化学装置的低温充放电性能。
在一些实施例中，所述碳质活性材料在5t压力下的压实密度CD g/cm 3，CD≤1.85。在一些实施例中，所述碳质活性材料在5t压力下的压实密度CD g/cm 3，CD≤1.84。在一些实施例中，所述碳质活性材料在5t压力下的压实密度CD g/cm 3，CD为约1.85、约1.84、约1.82、约1.80、约1.79、约1.78、约1.76、约1.75等。为了保证电池的能量密度，限定活性材料的粉末压实密度，活性材料的压实密度与负极极片的压实密度呈正相关，因此，适宜的活性材料的粉末压实密度，有利于提高电池的能量密度。
在一些实施例中，所述碳质活性材料的克容量Cap mAh/g，Cap≥340，所述Cap的数值与所述碳质活性材料在5t压力下的压实密度CD的数值满足Cap≤350-50×(1.90-CD)。在一些实施例中，所述碳质活性材料的克容量Cap≥340mAh/g，所述Cap的数值与所述碳质活性材料在5t压力下的压实密度CD的数值满足Cap≤350-50×(1.85-CD)。在一些实施例中，所述碳质活性材料的克容量Cap mAh/g为约340mAh/g、约341mAh/g、约342mAh/g、约343mAh/g、约344mAh/g、约345mAh/g、约346mAh/g、约347mAh/g、约348mAh/g、约349mAh/g、约350mAh/g等。
根据本申请实施例，为保证电池的能量密度，限制活性材料的克容量Cap mAh/g，Cap≥340，同时为了保证材料的克容量与压实密度的平衡，使其在高容量下具有高的压实密度，从而获得更高的电池能量密度，因此限定活性材料的满足条件：Cap≤350-50×(1.90-CD)。由此，在利于提升电池的低温充放电性能的同时，保证电池的能量密度。
在一些实施例中，所述碳质活性材料的石墨化度G为90％至95.5％。在一些实施例中，所述碳质活性材料的石墨化度G为90.5％至94.0％。在一些实施例中，所述碳质活性材料的石墨化度G为约90％、约90.5％、约90.8％、约91％、约91.5％、约92％、约92.1％、约92.5％、约93.0％、约93.5％、约94.0％、约94.5％、约95.0％、约95.2％、约95.5％或者这些数值中任意两者组成的范围。石墨化度是影响石墨克容量的一个重要参数，也是影响到材料动力学的关键参数，较低的石墨化度下石墨层间距较大，有利于锂离子的快速脱嵌，动力学较好，但是较低石墨化度下石墨克容量较低，压实密度也较低，影响电池能量密度。因此，本发明实施例通过使活性材料的石墨化度G满足90％≤G≤95.5％，使得该合适的范围的石墨化度可以兼顾动力学与能量密度，保证电池的性能。
在一些实施例中，所述碳质活性材料的比表面积BET≤3.0m 2/g。在一些实施例中，所述碳质活性材料的比表面积BET≤2.5m 2/g。在一些实施例中，所述负极活性颗粒的比表面积BET为约3.0m 2/g、约2.7m 2/g、约2.5m 2/g、约2.3m 2/g、约2.0m 2/g、约 1.9m 2/g、约1.6m 2/g、约1.5m 2/g、约1.3m 2/g、约1.0m 2/g、约0.8m 2/g等。材料的比表面积BET可以用本领域公知的方法进行测定，例如用比表面积分析仪(例如TriStarⅡ比表面分析仪)进行测量。
根据本申请实施例，为了保证电化学装置的存储等电化学性能，限定了活性材料的比表面积BET满足BET≤3.0m 2/g。活性材料的比表面积会影响到电池的存储性能，比表面积越大，其与电解液反应越剧烈，在高温存储时容易产气，降低电池性能，因此限制活性材料的比表面积BET在上述合适的范围内。
除非特别规定，本说明书中涉及的各种参数具有本领域公知的通用含义，可以按本领域公知的方法进行测量，在此不再详细描述。
在一些实施例中，所述碳质活性材料包括人造石墨、天然石墨或中间相碳微球中的至少一种。在一些实施例中，碳质活性材料可以包括石墨，在这种情况下，当使用该碳质活性材料时，可以改善低温放电倍率性能和低温充电性能。
根据本申请的实施例，所述的具有孔的碳质颗粒可以通过以下方法得到：选取一些挥发分比较高的石油焦或针状焦作为原料，在其经过特殊热处理转变为石墨的过程中，挥发分形成气体挥发，从而在颗粒中形成孔结构，最终得到多孔类型的碳质活性颗粒，此处以石油焦为例进行说明。通常制备石墨的前驱体石油焦不会选择高挥发分的石油焦，高挥发分的石油焦直接热处理难度较大，容易损坏加热设备以及具有起火风险，一般都是先经过低温热处理先去除一部分挥发分，再做热处理石墨化，但是该方法不易使得石墨颗粒产生孔结构，颗粒比较规整致密，即使有孔也是纳米级别的小微孔，不会对材料的动力学有改善，以该石墨颗粒作为负极材料的电池低温充电能力较差。本申请实施例选择高挥发分的石油焦作为原料(挥发分需要达到11％以上)，直接经过特殊热处理，可以得到微米级别的孔结构。高挥发分的石油焦具有较多烃类化合物，在石油焦加热过程中会分解溢出，但是常规的缓慢加热方式会使烃类化合物缓慢的分解溢出，颗粒的加热膨胀以及颗粒的小微孔足以使得气体缓慢溢出，不会形成微米级别的大孔，因此本申请实施例采用快速升温加热的方式，烃类化合物在快速升温过程中剧烈的分解成气体溢出，其短时间产气量大，难以从小微孔中排出，会使小微孔被气体的膨胀力改变为微米级别的大孔，此外，也会在颗粒中堆积成大的气孔并对外产生一定的张力，形成较大的多孔结构，在冷却过程中由于气孔对外具有一定张力，也不会因为冷却收缩而坍塌。为了达到前述效果，粉碎后的原料焦粒度不宜过小，粒度过小的话比表面积过大，气体无法堆积，很容易从小颗粒中溢出，不会对小微孔产生膨胀撑开的作用，也不会产生较大的微米级别孔径，因此本申请实施例要求粉碎 后的石油焦具有较大尺寸，粉碎后原料焦颗粒粒径Dv50应该在8μm以上，同时为了保证材料的动力学以及加工性能，粒度不宜过大，限制其原料焦颗粒的粒径Dv50应该在20μm以下。对于快速升温产生大量气体可能对设备及安全产生影响，本申请实施例通过增加排气孔或者主动排气等装置可以有效的保证气体顺利排除，不会对设备造成破坏，也不会因为易燃气体的堆积产生起火等问题。前期第一阶段以30℃/min以上的升温速度升温(高于石墨化常规升温速度)，可以使石油焦的挥发分快速挥发以及分解为气体，从而满足上述成孔条件。升温到1300℃以后，减缓升温速度，从而保证石油焦转变过程的受热充分及均匀性，避免石墨化过程中颗粒因受热不均而变形破裂，保证石墨化过程的稳定可靠。待升温到2850℃左右，开始保温处理，保温36小时左右后基本完成了石墨化转变，此时该石墨的石墨化度可以达到90％以上。降温冷却后对颗粒进行球磨整形处理，可以改变颗粒表面状态，保证颗粒的比表面积BET在合适的范围，颗粒球磨后表层的石墨缺陷会增加，有利于提升石墨材料的动力学，粉末压实也会有所提高。当然，该具有孔的碳质颗粒的制备方法并不限于此，而是还可以采用本领域熟知的其他方法进行制备。
在一些具体的实施方式中，所述具有孔的碳质颗粒通过以下方法制备得到：选择高挥发分的石油焦或针状焦原料，挥发分需要达到11％以上，将该原料粉碎到一定粒径范围，粉碎后的石油焦或针状焦原料的粒径Dv50控制在8μm至20μm；然后将该粉碎后的石油焦或针状焦原料单独进行热处理，或者混合一部分天然石墨或中间相碳微球一起进行热处理；其中的热处理包括先从常温快速升温到1300℃，升温速度≥30℃/min，然后再以10±3℃/min的速度缓慢升温2850℃并在2850±30℃下保温36±5小时，使其发生石墨化转变，最后降温冷却后进行球磨整形，然后进行筛分、除磁，即可得到负极材料。
二、电化学装置
在一些实施例中，本申请提供一种电化学装置，其包括负极、正极、电解液和设置于正极和负极之间的隔离膜。
本申请的电化学装置可以为锂离子电池，也可以为其他任何合适的电化学装置。在不背离本申请公开的内容的基础上，本申请实施例中的电化学装置包括发生电化学反应的任何装置，它的具体实例包括所有种类的一次电池、二次电池、燃料电池、太阳能电池或电容器。特别地，该电化学装置是锂二次电池，锂二次电池包括但不限于锂金属二次电池、锂离子二次电池、锂聚合物二次电池或锂离子聚合物二次电池。本 申请的电化学装置是具备具有能够吸留、放出金属离子的正极活性物质的正极以及具备能够吸留、放出金属离子的负极活性物质的负极的电化学装置，其主要特点在于，包括本申请的上述任何负极材料。
本申请的电化学装置中使用的负极材料为本申请的上述任何负极材料。此外，本申请的电化学装置中使用的负极材料还可包含不脱离本申请的主旨的范围内的其它负极材料。
负极
在一些实施例中，负极包括负极集流体和设置在负极集流体至少一个表面上的负极活性物质层，其中的负极活性物质层包括前述的负极材料。
在一些实施例中，所述负极的压实密度PD g/cm 3满足：1.45≤PD≤1.75。在一些实施例中，所述负极的压实密度PD g/cm 3满足：1.50≤PD≤1.68。在一些实施例中，所述负极的压实密度PD g/cm 3为约1.45g/cm 3、约1.50g/cm 3、约1.52g/cm 3、约1.56g/cm 3、约1.58g/cm 3、约1.60g/cm 3、约1.62g/cm 3、约1.65g/cm 3、约1.67g/cm 3、约1.68g/cm 3、约1.70g/cm 3、约1.75g/cm 3或者这些数值中任意两者组成的范围。若负极的压实密度过高会降低低温动力学，影响放电倍率，若负极的压实密度过低，会导致活性材料从极片掉落，影响电池稳定性。
在一些实施例中，所述负极的孔隙率Φ满足：Φ≥20％。在一些实施例中，所述负极的孔隙率Φ满足：Φ≥22％。在一些实施例中，所述负极的孔隙率Φ满足：Φ≥25％。从负极极片角度考虑，负极极片的孔隙率越大，其孔道结构越发达，电解液的浸润性越好，活性离子的液相传导速度变高，因此，负极极片的孔隙率越大，电池的动力学性能越好；但是负极极片的孔隙率越大，电池的能量密度也会有很明显的负面影响。因此，需要使负极的孔隙率在上述合适的范围内。
在一些实施例中，在本申请的一些实施例中，25℃条件下，经过循环500次循环后，容量保持率降低小于或等于20％。多孔材料有利于电解液的浸润流通，循环过程中随着电解液的消耗，电解液量减少，材料结构致密无孔的时候界面会影响性能，形成紫斑等不良，降低循环。而多孔材料电解液浸润更好，会大大延缓紫斑等不良的发生，从而可以改善循环，减缓了电池的容量衰减。
在一些实施例中，所述电化学装置在0℃的放电比率≥80％；其中，放电倍率为1C放电，0℃放电比率＝(0℃放电容量/25℃放电容量)×100％)。在一些实施例中，所述电化学装置满足0℃、0.3C充电不析锂。
根据本申请的实施例，采用如上任意一实施例的负极材料制备的负极，满足负极 压实密度PD g/cm 3为1.45至1.75，负极的孔隙率Φ满足为Φ≥20％时，电化学装置的低温放电性能及低温充电能力优异。新鲜电池拆解的负极以及循环后拆解负极仍满足上述压实密度和孔隙率范围，且从其中剥离提取的负极材料仍满足上述任一实施例所述的负极材料特征。以此负极搭配正极、电解液、隔离膜组成的电化学装置如锂离子电池，具有优异的低温放电性能和低温充电能力，满足0℃下的放电比率≥80％，0℃、0.3C下充电不析锂。
在一些实施例中，负极活性物质层还包含粘合剂。该粘合剂可以包括各种粘合剂聚合物，如聚乙烯醇、羧甲基纤维素、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂、尼龙等。
在一些实施例中，负极活性物质层还包含导电剂，来改善电极导电率。可以使用任何导电的材料作为该导电材料，只要它不引起化学变化即可。导电剂的示例包括，但不限于：碳基材料，例如天然石墨、人造石墨、炭黑、乙炔黑、科琴黑、碳纤维等；金属基材料，例如包括铜、镍、铝、银等的金属粉或金属纤维；导电聚合物，例如聚亚苯基衍生物等；或它们的混合物。
在一些实施例中，负极集流体包括，但不限于：铜箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜、覆有导电金属的聚合物基底和它们的任意组合。在一些实施例中，负极集流体为铜箔。
在一些实施例中，负极的结构为本领域技术公知的可被用于电化学装置的负极极片结构。
在一些实施例中，负极的制备方法是本领域技术公知的可被用于电化学装置的负极的制备方法。示例性的，负极可以通过如下方法获得：在溶剂中将活性材料、导电剂和粘合剂混合，并可以根据需要加热增稠剂，以制备活性材料组合物，并将该活性材料组合物涂覆在集流体上。在一些实施例中，溶剂可以包括，但不限于，水、N-甲基吡咯烷酮。
正极
在一些实施例中，正极包括正极集流体和设置在负极集流体至少一个表面上的正极活性物质层，正极活性物质层包括正极活性材料。正极活性材料的具体种类均不受到具体的限制，可根据需求进行选择。
在一些实施例中，正极活性材料包括可逆地嵌入和脱嵌锂离子的化合物(即，锂 化插层化合物)。在一些实施例中，正极活性材料可以包括锂过渡金属复合氧化物。该锂过渡金属复合氧化物含有锂以及从钴、锰和镍中选择的至少一种元素。在一些实施例中，所述正极活性材料选自以下中的至少一种：钴酸锂(LiCoO 2)、锂镍锰钴三元材料(NCM)、锰酸锂(LiMn 2O 4)、镍锰酸锂(LiNi 0.5Mn 1.5O 4)、磷酸铁锂(LiFePO 4)。
在一些实施例中，正极活性物质层还包括粘合剂，并且可选地还包括导电材料。粘合剂可提高正极活性材料颗粒彼此间的结合，并且可提高正极活性材料与正极集流体的结合。在一些实施例中，所述粘合剂包括，但不限于，聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂和尼龙等。
在一些实施例中，正极活性物质层包括导电材料，从而赋予电极导电性。该导电材料可以包括任何导电材料，只要它不引起化学变化。导电材料的非限制性示例包括基于碳的材料(例如，天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维等)、基于金属的材料(例如，金属粉、金属纤维等，包括例如铜、镍、铝、银等)、导电聚合物(例如，聚亚苯基衍生物)和它们的混合物。
在一些实施例中，正极集流体为金属，金属例如包括但不限于铝箔。
在一些实施例中，正极的结构为本领域技术公知的可被用于电化学装置的正极极片结构。
在一些实施例中，正极的制备方法是本领域技术公知的可被用于电化学装置的正极的制备方法。例如，正极可以通过如下方法获得：在溶剂中将活性材料、导电材料和粘合剂混合，以制备活性材料组合物，并将该活性材料组合物涂覆在集流体上。在一些实施例中，溶剂可以包括水、N-甲基吡咯烷酮等，但不限于此。
电解液
可用于本申请实施例的电解液可以为现有技术中已知的电解液。电解液可以分为水系电解液和非水系电解液，其中相较于水系电解液，采用非水系电解液的电化学装置可以在较宽的电压窗口下工作，从而达到较高的能量密度。在一些实施例中，非水系电解液包括有机溶剂、电解质和添加剂。
可用于本申请实施例的电解液中的电解质包括、但不限于：无机锂盐，例如LiClO 4、LiAsF 6、LiPF 6、LiBF 4、LiSbF 6、LiSO 3F、LiN(FSO 2) 2等；含氟有机锂盐，例如LiCF 3SO 3、LiN(FSO 2)(CF 3SO 2)、LiN(CF 3SO 2) 2、LiN(C 2F 5SO 2) 2、环状1,3-六氟丙烷二磺酰亚胺锂、环状1,2-四氟乙烷二磺酰亚胺锂、LiPF 4(CF 3) 2、LiN(CF 3SO 2)(C4F 9SO 2)、 LiC(CF 3SO 2) 3、LiPF 4(CF 3SO 2) 2、LiPF 4(C 2F 5) 2、LiPF 4(C 2F 5SO 2) 2、LiBF 2(CF 3) 2、LiBF 2(C 2F 5) 2、LiBF 2(CF 3SO 2) 2、LiBF 2(C 2F 5SO 2) 2；含二羧酸配合物锂盐，例如双(草酸根合)硼酸锂、二氟草酸根合硼酸锂、三(草酸根合)磷酸锂、二氟双(草酸根合)磷酸锂、四氟(草酸根合)磷酸锂等。另外，上述电解质可以单独使用一种，也可以同时使用两种或两种以上。例如，在一些实施例中，电解质包括LiPF 6和LiBF 4的组合。再如，在一些实施例中，电解质包括LiPF 6。
在一些实施例中，电解质的浓度在0.8mol/L至3mol/L的范围内，例如0.8mol/L至2.5mol/L的范围内、0.8mol/L至2mol/L的范围内、1mol/L至2mol/L的范围内、又例如为1mol/L、1.15mol/L、1.2mol/L、1.5mol/L、2mol/L或2.5mol/L。可用于本申请实施例的电解液中的添加剂可以为本领域技术公知的能够用于提高电池电化学性能的添加剂。在一些实施例中，该添加剂包括，但不限于，多腈化合物、含硫添加剂、氟代碳酸乙烯酯(FEC)、1,3-丙烷磺酸内酯(PS)、1,4丁烷磺内酯中的至少一种。可用于本申请实施例的电解液中的有机溶剂可为现有技术中已知的任何有机溶剂。在一些实施例中，有机溶剂，包括，但不限于：碳酸酯化合物、基于酯的化合物、基于醚的化合物、基于酮的化合物、基于醇的化合物、非质子溶剂或它们的组合。其中，碳酸酯化合物的实例包括，但不限于，链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或它们的组合。
在一些实施例中有机溶剂包括碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚丙酯、乙酸甲酯或丙酸乙酯中的至少一种。
本申请实施例的电解液的制备方法不受限制，可按照常规电解液的方式制备。在一些实施例中，本申请的电解液可通过混合各组分制备。
隔离膜
在一些实施例中，正极与负极之间设有隔离膜以防止短路。隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。
例如，在一些实施例中，隔离膜包括基材层。该基材层为具有多孔结构的无纺布、膜或复合膜。该基材层的材料可以选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，该基材层的材料可选自聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
三、应用
在一些实施例中，本申请提供一种电子设备，其包括前述的电化学装置。
根据本申请实施例的负极材料，能够改善电化学装置的低温放电性能及低温充电性能，使得由此制造的电化学装置适用于各种领域的电子设备，尤其是适用于有低温工况下工作需求的电子设备。
本申请的电化学装置的用途没有特别限定，其可用于现有技术中已知的任何电子设备。例如，该电子设备包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。另外，本申请的电化学装置除了适用于上述例举的电子装置外，还适用于储能电站、海运运载工具、空运运载工具。空运运载装置包含在大气层内的空运运载装置和大气层外的空运运载装置。
下面以锂离子电池为例并且结合具体的实施例、对比例对本申请进一步具体地进行说明，但只要不脱离其主旨，则本申请并不限于这些实施例。在以下实施例、对比例中，所使用到的试剂、材料以及仪器如没有特殊的说明，均可商购获得或合成获得。
实施例
以下说明根据本申请的锂离子电池的实施例和对比例进行性能评估。
一、锂离子电池的制备
1、负极的制备
将负极材料石墨、添加剂(导电剂)、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按照重量比95.7∶1.5∶1.8∶1在溶剂去离子水中充分搅拌混合，使其形成均匀的负极浆料。将负极浆料均匀地涂布在负极集流体铜箔上，烘干，冷压形成负极活性物质层，再经过裁片、焊接极耳，得到负极。
下述各实施例和对比例中，在负极的制备中的区别主要在于所采用的负极材料不同，具体详见下述各表。
2、正极的制备
将正极活性材料磷酸铁锂(LiFePO 4)、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按质量比96.3：2.2：1.5混合在溶剂N-甲基吡咯烷酮(NMP)中，在真空搅拌机下充 分搅拌均匀，得到正极浆料。将该正极料涂覆于正极集流体铝箔上，烘干，冷压形成正极活性物质层，再经过裁片、焊接极耳，得到正极。
3、电解液的制备
在干燥的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照质量比为EC：PC：EMC：DEC＝10：30：30：30进行混合均匀，接着加入2％的氟代碳酸乙烯酯和2％的1,3-丙烷磺内酯，溶解并充分搅拌后加入锂盐LiPF 6，混合均匀后得到电解液。其中LiPF 6的浓度为1mol/L。
4、隔离膜的制备
以聚乙烯(PE)多孔聚合物薄膜作为隔离膜。
5、锂离子电池的制备
将得到的正极、隔离膜、负极按顺序叠好，使隔离膜处于正极和负极之间起到隔离的作用，然后卷绕得到裸电池；将裸电池置于外包装箔铝塑膜中，注入电解液，经过真空封装、静置、化成等工艺流程得到锂离子电池。
二、测试方法
1、锂离子电池的低温放电比率测试流程如下所示：
(1)调整炉温至25℃，静置5min；(2)0.5CDC至2.5V；
(3)静置30min；(4)0.2CCC至3.6V，CV至0.025C；
(5)静置10min；(6)1.0CDC至2.5V(基准容量)；
(7)静置10min；(8)0.2CCC至3.6V，CV至0.025C；
(9)静置10min；(10)调节炉温至0℃，静置60min；
(11)1.0CDC至2.5V；(12)0.2CCC至3.6V，CV至0.025C；
(13)静置10min；(14)1.0CDC至2.5V(0℃放电容量)；
(15)调节炉温至25℃，静置60min；(16)测试结束。
锂离子电池的0℃的放电比率＝(0℃放电容量/25℃放电容量)×100％，放电倍率为1C放电。
2、锂离子电池的低温充电性能测试流程如下所示：
(1)调整炉温至25℃，静置30min；(2)0.5CDC至2.8V；
(3)静置30min；(4)调节炉温至0℃，静置60min；
(5)0.3CCC至3.6V，CV至0.025C；
(6)重复上述1-5充放电流程10次后，将电池在干燥房内拆解，拍照记录负极 的状态；
(7)拆解电池后观察负极极片是否析锂判定，析锂程度判定：根据满充拆解负极的状态来判定，当负极整体显示为金黄色且显示为灰色的面积<2％，则判定为不析锂；当负极大部分为金黄色，但有部分位置可观察到灰色，灰色面积在2％至20％之间，则判定为轻微析锂；当负极部分为灰色，但仍可观察到部分金黄色，灰色面积在20％至60％，则判定为析锂；当负极大部分显示为灰色，灰色面积＞60％时，则判定为严重析锂；
(8)测试结束。
3、5t压力下压实密度测试，粉末压实的测试标准参照GB/T24533-2009《锂离子电池石墨类负极材料》。具体测试方法如下：称量1.0000±0.0500g的样品置于测试模具(CARVER#3619(13mm)中，然后将样品置于测试设备中，测试设备为三思纵横UTM7305，测试吨位0.3t,0.5t,0.75t,1.0t,1.5t,2.0t,2.5t,3.0t,4.0t,5.0t,升压速率为10mm/min，升压保持时间为30s，泄压速率为30mm/min，泄压保持时间为10s，文中所述粉末压实密度均为5t泄压时测得的压实密度。压实密度的计算公式为：碳质活性材料在5t压力下的压实密度＝负极材料质量/负极材料受力面积/样品的厚度。
负极的压实密度＝负极活性物质层的质量/负极活性物质层的体积。
4、扫描电子显微镜(SEM)测试，如下简称扫描电镜(SEM)测试，其原理是利用聚焦电子束与样品的相互作用产生的二次电子信号成像来对样品测试的，常用来测试样品的微观形貌。本申请中使用的扫描电镜为JEOL公司的JSM-6360LV型及其配套的X射线能谱仪对样品的形貌结构进行分析。在使用过程中将所制备的样品均匀的涂于导电胶带上，在沾于样品台置于电镜中进行测试。具体测试步骤如下：
(1)活性材料的取样，如果活性物质是粉末状则直接均匀涂在导电胶带上即可，如果活性物质是已经被涂敷在铜箔上(可以理解为活性物质与铜箔组合成阳极极片)，则将其组合极片置于马弗炉中400℃高温保温40±5min，然后降温到室温取出，再将铜箔表面的活性物质剥离下来，轻轻研磨分散后即可涂在导电胶带上，准备下一步观察；
(2)SEM观察颗粒形貌所选择区域范围为80μm×100μm，在此范围基础上，还需要保证该区域中活性颗粒数量大于30个，满足这两个条件则可认为该选择区域是一个有效区域；
(3)区域选择确定后，即可在该区域内逐个观察颗粒结构，可以计数该有效区域中颗粒的数量，具有孔的颗粒数量以及单个颗粒具有孔的数量。
(4)将测试计数结果进行统计汇总，测试结束。
三、测试结果
通过SEM选取的80μm×100μm区域内，表1示出了实施例1至实施例16中以及对比例1至对比例3中的负极材料的相关性能参数以及所对应的电池的性能。表1中，实施例1至实施例16满足0.3μm≤Y≤2.0μm，0.6μm≤X≤1.5μm；或包含孔数量N≤2的碳质颗粒的数量占总碳质颗粒数量的比例(表1中简称为N ≤2/N 总)≤60％，包含孔数量3≤N≤5的碳质颗粒的数量占总碳质颗粒数量的比例(表1中简称为N 3-5/N 总)≤30％，而对比例1至对比例3的负极材料不满足上述条件。
表1
Figure PCTCN2021104653-appb-000001
从表1可以发现，实施例1至实施例16的负极材料具有多孔结构，并满足0.3μm≤Y≤2.0μm，0.6μm≤X≤1.5μm；或N ≤2/N 总≤60％，N 3-5/N 总≤30％的情况下，使得孔的大小合适，分布均匀，进而使得电池具有良好的低温放电比率性能和低温充电能力。这是因为活性材料孔结构的存在使得负极极片孔隙率大大增加，且活性材料颗粒与电解液的浸润接触面增加，锂离子的脱嵌路径减小，因此提高了活性材料的动力学，改善了低温放电倍率性能与低温充电能力。如实施例1-10，当活性材料同时满足0.3μm≤Y≤2.0μm，0.6μm≤X≤1.5μm与N ≤2/N 总≤60％，N 3-5/N 总≤30％的情况下，电池的低温性能得到明显改善，这是因为孔的大小尺寸合适且数量分布均匀，既可以保证电解液对活性材料的浸润性能又能保证颗粒的机械强度，因为低温改善效果最佳。当如实施例11-13，当活性材料满足0.3μm≤Y≤2.0μm，0.6μm≤X≤1.5μm而不满足N ≤2/N 总≤60％，N 3-5/N 总≤30％时，低温性能得到一定程度改善。满足0.3μm≤Y≤2.0μm，0.6μm≤X≤1.5μm活性材料的孔尺寸较大，可以改善电解液对活性材料的浸润性，提高电池的低温性能。不满足N ≤2/N 总≤60％，N 3-5/N 总≤30％时孔的数量偏多，会导致活性材料机械强度有所降低，在极片冷压后活性材料颗粒容易碎裂，破坏一部分孔结构且产生新的未成膜石墨界面，重新成膜会继续消耗电解液，会损失一部分电池的低温性能。如实施例14-16，当活性材料不满足0.3μm≤Y≤2.0μm，0.6μm≤X≤1.5μm而满足N ≤2/N 总≤60％，N 3-5/N 总≤30％时，低温性能也得到一定程度改善。不满足0.3μm≤Y≤2.0μm，0.6μm≤X≤1.5μm时孔径太小或太大，孔径太小则电解液浸润较差，不足以改善低温性能，孔径太大时，活性材料机械强度降低，与前述相似，在极片冷压后活性材料颗粒容易碎裂，孔结构被破坏且产生新的未成膜石墨界面，重新成膜会继续消耗电解液，会损失电池的低温性能。满足N ≤2/N 总≤60％，N 3-5/N 总≤30％时孔的数量有限，可以提升或者材料的机械强度，避免冷压过程颗粒破裂，有利于改善电池的低温性能。如对比例1-3为负极材料均不满足上述条件(A)与(B)时所对应的电池性能，可以发现在孔径太小或太大且活性材料颗粒孔数量过多时，电池的低温性能明显降低。这是因为当活性材料中的孔太小时，不仅不足以明显提升活性材料与电解液的接触面积，而且还会使活性材料与电解液的副反应增加，降低电池低温性能。当活性材料的孔太大时且孔数量太多时，活性材料机械强度降低，在极片冷压后活性材料颗粒容易碎裂，孔结构被破坏且产生新的未成膜石墨界面，重新成膜会继续消耗电解液，降低了电池的低温性能。因此，活性材料需要满足合适的孔径大小与数量分布，才会达到最理想的低温性能改善效果。
表2示出了实施例17至实施例24的负极材料的相关性能参数以及所对应的电池的 性能。表2在实施例6的基础上继续改善电池性能，为了保证活性材料在具有多孔结构的同时具有一定的机械强度，限定Dv50与5Y之间的关系。
表2
Figure PCTCN2021104653-appb-000002
从表2可以发现，在满足Dv50≥5Y时，上述实施例的0℃低温放电比率较高，锂离子电池表现出优异的低温性能，说明可以通过限定Dv50≥5Y来保证颗粒的机械强度，进而可以有效的改善电池低温性能。这是由于在满足Dv50≥5Y的条件下，颗粒的尺寸大小是明显大于孔的尺寸大小，这样可以保证颗粒强度，能使活性材料在具有多孔结构的同时保证一定的机械强度，提高抗破裂能力，避免冷压的时候颗粒破裂，保证了电池的低温性能。
表3示出了实施例25至实施例28的负极材料的相关性能参数以及所对应的电池的性能。表3在实施例20的基础上继续改善电池低温充放电性能，为了保证活性材料的孔的均匀性，限定了单个颗粒存在两个或两个以上的孔时，相邻两个孔之间的距离L的范围，并限定了某一区域(如前述80μm×100μm区域)中孔的最大直径Y，X是该区域中具有孔的颗粒的最大直径平均值X，Y-X的差值范围。
表3
Figure PCTCN2021104653-appb-000003
Figure PCTCN2021104653-appb-000004
从表3可以发现，在满足Y-X≤1.0μm，L≤8.0μm时，相比于实施例20，实施例25至实施例28的0℃放电比率得到了提升；这是因为在孔在活性材料颗粒上分布均匀且大小一致性较好时，负极极片的电解液浸润性会明显改善，促进了锂离子在活性颗粒中的脱嵌速度并减小了脱嵌路径长度，从而改善了电池的低温放电性能。Y是某一所选区域(如前述80μm×100μm区域)中孔的最大直径Y，X是该区域中具有孔的颗粒的最大直径平均值X，Y-X可以用来表征孔大小的一致性，差值越大意味着孔大小一致性越差，这样是不利于电解液的浸润均匀性，影响电解液的浸润，降低电池性能，从而通过使Y-X满足Y-X≤1.0μm，可以保证负极材料孔大小尺寸的一致性。通过使相邻两个孔之间的距离L满足L≤8.0μm，可以保证孔分布的均匀性，使得孔在活性材料颗粒上均匀分布，提高了电解液的浸润，有效改善电池的低温性能。因此，在限定了孔大小的一致性以及孔分布的一致性后，电池的低温放电比率明显得到改善。
表4示出了实施例29至实施例33的负极材料的相关性能参数以及所对应的电池的性能。表4在实施例26的基础上继续改善电池低温充放电性能，为了保证负极材料的加工性能等相关性能，限定压实密度CD g/cm 3、克容量Cap mAh/g、克容量Cap mAh/g与压实密度CD g/cm 3的关系、Dv99与Dv50的关系在合适范围内。
表4
Figure PCTCN2021104653-appb-000005
从表4可以发现，相比于实施例26，实施例29至实施例33的0℃放电比率得到了提升，这表明通过限制活性材料的粒度，压实，克容量以及其组合关系，可以保证 活性材料的加工性和电性能得到充分发挥，有效改善电池的低温性能。其中，通过使活性材料的粒径分布满足Dv99≤3.5×Dv50，可以保证活性材料粒度大小适中且颗粒分布较窄，避免出现太多的大颗粒影响极片加工，同时，避免粒度过大会导致锂离子的脱嵌路径增加、降低材料动力学，避免粒度过小会影响极片压实以及降低存储性能。通过使活性材料的克容量Cap mAh/g，Cap≥340，可以保证电池的能量密度，同时为了克容量与压实密度的平衡，使其在高容量下具有高的压实密度，从而获得更高的电池能量密度，使活性材料满足Cap≤350-50×(1.90-CD)。
表5示出了实施例34至实施例40的负极材料的相关性能参数以及所对应的电池的性能。表5在实施例32的基础上继续改善电池低温充放电性能，为了保证材料的动力学和能量密度等电化学性能，限定活性材料的比表面积BET、石墨化度G在合适的范围内。
表5
Figure PCTCN2021104653-appb-000006
从表5可以发现，实施例34至实施例40的0℃放电比率优于实施例32，表明合适的石墨化度与比表面积范围对于电池的性能是有所改善的，在上述参数范围内可以兼顾活性材料的动力学与能量密度，保证电池的性能。其中石墨化度是影响石墨克容量的一个重要参数，也是影响到材料动力学的关键参数，较低的石墨化度下石墨层间距较大，有利于锂离子的快速脱嵌，动力学较好，但是较低石墨化度下石墨克容量较低，压实密度也较低，影响电池能量密度。因此石墨化度需要在合适的范围则可兼顾动力学与能量密度。活性材料的比表面积会影响到电池的存储性能，比表面积越大，其与电解液反应越剧烈，在高温存储时容易产气，降低电池性能。因此通过使活性材 料的石墨化度G满足90％≤G≤95.5％，比表面积BET≤3.0m 2/g，利于优化电池的性能。
表6示出了实施例41至实施例46的负极材料的相关性能参数以及所对应的电池的性能。表6在实施例36的基础上继续改善电池低温充放电性能，通过使负极的压实密度PD g/cm 3和负极的孔隙率Φ在合适的范围内，可以提升电池的低温放电性能。
表6
Figure PCTCN2021104653-appb-000007
从表6可以发现，实施例41至实施例46的0℃放电比率优于实施例36，表明合适的负极极片压实密度与孔隙率对于电池的性能是有所改善的，合适的压密范围可以兼顾负极极片粘结力与颗粒不破裂，较高的孔隙率保证了电解液对负极极片的浸润性，可以有效的提升电池的低温性能。
具体地，通过使负极的压实密度PD g/cm 3满足1.45≤PD≤1.75，可以保证负极极片的粘结力以及活性材料颗粒冷压时不被压破裂；若极片的压实密度过低，极片粘结力低，活性材料容易从负极极片上掉落，降低电池的性能，若极片的压实密度过高，极片冷压过程受力大，活性材料容易发生破裂，降低电池性能。通过使负极的孔隙率Φ满足Φ≥20％，可以保证电池的浸润性能，若负极的孔隙率太低会导致电解液对负极的浸润不良，电池的低温性能降低。
尽管已经演示和描述了说明性实施例，本领域技术人员应该理解上述实施例不能被解释为对本申请的限制，并且可以在不脱离本申请的精神、原理及范围的情况下对实施例进行改变，替代和修改。

Claims (10)

  1. 一种负极材料，所述负极材料包含碳质活性材料，通过观察SEM图像，在80μm×100μm区域，所述碳质活性材料包括具有孔的碳质颗粒；
    所述负极材料满足以下条件(A)或(B)：
    (A)所述孔的长度最长的方向为孔的最大直径Y，单个所述碳质颗粒孔最大直径Y的范围满足0.3μm≤Y≤2.0μm，且所述碳质颗粒的孔最大直径平均值X满足0.6μm≤X≤1.5μm；
    (B)包含孔数量N≤2的所述碳质颗粒的数量占所述区域所述碳质颗粒总数量的比例为≤60％，包含孔数量3≤N≤5的所述碳质颗粒的数量占所述区域所述碳质颗粒总数量的比例为≤30％。
  2. 根据权利要求1所述的负极材料，其特征在于，所述碳质颗粒的中值粒径Dv50与所述Y满足以下关系：Dv50≥5Y，Dv50的单位为μm。
  3. 根据权利要求1所述的负极材料，其特征在于，所述孔满足条件(a)或(b)中的至少一种：
    (a)所述孔的最大直径Y与所述孔最大直径平均值X满足以下关系：Y-X≤1.0μm；
    (b)单个所述具有孔的碳质颗粒中，相邻两个所述孔之间的距离L≤8.0μm。
  4. 根据权利要求1所述的负极材料，其特征在于，所述孔包括通孔或盲孔中的至少一种。
  5. 根据权利要求1所述的负极材料，其特征在于，所述碳质活性材料满足条件(c)至(e)中的至少一种：
    (c)所述碳质活性材料在5t压力下的压实密度为CD g/cm 3，且CD≤1.85；
    (d)所述碳质活性材料的克容量为Cap mAh/g，且Cap≥340，所述Cap的数值与所述碳质活性材料在5t压力下的压实密度为CD g/cm 3，满足Cap≤350-50×(1.90-CD)；
    (e)所述碳质活性材料的粒径分布满足Dv99≤3.5×Dv50，Dv99的单位为μm。
  6. 根据权利要求1至5任一项所述的负极材料，其特征在于，所述碳质活性材料满足条件(f)至(h)中的至少一种：
    (f)所述碳质活性材料的石墨化度G为90％至95.5％；
    (g)所述碳质活性材料的比表面积BET≤3.0m 2/g；
    (h)所述碳质活性材料包括人造石墨、天然石墨或中间相碳微球中的至少一种。
  7. 一种电化学装置，包括负极，其特征在于，所述负极包括负极集流体和设置在所述负极集流体至少一个表面上的负极活性物质层，其中所述负极活性物质层包 括如权利要求1至6任一项所述的负极材料。
  8. 根据权利要求7所述的电化学装置，其特征在于，所述负极满足条件(i)和(j)中的至少一种：
    (i)所述负极的压实密度PD g/cm 3满足：1.45≤PD≤1.75；
    (j)所述负极的孔隙率Φ满足：Φ≥20％。
  9. 根据权利要求7所述的电化学装置，其特征在于，25℃条件下，经过循环500次循环后，容量保持率降低小于或等于20％。
  10. 一种电子设备，其特征在于，包括权利要求7至9任一项所述的电化学装置。
PCT/CN2021/104653 2021-03-30 2021-07-06 负极材料及包含其的电化学装置和电子设备 WO2022205658A1 (zh)

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