WO2022099457A1 - 负极活性材料及使用其的电化学装置和电子装置 - Google Patents

负极活性材料及使用其的电化学装置和电子装置 Download PDF

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WO2022099457A1
WO2022099457A1 PCT/CN2020/127812 CN2020127812W WO2022099457A1 WO 2022099457 A1 WO2022099457 A1 WO 2022099457A1 CN 2020127812 W CN2020127812 W CN 2020127812W WO 2022099457 A1 WO2022099457 A1 WO 2022099457A1
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active material
negative electrode
electrode active
electrochemical device
material layer
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PCT/CN2020/127812
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English (en)
French (fr)
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王硕
董佳丽
唐佳
谢远森
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宁德新能源科技有限公司
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Priority to CN202080020265.1A priority Critical patent/CN113597684B/zh
Priority to PCT/CN2020/127812 priority patent/WO2022099457A1/zh
Priority to EP20961016.1A priority patent/EP4246613A4/en
Publication of WO2022099457A1 publication Critical patent/WO2022099457A1/zh
Priority to US18/188,686 priority patent/US20230223538A1/en

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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
    • H01M4/58—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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/13—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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/446—Initial charging measures
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • 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 field of energy storage, in particular to a negative electrode active material and an electrochemical device and an electronic device using the same.
  • Electrochemical devices eg, lithium-ion batteries
  • Small-sized lithium-ion batteries are often used as power sources for driving portable electronic communication devices (eg, camcorders, mobile phones, or notebook computers, etc.), especially high-performance portable devices.
  • Medium-sized and large-sized lithium-ion battery cells with high output characteristics are developed for electric vehicles (EVs) and large-scale energy storage systems (ESSs).
  • EVs electric vehicles
  • ESSs large-scale energy storage systems
  • Embodiments of the present application solve at least one problem in the related art to at least some extent by providing a negative electrode active material and an electrochemical device and an electronic device using the same.
  • the present application provides a negative electrode active material, wherein the area average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.4; SMD is The value of the area-average particle diameter of the negative electrode active material is in the range of 10 to 16, and the unit is ⁇ m; lg is the frequency.
  • the area-average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.5. In some embodiments, the area-average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 1.0. In some embodiments, the area-average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.8. In some embodiments, the area-average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.6.
  • the area-average particle size SMD of the anode active material is in the range of 12 ⁇ m to 14 ⁇ m. In some embodiments, the area-average particle size SMD of the negative electrode active material is 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, or a range composed of any two of the above values.
  • the volume specific surface area Sv of the negative electrode active material is not greater than 0.3 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not greater than 0.2 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not less than 0.01 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not less than 0.05 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not less than 0.1 m 2 /cm 3 .
  • the volume specific surface area Sv of the negative electrode active material is 0.1 m 2 /cm 3 , 0.2 m 2 /cm 3 , 0.3 m 2 /cm 3 or within a range composed of any two values above.
  • the present application provides an electrochemical device comprising a positive electrode, an electrolyte, and a negative electrode, the negative electrode comprising a negative electrode active material layer, and the negative electrode active material layer comprising the negative electrode active material according to the present application Material.
  • the areal density of the anode active material layer is 0.077 mg/mm 2 to 0.121 mg/mm 2 . In some embodiments, the areal density of the anode active material layer is 0.080 mg/mm 2 to 0.120 mg/mm 2 . In some embodiments, the anode active material layer has an areal density of 0.085 mg/mm 2 to 0.110 mg/mm 2 . In some embodiments, the areal density of the anode active material layer is 0.090 mg/mm 2 to 0.100 mg/mm 2 .
  • the areal density of the negative active material layer is 0.077 mg/mm 2 , 0.080 mg/mm 2 , 0.085 mg/mm 2 , 0.090 mg/mm 2 , 0.095 mg/mm 2 , 0.100 mg/mm 2 2 , 0.105 mg/mm 2 , 0.110 mg/mm 2 , 0.115 mg/mm 2 , 0.120 mg/mm 2 , 0.121 mg/mm 2 or within the range of any two of the above values.
  • the compaction density of the negative electrode is 1.20 g/cm 3 to 1.83 g/cm 3 .
  • the negative electrode active material layer has a compacted density of 1.30 g/cm 3 to 1.80 g/cm 3 .
  • the negative electrode active material layer has a compacted density of 1.40 g/cm 3 to 1.60 g/cm 3 .
  • the compacted density of the negative electrode active material layer is 1.20 g/cm 3 , 1.30 g/cm 3 , 1.40 g/cm 3 , 1.50 g /cm 3 , 1.60 g/cm 3 , 1.70 g/cm 3 , 1.80 g/cm 3 , 1.83 g/cm 3 or within the range of any two of the above values.
  • the ratio C004/C110 of the peak area C004 of the (004) plane and the peak area C110 of the (110) plane of the negative electrode active material layer measured from the X-ray diffraction pattern is in the range of 5 to 15 Inside.
  • the negative electrode active material layer C004/C110 is in the range of 6 to 12 as measured by an X-ray diffraction pattern.
  • the negative electrode active material layer C004/C110 is in the range of 8 to 10 as measured by an X-ray diffraction pattern.
  • the negative electrode active material layer C004/C110 measured by X-ray diffraction pattern is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or any two of the above within the range of values.
  • the binding force between the negative electrode active material layer and the negative electrode current collector is 8 N/m to 14 N/m.
  • the bonding force between the negative electrode active material layer and the negative electrode current collector is 10 N/m to 12 N/m.
  • the bonding force between the negative electrode active material layer and the negative electrode current collector is 8N/m, 9N/m, 10N/m, 11N/m, 12N/m, 13N/m, 14N/m or any of the above. within the range of two values.
  • the anode active material layer has a porosity of 20% to 40%. In some embodiments, the anode active material layer has a porosity of 25% to 35%. In some embodiments, the anode active material layer has a porosity of 28% to 32%. In some embodiments, the negative active material layer has a porosity of 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, or any two of the above values. within the range.
  • the electrochemical device satisfies the following relationship:
  • the charge-discharge test is carried out according to the following steps:
  • step (b) DC discharge the electrochemical device to 3V at 1C after step (a), record the discharge capacity, and stay for 5 minutes;
  • step (c) DC discharge the electrochemical device to 3V at 0.5C after step (b), record the discharge capacity, and stay for 5 minutes;
  • step (d) after step (c), the electrochemical device is DC-discharged to 3V at 0.05C, and the discharge capacity is recorded, and left for 5 minutes;
  • step (e) DC discharge the electrochemical device to 3V at 0.005C after step (d), record the discharge capacity, and stay for 5 minutes;
  • C1 is the capacity of the electrochemical device after step (a) in the first charge-discharge test
  • D1 is the sum of the capacities of the electrochemical device through steps (b), (c), (d) and (e) in the first charge-discharge test;
  • D10 is the sum of the capacities of the electrochemical device after steps (b), (c), (d) and (e) in the 10th charge-discharge test.
  • the present application provides an electronic device comprising the electrochemical device according to the present application.
  • FIG. 1 shows a graph of the area average particle size and density distribution of the negative electrode active materials used in Example 3 and Comparative Example 3 of the present application.
  • a list of items linked by the term "at least one of” can mean any combination of the listed items.
  • the phrase "at least one of A and B” means A only; B only; or A and B.
  • the phrase "at least one of A, B, and 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 may contain a single element or multiple elements.
  • Item C may contain a single element or multiple elements.
  • the present application solves the above-mentioned problems by optimizing the negative electrode active material.
  • the present application provides a negative electrode active material, wherein the area average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.4; SMD is the negative electrode The area-average particle size of the active material, and is in the range of 10 ⁇ m to 16 ⁇ m; lg is the frequency.
  • lg(SMD-2)+lg(SMD+2) indicates the ratio of the number of particles with the area average particle diameter of SMD to the total number of particles.
  • the particles with the area average particle diameter of SMD are greater than or equal to 40% of the total number of particles.
  • the area-average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.5. In some embodiments, the area-average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 1.0. In some embodiments, the area-average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.8. In some embodiments, the area average particle size of the negative electrode active material satisfies the following relationship: lg(SMD-2)+lg(SMD+2) ⁇ 0.6.
  • the area-average particle size SMD of the anode active material is in the range of 12 ⁇ m to 14 ⁇ m. In some embodiments, the area-average particle size SMD of the negative electrode active material is 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, or a range composed of any two of the above values.
  • the "area-average particle size" of the negative electrode active material refers to the ratio of the total volume of all negative electrode active material particles to the total area of all negative electrode active material particles, namely:
  • i represents an ordinal number
  • D represents the volume of the corresponding negative electrode active material particle
  • Ni represents the number of particles with a particle size of Di.
  • the area-average particle size of the negative electrode active material can reflect the size of the negative electrode active material particle, which plays a crucial role in the diffusion of lithium ions.
  • the negative electrode active material particles are large, the diffusion path of lithium ions is longer and the transmission rate is low, so that some lithium ions cannot be quickly embedded in the negative electrode active material and accumulate on the surface of the negative electrode active material.
  • the potential reaches below 0V, lithium ions are precipitated as lithium metal, resulting in the phenomenon of lithium precipitation.
  • lithium ions can diffuse rapidly in the negative electrode active material, but the negative electrode active material will expose more active sites, thereby increasing the irreversible lithium content, reducing the first Coulomb efficiency of lithium ion batteries, and then reducing Energy density of lithium-ion batteries.
  • lg(SMD-2)+lg(SMD+2) can reflect the particle size distribution of the negative electrode active material.
  • the particle size distribution of the negative electrode active material reaches the threshold, it is difficult to further significantly improve the lithium deposition phenomenon of the lithium ion battery by continuing to increase the particle size distribution of the negative electrode active material, but it will increase the cost.
  • the area average particle size SMD of the negative electrode active material complies with the above relationship and is within the above range, the negative electrode active material particle size is appropriate and the distribution is concentrated, so that the electrochemical device has a high volume energy density without lithium precipitation, and achieves comprehensive performance. balance.
  • the volume specific surface area Sv of the negative electrode active material is not greater than 0.3 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not greater than 0.2 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not less than 0.01 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not less than 0.05 m 2 /cm 3 . In some embodiments, the volume specific surface area Sv of the negative electrode active material is not less than 0.1 m 2 /cm 3 .
  • the volume specific surface area Sv of the negative electrode active material is 0.1 m 2 /cm 3 , 0.2 m 2 /cm 3 , 0.3 m 2 /cm 3 or within a range composed of any two values above.
  • volume specific surface area of the negative electrode active material refers to the ratio of the total surface area of the negative electrode active material particles to the total volume, namely:
  • n represents the number of particles of the negative electrode active material
  • d represents the diameter of the negative electrode active material particles
  • graphite As the negative electrode active material as an example, graphite has a hexagonal layered structure, carbon atoms in the same layer are hybridized with sp 2 to form covalent bonds, and each carbon atom is connected to three other atoms by three covalent bonds. Lithium ions are intercalated between the graphite layers. When the graphite particles are flat, there are fewer layers in the graphite particles, and the length of each layer is longer.
  • the length of each layer in the graphite particles is shorter, which is conducive to the rapid deintercalation of lithium ions, thereby reducing the DC impedance of the lithium ion battery and improving the lithium ion deposition phenomenon of the lithium ion battery.
  • the volume specific surface area of the negative electrode active material is within the above range, the degree of lithium deposition and the energy density of the lithium ion battery can be further balanced.
  • the area average particle size and volume specific surface area of the negative active material can be obtained by dynamic particle image analysis.
  • the area-average particle size of the negative electrode active material can be obtained by the following method: using the new Patek QICPIC dynamic particle image analyzer, the negative electrode active material sample to be tested is placed in a strong dry dispersion device and completely dispersed into single particles, Images with sharp particle edges are obtained with an exposure time of less than 1 nanosecond by a high-frequency pulsed light source. 450 images per second are obtained by a high-speed imaging system. The left and right images were analyzed to obtain the area average particle size and volume specific surface area of the negative electrode active material.
  • the present application also provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator, and an electrolyte.
  • a positive electrode positive electrode
  • a negative electrode negative electrode
  • a separator separator
  • electrolyte an electrolyte
  • the negative electrode used in the electrochemical device of the present application includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including the negative electrode active material according to the present application.
  • the areal density of the anode active material layer is 0.077 mg/mm 2 to 0.121 mg/mm 2 . In some embodiments, the areal density of the anode active material layer is 0.080 mg/mm 2 to 0.120 mg/mm 2 . In some embodiments, the anode active material layer has an areal density of 0.085 mg/mm 2 to 0.110 mg/mm 2 . In some embodiments, the areal density of the anode active material layer is 0.090 mg/mm 2 to 0.100 mg/mm 2 .
  • the areal density of the negative active material layer is 0.077 mg/mm 2 , 0.080 mg/mm 2 , 0.085 mg/mm 2 , 0.090 mg/mm 2 , 0.095 mg/mm 2 , 0.100 mg/mm 2 2 , 0.105 mg/mm 2 , 0.110 mg/mm 2 , 0.115 mg/mm 2 , 0.120 mg/mm 2 , 0.121 mg/mm 2 or within the range of any two of the above values.
  • the areal density of the negative electrode active material layer can be measured by the following method: use a punching machine to punch the area with active material layers on both sides of the negative electrode current collector into 12 small discs with an area of S, which are called negative electrode sheets.
  • the punching machine uses the punching machine to punch the negative electrode current collector from the negative electrode active material layer into 12 small discs with the same area as the above negative electrode sheet, and measure the average mass of the negative electrode current collector small disc by weighing m2, the weight of the single-layer negative electrode active material layer in the small disc region is (m1-m2)/2, and the negative electrode sheet density is (m1-m2)/2S.
  • the compaction density of the negative electrode active material layer is 1.20 g/cm 3 to 1.83 g/cm 3 .
  • the negative electrode active material layer has a compacted density of 1.30 g/cm 3 to 1.80 g/cm 3 .
  • the negative electrode active material layer has a compacted density of 1.40 g/cm 3 to 1.60 g/cm 3 .
  • the compacted density of the negative electrode active material layer is 1.20 g/cm 3 , 1.30 g/cm 3 , 1.40 g/cm 3 , 1.50 g /cm 3 , 1.60 g/cm 3 , 1.70 g/cm 3 , 1.80 g/cm 3 , 1.83 g/cm 3 or within the range of any two of the above values.
  • the compaction density of the negative electrode active material layer can be measured by the following method: use a punching machine to punch the area with active material layers on both sides of the negative electrode current collector into 12 small discs with an area of S, which are called negative electrode sheets.
  • the thickness of the negative electrode sheet is measured with a ruler and the average value is recorded as L1, and the average mass of the negative electrode sheet is measured by weighing m1. Then, use a punching machine to punch the negative electrode current collector from the negative electrode active material layer into 12 small circles with the same area as the above negative electrode sheet. Use a micrometer to test the thickness of the negative electrode current collector and take the average value and record it as L2, and measure the average mass m2 of the negative electrode current collector small disc by weighing, and the weight of the single-layer negative electrode active material layer is (m1-m2)/2, and the single-layer negative electrode active material layer weight is (m1-m2)/2. The thickness of the negative electrode active material layer is (L1-L0)/2, and the compaction density of the negative electrode sheet is (m1-m2)/S ⁇ (L1-L0).
  • the ratio C004/C110 of the peak area C004 of the (004) plane and the peak area C110 of the (110) plane of the negative electrode active material layer measured from the X-ray diffraction pattern is in the range of 5 to 15 Inside.
  • the negative electrode active material layer C004/C110 is in the range of 6 to 12 as measured by an X-ray diffraction pattern.
  • the negative electrode active material layer C004/C110 is in the range of 8 to 10 as measured by an X-ray diffraction pattern.
  • the negative electrode active material layer C004/C110 measured by X-ray diffraction pattern is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or any two of the above within the range of values.
  • C004/C110 can characterize the orientation degree of the negative electrode active material layer. The larger the C004/C110, the larger the anisotropy of the anode active material layer. The smaller the C004/C110, the greater the isotropy of the negative electrode active material layer.
  • the degree of orientation of the negative electrode active material layer can be measured in accordance with the Machinery Industry Standard of the People's Republic of China JB/T4220-2011 "Method for Determination of Lattice Parameters of Artificial Graphite". Specifically, the test conditions were as follows: X-rays were irradiated with CuK alpha , and the CuK alpha radiation was removed by a filter or a monochromator. The working voltage of the X-ray tube is (30-35) kV, and the working current is (15-20) mA. The scan speed of the counter is 1/4 (°) /min. When recording the 004 diffraction line pattern, the scanning range of the diffraction angle 2 ⁇ is 53°-57°.
  • the scanning range of the diffraction angle 2 ⁇ is 75°-79°.
  • the peak area of the negative electrode active material layer obtained from the (004) plane diffraction pattern was denoted as C004.
  • the peak area of the negative electrode active material layer obtained from the (110) plane diffraction pattern was designated as C110.
  • the ratio of C004/C110 of the negative electrode active material layer is obtained by calculation, which is the degree of orientation of the negative electrode active material layer.
  • the binding force between the negative electrode active material layer and the negative electrode current collector is 8 N/m to 14 N/m.
  • the bonding force between the negative electrode active material layer and the negative electrode current collector is 10 N/m to 12 N/m.
  • the bonding force between the negative electrode active material layer and the negative electrode current collector is 8N/m, 9N/m, 10N/m, 11N/m, 12N/m, 13N/m, 14N/m or any of the above. within the range of two values.
  • the bonding force between the negative electrode active material layer and the negative electrode current collector can be obtained by tensile testing, as follows: use an Instron (model 33652) tester to test the bonding between the negative electrode active material layer and the negative electrode current collector: take 15-20mm long pole piece, fix it on the steel plate with 3M double-sided tape, stick the tape on the surface of the negative electrode active material layer, connect one side of the tape with the paper tape of the same width, and adjust the tension limit. Position the block to a suitable position, fold the paper tape upwards and slide it by 40mm, and the sliding speed is 50mm/min, and test the adhesion between the negative electrode active material layer and the negative electrode current collector at 180° (ie, stretch in the opposite direction). force.
  • the anode active material layer has a porosity of 20% to 40%. In some embodiments, the anode active material layer has a porosity of 25% to 35%. In some embodiments, the anode active material layer has a porosity of 28% to 32%. In some embodiments, the negative active material layer has a porosity of 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, or any two of the above values. within the range. The larger the porosity of the negative electrode active material layer, the easier the diffusion of lithium ions in the negative electrode active material layer.
  • the porosity of the negative electrode active material layer can be obtained by the standard test of "GB/T24586-2009 Determination of Apparent Density, True Density and Porosity of Iron Ore".
  • the compaction density of the negative electrode active material layer is relatively high, the bulk density of the negative electrode active material layer is relatively high, making it difficult for the electrolyte to infiltrate the negative electrode active material layer, which is not conducive to the diffusion of lithium ions in the direction perpendicular to the negative electrode, thus aggravating the lithium ion Lithium deposition in ion batteries.
  • the compaction density of the negative active material is small, the energy density of the lithium-ion battery decreases.
  • the areal density of the negative electrode active material layer is constant, reducing the compaction density of the negative electrode active material layer will reduce the anisotropy and porosity of the negative electrode active material layer and reduce the bonding between the negative electrode active material layer and the negative electrode current collector force.
  • the electrochemical device satisfies the following relationship:
  • the charge-discharge test is carried out according to the following steps:
  • step (b) DC discharge the electrochemical device to 3V at 1C after step (a), record the discharge capacity, and stay for 5 minutes;
  • step (c) DC discharge the electrochemical device to 3V at 0.5C after step (b), record the discharge capacity, and stay for 5 minutes;
  • step (d) DC discharge the electrochemical device to 3V at 0.05C after step (c), record the discharge capacity, and stay for 5 minutes;
  • step (e) DC discharge the electrochemical device to 3V at 0.005C after step (d), record the discharge capacity, and stay for 5 minutes;
  • C1 is the capacity of the electrochemical device after step (a) in the first charge-discharge test
  • D1 is the sum of the capacities of the electrochemical device through steps (b), (c), (d) and (e) in the first charge-discharge test;
  • D10 is the sum of the capacities of the electrochemical device after steps (b), (c), (d) and (e) in the 10th charge-discharge test.
  • D10/D1 and (C1-D10)/C1 can characterize the degree of lithium deposition in electrochemical devices. When D10/D1 and (C1-D10)/C1 are within the above ranges, the electrochemical device does not exhibit lithium deposition during cycling.
  • the negative current collectors used in the present application may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, conductive metal clad polymer substrates, and combinations thereof.
  • the negative electrode further includes a conductive layer.
  • the conductive material of the conductive layer may include any conductive material as long as it does not cause chemical changes.
  • conductive materials include carbon-based materials (eg, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotubes, graphene, etc.), metal-based materials (eg, metal powders, metal fibers, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (eg, polyphenylene derivatives), and mixtures thereof.
  • the negative electrode further includes a binder
  • the binder is at least one selected from the following: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, and diacetyl cellulose , polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polyvinyl Propylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin or nylon, etc.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector.
  • the specific types of the positive electrode active materials are not specifically limited, and can be selected according to requirements.
  • the cathode active material includes a cathode material capable of absorbing and releasing lithium (Li).
  • cathode materials capable of absorbing/releasing lithium (Li) may include lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, phosphoric acid Lithium iron, lithium titanate, and lithium-rich manganese-based materials.
  • the chemical formula of lithium cobalt oxide can be as chemical formula 1:
  • M1 represents selected from nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), Copper (Cu), Zinc (Zn), Molybdenum (Mo), Tin (Sn), Calcium (Ca), Strontium (Sr), Tungsten (W), Yttrium (Y), Lanthanum (La), Zirconium (Zr) and At least one of silicon (Si), the values of x, a, b and c are respectively in the following ranges: 0.8 ⁇ x ⁇ 1.2, 0.8 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 0.2, -0.1 ⁇ c ⁇ 0.2.
  • nickel cobalt lithium manganate or nickel cobalt aluminate can be as chemical formula 2:
  • M2 represents selected from cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), at least one of copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr) and silicon (Si),
  • the values of y, d, e and f are respectively in the following ranges: 0.8 ⁇ y ⁇ 1.2, 0.3 ⁇ d ⁇ 0.98, 0.02 ⁇ e ⁇ 0.7, -0.1 ⁇ f ⁇ 0.2.
  • the chemical formula of lithium manganate can be as chemical formula 3:
  • M3 represents selected from cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), At least one of copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W), with z, g and h values in the following ranges, respectively Inside: 0.8 ⁇ z ⁇ 1.2, 0 ⁇ g ⁇ 1.0 and -0.2 ⁇ h ⁇ 0.2.
  • the weight of the positive electrode active material layer is 1.5 to 15 times the weight of the negative electrode active material layer. In some embodiments, the weight of the positive electrode active material layer is 3 to 10 times the weight of the negative electrode active material layer. In some embodiments, the weight of the positive electrode active material layer is 5 to 8 times the weight of the negative electrode active material layer. In some embodiments, the weight of the positive electrode active material layer is 1.5 times, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times the weight of the negative electrode active material layer. , 10 times, 11 times, 12 times, 13 times, 14 times or 15 times.
  • the cathode active material layer may have a coating on the surface, or may be mixed with another compound having a coating.
  • the coating may include elements selected from the group consisting of oxides of the coating elements, hydroxides of the coating elements, oxyhydroxides of the coating elements, oxycarbonates of the coating elements, and hydroxycarbonates of the coating elements. At least one coating element compound selected from hydroxycarbonate).
  • the compound used for the coating can be amorphous or crystalline.
  • Coating elements contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F or mixtures thereof.
  • the coating can be applied by any method as long as the method does not adversely affect the performance of the positive electrode active material.
  • the method may include any coating method well known to those of ordinary skill in the art, such as spraying, dipping, and the like.
  • the positive electrode active material layer further includes a binder, and optionally a positive electrode conductive material.
  • the binder can improve the bonding of the positive electrode active material particles to each other, and also improve the bonding of the positive electrode active material and the current collector.
  • binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl Vinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin, nylon, etc.
  • the positive electrode active material layer includes a positive electrode conductive material, thereby imparting conductivity to the electrode.
  • the positive electrode conductive material may include any conductive material as long as it does not cause chemical changes.
  • Non-limiting examples of positive conductive materials include carbon-based materials (eg, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (eg, metal powder, metal fiber, etc., These include, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (eg, polyphenylene derivatives), and mixtures thereof.
  • the positive electrode current collector for the electrochemical device according to the present application may be aluminum (Al), 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 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, LiN(CF 3 SO 2 )(C 4 F 9 SO 2 ), LiC(CF 3 SO 2 ) 3 , LiPF 4 (CF 3 ) 2 , LiPF 4 (C 2 F 5 ) 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 a combination of an inorganic lithium salt such as LiPF6 or LiBF4 and a fluorine - containing organolithium salt such as LiCF3SO3 , LiN ( CF3SO2 ) 2 , LiN ( C2F5SO2 ) 2 , etc. .
  • the electrolyte includes LiPF6.
  • 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.
  • Solvents that can be used in the electrolyte in the embodiments of the present application include, but are not limited to, cyclic carbonate, chain carbonate, cyclic carboxylate, chain carboxylate, cyclic ether, chain ether, phosphorus-containing Organic solvents, sulfur-containing organic solvents and aromatic fluorinated solvents.
  • cyclic carbonates include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate.
  • the cyclic carbonate has 3-6 carbon atoms.
  • chain carbonates include, but are not limited to: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate
  • Chain carbonates such as base ester and di-n-propyl carbonate, as chain carbonates substituted by fluorine, such as bis(fluoromethyl)carbonate, bis(difluoromethyl)carbonate, bis(trifluoromethyl)carbonate ) carbonate, bis(2-fluoroethyl)carbonate, bis(2,2-difluoroethyl)carbonate, bis(2,2,2-trifluoroethyl)carbonate, 2-fluoroethyl Methyl carbonate, 2,2-difluoroethyl methyl carbonate and 2,2,2-trifluoroethyl methyl carbonate.
  • cyclic carboxylic acid esters include, but are not limited to, gamma-butyrolactone and gamma-valerolactone. In some embodiments, some of the hydrogen atoms of the cyclic carboxylate may be replaced by fluorine.
  • chain carboxylates include, but are not limited to: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate Butyl, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate , methyl valerate, ethyl valerate, methyl pivalate and ethyl pivalate.
  • fluorine-substituted chain carboxylates include, but are not limited to: methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2 trifluoroacetate , 2-trifluoroethyl ester.
  • cyclic ethers include, but are not limited to, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl 1,3-dioxolane, 4-methyl 1 , 3-dioxolane, 1,3-dioxane, 1,4-dioxane and dimethoxypropane.
  • chain ethers include, but are not limited to, dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1 , 1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane and 1,2-ethoxymethyl oxyethane.
  • phosphorus-containing organic solvents include, but are not limited to, trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene phosphate Ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate and tris(2,2, phosphate) 3,3,3-pentafluoropropyl) ester.
  • sulfur-containing organic solvents include, but are not limited to, sulfolane, 2-methyl sulfolane, 3-methyl sulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone Sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate.
  • some of the hydrogen atoms of the sulfur-containing organic solvent may be replaced by fluorine.
  • aromatic fluorine-containing solvents include, but are not limited to, fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.
  • the solvent used in the electrolyte of the present application includes one or more of the above.
  • the solvent used in the electrolyte of the present application includes cyclic carbonate, chain carbonate, cyclic carboxylate, chain carboxylate, and combinations thereof.
  • the solvent used in the electrolyte of the present application comprises an organic solvent selected from the group consisting of: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propionic acid Propyl ester, n-propyl acetate, ethyl acetate, and combinations thereof.
  • the solvent used in the electrolyte of the present application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, ⁇ -butyrolactone or a combination thereof .
  • the additives that can be used in the electrolyte of the embodiments of the present application include, but are not limited to, cyclic carbonates containing carbon-carbon double bonds, and compounds containing sulfur-oxygen double bonds.
  • cyclic carbonates with carbon-carbon double bonds specifically include, but are not limited to: vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, vinyl vinyl ethylene carbonate or at least one of 1,2-dimethyl vinylene carbonate.
  • compounds containing sulfur-oxygen double bonds include, but are not limited to: vinyl sulfate, 1,2-propanediol sulfate, 1,3-propane sultone, 1-fluoro-1,3-propane At least one of sultone, 2-fluoro-1,3-propane sultone or 3-fluoro-1,3-propane sultone.
  • a separator is provided between the positive electrode and the negative electrode to prevent short circuits.
  • the material and shape of the isolation membrane that can be used in the embodiments of the present application are not particularly limited, and may be any of the techniques 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 may include a substrate layer and a surface treatment layer.
  • the base material layer is a non-woven fabric, film or composite film with a porous structure, and the material of the base material layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.
  • the porous structure can improve the heat resistance, oxidation resistance and electrolyte wettability of the separator, and enhance the adhesion between the separator and the pole piece.
  • At least one surface of the base material layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic material layer, or a layer formed by mixing a polymer and an inorganic material.
  • the inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, One or a combination of yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate.
  • the binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, One or a combination of polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer is selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, polyvinylidene At least one of (vinylidene fluoride-hexafluoropropylene).
  • the present application also provides an electrochemical device, which includes a positive electrode, an electrolyte, and a negative electrode, the positive electrode includes a positive electrode active material layer and a positive electrode current collector, the negative electrode includes a negative electrode active material layer and a negative electrode current collector, and the negative electrode active material layer
  • the material layer includes the anode active material according to the present application.
  • the electrochemical device of the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors.
  • the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.
  • the present application further provides an electronic device comprising the electrochemical device according to the present application.
  • 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 electrochemical devices of the present application may be used in, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets stereo headphones, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power, motors, cars, motorcycles, power Bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • lithium ion batteries The preparation of lithium ion batteries is described below by taking lithium ion batteries as an example and in conjunction with specific embodiments. Those skilled in the art will understand that the preparation methods described in this application are only examples, and any other suitable preparation methods are included in the scope of this application. within the range.
  • the prepared negative electrode active material, styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in an appropriate amount of deionized water according to the weight ratio of 97.7:1.2:1.1 to form a uniform negative electrode slurry. material.
  • the negative electrode slurry is coated by weight on the negative electrode current collector (copper foil), dried and cold pressed to obtain a negative electrode active material layer, and then the negative electrode is obtained after cutting and slitting.
  • Lithium cobaltate (LiCoO 2 ), acetylene black and polyvinylidene fluoride (PVDF) are mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1:2 to form a uniform mixture.
  • NMP N-methylpyrrolidone
  • Positive electrode paste The slurry is coated on the positive electrode current collector aluminum foil, dried and cold pressed to obtain a positive electrode active material layer, and then the positive electrode is obtained after cutting and slitting.
  • a 6 ⁇ m polyethylene (PE) porous polymer film is used as a separator, and an organic polymer protective layer is coated on the separator, the thickness of the organic polymer protective layer is about 1-3 ⁇ m, and the organic polymer layer contains PVDF.
  • PE polyethylene
  • the positive electrode, the separator and the negative electrode in order, so that the separator is placed between the positive electrode and the negative electrode for isolation, and then coil to obtain a bare cell; after welding the tabs, place the bare cell in the outer packaging foil aluminum-plastic
  • the electrolyte prepared above is injected into the dried bare cell, and a lithium ion battery is obtained through the processes of vacuum packaging, standing, chemical formation, shaping, and capacity testing.
  • the negative active material sample to be tested is placed in a strong dry dispersion device and completely dispersed into single particles, and the particle edges are obtained by a high-frequency pulsed light source in an exposure time of less than 1 nanosecond clear image. 450 images per second are obtained by a high-speed imaging system. The left and right images were analyzed to obtain the area average particle size and volume specific surface area of the negative electrode active material.
  • the lithium-ion battery was charged to 4.45V with a constant current of 1.5C, and then charged to 0.05C with a constant voltage of 4.45V, and left for 30 minutes. Then, discharge at 0.1C for 10 seconds, and record the voltage value U1; then discharge at 1C for 360 seconds, and record the voltage value U2.
  • “1C” is the current value that fully discharges the battery capacity within 1 hour.
  • the DCR described in this application is obtained by testing the lithium-ion battery at 10% state of charge (SOC).
  • the lithium-ion battery was discharged to 3.0V at a constant current of 0.5C and left to stand for 10 minutes. Then charge to 4.1V with a current of 1.5C and constant current, charge to 0.05C with a voltage and constant voltage of 4.1V, charge to 4.3V with a constant current of 0.7C, and charge to 0.05C with a voltage of 4.3V and constant voltage.
  • the degree of lithium deposition of lithium-ion batteries is judged according to the following criteria:
  • the disassembled negative electrode is golden yellow as a whole, and gray is observed in a very small part; and the area of the gray area is less than 2%, it is determined that no lithium is precipitated.
  • the disassembled negative electrode is gray as a whole, and golden yellow can be observed in some positions; and the area of the gray area is between 20% and 60%, it is determined to be lithium precipitation.
  • the disassembled negative electrode is gray as a whole and the area of the gray area is greater than 60%, it is judged as severe lithium precipitation.
  • the lithium-ion battery is charged and discharged according to the following steps:
  • step (b) after step (a), the lithium-ion battery is DC-discharged to 3V at 1C, and stays for 5 minutes;
  • step (c) after step (b), the lithium ion battery is DC-discharged to 3V at 0.5C, and stays for 5 minutes;
  • step (d) after step (c), the lithium-ion battery is DC-discharged to 3V at 0.05C, and stays for 5 minutes;
  • the lithium-ion battery is DC-discharged to 3V at 0.005C, and stays for 5 minutes;
  • the capacity of the lithium-ion battery after step (a) in the first charge-discharge test is recorded as C1; the lithium-ion battery undergoes steps (b), (c), (d) and The sum of the capacity of (e) is denoted as D1; and the sum of the capacity of the lithium-ion battery after steps (b), (c), (d) and (e) in the 10th charge and discharge test is denoted as D10.
  • D1 the capacity of the lithium-ion battery after steps (b), (c), (d) and (e) in the 10th charge and discharge test
  • volume energy density (capacity ⁇ discharge platform) / volume of lithium-ion battery ⁇ 100%
  • Table 1 shows the influence of the characteristics of the negative active material on the performance of the lithium ion battery.
  • the areal density is about 0.10 mg/mm 2
  • the compacted density is about 1.75 g/cm 3
  • the C004/C110 is about 11
  • the porosity is about 27%.
  • the results show that the lithium deposition phenomena obtained by the D10/D1 and (C1-D10)/C1 calculation methods are consistent with the observation methods. Specifically, as shown in Examples 1-9, when D10/D1 ⁇ 95% and (C1-D10)/C1 ⁇ 7%, the lithium ion battery does not precipitate lithium. As shown in Comparative Example 2, when D10/D1 ⁇ 95% and (C1-D10)/C1 ⁇ 7%, the lithium ion battery will precipitate lithium. As shown in Comparative Examples 3 and 4, when D10/D1 ⁇ 95% and (C1-D10)/C1 ⁇ 7%, the lithium ion battery suffers from severe lithium precipitation.
  • the D10/D1 and (C1-D10)/C1 calculation methods provide a quantitative method for judging the lithium-evolution phenomenon of lithium-ion batteries, which can more accurately determine the degree of lithium-evolution of lithium-ion batteries, avoiding the need for different observations when using the observation method.
  • the subjective error caused by the person and the error limited by the observation field.
  • the areal density SMD of the negative electrode active material is less than 10 ⁇ m but lg(SMD-2)+lg(SMD+2) is less than 0.4, the DC resistance (DCR) of the lithium ion battery is small and no lithium precipitation occurs , but its volumetric energy density is low.
  • the areal density of the negative electrode active material conforms to lg(SMD-2)+lg(SMD+2) ⁇ 0.4 but the SMD is less than 10 ⁇ m, the direct current resistance (DCR) of the lithium ion battery is small, but lithium precipitation occurs phenomenon and low volume energy density.
  • the areal density of the negative active material conforms to lg(SMD-2)+lg(SMD+2) ⁇ 0.4 but the SMD is greater than 16 ⁇ m (as shown in Comparative Example 3 in Figure 1), the volume of the lithium ion battery The energy density is high, but severe lithium precipitation occurs and the direct current resistance (DCR) is large.
  • the surface density SMD of the negative electrode active material is greater than 16 ⁇ m and lg(SMD-2)+lg(SMD+2) is less than 0.4, the volumetric energy density of the lithium-ion battery is high, but serious lithium precipitation occurs and DC The resistance (DCR) is large.
  • the lithium-ion battery not only has a lower direct current resistance (DCR) without lithium deposition, but also has a higher energy density, achieving a balance between lithium deposition and energy density.
  • DCR direct current resistance
  • the direct current resistance (DCR) of the lithium ion battery can be further reduced and the volumetric energy density of the lithium ion battery can be further improved.
  • Table 2 shows the influence of the characteristics of the negative active material on the performance of the lithium ion battery, wherein Examples 10-28 are similar to Example 5, except for the parameters listed in Table 2.
  • the results show that when the areal density of the anode active material layer is in the range of 0.077 mg/mm 2 to 0.121 mg/mm 2 and/or the compacted density is in the range of 1.20 g/cm 3 to 1.83 g/cm 3 , the In order to achieve the balance between the lithium deposition phenomenon and the volume energy density of the lithium ion battery, the anode active material layer can maintain good processability.
  • the orientation of the negative electrode active material is in the appropriate range, and the amount of the end face (ie, the plane where the C axis of the graphite crystal is located) is in the appropriate range, and the negative electrode can be avoided. Lithium precipitation and expansion are avoided, while avoiding the detachment of the negative active material layer from the negative current collector, and the lithium-ion battery has a high volumetric energy density.
  • the bonding force between the negative electrode active material layer and the negative electrode current collector is 8 N/m to 14 N/m and/or the negative electrode active material layer has a porosity of 20% to 40%, it is helpful to realize the deposition of lithium ion batteries. Balance of Lithium and Volumetric Energy Density.

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Abstract

涉及一种负极活性材料及使用其的电化学装置和电子装置。提供一种负极活性材料，其面积平均粒径满足特定关系且在一定的范围内。负极活性材料可使电化学装置实现高能量密度和低析锂现象的平衡。

Description

负极活性材料及使用其的电化学装置和电子装置 技术领域
本申请涉及储能领域，具体涉及一种负极活性材料及使用其的电化学装置和电子装置。
背景技术
电化学装置(例如，锂离子电池)由于具有环境友好、工作电压高、比容量大和循环寿命长等优点而被广泛应用，已成为当今世界最具发展潜力的新型绿色化学电源。小尺寸锂离子电池通常用作驱动便携式电子通讯设备(例如，便携式摄像机、移动电话或者笔记本电脑等)的电源，特别是高性能便携式设备的电源。具有高输出特性的中等尺寸和大尺寸锂例子电池被发展应用于电动汽车(EV)和大规模储能系统(ESS)。随着锂离子电池的广泛应用，其能量密度和析锂现象已成为亟待解决的关键技术问题。改进极片中的活性材料是解决上述问题的研究方向之一。
有鉴于此，确有必要提供一种改进的、性能平衡的负极活性材料及使用其的电化学装置和电子装置。
发明内容
本申请实施例通过提供一种负极活性材料及使用其的电化学装置和电子装置以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。
根据本申请的一个方面，本申请提供了一种负极活性材料，其中所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≥0.4；SMD为所述负极活性材料的面积平均粒径的值，且在10至16的范围内，单位为μm；lg为频度。
在一些实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≥0.5。在一些实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≤1.0。在一些实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≤0.8。在一些 实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≤0.6。
在一些实施例中，所述负极活性材料的面积平均粒径SMD在12μm至14μm的范围内。在一些实施例中，所述负极活性材料的面积平均粒径SMD为10μm、11μm、12μm、13μm、14μm、15μm、16μm或在上述任意两个数值所组成的范围内。
根据本申请的实施例，所述负极活性材料的体积比表面积Sv不大于0.3m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不大于0.2m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不小于0.01m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不小于0.05m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不小于0.1m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv为0.1m 2/cm 3、0.2m 2/cm 3、0.3m 2/cm 3或在上述任意两个数值所组成的范围内。
根据本申请的另一方面，本申请提供一种电化学装置，其包括正极、电解液和负极，所述负极包括负极活性材料层，所述负极活性材料层包括根据本申请所述的负极活性材料。
根据本申请的实施例，所述负极活性材料层的面密度为0.077mg/mm 2至0.121mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.080mg/mm 2至0.120mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.085mg/mm 2至0.110mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.090mg/mm 2至0.100mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.077mg/mm 2、0.080mg/mm 2、0.085mg/mm 2、0.090mg/mm 2、0.095mg/mm 2、0.100mg/mm 2、0.105mg/mm 2、0.110mg/mm 2、0.115mg/mm 2、0.120mg/mm 2、0.121mg/mm 2或在上述任意两个数值的范围内。
根据本申请的实施例，在所述电化学装置为50％SOC状态下，述负极的压实密度为1.20g/cm 3至1.83g/cm 3。在一些实施例中，在所述电化学装置为50％SOC状态下，所述负极活性材料层的压实密度为1.30g/cm 3至1.80g/cm 3。在一些实施例中，在所述电化学装置为50％SOC状态下，所述负极活性材料层的压实密度为1.40g/cm 3至1.60g/cm 3。在一些实施例中，在所述电化学装置为50％SOC状态下，所述负极活性材料层的压实密度为1.20g/cm 3、1.30g/cm 3、1.40 g/cm 3、1.50g/cm 3、1.60g/cm 3、1.70g/cm 3、1.80g/cm 3、1.83g/cm 3或在上述任意两个数值的范围内。
根据本申请的实施例，由X射线衍射图谱测定得到的所述负极活性材料层的(004)面的峰面积C004和(110)面的峰面积C110的比值C004/C110在5至15的范围内。在一些实施例中，由X射线衍射图谱测定得到的所述负极活性材料层C004/C110在6至12的范围内。在一些实施例中，由X射线衍射图谱测定得到的所述负极活性材料层C004/C110在8至10的范围内。在一些实施例中，由X射线衍射图谱测定得到的所述负极活性材料层C004/C110为5、6、7、8、9、10、11、12、13、14、15或在上述任意两个数值的范围内。
根据本申请的实施例，所述负极活性材料层与所述负极集流体之间的粘结力为8N/m至14N/m。在一些实施例中，所述负极活性材料层与所述负极集流体之间的粘结力为10N/m至12N/m。所述负极活性材料层与所述负极集流体之间的粘结力为8N/m、9N/m、10N/m、11N/m、12N/m、13N/m、14N/m或在上述任意两个数值的范围内。
根据本申请的实施例，所述负极活性材料层具有20％至40％的孔隙率。在一些实施例中，所述负极活性材料层具有25％至35％的孔隙率。在一些实施例中，所述负极活性材料层具有28％至32％的孔隙率。在一些实施例中，所述负极活性材料层的孔隙率为20％、22％、25％、28％、30％、32％、35％、38％、40％或在上述任意两个数值的范围内。
根据本申请的实施例，通过充放电测试，所述电化学装置满足以下关系：
D10/D1≥95％；以及
(C1-D10)/C1≤7％
其中：
所述充放电测试根据以下步骤进行：
(a)使所述电化学装置在3C下直流充电至100％荷电状态，记录充电容量；
(b)在步骤(a)后使所述电化学装置在1C下直流放电至3V，记录放电容量，并停留5分钟；
(c)在步骤(b)后使所述电化学装置在0.5C下直流放电至3V，记录放电容量，并停留5分钟；
(d)在步骤(c)后使所述电化学装置在0.05C下直流放电至3V，记录放电容 量，并停留5分钟；
(e)在步骤(d)后使所述电化学装置在0.005C下直流放电至3V，记录放电容量，并停留5分钟；
(f)重复步骤(a)-(e)10次，
C1是所述电化学装置在第1次充放电测试中经过步骤(a)的容量；
D1是所述电化学装置在第1次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和；并且
D10是所述电化学装置在第10次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和。
根据本申请的又一个方面，本申请提供了一种电子装置，其包括根据本申请所述的电化学装置。
本申请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，在不需要创造性劳动的前提下，依然可以根据这些附图中所例示的结果来获得其他实施例的附图。
图1展示了本申请实施例3与对比例3中使用的负极活性材料的面积平均粒径与密度分布的曲线图。
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。在本申请说明书中，将相同或相似的组件以及具有相同或相似的功能的组件通过类似附图标记来表示。在此所描述的有关附图的实施例为说明性质的、图解性质的且用于提供对本申请的基本理解。本申请的实施例不应该被解释为对本申请的限制。
在具体实施方式及权利要求书中，由术语“中的至少一者”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及B，那么短语“A及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及C，那么短语“A、B及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。
随着电化学装置(例如，锂离子电池)的广泛应用，对其性能的要求不断提升。能量密度、循环性能和倍率性能是评价锂离子电池性能的重要指标。迄今为止，尚未研发出能够平衡锂离子电池的能量密度和析锂现象的有效手段。
本申请通过优化负极活性材料以解决上述问题。具体而言，本申请提供了一种负极活性材料，其中所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≥0.4；SMD为所述负极活性材料的面积平均粒径，且在10μm至16μm的范围内；lg为频度。lg(SMD-2)+lg(SMD+2)表明面积平均粒径为SMD的颗粒的数量占总颗粒数量的比例。当lg(SMD-2)+lg(SMD+2)≥0.4时，面积平均粒径为SMD的颗粒大于等于总颗粒数量的40％。
在一些实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≥0.5。在一些实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≤1.0。在一些实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≤0.8。在一些实施例中，所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≤0.6。
在一些实施例中，所述负极活性材料的面积平均粒径SMD在12μm至14μm的范围内。在一些实施例中，所述负极活性材料的面积平均粒径SMD为10μm、11μm、12μm、13μm、14μm、15μm、16μm或在上述任意两个数值所组成的范围内。
负极活性材料的“面积平均粒径”指的是所有负极活性材料颗粒的总体积与所有负极活性材料颗粒的总面积的比值，即：
Figure PCTCN2020127812-appb-000001
其中i表示序数，D表示对应的负极活性材料颗粒的体积，Ni表示粒径为Di的颗粒个数。
负极活性材料的面积平均粒径可反映出负极活性材料颗粒的大小，其对锂离子的扩散具有至关重要的作用。当负极活性材料颗粒较大时，锂离子的扩散路径较长，传输速率较低，导致部分锂离子无法快速嵌入负极活性材料中从而堆积在 负极活性材料表面。当电势达到0V以下时，锂离子析出为锂金属，导致析锂现象。当负极活性材料颗粒较小时，锂离子可在负极活性材料中快速扩散，但负极活性材料会暴露出较多的活性位点，从而增加不可逆锂含量，降低锂离子电池的首次库伦效率，进而降低锂离子电池的能量密度。
lg(SMD-2)+lg(SMD+2)可反映出负极活性材料的粒度分布。负极活性材料的粒度分布越集中，大尺寸颗粒含量越少，同时负极活性材料层在一定压实密度下的孔隙率越大，有利于锂离子在负极活性材料层中的扩散，因此电化学装置的直流电阻越小，从而可减轻电化学装置的析锂现象。当负极活性材料的粒度分布达到阈值时，继续增大负极活性材料的粒度分布难以进一步显著改善锂离子电池的析锂现象，反而会增加成本。
当负极活性材料的面积平均粒径SMD符合上述关系且在上述范围内时，负极活性材料颗粒尺寸适当且分布集中，使电化学装置具有高体积能量密度同时不出现析锂现象，实现综合性能的平衡。
根据本申请的实施例，所述负极活性材料的体积比表面积Sv不大于0.3m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不大于0.2m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不小于0.01m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不小于0.05m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv不小于0.1m 2/cm 3。在一些实施例中，所述负极活性材料的体积比表面积Sv为0.1m 2/cm 3、0.2m 2/cm 3、0.3m 2/cm 3或在上述任意两个数值所组成的范围内。
负极活性材料的“体积比表面积”指的是负极活性材料颗粒的总表面积与总体积的比值，即：
S v＝∑(6nd 2)/∑(nd 3)
其中n表示负极活性材料的颗粒的数量，d表示负极活性材料颗粒的直径。
负极活性材料的体积比表面积Sv越小，负极活性材料颗粒越趋于类球形形状。以石墨作为负极活性材料为例，石墨为六边形层状结构，同层的碳原子以sp 2杂化形成共价键，每一个碳原子以三个共价键与另外三个原子相连，锂离子嵌入在石墨层之间。石墨颗粒呈扁平状时，石墨颗粒中层数较少，每一层的长度较长。石墨颗粒呈类球形时，石墨颗粒中的每一层的长度越短，有利于锂离子的快速脱嵌，从而可降低锂离子电池的直流阻抗，改善锂离子电池的析锂现象。当 负极活性材料的体积比表面积在上述范围内时，可进一步平衡锂离子电池的析锂程度和能量密度。
负极活性材料的面积平均粒径和体积比表面积可通过动态颗粒图像分析获得。具体地，负极活性材料的面积平均粒径可通过以下方法得到：使用新帕泰克QICPIC动态颗粒图像分析仪，将待测试的负极活性材料样品置于强力干法分散装置中完全分散成单个颗粒，通过高频脉冲光源在小于1纳秒的曝光时间内得到颗粒边缘清晰的图像。通过高速成像系统每秒得到450幅图像。对左右图像进行分析得到负极活性材料的面积平均粒径和体积比表面积。
本申请还提供了一种电化学装置，其包括正极、负极、隔离膜和电解液。以下说明可用于本申请中正极、负极、隔离膜和电解液。
负极
本申请的电化学装置所使用的负极包括负极集流体和负极活性材料层，所述负极活性材料层包含根据本申请所述的负极活性材料。
根据本申请的实施例，所述负极活性材料层的面密度为0.077mg/mm 2至0.121mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.080mg/mm 2至0.120mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.085mg/mm 2至0.110mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.090mg/mm 2至0.100mg/mm 2。在一些实施例中，所述负极活性材料层的面密度为0.077mg/mm 2、0.080mg/mm 2、0.085mg/mm 2、0.090mg/mm 2、0.095mg/mm 2、0.100mg/mm 2、0.105mg/mm 2、0.110mg/mm 2、0.115mg/mm 2、0.120mg/mm 2、0.121mg/mm 2或在上述任意两个数值的范围内。负极活性材料层的面密度可通过以下方法测试得到：使用冲片机将负极集流体两面均具有活性材料层的区域冲成12个面积为S的小圆片，称为负极片，称重测得负极片平均质量m1，再使用冲片机将除去负极活性材料层的负极集流体冲成12个与上述负极片面积相同的小圆片，称重测得负极集流体小圆片的平均质量m2，小圆片区域内单层负极活性材料层重量为(m1-m2)/2，负极片面密度为(m1-m2)/2S。
根据本申请的实施例，在所述电化学装置为50％SOC状态下，所述负极活性材料层的压实密度为1.20g/cm 3至1.83g/cm 3。在一些实施例中，在所述电化学装置为50％SOC状态下，所述负极活性材料层的压实密度为1.30g/cm 3至1.80g/cm 3。在一些实施例中，在所述电化学装置为50％SOC状态下，所述负极活性 材料层的压实密度为1.40g/cm 3至1.60g/cm 3。在一些实施例中，在所述电化学装置为50％SOC状态下，所述负极活性材料层的压实密度为1.20g/cm 3、1.30g/cm 3、1.40g/cm 3、1.50g/cm 3、1.60g/cm 3、1.70g/cm 3、1.80g/cm 3、1.83g/cm 3或在上述任意两个数值的范围内。负极活性材料层的压实密度可通过以下方法测试得到：使用冲片机将负极集流体两面均具有活性材料层的区域冲成12个面积为S的小圆片，称为负极片，使用万分尺测试负极片厚度取平均值记为L1，称重测得负极片平均质量m1，再使用冲片机将除去负极活性材料层的负极集流体冲成12个与上述负极片面积相同的小圆片，使用万分尺测试负极集流体厚度取平均值记为L2，称重测得负极集流体小圆片的平均质量m2，单层负极活性材料层重量为(m1-m2)/2，单层负极活性材料层厚度为(L1-L0)/2，负极片压实密度为(m1-m2)/S×(L1-L0)。
根据本申请的实施例，由X射线衍射图谱测定得到的所述负极活性材料层的(004)面的峰面积C004和(110)面的峰面积C110的比值C004/C110在5至15的范围内。在一些实施例中，由X射线衍射图谱测定得到的所述负极活性材料层C004/C110在6至12的范围内。在一些实施例中，由X射线衍射图谱测定得到的所述负极活性材料层C004/C110在8至10的范围内。在一些实施例中，由X射线衍射图谱测定得到的所述负极活性材料层C004/C110为5、6、7、8、9、10、11、12、13、14、15或在上述任意两个数值的范围内。C004/C110可表征负极活性材料层的取向度。C004/C110越大，负极活性材料层的各向异性越大。C004/C110越小，负极活性材料层的各向同性越大。
负极活性材料层的取向度可按照中华人民共和国机械行业标准JB/T4220-2011《人造石墨的点阵参数测定方法》测试得到。具体地，试验条件如下：X射线采用CuK α辐射，CuK α辐射由滤波片或单色器除去。X射线管的工作电压为(30-35)kV，工作电流为(15-20)mA。计数器的扫描速度为1/4 (°)/min。在记录004衍射线图形时，衍射角2θ的扫描范围为53°-57°。在记录110衍射线图形时，衍射角2θ的扫描范围为75°-79°。由(004)面衍射线图形得到的负极活性材料层的峰面积记为C004。由(110)面衍射线图形得到的负极活性材料层的峰面积记为C110。通过计算得到负极活性材料层的C004/C110的比值，即为负极活性材料层的取向度。
根据本申请的实施例，所述负极活性材料层与所述负极集流体之间的粘结力 为8N/m至14N/m。在一些实施例中，所述负极活性材料层与所述负极集流体之间的粘结力为10N/m至12N/m。所述负极活性材料层与所述负极集流体之间的粘结力为8N/m、9N/m、10N/m、11N/m、12N/m、13N/m、14N/m或在上述任意两个数值的范围内。
负极活性材料层与负极集流体之间的粘结力可通过拉伸测试得到，具体如下：使用Instron(型号为33652)测试仪进行测试负极活性材料层与负极集流体之间的粘结：取15-20mm长的极片，用3M双面胶纸将其固定于钢板上，将胶纸贴在负极活性材料层表面，该胶纸一侧与其等宽的纸带相连接，调整拉力机限位块至合适位置，将纸带向上翻折及滑移40mm，滑移速率为50mm/min，测试180°下(即，反方向拉伸)负极活性材料层与负极集流体之间的粘结力。
根据本申请的实施例，所述负极活性材料层具有20％至40％的孔隙率。在一些实施例中，所述负极活性材料层具有25％至35％的孔隙率。在一些实施例中，所述负极活性材料层具有28％至32％的孔隙率。在一些实施例中，所述负极活性材料层的孔隙率为20％、22％、25％、28％、30％、32％、35％、38％、40％或在上述任意两个数值的范围内。负极活性材料层的孔隙率越大，锂离子在负极活性材料层中的扩散越容易。
负极活性材料层的孔隙率可根据《GB/T24586-2009铁矿石表观密度真密度和孔隙率的测定》标准测试得到。
当负极活性材料层的压实密度较大时，负极活性材料的堆积密度较大，使得电解液难以浸润负极活性材料层，不利于锂离子在垂直于负极的方向上的扩散，从而会加剧锂离子电池的析锂现象。当负极活性材料的压实密度较小时，锂离子电池的能量密度会下降。在负极活性材料层的面密度一定的情况下，降低负极活性材料层的压实密度会降低负极活性材料层的各向异性和孔隙率并且降低负极活性材料层与负极集流体之间的粘结力。在负极活性材料层的压实密度一定的情况下，降低负极活性材料层的面密度会增大负极活性材料层的各向异性、降低负极活性材料层的孔隙率并且降低负极活性材料层与负极集流体之间的粘结力。当负极活性材料的面密度、压实密度、取向度C004/C110、孔隙率和/或负极活性材料与负极集流体之间的粘结力在上述范围内时，有助于进一步平衡锂离子电池的能量密度和析锂程度。
根据本申请的实施例，通过充放电测试，所述电化学装置满足以下关系：
D10/D1≥95％；以及
(C1-D10)/C1≤7％
其中：
所述充放电测试根据以下步骤进行：
(a)使所述电化学装置在3C下直流充电至100％荷电状态，记录充电容量；
(b)在步骤(a)后使所述电化学装置在1C下直流放电至3V，记录放电容量，并停留5分钟；
(c)在步骤(b)后使所述电化学装置在0.5C下直流放电至3V，记录放电容量，并停留5分钟；
(d)在步骤(c)后使所述电化学装置在0.05C下直流放电至3V，记录放电容量，并停留5分钟；
(e)在步骤(d)后使所述电化学装置在0.005C下直流放电至3V，记录放电容量，并停留5分钟；
(f)重复步骤(a)-(e)10次，
C1是所述电化学装置在第1次充放电测试中经过步骤(a)的容量；
D1是所述电化学装置在第1次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和；并且
D10是所述电化学装置在第10次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和。
D10/D1以及(C1-D10)/C1可表征电化学装置的析锂程度。当D10/D1以及(C1-D10)/C1在上述范围内时，电化学装置在循环过程中不出现析锂现象。
用于本申请所述的负极集流体可以选自铜箔、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组合。
根据本申请的实施例，所述负极进一步包括导电层。在一些实施方案中，所述导电层的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、碳纳米管、石墨烯等)、基于金属的材料(例如，金属粉、金属纤维等，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。
根据本申请的实施例，所述负极进一步包括粘结剂，所述粘结剂选自以下的 至少一种：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、环氧树脂或尼龙等。
正极
正极包括正极集流体和设置在所述正极集流体上的正极活性材料。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。
在一些实施方案中，正极活性材料包括够吸收和释放锂(Li)的正极材料。能够吸收/释放锂(Li)的正极材料的例子可以包括钴酸锂、镍钴锰酸锂、镍钴铝酸锂、锰酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、磷酸铁锂、钛酸锂和富锂锰基材料。
具体的，钴酸锂的化学式可以如化学式1：
Li xCo aM1 bO 2-c化学式1
其中M1表示选自镍(Ni)、锰(Mn)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)、钨(W)、钇(Y)、镧(La)、锆(Zr)和硅(Si)中的至少一种，x、a、b和c值分别在以下范围内：0.8≤x≤1.2、0.8≤a≤1、0≤b≤0.2、-0.1≤c≤0.2。
镍钴锰酸锂或镍钴铝酸锂的化学式可以如化学式2：
Li yNi dM2 eO 2-f化学式2
其中M2表示选自钴(Co)、锰(Mn)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)、钨(W)、锆(Zr)和硅(Si)中的至少一种，y、d、e和f值分别在以下范围内：0.8≤y≤1.2、0.3≤d≤0.98、0.02≤e≤0.7、-0.1≤f≤0.2。
锰酸锂的化学式可以如化学式3：
Li zMn 2-gM3 gO 4-h化学式3
其中M3表示选自钴(Co)、镍(Ni)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)和钨(W)中的至少一种，z、g和h值分别在以下范围内：0.8≤z≤1.2、0≤g＜1.0和-0.2≤h≤0.2。
在一些实施例中，所述正极活性材料层的重量是所述负极活性材料层的重量的1.5至15倍。在一些实施例中，所述正极活性材料层的重量是所述负极活性材料层的重量的3至10倍。在一些实施例中，所述正极活性材料层的重量是所述负极活性材料层的重量的5至8倍。在一些实施例中，所述正极活性材料层的重量是所述负极活性材料层的重量的1.5倍、2倍、3倍、4倍、5倍、6倍、7倍、8倍、9倍、10倍、11倍、12倍、13倍、14倍或15倍。
在一些实施例中，正极活性材料层可以在表面上具有涂层，或者可以与具有涂层的另一化合物混合。所述涂层可以包括从涂覆元素的氧化物、涂覆元素的氢氧化物、涂覆元素的羟基氧化物、涂覆元素的碳酸氧盐(oxycarbonate)和涂覆元素的羟基碳酸盐(hydroxycarbonate)中选择的至少一种涂覆元素化合物。用于涂层的化合物可以是非晶的或结晶的。在涂层中含有的涂覆元素可以包括Mg、Al、Co、K、Na、Ca、Si、Ti、V、Sn、Ge、Ga、B、As、Zr、F或它们的混合物。可以通过任何方法来施加涂层，只要所述方法不对正极活性材料的性能产生不利影响即可。例如，所述方法可以包括对本领域普通技术人员来说众所周知的任何涂覆方法，例如喷涂、浸渍等。
在一些实施方案中，正极活性材料层还包含粘合剂，并且可选地还包括正极导电材料。
粘合剂可提高正极活性材料颗粒彼此间的结合，并且还提高正极活性材料与集流体的结合。粘合剂的非限制性示例包括聚乙烯醇、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、尼龙等。
正极活性材料层包括正极导电材料，从而赋予电极导电性。所述正极导电材料可以包括任何导电材料，只要它不引起化学变化。正极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。
用于根据本申请的电化学装置的正极集流体可以是铝(Al)，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。
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、LiN(CF 3SO 2)(C 4F 9SO 2)、LiC(CF 3SO 2) 3、LiPF 4(CF 3) 2、LiPF 4(C 2F 5) 2、LiPF 4(CF 3SO 2) 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。在一些实施例中，电解质包括LiPF 6和LiBF 4的组合。在一些实施例中，电解质包括LiPF 6或LiBF 4等无机锂盐与LiCF 3SO 3、LiN(CF 3SO 2) 2、LiN(C 2F 5SO 2) 2等含氟有机锂盐的组合。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溶剂包括，但不限于，环状碳酸酯、链状碳酸酯、环状羧酸酯、链状羧酸酯、环状醚、链状醚、含磷有机溶剂、含硫有机溶剂和芳香族含氟溶剂。
在一些实施例中，环状碳酸酯包括，但不限于，碳酸亚乙酯(ethylene carbonate，EC)、碳酸亚丙酯(propylene carbonate，PC)和碳酸亚丁酯。
在一些实施例中，环状碳酸酯具有3-6个碳原子。
在一些实施例中，链状碳酸酯包括，但不限于：碳酸二甲酯、碳酸甲乙酯、碳酸二乙酯(diethyl carbonate，DEC)、碳酸甲基正丙基酯、碳酸乙基正丙基酯、碳酸二正丙酯等链状碳酸酯，作为被氟取代的链状碳酸酯，例如双(氟甲基)碳酸酯、双(二氟甲基)碳酸酯、双(三氟甲基)碳酸酯、双(2-氟乙基)碳酸酯、双(2，2-二氟乙基)碳酸酯、双(2，2，2-三氟乙基)碳酸酯、2-氟乙基甲基碳酸酯、2，2-二氟乙基甲基碳酸酯和2，2，2-三氟乙基甲基碳酸酯。
在一些实施例中，环状羧酸酯包括，但不限于，γ-丁内酯和γ-戊内酯。在一些实施例中，环状羧酸酯的部分氢原子可被氟取代。
在一些实施例中，链状羧酸酯包括，但不限于：乙酸甲酯、乙酸乙酯、乙酸 丙酯、乙酸异丙酯、乙酸丁酯、乙酸仲丁酯、乙酸异丁酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丙酸异丙酯、丁酸甲酯、丁酸乙酯、丁酸丙酯、异丁酸甲酯、异丁酸乙酯、戊酸甲酯、戊酸乙酯、特戊酸甲酯和特戊酸乙酯。在一些实施例中，链状羧酸酯的部分氢原子可被氟取代。在一些实施例中，氟取代的链状羧酸酯包括，但不限于：三氟乙酸甲酯、三氟乙酸乙酯、三氟乙酸丙酯、三氟乙酸丁酯和三氟乙酸2，2，2-三氟乙酯。
在一些实施例中，环状醚包括，但不限于，四氢呋喃、2-甲基四氢呋喃、1，3-二氧戊环、2-甲基1，3-二氧戊环、4-甲基1，3-二氧戊环、1，3-二氧六环、1，4-二氧六环和二甲氧基丙烷。
在一些实施例中，链状醚包括，但不限于，二甲氧基甲烷、1，1-二甲氧基乙烷、1，2-二甲氧基乙烷、二乙氧基甲烷、1，1-二乙氧基乙烷、1，2-二乙氧基乙烷、乙氧基甲氧基甲烷、1，1-乙氧基甲氧基乙烷和1，2-乙氧基甲氧基乙烷。
在一些实施例中，含磷有机溶剂包括，但不限于，磷酸三甲酯、磷酸三乙酯、磷酸二甲基乙酯、磷酸甲基二乙酯、磷酸亚乙基甲酯、磷酸亚乙基乙酯、磷酸三苯酯、亚磷酸三甲酯、亚磷酸三乙酯、亚磷酸三苯酯、磷酸三(2，2，2-三氟乙基)酯和磷酸三(2，2，3，3，3-五氟丙基)酯。
在一些实施例中，含硫有机溶剂包括，但不限于，环丁砜、2-甲基环丁砜、3-甲基环丁砜、二甲基砜、二乙基砜、乙基甲基砜、甲基丙基砜、二甲基亚砜、甲磺酸甲酯、甲磺酸乙酯、乙磺酸甲酯、乙磺酸乙酯、硫酸二甲酯、硫酸二乙酯和硫酸二丁酯。在一些实施例中，含硫有机溶剂的部分氢原子可被氟取代。
在一些实施例中，芳香族含氟溶剂包括，但不限于，氟苯、二氟苯、三氟苯、四氟苯、五氟苯、六氟苯和三氟甲基苯。
在一些实施例中，本申请的电解液中使用的溶剂包括如上所述的一种或多种。在一些实施例中，本申请的电解液中使用的溶剂包括环状碳酸酯、链状碳酸酯、环状羧酸酯、链状羧酸酯及其组合。在一些实施例中，本申请的电解液中使用的溶剂包含选自由下列物质组成的群组的有机溶剂：碳酸亚乙酯、碳酸亚丙酯、碳酸二乙酯、丙酸乙酯、丙酸丙酯、乙酸正丙酯、乙酸乙酯及其组合。在一些实施例中，本申请的电解液中使用的溶剂包含：碳酸亚乙酯、碳酸亚丙酯、碳酸二乙酯、丙酸乙酯、丙酸丙酯、γ-丁内酯或其组合。
可用于本申请实施例的电解液中的添加剂包括，但不限于，含碳碳双键的环 状碳酸酯、含硫氧双键的化合物。
在一些实施例中，具有碳-碳双键的环状碳酸酯具体包括，但不限于：碳酸亚乙烯酯、碳酸甲基亚乙烯酯、碳酸乙基亚乙烯酯、乙烯基碳酸乙烯亚乙酯或碳酸-1，2-二甲基亚乙烯酯中的至少一种。
在一些实施例中，含硫氧双键的化合物包括，但不限于：硫酸乙烯酯、1，2-丙二醇硫酸酯、1，3-丙磺酸内酯、1-氟-1，3-丙磺酸内酯、2-氟-1，3-丙磺酸内酯或3-氟-1，3-丙磺酸内酯中的至少一种。
隔离膜
在一些实施方案中，正极与负极之间设有隔离膜以防止短路。可用于本申请的实施例中使用的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。在一些实施方案中，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，隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、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，可选用聚丙烯多孔膜、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。多孔结构可以提升隔离膜的耐热性能、抗氧化性能和电解质浸润性能，增强隔离膜与极片之间的粘接性。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的一种或几种的组合。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的一种或几种的组合。
聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
电化学装置
本申请还提供了一种电化学装置，其包括正极、电解液和负极，所述正极包 括正极活性材料层和正极集流体，所述负极包括负极活性材料层和负极集流体，所述负极活性材料层包括根据本申请所述的负极活性材料。
本申请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，包括锂金属二次电池、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。
电子装置
本申请另提供了一种电子装置，其包括根据本申请的电化学装置。
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装置。在一些实施方案中，本申请的电化学装置可用于，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。
下面以锂离子电池为例并且结合具体的实施例说明锂离子电池的制备，本领域的技术人员将理解，本申请中描述的制备方法仅是实例，其他任何合适的制备方法均在本申请的范围内。
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
选取针状焦、石油焦、沥青焦的中至少一种使用机械磨或辊压磨对针状焦进行破碎分级面积平均粒径，破碎后的颗粒使用整形机进行整形，从而控制其平均粒径和体积比表面积。将分级和整形后的骨料与辅料(沥青、树脂等)以9∶1至5∶5的重量比加入竖式釜，卧式釜，或滚筒炉中进行造粒，造粒后的样品进一步分级整形，通过控制分级出料口的频率以及整形的功率来得到不同面积平均粒径，分布以及体积比表面积Sv的石墨。
将制备好的负极活性材料与丁苯橡胶(SBR)和羧甲基纤维素钠(CMC)按 照97.7∶1.2∶1.1的重量比在适量的去离子水中充分搅拌混合，使其形成均匀的负极浆料。将负极浆料涂覆重量涂覆于负极集流体(铜箔)上，烘干、冷压得到负极活性材料层，之后经过裁片、分切后，得到负极。
2、正极的制备
将钴酸锂(LiCoO 2)、乙炔黑和聚偏二氟乙烯(PVDF)按重量比97∶1∶2在适量的N-甲基吡咯烷酮(NMP)溶剂中充分搅拌混合，使其形成均匀的正极浆料。将此浆料涂覆于正极集流体铝箔上，烘干、冷压得到正极活性材料层，之后经过裁片、分切后，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)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照质量比为EC∶EMC∶DEC＝30∶50∶20进行混合，接着加入4％的氟代碳酸乙烯酯，2％的1，3-丙烷磺内酯，2％的丁二腈，溶解并充分搅拌后加入锂盐LiPF6，混合均匀后获得电解液，其中LiPF6的浓度为1mol/L。
4、隔离膜的制备
以6μm的聚乙烯(PE)多孔聚合物薄膜作为隔离膜，并且在隔膜上涂覆有机聚合物保护层，有机聚合物保护层厚度为约1-3μm，有机聚合物层包含PVDF。
5、锂离子电池的制备
将正极、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，然后卷绕得到裸电芯；焊接极耳后将裸电芯置于外包装箔铝塑膜中，将上述制备好的电解液注入到干燥后的裸电芯中，经过真空封装、静置、化成、整形、容量测试等工序，获得锂离子电池。
二、测试方法
1、负极活性材料的面积平均粒径和体积比表面积的测试方法
使用新帕泰克QICPIC动态颗粒图像分析仪，将待测试的负极活性材料样品置于强力干法分散装置中完全分散成单个颗粒，通过高频脉冲光源在小于1纳秒的曝光时间内得到颗粒边缘清晰的图像。通过高速成像系统每秒得到450幅图像。对左右图像进行分析得到负极活性材料的面积平均粒径和体积比表面积。
2、锂离子电池的直流电阻(DCR)的测试方法
在25℃下，将锂离子电池以1.5C恒流充电至4.45V，再以4.45V恒压充电至0.05C，静置30分钟。然后，以0.1C放电10秒，记录电压值U1；接着以1C 放电360秒，记录电压值U2。“1C”是在1小时内将电池容量完全放完的电流值。
根据下式计算锂离子电池的直流电阻R
R＝(U2-U1)/(1C-0.1C)。
除非有特别说明，本申请所述的DCR是锂离子电池在10％荷电状态(SOC)下测试得到的。
3、锂离子电池析锂现象的测试方法
(1)观察法
在25℃下，将锂离子电池以0.5C的电流恒流放电至3.0V，静置10分钟。然后以1.5C的电流恒流充电至4.1V，以4.1V的电压恒压充电至0.05C，以0.7C的电流恒流充电至4.3V，以4.3V的电压恒压充电至0.05C，以0.5C的电流恒流充电至4.4V，以4.4V的电压恒压充电至0.05C，最后以0.5C的电流恒流放电至3.0V，静止10分钟。重复上述充放电过程10次。在干燥条件下拆解，拍照记录负极的状态。
根据以下标准判断锂离子电池的析锂程度：
当拆解后的负极整体呈现金黄色，极少部分可观察到灰色；且灰色区域的面积＜2％，则判定为不析锂。
当拆解后的负极大部分呈现金黄色，部分位置可观察到灰色；且灰色区域的面积在2％至20％之间，则判定为轻微析锂。
当拆解后的负极整体呈现为灰色，部分位置可观察到金黄色；且灰色区域的面积在20％至60％之间，则判定为析锂。
当拆解后的负极整体呈现灰色且灰色区域的面积＞60％时，则判定为严重析锂。
(2)计算法
将锂离子电池按照以下步骤进行充放电测试：
(a)使锂离子电池在3C下直流充电至100％荷电状态；
(b)在步骤(a)后使锂离子电池在1C下直流放电至3V，停留5分钟；
(c)在步骤(b)后使锂离子电池在0.5C下直流放电至3V，停留5分钟；
(d)在步骤(c)后使锂离子电池在0.05C下直流放电至3V，停留5分钟；
(e)在步骤(d)后使锂离子电池在0.005C下直流放电至3V，停留5分钟；
(f)重复步骤(a)-(e)10次。
期间测试锂离子电池在第1次充放电测试中经过步骤(a)的容量，记为C1；锂离子电池在第1次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和，记为D1；以及锂离子电池在第10次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和，记为D10。计算D10/D1以及(C1-D10)/C1以判断锂离子电池的析锂程度。
4、锂离子电池的体积能量密度的测试方法
在25℃下，使用新威机以0.5C电流恒流充电至4.45V，恒压至电流为0.05C；静置5分钟，以0.5C恒流放电至电压为3.0V，记录放电容量以及放电平台。通过排水法测量锂离子电池的体积。通过下式计算锂离子电池的体积能量密度：
体积能量密度＝(容量×放电平台)/锂离子电池的体积×100％
5、锂离子电池的循环圈数的测试方法
将锂离子电池置于25℃恒温箱中，静置30分钟，使锂离子电池达到恒温。然后以0.7C恒流充电至4.45V，恒压充电至电流为0.05C；再以0.7C放电至3.0V，以此步容量为基准，记为初始容量。采用相同步骤循环至锂离子电池的容量为初始容量的80％时，记录循环圈数。
三、测试结果
表1展示了负极活性材料的特性对锂离子电池的性能的影响，实施例1-9中面密度为约0.10mg/mm 2压实密度为约1.75g/cm 3，C004/C110为约11，孔隙率为约27％。
结果表明，采用D10/D1和(C1-D10)/C1计算法和观察法所得到的析锂现象一致。具体来说，如实施例1-9所示，当D10/D1≥95％且(C1-D10)/C1≤7％时，锂离子电池不析锂。如对比例2所示，当D10/D1≥95％且(C1-D10)/C1＜7％，锂离子电池析锂。如对比例3和4所示，当D10/D1＜95％且(C1-D10)/C1＜7％，锂离子电池严重析锂。D10/D1和(C1-D10)/C1计算法为判断锂离子电池的析锂现象提供了定量手段，其可更精确的判断锂离子电池的析锂程度，避免了采用观察法时由不同观察者导致的主观误差以及受观察视野限制的误差。
如对比例1所示，负极活性材料的面密度SMD小于10μm但lg(SMD-2)+lg(SMD+2)小于0.4，锂离子电池的直流电阻(DCR)较小且没有出现析锂现象，但其体积能量密度较低。如对比例2所示，负极活性材料的面密度符合lg(SMD-2)+lg(SMD+2)≥0.4但SMD小于10μm，锂离子电池的直流电阻(DCR)较小， 但出现析锂现象且体积能量密度较低。如对比例3所示，负极活性材料的面密度符合lg(SMD-2)+lg(SMD+2)≥0.4但SMD大于16μm(如图1中对比例3所示)，锂离子电池的体积能量密度较高，但出现严重析锂且直流电阻(DCR)较大。如对比例4所示，负极活性材料的面密度SMD大于16μm且lg(SMD-2)+lg(SMD+2)小于0.4，锂离子电池的体积能量密度较高，但出现严重析锂且直流电阻(DCR)较大。
如实施例1-9所示，当负极活性材料的面密度符合lg(SMD-2)+lg(SMD+2)≥0.4且SMD在10μm至16μm的范围内(例如，图1中实施例3所示)时，锂离子电池不仅具有较低的直流电阻(DCR)，没有出现析锂现象，同时具有较高的能量密度，实现了析锂现象与能量密度的平衡。负极活性材料的面积平均粒径SMD越小，锂离子电池的直流电阻(DCR)越小，析锂程度程度越小。当负极活性材料的体积表面积Sv不大于0.3m 2/cm 3时，可进一步降低锂离子电池的直流电阻(DCR)并进一步提升锂离子电池的体积能量密度。
表2展示负极活性材料的特性对锂离子电池的性能的影响，其中实施例10-28与实施例5相似，不同之处仅在于表2所列参数。
结果表明，当负极活性材料层的面密度在0.077mg/mm 2至0.121mg/mm 2的范围内和/或压实密度在1.20g/cm 3至1.83g/cm 3范围内时，有助于实现锂离子电池的析锂现象和体积能量密度的平衡，同时可使负极活性材料层保持良好的加工性能。
当负极活性材料层的C004/C110在5至15的范围内时，负极活性材料的取向在合适的范围，端面(即，石墨晶体C轴所在的平面)的量在适宜范围内，可避免负极析锂和膨胀，同时避免负极活性材料层从负极集流体上脱落，同时锂离子电池具有较高体积能量密度。
当负极活性材料层与负极集流体之间的粘结力为8N/m至14N/m和/或负极活性材料层具有20％至40％的孔隙率时，有助于实现锂离子电池的析锂和体积能量密度的平衡。
Figure PCTCN2020127812-appb-000002
Figure PCTCN2020127812-appb-000003
整个说明书中对“实施例”、“部分实施例”、“一个实施例”、“另一举例”、“举例”、“具体举例”或“部分举例”的引用，其所代表的意思是在本申请中的至少一个实施例或举例包含了该实施例或举例中所描述的特定特征、结构、材料或特性。因此，在整个说明书中的各处所出现的描述，例如：“在一些实施方案中”、“在实施例中”、“在一个实施例中”、“在另一个举例中”，“在一个举例中”、“在特定举例中”或“举例”，其不必然是引用本申请中的相同的实施例或示例。此外，本文中的特定特征、结构、材料或特性可以以任何合适的方式在一个或多个实施例或举例中结合。
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. 一种负极活性材料，其中所述负极活性材料的面积平均粒径满足以下关系：lg(SMD-2)+lg(SMD+2)≥0.4；
    SMD为所述负极活性材料的面积平均粒径的值，且在10至16的范围内，单位为μm；
    lg为频度。
  2. 根据权利要求1所述的负极活性材料，其中所述负极活性材料的体积比表面积Sv不大于0.3m 2/cm 3。
  3. 一种电化学装置，其包括正极、电解液和负极，所述负极包括负极活性材料层，所述负极活性材料层包括根据权利要求1和2中任一权利要求所述的负极活性材料。
  4. 根据权利要求3所述的电化学装置，其中所述负极活性材料层的面密度为0.077mg/mm 2至0.121mg/mm 2。
  5. 根据权利要求3所述的电化学装置，其中在所述电化学装置为50％SOC状态下，所述负极活性材料层的压实密度为1.20g/cm 3至1.83g/cm 3。
  6. 根据权利要求3所述的电化学装置，其中由X射线衍射图谱测定得到的所述负极活性材料层的(004)面的峰面积C004和(110)面的峰面积C110的比值C004/C110在5至15的范围内。
  7. 根据权利要求3所述的电化学装置，其中所述负极活性材料层与所述负极集流体之间的粘结力为8N/m至14N/m。
  8. 根据权利要求3所述的电化学装置，其中所述负极活性材料层具有20％至40％的孔隙率。
  9. 根据权利要求3所述的电化学装置，其中通过充放电测试，所述电化学装置满足以下关系：
    D10/D1≥95％；以及
    (C1-D10)/C1≤7％
    其中：
    所述充放电测试根据以下步骤进行：
    (a)使所述电化学装置在3C下直流充电至100％荷电状态，记录充电容量；
    (b)在步骤(a)后使所述电化学装置在1C下直流放电至3V，记录放电容量，并停留5分钟；
    (c)在步骤(b)后使所述电化学装置在0.5C下直流放电至3V，记录放电容量，并停留5分钟；
    (d)在步骤(c)后使所述电化学装置在0.05C下直流放电至3V，记录放电容量，并停留5分钟；
    (e)在步骤(d)后使所述电化学装置在0.005C下直流放电至3V，记录放电容量，并停留5分钟；
    (f)重复步骤(a)-(e)10次，
    C1是所述电化学装置在第1次充放电测试中经过步骤(a)的容量；
    D1是所述电化学装置在第1次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和；并且
    D10是所述电化学装置在第10次充放电测试中经过步骤(b)、(c)、(d)和(e)的容量之和。
  10. 一种电子装置，其包括根据权利要求3至9任一项所述的电化学装置。
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