CN114447275B - Negative pole piece and secondary battery - Google Patents

Negative pole piece and secondary battery Download PDF

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Publication number
CN114447275B
CN114447275B CN202210371335.9A CN202210371335A CN114447275B CN 114447275 B CN114447275 B CN 114447275B CN 202210371335 A CN202210371335 A CN 202210371335A CN 114447275 B CN114447275 B CN 114447275B
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active material
negative pole
pole piece
negative
negative electrode
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CN114447275A (en
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彭宇东
郝嵘
慈祥云
齐成紫
张笑莉
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BYD Co Ltd
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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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • 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
    • H01M10/058—Construction or manufacture
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The application provides a negative pole piece and secondary battery, this negative pole piece includes that the negative pole collects the body and sets up the negative pole active material layer on its at least side surface, defines parameter k: k = [ F × R = 1 +(1‑F)×R 2 ]X PD multiplied by Dv50 multiplied by P/span, and k is more than or equal to 2.0 and less than or equal to 20.0; wherein F represents the number ratio of primary particles to total particles in the anode active material, and R 1 Represents an average aspect ratio, R, of primary particles in the anode active material 2 Represents an average width-to-length ratio of secondary particles in the anode active material; span represents the dispersion of the particle size distribution of the negative electrode active material, and Dv50 represents the median particle diameter of the negative electrode active material in μm; PD represents the compacted density of the negative pole piece and the unit is g/cm 3 (ii) a P represents the mercury intrusion porosity of the negative pole piece. The secondary battery containing the negative pole piece has higher energy density, and can give consideration to excellent dynamic performance, long cycle life and the like.

Description

Negative pole piece and secondary battery
Technical Field
The application relates to the technical field of batteries, in particular to a negative pole piece and a secondary battery.
Background
As a reversible energy storage carrier, a secondary battery is widely used in the fields of mobile electronic devices (such as mobile phones), automobiles, household appliances and the like, and with the continuous development of secondary batteries and products using the same, consumers have higher requirements on the energy density, the cycle performance and other performances of the battery.
Generally, the way of increasing the energy density of the secondary battery includes increasing the thickness or compaction density of the pole piece, but excessively pursuing the high compaction density of the pole piece may reduce the cycle performance and safety performance of the battery, and excessively increasing the thickness of the pole piece may increase the migration path of lithium ions and electrons, and may also affect the cycle performance of the battery.
Disclosure of Invention
In view of this, the application provides a negative pole piece and secondary battery to under the prerequisite of guaranteeing battery cycle performance and security performance etc. promote the compaction density of negative pole piece, and then promote the energy density of battery.
In a first aspect, the present application provides a negative electrode plate, the negative electrode plate includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, the negative active material layer contains a negative active material, and defines the following parameter k:
k=[F×R 1 +(1-F)×R 2 ]x PD x Dv50 x P/span, and k is more than or equal to 2.0 and less than or equal to 20.0;
wherein F represents a ratio of the number of primary particles to the number of total particles in the anode active material, and R 1 Represents an average aspect ratio, R, of primary particles in the anode active material 2 Represents an average width-to-length ratio of secondary particles in the anode active material; span represents the dispersion of the particle size distribution of the negative active material, span = (Dv 90-Dv 10)/Dv 50, Dv10, Dv50 and Dv90 represent the corresponding particle sizes when the cumulative volume distribution percentage of the particles of the negative active material reaches 10%, 50% and 90%, and the units are mum; PD represents the compaction density of the negative pole piece and has the unit of g/cm 3 (ii) a P represents the mercury intrusion porosity of the negative pole piece.
The average width-length ratio of primary particles and secondary particles, the number ratio of the primary particles, the particle size distribution parameter (Dv 50, span) of the whole particles, the porosity and the compaction density of the negative electrode plate are linked, the parameter k is defined, and the k is controlled within the range of 2.0 to 20.0, so that the rate capability, the quick charging capability, the cycle performance, the safety performance and the like of the battery manufactured by the negative electrode plate can be ensured to be excellent under the condition that the energy density of the battery manufactured by the negative electrode plate is higher.
In some embodiments of the present application, the parameter k is in the range of 2.0 to 20.0.
In a second aspect, the present application provides a secondary battery comprising a negative electrode tab as described above. When the secondary battery is circulated under a large multiplying power, the high capacity can be kept, and the circulation stability is good.
Detailed Description
The following describes the technical solution of the embodiments of the present application in detail.
The embodiment of the application provides a negative pole piece, this negative pole piece includes the mass flow body and sets gradually the negative pole active material layer on the at least side surface of the mass flow body of negative pole, and the negative pole active material layer contains negative pole active material, defines following parameter k:
k=[F×R 1 +(1-F)×R 2 ]x PD x Dv50 x P/span, and k is more than or equal to 2.0 and less than or equal to 20.0;
wherein F represents a ratio of the number of primary particles to the number of total particles in the anode active material, and R 1 Represents an average aspect ratio, R, of primary particles in the anode active material 2 Represents an average width-to-length ratio of secondary particles in the anode active material; span represents the dispersion of the particle size distribution of the negative active material, span = (Dv 90-Dv 10)/Dv 50, Dv10, Dv50 and Dv90 represent the corresponding particle sizes when the cumulative volume distribution percentage of the particles of the negative active material reaches 10%, 50% and 90%, and the units are mum; PD represents the compacted density of the negative pole piece and has the unit of g/cm 3 (ii) a P represents the mercury pressing porosity of the negative pole piece.
R is as defined above 1 、R 2 May be obtained from a Scanning Electron Microscope (SEM) photograph of the anode active material particles. Wherein R is 1 The average of the ratio of the width to the length of the plurality of primary particles may be obtained by taking a photograph of the anode active material. Specifically, for an SEM photograph of the negative electrode active material (containing a certain number of negative electrode active material particles), Image J software is used to measure the width and length of each primary particle, the ratio of the width to the length of each primary particle is calculated, and the ratios of the plurality of primary particles in the picture are averaged to obtain R 1 . Here, the "wide diameter" refers to a minimum value between parallel lines tangent to a projected image of the anode active material particle. The "major axis" refers to the maximum value between parallel lines tangent to the projected image of the anode active material particle. R 2 By the way of obtaining with R 1 Similarly, it is only counted as a size parameter of the secondary particles in the SEM photograph of the anode active material. When R is 1 、R 2 When smaller, the primary particles and the secondary particles representing the anode active material have elongated shapes, R 1 、R 2 The closer to 1, illustrateThe more the pellet tends to be perfectly spherical.
F is the ratio of the number of all particles counted from the SEM photograph of the anode active material and the number of primary particles counted therein. F. R 1 、R 2 Are all dimensionless.
Specific values of Dv50, Dv10, and Dv90 described above are known from a particle size distribution map of the negative electrode active material particles obtained by a laser diffraction method, and span can be calculated from Dv50, Dv10, and Dv90 values. The specific test method comprises the following steps: soaking the negative pole piece in water, removing the copper foil after the pole piece dressing falls off, filtering the water solution, taking the residue, burning the residue in an oxygen atmosphere by using acetylene flame at the burning temperature of 600-800 ℃, wherein the burned residue is negative active material powder, and taking the burned residue for particle size test. The specific test method of the particle size parameter can be seen in GB/T19077-2016/ISO 13320:2009 particle size distribution laser diffraction method. Among them, the instruments used for testing Dv50, Dv10, Dv90 are generally called laser particle sizers, for example, malvern model 3000. According to the negative pole piece, the average width-length ratio of primary particles and secondary particles, the number proportion of the primary particles, the particle size distribution parameters (Dv 50, span) of the whole particles, the porosity and the compaction density of the negative pole piece are linked, a parameter k is defined, and the k is controlled within the range of 2-20, so that the utilization rate of the active material in the unit volume of the pole piece is high, the energy density of the battery is high, the diffusion resistance, the path and the like of ions in a liquid phase are reduced, and the rate performance, the quick charging capacity, the cycle performance and the safety performance of the battery are excellent.
According to the negative pole piece provided by the application, the average width-length ratio of primary particles and secondary particles in the negative active material, the number proportion of the primary particles, the particle size distribution parameters (Dv 50, span) of the whole particles, the porosity and the compaction density of the negative pole piece are linked, a parameter k is defined, and the k is controlled to be in a range of more than 0 to 20, so that the compaction density of the pole piece is higher, the utilization rate of the active material in unit volume is higher, the improvement of the energy density of the battery is facilitated, the diffusion resistance, the path and the like of ions in a liquid phase and a solid phase are reduced, and the rate performance, the quick charging capacity, the cycle performance and the safety performance of the battery are also excellent.
In some embodiments of the present application, the parameter k is in the range of 4 to 9. At this time, the secondary battery using the negative electrode sheet can balance various performances better.
It can be understood that 0. ltoreq. F.ltoreq.1, 0. ltoreq. R 1 ≤1，0≤R 2 Less than or equal to 1. Further, F is more than or equal to 0 and less than or equal to 1, and R is more than 0 1 ≤1，0＜R 2 ≤1。
The average width-to-length ratio of the primary particles and the secondary particles of the negative electrode active material influences the accumulation condition of the negative electrode active material powder, and further influences the compaction density of the porosity of the negative electrode. To ensure that the porosity and compacted density of the negative electrode are within suitable ranges, the present application, in some embodiments, controls the R 1 In the range of 0.5 to 1, the R 2 In the range of 0.5-1. Therefore, the problems of difficult electrolyte infiltration, low utilization rate of active substances, low dynamic performance of a battery cell, low capacity exertion and the like caused by the reduction of the porosity of the negative active material after rolling are solved; meanwhile, the problems of reduced compaction density, easy falling of active materials, low energy density of the battery and the like caused by reduced maximum stacking density of particles and excessive gaps are avoided. Exemplary, R 1 、R 2 And independently 0.55, 0.6, 0.7, 0.8, 0.9, or 0.95, etc. Preferably, R 1 、R 2 In the range of 0.6-0.9.
In the practice of the present application, the Dv50 may be in the range of 7 μm to 17 μm. The Dv50 may also be referred to as the average particle diameter of the particles of the anode active material, which may be specifically 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, or the like. In some embodiments, Dv50 is in the range of 11 μm to 17 μm. The Dv50 of the anode active material particles may exhibit an overall particle distribution, and the proportion of secondary particles may also affect Dv 50. In general, the larger the Dv50 particle size of the negative electrode active material is, the greater the resistance of the ions to solid-phase migration and diffusion inside thereof is, and the rate performance of the battery is reduced; when the particle size of the negative active material is too small, the volume of through holes of the negative active material layer may be reduced (porosity is reduced), and resistance to diffusion and migration of ionic liquid phase may be increased, which may ultimately affect rate performance and cycle performance of the battery.
The application controls the Dv50 in the range, so that the accumulation condition of the negative active material particles is ensured to be proper, the polarization intensity of the pole piece is low, the lithium ion transmission speed in the battery circulation process is high, and the secondary battery has high energy density and is not easy to expand.
In embodiments of the present application, the Dv10 may be in the range of 3 μm to 10 μm, and in some embodiments, the Dv10 is in the range of 5 μm to 10 μm. Wherein said Dv90 may be in the range of 12 μm-30 μm. In some embodiments, the Dv90 is in the range of 20 μm to 25 μm.
By controlling the Dv10 and Dv90 within the above ranges, reasonable particle size distribution of the negative active material can be ensured, and the battery can better give consideration to high energy density, good cycle performance and the like. If the number of the small particles in the negative active material is excessive, the side reaction of the negative electrode is aggravated, the gas production is increased, and the cycle life of the battery is shortened; if the quantity of large particles in the negative active material is too much, the processing difficulty of the pole piece is increased, the flatness of the pole piece is reduced, and lithium is separated at low temperature.
In the present application, the larger the span value is, the larger the particle size dispersion and the smaller the particle size concentration representing the negative electrode active material are. In some embodiments of the present application, the span is in the range of 0.11 to 2.5, preferably the span is in the range of 0.11 to 1.5.
In the present application, PD and P are actually measured values of the negative electrode sheet. The test method of the compacted density PD of the negative pole piece comprises the steps of cutting the negative pole piece into small pieces with certain sizes according to a certain direction, measuring the weight of a negative active material in the small piece in unit area, calculating the surface density, measuring the thickness of the negative active material, and calculating to obtain the PD through the surface density/(the thickness of the pole piece-the thickness of a current collector); the mercury-pressing porosity P of the negative electrode plate is obtained by mercury-pressing method (also called mercury pressing method) test, and the specific reference standard is as follows: GB/T21650.1-2008 mercury intrusion method and gas adsorption method for measuring pore size distribution and porosity of solid material, part 1 mercury intrusion method. The porosity P can be regulated and controlled by controlling the rolling pressure in the preparation process of the cathode.
Generally, the negative electrode plate has rich gaps/through holes and larger area, which is beneficial to the infiltration of electrolyte in the electrode plate in a proper range, improves the electrolyte retention of the electrode plate, improves the liquid phase diffusion rate in low-temperature working condition and high-rate charge and discharge, can avoid the reduction and deposition of lithium metal on the surface of the negative active material, and improves the low-temperature performance and the rapid charge and discharge capacity of the battery cell; the excessively high porosity of the negative pole piece is aggravated by side reactions in the formation and circulation processes, and is not beneficial to long circulation; if the porosity is too low, the infiltration effect of the electrolyte in the pole piece is reduced, the liquid retention amount is reduced, the lithium ion liquid phase conduction is not facilitated, and the circulation and dynamic performance of the battery cell are influenced. In order to better consider the liquid retention capacity of the pole piece, the cycle performance and the dynamic performance of the battery and the like, in the embodiment of the application, the mercury pressing porosity P of the negative pole piece is controlled within the range of 25% -50%. Namely, P is more than or equal to 25 percent and less than or equal to 50 percent. Specifically, P may be 25%, 30%, 35%, 40%, or 45%, etc. In some embodiments, P is in the range of 30% -45%.
In the embodiment of the application, the compacted density PD of the negative pole piece is 1.3g/cm 3 -1.8g/cm 3 Within the range of (1). The compaction density PD of the negative pole piece is in a properly high range, which is beneficial to improving the energy density of the battery. In some embodiments, the PD is between 1.4 and 1.7g/cm 3 In the presence of a surfactant.
In the present application, the anode active material contained in the anode active material layer may be one material or a plurality of materials. Specifically, the negative active material includes one or more of lithium titanate, a carbon material, a silicon-based material, a tin-based material, and the like, but is not limited thereto. Wherein, when the negative active material comprises a plurality of materials (for example, graphite and simple substance silicon), the above Dv10, Dv50 and Dv90 refer to the relative particle size values of the mixed negative active material, R 1 、R 2 F was also calculated from the SEM photograph of the negative electrode active material after mixing.
The carbon material may be one or more of graphite (artificial graphite, natural graphite), soft carbon, hard carbon, mesocarbon microbeads, carbon fibers, graphene, and the like, but is not limited thereto, and graphite is preferred. The silicon-based material may include elemental silicon, silicon alloys, silicon oxides, silicon carbon composites, and the like. Tin-based materials may include elemental tin, tin oxides, tin-based alloys, and the like.
Preferably, the negative active material includes graphite. In some embodiments, the negative active material includes a plurality of materials with different materials, and contains graphite, wherein the mass ratio of the graphite in the negative active material is 40-95%, and preferably more than 50%.
In the present application, the anode active material layer may include a binder in addition to the anode active material. In some cases, a conductive agent may also be included. Among them, binders and conductive agents are conventional choices in the battery field. By way of example, binders include, but are not limited to, binders that may include one or more of Styrene Butadiene Rubber (SBR), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), Polyacrylonitrile (PAN), Polyimide (PI), polyacrylic acid (PAA), polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, etc.), polyolefins (such as polypropylene, polyethylene, etc.), carboxymethyl cellulose (CMC), sodium alginate, etc. Illustratively, the conductive agent includes, but is not limited to, one or more of carbon nanotubes, graphene, carbon fibers, carbon black, and the like.
The negative pole piece can be obtained by coating slurry containing a negative active material, a binder and an optional conductive agent on a negative current collector, drying and rolling. The negative electrode current collector may be single-coated or double-coated. In other words, the negative electrode current collector may have the negative electrode active material layer on one surface thereof, or may have the negative electrode active material layers on both opposite surfaces thereof. When the negative electrode current collector is double-coated, it is sufficient that the negative electrode active material layer on any one side satisfies the parameter k in the aforementioned range. The negative electrode current collector carrying the negative electrode active material layer may include, but is not limited to, a copper foil, a stainless steel foil, a copper alloy foil, a carbon-coated copper foil, a copper-plated film, or the like.
The embodiment of the application also provides a secondary battery, and the secondary battery comprises the negative pole piece.
The secondary battery also comprises a positive pole piece, a diaphragm and electrolyte, wherein the diaphragm and the electrolyte are arranged between the positive pole piece and the negative pole piece. The secondary battery is any battery which can use the negative electrode plate, and includes but is not limited to lithium secondary batteries, sodium secondary batteries, potassium secondary batteries, magnesium secondary batteries, aluminum secondary batteries, zinc secondary batteries, and the like.
The positive pole piece comprises a positive pole current collector and a positive pole active material layer arranged on the positive pole current collector, wherein the positive pole active material layer comprises a positive pole active material, a binder and an optional conductive agent. The positive electrode active material may be selected according to active ions on which a specific secondary battery depends for energy storage. The active ions may include lithium ions, sodium ions, potassium ions, magnesium ions, aluminum ions, zinc ions, and the like. For the lithium ion battery, the positive active material may include, but is not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), and lithium phosphate containing olivine structure (e.g., lithium iron phosphate (LFP), lithium iron manganese phosphate (LFMP)). For sodium ion batteries, positive active materials include, but are not limited to: one or more of transition metal oxide, polyanion compound, organic polymer and Prussian blue material.
The diaphragm is arranged between the positive pole piece and the negative pole piece and plays a role in isolating the positive pole from the negative pole. The type of separator is not limited in this application and any separator material in existing batteries can be used. Exemplary separators include, but are not limited to, single layer PP (polypropylene) films, single layer PE (polyethylene) films, dual layer PP/PE, dual layer PP/PP, and tri-layer PP/PE/PP. The electrolyte comprises electrolyte salt and an organic solvent, wherein the specific types and the compositions of the electrolyte salt and the organic solvent are conventional choices in the field of batteries and can be selected according to actual requirements.
Because the secondary battery contains the negative pole piece, the secondary battery can be ensured to have higher energy density, good cycle performance, high safety performance and the like.
The technical solution of the present application is further described below with reference to a plurality of specific embodiments.
Example 1
Preparation of a negative electrode sheet comprising:
mixing a negative electrode active material (specifically graphite, the particle size and the size parameters of which are shown in table 1), a conductive agent (carbon black), a binder (CMC and PVDF in a mass ratio of 1.5: 2.2) according to a ratio of 95.4: 0.9: 3.7, placing the mixed powder into a vacuum stirrer, adding deionized water and stirring to obtain cathode slurry; the negative electrode slurry is uniformly coated on the surfaces of the two opposite sides of the copper foil of the negative electrode current collector, the copper foil is baked in an oven at 100 ℃ until the copper foil is dried, and then the copper foil is rolled and cut to obtain a negative electrode piece, wherein the test results of the compaction density PD and the porosity P of the negative electrode piece and the calculation result of the defined parameter k are summarized in table 1.
A method of manufacturing a lithium secondary battery, comprising:
1) preparing a positive pole piece:
mixing a positive electrode active material, a conductive agent-carbon black and a binder (specifically PVDF) according to a ratio of 96: 2: 2, placing the mixed powder into a vacuum stirrer, adding a solvent N-methylpyrrolidone (NMP), and uniformly stirring to obtain anode slurry; and sieving the positive electrode slurry (200-mesh sieve), coating the sieved positive electrode slurry on a positive electrode current collector aluminum foil, and drying at 120 ℃, rolling and cutting to obtain a positive electrode piece.
2) Assembling the battery:
preparing an electrolyte: mixing Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) according to the volume ratio of 1:1:1 to obtain a mixed solvent, and adding dried lithium salt LiPF 6 Is prepared into LiPF 6 Electrolyte with the concentration of 1 mol/L;
stacking the positive pole piece, the diaphragm and the negative pole piece in sequence in a glove box filled with argon to obtain a battery cell; the diaphragm is required to completely isolate a positive pole piece and a negative pole piece, then the stacked battery cell is arranged in an aluminum plastic film soft package, electrolyte is injected, and the lithium ion battery is obtained after the procedures of vacuum packaging, standing, formation, cutting, sealing and the like.
Other embodiments
Negative electrode sheets and batteries of the remaining examples and comparative examples were prepared according to the parameters listed in table 1.
To strongly support the beneficial effects of the present application, the following electrochemical performance of each of the above examples and comparative examples cells was tested and the results are summarized in table 2 below.
The energy density testing method comprises the following steps: weighing each negative pole piece by using an electronic balance at 25 ℃; each of the lithium ion batteries thus obtained was charged at a rate of 1C and discharged at a rate of 1C at 25 ℃, and the actual discharge amount at that time was recorded. Wherein, the ratio of the actual discharge energy of the battery 1C to the weight of the negative electrode plate is the actual energy density of the negative electrode plate.
The test method of the cycle performance comprises the following steps: at 25 ℃, each lithium ion battery was charged at a rate of 3C, discharged at a rate of 1C, subjected to a full charge discharge cycle test, and the capacity retention rate after 1000 cycles of the cycle was recorded.
The dynamic performance test method comprises the following steps: fully charging each lithium ion battery with nC and fully discharging each lithium ion battery with 1C at 25 ℃, repeating 10 charging and discharging cycles, then charging the battery with nC multiplying power to a full state, then disassembling a negative pole piece, and observing the lithium separation condition on the surface of the negative pole piece. Wherein, the area of the lithium separating region on the surface of the negative pole piece is less than 5 percent, the lithium separating region is considered to be slightly lithium separating, the area of the lithium separating region on the surface of the negative pole is 5 to 40 percent, the lithium separating region is considered to be moderately lithium separating, and the area of the lithium separating region on the surface of the negative pole is more than 40 percent, the lithium separating region is considered to be severely lithium separating. And if no lithium is separated from the surface of the negative pole piece, gradually increasing the charging multiplying power from nC by a gradient of 0.1C, and testing again until lithium is separated from the surface of the negative pole, wherein the maximum charging multiplying power of the battery under the condition of not separating lithium is obtained by subtracting 0.1C from the charging multiplying power nC at the moment.
TABLE 1 summary of parameters for each example
Figure 729879DEST_PATH_IMAGE001
Table 2 summary of electrochemical properties of batteries made from the negative electrode sheets of each example
Figure 593930DEST_PATH_IMAGE002
With reference to table 1, it can be known from table 2 that when the configuration of the negative electrode plate enables the custom parameter k to be in the range of 2.0 to 20.0, the lithium ion battery containing the negative electrode plate has high energy density, good cycle performance and high capacity retention; the lithium ion battery has the advantages of good dynamic performance, high quick charging efficiency and good safety performance, lithium is not easy to precipitate at a cathode multiplying power of about 2C, and the multiplying power of the battery is high when the lithium is precipitated at the cathode. The preferable k is in the range of 4.0 to 9.0, and the cycle performance and the dynamic performance of the lithium ion battery adopting the negative pole piece are better. Therefore, the lithium secondary battery of the embodiment of the present application can achieve high energy density, long cycle life, high safety, and the like.
The above description is of the preferred embodiment of the present application, but should not be taken as limiting the scope of the application. It should be noted that, for those skilled in the art, without departing from the principle of the present application, several improvements and modifications can be made, and these improvements and modifications are also considered to be within the scope of the present application.

Claims (7)

1. The negative pole piece is characterized by comprising a negative pole current collector and a negative pole active material layer arranged on at least one side surface of the negative pole current collector, wherein the negative pole active material layer contains a negative pole active material, and the following parameter k is defined:
k=[F×R 1 +(1-F)×R 2 ]x PD x Dv50 x P/span, and k is more than or equal to 4.0 and less than or equal to 9.0;
wherein F represents a ratio of the number of primary particles to the number of total particles in the anode active material, and R 1 Represents an average aspect ratio, R, of primary particles in the anode active material 2 Representing the average width-to-length ratio of the secondary particles in the negative electrode active material, F is more than or equal to 0 and less than or equal to 0.6, and R is more than or equal to 0 and less than or equal to 0 1 ＜1，0.6≤R 2 Less than or equal to 0.95; span represents the dispersion of the particle size distribution of the negative electrode active material, span = (Dv 90-Dv 10)The corresponding particle diameters of the anode active material when the cumulative volume distribution percentage of the particles reaches 10%, 50% and 90% are represented by/Dv 50, Dv10, Dv50 and Dv90 respectively, and the units are all mum, wherein Dv50 is in the range of 12 μm to 17 μm, Dv10 is in the range of 3 μm to 10 μm, and Dv90 is in the range of 16 μm to 25.3 μm; PD represents the compacted density of the negative pole piece and is in g/cm 3 PD is 1.3-1.73g/cm 3 Within the range of (1); p represents the mercury intrusion porosity of the negative pole piece, and P is in the range of 30-40%.
2. The negative electrode tab of claim 1, wherein the PD has a range of values: 1.4g/cm 3 ≤PD≤1.7g/cm 3 。
3. The negative electrode tab of claim 1, wherein Dv10 is in the range of 5 μ ι η to 10 μ ι η.
4. The negative electrode tab of claim 1, wherein Dv90 is in the range of 20 μ ι η to 25 μ ι η.
5. The negative electrode tab of claim 1, wherein R is 1 In the range of 0.5-0.95.
6. The negative electrode tab of any one of claims 1-5, wherein the negative active material comprises one or more of lithium titanate, a carbon material, a silicon-based material, and a tin-based material.
7. A secondary battery comprising the negative electrode tab according to any one of claims 1 to 6.
CN202210371335.9A 2022-04-11 2022-04-11 Negative pole piece and secondary battery Active CN114447275B (en)

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