Battery cell, manufacturing method for battery cell, starting battery for fuel engine, and vehicle

Abstract

Disclosed is a vehicle, comprising a battery cell or a starting battery for a fuel engine, the starting battery comprising the battery cell. Also disclosed is a manufacturing method for the battery cell. The battery cell comprises a positive electrode and a negative electrode. The positive electrode comprises lithium iron phosphate composite particles, the lithium iron phosphate composite particles comprising lithium iron phosphate particles of at least two D50 particle sizes. The negative electrode comprises graphite composite particles, the graphite composite particles comprising graphite particles of at least two D50 particle sizes.

Description

Battery cell, method for preparing battery cell, starting battery for fuel engine and vehicle

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on December 5, 2023, with application number 202311660714.0 and entitled “Battery Cell, Method for Preparing Battery Cell, Starting Battery for Fuel Engine and Vehicle”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of lithium-ion batteries, and in particular to a battery cell and a preparation method thereof, a starting battery for a fuel engine, and a vehicle. Background Art

[0004] The normal operating temperature of lithium iron phosphate batteries is 0-60°C. At -10°C, the battery capacity begins to decline rapidly, decreasing to approximately 50%. At -20°C, only 20-40% of the capacity remains. When the temperature exceeds 60°C, the side reaction between lithium ions and the electrolyte intensifies, causing capacity decline.

[0005] To address the problem of poor low-temperature performance of lithium iron phosphate batteries, the currently commonly used method is to improve the low-temperature performance at the electrode level, such as shortening the Li+ transmission path and reducing impedance by increasing the amount of conductive agent and reducing surface density.

[0006] Related technologies often fail to take into account both the low-temperature high-rate discharge performance and high-temperature cycle performance required by starting batteries.

[0007] Therefore, there is an urgent need for a lithium iron phosphate battery and a preparation process thereof that can simultaneously have excellent low-temperature high-rate discharge performance and high-temperature cycle performance.

[0008] Public content

[0009] The purpose of this application is to overcome the problem in the prior art that lithium iron phosphate batteries cannot simultaneously have excellent low-temperature high-rate discharge performance and high-temperature cycle performance, and to provide a battery cell and a preparation method thereof, a starting battery for a fuel engine, and a vehicle.

[0010] In order to achieve the above object, the present application provides a battery cell in a first aspect, wherein the battery cell includes a positive electrode, the positive electrode includes lithium iron phosphate composite particles, and the lithium iron phosphate composite particles include at least two D 50 Particle size of lithium iron phosphate particles; and a negative electrode, the negative electrode comprising graphite composite particles, the graphite composite particles comprising at least two D 50 Graphite particles of different particle sizes.

[0011] According to some embodiments of the present application, the OI value of the graphite composite particles is less than or equal to 7.

[0012] According to some embodiments of the present application, the negative electrode further includes hard carbon.

[0013] According to some embodiments of the present application, the D 50 The particle size is 3-10μm.

[0014] According to some embodiments of the present application, the weight ratio of the graphite composite particles to the hard carbon is (85-95):(5-15).

[0015] According to some embodiments of the present application, the graphite composite particles include graphite particles A and graphite particles B. 50 The particle size is 5-7 μm, the graphite particles B D 50 The particle size is 9-11μm.

[0016] According to some embodiments of the present application, based on the total weight of the graphite composite particles, the contents of the graphite particles A and the graphite particles B in the graphite composite particles are 25-75 wt % and 25-75 wt %, respectively.

[0017] According to some embodiments of the present application, the lithium iron phosphate composite particles include at least two of lithium iron phosphate particles A, lithium iron phosphate particles B, lithium iron phosphate particles C, and lithium iron phosphate particles D. The lithium iron phosphate particles A, the lithium iron phosphate particles B, the lithium iron phosphate particles C, and the lithium iron phosphate particles D are each D 50 The particle sizes are 1-3μm, 5-7μm, 9-11μm and 18-20μm respectively.

[0018] According to some embodiments of the present application, based on the total weight of the lithium iron phosphate composite particles, the total content of the lithium iron phosphate particles A and the lithium iron phosphate particles B is less than or equal to 75 wt %.

[0019] According to some embodiments of the present application, the lithium iron phosphate composite particles are a mixture of lithium iron phosphate particles A, lithium iron phosphate particles B and lithium iron phosphate particles C; preferably, based on the total weight of the lithium iron phosphate composite particles, the contents of the lithium iron phosphate particles A, the lithium iron phosphate particles B and the lithium iron phosphate particles C in the lithium iron phosphate composite particles are 10-30wt%, 20-40wt% and 30-70wt%, respectively.

[0020] According to some embodiments of the present application, the battery cell further includes an electrolyte, which includes a lithium salt; preferably, the lithium salt includes lithium hexafluorophosphate and further includes at least one selected from lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium dioxalatoborate and lithium difluorooxalatoborate; preferably, the lithium salt is a mixture of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorooxalatoborate; preferably, in the lithium salt, the weight ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorooxalatoborate is (5-10):(2-5):(0.5-1); preferably, the content of the lithium salt in the electrolyte is 0.8-1.2 mol / L.

[0021] According to some embodiments of the present application, the battery cell further includes an electrolyte, and the electrolyte further includes an additive, and the additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate; preferably, the additive is a mixture of vinylene carbonate and fluoroethylene carbonate; preferably, the content of the additive in the electrolyte is 1.5-5 mol / L; preferably, in the additive, the weight ratio of vinylene carbonate and fluoroethylene carbonate is (1.5-3.5): (2-5).

[0022] According to some embodiments of the present application, the battery cell further includes an electrolyte, and the electrolyte further includes a solvent, and the solvent is selected from at least one of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate; preferably, the solvent is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; preferably, in the solvent, the weight ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is (2-4): (2-4): (3-5).

[0023] According to some embodiments of the present application, the positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. Preferably, based on the total weight of the positive electrode material layer, the content of the lithium iron phosphate composite particles in the positive electrode material layer is 90-94 wt%; preferably, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector. Preferably, based on the total weight of the negative electrode material layer, the total content of the graphite composite particles and hard carbon in the negative electrode material layer is 90-95 wt%; preferably, based on the total weight of the graphite composite particles and the hard carbon, the content of the hard carbon is less than or equal to 15 wt%.

[0024] The second aspect of the present application provides a method for preparing a battery cell, wherein the preparation method comprises: providing a positive electrode, wherein the positive electrode sheet comprises lithium iron phosphate composite particles, and the lithium iron phosphate composite particles comprise at least two D 50 Particle size of lithium iron phosphate particles; providing a negative electrode, the negative electrode sheet negative electrode comprises graphite composite particles, the graphite composite particles comprising at least two D50 Graphite particles of particle size; the positive electrode and the negative electrode are assembled into a battery core.

[0025] According to some embodiments of the present application, the method for preparing the positive electrode includes: mixing at least two lithium iron phosphate particles with a D50 particle size to obtain the lithium iron phosphate composite particles; mixing the lithium iron phosphate composite particles, a conductive agent 1, a binder 1 and a solvent 1 to obtain a positive electrode slurry, and then coating the positive electrode slurry on the surface of the positive electrode collector, and then rolling to obtain the positive electrode; preferably, the method for preparing the negative electrode includes: mixing at least two graphite particles with a D50 particle size to obtain the graphite composite particles; mixing the graphite composite particles, hard carbon, a conductive agent 2, a binder 2 and a solvent 2 to obtain a negative electrode slurry, and then coating the negative electrode slurry on the surface of the negative electrode collector, and then rolling to obtain the negative electrode.

[0026] A third aspect of the present application provides a starting battery for a fuel engine, comprising the battery cell provided in the present application or the battery cell prepared by the preparation method provided in the present application.

[0027] A fourth aspect of the present application provides a vehicle, comprising the battery cell provided in the present application, or the battery cell prepared by the preparation method provided in the present application, or the starting battery of the fuel engine provided in the present application.

[0028] Through the above technical solution, the beneficial effects of this application are:

[0029] This application uses at least two different 50 The lithium iron phosphate composite particles obtained by mixing lithium iron phosphate particles of different particle sizes are used as the positive electrode active material, and at least two different D 50 The mixing of graphite particles of different particle sizes as the negative electrode active material can reduce the tortuosity of the positive and negative electrodes, shorten the transmission path of lithium ions, and thus reduce the migration impedance of lithium ions, so that the prepared lithium iron phosphate battery can take into account both low-temperature high-rate discharge performance and high-temperature cycle performance.

[0030] In a preferred embodiment of the present application, by adjusting the particle size of lithium iron phosphate particles and the ratio of lithium iron phosphate particles of different particle sizes, the particle size of graphite particles and the ratio of graphite particles of different particle sizes, and the particle size and ratio of hard carbon, the OI value of the graphite particles is controlled, and by adjusting the types and ratios of electrolyte lithium salts and additives, the low-temperature high-rate discharge performance of the battery can be further improved, and the high-temperature performance of the battery can be further improved. At the end of its life (deterioration to 80% SOH), the prepared lithium iron phosphate battery is discharged at 5C for 2s at -30°C and 50% SOC, and the cut-off voltage can reach 2.62V. The low-temperature cold starting capability is much higher than that of the same type of lithium iron phosphate battery. In addition, according to the requirements of the fuel engine for the starting battery, it can achieve the same life as the 8-year warranty of the whole vehicle, that is, the 8-year capacity retention rate is greater than or equal to 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a -30°C cold start discharge curve of the soft-pack lithium iron phosphate battery prepared in Example 1 of the present application;

[0032] FIG2 is a graph showing the capacity retention rate of the soft-pack lithium iron phosphate battery obtained in Example 1 of the present application after 1000 cycles at 60° C.;

[0033] FIG3 is a schematic block diagram of a starting battery for a fuel engine according to an embodiment of the present application;

[0034] FIG4 is a schematic block diagram of a vehicle according to an embodiment of the present application;

[0035] FIG5 is another schematic block diagram of a vehicle according to an embodiment of the present application.

[0036] Reference numerals:

[0037] Vehicle 100

[0038] Starting battery 2 and battery cell 1 of a fuel engine. DETAILED DESCRIPTION

[0039] The endpoints of the ranges and any values ​​disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in this application.

[0040] The first aspect of the present application provides a battery cell, wherein the battery cell comprises a positive electrode and a negative electrode. The positive electrode comprises lithium iron phosphate composite particles, and the lithium iron phosphate composite particles comprise at least two (ie, two or more) D 50 The negative electrode comprises graphite composite particles, the graphite composite particles comprising at least two D 50 Graphite particles of different particle sizes.

[0041] The present application mixes at least two lithium iron phosphate particles of different particle sizes as the positive electrode active material and mixes at least two graphite particles of different particle sizes as the negative electrode active material, thereby reducing the tortuosity of the positive and negative electrodes, shortening the transmission path of lithium ions, and thereby reducing the migration impedance of lithium ions. The resulting lithium iron phosphate battery can have excellent low-temperature high-rate discharge performance and a long high-temperature cycle life.

[0042] Specifically, in this application, D 50 It can be understood as D n50 .

[0043] In some embodiments, the OI value of the graphite composite particles is less than or equal to 7. The OI value is an orientation index, which represents the degree of isotropic distribution of the graphite particles. The smaller the OI value, the more the graphite tends to be distributed perpendicular to the current collector, and the isotropy is high, which is beneficial to low temperature and rate performance. The use of graphite composite particles with an OI value less than or equal to 7 can shorten the diffusion path of lithium ions and increase the migration rate of lithium ions, thereby improving the low-temperature and high-rate discharge performance of the prepared lithium iron phosphate battery. By measuring the crystals of graphite by XRD, the peak intensity (I110) of the surface (110) and the peak intensity (I004) of the surface (004) can be obtained. The OI value refers to the ratio of I004 / I110.

[0044] In some embodiments, the negative electrode further comprises hard carbon.

[0045] In some embodiments, the D of the hard carbon 50 The particle size is 3μm-10μm. Hard carbon has a high degree of disorder, multiple lithium insertion directions, low diffusion resistance, and is suitable for large current discharge, but its conductivity is slightly poor. 50 When the particle size meets this range, it can take into account both power and high temperature performance, improve impedance, be beneficial to the performance of power, and be beneficial to high temperature performance and reduce side reactions. 50 The particle size may be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm and 10 μm, and any value in the range between any two of the above values.

[0046] In some embodiments, the weight ratio of the graphite composite particles to the hard carbon is (85-95):(5-15). Specifically, the weight ratio of the graphite composite particles to the hard carbon can be, for example, 85:15, 90:15, or 95:15.

[0047] By adjusting the combination of graphite particles of different particle sizes in the graphite composite particles, as well as the ratio of graphite composite particles to hard carbon, the positive electrode active material and the negative electrode active material can produce a synergistic effect, so that the prepared lithium iron phosphate battery can have better low-temperature high-rate discharge and high-temperature cycle performance.

[0048] In some embodiments, the graphite composite particles include graphite particles A and graphite particles B. Preferably, the graphite composite particles are a mixture of graphite particles A and graphite particles B. 50 The particle sizes are 5μm-7μm and 9μm-11μm respectively.

[0049] D 50Graphite particles A and B with particle sizes of 5μm-7μm and 9μm-11μm are compounded with hard carbon. The slightly larger interlayer spacing of hard carbon promotes the insertion and extraction of lithium ions, thereby improving the low-temperature rate performance and power performance of lithium iron phosphate batteries (generally, good rate performance and good power performance are also good). At the same time, compound D 50 Graphite particles with particle sizes of 5μm-7μm and 9μm-11μm, respectively, can inhibit the side reactions between the electrolyte and the negative electrode active material at high temperatures, thereby taking into account high-temperature cycle performance.

[0050] In some embodiments, based on the total weight of the graphite composite particles, the contents of the graphite particles A and the graphite particles B in the graphite composite particles are 25 wt%-75 wt% and 25 wt%-75 wt%, respectively.

[0051] In some embodiments, the lithium iron phosphate composite particles include at least two of lithium iron phosphate particles A, lithium iron phosphate particles B, lithium iron phosphate particles C, and lithium iron phosphate particles D. The lithium iron phosphate particles A, lithium iron phosphate particles B, lithium iron phosphate particles C, and lithium iron phosphate particles D are each D 50 The particle sizes are 1μm-3μm, 5μm-7μm, 9μm-11μm and 18μm-20μm respectively.

[0052] In some embodiments, the lithium iron phosphate composite particles include lithium iron phosphate particles A and lithium iron phosphate particles B, and further include lithium iron phosphate particles C and / or lithium iron phosphate particles D. Preferably, the total content of the lithium iron phosphate particles A and the lithium iron phosphate particles B is less than or equal to 75 wt %, based on the total weight of the lithium iron phosphate composite particles.

[0053] In some embodiments, the lithium iron phosphate composite particles are a mixture of lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C. 50 A mixture of lithium iron phosphate particles A, lithium iron phosphate particles B and lithium iron phosphate particles C with particle sizes of 1μm-3μm, 5μm-7μm and 9μm-11μm respectively is used as the positive electrode active material. Particles of different sizes are accumulated in a certain space to construct a multi-dimensional pore structure.

[0054] In some embodiments, based on the total weight of the lithium iron phosphate composite particles, in the lithium iron phosphate composite particles, the contents of lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C are 10 wt%-30 wt%, 20 wt%-40 wt%, and 30 wt%-70 wt%, respectively.

[0055] By adjusting the combination and mixing ratio of lithium iron phosphate particles of different particle sizes in the lithium iron phosphate composite particles, the porosity and tortuosity of the positive electrode can be adjusted, and the diffusion of lithium ions can be promoted, thereby further improving the low-temperature, high-rate discharge and high-temperature cycle performance of the prepared lithium iron phosphate battery.

[0056] In some embodiments, the double-area density of the positive electrode is 200 g / m 2 -250g / m 2 , compacted density is 1.8g / cm 3 -3g / cm 3 .

[0057] Specifically, the double-sided density of the positive electrode can be understood as the sum of the surface densities of the positive electrode material layers on both sides in the thickness direction of the positive electrode. For example, the surface density of the positive electrode material layer on one side in the thickness direction of the positive electrode is 100 g / m 2 The surface density of the positive electrode material layer on the other side of the thickness direction of the positive electrode is 100g / m 2 The double-sided density of the positive electrode is 200g / m 2 .

[0058] In some embodiments, the double-area density of the negative electrode is 80 g / m 2 -110g / m 2 , compacted density is 1g / cm 3 -2g / cm 3 .

[0059] Specifically, the double-sided density of the negative electrode can be understood as the sum of the surface densities of the negative electrode material layers on both sides in the thickness direction of the negative electrode. For example, the surface density of the negative electrode material layer on one side in the thickness direction of the negative electrode is 50 g / m 2 The surface density of the negative electrode material layer on the other side of the thickness direction of the negative electrode is 50g / m 2 The double-sided density of the negative electrode is 100g / m 2 .

[0060] In some embodiments, the battery cell further includes an electrolyte, and the electrolyte includes a lithium salt.

[0061] In some embodiments, the electrolyte filling coefficient in the battery cell is 3.8 g / Ah-6 g / Ah.

[0062] In some embodiments, the lithium salt includes lithium hexafluorophosphate and at least one selected from lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate) and lithium difluorooxalatoborate, preferably a mixture of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorooxalatoborate.

[0063] In some embodiments, the weight ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate in the lithium salt is (5-10):(2-5):(0.5-1).

[0064] By selecting the appropriate type and proportion of lithium salts, the SEI impedance of the lithium iron phosphate battery can be reduced, and high-temperature side reactions can be inhibited, thereby taking into account both high and low temperature performance.

[0065] In some embodiments, the content of lithium salt in the electrolyte is 0.8 mol / L-1.2 mol / L.

[0066] In some embodiments, the electrolyte further includes an additive, and the additive is selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC) and diethylene sulfate (DTD), preferably a mixture of vinylene carbonate and fluoroethylene carbonate.

[0067] In some embodiments, preferably, the content of the additive in the electrolyte is 1.5 mol / L-5 mol / L.

[0068] In some embodiments, the weight ratio of vinylene carbonate to fluoroethylene carbonate in the additive is (1.5-3.5):(2-5).

[0069] By selecting the appropriate type and proportion of electrolyte additives, the high-temperature performance of the prepared lithium iron phosphate battery can be further improved, thereby taking into account both low-temperature high-rate discharge and high-temperature life performance.

[0070] In some embodiments, the electrolyte further includes a solvent, and the solvent is selected from at least one of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate, preferably a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

[0071] In some embodiments, the weight ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in the solvent is (2-4):(2-4):(3-5).

[0072] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector, wherein the content of the lithium iron phosphate composite particles in the positive electrode material layer is 90 wt% to 94 wt% based on the total weight of the positive electrode material layer.

[0073] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, wherein the total content of the graphite composite particles and the hard carbon in the negative electrode material layer is 90 wt % to 95 wt % based on the total weight of the negative electrode material layer.

[0074] In some embodiments, based on the total weight of the negative electrode material layer, the content of the hard carbon in the negative electrode material layer is less than or equal to 15 wt %.

[0075] In some embodiments, the battery cell further includes a separator.

[0076] The present application has no particular limitation on the type of the diaphragm, and conventional diaphragms in the art may be selected, for example, PP / PE / PP diaphragms. Preferably, the porosity of the diaphragm is less than 45%.

[0077] In some embodiments, the separator has a thickness of 9 μm to 25 μm.

[0078] A second aspect of the present application provides a method for preparing a battery cell, wherein the preparation method comprises:

[0079] A positive electrode is provided, the positive electrode includes lithium iron phosphate composite particles, the lithium iron phosphate composite particles include at least two D 50 Particle size of lithium iron phosphate particles;

[0080] Provide a negative electrode, the negative electrode includes graphite composite particles, the graphite composite particles include at least two D 50 Particle size of graphite particles;

[0081] Assemble the positive and negative electrodes into a battery cell.

[0082] It is understood that although the above preparation method only mentions assembling the positive electrode and the negative electrode into a battery cell, it does not mean that the battery cell only contains the positive electrode and the negative electrode. The battery cell may also include other known components such as a separator, an electrolyte and / or a solid electrolyte.

[0083] In some embodiments, the preparation method of the battery cell comprises: winding a positive electrode, a negative electrode and a separator into an electrode group, and injecting an electrolyte to prepare a battery cell. The positive electrode comprises lithium iron phosphate composite particles, and the lithium iron phosphate composite particles comprise at least two D 50 The negative electrode includes graphite composite particles, which include at least two D 50 Graphite particles of different particle sizes.

[0084] In the preparation method of the battery cell in the second aspect of the present application, the types and amounts of the positive electrode, negative electrode, separator and electrolyte are exactly the same as those in the battery cell in the first aspect of the present application. In order to avoid repetition, the present application will not go into details in the second aspect, and those skilled in the art should not understand it as a limitation of the present application.

[0085] In some embodiments, the negative electrode further comprises hard carbon.

[0086] In some embodiments, the positive electrode is obtained by coating the surface of the positive electrode current collector with a positive electrode slurry obtained by mixing positive electrode powder and solvent 1. The content of the lithium iron phosphate composite particles is 90 wt% to 94 wt% based on the total weight of the positive electrode powder. When the content of the lithium iron phosphate composite particles falls within this range, sufficient battery energy density can be provided.

[0087] In some embodiments, the negative electrode is formed by coating the surface of a negative electrode current collector with a negative electrode slurry obtained by mixing negative electrode powder and solvent 2. The total content of the graphite composite particles and hard carbon is 90% to 95% by weight, based on the total weight of the negative electrode powder. The content of the hard carbon is less than or equal to 15% by weight, based on the total weight of the graphite composite particles and hard carbon. When the total content of the graphite composite particles and hard carbon falls within this range, high-rate performance can be achieved for the battery.

[0088] Furthermore, based on the total weight of the graphite composite particles and the hard carbon, the content of the hard carbon is 8 wt%-12 wt%.

[0089] In the present application, the positive electrode powder includes lithium iron phosphate composite particles, a conductive agent 1 and a binder 1; the negative electrode powder includes graphite composite particles, hard carbon, a conductive agent 2 and a binder 2.

[0090] In some embodiments, the method for preparing a positive electrode comprises: 50 Lithium iron phosphate particles of different particle sizes are mixed to obtain lithium iron phosphate composite particles; the lithium iron phosphate composite particles, conductive agent 1, binder 1 and solvent 1 are mixed to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the surface of the positive electrode collector, and then rolled to obtain a positive electrode.

[0091] Preferably, the preparation method of the negative electrode comprises: 50 Graphite particles of different particle sizes are mixed to obtain graphite composite particles; the graphite composite particles, hard carbon, a conductive agent 2, a binder 2 and a solvent 2 are mixed to obtain a negative electrode slurry, and then the negative electrode slurry is coated on the surface of the negative electrode collector, and then rolled to obtain a negative electrode.

[0092] In some embodiments, based on the total weight of the positive electrode powder, the content of the conductive agent 1 is less than or equal to 5wt%, preferably 3wt%-5wt%; the content of the binder 1 is less than or equal to 5wt%, preferably 3wt%-5wt%. When the content of the conductive agent 1 and the binder 1 falls within this range, the positive electrode can enhance electronic conductivity, reduce charge transfer impedance, and improve the rate performance and power performance of the battery while maintaining a certain degree of manufacturability.

[0093] In some embodiments, the conductive agent 1 is selected from at least one of carbon black (SP), carbon nanotubes (CNTs), graphene, Ketjen black, and carbon nanofibers, preferably a mixture of carbon black and carbon nanotubes. Using the carbon black and carbon nanotube mixture as the positive electrode conductive agent can synergize with the lithium iron phosphate composite particles to provide a multidimensional conductive network of points and lines, enhancing electronic conductivity and improving the battery's low-temperature performance.

[0094] In some embodiments, based on the total weight of the positive electrode powder, the content of carbon black in the conductive agent 1 is 1 wt%-3 wt%, and the content of carbon nanotubes is 1.5 wt%-3 wt%.

[0095] In some embodiments, the binder 1 is selected from polyvinylidene fluoride (PVDF) and / or polytetrafluoroethylene (PTFE), preferably polyvinylidene fluoride.

[0096] Furthermore, the binder 1 is selected from polyvinylidene fluoride having a weight average molecular weight of 1 million g / mol to 1.2 million g / mol.

[0097] In some embodiments, based on 1 g of the positive electrode powder, the amount of solvent 1 is 0.5 mL-1 mL.

[0098] In some embodiments, Solvent 1 is N-methylpyrrolidone (NMP).

[0099] In some embodiments, based on the total weight of the negative electrode powder, the content of the conductive agent 2 is less than or equal to 5 wt %, and the content of the binder 2 is less than or equal to 5 wt %. When the contents of the conductive agent 2 and the binder 2 meet this range, the electronic conductivity of the negative electrode can be enhanced, the charge transfer impedance can be reduced, and the rate performance and power performance of the battery can be improved while maintaining a certain degree of manufacturability of the negative electrode.

[0100] In some embodiments, the conductive agent 2 is selected from at least one of carbon black (SP), carbon nanotubes (CNTs), graphene, Ketjen black, and carbon nanofibers, preferably carbon black. Using carbon black as the conductive agent for the negative electrode can achieve an optimal balance between cost and conductive performance.

[0101] In some embodiments, the binder 2 is selected from one or two of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and polyacrylic acid (PAA), preferably a mixture of sodium carboxymethyl cellulose and styrene-butadiene rubber, more preferably a mixture of sodium carboxymethyl cellulose and styrene-butadiene rubber with a weight-average molecular weight of 300,000 g / mol-500,000 g / mol.

[0102] Furthermore, in binder 2, the weight ratio of sodium carboxymethyl cellulose to styrene-butadiene rubber is (1-3): (2-4). Using a mixture of sodium carboxymethyl cellulose and styrene-butadiene rubber in this weight ratio as a negative electrode binder can make the powder material evenly adhere together and firmly adhere to the current collector.

[0103] In some embodiments, based on 1 g of the negative electrode powder, the amount of solvent 2 is 0.8 mL-1.2 mL.

[0104] In some embodiments, solvent 2 is water.

[0105] According to a preferred embodiment of the present application, the method for preparing the battery cell includes the following steps:

[0106] S1. Preparation of positive electrode. Based on the total weight of the positive electrode powder, 90wt%-94wt% of lithium iron phosphate composite particles, 3wt%-5wt% of conductive agent 1 and 3wt%-5wt% of binder 1 were weighed according to the mass percentage to prepare positive electrode powder. Then, solvent 1 was added (based on the amount of positive electrode powder being 1g, the amount of solvent 1 was 0.5mL-1mL). The materials were mixed in a vacuum mixer to obtain positive electrode slurry. After coating and roller pressing, a double-sided density of 200g / m 2 -250g / m 2 , compacted density is 1.8-3g / cm 3 positive electrode.

[0107] Among them, lithium iron phosphate composite particles are D 50 A mixture of lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C having particle sizes of 1 μm-3 μm, 5 μm-7 μm, and 9 μm-11 μm, respectively. Based on the total weight of the lithium iron phosphate composite particles, the contents of the lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C in the lithium iron phosphate composite particles are 10 wt%-30 wt%, 20 wt%-40 wt%, and 30 wt%-70 wt%, respectively.

[0108] S2. Preparation of negative electrode. Based on the total weight of the negative electrode powder, weigh 90wt%-95wt% of a mixture of graphite composite particles and hard carbon (based on the total weight of the mixture of graphite composite particles and hard carbon, the content of hard carbon is less than or equal to 15wt%, and the D of hard carbon is less than 15wt%). 50 The negative electrode powder is prepared by mixing the conductive agent 2 with a particle size of 3 μm-10 μm, less than or equal to 5 wt% of the conductive agent 2 and less than or equal to 5 wt% of the binder 2, and then adding the solvent 2 (based on the amount of the negative electrode powder being 1 g, the amount of the solvent 2 is 0.8 mL-1.2 mL). The negative electrode slurry is obtained by mixing the materials with a vacuum mixer, and the double-sided density of 80 g / m is obtained by coating and rolling. 2-110g / m 2 , compacted density is 1-2g / cm 3 of the negative electrode.

[0109] Among them, graphite composite particles are D 50 A mixture of graphite particles A and graphite particles B having particle sizes of 5 μm to 7 μm and 9 μm to 11 μm, respectively, wherein the OI values ​​of the graphite particles A and the graphite particles B are both less than or equal to 7. The contents of the graphite particles A and the graphite particles B are 25 wt% to 75 wt% and 25 wt% to 75 wt%, respectively, based on the total weight of the graphite composite particles.

[0110] S3. Preparation of an electrolyte. Based on the total weight of the electrolyte, weigh 0.8 mol / L-1.2 mol / L of a lithium salt, 1.5 mol / L-5 mol / L of an additive, and solvent 3 and mix them. The lithium salt is a mixture of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate in a weight ratio of (5-10):(2-5):(0.5-1); the additive is a mixture of vinylene carbonate and fluoroethylene carbonate in a weight ratio of (1.5-3.5):(2-5); and solvent 3 is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a weight ratio of (2-4):(2-4):(3-5).

[0111] S4. Wind the positive electrode, negative electrode and separator into an electrode group, and inject electrolyte with an injection coefficient of 3.8g / Ah-6g / Ah to obtain a battery cell.

[0112] A third aspect of the present application provides a starting battery 2 for a fuel engine, wherein the starting battery 2 includes the battery cell 1 provided in any embodiment of the present application or the battery cell prepared according to the preparation method provided in any embodiment of the present application, as shown in FIG3 .

[0113] In a fourth aspect, the present application provides a vehicle 100, comprising the battery cell 1 provided in any embodiment of the present application, or the battery cell prepared according to the preparation method provided in any embodiment of the present application, or the starting battery 2 of the fuel engine provided in any embodiment of the present application, as shown in Figures 4 and 5.

[0114] The present application will be described in detail below through examples and comparative examples. In the following examples and comparative examples, unless otherwise specified, conventional methods are used, and the reagents and materials used are commercially available unless otherwise specified. The determination methods involved in each example and comparative example are as follows.

[0115] Cold cranking voltage test method: The battery is stored at 65°C and 100% SOC until it degrades to 80% SOH, then discharged at -30°C and 50% SOC at 5C for 2s, and the cut-off voltage is recorded.

[0116] 60℃ cycle capacity retention test method: Perform 1C charge and discharge cycle test at 60℃ and 82.5%-100% SOC conditions for 1000 cycles, record the capacity of each cycle, and calculate the retention rate relative to the initial capacity.

[0117] The following examples are used to illustrate the preparation of soft-pack lithium iron phosphate batteries.

[0118] Example 1

[0119] S1. Preparation of positive electrode. Based on the total weight of the positive electrode powder, 92 wt% of lithium iron phosphate composite particles, 4.5 wt% of conductive agent 1 (2 wt% of SP + 2.5 wt% of CNTs) and 3.5 wt% of binder 1 (PVDF with a weight average molecular weight of 1.1 million g / mol) were weighed according to the mass percentage to prepare the positive electrode powder. Then, solvent 1 (NMP, based on the amount of positive electrode powder as 1 g, the amount of NMP is 0.7 mL) was added, and the materials were mixed in a vacuum mixer to obtain a positive electrode slurry. After coating and rolling, a double-sided density of 220 g / m 2 , compacted density is 2.2g / cm 3 positive electrode.

[0120] Among them, lithium iron phosphate composite particles are D 50 A mixture of lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C having particle sizes of 2 μm, 6 μm, and 10 μm, respectively. The lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C comprise 20 wt%, 30 wt%, and 50 wt%, respectively, of the lithium iron phosphate composite particles, based on the total weight of the lithium iron phosphate composite particles.

[0121] S2. Preparation of negative electrode. Based on the total weight of the negative electrode powder, 92 wt% of a mixture of graphite composite particles and hard carbon was weighed according to the mass percentage (based on the total weight of the mixture of graphite composite particles and hard carbon, the content of hard carbon was 10 wt%, and the D of hard carbon was 10 wt%). 50 The negative electrode powder was prepared by adding 4 wt% of conductive agent 2 (SP) and 4 wt% of binder 2 (1.5 wt% of CMC with a weight average molecular weight of 400,000 g / mol and 2.5 wt% of SBR). Solvent 2 (deionized water, 1 mL of deionized water based on 1 g of negative electrode powder) was added and mixed in a vacuum mixer to obtain a negative electrode slurry. After coating and rolling, a double-sided density of 95 g / m 2 , compacted density is 1.4g / cm 3 of the negative electrode.

[0122] Among them, graphite composite particles are D 50A mixture of graphite particles A and B, each having a particle size of 6 μm and 10 μm, respectively. The OI values ​​of graphite particles A and B are 5 and 4.5, respectively, resulting in an OI value of 4.6 for the composite graphite particles. The amounts of graphite particles A and B, based on the total weight of the composite graphite particles, are 25 wt% and 75 wt%, respectively.

[0123] S3. Preparation of an electrolyte. Based on the total weight of the electrolyte, 1.1 mol / L of a lithium salt, 4.5 mol / L of an additive, and solvent 3 were weighed and mixed. The lithium salt was a mixture of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate in a weight ratio of 7:3:1. The additive was a mixture of VC and FEC in a weight ratio of 2.5:3. Solvent 3 was a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a weight ratio of 3:3:4.

[0124] S4. The positive electrode, negative electrode and separator (purchased from Enjie New Material Technology Co., Ltd., PP / PE / PP separator, porosity of 40%, thickness of 15μm) are wound to form a pole group, and the electrolyte is injected with an injection coefficient of 6g / Ah to obtain a battery cell. The battery cell is packaged to obtain a 20Ah soft-pack lithium iron phosphate battery.

[0125] From the -30°C cold start discharge curve of the soft-pack lithium iron phosphate battery in Figure 1, it can be seen that the voltage is 2.627V and the temperature rise is 0.9°C when discharging at 5C for 2s, indicating that the soft-pack lithium iron phosphate battery has excellent low-temperature starting performance.

[0126] From the capacity retention rate curve of the soft-pack lithium iron phosphate battery after 1000 cycles at 60°C in Figure 2, it can be seen that the capacity retention rate of the soft-pack lithium iron phosphate battery prepared in this embodiment is 95.25% after 1000 cycles, indicating that the soft-pack lithium iron phosphate battery has very excellent high-temperature cycle performance.

[0127] Example 2

[0128] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material lithium iron phosphate composite particles were D 50 Lithium iron phosphate particles A and D with a particle size of 2 μm 50 A mixture of lithium iron phosphate particles A and lithium iron phosphate particles B with a particle size of 6 μm. Specifically, in S1, based on the total weight of the lithium iron phosphate composite particles, the contents of lithium iron phosphate particles A and lithium iron phosphate particles B in the lithium iron phosphate composite particles are 54.3 wt% and 45.7 wt%, respectively. A soft-pack lithium iron phosphate battery is produced.

[0129] Example 3

[0130] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material lithium iron phosphate composite particles were D50 Lithium iron phosphate particles A and D with a particle size of 2 μm 50 A mixture of lithium iron phosphate particles A and lithium iron phosphate particles D having a particle size of 20 μm. Specifically, in S1, based on the total weight of the lithium iron phosphate composite particles, the contents of the lithium iron phosphate particles A and lithium iron phosphate particles D in the lithium iron phosphate composite particles are 60 wt% and 40 wt%, respectively, to produce a soft-pack lithium iron phosphate battery.

[0131] Example 4

[0132] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material lithium iron phosphate composite particles were D 50 A mixture of lithium iron phosphate particles B, lithium iron phosphate particles C, and lithium iron phosphate particles D having particle sizes of 6 μm, 10 μm, and 20 μm, respectively. Specifically, in S1, based on the total weight of the lithium iron phosphate composite particles, the contents of lithium iron phosphate particles B, lithium iron phosphate particles C, and lithium iron phosphate particles D in the lithium iron phosphate composite particles are 40 wt%, 50 wt%, and 10 wt%, respectively. A soft-pack lithium iron phosphate battery is produced.

[0133] Example 5

[0134] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material lithium iron phosphate composite particles were D 50 A mixture of lithium iron phosphate particles A, B, C, and D having particle sizes of 2 μm, 6 μm, 10 μm, and 20 μm, respectively. Specifically, in S1, based on the total weight of the lithium iron phosphate composite particles, the contents of the lithium iron phosphate particles A, B, C, and D in the lithium iron phosphate composite particles are 15 wt%, 25 wt%, 50 wt%, and 10 wt%, respectively. A soft-pack lithium iron phosphate battery is produced.

[0135] Example 6

[0136] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material lithium iron phosphate composite particles were D 50 A mixture of lithium iron phosphate particles A, B, and D having particle sizes of 2 μm, 6 μm, and 20 μm, respectively. Specifically, in S1, based on the total weight of the lithium iron phosphate composite particles, the contents of lithium iron phosphate particles A, B, and D in the lithium iron phosphate composite particles are 21.7 wt%, 50 wt%, and 28.3 wt%, respectively. A soft-pack lithium iron phosphate battery is produced.

[0137] Example 7

[0138] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the ratios of lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C in the positive electrode active material lithium iron phosphate composite particles were different. Specifically, in S1, based on the total weight of the lithium iron phosphate composite particles, the contents of lithium iron phosphate particles A, lithium iron phosphate particles B, and lithium iron phosphate particles C in the lithium iron phosphate composite particles were 5 wt%, 10 wt%, and 85 wt%, respectively. A soft-pack lithium iron phosphate battery was produced.

[0139] Example 8

[0140] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the ratio of the graphite composite particles to the hard carbon in the negative electrode active material was different. Specifically, in S2, the hard carbon content was 5 wt % based on the total weight of the mixture of the graphite composite particles and the hard carbon. A soft-pack lithium iron phosphate battery was produced.

[0141] Example 9

[0142] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the ratio of graphite particles A to graphite particles B in the negative electrode active material was different. Specifically, in S2, the contents of graphite particles A and graphite particles B were 80 wt% and 20 wt%, respectively, based on the total weight of the graphite composite particles. A soft-pack lithium iron phosphate battery was produced.

[0143] Example 10

[0144] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that D 50 Hard carbon with a particle size of 15 μm was used to prepare a soft-pack lithium iron phosphate battery.

[0145] Example 11

[0146] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that graphite particles A and graphite particles B having OI values ​​of 9 and 8, respectively, were selected as the negative electrode active material, and the OI value of the resulting mixed graphite composite particles was 8.3. A soft-pack lithium iron phosphate battery was obtained.

[0147] Example 12

[0148] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the graphite composite particles in the negative electrode active material were D 50 Graphite particles C and D with a particle size of 3 μm 50A mixture of graphite particles C and D with a particle size of 15 μm was prepared. Specifically, in S2, the OI values ​​of graphite particles C and D were 5 and 6, respectively, and the OI value of the graphite composite particles was 5.4. The contents of graphite particles C and D were 25 wt% and 75 wt%, respectively, based on the total weight of the graphite composite particles. A soft-pack lithium iron phosphate battery was produced.

[0149] Example 13

[0150] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the type of lithium salt in the electrolyte was different. Specifically, in S3, the lithium salt was a mixture of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a weight ratio of 2:1. A soft-pack lithium iron phosphate battery was obtained.

[0151] Example 14

[0152] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the type of lithium salt in the electrolyte was different. Specifically, in S3, the lithium salt was a mixture of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, and lithium dioxalatoborate in a weight ratio of 35:10:8:1. A soft-pack lithium iron phosphate battery was obtained.

[0153] Example 15

[0154] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the weight ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate in the lithium salt was different. Specifically, in S3, the lithium salt was a mixture of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalatoborate in a weight ratio of 3:7:1. A soft-pack lithium iron phosphate battery was produced.

[0155] Example 16

[0156] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the type of additive in the electrolyte was different. Specifically, in S3, the additive was a mixture of VC, DTD, and FEC in a weight ratio of 2:1:1.5. A soft-pack lithium iron phosphate battery was obtained.

[0157] Example 17

[0158] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the weight ratio of VC to FEC in the additive was different. Specifically, the weight ratio of VC to FEC was 3:1. A soft-pack lithium iron phosphate battery was prepared.

[0159] Example 18

[0160] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the type of conductive agent 1 was different when preparing the positive electrode. Specifically, in S1, "4.5 wt % conductive agent 1 (2 wt % SP + 1.5 wt % CNTs + 1 wt % graphene)" was replaced with "4.5 wt % conductive agent 1 (2 wt % SP + 2.5 wt % CNTs)". A soft-pack lithium iron phosphate battery was prepared.

[0161] Example 19

[0162] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the type of conductive agent 2 was different when preparing the negative electrode. Specifically, in S2, "4 wt % conductive agent 2 (CNTs)" was replaced with "4 wt % conductive agent 2 (SP)." A soft-pack lithium iron phosphate battery was produced.

[0163] Example 20

[0164] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles A and D with a particle size of 2 μm 50 A mixture of lithium iron phosphate particles B with a particle size of 6 μm; the negative electrode active material does not contain hard carbon, which is D 50 Graphite particles A and D with a particle size of 6 μm 50 A mixture of graphite particles B having a particle size of 10 μm was prepared. Specifically, in S1, the contents of the lithium iron phosphate particles A and B were 54.3 wt% and 45.7 wt%, respectively, based on the total weight of the lithium iron phosphate composite particles. In S2, the contents of the graphite particles A and B were 25 wt% and 75 wt%, respectively, based on the total weight of the graphite composite particles. A soft-pack lithium iron phosphate battery was produced.

[0165] Example 21

[0166] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the negative electrode active material did not contain hard carbon, but was D 50 Graphite particles A and D with a particle size of 6 μm 50 A mixture of graphite particles B having a particle size of 10 μm. Specifically, in S2, based on the total weight of the graphite composite particles, the contents of graphite particles A and graphite particles B are 25 wt% and 75 wt%, respectively. A soft-pack lithium iron phosphate battery is prepared.

[0167] Example 22

[0168] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles A and D with a particle size of 2 μm 50A mixture of lithium iron phosphate particles D with a particle size of 20 μm; the negative electrode active material does not contain hard carbon, which is D 50 Graphite particles A and D with a particle size of 6 μm 50 A mixture of graphite particles B having a particle size of 10 μm was prepared. Specifically, in S1, the contents of lithium iron phosphate particles A and lithium iron phosphate particles D were 60 wt% and 40 wt%, respectively, based on the total weight of the lithium iron phosphate composite particles. In S2, the contents of graphite particles A and graphite particles B were 25 wt% and 75 wt%, respectively, based on the total weight of the graphite composite particles. A soft-pack lithium iron phosphate battery was produced.

[0169] Example 23

[0170] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 A mixture of lithium iron phosphate particles B, lithium iron phosphate particles C and lithium iron phosphate particles D with particle sizes of 6 μm, 10 μm and 20 μm respectively; the negative electrode active material does not contain hard carbon, which is D 50 Graphite particles A and D with a particle size of 6 μm 50 A mixture of graphite particles B having a particle size of 10 μm was prepared. Specifically, in S1, the contents of the lithium iron phosphate particles B, lithium iron phosphate particles C, and lithium iron phosphate particles D were 40 wt%, 50 wt%, and 10 wt%, respectively, based on the total weight of the lithium iron phosphate composite particles. In S2, the contents of the graphite particles A and graphite particles B were 25 wt% and 75 wt%, respectively, based on the total weight of the graphite composite particles. A soft-pack lithium iron phosphate battery was produced.

[0171] Example 24

[0172] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 A mixture of lithium iron phosphate particles A, lithium iron phosphate particles B, lithium iron phosphate particles C and lithium iron phosphate particles D with particle sizes of 2 μm, 6 μm, 10 μm and 20 μm respectively; the negative electrode active material does not contain hard carbon, which is D 50 Graphite particles A and D with a particle size of 6 μm 50 A mixture of graphite particles B having a particle size of 10 μm was prepared. Specifically, in S1, the contents of lithium iron phosphate particles A, lithium iron phosphate particles B, lithium iron phosphate particles C, and lithium iron phosphate particles D were 15 wt%, 25 wt%, 50 wt%, and 10 wt%, respectively, based on the total weight of the lithium iron phosphate composite particles. In S2, the contents of graphite particles A and graphite particles B were 25 wt% and 75 wt%, respectively, based on the total weight of the graphite composite particles. A soft-pack lithium iron phosphate battery was produced.

[0173] Comparative Example 1

[0174] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles A with a particle size of 2 μm, and the negative electrode active material is D 50 Graphite particles A with a particle size of 6 μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92 wt% of lithium iron phosphate particles A, 4.5 wt% of conductive agent 1 (2 wt% of SP + 2.5 wt% of CNTs) and 3.5 wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92 wt% of graphite particles A (OI value of 5), 4 wt% of conductive agent 2 (SP) and 4 wt% of binder 2 (1.5 wt% of CMC with a weight-average molecular weight of 400,000 g / mol and 2.5 wt% of SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0175] Comparative Example 2

[0176] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles B with a particle size of 6 μm, and the negative electrode active material is D 50 Graphite particles A with a particle size of 6μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92wt% of lithium iron phosphate particles B, 4.5wt% of conductive agent 1 (2wt% SP + 2.5wt% CNTs) and 3.5wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92wt% of graphite particles A (OI value of 5), 4wt% of conductive agent 2 (SP) and 4wt% of binder 2 (1.5wt% CMC with a weight average molecular weight of 400,000 and 2.5wt% SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0177] Comparative Example 3

[0178] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles C with a particle size of 10 μm, and the negative electrode active material is D 50Graphite particles A with a particle size of 6 μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92 wt% of lithium iron phosphate particles C, 4.5 wt% of conductive agent 1 (2 wt% of SP + 2.5 wt% of CNTs) and 3.5 wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92 wt% of graphite particles A (OI value of 5), 4 wt% of conductive agent 2 (SP) and 4 wt% of binder 2 (1.5 wt% of CMC with a weight average molecular weight of 400,000 g / mol and 2.5 wt% of SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0179] Comparative Example 4

[0180] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 The particle size of lithium iron phosphate particles D is 20 μm, and the negative electrode active material is D 50 Graphite particles A with a particle size of 6 μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92 wt% of lithium iron phosphate particles D, 4.5 wt% of conductive agent 1 (2 wt% of SP + 2.5 wt% of CNTs) and 3.5 wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92 wt% of graphite particles A (OI value of 5), 4 wt% of conductive agent 2 (SP) and 4 wt% of binder 2 (1.5 wt% of CMC with a weight-average molecular weight of 400,000 g / mol and 2.5 wt% of SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0181] Comparative Example 5

[0182] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles A with a particle size of 2 μm, and the negative electrode active material is D 50 Graphite particles B with a particle size of 10 μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92wt% of lithium iron phosphate particles A, 4.5wt% of conductive agent 1 (2wt% SP + 2.5wt% CNTs) and 3.5wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92wt% of graphite particles B (OI value of 4.5), 4wt% of conductive agent 2 (SP) and 4wt% of binder 2 (1.5wt% CMC with a weight-average molecular weight of 400,000 g / mol and 2.5wt% SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0183] Comparative Example 6

[0184] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles B with a particle size of 6 μm, and the negative electrode active material is D 50 Graphite particles B with a particle size of 10 μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92wt% of lithium iron phosphate particles B, 4.5wt% of conductive agent 1 (2wt% SP + 2.5wt% CNTs) and 3.5wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92wt% of graphite particles B (OI value of 4.5), 4wt% of conductive agent 2 (SP) and 4wt% of binder 2 (1.5wt% CMC with a weight-average molecular weight of 400,000 g / mol and 2.5wt% SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0185] Comparative Example 7

[0186] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 Lithium iron phosphate particles C with a particle size of 10 μm, and the negative electrode active material is D 50 Graphite particles B with a particle size of 10 μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92wt% of lithium iron phosphate particles C, 4.5wt% of conductive agent 1 (2wt% SP + 2.5wt% CNTs) and 3.5wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92wt% of graphite particles B (OI value of 4.5), 4wt% of conductive agent 2 (SP) and 4wt% of binder 2 (1.5wt% CMC with a weight-average molecular weight of 400,000 g / mol and 2.5wt% SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0187] Comparative Example 8

[0188] A soft-pack lithium iron phosphate battery was prepared according to the method of Example 1, except that the positive electrode active material was D 50 The particle size of lithium iron phosphate particles D is 20 μm, and the negative electrode active material is D 50Graphite particles B with a particle size of 10 μm. Specifically, in S1, based on the total weight of the positive electrode powder, 92wt% of lithium iron phosphate particles D, 4.5wt% of conductive agent 1 (2wt% SP + 2.5wt% CNTs) and 3.5wt% of binder 1 were weighed in percentage by mass to prepare the positive electrode powder. In S2, based on the total weight of the negative electrode powder, 92wt% of graphite particles B (OI value of 4.5), 4wt% of conductive agent 2 (SP) and 4wt% of binder 2 (1.5wt% CMC with a weight-average molecular weight of 400,000 g / mol and 2.5wt% SBR) were weighed in percentage by mass to prepare the negative electrode powder. A soft-pack lithium iron phosphate battery was prepared.

[0189] Test Case

[0190] The cold starting voltage and the capacity retention rate after 1000 cycles of the soft-pack lithium iron phosphate batteries prepared in each embodiment and comparative example were measured.

[0191] The results are shown in Table 1.

[0192] Table 1

[0193] From the results in Table 1, it can be seen that the lithium iron phosphate batteries provided by Examples 1-24 in this application can have excellent high and low temperature performance, while the positive electrode active materials of Comparative Examples 1-8 are all single D 50 The lithium iron phosphate particles are of a single D 50 Compared with Examples 1-24, the low-temperature cold start performance and / or life of the battery are significantly reduced. This shows that by mixing at least two lithium iron phosphate particles with different particle sizes as the positive electrode active material and mixing at least two graphite particles with different particle sizes as the negative electrode active material, the resulting lithium iron phosphate battery can have both good low-temperature high-rate discharge performance and a long high-temperature cycle life.

[0194] In addition, the lithium iron phosphate composite particles of Example 2 only have small particles (D 50 The cold starting voltage of lithium iron phosphate particles A and lithium iron phosphate particles B with a particle size of less than or equal to 7 μm did not change significantly compared with Example 1, but the high temperature cycle capacity retention rate was significantly reduced, indicating that the positive electrode active material only contained D 50 When the lithium iron phosphate particles are small in size and less than or equal to 7 μm, the cold starting voltage of the battery is higher, but the high temperature cycle capacity retention rate is lower. 50The combination of lithium iron phosphate particles of different particle sizes, Example 7 changes the ratio of lithium iron phosphate particles A, lithium iron phosphate particles B and lithium iron phosphate particles C in the lithium iron phosphate composite particles, Example 8 changes the ratio of graphite composite particles and hard carbon, Example 9 changes the ratio of graphite particles A and graphite particles B, Example 10 changes the ratio of hard carbon D 50 Particle size, Example 11 changed the OI value of the graphite composite particles, Example 12 changed the different D 50 The combination of graphite particles of different particle sizes, Examples 13-15 respectively changed the type of lithium salt in the electrolyte and the distribution ratio of the group, Examples 16 and 17 respectively changed the type of additive in the electrolyte and the distribution ratio of the group, Examples 18 and 19 respectively changed the type of positive and negative electrode conductive agents, the negative electrode active material of Example 21 did not contain hard carbon, and the negative electrode active materials of Examples 20, 22-24 did not contain hard carbon and changed the different D in the positive electrode active material. 50 The combination of lithium iron phosphate particles with different particle sizes shows that the cold starting voltage or high temperature cycle capacity retention rate of the obtained battery is reduced to a certain extent compared with Example 1, indicating that the different D 50 The compounding method of lithium iron phosphate particles with different particle sizes, different D 50 The compounding method of graphite particles of different particle size, the proportion of hard carbon, the D 50 The particle size and OI value of the graphite composite particles, the types of positive and negative electrode conductive agents, and the types and group distribution ratios of lithium salts and additives in the electrolyte jointly affect the cold starting voltage and high-temperature cycle capacity retention rate of the manufactured battery. The positive and negative electrode conductive agents, electrolyte and positive and negative electrode materials cooperate with each other to further improve the cold starting performance and high-temperature life of the manufactured battery, and can take into account excellent high and low temperature performance.

[0195] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, including combining the various technical features in any other appropriate manner. These simple modifications and combinations should also be regarded as the contents disclosed in the present application and fall within the scope of protection of the present application.

Claims

1. A battery cell (1), characterized in that: The battery cell comprises: The positive electrode comprises a lithium iron phosphate composite particle, wherein the lithium iron phosphate composite particle comprises at least two kinds of D 50 particle size of lithium iron phosphate particles; and A negative electrode, the negative electrode comprising graphite composite particles, the graphite composite particles comprising at least two D 50 Graphite particles of different particle sizes.

2. The battery cell (1) according to claim 1, characterized in that: The OI value of the graphite composite particles is less than or equal to 7.

3. The battery cell (1) according to claim 1 or 2, characterized in that: The negative electrode further includes hard carbon.

4. The battery cell (1) according to claim 3, characterized in that: The hard carbon D 50 The particle size is 3μm-10μm.

5. The battery cell (1) according to claim 3 or 4, characterized in that: The weight ratio of the graphite composite particles to the hard carbon is (85-95):(5-15).

6. The battery cell (1) according to any one of claims 1 to 5, characterized in that: The graphite composite particles include graphite particles A and graphite particles B, wherein the graphite particles A have a 50 The particle size is 5μm-7μm, and the graphite particles B have a D 50 The particle size is 9μm-11μm.

7. The battery cell (1) according to claim 6, characterized in that: Based on the total weight of the graphite composite particles, in the graphite composite particles, the contents of the graphite particles A and the graphite particles B are 25wt%-75wt% and 25wt%-75wt%, respectively.

8. The battery cell (1) according to any one of claims 1 to 7, characterized in that: The lithium iron phosphate composite particles include at least two of lithium iron phosphate particles A, lithium iron phosphate particles B, lithium iron phosphate particles C and lithium iron phosphate particles D, wherein the lithium iron phosphate particles A, the lithium iron phosphate particles B, the lithium iron phosphate particles C and the lithium iron phosphate particles D are each 50 The particle sizes are 1μm-3μm, 5μm-7μm, 9μm-11μm and 18μm-20μm respectively.

9. The battery cell (1) according to claim 8, characterized in that: Based on the total weight of the lithium iron phosphate composite particles, the total content of the lithium iron phosphate particles A and the lithium iron phosphate particles B is less than or equal to 75 wt %.

10. The battery cell (1) according to claim 8 or 9, characterized in that: The lithium iron phosphate composite particles are a mixture of lithium iron phosphate particles A, lithium iron phosphate particles B and lithium iron phosphate particles C; Preferably, based on the total weight of the lithium iron phosphate composite particles, in the lithium iron phosphate composite particles, the contents of the lithium iron phosphate particles A, the lithium iron phosphate particles B and the lithium iron phosphate particles C are 10wt%-30wt%, 20wt%-40wt% and 30wt%-70wt% respectively.

11. The battery cell (1) according to any one of claims 1 to 10, characterized in that: The battery cell (1) further comprises an electrolyte, wherein the electrolyte comprises a lithium salt; Preferably, the lithium salt includes lithium hexafluorophosphate and at least one selected from lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate) and lithium difluorooxalatoborate; Preferably, the lithium salt is a mixture of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorooxalatoborate; Preferably, in the lithium salt, the weight ratio of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium difluorooxalatoborate is (5-10): (2-5): (0.5-1); Preferably, the content of the lithium salt in the electrolyte is 0.8 mol / L-1.2 mol / L.

12. The battery cell (1) according to any one of claims 1 to 11, characterized in that: The battery cell (1) further comprises an electrolyte, wherein the electrolyte further comprises an additive, wherein the additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate; Preferably, the additive is a mixture of vinylene carbonate and fluoroethylene carbonate; Preferably, the content of the additive in the electrolyte is 1.5 mol / L-5 mol / L; Preferably, in the additive, the weight ratio of vinylene carbonate to fluoroethylene carbonate is (1.5-3.5):(2-5).

13. The battery cell (1) according to any one of claims 1 to 12, characterized in that: The battery cell further comprises an electrolyte, and the electrolyte further comprises a solvent, wherein the solvent is selected from at least one of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate; Preferably, the solvent is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; Preferably, in the solvent, the weight ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is (2-4): (2-4): (3-5).

14. The battery cell (1) according to any one of claims 1 to 13, characterized in that: The positive electrode comprises a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector, wherein, based on the total weight of the positive electrode material layer, the content of the lithium iron phosphate composite particles in the positive electrode material layer is 90wt%-94wt%; Preferably, the negative electrode comprises a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, wherein, based on the total weight of the negative electrode material layer, the total content of the graphite composite particles and the hard carbon in the negative electrode material layer is 90wt%-95wt%; Preferably, based on the total weight of the graphite composite particles and the hard carbon, the content of the hard carbon is less than or equal to 15 wt %.

15. A method for preparing a battery cell (1), characterized in that: The preparation method comprises: A positive electrode is provided, the positive electrode comprising lithium iron phosphate composite particles, the lithium iron phosphate composite particles comprising at least two D 50 Particle size of lithium iron phosphate particles; A negative electrode is provided, the negative electrode comprising graphite composite particles, the graphite composite particles comprising at least two D 50 Graphite particles of particle size; and The positive electrode and the negative electrode are assembled into a battery cell.

16. The preparation method according to claim 15, characterized in that: The preparation method of the positive electrode (1) comprises: 50 The lithium iron phosphate particles with different particle sizes are mixed to obtain the lithium iron phosphate composite particles; the lithium iron phosphate composite particles, the conductive agent 1, the binder 1 and the solvent 1 are mixed to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the surface of the positive electrode current collector, and then rolled to obtain the positive electrode; Preferably, the method for preparing the negative electrode comprises: mixing at least two D 50 Graphite particles of different particle sizes are mixed to obtain the graphite composite particles; the graphite composite particles, hard carbon, a conductive agent 2, a binder 2 and a solvent 2 are mixed to obtain a negative electrode slurry, and then the negative electrode slurry is coated on the surface of a negative electrode collector, and then rolled to obtain the negative electrode.

17. A starting battery (2) for a fuel engine, characterized in that: It comprises a battery cell (1) according to any one of claims 1 to 14 or a battery cell (1) prepared by the preparation method according to claim 15 or 16.

18. A vehicle (100), characterized in that: It comprises the battery cell (1) according to any one of claims 1 to 14, or the battery cell (1) prepared by the preparation method according to claim 15 or 16, or the starting battery (2) for the fuel engine according to claim 17.

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