A lithium battery

Abstract

The application provides a lithium battery, which comprises a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode active material layer, and the positive electrode active material layer comprises a lithium iron phosphate positive electrode material and a lithium supplement agent; the lithium iron phosphate positive electrode material contains a doping element A, and the doping element A comprises at least one of Ti, V, Mg, Nb, Zr, Zn and Al; the lithium supplement agent comprises a lithium-rich lithium nickelate material, and the chemical formula of the lithium-rich lithium nickelate material is Li 2+ x NiByO 2+z , x>0, y>0, z>0 or z<0; the element B comprises at least one of Ti, Al, Mg, Mn and Fe; the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises a carbon-based negative electrode material and a silicon-based negative electrode material; the silicon-based negative electrode material comprises at least one of a porous silicon material, a core-shell silicon-carbon material, a yolk-shell silicon-carbon material and a SiO X / C graphite structure silicon-carbon material; the D50 of the silicon-based negative electrode material is 5-15 mu m, wherein the porosity of the porous silicon material is 5-40%; in the core-shell silicon-carbon material and the yolk-shell silicon-carbon material, the inner core is nano silicon powder, and the outer shell is carbon material. The battery effectively improves the battery performance by optimizing the collocation of the positive and negative electrode active materials, so that the battery has the advantages of high energy density, good fast charging performance, long cycle life and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a lithium battery. BACKGROUND

[0002] During the first charging process of the lithium battery, an SEI film is formed, resulting in irreversible capacity loss, which is the main reason for the low capacity and energy density of the lithium ion battery. In addition, during the charging and discharging process, the negative electrode material may be deactivated due to swelling and falling off, or irreversible lithium deposition may occur, which will consume the active lithium of the positive electrode and reduce the capacity and energy density of the battery. In order to compensate for the loss of active lithium of the positive electrode material and further improve the energy density of the battery, a lithium supplement technology is often used. The irreversible capacity loss of the most widely used graphite negative electrode can reach 10%, while for silicon-based and tin-based alloy negative electrodes with high specific capacity, the irreversible capacity loss can even reach ~ 30%, and the lithium supplement technology can improve the short board of low initial efficiency and fully exert the advantages of high capacity. Since the battery manufacturing process of the negative electrode lithium supplement is difficult and the investment is high, the positive electrode lithium supplement is often used.

[0003] In addition, the fast charging performance of the lithium battery can be improved by improving the rate performance of the positive and negative electrode materials, optimizing the electrolyte formula, and selecting a thin film with high porosity. In addition, electrode design (such as the coating amount of the electrode sheet, the compaction density, the thickness of the copper foil and aluminum foil, the size of the tab, the width of the electrode sheet, etc.) is also crucial to the fast charging performance, and the surface density and compaction density of the battery also have a great influence on the rate, cycle, etc. of the battery. Fast charging lithium ion batteries require low surface density design, while too high or too low compaction density will lead to poor performance. If the compaction density is too high, the active material of the electrode sheet will be "pressed to death", leading to a rapid drop in cycle capacity, while if the compaction density is too low, the contact between the active materials will not be sufficient, the impedance of the battery will be large, and the volumetric energy density will be small, leading to poor fast charging performance.

[0004] The selection of the lithium supplement agent also has a great influence on improving the electrochemical performance of the positive electrode material. In addition, in order to match the positive electrode material, how to further optimize the negative electrode material to make the positive and negative electrodes exhibit better cycle performance, high rate fast charging performance and high energy density in the charging and discharging cycle has also become a technical difficulty in the preparation of high-performance lithium batteries.

[0005] Therefore, there are still some challenges in the manufacture of batteries with high volumetric energy density, good fast charging performance and long cycle life. SUMMARY

[0006] In order to solve the problems and deficiencies in the prior art, the present application provides a lithium battery, which effectively improves the battery performance by optimizing the matching of the positive and negative electrode active materials, and has the advantages of high energy density, good fast charging performance, long cycle life and the like.

[0007] The application provides a lithium battery, comprising a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode active material layer, and the positive electrode active material layer comprises a lithium iron phosphate positive electrode material and a lithium supplementing agent; the lithium iron phosphate positive electrode material contains a doping element A, and the doping element A comprises at least one of Ti, V, Mg, Nb, Zr, Zn and Al; and the lithium supplementing agent comprises a lithium-rich lithium nickelate material, and the chemical formula of the lithium-rich lithium nickelate material is Li 2+x NiB y O 2+z , x>0, y>0, z>0 or z<0; the element B comprises at least one of Ti, Al, Mg, Mn and Fe; the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises a carbon-based negative electrode material and a silicon-based negative electrode material; the silicon-based negative electrode material comprises at least one of a porous silicon material, a core-shell silicon-carbon material, a yolk-shell silicon-carbon material and a SiO X / C graphite structure silicon-carbon material; the D50 of the silicon-based negative electrode material is 5-15 mu m, wherein the porosity of the porous silicon material is 5-40%; in the core-shell silicon-carbon material and the yolk-shell silicon-carbon material, the inner core is nano silicon powder, and the outer shell is carbon material.

[0008] The lithium iron phosphate positive electrode material (LFP) is considered to be one of the most promising lithium battery positive electrode materials due to its excellent structural stability, long cycle life and high safety performance. In the current lithium iron phosphate battery, the most common is still the LFP / graphite system, and the energy density is 160-180 Wh / kg. However, with the rapid development of the new energy industry, there is an urgent need to develop high-energy density, high-fast-charging performance and long cycle performance. Moreover, the volume energy density and ionic conductivity of LFP are low, which limits the play of its fast-charging performance.

[0009] To improve the performance of the LFP battery, first, a lithium supplementing agent lithium nickelate positive electrode material (LNO) is introduced into the positive electrode active material, which can effectively make up for the lithium consumption of the formation of the negative electrode SEI film during the first charge and discharge of the battery, thereby effectively improving the gram capacity of the LFP positive electrode material. Moreover, the lithium supplementing effect of the LNO can improve the cycle life. Moreover, the LFP positive electrode material in the application is doped with metal elements. These additional doped metal elements can widen the Li + transport channel, increase the Li + diffusion coefficient, optimize the Li + transport performance, and make the Li +In the charge and discharge cycle process, the deintercalation is more smooth, and the battery cycle performance is optimized. At the same time, the introduction of additional doping metal elements can also improve the conductivity of the LFP positive electrode material, and further optimize the performance of the LFP battery. In addition, the lithium supplementing agent LNO contains Li, Ni metal elements, and also contains a certain amount of other metal elements, which can form a stable lattice structure with Li, Ni and O, and the addition of these metal elements can promote the lithium supplementing effect of LNO, improve the Li+ transmission performance and conductivity of the positive electrode material as a whole, and further optimize the electrochemical performance of the positive electrode material.

[0010] Secondly, in the negative electrode active material, the negative electrode active material used in the present application is a combination of carbon-based negative electrode material and silicon-based negative electrode material, because only silicon-based negative electrode material is used, the negative electrode volume expansion effect is too large, even if the silicon-based negative electrode material is modified, in the process of charge and discharge cycle, because the negative electrode material is only silicon-based negative electrode material, the volume expansion stress is very large, and the structure stability of the silicon-based negative electrode material cannot be maintained for a long time, thus it is not conducive to the fast charging performance and long cycle performance of the battery. In addition, the silicon-based negative electrode material used in the present application is a porous silicon core-shell structure silicon-carbon material or a yolk-shell structure silicon-carbon material or SiO X / C class graphite structure silicon-carbon material, these silicon-based negative electrode materials have a D50 of micron level, which will not significantly agglomerate in the preparation of negative electrode slurry and negative electrode sheet (D50 is too small, such as nano-level particles, which are more prone to agglomeration), and will not affect the performance of the silicon-based negative electrode material and the subsequent processing of the negative electrode. And the D50 of the silicon-based negative electrode material cannot be too large, which can ensure that it can be well infiltrated by the electrolyte, and ensure that it has good lithium ion transmission performance and conductivity.

[0011] Moreover, the porous silicon material has a porosity of 5-40%, which can effectively alleviate the volume expansion effect, so that it is not easy to break and collapse in the process of charge and discharge cycle, which deteriorates the cycle performance and fast charging performance of the battery. At the same time, such porosity is also conducive to the rapid transmission of lithium ions, optimizing the fast charging performance of the battery. The porosity cannot be too high or too low, too high will deteriorate the structure stability of the porous silicon itself, because the higher the porosity, the more surface pore defects, which are more prone to damage under external forces such as cycle stress; too low is not enough to alleviate the volume expansion effect, and is not conducive to the structure stability of the silicon-based material in the process of charge and discharge cycle. Similarly, the core-shell structure silicon-carbon material, yolk-shell structure silicon-carbon material, SiO X / C class graphite structure silicon-carbon material, etc. have a core-shell structure or certain porosity, which can also effectively alleviate the volume expansion stress of the silicon-based material, so that it is not easy to break in the process of charge and discharge cycle, and the cycle performance and fast charging performance of the battery are optimized.

[0012] More importantly, in the above specific combination of positive electrode active material and negative electrode active material, the deintercalation of lithium ions is balanced on the positive and negative electrode sides during the charge and discharge cycle, which is conducive to the smooth transportation of lithium ions in the battery, and thus is more conducive to the improvement of the cycle performance, fast charging performance and energy density of the battery. Moreover, because of the relatively balanced lithium ion transmission efficiency of the positive and negative electrodes, the formation of lithium dendrites on the negative electrode side is less, so the cycle performance of the battery can be further optimized. In addition, the combination of LFP+LNO in the positive electrode active material of the present application can also effectively improve the compaction density of the positive electrode sheet, so as to reduce the surface density design while improving the energy density of the battery.

[0013] Preferably, the inner shell is a nano-silicon powder, and the nano-silicon powder is a silicon oxide powder including at least one of silicon dioxide and silicon monoxide.

[0014] Preferably, the porosity of the porous silicon material is 20-35%. Further adjusting the porosity of the porous silicon can more effectively balance the self-volume expansion performance, structural strength and lithium ion transmission performance of the porous silicon, and can more effectively exert the performance of the porous silicon material in all aspects.

[0015] Preferably, the mass ratio of the lithium supplement agent in the total mass of the lithium iron phosphate positive electrode material and the lithium supplement agent is 0.5-20%. If the content of the lithium supplement agent is too low, it cannot effectively improve the specific capacity of the LFP positive electrode material, and thus cannot effectively improve the energy density of the battery. Moreover, if the content of the lithium supplement agent is too low, it cannot supplement lithium in time, which will affect the insertion and extraction reactions of lithium ions in the positive electrode material, and thus reduce the cycle life of the battery. In addition, if the content of the lithium supplement agent is too low, the total lithium will also be less, and too little lithium will cause the discharge performance of the battery to decrease, and will also affect the charging efficiency of the battery, which will cause the capacity of the battery to decrease and the charging time to become longer, and will deteriorate the fast charging performance of the battery. If the content of the lithium supplement agent is too high, the total lithium will also be too much, and too much lithium will cause the chemical reaction process in the battery to accelerate, and thus will accelerate the aging of the battery and shorten the life of the battery. Moreover, if the content of lithium in the positive electrode material is too high, the battery will exhibit polarization, which will cause the internal resistance of the battery to increase and the voltage of the battery to decrease during discharge, and thus will affect the electrical performance of the battery. In addition, too much lithium will also increase the risk of combustion of the battery, because too much lithium will cause the excess lithium ions in the positive electrode material of the battery to produce thermal decomposition or reaction to produce gas during charging or discharging, which will cause the internal pressure of the battery to increase, and will cause short circuit, leakage, and even explosion and other dangers.

[0016] Preferably, the mass ratio of the lithium supplement agent in the total mass of the lithium iron phosphate positive electrode material and the lithium supplement agent is 5-15%.

[0017] Preferably, the mass ratio of the silicon-based negative electrode material in the total mass of the carbon-based negative electrode material and the silicon-based negative electrode material is 2-50%. If the silicon-based negative electrode material is too little, the battery energy density, capacity and fast charging performance will not be significantly improved, and if the silicon-based negative electrode material is too much, the silicon volume expansion effect will be too obvious, the negative electrode material is more likely to break during charging and discharging, and it is not conducive to the cycle performance and fast charging performance of the battery.

[0018] Preferably, the mass ratio of the silicon-based negative electrode material in the total mass of the carbon-based negative electrode material and the silicon-based negative electrode material is 10-35%.

[0019] Preferably, the D50 of the secondary particle size of the lithium iron phosphate positive electrode material is 0.5-3.5 μm, the primary particle size is 0.1-2.0 μm, and the D50 of the lithium supplement agent is 2-15 μm. Controlling the D50 of the secondary particle size of the lithium iron phosphate positive electrode material and the lithium supplement agent within the above range can take into account the cycle performance and processing performance of the material. If the D50 is too large, the material is easy to break, which affects the cycle performance. If the D50 is too small, the material is easy to agglomerate and block the screen, which affects the processing. Moreover, within the above D50 range, the particle matching between the lithium iron phosphate positive electrode material and the lithium supplement agent is better, which can reduce the gap between the particles, improve the compaction density of the positive electrode material, and optimize the energy density of the battery. Controlling the primary particle size of the lithium iron phosphate positive electrode material within a smaller particle size range can increase the specific surface area of the primary particle, which is beneficial to the diffusion of Li+. + The transmission unit can reduce the Li + The transmission path improves the electrical performance and optimizes the cycle performance of the battery. Therefore, if the primary particle size is too large, the Li + The transmission path increases, which is not conducive to the Li + transport; and if the primary particle size is too small, the secondary particles are too many grain boundaries, which makes the secondary particles easy to break and deteriorate the electrochemical performance of the positive electrode material. It should be noted that the single particle before agglomeration is the primary particle (particle size), and the particle after agglomeration is the secondary particle (particle size).

[0020] Preferably, in the core-shell structure silicon-carbon material and the yolk-shell structure silicon-carbon material, the carbon material for preparing the shell includes at least one of phenolic resin, polyvinyl alcohol, epoxy resin and polyaniline.

[0021] Preferably, the doping amount of the doping element A in the lithium iron phosphate positive electrode material is 300-9000 ppm. If the doping amount is too small, it cannot effectively widen the Li+ transmission path and increase the Li+ diffusion coefficient, so the improvement of the electrical performance of the material is limited. If the doping amount is too much, it will affect the performance of the lithium iron phosphate positive electrode material itself, and may also affect the structural stability of the material itself, which will also cause the performance of the material to decrease.

[0022] Preferably, the doping amount of the doping element A in the lithium iron phosphate positive electrode material is 2000-7500 ppm. Under these selected B element species, the obtained LNO lithium supplementing agent has better matching with the lithium iron phosphate positive electrode material, especially can jointly act with the doping element A in the lithium iron phosphate, can further improve the Li+ transmission performance and the electrical conductivity of the positive electrode material, and further optimizes the performance of the battery.

[0023] Preferably, the single surface density of the positive electrode sheet is 150-350 g / m 2 , and the compacted density is 2.35-2.70 g / cm 3 ; the single surface density of the negative electrode sheet is 90-120 g / m 2 , and the compacted density is 1.40-1.90 g / cm 3 . The positive electrode sheet prepared by using the positive electrode material has a high compacted density, so the surface density of the present application is not too high, and even in the case that the surface density is not too high, the battery provided by the present application can also have a high energy density due to the high compacted density. Further, by designing the negative electrode sheet and the positive electrode sheet with certain surface density and compacted density, the transmission balance of the positive and negative lithium ions can be more beneficial, the lithium dendrite situation can be reduced, and the transmission resistance can be reduced, thereby optimizing the battery performance.

[0024] Preferably, the doping element A includes Ti and V; or the doping element A includes Ti and Zn. The doping element can have a synergistic effect under the above matching, which is more beneficial to widening the Li+ transmission channel and increasing the Li+ diffusion coefficient, and further optimizes the material performance, the cycle performance, the fast charging performance and the energy density of the battery.

[0025] Preferably, the B element includes at least one of Al, Mn and Mg.

[0026] Preferably, the lithium-rich lithium nickelate positive electrode material is at least one of Li3NiMnO4, Li3NiMgO4, Li3NiMn2O5, Li3NiMnO5, Li5NiMgO5, Li3NiMg2O5 and Li4NiAlO5.

[0027] Preferably, the silicon-based negative electrode material includes porous silicon material and core-shell structure silicon-carbon material, and the mass ratio of the porous silicon material and the core-shell structure silicon-carbon material is 1:1-1.5; or the silicon-based negative electrode material includes porous silicon material and yolk-shell structure silicon-carbon material, and the mass ratio of the porous silicon material and the yolk-shell structure silicon-carbon material is 1:1-1.5. When the silicon-based negative electrode material adopts the above two matching, the two materials can make up for the shortcomings of each other, so that the volume expansion stress of the negative electrode can be better relieved, and the Li +The battery has high transmission performance, and the cycle performance and fast charging performance of the battery are further improved.

[0028] Preferably, in the lithium battery provided by the application, the positive active material layer of the positive electrode sheet further comprises a first conductive agent and a first binder.

[0029] Preferably, the mass ratio of the lithium iron phosphate positive electrode material, the lithium supplement agent, the first conductive agent, and the first binder is 81.6-92.2:0.2-14.6:1.5-2.5:1.5-2.5.

[0030] Preferably, the first conductive agent comprises conductive carbon black (SP) and carbon nanotubes (CNT), and the mass ratio of the conductive carbon black and the carbon nanotubes is 0.8-1.0:1-1.25.

[0031] Preferably, in the lithium battery provided by the application, the negative active material layer of the negative electrode sheet further comprises a second conductive agent and a second binder.

[0032] Preferably, the mass ratio of the carbon-based negative electrode material, the silicon-based negative electrode material, the second conductive agent, and the second binder is 62.4-87.3:9.6-34.0:0.5-1.5:2.5-3.5.

[0033] Preferably, the carbon-based negative electrode material comprises graphite.

[0034] Preferably, the second conductive agent comprises conductive carbon black (SP).

[0035] Preferably, the second binder comprises styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC), and the mass ratio of the styrene butadiene rubber and the carboxymethyl cellulose is 0.8-1.0:1-1.25.

[0036] Preferably, the preparation method of the lithium iron phosphate positive electrode material comprises the following steps: a1. mixing a FePO4 precursor, a first lithium source, a first carbon source, and an A compound containing a doping element A in water; a2. granulating and drying the mixture obtained in a1 by spray drying; a3. sintering after drying in an inert gas atmosphere, and the sintering temperature is 600-720℃, and the sintering time is 8-12h; a4. after sintering, airflow crushing is performed to obtain the lithium iron phosphate positive electrode material.

[0037] Preferably, the first lithium source comprises lithium carbonate; the first carbon source comprises at least one of glucose and PEG; and the A compound comprises at least one of titanium dioxide and V2O5.

[0038] Preferably, in a1, the molar ratio of the FePO4 precursor to the first carbon source is 0.96-1:0.48-0.59; and the total addition amount of the first carbon source is 1-2wt% (mass ratio in the total of all substances excluding the solvent).

[0039] Preferably, when the first carbon source comprises glucose, the mass ratio of glucose to PEG is 0.8-1:1-1.25.

[0040] Preferably, the amount of the added A compound is calculated based on the content of the doping element A in the final lithium iron phosphate positive electrode material, which is 300-9000 ppm.

[0041] Preferably, in a3, the inert gas atmosphere comprises nitrogen.

[0042] Preferably, the above-mentioned lithium supplementing agent is Li 2+x NiB y O 2+z When the lithium supplementing agent is Li

[0043] Preferably, the second lithium source comprises at least one of lithium hydroxide, lithium carbonate, lithium carbide, lithium hydride, lithium nitride, lithium amide, lithium chloride, lithium acetate, and lithium nitrate; the first nickel source comprises at least one of nickel chloride, nickel sulfate, nickel carbonate, nickel oxide, nickel bromide, and nickel acetate; and the B compound comprises at least one of aluminum nitrate, aluminum chloride, aluminum oxide, titanium dioxide, magnesium oxide, manganese dioxide, and iron oxide.

[0044] Preferably, in b1, the molar ratio of the second lithium source to the first nickel source is 1.05-1.3:0.92-1.0; and the total amount of the added B compound is 10-30 wt% (mass ratio in the total amount of all substances except the solvent).

[0045] Preferably, in b3, the inert gas atmosphere comprises nitrogen.

[0046] Preferably, the preparation method of the above-mentioned porous silicon material comprises the following steps: c1. pyrolyzing a second carbon source to form a porous carbon skeleton; the second carbon source can be pyrolyzed to form a porous structure; c2. placing the carbon skeleton in a reactor, and under an inert gas atmosphere, mixing a third carbon source with a first silicon source and then introducing the mixture into the reactor to deposit and form a silicon-carbon composite material precursor; c3. ball-milling the silicon-carbon composite material precursor with a fourth carbon source, and then sintering to obtain a porous silicon material; the porous silicon material is a porous silicon-carbon composite material.

[0047] Preferably, the second carbon source comprises at least one of sucrose, polystyrene, polyamide; the third carbon source comprises at least one of glucose, sucrose, SP (conductive carbon black); the first silicon source comprises at least one of silane, siloxane; the fourth carbon source comprises sucrose.

[0048] Preferably, in c2, the molar ratio of the third carbon source to the first silicon source is 0.65-0.85:1.12-1.25.

[0049] Preferably, in c3, the inert gas atmosphere comprises nitrogen.

[0050] Preferably, the core-shell structure silicon-carbon material comprises a hollow core-shell structure silicon-carbon material.

[0051] Preferably, the preparation method of the hollow core-shell structure silicon-carbon material comprises the following steps: d1. mixing silicon powder (referring to silicon dioxide powder), expanded graphite, a surfactant and a grinding agent, and then performing ball milling to obtain a nano-silicon slurry; d2. mixing and dispersing the nano-silicon slurry with a soluble resin, an additive, a foaming agent and a dispersant to form a homogeneous dispersion liquid, and then performing spray drying on the homogeneous dispersion liquid to obtain nano-silicon / resin microspheres; d3. performing carbonization treatment on the obtained microspheres at 850-1000°C under the protection of an inert gas to form a core-shell structure silicon-carbon material; and d4. cooling the carbonization-treated material to room temperature, sieving, and then using HF to etch the SiO2 shell and remove the internal SiO2, thereby forming a hollow core-shell structure silicon-carbon material.

[0052] Preferably, in d1, the mass ratio of the silicon powder, the expanded graphite, the surfactant and the grinding agent is 30-50:30-59.5:0.5-5:10-15; the surfactant comprises a silicon hydroxide surfactant; and the grinding agent comprises a silicon dioxide grinding liquid.

[0053] Preferably, in d2, the soluble resin comprises at least one of phenolic resin, polyvinyl alcohol, epoxy resin, polyaniline; the additive comprises at least one of lignin, polyaniline; the foaming agent comprises azodicarbonamide; and the dispersant comprises hydrolyzed polymaleic anhydride.

[0054] Preferably, in d2, the mass ratio of the nano-silicon slurry, the soluble resin, the additive, the foaming agent and the dispersant is 40-55:35-57:1-2:1-3:1-5.

[0055] Preferably, in d3, the core-shell structure silicon-carbon material after the carbonization treatment is in the structure of Si@SiO2@C, that is, a SiO2 layer is coated outside a Si layer, and then a C layer is coated. It should be noted that the main component of the silicon powder is SiO2, and part of it is Si element, which is helpful to form Si@SiO2 through ball milling with the expanded graphite, and then Si@SiO2@C is formed after carbonization.

[0056] Preferably, the preparation method of the egg yolk shell structure silicon-carbon material comprises the following steps: e1. uniformly mixing silicon particles (referring to metal silicon particles), a dispersing agent, a soluble inorganic salt in deionized water, evaporating the solvent by heating, and filtering and drying after cooling; e2. mixing the dried sample with a carbon source, carbonizing at 650-750 DEG C under an inert gas atmosphere, and then washing with deionized water and drying to obtain the egg yolk shell structure silicon-carbon material.

[0057] Preferably, in e1, the dispersing agent comprises polyvinylpyrrolidone; and the soluble inorganic salt comprises sodium carbonate.

[0058] Preferably, in e1, the mass ratio of the silicon particles, the dispersing agent and the soluble inorganic salt is 20-35:5-10:55-70.

[0059] Preferably, in e2, the inert gas atmosphere comprises nitrogen.

[0060] Preferably, the SiOx / C graphite structure silicon-carbon material has a specific surface area of 1000-2000 m2 / g, a pore volume of 0.8-1.5 cm3 / g, and a pore size of 2-4 nm. X The preparation method of the SiOx / C graphite structure silicon-carbon material comprises the following steps: f1. placing silicon oxide compound powder under an inert gas protection atmosphere, and heat treating at 800-1100 DEG C, and then cooling to room temperature in the furnace; f2. adding a carbon source (glucose or sucrose) and deionized water to the cooled silicon oxide compound powder, and performing sand milling to obtain a nano slurry, wherein the silicon oxide compound powder and the carbon source are added in a mass ratio of 1:1; f3. performing spray drying on the obtained nano slurry, wherein the inlet temperature of the spray drying is 200-350 DEG C, and the outlet temperature is 90-150 DEG C, to obtain spherical particle precursors; f4. baking the spherical particle precursors under an inert gas protection atmosphere at 500-900 DEG C for 2-12 hours, and then cooling to room temperature; and f5. crushing the baked material, and obtaining the SiOx / C graphite structure silicon-carbon material by sieving.

[0061] Preferably, in f1, the silicon oxide compound comprises silicon monoxide.

[0062] Preferably, in f2, the carbon source comprises at least one of glucose and sucrose.

[0063] Preferably, in f1 and f4, the inert gas protection atmosphere comprises argon. DETAILED DESCRIPTION

[0064] In order to enable personnel in the technical field to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0065] Embodiment 1

[0066] 1. Preparation of lithium iron phosphate cathode material (LFP)

[0067] The lithium iron phosphate cathode material of the present example is prepared according to the following steps:

[0068] a1. The FePO4 precursor is mixed with lithium carbonate, glucose, PEG, etc. and sand-milled with H2O as the solvent, and A compound (titanium dioxide) is added thereto, wherein the molar ratio of the FePO4 precursor to lithium carbonate is 0.98:0.48, and the total amount of glucose and PEG added is 1.2%wt (the mass ratio of glucose to PEG is 0.85:1); a2. After sand-milling, granulation and drying are performed by spray drying; a3. After drying, sintering is performed under a N2 atmosphere, the sintering temperature is 650°C, and the sintering duration is 9h; a4. After sintering, airflow pulverization is performed, and the lithium iron phosphate cathode material is obtained.

[0069] In the preparation of the above lithium iron phosphate cathode material, the doping element A is Ti, and the amount of titanium dioxide added is calculated based on the content of Ti in the lithium iron phosphate cathode material being 4000ppm. The D50 of the lithium iron phosphate secondary particle size is 1.3μm, and the primary particle size is 0.1-1.2μm.

[0070] 2. Preparation of lithium supplement agent

[0071] The lithium supplement agent of the present example is prepared according to the following steps:

[0072] b1. The lithium source (lithium carbonate) and the nickel source (nickel chloride) are mixed and sand-milled, the molar ratio of the lithium source to the nickel source is 1.08:0.95, H2O is used as the solvent, and B compound (titanium dioxide) is added thereto, the additive being 12.5wt%; b2. After sand-milling, granulation and drying are performed by spray drying; b3. After drying, sintering is performed under a N2 atmosphere, the sintering temperature is 350°C, and the sintering duration is 6h; b4. After sintering, airflow pulverization is performed, and the LNO finished product is obtained.

[0073] The lithium supplement agent prepared above is LNO, the element B is Ti, and the chemical formula is Li3NiTiO4. The D50 of the LNO is 3.5μm.

[0074] 3. Preparation of silicon-based negative electrode material

[0075] The silicon-based negative electrode material used in this embodiment is a porous silicon material, and its preparation method comprises the following steps: c1. Selecting sucrose, pyrolyzing it to prepare a porous carbon skeleton; c2. Placing the porous carbon skeleton in a reactor, and under N2atmosphere, mixing glucose and silane at a molar ratio of 0.7:1.2 and then introducing them into the reactor to deposit, forming a silicon-carbon composite material precursor; c3. Ball milling the silicon-carbon composite material precursor with sucrose, and then high-temperature sintering (temperature 850°C, time 12h) to form the final porous silicon-carbon composite material. The porosity of the porous silicon material is 35%, and the D50 is 7μm.

[0076] 4. Preparation of the battery

[0077] (1) Preparation of the positive electrode sheet

[0078] Mixing the LFP and LNO prepared above with SP, CNT and PVDF in a mass ratio of 90:6:1:1:2 in NMP (N-methyl pyrrolidone) to obtain a positive electrode slurry, and then coating, rolling, slitting and the like to obtain a positive electrode sheet. The area density of the positive electrode sheet is 210g / m 2 , and the compacted density is 2.56g / cm 3 .

[0079] (2) Preparation of the negative electrode sheet

[0080] Mixing graphite, the silicon-based negative electrode material (porous silicon material) prepared above, SP, SBR and CMC in a mass ratio of 80:16:2:1:1 in water to obtain a negative electrode slurry, and then coating, rolling, slitting and the like to obtain a negative electrode sheet. The area density of the negative electrode sheet is 95g / m 2 , and the compacted density is 1.52g / cm 3 .

[0081] (3) Preparation of the battery

[0082] Assembling the positive and negative electrode sheets prepared above and the separator, and then injecting electrolyte under high-temperature negative pressure to obtain a square aluminum shell battery; the electrolyte used is 1M LiPF6, dimethyl carbonate (DMC) and ethylene carbonate (EC) at a mass ratio of 1:1.1.

[0083] Example 2

[0084] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0085] The difference between this embodiment and Example 1 in the preparation of lithium iron phosphate positive electrode material is that the doping element A is V, i.e. replacing titanium dioxide (Ti source) with V2O5 (V source), and the addition amount of V source is adjusted according to the content of V in the lithium iron phosphate positive electrode material, which is 4000ppm. The rest of the operations are the same as those of Example 1.

[0086] 2. Preparation of lithium supplement agent

[0087] The embodiment differs from embodiment 1 in that the element B is Al, i.e., the titanium dioxide (Ti source) is replaced by aluminum oxide (Al source) in the preparation of the lithium supplement agent, and the chemical formula of the prepared LNO is Li3NiAlO4. The amount of the Al source is adjusted according to the chemical formula. The rest of the operations are consistent with embodiment 1.

[0088] 3. Preparation of silicon-based negative electrode material

[0089] The preparation of the silicon-based negative electrode material in this embodiment is consistent with that in embodiment 1.

[0090] 4. Preparation of battery

[0091] The preparation of the positive electrode sheet, the negative electrode sheet, and the battery in this embodiment is consistent with that in embodiment 1.

[0092] Embodiment 3

[0093] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0094] The embodiment differs from embodiment 1 in that the doping element A is Nb and Al in the preparation of the lithium iron phosphate positive electrode material, i.e., the titanium dioxide (Ti source) is replaced by niobium dioxide and aluminum oxide (Nb source and Al source). The content of Nb and Al in the lithium iron phosphate positive electrode material is 1500 ppm and 1000 ppm, respectively, to adjust the amount of the Nb source and the Al source. The rest of the operations are consistent with embodiment 1.

[0095] 2. Preparation of lithium supplement agent

[0096] The embodiment differs from embodiment 1 in that the element B is Mg in the preparation of the lithium supplement agent, i.e., the titanium dioxide (Ti source) is replaced by magnesium oxide (Mg source), and the chemical formula of the prepared LNO is Li3NiMn2O5. The amount of the Mg source is adjusted according to the chemical formula. The rest of the operations are consistent with embodiment 1.

[0097] 3. Preparation of silicon-based negative electrode material

[0098] The preparation of the silicon-based negative electrode material in this embodiment is consistent with that in embodiment 1.

[0099] 4. Preparation of battery

[0100] The preparation of the positive electrode sheet, the negative electrode sheet, and the battery in this embodiment is consistent with that in embodiment 1.

[0101] Embodiment 4

[0102] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0103] The embodiment is different from embodiment 1 in the preparation process of the lithium iron phosphate positive electrode material in that the doping element A is Ti and V, that is, titanium dioxide (Ti source) is replaced by titanium dioxide and V2O5 (Ti source and V source), and the mass proportion of Ti and V in the lithium iron phosphate positive electrode material is 2000 ppm and 2000 ppm respectively. The addition amount of the Ti source and the V source is adjusted according to the mass proportion. The remaining operations are consistent with those of embodiment 1.

[0104] 2. Preparation of lithium supplement

[0105] The preparation of the lithium supplement in the embodiment is consistent with that of embodiment 1.

[0106] 3. Preparation of silicon-based negative electrode material

[0107] The preparation of the silicon-based negative electrode material in the embodiment is consistent with that of embodiment 1.

[0108] 4. Preparation of battery

[0109] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in the embodiment is consistent with that of embodiment 1.

[0110] Embodiment 5

[0111] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0112] The embodiment is different from embodiment 1 in the preparation process of the lithium iron phosphate positive electrode material in that the doping element A is Ti and Zn, that is, titanium dioxide (Ti source) is replaced by titanium dioxide and zinc oxide (Ti source and Zn source), and the content of Ti and Zn in the lithium iron phosphate positive electrode material is 2000 ppm and 2500 ppm respectively. The addition amount of the Ti source and the Zn source is adjusted. The remaining operations are consistent with those of embodiment 1.

[0113] 2. Preparation of lithium supplement

[0114] The preparation of the lithium supplement in the embodiment is consistent with that of embodiment 1.

[0115] 3. Preparation of silicon-based negative electrode material

[0116] The preparation of the silicon-based negative electrode material in the embodiment is consistent with that of embodiment 1.

[0117] 4. Preparation of battery

[0118] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in the embodiment is consistent with that of embodiment 1.

[0119] Embodiment 6

[0120] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0121] The embodiment is different from embodiment 1 in the preparation of lithium iron phosphate positive electrode material in that the doping element A is Ti and V, that is, titanium dioxide (Ti source) is replaced by titanium dioxide and V2O5 (Ti source and V source), and the mass proportion of Ti and V in the lithium iron phosphate positive electrode material is 3000 ppm and 3500 ppm respectively. The addition amount of Ti source and V source is adjusted according to the mass proportion. The remaining operations are consistent with embodiment 1.

[0122] 2. Preparation of lithium supplement agent

[0123] The embodiment is different from embodiment 1 in the preparation of lithium supplement agent in that the B element is Ti and Fe, that is, titanium dioxide (Ti source) is replaced by manganese dioxide (Mn source), and the chemical formula of the finally prepared LNO is Li3NiMnO5. The addition amount of Ti source and Fe source is adjusted according to the chemical formula. The remaining operations are consistent with embodiment 1.

[0124] 3. Preparation of silicon-based negative electrode material

[0125] The preparation of silicon-based negative electrode material in the embodiment is consistent with embodiment 1.

[0126] 4. Preparation of battery

[0127] The preparation of positive electrode sheet, negative electrode sheet and battery in the embodiment is consistent with embodiment 1.

[0128] Embodiment 7

[0129] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0130] The preparation of lithium iron phosphate positive electrode material in the embodiment is consistent with embodiment 1.

[0131] 2. Preparation of lithium supplement agent

[0132] The preparation of lithium supplement agent in the embodiment is consistent with embodiment 1.

[0133] 3. Preparation of silicon-based negative electrode material

[0134] In the preparation of the silicon-based negative electrode material in this embodiment, which is different from that in Embodiment 1, the silicon-based negative electrode material used is a hollow core-shell structure silicon-carbon material, and the specific preparation method comprises the following steps: d1. mixing silicon powder (silicon dioxide powder containing part of silicon element), expanded graphite, a surfactant (silicon dioxide surfactant), and a grinding agent (silicon dioxide grinding liquid) in a mass ratio of 45:40:5:10, and then performing ball milling to obtain a nano-silicon slurry; d2. mixing and dispersing the nano-silicon slurry obtained by ball milling with phenolic resin, an additive (lignin), a foaming agent (azo dimethylamide), and a dispersing agent (hydrolyzed polymaleic anhydride) in a mass ratio of 50:44:1.5:1.5:3, and forming a homogeneous dispersion liquid under high-speed stirring, and then performing spray drying on the homogeneous dispersion liquid under certain conditions to obtain nano-silicon / resin microspheres; d3. performing carbonization treatment on the obtained microspheres at 900°C under the protection of inert gas, which will cause the soluble resin to be converted into carbon material, and form a core-shell structure silicon-carbon material (Si@SiO2@C); d4. cooling the material after carbonization treatment to room temperature, sieving, and then using HF to etch the SiO2 shell layer and remove the internal SiO2, thereby forming a hollow core-shell structure. The D50 of the hollow core-shell structure silicon-carbon material is 7.5 μm.

[0135] 4. Preparation of the battery

[0136] In this embodiment, the preparation of the positive electrode sheet, the negative electrode sheet, and the battery is consistent with that in Embodiment 1.

[0137] Embodiment 8

[0138] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0139] In this embodiment, the preparation of the lithium iron phosphate positive electrode material is consistent with that in Embodiment 1.

[0140] 2. Preparation of lithium supplement agent

[0141] In this embodiment, the preparation of the lithium supplement agent is consistent with that in Embodiment 1.

[0142] 3. Preparation of silicon-based negative electrode material

[0143] In the preparation of the silicon-based negative electrode material in this embodiment, which is different from that in Embodiment 1, the silicon-based negative electrode material used is a complex of three-dimensional porous silicon material and hollow core-shell structure silicon-carbon material, and the mass ratio of the three-dimensional porous silicon material to the hollow core-shell structure silicon-carbon material is 1:1.2. The preparation methods of the three-dimensional porous silicon material and the hollow core-shell structure silicon-carbon material are respectively referred to Embodiment 1 and Embodiment 7.

[0144] 4. Preparation of the battery

[0145] In this embodiment, the preparation of the positive electrode sheet, the negative electrode sheet, and the battery is consistent with that in Embodiment 1.

[0146] Example 9

[0147] 1. Preparation of lithium iron phosphate cathode material (LFP)

[0148] The preparation of lithium iron phosphate cathode material in this example is consistent with that in Example 1.

[0149] 2. Preparation of lithium supplement agent

[0150] The preparation of lithium supplement agent in this example is consistent with that in Example 1.

[0151] 3. Preparation of silicon-based anode material

[0152] In the preparation of silicon-based anode material in this example, the difference from Example 1 is that the silicon-based anode material used is a yolk-shell structure silicon-carbon material, and the specific preparation method includes the following steps: e1. Silicon particles (metallic silicon particles), dispersing agent (polyvinylpyrrolidone), and soluble inorganic salt (sodium carbonate) are mixed uniformly in deionized water at a mass ratio of 30:5:65, heated to evaporate the solvent, and then filtered and dried after cooling; e2. The dried sample is mixed with a carbon source, carbonized at 700°C under N2 atmosphere, and then washed with deionized water and dried.

[0153] 4. Preparation of battery

[0154] The preparation of the positive electrode sheet, the negative electrode sheet, and the battery in this example is consistent with that in Example 1.

[0155] Example 10

[0156] 1. Preparation of lithium iron phosphate cathode material (LFP)

[0157] The preparation of lithium iron phosphate cathode material in this example is consistent with that in Example 1.

[0158] 2. Preparation of lithium supplement agent

[0159] The preparation of lithium supplement agent in this example is consistent with that in Example 1.

[0160] 3. Preparation of silicon-based anode material

[0161] In the preparation of silicon-based anode material in this example, the difference from Example 1 is that the silicon-based anode material used is SiO XClass C graphite structure silicon-carbon material, its specific preparation method comprises the following steps: f1. Silicon monoxide powder is heat treated at 950 DEG C under argon protection condition, and then furnace cooling is carried out to room temperature; f2. After cooling, silicon monoxide powder is added with carbon source (glucose or sucrose) deionized water, sand grinding is carried out, and nanoscale slurry is obtained, wherein the mass ratio of silicon oxide compound powder and carbon source is 1:1; f3. The obtained nanoscale slurry is carried out spray drying, wherein the inlet temperature of spray drying is 275 DEG C, and the outlet temperature is 120 DEG C, and spherical particle precursor is obtained; f4. The precursor is calcined at 700 DEG C for 7 hours under argon protection atmosphere, and then cooling is carried out to room temperature.

[0162] 4. Preparation of battery

[0163] The preparation of the positive sheet, the negative sheet and the battery in the embodiment is consistent with that in embodiment 1.

[0164] Embodiment 11

[0165] 1. Preparation of lithium iron phosphate positive material (LFP)

[0166] The embodiment is different from embodiment 1 in the process of preparing lithium iron phosphate positive material, and the sintering temperature is reduced to 550 DEG C, so that the secondary particle size D50 of the finally obtained lithium iron phosphate positive material is 0.4 μm, and the primary particle size is 0.1-1.0 μm. The rest of the operation is consistent with embodiment 1.

[0167] 2. Preparation of lithium supplement agent

[0168] The preparation of the lithium supplement agent in the embodiment is consistent with that in embodiment 1.

[0169] 3. Preparation of silicon-based negative material

[0170] The preparation of the silicon-based negative material in the embodiment is consistent with that in embodiment 1.

[0171] 4. Preparation of battery

[0172] The preparation of the positive sheet, the negative sheet and the battery in the embodiment is consistent with that in embodiment 1.

[0173] Embodiment 12

[0174] 1. Preparation of lithium iron phosphate positive material (LFP)

[0175] The preparation of the lithium iron phosphate positive material in the embodiment is consistent with that in embodiment 1.

[0176] 2. Preparation of lithium supplement agent

[0177] The preparation of the lithium supplement agent in the embodiment is consistent with that in embodiment 1.

[0178] The embodiment is different from embodiment 1 in the preparation of the lithium supplementing agent in that the sintering temperature is adjusted to 720 DEG C to make the D50 of the LNO positive electrode material finally obtained 16.5 μm. The rest is the same as embodiment 1.

[0179] 3. Preparation of silicon-based negative electrode material

[0180] The preparation of the silicon-based negative electrode material in the embodiment is the same as that in embodiment 1.

[0181] 4. Preparation of battery

[0182] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in the embodiment is the same as that in embodiment 1.

[0183] Embodiment 13

[0184] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0185] The embodiment is different from embodiment 1 in the preparation of the lithium iron phosphate positive electrode material in that the addition amount of the Ti source is adjusted to make the content of Ti in the lithium iron phosphate positive electrode material 250 ppm. The rest is the same as embodiment 1.

[0186] 2. Preparation of lithium supplementing agent

[0187] The preparation of the lithium supplementing agent in the embodiment is the same as that in embodiment 1.

[0188] 3. Preparation of silicon-based negative electrode material

[0189] The preparation of the silicon-based negative electrode material in the embodiment is the same as that in embodiment 1.

[0190] 4. Preparation of battery

[0191] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in the embodiment is the same as that in embodiment 1.

[0192] Embodiment 14

[0193] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0194] The embodiment is different from embodiment 1 in the preparation of the lithium iron phosphate positive electrode material in that the addition amount of the Ti source is adjusted to make the content of Ti in the lithium iron phosphate positive electrode material 10000 ppm. The rest is the same as embodiment 1.

[0195] 2. Preparation of lithium supplementing agent

[0196] The preparation of the lithium supplementing agent in the embodiment is the same as that in embodiment 1.

[0197] 3. Preparation of silicon-based negative electrode material

[0198] The preparation of the silicon-based negative electrode material in this example is consistent with that in Example 1.

[0199] 4. Preparation of the battery

[0200] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in this example is consistent with that in Example 1.

[0201] Example 15

[0202] 1. Preparation of the lithium iron phosphate positive electrode material (LFP)

[0203] The difference between this example and Example 1 in the preparation of the lithium iron phosphate positive electrode material is that the amount of the Ti source is adjusted so that the content of Ti in the lithium iron phosphate positive electrode material is 5000 ppm. The rest of the operations are consistent with those in Example 1.

[0204] 2. Preparation of the lithium supplement agent

[0205] The preparation of the lithium supplement agent in this example is consistent with that in Example 1.

[0206] 3. Preparation of the silicon-based negative electrode material

[0207] The preparation of the silicon-based negative electrode material in this example is consistent with that in Example 1.

[0208] 4. Preparation of the battery

[0209] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in this example is consistent with that in Example 1.

[0210] Example 16

[0211] 1. Preparation of the lithium iron phosphate positive electrode material (LFP)

[0212] The preparation of the lithium iron phosphate positive electrode material in this example is consistent with that in Example 1.

[0213] 2. Preparation of the lithium supplement agent

[0214] The preparation of the lithium supplement agent in this example is consistent with that in Example 1.

[0215] 3. Preparation of the silicon-based negative electrode material

[0216] The preparation of the silicon-based negative electrode material in this example is consistent with that in Example 1.

[0217] 4. Preparation of the battery

[0218] The difference between the preparation process of the positive plate in this embodiment and that in Embodiment 1 is that the proportions of the raw materials in the positive slurry are adjusted so that the mass proportion of the lithium supplement positive material in the total mass of the lithium iron phosphate positive material and the lithium supplement is 3%, and the mass ratio of LFP, LNO to SP, CNT and PVDF is 93:3:1:1:2. The remaining operations are the same as those in Embodiment 1.

[0219] The preparation of the negative plate and the battery in this embodiment is the same as that in Embodiment 1.

[0220] Embodiment 17

[0221] 1. Preparation of lithium iron phosphate positive material (LFP)

[0222] The preparation of the lithium iron phosphate positive material in this embodiment is the same as that in Embodiment 1.

[0223] 2. Preparation of lithium supplement

[0224] The preparation of the lithium supplement in this embodiment is the same as that in Embodiment 1.

[0225] 3. Preparation of silicon-based negative material

[0226] The preparation of the silicon-based negative material in this embodiment is the same as that in Embodiment 1.

[0227] 4. Preparation of battery

[0228] The difference between the preparation process of the positive plate in this embodiment and that in Embodiment 1 is that the proportions of the raw materials in the positive slurry are adjusted so that the mass proportion of the lithium supplement positive material in the total mass of the lithium iron phosphate positive material and the lithium supplement is 17.8%, and the mass ratio of LFP, LNO to SP, CNT and PVDF is 79:17:1:1:2. The remaining operations are the same as those in Embodiment 1.

[0229] The preparation of the negative plate and the battery in this embodiment is the same as that in Embodiment 1.

[0230] Embodiment 18

[0231] 1. Preparation of lithium iron phosphate positive material (LFP)

[0232] The preparation of the lithium iron phosphate positive material in this embodiment is the same as that in Embodiment 1.

[0233] 2. Preparation of lithium supplement

[0234] The preparation of the lithium supplement in this embodiment is the same as that in Embodiment 1.

[0235] 3. Preparation of silicon-based negative material

[0236] The preparation of the silicon-based negative material in this embodiment is the same as that in Embodiment 1.

[0237] 4. Preparation of the battery

[0238] The difference between this embodiment and embodiment 1 in the preparation of the negative electrode sheet is that the proportion of each raw material in the negative electrode slurry is adjusted so that the mass proportion of the silicon-based negative electrode material in the total mass of the carbon-based negative electrode material and the silicon-based negative electrode material is 8.3%, and the mass ratio of graphite, silicon-based negative electrode material (porous silicon material), SP, SBR, and CMC is 88:8:2:1:1. The remaining operations are consistent with embodiment 1.

[0239] The preparation of the positive electrode sheet and the battery in this embodiment is consistent with embodiment 1.

[0240] Example 19

[0241] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0242] The preparation of the lithium iron phosphate positive electrode material in this embodiment is consistent with embodiment 1.

[0243] 2. Preparation of lithium supplement agent

[0244] The preparation of the lithium supplement agent in this embodiment is consistent with embodiment 1.

[0245] 3. Preparation of silicon-based negative electrode material

[0246] The preparation of the silicon-based negative electrode material in this embodiment is consistent with embodiment 1.

[0247] 4. Preparation of the battery

[0248] The difference between this embodiment and embodiment 1 in the preparation of the negative electrode sheet is that the proportion of each raw material in the negative electrode slurry is adjusted so that the mass proportion of the silicon-based negative electrode material in the total mass of the carbon-based negative electrode material and the silicon-based negative electrode material is 40%, and the mass ratio of graphite, silicon-based negative electrode material (porous silicon material), SP, SBR, and CMC is 57.6%:38.4%:2%:1%:1%. The remaining operations are consistent with embodiment 1.

[0249] The preparation of the positive electrode sheet and the battery in this embodiment is consistent with embodiment 1.

[0250] Comparative Example 1

[0251] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0252] The preparation of the lithium iron phosphate positive electrode material in this comparative example is consistent with embodiment 1.

[0253] 2. Preparation of lithium supplement agent

[0254] No lithium supplement agent is prepared in this comparative example.

[0255] 3. Preparation of silicon-based negative electrode material

[0256] The preparation of the silicon-based negative electrode material in the present comparative example is consistent with that in Example 1.

[0257] 4. Preparation of battery

[0258] The present example is different from Example 1 in the preparation process of the positive electrode sheet in that only LFP is used as the positive electrode active material, and the input amount of LFP is the total mass of the input of LFP and LNO in Example 1. The remaining operations are consistent with those in Example 1.

[0259] The preparation of the negative electrode sheet and the battery in the present example is consistent with that in Example 1.

[0260] Comparative Example 2

[0261] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0262] In the preparation process of the lithium iron phosphate positive electrode material in the present comparative example, it is different from Example 1 in that no doping element A is added, i.e. no Ti source is added. The remaining operations are consistent with those in Example 1.

[0263] 2. Preparation of lithium supplement agent

[0264] The preparation of the lithium supplement agent in the present comparative example is consistent with that in Example 1.

[0265] 3. Preparation of silicon-based negative electrode material

[0266] The preparation of the silicon-based negative electrode material in the present comparative example is consistent with that in Example 1.

[0267] 4. Preparation of battery

[0268] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in the present example is consistent with that in Example 1.

[0269] Comparative Example 3

[0270] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0271] The preparation of the lithium iron phosphate positive electrode material in the present comparative example is consistent with that in Example 1.

[0272] 2. Preparation of lithium supplement agent

[0273] The preparation of the lithium supplement agent in the present comparative example is consistent with that in Example 1.

[0274] 3. Preparation of silicon-based negative electrode material

[0275] No silicon-based negative electrode material is prepared in the present comparative example.

[0276] 4. Preparation of battery

[0277] The difference between the preparation process of the negative electrode sheet in this example and Example 1 is that only graphite is used as the negative active material, and the input amount of the graphite is the total mass of the graphite and the silicon-based negative active material in Example 1. The remaining operations are consistent with Example 1.

[0278] The preparation of the positive electrode sheet and the battery in this example is consistent with Example 1.

[0279] Comparative Example 4

[0280] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0281] The preparation of lithium iron phosphate positive electrode material in this comparative example is consistent with Example 1.

[0282] 2. Preparation of lithium supplement agent

[0283] The preparation of lithium supplement agent in this comparative example is consistent with Example 1.

[0284] 3. Preparation of silicon-based negative electrode material

[0285] In the preparation process of the silicon-based negative electrode material in this comparative example, the sintering temperature and sintering time are adjusted to 750°C and 7h respectively, so that the porosity of the final obtained three-dimensional porous silicon material is 3.5% and the D50 is 4.8μm. The remaining operations are consistent with Example 1.

[0286] 4. Preparation of battery

[0287] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in this example is consistent with Example 1.

[0288] Comparative Example 5

[0289] 1. Preparation of lithium iron phosphate positive electrode material (LFP)

[0290] The preparation of lithium iron phosphate positive electrode material in this comparative example is consistent with Example 7.

[0291] 2. Preparation of lithium supplement agent

[0292] The preparation of lithium supplement agent in this comparative example is consistent with Example 7.

[0293] 3. Preparation of silicon-based negative electrode material

[0294] In the preparation process of the silicon-based negative electrode material in this comparative example, the carbonization temperature is increased to 1100°C, so that the D50 of the final obtained hollow core-shell structure silicon-carbon material is 17μm. The remaining operations are consistent with Example 7.

[0295] 4. Preparation of battery

[0296] The preparation of the positive electrode sheet, the negative electrode sheet and the battery in this embodiment is consistent with that in Embodiment 7.

[0297] Test Example

[0298] 1. Experimental construction

[0299] The batteries prepared in all the above examples and comparative examples were tested for energy density, cycle capacity retention rate and fast charging performance, and the specific testing methods were as follows:

[0300] (1) Energy density: the ratio of the rated energy of the battery to the weight of the battery. The rated energy of the battery was tested according to the following steps: constant current and constant voltage charging of the battery at 0.33C, and then discharging at 0.33C, and the discharging energy was the rated energy of the battery.

[0301] (2) Cycle capacity retention rate (long cycle): at 25℃, the ratio of the discharge capacity at 1C / 1C cycle for 4500 times to the maximum discharge capacity during the cycle.

[0302] (3) Fast charging performance: the battery was fully charged, and then discharged to 20% SOH, and the time required for charging to 80% SOH was recorded. The specific steps for full charging were as follows: 0.5C for 10%, 1C for 5%, 2C for 5%, 4.2C for 25%, 4C for 5%, 3.8C for 5%, 3.6C for 5%, 3.4C for 5%, 3.2C for 5%, 3C for 5%, 2.8C for 5%, 2.6C for 5%, 0.5C for 5%, 0.33C for 10%.

[0303] 2. Experimental results

[0304] The test results of the batteries prepared in all the above examples and comparative examples for energy density, cycle capacity retention rate and fast charging performance are shown in Table 1.

[0305] Table 1 Test results of the batteries prepared in examples and comparative examples

[0306]

[0307]

[0308] As can be seen from Table 1, the battery provided by the present application has better positive and negative electrode matching by optimizing the matching of positive and negative electrode materials, and the deintercalation of lithium ions is better balanced on the positive and negative electrode sides, which is conducive to the smooth transportation of lithium ions in the battery, thus effectively improving the energy density, cycle performance and fast charging performance of the lithium battery.

[0309] The positive electrode material in Comparative Example 1 does not contain a lithium supplement agent, and the lithium consumption of the negative electrode is more serious during the charge-discharge cycle and cannot be effectively compensated, resulting in a decrease in the cycle performance of the positive electrode material, and the Li + transportation performance and the electrical conductivity, resulting in a decrease in the fast-charging performance of the battery.

[0310] The lithium iron phosphate positive electrode material in Comparative Example 2 does not contain the doping element A, which is not conducive to widening the Li + transportation channels and increasing the Li + diffusion coefficient, and reducing the Li + transportation performance, so that the Li + is more difficult to be deintercalated during the charge-discharge cycle, and the doping element A is also not conducive to improving the electrical conductivity of the material, so the energy density, cycle performance and fast-charging performance of the battery all decrease.

[0311] The negative electrode material in Comparative Example 3 does not contain a silicon-based negative electrode material, so the energy density of the battery decreases significantly, and the cycle performance and fast-charging performance of the battery are also reduced due to the lack of the joint action of the silicon-based negative electrode material and the carbon-based negative electrode material.

[0312] The porosity of the porous silicon material in Comparative Example 4 is low, which is not conducive to the rapid transportation of lithium ions and also not conducive to relieving the volume expansion effect of the material itself, so the cycle performance and fast-charging performance of the battery decrease significantly.

[0313] The D50 of the hollow core-shell structure silicon-carbon material in Comparative Example 5 is large, which is not conducive to the infiltration of the electrolyte, so it is also not conducive to the transportation of lithium ions and the electrical conductivity, resulting in a decrease in the cycle performance and fast-charging performance of the battery.

[0314] Further comparison of Example 1 and Examples 2-6 shows that when the doping elements A or B elements are replaced by other types of elements, the battery still has a high energy density and cycle capacity retention rate, a short fast-charging time, and good comprehensive performance. Moreover, through further comparison, the battery in Example 6 has the best performance, which shows that when the doping element A is Ti and V and the B element is Mn, the performance of the lithium iron phosphate positive electrode material and the lithium supplement agent can be further improved, and a certain synergistic effect can be produced, which is more conducive to widening the Li + transportation channels, increasing the Li + diffusion coefficient, and further optimizing the material performance, thereby optimizing the cycle performance, fast-charging performance and energy density of the battery.

[0315] Comparing example 1 with examples 7-10, it can be seen that when other kinds of silicon-based negative electrode materials are replaced or matched, the battery also has higher energy density and cycle capacity retention rate, and the fast charging time is shorter, and the comprehensive performance of the battery is better. It can also be seen that when the silicon-based negative electrode material is a mixture of three-dimensional porous silicon material and hollow core-shell structure silicon-carbon material, the performance of the battery is better, which shows that the matching of the two kinds of silicon-based negative electrode materials is more conducive to the performance of the negative electrode and the performance of the battery.

[0316] Comparing example 1 with examples 11 and 12, the D50 of lithium iron phosphate in example 11 is too small, and the D50 of the lithium supplement agent in example 12 is too large, which leads to a decrease in the performance of the battery. This is because the D50 of lithium iron phosphate and the D50 of the lithium supplement agent will affect the overall performance of the positive electrode, and thus affect the related performance of the battery.

[0317] Comparing example 1 with examples 13-14, the doping amount of element A in the lithium iron phosphate positive electrode material in example 13 is too small, and the doping amount of element A in the lithium iron phosphate positive electrode material in example 14 is too large, which leads to a decrease in the related performance of the battery in examples 13 and 14. This shows that the content of element A has a certain influence on the performance of the positive electrode material, and further limiting the content of element A within a certain range is more conducive to the performance of the positive electrode material, and further optimizes the performance of the battery.

[0318] Comparing example 1 with examples 16-19, the mass proportion of the lithium supplement agent in the total mass of the lithium iron phosphate positive electrode material and the lithium supplement agent is smaller and larger in examples 16 and 17, respectively, and the mass proportion of the silicon-based negative electrode material in the total mass of the carbon-based negative electrode material and the silicon-based negative electrode material is smaller and larger in examples 18 and 19, respectively, which leads to a decrease in the related performance of the battery in examples 16-19. This shows that the content or proportion of each active material has a certain influence on the positive electrode or the negative electrode, and thus the performance of the battery is also affected.

[0319] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents, and these modifications or replacements are within the scope of protection of the present application.

Claims

1. A lithium battery, characterized in that: Including positive electrode plates and negative electrode plates; The positive electrode sheet includes a positive electrode active material layer, which includes lithium iron phosphate positive electrode material and a lithium replenishing agent; The lithium iron phosphate cathode material contains a doping element A, which includes Ti and V or Ti and Zn. The lithium supplement agent includes lithium-rich nickel oxide material, the chemical formula of which is Li. 2+x NiB y O 2+z x > 0, y > 0, z > 0 or z < 0; element B includes at least one of Ti, Al, Mg, Mn, and Fe; The negative electrode sheet includes a negative electrode active material layer, which includes a carbon-based negative electrode material and a silicon-based negative electrode material; The silicon-based anode material includes at least one of porous silicon material, core-shell silicon-carbon material, and silicon oxide / graphite structure silicon-carbon material. The D50 of the silicon-based anode material is 5–15 μm.

2. The lithium battery as described in claim 1, characterized in that: When the silicon-based anode material includes the porous silicon material, the porosity of the porous silicon material is 5-40%.

3. The lithium battery as described in claim 1, characterized in that: When the silicon-based anode material includes the core-shell structured silicon-carbon material, the core of the core-shell structured silicon-carbon material is nano-silicon powder and the outer shell is carbon material.

4. The lithium battery as described in claim 1, characterized in that: The lithium replenishing agent accounts for 0.5% to 20% of the total mass of the lithium iron phosphate cathode material and the lithium replenishing agent.

5. The lithium battery as described in claim 1, characterized in that: The silicon-based anode material accounts for 2% to 50% of the total mass of the carbon-based anode material and the silicon-based anode material.

6. The lithium battery as described in claim 1, characterized in that: The secondary particle size (D50) of the lithium iron phosphate cathode material is 0.5–3.5 μm, and the primary particle size is 0.1–2.0 μm. The lithium supplement has a D50 of 2–15 μm.

7. The lithium battery as described in claim 1, characterized in that: The doping amount of doping element A in the lithium iron phosphate cathode material is 300 to 9000 ppm.

8. The lithium battery as described in claim 1, characterized in that: The areal density of the positive electrode sheet is 150–350 g / m². 2 The compacted density is 2.35–2.70 g / cm³. 3 ; The areal density of the negative electrode sheet is 90–120 g / m². 2 The compacted density is 1.40–1.90 g / cm³. 3 .

9. The lithium battery as described in claim 1, characterized in that: The element B includes at least one of Al, Mn, and Mg.

10. The lithium battery as described in claim 1, characterized in that: The lithium-rich nickel oxide material has at least one chemical formula selected from Li3NiMnO4, Li3NiMgO4, Li3NiMn2O5, Li3NiMnO5, Li5NiMgO5, Li3NiMg2O5, and Li4NiAlO5.

11. The lithium battery as described in claim 1, characterized in that: The silicon-based anode material includes porous silicon material and core-shell silicon-carbon material; the mass ratio of the porous silicon material to the core-shell silicon-carbon material is 1:1 to 1.5.

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