High-energy-density lithium-ion battery

Abstract

Provided is a high-energy-density lithium-ion battery, comprising a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises a negative electrode active material. The positive electrode active material comprises a lithium iron phosphate material and a lithium-rich material, and the negative electrode active material comprises a graphite material and a silicon negative electrode material.

Description

High energy density lithium-ion batteries

[0001] This application claims priority to Chinese Patent Application No. 202411596853.6, filed with the Chinese Patent Office on November 8, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of lithium-ion battery technology, specifically relating to a high-energy-density lithium-ion battery. Background Technology

[0003] In recent years, with the gradual depletion of traditional fossil fuels and the increasingly serious problem of global warming, people have become more and more aware of the importance of new energy sources in the future society. Among all new energy systems, solar, wind, hydro, and nuclear energy do not have convenient mobility; while lithium-ion batteries, as a lightweight form of energy storage, have specific irreplaceable advantages in practical applications and are therefore widely used.

[0004] Lithium-ion batteries possess advantages such as high energy density, low self-discharge, long cycle life, and safety and environmental friendliness, making them widely used in consumer electronics, electric vehicles, power and communication energy storage, and other fields. Based on the different cathode materials, lithium-ion batteries can be classified into lithium cobalt oxide batteries, lithium manganese oxide batteries, ternary lithium batteries, and lithium iron phosphate batteries, corresponding to cathode materials such as lithium cobalt oxide (LiCoO2, LCO), lithium manganese oxide (LiMn2O4, LMO), ternary lithium nickel cobalt manganese oxide (NMC), ternary lithium nickel cobalt aluminum oxide (NCA), and lithium iron phosphate (LiFePO4, LFP). Among them, lithium cobalt oxide (LCO) has the highest charge and discharge voltage, but the price of its main element Co is relatively high, so it is mainly used in consumer electronics; spinel-type lithium manganese oxide (LMO) is relatively inexpensive, but its energy density and cycle life are slightly lower, so it is mainly used in electric two-wheelers; ternary lithium nickel cobalt manganese oxide (NMC) and ternary lithium nickel cobalt aluminum oxide (NCA) have higher energy densities and prices, so they are mainly used as power batteries for high-end passenger vehicles; lithium iron phosphate (LFP) cathode materials are widely used in passenger vehicle power batteries, commercial vehicle power batteries, and power & communication energy storage batteries due to their advantages such as stable structure, abundant reserves of main elements Fe & P, low price, ultra-long cycle life, and high safety.

[0005] However, the current energy density of the LFP-graphite system is already close to the upper limit of conventional battery design (180Wh / kg). Therefore, it is urgent to optimize the system to improve the upper limit of the energy density design of lithium iron phosphate batteries. Invention Overview

[0006] This application provides a high-energy-density lithium-ion battery, aiming to solve the problem of how to improve the energy density of lithium batteries while taking into account their rate performance and cycle performance.

[0007] This application provides a high-energy-density lithium-ion battery, including a positive electrode and a negative electrode. The positive electrode includes a positive active material layer, which includes a positive active material. The negative electrode includes a negative active material layer, which includes a negative active material.

[0008] The positive electrode active material includes lithium iron phosphate material and lithium-rich material, wherein the lithium-rich material accounts for 0.2% to 8% of the mass of the positive electrode active material;

[0009] The chemical formula of the lithium iron phosphate material LFP is Li 1+x Fe 1-y M y (PO4) 1+z , 0≤x≤0.1, 0≤y≤0.01, 0≤z≤0.04;

[0010] The M includes at least one of Ti, V, Zr, Nb, Mg, Mo, W, and Al;

[0011] The lithium-rich material includes at least one of LFO and LNO; wherein the chemical formula of the LFO is Li. 5+a Fe 1-b Z b O 4+c , 0≤a≤0.5, 0≤b≤0.01, 0≤c≤0.03; Z includes at least one of Ti, V, Zr, Nb, Mg, Mo, W, and Al;

[0012] The chemical formula of the LNO is Li 2+d Ni 1-e Y e O 2+f -0.5≤d≤0.5, e≥0, -0.5≤f≤0.5; the Y includes at least one of Ti, V, Al, Mg, Mn, and Fe;

[0013] The negative electrode active material includes graphite material and silicon negative electrode material, wherein the silicon negative electrode material accounts for 1% to 50% of the total mass of the negative electrode active material. Beneficial effects

[0014] The initial coulombic efficiency of lithium iron phosphate (LFP) is relatively high (generally above 96%), while the initial coulombic efficiency of the anode active material obtained by combining graphite and silicon anode materials is relatively low (generally below 90%). Therefore, the reversible specific capacity of lithium batteries is limited by the initial coulombic efficiency of the anode.

[0015] First, this application introduces lithium-rich materials into the positive electrode active material. The high specific capacity of the lithium-rich materials during the first charge can compensate for the consumption of active lithium caused by the formation of the SEI film at the negative electrode during the first charge, thereby increasing the amount of active lithium intercalation and deintercalation at the negative electrode during the discharge process. This achieves the effect of improving the reversible specific capacity of the lithium battery, and the energy density of the lithium battery reaches 200-280Wh / kg. Furthermore, since the lithium-rich materials in the positive electrode system can significantly improve the specific capacity of the positive electrode and greatly reduce the coating thickness or areal density of the positive electrode active material layer, and the silicon in the (graphite + silicon) negative electrode system can significantly improve the specific capacity of the negative electrode and greatly reduce the thickness or areal density of the negative electrode active material layer, the energy density of the lithium battery can be significantly improved by using the (LFP + lithium-rich material) positive electrode system combined with the (graphite + silicon) negative electrode system in this application.

[0016] At the same time, due to the significant reduction in the thickness and areal density of the positive and negative active material layers, the transport paths of electrons and lithium ions in the electrodes are shortened. This will effectively improve the kinetic performance of electron and lithium ion mass transfer, reduce the DC internal resistance (DCR) of the lithium battery, and thus help improve the energy efficiency, rate performance and low-temperature performance of the lithium battery.

[0017] Secondly, the lithium replenishment effect of lithium-rich materials can also improve the cycle life of lithium batteries to a certain extent. More importantly, the introduction of lithium-rich materials can change the SEI film composition and reduce the DC resistance (DCR) of lithium batteries, thereby improving the cycle life and energy efficiency of lithium batteries. Since the volume of lithium-rich materials shrinks by 20%-70% after the first charge and lithium insertion / extraction, while the volume of LFP remains basically unchanged (within 5%) after the first charge and lithium insertion / extraction, the volume shrinkage of lithium-rich materials will form a new porous structure in the positive electrode active material layer of the positive electrode sheet of this application. This will facilitate the full wetting and adsorption of electrolyte in the positive electrode sheet, improve the electrolyte retention capacity of the positive electrode sheet, effectively enhance the mass transfer kinetics of lithium ions in the electrode, and thus significantly improve the cycle life of lithium batteries.

[0018] Third, by doping elements in lithium iron phosphate materials and lithium-rich materials, the structural stability of lithium iron phosphate materials and lithium-rich materials can be improved respectively. Moreover, when the two are combined with silicon anodes, the rate performance of lithium batteries can be further improved.

[0019] Fourth, since the potential of silicon anode material to Li+ / Li during lithium intercalation is naturally higher than that of graphite material, the mixed potential of silicon anode material and graphite material is still higher than that of graphite material. Therefore, the potential of the (graphite + silicon) anode system in this application will not approach the lithium plating potential and cause lithium plating when charged at high rate. It is safer than a simple graphite anode when fast charging, giving the battery higher fast charging performance. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 shows the DCR value test results of lithium batteries in Embodiment 1, Comparative Example 1, and Comparative Example 3 of this application.

[0022] Figure 2 shows the cycle capacity performance test results of the lithium batteries in Embodiment 1, Comparative Example 1, and Comparative Example 3 of this application.

[0023] Figure 3 is a cross-sectional view of the positive electrode sheet in the lithium battery of Embodiment 1 of this application.

[0024] Figure 4 is a cross-sectional view of the positive electrode in the lithium battery of Comparative Example 1 of this application. Embodiments of the present invention

[0025] This application provides a high-energy-density lithium-ion battery, including a positive electrode and a negative electrode. The positive electrode includes a positive active material layer, which includes a positive active material. The negative electrode includes a negative active material layer, which includes a negative active material.

[0026] The positive electrode active material includes lithium iron phosphate material and lithium-rich material, wherein the lithium-rich material accounts for 0.2% to 8% of the mass of the positive electrode active material;

[0027] The chemical formula of the lithium iron phosphate material LFP is Li 1+x Fe 1-y M y (PO4) 1+z , 0≤x≤0.1, 0≤y≤0.01, 0≤z≤0.04;

[0028] The M includes at least one of Ti, V, Zr, Nb, Mg, Mo, W, and Al;

[0029] The lithium-rich material includes at least one of LFO and LNO; wherein the chemical formula of the LFO is Li. 5+a Fe 1-b Z b O 4+c , 0≤a≤0.5, 0≤b≤0.01, 0≤c≤0.03; Z includes at least one of Ti, V, Zr, Nb, Mg, Mo, W, and Al;

[0030] The chemical formula of the LNO is Li 2+d Ni 1-e Y e O 2+f -0.5≤d≤0.5, e≥0, -0.5≤f≤0.5; the Y includes at least one of Ti, V, Al, Mg, Mn, and Fe;

[0031] The negative electrode active material includes graphite material and silicon negative electrode material, wherein the silicon negative electrode material accounts for 1% to 50% of the total mass of the negative electrode active material.

[0032] The initial coulombic efficiency of lithium iron phosphate (LFP) is relatively high (generally above 96%), while the initial coulombic efficiency of the anode active material obtained by combining graphite and silicon anode materials is relatively low (generally below 90%). Therefore, the reversible specific capacity of lithium batteries is limited by the initial coulombic efficiency of the anode.

[0033] The beneficial effects of this application are:

[0034] First, this application introduces lithium-rich materials into the positive electrode active material. The high specific capacity of the lithium-rich materials during the first charge can compensate for the consumption of active lithium caused by the formation of the SEI film at the negative electrode during the first charge, thereby increasing the amount of active lithium intercalation and deintercalation at the negative electrode during the discharge process. This achieves the effect of improving the reversible specific capacity of the lithium battery, and the energy density of the lithium battery reaches 200-280 Wh / kg. Since the lithium-rich materials in the positive electrode system can significantly improve the specific capacity of the positive electrode and greatly reduce the coating thickness or areal density of the positive electrode active material layer, and the silicon in the (graphite + silicon) negative electrode system can significantly improve the specific capacity of the negative electrode and greatly reduce the thickness or areal density of the negative electrode active material layer, the combination of the above advantages, using the (LFP + lithium-rich material) positive electrode system and the (graphite + silicon) negative electrode system in this application can significantly improve the energy density of the lithium battery.

[0035] At the same time, due to the significant reduction in the thickness and areal density of the positive and negative active material layers, the transport paths of electrons and lithium ions in the electrodes are shortened. This will effectively improve the kinetic performance of electron and lithium ion mass transfer, reduce the DC internal resistance (DCR) of the lithium battery, and thus help improve the energy efficiency, rate performance and low-temperature performance of the lithium battery.

[0036] Secondly, the lithium replenishment effect of lithium-rich materials can also improve the cycle life of lithium batteries to a certain extent. More importantly, the introduction of lithium-rich materials can change the SEI film composition and reduce the DC resistance (DCR) of lithium batteries, thereby improving the cycle life and energy efficiency of lithium batteries. Since the volume of lithium-rich materials shrinks by 20% to 70% after the first charge and lithium insertion / extraction, while the volume of LFP remains basically unchanged after the first charge and lithium insertion / extraction (volume change within 5%), the volume shrinkage of lithium-rich materials will form a new porous structure in the positive electrode active material layer of the positive electrode sheet of this application. This will facilitate the full wetting and adsorption of electrolyte in the positive electrode sheet, improve the electrolyte retention capacity of the positive electrode sheet, effectively enhance the mass transfer kinetics of lithium ions in the electrode, and thus significantly improve the cycle life of lithium batteries.

[0037] Third, by doping elements in lithium iron phosphate materials and lithium-rich materials, the structural stability of lithium iron phosphate materials and lithium-rich materials can be improved respectively. Moreover, when the two are combined with silicon anodes, the rate performance of lithium batteries can be further improved.

[0038] Fourth, since the potential of silicon anode material to Li+ / Li during lithium intercalation is naturally higher than that of graphite material, the mixed potential of silicon anode material and graphite material is still higher than that of graphite material. Therefore, the potential of the (graphite + silicon) anode system in this application will not approach the lithium plating potential and cause lithium plating when charged at high rate. It is safer than a simple graphite anode when fast charging, giving the battery higher fast charging performance.

[0039] In some embodiments, the average primary particle size of the lithium iron phosphate material is 0.1–2 μm, and the average primary particle size of the lithium-rich material is 0.8–25 μm. Since the lithium-rich material undergoes volume shrinkage after the first charge and lithium insertion / extraction, with a maximum shrinkage of up to 60%, controlling the average primary particle size of the lithium-rich material allows for adjustment of the size of the new pore structure formed in the positive electrode active material layer. This results in a pore structure that is conducive to electrolyte wetting and has excellent liquid retention performance, thereby improving the mass transfer kinetics of lithium ions in the electrode, reducing liquid-phase ohmic polarization caused by the electrolyte, and consequently reducing the battery's DC internal resistance (DCR), which helps improve the battery's rate performance and cycle life.

[0040] In some embodiments, the doping amount of M in the lithium iron phosphate material is 500 to 8000 ppm, and / or the doping amount of Z in the lithium-rich material is 200 to 5000 ppm, and / or the doping amount of Y in the lithium-rich material is 200 to 5000 ppm.

[0041] In this embodiment, the lithium iron phosphate material is prepared by a method comprising the following steps:

[0042] The precursor is mixed with lithium carbonate and deionized water and then ground. A dopant source containing doping elements is added to the mixture to obtain a mixed slurry. The mixed slurry is then spray-dried and sintered in an inert atmosphere to obtain the lithium iron phosphate material.

[0043] The precursor includes iron phosphate; the doping source containing the doping element includes at least one of nano-titanium oxide, soluble organic titanium oxide, vanadium pentoxide, ammonium metavanadate, nano-zirconium oxide, niobium pentoxide, magnesium oxide, molybdenum oxide, tungsten oxide, and nano-alumina.

[0044] In this embodiment, the lithium-rich material is prepared using a method comprising the following steps:

[0045] The precursor is mixed with lithium carbonate and deionized water and then ground. A dopant source containing doping elements is added to the mixture to obtain a mixed slurry. The mixed slurry is then spray-dried and sintered in an inert atmosphere to obtain the lithium-rich material.

[0046] The precursor includes nickel phosphate; the doping source containing the doping element includes at least one of nano-titanium oxide, soluble organic titanium oxide, vanadium pentoxide, ammonium metavanadate, nano-zirconium oxide, niobium pentoxide, magnesium oxide, molybdenum oxide, tungsten oxide, nano-alumina, manganese oxide, and iron oxide.

[0047] In some embodiments, in the lithium iron phosphate material, M includes any two of Ti, V, and Nb.

[0048] In some embodiments, the lithium iron phosphate material has a Ti doping amount of 1000–2000 ppm, a V doping amount of 500–1000 ppm, and a Nb doping amount of 200–500 ppm.

[0049] By selecting the type of M and controlling the doping amount of the doping element, not only can the structural stability of lithium iron phosphate materials be improved, but also the rate performance of lithium iron phosphate materials can be enhanced.

[0050] In some embodiments, in the lithium-rich material, Z includes any two of Ti, V, and Nb, and Y includes any two of Ti, V, and Mg.

[0051] In some embodiments, the lithium-rich material has a Ti doping amount of 1000–2000 ppm, a V doping amount of 500–1000 ppm, a Nb doping amount of 200–500 ppm, and a Mg doping amount of 200–500 ppm.

[0052] By selecting the type of Z and controlling the doping amount of the doping element, not only can the structural stability of lithium-rich materials be improved, but also the stability of the combination of lithium-rich materials and lithium iron phosphate materials can be improved, which helps to improve the rate performance of lithium batteries.

[0053] Optionally, in some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent and a binder, wherein the mass ratio of the positive electrode active material, the positive electrode conductive agent and the binder is 95-100:0.5-1.5:1-3.

[0054] Optionally, in some embodiments, the positive conductive agent includes at least one of carbon nanotubes (CNTs) and conductive carbon black (SP); the binder includes polyvinylidene fluoride (PVDF).

[0055] In some embodiments, the average primary particle size of the silicon anode material is 0.05–0.5 μm, and the average primary particle size of the graphite material is 5–15 μm. The silicon anode material undergoes volume shrinkage after the first charge and lithium insertion / extraction. By controlling the average primary particle size of the silicon anode material and the graphite material, a suitable porous structure can be formed in the positive electrode active layer, creating a channel structure that facilitates electrolyte wetting and excellent liquid retention. Combined with the positive electrode sheet, this accelerates the transfer of lithium ions between the positive and negative electrodes without lithium plating, significantly improving the kinetic and cycle performance of the lithium battery.

[0056] Optionally, the silicon anode material includes at least one of monocrystalline silicon spherical particles, polycrystalline silicon spherical particles, amorphous silicon spherical particles, monocrystalline silicon-like spherical particles, polycrystalline silicon-like spherical particles, amorphous silicon-like spherical particles, monocrystalline silicon amorphous particles, polycrystalline silicon amorphous particles, and amorphous silicon amorphous particles.

[0057] In some embodiments, the silicon anode material accounts for 5% to 30% of the mass of the anode active material.

[0058] Optionally, in some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent, a thickener, and an adhesive, wherein the mass ratio of the negative electrode active material, the negative electrode conductive agent, the thickener, and the adhesive is 95-98:0.1-1.5:1-2:1-2.

[0059] The negative electrode conductive agent includes conductive carbon black SP; the thickener includes sodium carboxymethyl cellulose CMC; and the adhesive includes styrene-butadiene rubber SBR.

[0060] In some embodiments, the compaction density of the positive electrode is 2.2~2.81 g / cm³, and / or the compaction density of the negative electrode is 1.45~1.8 g / cm³. 3 .

[0061] Optionally, the lithium-ion battery in this application is applicable to button batteries, wound soft-pack batteries, stacked soft-pack batteries, wound square hard-shell batteries, stacked square hard-shell batteries, wound cylindrical batteries, etc.

[0062] Optionally, in some embodiments of this application, the lithium-ion battery is prepared using a method comprising the following steps:

[0063] 1. Preparation of positive electrode sheet

[0064] In the positive electrode slurry, the mass ratio of lithium iron phosphate (LFP), lithium-rich material, carbon nanotubes (CNT), conductive graphite (SP), and polyvinylidene fluoride (PVDF) is 96.0:1.5:0.5:0.5:2.0.

[0065] The first step involves mixing the positive electrode conductive agent with the first part of N-methylpyrrolidone (NMP) and stirring at a low speed of 2.0–5.0 m / s for 0.5–3 hours to obtain a positive electrode conductive slurry. The second step involves adding the positive electrode active material (obtained by mixing LFP and lithium-rich materials) sequentially (at least twice) to the above positive electrode conductive slurry, stirring at a low speed of 2.0–5.0 m / s for 0.5–3 hours. The third step involves continuing to stir at a speed of 10 m / s–25 m / s. The cathode slurry is obtained by high-speed stirring at a linear velocity of m / s for 0.5 to 3 hours. In the third step, polyvinylidene fluoride (PVDF) and the second part N-methylpyrrolidone (NMP) are mixed to obtain a gel, and the mixture is stirred at a linear velocity of 10 m / s to 25 m / s for 1 to 8 hours to obtain a premixed slurry. In the fifth step, N-methylpyrrolidone (NMP) is added to the above premixed slurry and the viscosity is adjusted to 5000 to 25000 mPa·s to obtain the cathode slurry.

[0066] The above-mentioned positive electrode slurry is coated on the two surfaces of carbon-coated aluminum foil (thickness of 10-15 μm) using a transfer coating machine or an extrusion coating machine. After drying, rolling and slitting, the positive electrode sheet (porosity of the positive electrode sheet is 23%-40%) is obtained.

[0067] 2. Preparation of negative electrode sheet

[0068] In the negative electrode slurry, the mass ratio of graphite material, silicon negative electrode material, conductive graphite SP, carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR is 96.0:1.5:0.5:0.5:2.0.

[0069] The first step involves adding the negative electrode active material (a mixture of graphite and silicon negative electrode materials) sequentially (at least twice) to deionized water to obtain a mixed slurry. The second step involves adding the negative electrode conductive agent (SP) to the mixed slurry and kneading it at a low linear speed of 2.0–5.0 m / s for 0.5–3 hours to obtain a conductive slurry. The third step involves adding the thickener (CMC) to the conductive slurry and stirring it at a low linear speed of 5–15 m / s for 0.5–3 hours to obtain a composite slurry. The fourth step involves adding the adhesive (SBR) to the composite slurry and stirring it at a linear speed of 5–20 m / s for 1–8 hours to obtain a premixed slurry. The fifth step involves adding deionized water to the premixed slurry and adjusting the viscosity to 3000–8000 mPa·s to obtain the negative electrode slurry.

[0070] The above-mentioned negative electrode slurry is coated on both surfaces of copper foil (thickness of 4.5-8 μm) using a transfer coating machine or an extrusion coating machine. After drying, rolling and slitting, the negative electrode sheet (porosity of negative electrode sheet is 22%-37%) is obtained.

[0071] 3. Lithium-ion battery manufacturing

[0072] (1) Winding: The positive electrode, separator, and negative electrode (the separator separates the positive and negative electrode, the negative electrode sandwiches the positive electrode, and the leads of the positive and negative electrodes are distributed on opposite sides) are stacked in sequence and wound manually or automatically / semi-automatically to obtain the core.

[0073] (2) Electrode welding: The aluminum electrode tabs are ultrasonically welded to the positive electrode lead-out end, and the nickel electrode tabs are ultrasonically welded to the negative electrode lead-out end. PET protective tape is applied to the welded joint.

[0074] (3) Baking: Place the above core in a vacuum environment and bake at 90-120°C for 8-24 hours to reduce the moisture content of each part of the core to below 400ppm (preferably below 300ppm).

[0075] (4) Inserting into the shell (sealing with aluminum-plastic film): Cut the aluminum-plastic film into rectangles of a certain length and width, tightly wrap the above core, and use a sealing machine to heat-seal the edges along the positive and negative electrode tabs, leaving the liquid injection port on the side;

[0076] (5) Electrolyte injection: Inject an appropriate amount of electrolyte into the aluminum-plastic encapsulation shell, wherein the electrolyte composition is 1.0M LiPF6+EC / EMC / DEC+VC / FEC / DTD and other additives;

[0077] (6) Vacuum settling: After the core is injected with electrolyte, it is placed in a vacuum chamber and vacuumed to maintain a negative pressure for 0.5 to 2 hours so that the positive / negative electrode plates and the diaphragm can be completely wetted with electrolyte;

[0078] (7) Sealing: The last opening of the aluminum-plastic packaging bag is sealed with a sealing machine. A distance is left between the sealing point and the core to facilitate the storage of a small amount of gas generated by the battery after subsequent formation (i.e., the so-called "gas bag").

[0079] (12) Settling: Place the sealed battery in a 45±5℃ incubator and let it stand for 24 to 48 hours to allow the electrolyte to fully wet the pores of the positive and negative electrodes and the separator again.

[0080] (13) Fixture formation: The lithium battery is clamped and charged by applying a certain current to the battery at a temperature of 45±5℃ through the formation cabinet. The battery is charged to 20%SOC~70%SOC, so that the negative electrode and the electrolyte form an SEI film, and at the same time a portion of gaseous byproducts are generated.

[0081] (14) Vacuuming: Use a vacuum pumping device to puncture the gas bag and then draw a vacuum to remove the by-product gas generated during the formation stage.

[0082] (15) Sealing: Use a sealing machine to heat-seal the part near the core and cut off the air bag to make a complete battery cell;

[0083] (16) High temperature aging: After sealing, the battery is left to stand at 45±5℃ for 12 to 72 hours to make the SEI film formed on the negative electrode surface more stable.

[0084] (17) Capacity grading: Charge the battery to 3.65V with a constant current of 0.5C and maintain a constant voltage at 3.65V until the current decreases to below 0.05C and charging is stopped; after standing for 5 to 30 minutes, discharge the battery to 2.5V with a constant current of 0.2C; then the initial coulombic efficiency = capacity grading discharge capacity / (formation charging capacity + capacity grading continued charging capacity); charge the battery to a specific state of charge (20%SOC to 50%SOC) with a constant current of 0.5C and store at 25°C;

[0085] (18) OCV test: Before storing at 25℃, test the open circuit voltage of the battery and record it as OCV1; after storing at 25℃ for a period of time t (24~72h), test the open circuit voltage of the battery again and record it as OCV2; then the battery self-discharge K value = (OCV1~OCV2) / t. Qualified lithium batteries are screened by K value, and batteries with excessively high K value are downgraded or scrapped.

[0086] The preparation process of the positive and negative electrode sheets in this application is very simple. It can adopt the slurrying, coating, drying, rolling, and slitting / sheet making processes commonly used in the industrial production of lithium-ion batteries. This can effectively ensure the scalable manufacturability and cost control of the positive and negative electrode sheets, and has excellent economic value.

[0087] Optionally, the base film includes at least one of polyethylene (PE) and polypropylene (PP); the thickness of the base film is 5–20 μm, and the porosity is 0.4–0.6.

[0088] Optionally, a coating layer is provided on at least one surface of the base film, the coating layer having a thickness of 1–4 μm; the coating layer comprises particulate adhesive and ceramic powder, the particulate adhesive comprising at least one of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and polyacrylic acid (PAA), the particulate adhesive having a particle size of 0.5–4 μm; the ceramic powder comprising at least one of boehmite powder and alumina powder, the ceramic powder having a particle size of 0.5–1 μm.

[0089] Optionally, the electrolyte includes a lithium salt, a solvent, and an additive, wherein the solvent includes at least one of ethylene carbonate EC, diethylene carbonate DEC, ethyl methyl carbonate EMC, dimethyl carbonate DMC, propylene carbonate PC, and methyl acetate MA.

[0090] The lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), and lithium di(fluorooxalateborate)borate (LiODFB).

[0091] The additives include, but are not limited to, at least one of the following: vinylene carbonate (VC), ethylene ethylene carbonate (VEC), propylene sulfite (PS), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), dimethyl sulfate (DMS), diethyl oxalate (DEP), trimethyl borate (TMB), fluorobenzene (FB), biphenyl (BP), and phenylcyclohexane (CHB).

[0092] Optionally, the lithium battery further includes encapsulation material; the encapsulation material includes any one of aluminum-plastic film, steel shell, aluminum shell, and aluminum alloy shell.

[0093] Example 1

[0094] Lithium-ion batteries are prepared using a method comprising the following steps:

[0095] 1. Preparation of positive electrode sheet

[0096] In the cathode slurry, lithium iron phosphate (LFP) material... 1.05 Fe 0.995 M 0.005 (PO4) 1.02 Where M represents Ti and V, with Ti doping at 1500 ppm and V doping at 700 ppm, and lithium-rich material LFO (Li 5.3 Fe 0.995 Z 0.005 O 4.02Where Z represents Ti and Nb, with Ti doping amount of 1000ppm and Nb doping amount of 500ppm, and the mass ratio of carbon nanotubes (CNT), conductive graphite (SP), and polyvinylidene fluoride (PVDF) is 96.0:1.5:0.5:0.5:2.0.

[0097] The first step involves mixing the positive electrode conductive agent with the first part of N-methylpyrrolidone (NMP) and stirring at a low linear speed of 3 m / s for 2 hours to obtain a positive electrode conductive slurry. The second step involves adding the positive electrode active material (a mixture of LFP and LFO) sequentially (at least twice) to the above positive electrode conductive slurry and stirring at a low linear speed of 3 m / s for 2 hours. The third step involves continuing to stir at a high linear speed of 15 m / s for 2 hours to obtain a positive electrode mixed slurry. The fourth step involves mixing polyvinylidene fluoride (PVDF) with the second part of N-methylpyrrolidone (NMP) to obtain a gel solution and stirring at a high linear speed of 16 m / s for 4 hours to obtain a premixed slurry. The fifth step involves adding N-methylpyrrolidone (NMP) to the above premixed slurry and adjusting the viscosity to 15000 mPa·s to obtain the positive electrode slurry.

[0098] Using a transfer coating machine, the above positive electrode slurry is coated on both surfaces of carbon-coated aluminum foil (the thickness of the aluminum foil is 12μm). After drying, rolling and cutting, the positive electrode sheet (the porosity of the positive electrode sheet is 32%) is obtained.

[0099] 2. Preparation of negative electrode sheet

[0100] In the negative electrode slurry, the mass ratio of graphite material, silicon negative electrode material, conductive graphite SP, carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR is 96.0:1.5:0.5:0.5:2.0.

[0101] The first step involves adding the negative electrode active material (a mixture of graphite and silicon negative electrode materials) sequentially (at least twice) to deionized water to obtain a mixed slurry. The second step involves adding the negative electrode conductive agent (SP) to the mixed slurry and kneading it at a low linear speed of 4 m / s for 1 hour to obtain a conductive slurry. The third step involves adding the thickener (CMC) to the conductive slurry and stirring it at a low linear speed of 10 m / s for 2 hours to obtain a composite slurry. The fourth step involves adding the adhesive (SBR) to the composite slurry and stirring it at a linear speed of 12 m / s for 4 hours to obtain a premixed slurry. The fifth step involves adding deionized water to the premixed slurry and adjusting the viscosity to 6000 mPa·s to obtain the negative electrode slurry.

[0102] Using a transfer coating machine, the above-mentioned negative electrode slurry is coated on both surfaces of a copper foil (5μm thick). After drying, rolling, and slitting, the negative electrode sheet (with a porosity of 30%) is obtained.

[0103] 3. Lithium-ion battery manufacturing

[0104] (1) Winding: The above-mentioned positive electrode sheet, base film, and negative electrode sheet (the base film separates the positive and negative electrode sheets, the negative electrode sheet sandwiches the positive electrode sheet, and the leads of the positive and negative electrode tabs are distributed on opposite sides) are stacked in sequence and wound manually or automatically / semi-automatically to obtain a core; wherein, a coating layer is provided on the surface of the base film, and the thickness of the coating layer is 2μm; the coating layer includes polyvinylidene fluoride PVDF (particle size of 0.5~4μm) and boehmite powder (particle size of 0.5~1μm).

[0105] (2) Electrode welding: The aluminum electrode tabs are ultrasonically welded to the positive electrode lead-out end, and the nickel electrode tabs are ultrasonically welded to the negative electrode lead-out end. PET protective tape is applied to the welded joint.

[0106] (3) Baking: Place the above core in a vacuum environment and bake at 100°C for 16 hours to reduce the moisture content of each part of the core to below 400ppm;

[0107] (4) Inserting into the shell (sealing with aluminum-plastic film): Cut the aluminum-plastic film into rectangles of a certain length and width, tightly wrap the above core, and use a sealing machine to heat-seal the edges along the positive and negative electrode tabs, leaving the liquid injection port on the side;

[0108] (5) Electrolyte injection: Inject an appropriate amount of electrolyte into the aluminum-plastic encapsulation shell, wherein the electrolyte composition is 1.0M LiPF6+EC / EMC / DEC+VC / FEC / DTD and other additives;

[0109] (6) Vacuum settling: After the core is injected with electrolyte, it is placed in a vacuum chamber and vacuumed to maintain negative pressure for 1 hour so that the positive / negative electrode plates and the diaphragm can be completely wetted with electrolyte.

[0110] (7) Sealing: The last opening of the aluminum-plastic packaging bag is sealed with a sealing machine. A distance is left between the sealing point and the core to facilitate the storage of a small amount of gas generated by the battery after subsequent formation (i.e., the so-called "gas bag").

[0111] (12) Settling: Place the sealed battery in a 45±5℃ incubator and let it stand for 36 hours to allow the electrolyte to fully wet the pores of the positive and negative electrodes and the separator again.

[0112] (13) Fixture formation: The lithium battery is clamped and charged by applying a certain current to the battery at a temperature of 45±5℃ through the formation cabinet. The battery is charged to 50% SOC, so that the negative electrode reacts with the electrolyte to produce an SEI film, and at the same time, some gaseous byproducts are generated.

[0113] (14) Vacuuming: Use a vacuum pumping device to puncture the gas bag and then draw a vacuum to remove the by-product gas generated during the formation stage.

[0114] (15) Sealing: Use a sealing machine to heat-seal the part near the core and cut off the air bag to make a complete battery cell;

[0115] (16) High temperature aging: The sealed battery is left to stand at 45±5℃ for 45h to make the SEI film formed on the negative electrode surface more stable.

[0116] (17) Capacity grading: Charge the battery to 3.65V with a constant current at a rate of 0.5C, and maintain a constant voltage at 3.65V until the current decreases to below 0.05C and charging is stopped; after standing for 20 minutes, discharge the battery to 2.5V with a constant current at a rate of 0.2C; then the initial coulombic efficiency = capacity grading discharge capacity / (formation charging capacity + capacity grading continued charging capacity); charge the battery to a specific state of charge (40% SOC) with a constant current of 0.5C, and store it at 25℃;

[0117] (18) OCV test: Before storing at 25℃, test the open circuit voltage of the battery and record it as OCV1; after storing at 25℃ for a period of time t (24~72h), test the open circuit voltage of the battery again and record it as OCV2; then the self-discharge K value of the lithium battery = (OCV1-OCV2) / t. Qualified lithium batteries are screened by K value, and batteries with excessively high K value are downgraded or scrapped.

[0118] The DCR value test diagram and cycle capacity performance test diagram of the lithium battery in this embodiment are shown in Figures 1 and 2, respectively; the cross-sectional view of the positive electrode of the lithium battery in this embodiment is shown in Figure 3.

[0119] Example 2

[0120] The difference between this embodiment and Embodiment 1 is that the mass ratio of LFP, LFO, CNT, SP, and PVDF in the positive electrode slurry is 95.0:2.5:0.5:0.5:2.0; all other steps and parameter settings are consistent with Embodiment 1.

[0121] Example 3

[0122] The difference between this embodiment and Embodiment 1 is that the mass ratio of LFP, LFO, CNT, SP, and PVDF in the positive electrode slurry is 91.0:6.5:0.5:0.5:2.0; all other steps and parameter settings are consistent with Embodiment 1.

[0123] Example 4

[0124] The difference between this embodiment and Embodiment 1 is that the mass ratio of graphite material, silicon anode material, SP, CMC, and SBR in the anode slurry is 91.0:6.5:0.5:0.5:2.0; all other steps and parameter settings are consistent with Embodiment 1.

[0125] Example 5

[0126] The difference between this embodiment and Embodiment 1 is that the mass ratio of graphite material, silicon anode material, SP, CMC, and SBR in the anode slurry is 86.0:10.5:0.5:1.5:1.5; all other steps and parameter settings are consistent with Embodiment 1.

[0127] Example 6

[0128] The difference between this embodiment and Embodiment 1 is that the positive electrode active material used in the positive electrode slurry is lithium iron phosphate (LFP). 0.999 M 0.001 (PO4) 1.04 Where M represents Ti and Nb, with Ti doping at 1000 ppm and Nb doping at 200 ppm, and lithium-rich material LFO (Li5Fe 0.09 Z 0.01 O 4.03 (where Z represents Ti and V, with Ti doping at 2000 ppm and V doping at 1000 ppm); other steps and parameter settings are consistent with those in Example 1.

[0129] Example 7

[0130] The difference between this embodiment and Embodiment 1 is that the positive electrode active materials used in the positive electrode slurry are lithium iron phosphate material LFP (Li1.01Fe0.99M0.01(PO4)1.01, where M represents V and Nb, with V doping amount of 1000ppm and Nb doping amount of 500ppm) and lithium-rich material LFO (Li5.5Fe0.99Z0.01O4.3, where Z represents V and Nb, with V doping amount of 500ppm and Nb doping amount of 200ppm); other steps and parameter settings are consistent with Embodiment 1.

[0131] Example 8

[0132] The difference between this embodiment and Embodiment 1 is that the lithium-rich material is LNO (Li2.2Ni0.95Y0.05O2.1, where Y is V and Mg, with V doping amount of 500ppm and Mg doping amount of 200ppm); other steps and parameter settings are consistent with Embodiment 1.

[0133] Example 9

[0134] The difference between this embodiment and Embodiment 1 is that the average primary particle size of the lithium-rich material LFO is 0.5 μm, and the average primary particle size of the lithium iron phosphate material is 3 μm; the other steps and parameter settings are consistent with Embodiment 1.

[0135] Example 10

[0136] The difference between this embodiment and Embodiment 1 is that the compaction density of the positive electrode is 3 g / cm3; all other steps and parameter settings are consistent with Embodiment 1.

[0137] Example 11

[0138] The difference between this embodiment and Embodiment 1 is that the average primary particle size of the silicon anode material is 1.5 μm and the average primary particle size of the graphite material is 30 μm; the other steps and parameter settings are consistent with Embodiment 1.

[0139] Example 12

[0140] The difference between this embodiment and Embodiment 1 is that the compaction density of the negative electrode sheet is 2 g / cm3; all other steps and parameter settings are consistent with Embodiment 1.

[0141] Comparative Example 1

[0142] The difference between this embodiment and Embodiment 1 is that the positive electrode active material does not contain lithium-rich materials, and the negative electrode active material does not contain silicon negative electrode materials.

[0143] Specifically, in the positive electrode slurry, the mass ratio of LFP, CNT, SP, and PVDF is 97.0:0.5:0.5:2.0; in the negative electrode slurry, the mass ratio of graphite, SP, CMC, and SBR is 96.5:0.5:1.5:1.5.

[0144] All other steps and parameter settings are consistent with those in Example 1.

[0145] The DCR value test chart and cycle capacity performance test chart of the lithium battery in this comparative example are shown in Figure 1 and Figure 2, respectively; the cross-sectional view of the positive electrode of the lithium battery in this comparative example is shown in Figure 4.

[0146] Comparative Example 2

[0147] The difference between this embodiment and Embodiment 1 is that the positive electrode active material does not contain lithium-rich materials. Specifically, the mass ratio of LFP, CNT, SP, and PVDF in the positive electrode slurry is 97.0:0.5:0.5:2.0; other steps and parameter settings are consistent with Embodiment 1.

[0148] Comparative Example 3

[0149] The difference between this embodiment and Embodiment 1 is that the negative electrode active material does not contain silicon negative electrode material. Specifically, the mass ratio of graphite, SP, CMC, and SBR in the negative electrode slurry is 96.5:0.5:1.5:1.5; other steps and parameter settings are consistent with Embodiment 1.

[0150] The DCR value test chart and cycle capacity performance test chart of the lithium battery in this comparative example are shown in Figure 1 and Figure 2, respectively.

[0151] Comparative Example 4

[0152] The difference between this comparative example and Example 1 is that neither the lithium iron phosphate material nor the lithium-rich material contains any doping elements; all other steps and parameter settings are consistent with Example 1.

[0153] Test methods

[0154] I. Energy Density Test

[0155] The energy density of the lithium batteries in the above embodiments and comparative examples was tested. The specific test method was as follows: the weight of the lithium battery was weighed and recorded as m; the battery was placed in a fixture and a force of 3000N was applied. The single cell was charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 3.65V until the current dropped to 0.05C; it was left to rest for 30 minutes, and then discharged at a constant current of 0.33C to 2.5V, and left to rest for 30 minutes. This cycle was repeated 3 times. The discharge capacity (in Ah) and energy E (average of three cycles) were calculated. The discharge energy density = E / m (in Wh / kg).

[0156] II. Electrode Capacitance Testing

[0157] The electrode sheets in the above embodiments and comparative examples were subjected to the first charge-discharge specific capacity test. The specific test method was as follows: For the first charge specific capacity test of the positive electrode, one side of the positive electrode sheet was wiped with a wet cloth until the foil was exposed. After drying the electrode sheet, it was punched with a punching machine and weighed. The mass was recorded as m1. In addition, the foil was punched with a punching machine and weighed. The mass was recorded as m2. Then the coating mass m3 = m1 - m2. The punched electrode sheet was taken and made into a button cell together with lithium sheet, electrolyte and separator. The button cell was placed on the Blue Battery Test Cabinet for testing. The test steps were as follows: Charged at a constant current of 0.1C to 3.75V, then charged at a constant voltage of 3.75V until the current dropped to 0.05C and cut off. The charging capacity was recorded as q1. The initial charge capacity of the positive electrode was then calculated as q1 / (m1 × percentage of active material in the positive electrode coating). After standing for 10 minutes, the battery was discharged at a constant current of 0.1C to 2.0V and cut off. The discharge capacity was recorded as q2. The initial discharge capacity of the positive electrode was then calculated as q2 / (m1 × percentage of active material in the positive electrode coating).

[0158] The test process for the specific capacity of the negative electrode during the first charge is basically the same as that for the coin cell and the positive electrode. The mass of the negative electrode sheet is m4, the mass of the copper foil is m5, and the mass of the negative electrode coating is m6. The test steps are as follows: charge at a constant current of 0.1C to 0.005V and record the first charge capacity as q3. Then the specific capacity of the negative electrode during the first charge = q3 / (m1 × the proportion of active material in the negative electrode coating); discharge at 0.1C to 0.5V and record the first discharge capacity as q4. Then the specific capacity of the negative electrode during the first discharge = q4 / (m1 × the proportion of active material in the negative electrode coating).

[0159] III. Ratio Performance Test

[0160] The lithium batteries in the above embodiments and comparative examples were subjected to rate performance testing. The specific testing method was as follows: the lithium batteries were pretreated at 25±2℃, with the following steps: constant current and constant voltage charging at 0.5C, cutoff voltage 3.65V, cutoff current 0.05C; resting for 5 minutes; resting for 5 minutes; constant current discharging at 0.5C, cutoff voltage 2.5V; after 13 cycles, a 0.1C charge-discharge cycle was performed once. The capacity of the last 0.1C discharge was taken as the initial capacity and recorded as Q0.

[0161] Test the capacity retention rate at 1C rate: The battery is fully charged at 0.5C constant current and constant voltage with a cutoff voltage of 3.65V, and then discharged at 1C rate constant current. The discharge capacity Q1 of the battery is recorded, and the 1C capacity retention rate is calculated as Q1 / Q0×100%.

[0162] IV. Cyclic Performance Testing

[0163] The lithium batteries in the above embodiments and comparative examples were subjected to cycle performance tests. The specific test method was as follows: based on 25°C and a voltage range of 2.5 to 3.65V, the prepared batteries were charged and discharged at a 1C rate. During the charging process, the batteries were charged at a constant current of 1C to 3.65V, and then charged at a constant voltage of 3.65V until the current dropped to 0.05C cutoff. During the discharging process, the batteries were discharged at a constant current of 1C to 2.5V cutoff. After 1000 cycles, the cycle capacity retention rate was recorded.

[0164] V. DC Internal Resistance Test

[0165] The DC internal resistance of the lithium batteries in the above embodiments and comparative examples was tested. The specific test method was as follows: at 25°C, the batteries of the embodiments and comparative examples were charged to 95% SOC and discharged at a current of 1C rate for 10s. The battery voltage U1 and current I before discharge and the battery voltage U2 after 10s of discharge were recorded. The DC internal resistance DCR was calculated according to the formula R=(U1-U2) / I.

[0166] Table 1

[0167] Serial Number | Energy Density / Wh.kg⁻¹ | Positive Electrode Reversible Capacity / mAh.g⁻¹ | Positive Electrode First Charge Capacity / mAh.g⁻¹ | Negative Electrode First Charge Capacity / mAh.g⁻¹ | Rate Performance (1C Capacity Retention) | Capacity Retention after 1000 Cycles | Example 1 | 193 | 149.7 | 166.3 | 403 | 96.0% | 93.0% | Example 2 | 200 | 155.3 | 172.5 | 403 | 96.8 93.5% Example 3 228 177.3 197.0 403 98.4% 94.0% Example 4 195 149.7 166.3 417.5 96.3% 92.6% Example 5 205 149.7 166.3 490 97.1% 92.0% Example 6 193 149.7 166.3 403 95.5% 92.8% Example 7 193 149.7 166 .340395.0% 92.7% Example 8 191148164.4 40395.8% 93.2% Example 9 189146.7 166.3 40394.5% 90.5% Example 10 191147.5 166.3 40392.7% 89.0% Example 11 190149.7 166.3 39592.1% 92.3% Example 12 192 149.7 166.3 399 91.6% 88.6% Comparative Example 1 180 145.0 161.0 350 94.0% 90.0% Comparative Example 2 188 145.0 161.0 403 94.8% 91.0% Comparative Example 3 185 149.7 166.3 350 94.3% 91.5% Comparative Example 4 193 149.7 166.3 403 94.9% 92.5%

[0168] Based on Examples 1-8, Comparative Examples 1-4, and Table 1, it can be seen that by using lithium iron phosphate and lithium-rich materials as positive electrode active materials, and graphite and silicon anode materials in combination as negative electrode active materials, and by doping the lithium iron phosphate and lithium-rich materials with appropriate elements, the energy density, rate performance, and low-temperature performance of lithium batteries can be significantly improved. Furthermore, the combination of lithium iron phosphate and lithium-rich materials can form a porous structure in the positive electrode active material layer that facilitates lithium-ion and electron transport, which is beneficial to improving the cycle performance of the electrolyte for lithium batteries. Finally, the combination of positive and negative electrode active materials in this application can significantly improve the charge and discharge safety performance of lithium batteries.

[0169] Based on Examples 1, 9-10, and Table 1, it can be seen that by controlling the average primary particle size of the lithium-rich material in the positive electrode active material to be greater than that of the lithium iron phosphate material, the size of the pore structure formed in the positive electrode active material layer can be adjusted, thereby adjusting the positive electrode sheet to obtain a suitable areal density and forming a pore structure that is conducive to electrolyte wetting and excellent liquid retention performance. Furthermore, the combination of the two types of positive electrode active materials helps to improve the compaction density of the positive electrode sheet. The combined effect of these factors can improve the mass transfer kinetics performance in the electrode, reduce the liquid phase ohmic polarization caused by the electrolyte, and thus reduce the DC internal resistance (DCR) of the battery, which helps to improve the rate performance, cycle life, and energy density of the battery.

[0170] Based on Examples 1, 11-12 and Table 1, it can be seen that by controlling the average primary particle size of the silicon anode material and the average primary particle size of the graphite material in the anode active material, not only can the anode sheet obtain a compaction density range that has a good matching effect with the cathode sheet, but also a layer of anode active material with a suitable pore structure can be formed, avoiding lithium plating during the charging and discharging process of the lithium battery. When combined with the cathode sheet, it can significantly improve the dynamic performance and cycle performance of the lithium battery.

Claims

1. A high-energy-density lithium-ion battery, comprising: A positive electrode and a negative electrode, wherein the positive electrode includes a positive active material layer, the positive active material layer includes a positive active material, and the negative electrode includes a negative active material layer, the negative active material layer includes a negative active material; The positive electrode active material includes lithium iron phosphate material and lithium-rich material, wherein the lithium-rich material accounts for 0.2% to 8% of the mass of the positive electrode active material; The chemical formula of the lithium iron phosphate material LFP is Li 1+x Fe 1-y M y (PO4) 1+z , 0≤x≤0.1, 0≤y≤0.01, 0≤z≤0.04; The M includes at least one of Ti, V, Zr, Nb, Mg, Mo, W, and Al; The lithium-rich material includes at least one of LFO and LNO; wherein the chemical formula of the LFO is Li. 5+a Fe 1-b Z b O 4+c , 0≤a≤0.5, 0≤b≤0.01, 0≤c≤0.03; Z includes at least one of Ti, V, Zr, Nb, Mg, Mo, W, and Al; The chemical formula of the LNO is Li 2+d Ni 1-e Y e O 2+f -0.5≤d≤0.5, e≥0, -0.5≤f≤0.5; the Y includes at least one of Ti, V, Al, Mg, Mn, and Fe; The negative electrode active material includes graphite material and silicon negative electrode material, wherein the silicon negative electrode material accounts for 1% to 50% of the total mass of the negative electrode active material.

2. The high energy density lithium-ion battery according to claim 1, wherein, The average primary particle size of the lithium iron phosphate material is 0.1–2 μm, and the average primary particle size of the lithium-rich material is 0.8–25 μm.

3. The high energy density lithium-ion battery according to claim 1, wherein, The doping amount of M in the lithium iron phosphate material is 500-8000 ppm, and / or the doping amount of Z in the lithium-rich material is 200-5000 ppm, and / or the doping amount of Y in the lithium-rich material is 200-5000 ppm.

4. The high energy density lithium-ion battery according to claim 3, wherein, In the lithium iron phosphate material, M includes any two of Ti, V, and Nb.

5. The high energy density lithium-ion battery according to claim 4, wherein, In the lithium iron phosphate material, the doping amount of Ti is 1000-2000 ppm, the doping amount of V is 500-1000 ppm, and the doping amount of Nb is 200-500 ppm.

6. The high energy density lithium-ion battery according to claim 3, wherein, In the lithium-rich material, Z includes any two of Ti, V, and Nb, and Y includes any two of Ti, V, and Mg.

7. The high energy density lithium-ion battery according to claim 6, wherein, In the lithium-rich material, the doping amount of Ti is 1000-2000 ppm, the doping amount of V is 500-1000 ppm, the doping amount of Nb is 200-500 ppm, and the doping amount of Mg is 200-500 ppm.

8. The high energy density lithium-ion battery according to claim 1, wherein, The average primary particle size of the silicon anode material is 0.05–0.5 μm, and the average primary particle size of the graphite material is 5–15 μm.

9. The high energy density lithium-ion battery according to claim 1, wherein, The silicon anode material includes at least one of the following: monocrystalline silicon spherical particles, polycrystalline silicon spherical particles, amorphous silicon spherical particles, monocrystalline silicon-like spherical particles, polycrystalline silicon-like spherical particles, amorphous silicon-like spherical particles, monocrystalline silicon amorphous particles, polycrystalline silicon amorphous particles, and amorphous silicon amorphous particles.

10. The high energy density lithium-ion battery according to claim 1, wherein, The silicon anode material accounts for 5% to 30% of the mass of the anode active material.

11. The high energy density lithium-ion battery according to any one of claims 1 to 10, wherein, The compaction density of the positive electrode sheet is 2.2–2.81 g / cm³. 3 And / or, the compaction density of the negative electrode sheet is 1.45–1.8 g / cm³. 3 .

12. The high energy density lithium-ion battery according to claim 1, wherein, The positive electrode active material layer further includes a positive electrode conductive agent and a binder, wherein the mass ratio of the positive electrode active material, the positive electrode conductive agent and the binder is 95-100:0.5-1.5:1-3.

13. The high energy density lithium-ion battery according to claim 12, wherein, The positive electrode conductive agent includes at least one of carbon nanotubes (CNTs) and conductive carbon black (SP); the binder includes polyvinylidene fluoride (PVDF).

14. The high energy density lithium-ion battery according to claim 1, wherein, The negative electrode active material layer further includes a negative electrode conductive agent, a thickener, and an adhesive, wherein the mass ratio of the negative electrode active material, the negative electrode conductive agent, the thickener, and the adhesive is 95-98:0.1-1.5:1-2:1-2.

15. The high energy density lithium-ion battery according to claim 13, wherein, The negative electrode conductive agent includes conductive carbon black SP; the thickener includes sodium carboxymethyl cellulose CMC; and the adhesive includes styrene-butadiene rubber SBR.

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