A lithium ion battery and an electric device

Abstract

The application discloses a lithium ion battery and an electric device, and relates to the technical field of secondary batteries. The application creatively introduces a specific proportion of a negative thermal expansion material (such as ZrW2O8) into a positive active material layer, utilizes the volume shrinkage effect of the negative thermal expansion material when heated, effectively offsets the thermal expansion of a high-nickel positive electrode and the mechanical expansion internal stress of a silicon-carbon negative electrode, and reserves a safety buffer space for the battery cell from a macro-physical level. Meanwhile, in combination with a strictly defined positive / negative electrode capacity ratio (N / P), the risk of lithium precipitation and dendrite puncture under a large rate is further prevented, so that the lithium ion battery provided by the application can have high energy density, extreme safety and excellent fast charging and discharging performance.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and more specifically, to a lithium-ion battery and an electrical device. Background Technology

[0002] With the rapid development of the new energy vehicle and energy storage markets, higher demands are being placed on the energy density of lithium-ion batteries. Currently, using a high-nickel ternary cathode paired with a silicon-carbon composite anode is the mainstream technical route for achieving high energy density (such as the 21700 cylindrical battery). However, this high-energy-density system faces severe safety and cycle life bottlenecks in practical applications: On the one hand, high-nickel cathodes are prone to lattice anisotropic contraction and phase transition under deep lithium insertion / extraction and high temperature conditions, accompanied by oxygen release and heat generation, which can easily lead to irreversible thermal runaway. On the other hand, the silicon-based anode undergoes a huge volume expansion (up to 300%) during the lithium insertion and extraction process. This not only causes the electrode to pulverize and fall off, and the SEI film to rupture repeatedly, thus drastically consuming active lithium, but the huge mechanical internal stress generated can also easily puncture the separator when the battery is damaged by external forces such as squeezing or puncturing, causing serious internal short circuits and fires and explosions.

[0003] In addition, traditional methods to improve safety (such as simply adding large doses of flame retardants) often increase electrolyte viscosity and severely disrupt film-forming kinetics at the electrode interface, resulting in a significant decrease in the battery's high-rate discharge performance. It is difficult for the industry to effectively balance high specific energy, high safety, and high power performance.

[0004] Therefore, there is an urgent need to develop lithium-ion batteries that combine high energy density, extreme safety, and excellent fast charging and discharging performance.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-ion battery and an electrical device that combines high energy density, extreme safety and excellent fast charging and discharging performance.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer coated on the surface of the positive current collector. The positive active material layer includes a positive active material matrix and a negative thermal expansion material. The negative electrode includes a negative current collector and a negative active material layer coated on the surface of the negative current collector. The negative active material in the negative active material layer is a silicon-carbon material.

[0008] In an optional embodiment, the negative thermal expansion material is selected from HfW2O8 and Sc2W3O.12 The material contains at least one of β-LiAlSiO4 and ZrW2O8, and the mass of the negative thermal expansion material accounts for 3% to 7% of the total mass of the positive electrode active material layer. And / or, the mass of silicon-carbon material accounts for 10% to 25% of the total mass of the negative electrode active material.

[0009] In an optional embodiment, the chemical formula of the positive electrode active material matrix is ​​LiNi. x Mn y Co z O2, x≥0.6, and x+y+z=1; And / or, the capacity ratio N / P of the positive electrode and the negative electrode is 1.06~1.12.

[0010] In an optional embodiment, the positive electrode active material layer comprises 88%~93% positive electrode active material matrix, 3%~7% negative thermal expansion material, 1%~3% conductive agent and 1%~3% binder; Preferably, the conductive agent is selected from at least one of conductive carbon black and multi-walled carbon nanotubes; Preferably, the adhesive is selected from at least one of polyvinylidene fluoride, polyimide, polytetrafluoroethylene, and polyacrylic acid; Preferably, the surface density of the coating on one side of the positive electrode sheet is 16 mg / cm³. 2 ~25mg / cm 2 The compacted density is 3.4 g / cm³. 3 ~3.7g / cm 3 .

[0011] In an optional embodiment, the electrolyte includes a carbonate-based solvent, a lithium salt, and a composite functional additive, wherein the composite functional additive includes a fluorinated cyclic carbonate, a fluorine-free lithium salt film-forming additive, and an organophosphorus flame retardant. Preferably, the lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.0 mol / L to 1.5 mol / L.

[0012] In an optional embodiment, the carbonate-based solvent in the electrolyte includes ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate, and the volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 1:(0.5~1.5):(0.5~1.5). Preferably, in the electrolyte, the mass fraction of fluorinated cyclic carbonate is 5%~10%, the mass fraction of fluorine-free lithium salt film-forming additive is 0.5%~2.0%, and the mass fraction of organophosphorus flame retardant is 3%~8%. Preferably, the fluorinated cyclic carbonate is selected from at least one of fluoroethylene carbonate, trifluoromethyl ethylene carbonate, and fluoropropylene carbonate; Preferably, the lithium salt film-forming additive is selected from at least one of lithium dioxalatoborate and lithium difluorooxalatoborate; Preferably, the organophosphorus flame retardant is selected from at least one of trimethyl phosphate, triphosphate, and triethyl phosphate.

[0013] In an optional embodiment, the diaphragm includes a composite base membrane and a ceramic coating located on at least one side surface of the composite base membrane, wherein the composite base membrane includes a first polypropylene membrane, a polyethylene membrane and a second polypropylene membrane arranged sequentially. Preferably, the thickness of the ceramic coating is 1 μm to 3 μm, and the total thickness of the diaphragm is 9 μm to 14 μm; more preferably, the ceramic coating is an Al2O3 ceramic coating. In an optional embodiment, the negative electrode active material layer comprises, by mass fraction, 13%–18% deposited silicon carbon, 78%–84% artificial graphite, 1.0%–2.0% conductive agent, and 2.0%–3.0% binder; Preferably, the conductive agent in the negative electrode active material layer includes single-walled carbon nanotubes and conductive carbon black, and the mass ratio of single-walled carbon nanotubes to conductive carbon black is 1:(1.5~2.5). Preferably, the binder in the negative electrode active material layer includes sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber, and the mass ratio of sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber is 1:(0.5~1.0):(0.5~1.0).

[0014] In an optional implementation, at 25°C, the capacity retention rate of the lithium-ion battery discharged at a 10C rate is ≥75%, and the capacity retention rate is calculated based on the 1C rate discharge capacity. And / or, in the 70% deformation compression test, the lithium-ion battery does not catch fire or explode; And / or, in the needle penetration test, the steel nail diameter is 5mm, the penetration speed is 10mm / s, and the lithium-ion battery meets the following requirements: the highest surface temperature within 1 minute after needle penetration is ≤120℃, and there is no fire or explosion.

[0015] Secondly, the present invention provides an electrical device comprising any of the lithium-ion batteries described in the foregoing embodiments.

[0016] This invention offers the following advantages: Firstly, it creatively introduces a negative thermal expansion material into the positive electrode active material layer to counteract the mechanical expansion stress of the silicon-carbon negative electrode, thus reserving a safe buffer space for the battery cell from a macroscopic physical perspective. Furthermore, by controlling the specific proportion of the negative thermal expansion material, the battery can achieve an ideal dynamic balance between high specific energy and high safety, while maintaining safety. Additionally, by controlling the silicon-carbon content in the negative electrode, the battery system can effectively absorb and buffer expansion stress, ensuring high energy density and maintaining an excellent conductive network and good kinetic performance. Simultaneously, the strictly defined positive / negative electrode capacity ratio (N / P) further prevents the risk of lithium plating and dendrite puncture at high rates, enabling the lithium-ion battery provided by this invention to balance high energy density, extreme safety, and excellent fast charging and discharging performance.

[0017] On the other hand, this invention introduces a negative thermal expansion material into the high-nickel active layer of the positive electrode. Utilizing its volume contraction effect upon heating, this material offsets the thermal expansion of the high-nickel positive electrode and the mechanical expansion stress of the silicon-carbon negative electrode, providing a safe buffer space for the battery cell. By controlling the proportion of the negative thermal expansion material, a balance is achieved between high energy density and high safety. Simultaneously, by controlling the content of silicon-carbon material in the negative electrode, expansion stress is effectively absorbed and buffered, ensuring high energy density and maintaining a stable conductive network and kinetic performance. Furthermore, a strictly defined positive / negative electrode capacity ratio (N / P) effectively prevents the risk of lithium plating and dendrite puncture at high charge / discharge rates. Therefore, the lithium-ion battery using a high-nickel positive electrode provided by this invention can achieve a balance of high energy density, high safety, and excellent rate performance. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, an electrolyte, and a cylindrical steel shell. The following describes each component: [Positive electrode plate] The positive electrode sheet includes a positive current collector and a positive active material layer coated on the surface of the positive current collector. The positive active material layer includes a positive active material matrix and a negative thermal expansion material. By introducing a negative thermal expansion material into the positive active material layer, its volume contraction effect when heated cleverly offsets the thermal expansion of the high-nickel positive electrode and the mechanical expansion internal stress of the silicon-carbon negative electrode, thus reserving a safe buffer space for the battery cell from a macroscopic physical level.

[0020] The mass of the negative thermal expansion material accounts for 3% to 7% of the total mass of the positive electrode active material layer, such as 3%, 4%, 5%, 6%, 7%, etc. A mass percentage of negative thermal expansion material within this range is preferable, as it better offsets the thermal expansion of the high-nickel positive electrode and the mechanical expansion internal stress of the silicon-carbon negative electrode, thus improving the cell's safety performance.

[0021] Negative thermal expansion materials are selected from HfW2O8 and Sc2W3O 12 The negative thermal expansion material can be any one or more of the following: β-LiAlSiO4 and ZrW2O8. All of these negative thermal expansion materials can effectively offset the thermal expansion of the high-nickel cathode and the mechanical expansion internal stress of the silicon-carbon anode when heated, thereby improving the safety performance of the battery.

[0022] In some embodiments, the chemical formula of the positive electrode active material matrix is ​​LiNi. x Mn y Co z O2, x≥0.6, and x+y+z=1. Specifically, x can be 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, etc.; y and z can be 0, or 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, etc.

[0023] In some embodiments, the positive electrode active material layer comprises, by mass fraction, 88%–93% of a positive electrode active material matrix, 3%–7% of a negative thermal expansion material, 1%–3% of a conductive agent, and 1%–3% of a binder. Specifically, the mass fraction of the positive electrode active material matrix can be 88%, 89%, 90%, 91%, 92%, 93%, etc.; the mass fraction of the negative thermal expansion material can be 3%, 4%, 5%, 6%, 7%, etc.; the mass fraction of the conductive agent can be 1%, 2%, 3%, etc.; and the mass fraction of the binder can be 1%, 2%, 3%, etc.

[0024] Furthermore, the conductive agent is selected from at least one of conductive carbon black (SuperP) and multi-walled carbon nanotubes (CNTs), and the conductive agent can be any one or more of the above. The binder is selected from at least one of polyvinylidene fluoride, polyimide, polytetrafluoroethylene, and polyacrylic acid, and the binder can be any one or more of the above.

[0025] Furthermore, the surface density of the coating on one side of the positive electrode is 16 mg / cm³. 2 ~25mg / cm 2 For example, it can be 16mg / cm 2 17mg / cm 2 18mg / cm 2 19mg / cm 220mg / cm 2 21mg / cm 2 22mg / cm 2 23mg / cm 2 24mg / cm 2 25mg / cm 2 Etc.; compacted density is 3.4 g / cm³. 3 ~3.7g / cm 3 For example, it can be 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 wait.

[0026] [Negative electrode plate] The negative electrode sheet includes a negative current collector and a negative active material layer coated on the surface of the negative current collector. The negative active material in the negative active material layer is a silicon-carbon material. The mass of the silicon-carbon material accounts for 10% to 25% of the total mass of the negative active material, such as 10%, 13%, 15%, 18%, 20%, 23%, 25%, etc.

[0027] The capacity ratio (N / P) of the positive and negative electrodes is 1.06~1.12, such as 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, etc. By introducing a specific proportion of negative thermal expansion material into the positive electrode, and with a strictly defined N / P capacity ratio, the risks of lithium plating and dendrite puncture at high rates are further prevented. The test method for the N / P capacity ratio is described below in the instruction manual.

[0028] The N / P ratio represents the ratio of the capacity of the negative electrode to the capacity of the positive electrode. In some embodiments, the N / P ratio can be controlled by adjusting the areal density of the negative electrode coating.

[0029] In some embodiments, the negative electrode active material layer comprises, by mass fraction, 13%–18% deposited silicon carbon, 78%–84% artificial graphite, 1.0%–2.0% conductive agent, and 2.0%–3.0% binder. Specifically, the deposited silicon carbon is a commercially available material, and its mass fraction can be 13%, 14%, 15%, 16%, 17%, 18%, etc.; the mass fraction of artificial graphite can be 78%, 79%, 80%, 81%, 82%, 83%, 84%, etc.; the mass fraction of conductive agent can be 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, etc.; and the mass fraction of binder can be 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, etc.

[0030] Furthermore, the conductive agent in the negative electrode active material layer includes single-walled carbon nanotubes (SWCNTs) and conductive carbon black, and the mass ratio of SWCNTs to conductive carbon black (SuperP) is 1:(1.5~2.5), such as 1:1.5, 1:1.8, 1:2.0, 1:2.3, 1:2.5, etc. The binder in the negative electrode active material layer includes sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR), and the mass ratio of sodium carboxymethyl cellulose, polyacrylic acid, and styrene-butadiene rubber is 1:(0.5~1.0):(0.5~1.0), such as 1:0.5:0.5, 1:0.6:0.6, 1:0.7:0.7, 1:0.8:0.8, 1:0.9:0.9, 1:1.0:1.0, etc.

[0031] Electrolyte The electrolyte comprises a carbonate-based solvent, a lithium salt, and a composite functional additive. In this embodiment of the invention, the composition of the composite functional additive is improved. The composite functional additive includes a fluorinated cyclic carbonate, a fluorine-free lithium salt film-forming additive, and an organophosphorus flame retardant.

[0032] In some embodiments, the mass fraction of fluorinated cyclic carbonate in the electrolyte is 5% to 10%, such as 5%, 6%, 7%, 8%, 9%, 10%, etc.; the mass fraction of non-fluorinated lithium salt film-forming additive is 0.5% to 2.0%, such as 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, etc.; and the mass fraction of organophosphorus flame retardant is 3% to 8%, such as 3%, 4%, 5%, 6%, 7%, 8%, etc. That is, the mass ratio of fluorinated cyclic carbonate, non-fluorinated lithium salt film-forming additive, and organophosphorus flame retardant is (5~10):(0.5~2):(3~8).

[0033] In some embodiments, the fluorinated cyclic carbonate is selected from at least one of fluoroethylene carbonate (FEC), trifluoromethyl ethylene carbonate, and fluoropropylene carbonate, and the fluorinated cyclic carbonate can be any one or more of the above; the fluorine-free lithium salt film-forming additive is selected from at least one of lithium dioxolane borate (LiBOB) and lithium difluorooxolane borate, and the fluorine-free lithium salt film-forming additive can be any one or more of the above; the organophosphorus flame retardant is selected from at least one of trimethyl phosphate (TMP), triphosphate, and triethyl phosphate, and the organophosphorus flame retardant can be any one or more of the above.

[0034] In some embodiments, the lithium salt may be lithium hexafluorophosphate (LiPF6), but is not limited thereto. The concentration of the lithium salt in the electrolyte is 1.0 mol / L to 1.5 mol / L, such as 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc. The carbonate-based solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and the volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 1:(0.5~1.5):(0.5~1.5), such as 1:0.5:0.5, 1:0.8:0.8, 1:1.0:1.0, 1:1.3:1.3, 1:1.5:1.5, etc.

[0035] It should be noted that, at the liquid phase level, this invention, by optimizing specific concentrations of lithium salts and composite functional additives (e.g., using a specific ratio of TMP combined with FEC and LiBOB), constructs a thermal runaway suppression system that blocks the chain reaction of thermal runaway without hindering the rapid transport kinetics of lithium ions. Combined with improvements to the positive and negative electrode sheets, and through the synergistic effect of multi-dimensional refined parameters of "solid-phase mechanical explosion protection + liquid-phase chemical flame retardancy," this invention successfully breaks through the "performance bottleneck" of battery performance, achieving an excellent overall performance of ≥75% capacity retention at 10C high-rate discharge under conditions of a total energy density ≥270Wh / kg, and without ignition or explosion during stringent 70% deformation extrusion and nail penetration tests.

[0036] [Septum] The diaphragm includes a composite base membrane and a ceramic coating on at least one surface of the composite base membrane. The ceramic coating can be applied to one side or both sides. The composite base membrane comprises a first polypropylene membrane, a polyethylene membrane, and a second polypropylene membrane arranged sequentially, forming a three-layer composite base membrane structure.

[0037] In some embodiments, the thickness of the ceramic coating is 1 μm to 3 μm, such as 1 μm, 2 μm, 3 μm, etc.; the total thickness of the diaphragm is 9 μm to 14 μm, such as 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, etc. The ceramic coating can be an Al2O3 ceramic coating, but is not limited thereto.

[0038] The lithium-ion battery provided in this embodiment of the invention uses a cylindrical steel casing and can be assembled into a 21700 type lithium-ion cylindrical battery, but is not limited thereto. The lithium-ion battery cell adopts a full-tab winding structure, and the radial gap after the cell is inserted into the casing is 0.1mm~0.3mm, such as 0.1mm, 0.2mm, 0.3mm, etc.

[0039] Tests showed that at 25℃, the lithium-ion battery retained ≥75% of its capacity during 10C discharge, with the capacity retention calculated based on the 1C discharge capacity, demonstrating excellent rate performance. This lithium-ion battery also exhibits exceptional safety performance. Specific test results are as follows: In a 70% deformation compression test, the lithium-ion battery did not catch fire or explode; in a needle penetration test with a 5mm diameter steel nail and a penetration speed of 10mm / s, the lithium-ion battery met the following requirements: the highest surface temperature within 1 minute after needle penetration was ≤120℃, with no fire or explosion.

[0040] This invention also provides an electrical device, including a lithium-ion battery provided in this invention, which is used to supply power. The specific form of the electrical device is not limited.

[0041] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0042] Example 1 This embodiment provides a lithium-ion battery, the preparation steps of which are as follows: (1) Preparation of positive electrode sheet High-nickel ternary LiNi 0.8 Mn 0.1 Co 0.1 O2 matrix and ZrW2O8 powder were mixed uniformly in a planetary ball mill at a set mass ratio of 91wt% and 5wt%, respectively, with a ball-to-powder ratio of 10:1, a rotation speed of 200 rpm, and a milling time of 4 hours to obtain a mixed positive electrode active material (LiNi). 0.8 Mn 0.1 Co 0.1 O2+ZrW2O8); The modified positive electrode active material, Super-P conductive agent, and PVDF binder were weighed in a mass ratio of 96wt%:2wt%:2wt%. First, the PVDF was completely dissolved in NMP solvent to prepare a binder solution with a solid content of 8%. Then, the conductive agent was added and stirred for 2 hours to form a uniform conductive slurry. Finally, the modified positive electrode active material was added and stirred continuously for 4 hours to prepare a positive electrode slurry with a solid content of 65%. The slurry was then coated on both sides of an 8μm thick aluminum current collector surface using a slot coater (single-sided coating surface density was 20mg / cm²). 2 After drying in a three-stage oven at 120℃ and cold pressing at 10MPa, a positive electrode sheet with a thickness of 50μm and a compaction density of 3.6g / cm³ was obtained. 3 .

[0043] (2) Preparation of negative electrode sheet The negative electrode sheet comprises an 8μm thick copper current collector and a negative electrode active material layer coated on both sides of the current collector. The negative electrode active material layer comprises 15.0wt% deposited silicon carbon, 81.0wt% artificial graphite, 0.5wt% single-walled carbon nanotubes (SWCNTs), 0.9wt% conductive carbon black (SuperP), 1.0wt% sodium carboxymethyl cellulose (CMC), 0.8wt% polyacrylic acid (PAA), and 0.8wt% styrene-butadiene rubber (SBR). The above substances (50% solid content) are added to deionized water and stirred to form the negative electrode coating material. This coating material is then coated onto both sides of the current collector. After drying at 100℃ for 20 min and cold pressing at 8 MPa, the negative electrode sheet is formed with an active layer thickness of 55μm and a compaction density of 1.6 g / cm³. 3 .

[0044] (3) Diaphragm A commercially available membrane with high porosity (~40%) was selected. The thickness of the PP / PE / PP base membrane in the membrane is 9 μm, and the thickness of the Al2O3 ceramic coating on both sides of the base membrane is 1.0 μm.

[0045] (4) Electrolyte An electrolyte was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), and trimethyl phosphate (TMP) in a glove box at a mass percentage ratio of 28.66:21.93:23.22:15.19:5.0:1.0:5.0, with a lithium salt concentration of 1.2 mol / L.

[0046] (5) Assembly After the positive and negative electrode sheets are rolled and slit (N / P=1.08), they are wound together with the composite separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as injection and sealing, the lithium-ion battery described in Example 1 is obtained, with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0047] Example 2 The difference between this embodiment and Embodiment 1 is that LiNi is added during the preparation of the positive electrode. 0.8 Mn 0.1 Co 0.1 The mass percentages of O2 and ZrW2O8 are 93wt% and 3wt%, respectively, and all other parameters are the same as in Example 1.

[0048] Example 3 The difference between this embodiment and Embodiment 1 is that LiNi is added during the preparation of the positive electrode. 0.8 Mn 0.1 Co 0.1 The mass percentages of O2 and ZrW2O8 are 92wt% and 4wt%, respectively, and everything else is the same as in Example 1.

[0049] Example 4 The difference between this embodiment and Embodiment 1 is that LiNi is added during the preparation of the positive electrode. 0.8 Mn 0.1 Co 0.1 The mass percentages of O2 and ZrW2O8 are 89 wt% and 7 wt%, respectively, and everything else is the same as in Example 1.

[0050] Comparative Example 1 The difference between this comparative example and Example 1 is that LiNi was added during the preparation of the positive electrode. 0.8 Mn 0.1 Co 0.1 The mass percentages of O2 and ZrW2O8 are 95wt% and 1wt%, respectively, and all other parameters are the same as in Example 1.

[0051] Comparative Example 2 The difference between this comparative example and Example 1 is that LiNi was added during the preparation of the positive electrode. 0.8 Mn 0.1 Co 0.1 The mass percentages of O2 and ZrW2O8 are 87wt% and 9wt%, respectively, and everything else is the same as in Example 1.

[0052] Example 5 The difference between this embodiment and Embodiment 1 is that the mass percentages of deposited silicon carbon and artificial graphite added during the preparation of the negative electrode sheet are 10wt% and 86wt%, respectively, while all other aspects are the same as in Embodiment 1.

[0053] Example 6 The difference between this embodiment and Embodiment 1 is that the mass percentages of deposited silicon carbon and artificial graphite added during the preparation of the negative electrode sheet are 20wt% and 76wt%, respectively, while all other aspects are the same as in Embodiment 1.

[0054] Example 7 The difference between this embodiment and Embodiment 1 is that the mass percentages of deposited silicon carbon and artificial graphite added during the preparation of the negative electrode sheet are 25wt% and 71wt%, respectively, while all other aspects are the same as in Embodiment 1.

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is that the mass percentages of deposited silicon carbon and artificial graphite added during the preparation of the negative electrode sheet are 5 wt% and 91 wt%, respectively, while all other aspects are the same as in Example 1.

[0056] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass percentages of deposited silicon carbon and artificial graphite added during the preparation of the negative electrode are 30wt% and 66wt%, respectively, while all other aspects are the same as in Example 1.

[0057] Example 8 The difference between this embodiment and Embodiment 1 is that the N / P ratio of the positive electrode to the negative electrode is 1.06, while all other aspects are the same as in Embodiment 1.

[0058] Example 9 The difference between this embodiment and Embodiment 1 is that the N / P ratio of the positive electrode to the negative electrode is 1.1, while all other aspects are the same as in Embodiment 1.

[0059] Example 10 The difference between this embodiment and Embodiment 1 is that the N / P ratio of the positive electrode to the negative electrode is 1.12, while all other aspects are the same as in Embodiment 1.

[0060] Comparative Example 5 The difference between this comparative example and Example 1 is that the N / P ratio of the positive electrode to the negative electrode is 1.02, while all other aspects are the same as in Example 1.

[0061] Comparative Example 6 The difference between this comparative example and Example 1 is that the N / P ratio of the positive electrode to the negative electrode is 1.16, while all other aspects are the same as in Example 1.

[0062] Example 11 The difference between this embodiment and Example 1 is that the mass percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), and trimethyl phosphate (TMP) in the electrolyte are 29.64:22.68:24.02:12.66:5.0:1.0:5.0, and the lithium salt concentration is 1.0 mol / L. All other aspects are the same as in Example 1.

[0063] Example 12 The difference between this embodiment and Example 1 is that the mass percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), and trimethyl phosphate (TMP) in the electrolyte are 27.67:21.18:22.43:17.72:5.0:1.0:5.0, and the lithium salt concentration is 1.4 mol / L. All other aspects are the same as in Example 1.

[0064] Example 13 The difference between this embodiment and Example 1 is that the mass percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), and trimethyl phosphate (TMP) in the electrolyte are 27.18:20.8:22.03:18.99:5.0:1.0:5.0, and the lithium salt concentration is 1.5 mol / L. All other aspects are the same as in Example 1.

[0065] Comparative Example 7 The difference between this comparative example and Example 1 is that the mass percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), and trimethyl phosphate (TMP) in the electrolyte are 30.62:23.43:24.82:10.13:5.0:1.0:5.0, and the lithium salt concentration is 0.8 mol / L. All other aspects are the same as in Example 1.

[0066] Comparative Example 8 The difference between this comparative example and Example 1 is that the mass percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), and trimethyl phosphate (TMP) in the electrolyte are 25.70:19.67:20.84:22.79:5.0:1.0:5.0, and the lithium salt concentration is 1.8 mol / L. All other aspects are the same as in Example 1.

[0067] Example 14 The difference between this embodiment and Example 1 is that the mass percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), lithium dioxoborate (LiBOB), and trimethyl phosphate (TMP) in the electrolyte are 29.43:22.52:23.86:15.19:5.0:1.0:3.0, while all other aspects are the same as in Example 1.

[0068] Example 15 The difference between this embodiment and Example 1 is that the mass percentage of trimethyl phosphate (TMP) in the electrolyte is 6.0 (EC, EMC and DMC are reduced by the same mass ratio), while all other aspects are the same as in Example 1.

[0069] Example 16 The difference between this embodiment and Example 1 is that the mass percentage of trimethyl phosphate (TMP) in the electrolyte is 8.0 (EC, EMC and DMC are reduced by the same mass ratio), while all other aspects are the same as in Example 1.

[0070] Comparative Example 9 The difference between this comparative example and Example 1 is that the mass percentage of trimethyl phosphate (TMP) in the electrolyte is 1.0 (EC, EMC and DMC are increased in equal mass proportions), while all other aspects are the same as in Example 1.

[0071] Comparative Example 10 The difference between this comparative example and Example 1 is that the mass percentage of trimethyl phosphate (TMP) in the electrolyte is 12.0 (EC, EMC and DMC are reduced by the same mass ratio), while all other aspects are the same as in Example 1.

[0072] Example 17 The difference between this embodiment and Embodiment 1 is that the negative thermal expansion material is replaced with an equal amount of HfW2O8, while everything else is the same as in Embodiment 1.

[0073] Example 18 The difference between this embodiment and Embodiment 1 is that the negative thermal expansion material is replaced with an equal amount of Sc2W3O. 12 Everything else is the same as in Example 1.

[0074] Example 19 The difference between this embodiment and Embodiment 1 is that the negative thermal expansion material is replaced with an equal amount of β-LiAlSiO4, while everything else is the same as in Embodiment 1.

[0075] Comparative Example 11 The difference between this comparative example and Example 1 is that the negative thermal expansion material is replaced with an equal amount of Al2O3.

[0076] Comparative Example 12 The difference between this comparative example and Example 1 is that FEC is not added to the electrolyte; instead, it is replaced with an equal amount of LiBOB.

[0077] Comparative Example 13 The difference between this comparative example and Example 1 is that LiBOB is not added to the electrolyte; instead, it is replaced with an equal amount of FEC.

[0078] Comparative Example 14 The difference between this comparative example and Example 1 is that TMP is not added to the electrolyte, but is replaced with an equal amount of FEC.

[0079] Experimental Example 1 The performance of the lithium-ion batteries prepared in each embodiment and comparative example was tested, and the results are shown in Tables 1-5.

[0080] Test method: (1) Determination of mass energy density: The total mass m of the battery is weighed using a high-precision electronic balance. Then, the total energy E released by the battery when discharged to the cutoff voltage at 0.5C is recorded in the standard capacity test. The energy density is calculated by the formula Energy / Density = E / m.

[0081] (2) Test method for compaction density of positive electrode sheet: First, the positive electrode sheet that has been washed with dimethyl carbonate and vacuum dried is cut into 9 standard-sized (2.0cm×2.0cm) square samples; then, the active material on the front and back of 3 of the square samples is wiped off, rinsed with NMP and dried, weighed and the average mass M1 (in g) is calculated, and the average thickness L1 (in cm) of the sample is measured using a micrometer; then, the mass of the other 3 square samples is weighed and the average mass M2 (in g) is calculated, and the average thickness L2 (in cm) of the sample is measured.

[0082] Calculate the compaction density of the positive electrode sheet: Unit: g / cm 3 .

[0083] (3) Test method for single-sided surface density of positive electrode sheet: First, the positive / negative electrode sheet, after being washed with dimethyl carbonate and vacuum dried, is cut into 9 standard-sized (2.0cm×2.0cm) square samples; then, the active material on the front and back of 3 of the square samples is wiped off, rinsed with NMP, dried, weighed, and the average mass M1 of the bare current collector is calculated; subsequently, the remaining 6 square samples with double-sided active material coating are accurately weighed, and the average total mass M2 of the double-sided electrode sheet is calculated; finally, according to the single-sided surface density formula: ; Where S is the test area of ​​a single square sample, i.e., 4.0 cm². 2 The areal density of the electrode was calculated, and the final test results were expressed in mg / cm³. 2 Records are kept by unit.

[0084] (4) The method for determining the N / P (capacity ratio) of the positive and negative electrodes is as follows: Circular pieces of fixed area are cut from the prepared positive and negative electrodes respectively. Using lithium metal sheets as the counter electrode and the same electrolyte as the full cell, they are assembled into coin cells in a glove box. Subsequently, the first charge-discharge test is performed at a low rate (usually 0.1C) within their respective specified voltage windows on a battery testing system to obtain the first reversible lithium intercalation / deintercalation areal capacity (mAh / cm²) of the positive half-cell. 2 The first reversible lithium insertion / extraction areal capacity (mAh / cm²) of the negative electrode half-cell. 2 Finally, the measured reversible capacity per unit area of ​​the negative electrode is divided by the reversible capacity per unit area of ​​the positive electrode, and the quotient is the N / P ratio of the system.

[0085] (5) Needle penetration test: The battery to be tested was fully charged to 100% SOC and placed in a 25℃ environment for 2 hours to stabilize. Then, the battery was fixed on an insulating clamp, ensuring that its positive and negative terminals were placed horizontally. Using a stainless steel needle with a diameter of 5 mm, perpendicular to the surface of the battery and along the direction between the positive and negative terminals, the needle was inserted into the battery at a speed of 10±1 mm / s until it was completely penetrated (the penetration depth should exceed 90% of the battery thickness). After insertion, the needle was kept still and the battery status was continuously observed for 5 minutes. Any abnormal phenomena such as fire, explosion, or smoke were recorded, and the temperature change was monitored by a thermocouple attached to the surface of the battery.

[0086] (6) Test method for discharge performance at 25℃ and 10C rate The battery was placed in a 25°C constant temperature chamber for 6 hours and tested according to the following steps: (a) under 1.0C constant current and constant voltage charging to 4.2V, with a cutoff current of 0.1C, and allowed to stand for 30 minutes; (b) under 1.0C constant current discharging to 2.5V cutoff, with a capacity of Q1, and allowed to stand for 30 minutes; (c) under 1.0C constant current and constant voltage charging to 4.2V, with a cutoff current of 0.1C, and allowed to stand for 30 minutes; (d) under 10C constant current discharging to 2.5V cutoff, with a capacity of Q2, and allowed to stand for 30 minutes; the 10C capacity retention rate was calculated as: Q2 / Q1×100%.

[0087] (7) 70% Deformation Extrusion Test: After charging the lithium-ion battery to 100% state of charge, place it horizontally on the extrusion test platform. Use a cylindrical steel rod with a diameter of 32mm as the extrusion head, and apply extrusion force to the battery thickness direction at a rate of 10mm / min. At the same time, monitor the battery thickness change in real time through a displacement sensor. Stop extrusion immediately when the battery deformation reaches 70% of the original thickness. The test standard is: the battery must not catch fire or explode during short circuit.

[0088] The specific results are as follows: Table 1 shows the battery performance test results obtained in Examples 1-4 and Comparative Examples 1-2.

[0089] Table 1 shows the negative thermal expansion material ZrW2O8 in the positive electrode active layer. As an excellent negative thermal expansion (NTE) material, its core role lies in its physical lattice contraction when the internal temperature of the battery rises sharply (such as when subjected to needle-puncture internal short circuit, compression, or high-rate charge and discharge). This unique contraction effect can not only accurately offset the drastic volume expansion of the high-nickel positive electrode material under delithiation and heating conditions, maintaining the integrity of the positive electrode microcrystalline structure and thus effectively suppressing oxygen release and heat generation; it can also macroscopically free up valuable internal buffer space for the huge mechanical expansion of the silicon-carbon negative electrode, greatly alleviating the fatal compressive stress on the separator inside the densely wound cell.

[0090] The influence of the mass ratio of negative thermal expansion material ZrW2O8 on the overall performance of lithium-ion batteries: As the ZrW2O8 content increases (from 1% to 9%), the safety of the battery in nail penetration and extrusion tests is significantly enhanced. The maximum nail penetration temperature drops sharply from 338℃ to 76℃ and fire is eliminated. However, the cost is that the overall energy density decreases monotonically. At the same time, the capacity retention rate at 10C high-rate discharge shows a trend of first increasing and then decreasing. When the ZrW2O8 content is strictly controlled within the range of 3% to 7%, the battery can achieve an ideal dynamic balance between high specific energy and high safety. In particular, Example 1 with a content of 5% not only ensures excellent safety performance of not catching fire or exploding (the highest temperature reached by needle penetration is only 82°C), but also maintains a high energy density of 285 Wh / kg and an optimal rate performance of 88.4%. On the contrary, if the content of Comparative Example 1 is too low (1%), it will not be able to provide sufficient buffering effect, which will lead to fatal thermal runaway and fire. If the content of Comparative Example 2 is too high (9%), the energy density will fall below the bottom line and the kinetic performance will be significantly reduced due to the introduction of a large amount of inactive and low conductivity materials.

[0091] Table 2 shows the battery performance test results obtained in Examples 1, 5-7 and Comparative Examples 3-4.

[0092] Table 2 shows the impact of the mass ratio of silicon-carbon material in the negative electrode active layer on the core performance of the battery: As the amount of silicon-carbon composite material added gradually increases from 5% to 30%, thanks to the extremely high theoretical specific capacity of silicon material, the energy density of the battery achieves a leap from 255 Wh / kg to 305 Wh / kg. However, at the same time, due to the huge volume expansion that accompanies the silicon insertion and extraction of lithium, the structural stability and mechanical safety of the electrode sheet deteriorate sharply. When the silicon-carbon content is strictly controlled within the range of 10% to 25% (as in Examples 1 and 5 to 7), the battery system can effectively absorb and buffer expansion stress, ensuring not only a high energy density of ≥272Wh / kg, but also maintaining an excellent conductive network and good kinetic performance (10C capacity retention ≥82.3%). It also maintains a safety baseline of not catching fire or exploding during mechanical abuse tests such as nail penetration and extrusion (the best overall performance is in Example 1 with 15%). In contrast, for comparative examples outside this range, if the amount of silicon-carbon added is too low (such as 5% in Comparative Example 3), the system degenerates into a near-pure graphite anode and loses its high specific energy significance. If the amount added is too high (such as 30% in Comparative Example 4), the uncontrollable expansion internal stress will not only significantly reduce the capacity retention to 68.5%, but will also directly cause mechanical rupture of the separator under extrusion stress, leading to internal short circuit and fire, completely breaking the safety red line.

[0093] Table 3 shows the battery performance test results obtained in Examples 1, 8-10 and Comparative Examples 5-6.

[0094] Table 3 illustrates the "threshold effect" of the positive / negative electrode capacity ratio (N / P ratio) on the overall battery performance: the N / P ratio directly determines the redundancy of the lithium intercalation space in the negative electrode and the electrode thickness. When the N / P ratio is too low (e.g., 1.02 in Comparative Example 5), the negative electrode lacks sufficient lithium intercalation space, and lithium plating or even the formation of sharp lithium dendrites is easily triggered on the surface of the negative electrode during high-rate charging. This not only drastically consumes the limited active lithium, causing the 10C capacity retention rate to drop significantly to 65.2%, but also causes a serious internal short circuit due to dendrites piercing the separator during the extrusion test, resulting in a fire at a high temperature of 235°C and a complete loss of safety. Conversely, when the N / P ratio is too high (e.g., 1.16 in Comparative Example 6), although there is no risk of thermal runaway, the excessively thick negative electrode coating introduces a large amount of ineffective "dead weight," which not only significantly reduces the overall energy density of the pack to 268 Wh / kg, but also significantly lengthens the diffusion path of lithium ions in the solid phase, leading to increased polarization during high-rate discharge and a decrease in capacity retention rate to 71.3%. Only when the N / P ratio is precisely locked within the range of 1.06 to 1.12 can the battery achieve an excellent balance between the safety buffer space for preventing lithium plating and lightweight design. In particular, Example 1 with an N / P ratio of 1.08 is the optimal solution, taking into account the excellent fast discharge dynamic performance of 88.4%, the high specific energy of 285 Wh / kg, and the safety performance of not catching fire or exploding.

[0095] Table 4 shows the performance test results of the batteries obtained in Examples 1, 11-13 and Comparative Examples 7-8.

[0096] Table 4 clearly illustrates the profound impact of lithium hexafluorophosphate (LiPF6) concentration in the electrolyte on battery kinetic performance: the lithium salt concentration directly determines the number of free charge carriers in the system and the viscosity of the electrolyte. When the lithium salt concentration is too low (e.g., 0.8 mol / L in Comparative Example 7), the free lithium-ion charge carriers in the electrolyte are severely depleted, which easily leads to severe concentration polarization during high-rate discharge at 10C, resulting in impaired mass transfer in the liquid phase and a sharp drop in capacity retention to 62.1%. Conversely, when the concentration is too high (e.g., 1.8 mol / L in Comparative Example 8), although the absolute number of charge carriers increases, the macroscopic viscosity of the electrolyte rises sharply, and the association effect between ions (formation of ion pairs) is significantly enhanced. This, in turn, greatly hinders the ion migration rate, causing a surge in internal resistance, and the high-rate discharge performance also deteriorates to 69.8%. Only when the LiPF6 concentration is precisely controlled within the range of 1.0~1.5 mol / L (as in Examples 1 and 11 to 13) can the ionic conductivity and viscosity of the electrolyte achieve a perfect balance. Under the premise of high energy density (approximately 285 Wh / kg) without damage to the battery and extreme physical safety (no fire or explosion even under needle puncture or extrusion), excellent fast-release kinetic performance is guaranteed. In particular, Example 1 with a concentration of 1.2 mol / L pushed the 10C capacity retention rate to an optimal peak of 88.4%.

[0097] Table 5 shows the performance test results of the batteries obtained in Examples 1, 14-16 and Comparative Examples 9-10.

[0098] Table 5 visually reflects the core interplay between the mass ratio of flame retardant TMP (trimethyl phosphate) in the electrolyte additive and its role in "inhibiting thermal runaway" and "maintaining electrode interface kinetics." As a highly efficient flame retardant, TMP primarily breaks the thermal runaway chain by capturing free radicals in the combustion reaction. When its addition is too low (e.g., 1% in Comparative Example 9), the electrolyte system lacks sufficient fire extinguishing capability and is rapidly ignited at the high temperature generated during the needle-puncture internal short circuit, causing the maximum temperature to soar to 345°C and resulting in a severe fire and explosion, completely breaching the safety baseline. However, TMP exhibits poor reduction stability on the negative electrode surface. If the addition is too high (e.g., 12% in Comparative Example 10), the excess TMP will severely interfere with and damage the dense film quality of the SEI (solid electrolyte interphase) film on the negative electrode surface, significantly increasing interfacial impedance and reducing ionic conductivity, thus disrupting the battery's high-rate kinetic performance, with the 10C capacity retention rate dropping to only 55.3%. Only by precisely controlling the mass percentage of TMP within the protective range of 3% to 8% (as in Examples 1 and 14 to 16), and relying on the synergistic formulation with film-forming agents (FEC and LiBOB), can the excellent high-rate discharge performance (10C capacity retention ≥76.5%) be preserved to the maximum extent while ensuring that the high-energy-density battery cell passes the stringent extrusion and needle penetration tests (without ignition or explosion). Example 1, with an addition of 5%, pushes the comprehensive balance between safety and electrochemical performance to the optimal solution.

[0099] Table 6. Performance test results of batteries obtained from Example 1, Comparative Examples 17-18, and Comparative Example 11.

[0100] Table 6 reflects the composition of ZrW₂O₈, HfW₂O₈, and Sc₂W₃O₈. 12 β-LiAlSiO4, as a negative thermal expansion (NTE) material, can control the needle penetration temperature between 82-86℃, and does not catch fire or explode during 70% extrusion testing. This further indicates that introducing a negative thermal expansion material into the positive electrode active material layer can offset the mechanical expansion internal stress of the silicon-carbon negative electrode, thus reserving a safe buffer space for the battery cell from a macroscopic physical level.

[0101] Table 7. Performance test results of batteries obtained in Example 1 and Comparative Examples 12-14

[0102] In Table 7, comparing Example 1 and Comparative Example 12, the rate performance decreased significantly (74.5%) without FEC. FEC is the core film-forming agent of the silicon-carbon anode SEI film. The absence of FEC will affect the integrity of the SEI film, increase the interfacial impedance, and thus affect the rate performance. Comparing Example 1 and Comparative Example 13, the absence of LiBOB has a smaller impact on the rate performance than the absence of FEC in Comparative Example 12, mainly affecting the needle penetration safety. Comparing Example 1 and Comparative Example 14, the absence of TMP leads to a significant increase in the needle penetration temperature, indicating that the main function of TMP is to prevent thermal runaway. Therefore, the absence of any one of FEC, LiBOB, and MP will affect the performance of one aspect and cause degradation. Therefore, the electrolyte configuration in this invention is the key to achieving high rate performance and high safety performance.

[0103] In summary, this invention, through a multi-dimensional and refined combination of parameters from electrode material stress management to electrolyte thermodynamic blocking, effectively breaks through the technical barrier of "high specific energy, high rate and high safety are difficult to achieve simultaneously" in the traditional high-nickel / silicon-carbon system. Ultimately, it realizes a 21700-type lithium-ion cylindrical battery that combines high energy density (≥270 Wh / kg), extreme physical safety (no fire or explosion under severe needle penetration and 70% deformation compression), and excellent fast charge and discharge dynamics (10C high rate discharge capacity retention ≥75%), which has extremely high commercial application and promotion value.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The device includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer coated on the surface of the positive current collector. The positive active material layer includes a positive active material matrix and a negative thermal expansion material. The negative electrode includes a negative current collector and a negative active material layer coated on the surface of the negative current collector. The negative active material in the negative active material layer is a silicon-carbon material.

2. The lithium-ion battery according to claim 1, characterized in that, The negative thermal expansion material is selected from HfW2O8 and Sc2W3O. 12 The material contains at least one of β-LiAlSiO4 and ZrW2O8, and the mass of the negative thermal expansion material accounts for 3% to 7% of the total mass of the positive electrode active material layer. And / or, the mass of the silicon-carbon material accounts for 10% to 25% of the total mass of the negative electrode active material.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, The chemical formula of the positive electrode active material matrix is ​​LiNi. x Mn y Co z O2, x≥0.6, and x+y+z=1; And / or, the capacity ratio N / P of the positive electrode and the negative electrode is 1.06~1.

12.

4. The lithium-ion battery according to claim 1, characterized in that, By mass fraction, the positive electrode active material layer comprises 88%~93% positive electrode active material matrix, 3%~7% negative thermal expansion material, 1%~3% conductive agent and 1%~3% binder; Preferably, the conductive agent is selected from at least one of conductive carbon black and multi-walled carbon nanotubes; Preferably, the adhesive is selected from at least one of polyvinylidene fluoride, polyimide, polytetrafluoroethylene, and polyacrylic acid; Preferably, the single-sided coating surface density of the positive electrode sheet is 16 mg / cm³. 2 ~25mg / cm 2 The compacted density is 3.4 g / cm³. 3 ~3.7g / cm 3 .

5. The lithium-ion battery according to claim 1, characterized in that, The electrolyte includes a carbonate-based solvent, a lithium salt, and a composite functional additive, wherein the composite functional additive includes a fluorinated cyclic carbonate, a fluorine-free lithium salt film-forming additive, and an organophosphorus flame retardant. Preferably, the lithium salt is lithium hexafluorophosphate, and the concentration of the lithium salt in the electrolyte is 1.0 mol / L to 1.5 mol / L.

6. The lithium-ion battery according to claim 5, characterized in that, In the electrolyte, the carbonate-based solvent includes ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate, and the volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 1:(0.5~1.5):(0.5~1.5). Preferably, in the electrolyte, the mass fraction of the fluorinated cyclic carbonate is 5% to 10%, the mass fraction of the fluorine-free lithium salt film-forming additive is 0.5% to 2.0%, and the mass fraction of the organophosphorus flame retardant is 3% to 8%. Preferably, the fluorinated cyclic carbonate is selected from at least one of fluoroethylene carbonate, trifluoromethyl ethylene carbonate, and fluoropropylene carbonate; Preferably, the fluorine-free lithium salt film-forming additive is selected from at least one of lithium dioxalate borate and lithium difluorooxalate borate; Preferably, the organophosphorus flame retardant is selected from at least one of trimethyl phosphate, triphosphate, and triethyl phosphate.

7. The lithium-ion battery according to claim 1, characterized in that, The diaphragm includes a composite base membrane and a ceramic coating located on at least one side of the composite base membrane. The composite base membrane includes a first polypropylene membrane, a polyethylene membrane, and a second polypropylene membrane arranged sequentially. Preferably, the thickness of the ceramic coating is 1 μm to 3 μm, and the total thickness of the diaphragm is 9 μm to 14 μm; more preferably, the ceramic coating is an Al2O3 ceramic coating.

8. The lithium-ion battery according to claim 1, characterized in that, By mass fraction, the negative electrode active material layer comprises 13%~18% deposited silicon carbon, 78%~84% artificial graphite, 1.0%~2.0% conductive agent, and 2.0%~3.0% binder; Preferably, the conductive agent in the negative electrode active material layer includes single-walled carbon nanotubes and conductive carbon black, and the mass ratio of the single-walled carbon nanotubes to the conductive carbon black is 1:(1.5~2.5). Preferably, the binder in the negative electrode active material layer includes sodium carboxymethyl cellulose, polyacrylic acid, and styrene-butadiene rubber, and the mass ratio of sodium carboxymethyl cellulose, polyacrylic acid, and styrene-butadiene rubber is 1:(0.5~1.0):(0.5~1.0).

9. The lithium-ion battery according to claim 1, characterized in that, At 25°C, the capacity retention rate of the lithium-ion battery at a 10C discharge rate is ≥75%, and the capacity retention rate is calculated based on the 1C discharge rate capacity. And / or, in a 70% deformation compression test, the lithium-ion battery does not catch fire or explode; And / or, in the needle penetration test, the steel nail diameter is 5mm and the penetration speed is 10mm / s, the lithium-ion battery meets the following requirements: the highest surface temperature within 1 minute after needle penetration is ≤120℃, and there is no fire or explosion.

10. An electrical appliance, characterized in that, Includes the lithium-ion battery described in any one of claims 1 to 9.

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