A lithium-ion battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery with excellent high-temperature cycle performance under fast charging conditions. The lithium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode comprises a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector, the positive electrode current collector is an aluminum foil or an aluminum alloy, the positive electrode current collector contains Ga elements, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the lithium salt comprises LiPF6 and LiFSI; the lithium ion battery satisfies the following conditions: 1.5 <= lgc+b / a <= 7.6, 0.1 <= bxd <= 1.2, 0.1 <= a <= 1.5, 0.1 <= b <= 1, 10 <= c <= 400 and 0.5 <= d <= 1.6. The lithium ion battery can improve the conductivity of the electrolyte and the lithium ion transference number, can realize uniform current distribution and lithium ion movement in the battery charging process, can form a complete, uniform and high-temperature stable protective film on the positive electrode surface, and can improve the fast charging performance and the high-temperature cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and specifically to a lithium-ion battery with excellent high-temperature cycle performance under fast charging conditions. Background Technology

[0002] Lithium-ion batteries, with their long lifespan and high energy density, are widely used in the electric vehicle industry. However, with the increasing prevalence of new energy vehicles, consumers are experiencing anxiety regarding their range, charging capabilities, and battery lifespan, particularly under high-temperature and high-current conditions, where battery capacity and output power can rapidly decline. Therefore, maintaining good high-temperature cycle performance under fast charging is a key development focus for both battery manufacturers and vehicle manufacturers.

[0003] Currently, the most widely used electrolyte in commercial applications is lithium hexafluorophosphate (LiPF6). However, LiPF6 is sensitive to moisture and easily generates HF, which damages the SEI film and causes battery performance degradation. In addition, LiPF6 has poor thermal stability and begins to decompose to produce LiF and PF5 at temperatures above 80°C. - Compared to the aforementioned problems of LiPF6, lithium bisfluorosulfonyl imide (LiFSI) exhibits higher thermal stability, with a decomposition temperature reaching 200°C. Adding LiFSI to the electrolyte results in higher conductivity and lithium-ion transference number, which is beneficial for improving fast-charging performance. Furthermore, LiFSI helps form a stable protective film with better ionic conductivity, suppressing high-temperature gas generation in the battery. Therefore, it is considered a promising new lithium salt to replace LiPF6, as it benefits fast charging and high-temperature performance. However, high concentrations of LiFSI at high potentials can easily damage the protective film on the positive electrode side, leading to side reactions. Moreover, the quality of the protective film formed by LiFSI on the positive electrode surface is affected by multiple factors, such as the potential distribution and resistivity of the positive electrode active material and current collector, as well as the compatibility with the electrolyte, limiting its application and significantly restricting the lifespan of lithium-ion batteries.

[0004] Therefore, developing a lithium-ion battery with excellent fast-charging performance and good high-temperature cycle performance has become an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a lithium-ion battery that maintains excellent high-temperature cycle performance even under fast-charging conditions.

[0006] The present invention adopts the following technical solution:

[0007] A lithium-ion battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector. The positive electrode current collector is an aluminum foil or an aluminum alloy and contains Ga. The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive. The lithium salt includes LiPF6 and LiFSI.

[0008] The lithium-ion battery meets the following conditions:

[0009] 1.5≤lgc+b / a≤7.6, 0.1≤b×d≤1.2, and 0.1≤a≤1.5, 0.1≤b≤1, 10≤c≤400, 0.5≤d≤1.6;

[0010] Where a is the molar content of LiPF6 in the non-aqueous electrolyte, in mol / L;

[0011] b represents the molar content of LiFSI in the non-aqueous electrolyte, in mol / L.

[0012] c represents the Ga content in the positive electrode current collector, expressed in ppm.

[0013] d represents the surface roughness of the positive electrode current collector, in μm.

[0014] In existing lithium-ion batteries, the electrolyte primarily uses LiPF6 as the lithium salt. However, LiPF6 has poor thermal stability and easily decomposes during charging and discharging, producing acid that corrodes the negative electrode interface film, inducing interfacial instability and reducing the battery's high-temperature performance. Through extensive research, the inventors discovered that adding lithium salts containing both LiPF6 and LiFSI to the electrolyte, along with a certain amount of Ga in the positive electrode current collector and controlling the surface roughness of the current collector, can improve the ductility of the positive electrode current collector, reducing micro-fractures at high temperatures. Furthermore, it can reduce resistivity, enabling rapid current distribution and improving the film formation rate, integrity, and stability. This allows for high-flux Li in the LiFSI electrolyte under fast-charging conditions. + The absence of lithium plating during the insertion of the negative electrode helps improve the cycle stability of the battery. At the same time, by taking advantage of the high thermal stability of LiFSI itself and the fact that LiFSI also participates in the interface film formation process of the negative electrode, a highly conductive and more stable interface film can be formed, thereby achieving excellent high-temperature cycle performance even under fast charging conditions.

[0015] Specifically, LiSFI has high conductivity and lithium-ion transference number, enabling faster lithium-ion movement during battery charging and forming a complete, high-temperature stable protective film. Replacing part of LiPF6 with LiSFI can improve the electrolyte conductivity and lithium-ion transference number, allowing for faster lithium-ion movement during charging and thus improving fast-charging performance. It can also reduce the LiPF6 content in the electrolyte, thereby reducing the LiF and PF5 generated by the high-temperature decomposition of LiPF6. - This reduces the loss of active lithium and improves the battery's high-temperature cycle performance. When the cathode material layer is in full contact with a current collector containing a certain amount of Ga, the Ga element can control the current collector's ductility, reduce resistivity, achieve rapid current distribution, and reduce micro-fractures at high temperatures. At the same time, the appropriate surface roughness of the current collector facilitates contact between the protruding parts and the active material layer and the current collector, resulting in a uniform surface potential distribution and reducing the electrical connection between the current collector and the active material layer at high temperatures. Therefore, at high rates, LiFSI can more quickly form a complete and high-temperature stable protective film on the cathode material layer, ensuring that the battery's fast-charging performance is balanced with its high-temperature performance.

[0016] Compared to elements like copper, silicon, and iron, Ga (GaN) is more effective at improving the mechanical strength, ductility, and film stability of the positive electrode current collector aluminum foil. When the Ga content is too low or the LiFSI content is too high, the mechanical strength of the positive electrode current collector is insufficient, resulting in an inadequate current distribution rate. This makes the battery prone to cracking during high-temperature cycling, and also prevents LiFSI from quickly forming a complete and stable protective film. Conversely, excessively high Ga content or excessively low LiFSI content leads to reduced mechanical strength of the positive electrode current collector or hinders high-rate charging of the battery. A higher surface roughness of the positive electrode current collector not only results in uneven potential distribution but also uneven distribution of the positive electrode material layer, hindering the formation of a complete and uniform LiFSI protective film. Conversely, a lower surface roughness and smoother surface, while allowing for the formation of a stable protective film, increases the difficulty of adhesion between the positive electrode material layer and the current collector, increasing manufacturing complexity and making the material more prone to detachment, thus affecting battery performance.

[0017] Preferably, the lithium-ion battery meets the following conditions:

[0018] 1.6≤lgc+b / a≤7.0, 0.2≤b×d≤1.0.

[0019] Specifically, the molar content a of LiPF6 in the non-aqueous electrolyte is 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, or 1.5 mol / L; more preferably, the molar content a of LiPF6 in the non-aqueous electrolyte is 0.2 to 1.2 mol / L.

[0020] Specifically, the molar content b of LiFSI in the non-aqueous electrolyte is 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, or 1.0 mol / L; more preferably, the molar content b of LiFSI in the non-aqueous electrolyte is 0.2 to 0.8 mol / L.

[0021] In this invention, LiPF6 and LiFSI are used together as lithium salts in the non-aqueous electrolyte. When the content of LiPF6 is too low and the content of LiFSI is insufficient, the overall lithium salt content in the non-aqueous electrolyte will be low, affecting the ionic conductivity of the non-aqueous electrolyte. When the content of LiPF6 is too high and the content of LiFSI is too low, the high-temperature stability of the non-aqueous electrolyte is insufficient and it is sensitive to moisture, easily decomposing to produce acidic substances such as HF. This leads to the dissolution of transition metals on the surface of the positive electrode active material and the current collector, catalyzing the decomposition of the electrolyte and aggravating the occurrence of side reactions, thus consuming active lithium, which then migrates to the negative electrode. Surface damage to the SEI film reduces the capacity and lifespan of lithium-ion batteries, affecting their high-temperature cycle performance. When the content of LiPF6 is too low and the content of LiFSI is too high, side reactions can easily occur on the positive electrode side, leading to the dissolution of metal ions. The dissolved metal ions will embed into the negative electrode before lithium ions, increasing electrode polarization, losing irreversible capacity, and ultimately significantly degrading the battery cycle performance. When the contents of both LiPF6 and LiFSI are too high, the overall lithium salt content in the non-aqueous electrolyte will be too high, increasing the viscosity of the non-aqueous electrolyte, which is also detrimental to improving the ionic conductivity of the non-aqueous electrolyte.

[0022] Specifically, the Ga content (c) in the positive electrode current collector is 10 ppm, 30 ppm, 40 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 200 ppm, 300 ppm, or 400 ppm; more preferably, the Ga content (c) in the positive electrode current collector is 40–200 ppm. When the Ga doping amount is too low, the improvement in the current collector's ductility is not significant; when the doping amount is too high, the improvement in the current collector's ductility is limited, and the high price of Ga increases the cost.

[0023] Specifically, the surface roughness d of the positive electrode current collector is 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.3μm, 1.4μm, or 1.6μm; more preferably, the surface roughness d of the positive electrode current collector is 0.6 to 1.0μm.

[0024] The greater the surface roughness of the positive electrode current collector, the more uneven the surface becomes, leading to uneven potential distribution and uneven distribution of the positive electrode material layer. This is detrimental to the formation of a complete and uniform protective film for LiFSI, and also results in more reactive sites (active sites refer to lattice defect sites in metal crystals; metal atoms located at edges are most likely to detach from the lattice because their lattice binding energy is weaker, and they have a larger contact area with the solvent, making them more easily adsorbed). This makes the aluminum foil more susceptible to corrosion. Furthermore, under high temperature and high voltage conditions, the chemical reactivity of the electrolyte and the electrochemical reactivity at the electrode interface both increase, further exacerbating the corrosion of the aluminum foil. Conversely, if the surface roughness of the positive electrode current collector is too low and the surface is too smooth, the current collector and the positive electrode material layer cannot adhere tightly together. This not only affects the battery manufacturing process but also leads to delamination between the current collector and the positive electrode material layer, increasing battery impedance and ultimately affecting the battery's electrochemical performance.

[0025] Specifically, the lithium salts also include LiBOB, LiDFOB, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one of lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, or lithium tetraphenylborate.

[0026] Specifically, the additive is selected from at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds;

[0027] Based on the total mass of the non-aqueous electrolyte as 100%, the content of the additive is 0.01% to 30%.

[0028] Preferably, the cyclic sulfate compound is selected from at least one of vinyl sulfate (DTD), 4-methylvinyl sulfate, and propylene sulfate;

[0029] The sulfonyl lactone compound is selected from at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0030] The cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate (FEC), trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and the compound shown in structural formula 1 below:

[0031]

[0032] In the structural formula 1 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group;

[0033] More preferably, the compound shown in structural formula 1 includes at least one of the compounds shown in compounds 1-1 to 1-6 below:

[0034]

[0035]

[0036] The phosphate ester compound is selected from at least one of tris(trimethylsilane) phosphate (TMSP), tris(triethylsilane) phosphate, and the compound shown in structural formula 2 below:

[0037]

[0038] In structural formula 2, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33At least one of them is an unsaturated hydrocarbon group; more preferably, the compound represented by structural formula 2 includes at least one of the following: triargyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0039] The borate ester compound is selected from at least one of tris(trimethylsilane)borate ester and tris(triethylsilane)borate ester;

[0040] The nitrile compound is selected from at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitrile.

[0041] Specifically, the non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

[0042] In preferred embodiments, the ether solvent includes cyclic ethers or chain ethers. Specifically, the cyclic ether may be, but is not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ether may be, but is not limited to, at least one of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (TEGDME). The nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile. Carbonate solvents include cyclic carbonates or chain carbonates. Cyclic carbonates may specifically include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC). Chain carbonates may specifically include, but are not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). Carboxylic acid ester solvents may specifically include, but are not limited to, at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0043] Specifically, the positive electrode material layer includes a positive electrode active material, which is selected from LiFe. 1-x’ M'x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z At least one of O2; wherein M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V, or Ti; M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V, or Ti; 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1. The positive electrode active material may also be selected from at least one of sulfides, selenides, and halides.

[0044] More preferably, the positive electrode active material can be selected from LiCoO2, LiFePO4, or LiFe 0.4 Mn 0.6 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 At least one of O2.

[0045] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0046] The positive electrode binder includes one or more of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0047] The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0048] In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes one or more of carbon-based negative electrodes, silicon-based negative electrodes, tin-based negative electrodes, and lithium negative electrodes. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the tin-based negative electrode may include tin, tin-carbon, tin oxide, and tin metal compounds; the lithium negative electrode may include metallic lithium or lithium alloys. Specifically, the lithium alloy may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0049] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector may be the same as that of the positive electrode current collector, and will not be described in detail here.

[0050] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described in detail here.

[0051] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0052] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0053] The lithium-ion battery of this invention partially replaces LiPF6 with LiFSI in a non-aqueous electrolyte, which improves the electrolyte conductivity and lithium-ion transference number, enhances fast-charging performance, and reduces the loss of active lithium caused by the high-temperature decomposition of LiPF6. Simultaneously, doping the positive electrode current collector with Ga reduces resistivity and enables rapid current distribution. Controlling the surface roughness of the positive electrode current collector ensures uniform potential distribution in the positive electrode material layer, allowing LiFSI to form a complete and high-temperature stable protective film on the positive electrode material layer more rapidly at high rates. When ion batteries satisfy the relationships 1.5≤lgc+b / a≤7.6 and 0.1≤b×d≤1.2, they can fully leverage the synergistic effect between LiPF6, LiFSI, the roughness of the positive electrode current collector, and the doping amount of Ga. This not only improves the conductivity and lithium-ion transference number of the electrolyte, enabling faster and more uniform current distribution and lithium-ion movement during battery charging, but also forms a complete, uniform, and high-temperature stable protective film on the positive electrode surface. This improves both fast-charging performance and high-temperature cycle performance of the battery. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0055] Examples 1-28

[0056] The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0057] 1) Preparation of the positive electrode

[0058] The ternary cathode active material LiNi was mixed at a mass ratio of 93:4:3. 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black (Super-P), and binder polyvinylidene fluoride (PVDF) are dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of the positive electrode current collector aluminum foil (aluminum alloy) with Ga element content and surface roughness as shown in Table 1. After drying, rolling, and vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain the positive electrode. The average surface roughness of the positive electrode current collector can be tested by the method described in ISO 1302:2002.

[0059] 2) Preparation of the negative electrode

[0060] Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 94:1:2.5:2.5 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil, dried, calendered, and vacuum dried, and nickel leads are welded on using an ultrasonic welding machine to obtain the negative electrode.

[0061] 3) Preparation of electrolyte

[0062] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a volume ratio of EC:DEC:EMC = 1:1:1. Then, lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and vinylene carbonate (VC) were added. Based on the total mass of the electrolyte being 100% and the content of VC being 0.5%, the molar contents of LiPF6 and LiFSI in the non-aqueous electrolyte are shown in Table 1.

[0063] 4) Battery assembly

[0064] A separator is placed between the positive and negative electrodes. Then, the sandwich structure consisting of the positive electrode, negative electrode, and separator is wound up. The wound body is flattened and placed into a square aluminum metal shell. The leads of the positive and negative electrodes are welded to the corresponding positions on the cover plate. The cover plate and the metal shell are then welded together using a laser welding machine to obtain the battery cell to be injected with electrolyte. The electrolyte prepared above is injected into the battery cell through the injection hole. The amount of electrolyte should be sufficient to fill the gaps in the battery cell.

[0065] Then, perform the following routine formation steps: charge at a constant current of 0.05C for 180 minutes, charge at a constant current of 0.2C to 3.95V, vacuum seal a second time, and then charge at a constant current of 0.2C to 4.4V cutoff voltage. After resting at room temperature for 24 hours, discharge at a constant current of 0.2C to 3.0V to obtain the finished lithium-ion battery.

[0066] Comparative Examples 1-17

[0067] This comparative example is used to illustrate the lithium-ion battery disclosed in this invention, including most of the operating steps in the above embodiments. The difference is that the types and contents of lithium salts in the non-aqueous electrolyte, the doping elements and contents in the positive electrode current collector, and the roughness of the positive electrode current collector are shown in Table 1.

[0068] Comparative Example 18

[0069] This comparative example is used to illustrate the lithium-ion battery disclosed in this invention, including most of the operating steps in Example 11 above, except that the doping element in the positive electrode current collector is replaced by Fe instead of Ga.

[0070] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to performance testing according to the following methods:

[0071] 1) 25℃ DCIR performance test: At 25℃, the battery after capacity division is charged to 4.4V with 0.5C constant current and constant voltage, and the cutoff current is 0.05C. Then it is discharged to 3.0V with 0.5C constant current and constant voltage, and pre-cycled for 2 cycles. Then it is charged to 50% of the charging capacity with 0.5C constant current and constant voltage, and discharged at 2C for 10 seconds. The DCIR performance at 25℃ is calculated.

[0072] 2) Constant current ratio at room temperature: At 25℃, the batteries after capacity testing were charged to 4.4V using a constant current and constant voltage of 4C, and the cutoff current was 0.05C. The constant current charging ratio was recorded.

[0073] 3) High-temperature cycle performance: At 45℃, the battery, after capacity gradation, is charged to 80% SOC using a 4C constant current, then charged to 4.4V using a 1C constant current, with a cutoff current of 0.05C. It is then discharged to 3.0V using a 1C constant current, and the first discharge capacity is recorded. Subsequent charge-discharge cycles are performed following the same steps. The calculation formula is as follows:

[0074] Capacity retention rate after 800 cycles (%) = (Discharge capacity after 800 cycles / Discharge capacity after the first cycle) × 100%.

[0075] The test results are shown in Table 2.

[0076] Table 1

[0077]

[0078]

[0079] Table 2

[0080]

[0081]

[0082] As shown in Table 2, the test results of Examples 1-28 and Comparative Examples 1-9 indicate that when the molar content of LiPF6 (a), the molar content of LiFSI (b), the content of Ga in the positive electrode current collector (c), and the surface roughness of the positive electrode current collector (d) satisfy 1.0≤lgc+b / a≤15, 0.1≤b×d≤1.2, and 0.1≤a≤1.5, 0.1≤b≤1, 10≤c≤400, and 0.5≤d≤1.6, LiFSI, with its high conductivity and transport number, can rapidly achieve lithium-ion movement. Simultaneously, the Ga content and surface roughness of the positive electrode current collector play a significant role in achieving rapid current distribution and reducing micro-fractures at high temperatures, resulting in a positive electrode sheet with good mechanical strength. Furthermore, it forms a good conductive network, accelerates electron transport rate, balances the current distribution of the positive electrode sheet, and makes lithium-ion transport more uniform and thorough, forming a complete, uniform, and stable protective film, thus achieving good fast-charging performance and high-temperature performance of the lithium-ion battery. Preferably, when the preset relationships 1.6≤lgc+b / a≤7 and 0.2≤b×d≤1.0 are satisfied, the performance of lithium-ion batteries can be further improved.

[0083] The test results of Comparative Examples 10-13 show that both excessively large and small values ​​of lgc+b / a or b×d negatively impact the initial impedance, fast charging, and high-temperature cycling performance of lithium-ion batteries. This indicates that the molar content of LiPF6 (a) in the non-aqueous electrolyte, the molar content of LiFSI (b), the content of Ga in the positive electrode current collector (c), and the surface roughness (d) of the positive electrode current collector are interconnected and mutually influential. Only when these four factors are in a certain balance can LiFSI quickly form a complete, uniform, and stable protective film and improve the battery's high-temperature cycling performance. Furthermore, the test results of Comparative Examples 2-9 show that even if the values ​​of lgc+b / a and b×d are within the limits of the above relationships, if the values ​​of a, b, c, or d do not meet these limits, the resulting lithium-ion batteries will still not exhibit superior fast charging and high-temperature cycling performance.

[0084] The test results of Examples 17-20 and Comparative Examples 14-15 show that the greater the surface roughness of the positive electrode current collector, the less conducive it is to the formation of a complete and uniform protective film of LiFSI; while the smaller the surface roughness of the positive electrode current collector, the more difficult it is for the positive electrode material layer to adhere to the current collector, and the easier it is for the material to fall off, which affects the battery performance.

[0085] The test results from Examples 13-15 and Comparative Examples 16-17 show that partially replacing LiPF6 with LiFSI in a non-aqueous electrolyte can improve the electrolyte's conductivity and lithium-ion transference number, enabling faster lithium-ion movement during battery charging and thus improving fast-charging performance. Simultaneously, it can reduce the LiPF6 content in the electrolyte, thereby minimizing the LiF and PF5 generated by the high-temperature decomposition of LiPF6. -This reduces the loss of active lithium and improves the battery's high-temperature cycle performance.

[0086] The test results of Example 11, Comparative Example 1 and Comparative Example 18 show that doping the current collector with Ga helps to improve the film formation rate, integrity and stability, thereby improving battery performance, compared to doping with other elements or not doping.

[0087] The test results of Examples 11 and 26-28 show that adding vinyl sulfate, fluoroethylene carbonate or tris(trimethylsilane) phosphate as auxiliary additives to non-aqueous electrolytes can further improve the high-temperature cycle performance of batteries.

[0088] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all 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, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector. The positive electrode current collector is an aluminum foil or an aluminum alloy and contains Ga. The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, and additives. The lithium salt includes LiPF6 and LiFSI. The lithium-ion battery meets the following conditions: 1.5≤lgc+b / a≤7.6, 0.1≤b×d≤1.2, and 0.1≤a≤1.5, 0.1≤b≤1, 40≤c≤200, 0.5≤d≤1.6; Where a is the molar content of LiPF6 in the non-aqueous electrolyte, in mol / L; b represents the molar content of LiFSI in the non-aqueous electrolyte, in mol / L; c represents the Ga content in the positive electrode current collector, in ppm; d represents the surface roughness of the positive electrode current collector, in μm.

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery meets the following conditions: 1.6≤lgc+b / a≤7.0, 0.2≤b×d≤1.

0.

3. The lithium-ion battery according to claim 1, characterized in that, The molar content (a) of LiPF6 in the non-aqueous electrolyte is 0.2–1.2 mol / L.

4. The lithium-ion battery according to claim 1, characterized in that, The molar content b of LiFSI in the non-aqueous electrolyte is 0.2–0.8 mol / L.

5. The lithium-ion battery according to claim 1, characterized in that, The surface roughness d of the positive electrode current collector is 0.6~1.0μm.

6. The lithium-ion battery according to claim 1, characterized in that, The additive is selected from at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds.

7. The lithium-ion battery according to claim 6, characterized in that, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the additive is 0.01% to 30%.

8. The lithium-ion battery according to claim 6, characterized in that, The cyclic sulfate compound is selected from at least one of vinyl sulfate, 4-methyl vinyl sulfate, and propylene sulfate; The sulfonyl lactone compound is selected from at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone. The cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and the compound shown in structural formula 1 below: Structural Formula 1 In the structural formula 1 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group; The phosphate ester compound is selected from at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and the compound shown in structural formula 2 below: Structural Formula 2 In structural formula 2, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group; The borate ester compound is selected from at least one of tris(trimethylsilane)borate ester and tris(triethylsilane)borate ester; The nitrile compound is selected from at least one of succinic acid, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitrile.

9. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

10. The lithium-ion battery according to claim 1, characterized in that, The positive electrode material layer includes a positive electrode active material, which is selected from LiFe. 1-x’ M' x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z At least one of O2; Wherein, M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti; M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V, or Ti; 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

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