A lithium-ion battery

Abstract

The application belongs to the technical field of new energy batteries, and particularly relates to a lithium ion battery. The lithium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte; the positive electrode comprises a positive electrode active material comprising a lithium nickel manganese oxide material doped with a phosphorus element and / or coated with a phosphorus-containing compound; the non-aqueous organic solvent in the non-aqueous electrolyte comprises a first solvent and a second solvent; the first solvent comprises at least one of methyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether; the second solvent comprises one or both of dimethyl carbonate and methyl ethyl carbonate; the lithium ion battery satisfies 0.1 <= 100E x (F / L) <= 12, 0.005 <= E <= 0.045, 5 <= F <= 50 and 10 <= L <= 60. The lithium ion battery provided by the application can realize the synergistic optimization of material structure stability and electrolyte performance, and has high conductivity and high oxidation resistance.

Description

Technical Field

[0001] This invention belongs to the field of new energy battery technology and relates to a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high operating voltage, wide operating temperature range, high energy density, high output power, no memory effect, and long cycle life, are widely used not only in 3C digital products such as mobile phones and laptops, but also have a broad application market in new energy vehicles and large-scale energy storage. "Range anxiety" is a persistent issue in the electric vehicle industry, driving continuous improvements in battery energy density. High voltage is one of the mainstream future technologies. The chemical system of the positive and negative electrode materials determines the upper limit of the cell's energy density. Currently, the widely used nickel-cobalt-manganese ternary and lithium iron phosphate systems have an upper operating voltage limit of ≤4.5V. Under overcharge conditions, the capacity utilized in the 4.5V~5V range accounts for ≤15% of the total capacity across the entire voltage range, accompanied by irreversible structural damage and rapid capacity decay.

[0003] Balancing improved voltage resistance and conductivity is crucial for the electrolyte design of this system. Fluorinated solvents offer high oxidation stability but come with high viscosity and low conductivity, hindering performance at low temperatures and fast-charging applications. Carbonate solvents, on the other hand, are considered to decompose above 4.5V, negatively impacting overall system stability. Therefore, exploring the coupling design of solvents and additives to meet the application requirements of electrolytes under ultra-high voltage conditions warrants further investigation.

[0004] The high-voltage lithium nickel manganese oxide system operates at a voltage as high as approximately 4.7V, with a theoretical specific capacity of up to 133mAh / g. The Ni formed during its charging state... 4+ Its strong oxidizing properties can lead to the oxidative decomposition of the electrolyte, causing a series of problems such as the dissolution of transition metal ions and the formation of interfacial films at the electrode / electrolyte interface that hinder lithium-ion insertion and extraction, resulting in battery performance degradation. To match the battery performance under ultra-high voltage, it is necessary to develop a lithium-ion battery that combines high conductivity and high oxidation resistance. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a high-voltage lithium-ion battery that can combine high conductivity and high oxidation resistance, thereby improving the fast-charging performance and low-temperature performance of lithium-ion batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; the positive electrode comprises a positive electrode material layer containing a positive electrode active material, the positive electrode active material comprising lithium nickel manganese oxide material doped and / or coated with a phosphorus-containing compound, and the mass ratio of phosphorus to nickel in the positive electrode material layer is E;

[0008] The non-aqueous electrolyte comprises a non-aqueous organic solvent and a lithium salt, wherein the non-aqueous organic solvent includes a first solvent and a second solvent;

[0009] The first solvent includes at least one of methyl trifluoroethyl carbonate (FEMC, CAS: 156783-95-8), bis(2,2,2-trifluoroethyl) carbonate (FDEC, CAS: 1513-87-7), 2,2-difluoroethyl acetate (DFEA, CAS: 1550-44-3), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE458, CAS: 16627-68-2);

[0010] The second solvent includes one or both of dimethyl carbonate and ethyl methyl carbonate;

[0011] Based on the mass of the non-aqueous electrolyte, the mass percentage of the first solvent is F%, and the mass percentage of the second solvent is L%.

[0012] The lithium-ion battery satisfies the following conditions: 0.1≤100E×(F / L)≤12, and 0.005≤E≤0.045, 5≤F≤50, 10≤L≤60.

[0013] Although lithium nickel manganese oxide materials have a high voltage plateau, they are prone to severe structural damage and ion dissolution under high voltage, which exacerbates electrolyte decomposition and electrochemical performance degradation. Therefore, the lithium-ion battery of this invention dops and / or coats lithium nickel manganese oxide materials with phosphorus-containing compounds, using at least one of methyl trifluoroethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether as the first solvent, and one or two of dimethyl carbonate and methyl ethyl carbonate as the second solvent. Furthermore, the mass ratio E of phosphorus to nickel in the positive electrode material layer and the mass percentage F of the first solvent in the non-aqueous electrolyte are controlled. The mass percentage L of the second solvent in the non-aqueous electrolyte was limited. Through extensive research, the inventors discovered that when the mass ratio E of phosphorus to nickel in the cathode material layer, the mass percentage F of the first solvent in the non-aqueous electrolyte, and the mass percentage L of the second solvent in the non-aqueous electrolyte satisfy 0.1≤100E×(F / L)≤12, and 0.005≤E≤0.045, 5≤F≤50, 10≤L≤60, a synergistic mechanism is formed among these parameters, achieving stable cycling of the ultra-high voltage battery system. The speculated reason is that the doping and / or coating of phosphorus-containing compounds in the lithium nickel manganese oxide material can effectively reduce oxygen release from the cathode and interfacial side reactions. In this battery system, dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) can be used as the main solvent to regulate the high conductivity and low viscosity characteristics of the electrolyte, ensuring high rate performance and excellent low-temperature performance of the battery. Through the introduction of fluorinated solvents, Li + The strength of -F-solvents decreases, solvates involving DMC / EMC are stabilized, and the free structure in the electrolyte system is reduced, thereby achieving a higher LUMO energy level and good reduction stability. Preferably, the lithium-ion battery satisfies: 0.13 ≤ 100E × (F / L) ≤ 3.5. Within this range, it is beneficial to further improve the conductivity and oxidation stability of the lithium-ion battery.

[0014] E is defined as the mass ratio of phosphorus (P) to nickel (Ni) in the cathode material layer. A higher phosphorus (P) ratio indicates better protection of the material bulk. However, an excessively high P ratio, with excessive doping and / or coating, can disrupt the periodicity of the layered structure, leading to increased lattice distortion and reduced structural stability. Conversely, a higher Ni (Ni) ratio results in greater specific capacity potential, but also higher requirements for structural protection (e.g., phosphorus doping amount) and interfacial stability. Therefore, a phosphorus-to-nickel ratio E in the cathode material layer within the range of 0.005 ≤ E ≤ 0.045 is beneficial for achieving a balance between structural stability and specific capacity potential. This avoids structural damage caused by excessive P doping while fully utilizing the capacity advantages of high-nickel materials, and simultaneously optimizes the interfacial stability and electrochemical performance of the battery system. Specifically, the mass ratio E of phosphorus to nickel in the cathode material layer is within the range of any two of the following: 0.005, 0.006, 0.008, 0.01, 0.013, 0.014, 0.015, 0.017, 0.02, 0.023, 0.025, 0.027, 0.03, 0.033, 0.035, 0.037, 0.038, 0.041, 0.045. Preferably, the mass ratio E of phosphorus to nickel in the cathode material layer is between 0.008 and 0.03. Within this range, it is more beneficial to optimize the interfacial stability and electrochemical performance of the battery system.

[0015] Furthermore, adjusting the coordination strength and interfacial behavior of the electrode surface through dipole-dipole interactions is also an effective means to improve the stability of ultra-high voltage battery systems. In this invention, a fluorinated solvent is used as the first solvent to construct a fluorine-rich interfacial layer (SEI / CEI) containing different anions in the initial film formation stage, thereby improving the high-voltage oxidation resistance of the system and reducing electrolyte decomposition. In subsequent processes, due to the coexistence of DMC, EMC, and the fluorinated solvent, DMC, EMC-F-solvents, and Li + -F-solvents, Li + A microsolvent competition relationship was established between the -DMC / EMC pairs, while the fluorinated Li molecules... + Li has poor affinity. + The strength of -F-solvents decreases, DMC / EMC-involved solvates are stabilized, and the free structure in the electrolyte system is reduced, resulting in a higher LUMO energy level and good reduction stability. When the mass percentage (F%) of the first solvent in the non-aqueous electrolyte is too high, it may lead to over-fluorination of the interfacial layer, resulting in a rigid and dense structure that inhibits Li-. +Rapid migration of ions increases interfacial impedance; excessive fluorinated solvents also significantly increase electrolyte viscosity, increasing ion migration resistance and thus reducing electrolyte conductivity. When the mass percentage (F%) of the first solvent in the non-aqueous electrolyte is too low, the number of free structures in the electrolyte increases, the LUMO energy level decreases, and the reduction stability of the electrolyte on the negative electrode surface decreases, which may lead to instability or continuous decomposition / reconstruction of the SEI film. When the mass percentage (F%) of the first solvent in the non-aqueous electrolyte is in the range of 5% to 50%, a stable fluorine-rich interface can be constructed, achieving a balance with the electrolyte ion transport performance and optimizing the performance of the high-voltage lithium-ion battery system. Specifically, the mass percentage (F%) of the first solvent in the non-aqueous electrolyte is 5%, 7%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, or any two of these ranges. Preferably, the mass percentage (F%) of the first solvent in the non-aqueous electrolyte is 7% to 25%. Within this range, a better balance can be achieved between the construction of the fluorine-rich interface and the ion transport performance of the electrolyte.

[0016] Conventional carbonate solvents are not resistant to high voltages (≥4.5V), and the industry typically uses fluorine substitution strategies to improve the oxidation stability of the system. However, fluorinated solvents usually exhibit high viscosity and low conductivity, and their high proportion is detrimental to rate performance and low-temperature performance. DMC and EMC in the second solvent have advantages such as low viscosity and high dielectric constant, but at high voltages (≥4.5V), DMC and EMC molecules are easily attacked by strong oxidizing species on the surface of the cathode (such as NCM811, LNMO), decomposing and producing gases such as CO2 and CH3OH, leading to rapid capacity decay. However, the inventors discovered that phosphorus-doped and / or coated lithium nickel manganese oxide cathodes can effectively reduce oxygen release and interfacial side reactions, reducing the risk of conventional carbonate introduction. In this battery system, both DMC and EMC can be used as main solvents to regulate the high conductivity and low viscosity characteristics of the electrolyte, ensuring high rate performance and excellent low-temperature performance. Based on this logic, the higher the phosphorus doping content, the greater the protection of the structure, and the proportion of DMC and EMC can be appropriately increased. When the mass percentage (L%) of the second solvent is too high, it leads to an increase in solvent molecules participating in decomposition, generating gases such as CO2 and CH3OH, accelerating electrolyte consumption and cathode structure degradation. Excessive decomposition of DMC and EMC may also damage the stability of the SEI / CEI film, causing continuous contact between the active material and the electrolyte, exacerbating transition metal dissolution and electrolyte decomposition, and consequently causing rapid capacity decay. When the mass percentage (L%) of the second solvent is too low, the side effects of fluorinated solvents become prominent, resulting in decreased electrolyte ionic conductivity, deterioration of rate performance and low-temperature performance, and battery performance imbalance. When the mass percentage (L%) of the second solvent is within the range of 10% ≤ L% ≤ 60%, under the protection of the phosphorus-doped cathode, the ionic conductivity of the non-aqueous electrolyte (dependent on the low viscosity and high conductivity of DMC and EMC) and interfacial stability (dependent on the oxidation resistance of fluorinated solvents) can be balanced by controlling the ratio of DMC and EMC. Specifically, the mass percentage L% of the second solvent in the non-aqueous electrolyte is within any two of the following ranges: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or more. Preferably, the mass percentage L% of the second solvent in the non-aqueous electrolyte is 20% to 50%, which is beneficial for improving the ion conductivity and interfacial stability of the non-aqueous electrolyte.

[0017] In some embodiments of the present invention, based on the mass of the non-aqueous electrolyte, the total mass percentage of the first solvent and the second solvent satisfies: 50 ≤ F + L ≤ 70. Within this range, the ion conductivity and interfacial stability of the non-aqueous electrolyte can be better balanced.

[0018] In some embodiments of the present invention, the positive electrode active material includes lithium nickel manganese oxide material doped and / or coated with phosphorus-containing compounds. Phosphorus doping / coating utilizes the strong covalent properties of PO bonds to enhance lattice bonding energy, suppress structural distortion caused by the Jahn-Teller effect during charging and discharging, reduce phase transitions, and simultaneously block direct contact between the electrolyte and the active material, inhibiting transition metal dissolution and electrolyte decomposition.

[0019] In some embodiments of the present invention, when the first solvent contains multiple substances, the proportion of a single substance is ≥2%.

[0020] In some embodiments of the present invention, the charging cutoff voltage of the lithium-ion battery is 4.6~5V.

[0021] In some embodiments of the present invention, the non-aqueous electrolyte has a conductivity of ≥6.5 mS / cm at 25°C to ensure effective lithium-ion transport and improve the battery's fast charging capability. Specifically, the conductivity of the electrolyte at 25°C is 6.5 mS / cm, 6.6 mS / cm, 6.75 mS / cm, 6.88 mS / cm, 7.0 mS / cm, 7.2 mS / cm, 7.3 mS / cm, 7.5 mS / cm, 7.6 mS / cm, 7.7 mS / cm, 7.8 mS / cm, 8.0 mS / cm, 8.2 mS / cm, 8.3 mS / cm, 8.5 mS / cm, 8.6 mS / cm, 8.8 mS / cm, 9.0 mS / cm, 9.2 mS / cm, 9.5 mS / cm, 9.7 mS / cm, 9.8 mS / cm, 10 mS / cm, or any combination of two of the above values. Preferably, the conductivity of the electrolyte at 25°C is 6.5 mS / cm to 8.0 mS / cm.

[0022] The conductivity of the non-aqueous electrolyte at 25°C is the ionic conductivity, which can be detected using equipment and methods known in the art, such as by referring to industry standard HG-T 4067-2015.

[0023] In some embodiments of the present invention, the non-aqueous electrolyte further includes a first additive, which comprises at least one of fluoroethylene carbonate or difluoroethylene carbonate. Based on the mass of the non-aqueous electrolyte, the mass percentage A% of the first additive satisfies: 1 ≤ A ≤ 8. Specifically, the mass percentage A% of the first additive is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any combination of these values. Preferably, the mass percentage A% of the first additive satisfies: 1.5 ≤ A ≤ 7. Within this range, it is beneficial to improve the oxidation resistance of the electrolyte without causing uncontrollable gas production growth.

[0024] In some embodiments of the present invention, the non-aqueous electrolyte further includes a second additive, which comprises at least one selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propylene-1,3-sulfonic acid lactone. Based on the mass of the non-aqueous electrolyte, the mass percentage B% of the second additive satisfies the condition: 1 ≤ B ≤ 10. The mass percentage B% of the second additive is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any combination of these values. Preferably, the mass percentage B% of the second additive satisfies the condition: 3 ≤ B ≤ 8. Within this range, it is beneficial for the effective construction of the positive electrode interface film, forming an elastic cross-linked network on its surface, inhibiting structural damage, and improving high-temperature performance.

[0025] In some embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, LiPO₂F₂, LiBF₄, LiBOB, LiSbF₆, LiAsF₆, LiCF₃SO₃, LiDFOB, LiDFOP, LiC(SO₂CF₃)₃, LiN(SO₂C₂F₅)₂, LiCl, LiBr, LiI, LiClO₄, and LiB₂. 10 Cl 10 At least one of LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

[0026] In specific embodiments, the total molar content of the lithium salt is 0.5 mol / L to 3.5 mol / L. In preferred embodiments, the total molar content of the lithium salt is 0.8 mol / L to 2.0 mol / L. Specifically, the total molar content of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, etc. 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3.0 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, or any combination of these values.

[0027] Specifically, in some embodiments of the present invention, the positive electrode further includes a positive electrode binder and a positive electrode conductive agent. 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. The positive electrode conductive agent includes one or more of the following: conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0028] Specifically, in some embodiments of the present invention, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector. The positive electrode current collector includes a metallic material capable of conducting electrons; preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0029] Specifically, in some embodiments of the present invention, the negative electrode includes a negative electrode material layer containing a negative electrode active material, wherein the negative electrode active material includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, mesophase micro carbon spheres, silicon, silicon oxide, silicon-carbon composite or metallic lithium.

[0030] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode current collector, a negative electrode binder, and a negative electrode conductive agent. The negative electrode binder and negative electrode conductive agent can be the same as the positive electrode binder and positive electrode conductive agent, respectively, and will not be described in detail here.

[0031] Specifically, in some embodiments of the present invention, the diaphragm is a conventional diaphragm selected from one or more of ceramic diaphragms, polymer diaphragms, non-woven fabrics, and inorganic-organic composite diaphragms. For example, single-layer polypropylene (PP) diaphragms, single-layer polyethylene (PE) diaphragms, double-layer PP / PE diaphragms, double-layer PP / PP diaphragms, and triple-layer PP / PE / PP diaphragms.

[0032] The lithium-ion battery of the present invention uses lithium nickel manganese oxide material doped and / or coated with phosphorus-containing compounds as the positive electrode active material, and at least one of methyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether as the first solvent, and one or two of dimethyl carbonate and methyl ethyl carbonate as the second solvent. It has been found that a higher proportion of phosphorus indicates better protection of the material body, and the electrolyte design can use a lower content of fluorinated solvent. The first solvent (fluorinated solvent) needs to be used in combination with the second solvent (non-fluorinated solvent) in a specific ratio to adjust the solvation structure. Therefore, by defining the relationship between the mass ratio E of phosphorus to nickel in the cathode material layer, the mass percentage F of the first solvent in the non-aqueous electrolyte, and the mass percentage L of the second solvent in the non-aqueous electrolyte, and satisfying the following conditions, it is possible to achieve synergistic optimization of material structure stability and electrolyte performance, resulting in a high-voltage lithium-ion battery with both high conductivity and high oxidation resistance. Detailed Implementation

[0033] 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.

[0034] Example 1

[0035] The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0036] (1) Preparation of positive electrode: High-voltage phosphorus-doped lithium nickel manganese oxide active material, conductive carbon black and binder polyvinylidene fluoride are mixed in a mass ratio of 94.5:3.0:2.5 and dispersed in N-methyl-2-pyrrolidone to obtain positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of aluminum foil, dried, rolled and vacuum dried, and aluminum leads are welded on with an ultrasonic welding machine to obtain positive electrode plate; the mass ratio E of phosphorus to nickel in the positive electrode material layer is 0.020.

[0037] (2) Anode preparation: Graphite material, conductive carbon black, styrene-butadiene rubber binder, and carboxymethyl cellulose were mixed in a mass ratio of 95.2:1.0:2.4:1.4 and dispersed in deionized water to obtain anode slurry. The anode slurry was coated on both sides of copper foil, dried, rolled, and vacuum dried, and nickel leads were welded on using an ultrasonic welding machine to obtain anode plate. The compaction density of the anode material was controlled to be 1.6 g / cm³ by the areal density and rolling thickness of the anode material. 3 ;

[0038] (3) Preparation of non-aqueous electrolyte: Ethyl carbonate (EC), methyl trifluoroethyl carbonate (FEMC) and dimethyl carbonate (DMC) are mixed in a non-aqueous solvent, and then LiPF6 and FEC are added; wherein, based on the mass of the non-aqueous electrolyte, the concentration of LiPF6 is 1 mol / L, the mass percentage of FEC is 2%, the mass percentage of the first solvent (FEMC) is 10%, and the mass percentage of the second solvent (DMC) is 40%.

[0039] (4) Membrane preparation: A three-layer membrane of polypropylene, polyethylene and polypropylene is used;

[0040] (5) Battery assembly: Place a separator between the positive plate and the negative plate, then wind the sandwich structure composed of the positive plate, the negative plate and the separator, flatten the wound body and put it into the aluminum-plastic shell, weld the tabs and seal the aluminum-plastic shell to obtain the cell to be injected with electrolyte; cut the prepared electrolyte and inject it into the cell, let it stand for 1 hour and then seal it. After sealing, the battery is aged at 45°C for 48 hours.

[0041] Examples 1 to 21

[0042] Examples 1 to 21 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences:

[0043] The mass ratio E of phosphorus to nickel in the positive electrode material layer, the types and contents of the first and second solvents, and the types and contents of the first additive are shown in Table 1. In the non-aqueous electrolyte, the non-aqueous solvent, in addition to the first and second solvents, is ethylene carbonate.

[0044] Comparative Examples 1 to 11

[0045] Comparative Examples 1 to 11 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1. The difference is that the mass ratio E of phosphorus to nickel in the positive electrode material layer, the types and contents of the first solvent and the second solvent, the types and contents of the first additive and the second additive are shown in Table 1. In the non-aqueous electrolyte, the non-aqueous solvent, in addition to the first solvent and the second solvent, is ethylene carbonate.

[0046] Table 1

[0047]

[0048]

[0049] Note: " / " in the table indicates that the item is not present; "DMC" represents dimethyl carbonate; "EMC" represents ethyl methyl carbonate; "FEMC" represents methyl trifluoroethyl carbonate; "FDEC" represents di(2,2,2-trifluoroethyl) carbonate; when there are multiple types of first and second solvents, the content is evenly distributed.

[0050] Table 1 shows the parameters required for preparing lithium-ion batteries in Examples 1 to 21 and Comparative Examples 1 to 11. The differences between Examples 1 to 21 and Comparative Examples 1 to 11 and Example 1 are the relevant parameters in Table 1. The other parameters and preparation steps are the same as those in Example 1. The specific differences are: the mass ratio E of P and Ni in the positive electrode active material, the types and contents of the first solvent and the second solvent, and the types and contents of the first additive.

[0051] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to the following performance tests:

[0052] Performance testing: Perform the following routine formation for the first charge: 0.05C constant current charging for 3 hours, 0.1C constant current charging for 2 hours, 0.2C constant current charging for 2 hours, rest for 1 hour, age at 45℃ for 48 hours, and then further charge at 0.2C constant current to 4.85V, and discharge at 0.2C constant current to 3.4V.

[0053] 1) Test the conductivity of the non-aqueous electrolyte at 25℃.

[0054] 2) High-Temperature Fast-Charging Cycle Performance Test: First, the initial volume of the battery was tested using the water displacement method. Then, at 45℃, the formed battery was charged at a constant current of 2C to 4.7V, then charged at a constant current and constant voltage of 1C to the charging cutoff voltage of 4.85V, and finally discharged at a constant current of 1C to 3.4V. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is recorded as C1, the discharge capacity of the lithium-ion battery in the first cycle. This cycle is repeated for the same battery. After n cycles, the discharge capacity Cn of the nth cycle is recorded, and the volume of the battery after n cycles is measured.

[0055] Calculate the capacity retention rate and battery volume expansion rate after 500 charge / discharge cycles. The calculation formula is as follows:

[0056] Capacity retention rate after 500 cycles (%) = (Discharge capacity after 500 cycles / Discharge capacity after 1st cycle) × 100%;

[0057] Volume expansion rate (%) = (volume after cycle - initial volume) / initial volume × 100%;

[0058] 3) Low-Temperature Capacity Retention: After formation, the battery is charged at room temperature using a constant current and constant voltage (0.5C) to 4.85V, then discharged at a constant current (0.5C) to 3.4V. The initial discharge capacity is recorded. The battery is then charged again at a constant current and constant voltage (0.5C) to 4.85V. After cooling to -20℃ and stabilizing in a constant temperature chamber, the battery is discharged at a constant current (0.5C) to 3.4V, and the low-temperature discharge capacity is recorded. The low-temperature capacity retention rate is calculated. The calculation formula is as follows:

[0059] Low-temperature capacity retention rate (%) = Low-temperature discharge capacity / Initial discharge capacity × 100%;

[0060] The test results of the lithium-ion batteries prepared in Examples 1 to 21 and Comparative Examples 1 to 11 are shown in Table 2.

[0061] Table 2

[0062]

[0063] Note: A "diving" refers to a capacity retention rate of less than 70%.

[0064] As can be seen from the test results in Table 2, the lithium-ion battery provided by this invention uses lithium nickel manganese oxide material doped and / or coated with phosphorus-containing compounds as the positive electrode active material, and at least one of methyl trifluoroethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether as the first solvent, and one or two of dimethyl carbonate and methyl ethyl carbonate as the second solvent. Furthermore, by controlling the mass ratio E of phosphorus to nickel in the positive electrode material layer, the mass percentage F of the first solvent in the non-aqueous electrolyte, the mass percentage L of the second solvent in the non-aqueous electrolyte, and the relationship 100E×(F / L) satisfying 0.1≤100E×(F / L)≤12, and 0.005≤E≤0.045, 5≤F≤50, and 10≤L≤60, a synergistic mechanism is formed among the above parameters, thereby achieving stable cycling of the ultra-high voltage battery system.

[0065] As can be seen from the test results of Example 1 and Comparative Examples 1 to 11, when any one or more parameters, such as the mass ratio E of phosphorus to nickel in the positive electrode material layer, the mass percentage F of the first solvent in the non-aqueous electrolyte, and the mass percentage L of the second solvent in the non-aqueous electrolyte, do not meet the specified range, or when the value of the relationship between them, 100E×(F / L), is too large or too small, the synergistic effect between the parameters cannot be achieved. Therefore, the synergistic optimization of material structure stability and electrolyte performance cannot be achieved, and a high-voltage lithium-ion battery with both high conductivity and high oxidation resistance cannot be obtained.

[0066] When the mass ratio E of phosphorus to nickel in the cathode material layer, the mass percentage F of the first solvent in the non-aqueous electrolyte, the mass percentage L of the second solvent in the non-aqueous electrolyte, and the value of the relationship 100E×(F / L) satisfy 0.13≤100E×(F / L)≤3.5, and 0.008≤E≤0.03, 7≤F≤25, 20≤L≤50, the free structure in the electrolyte system is reduced, thereby obtaining a higher LUMO energy level and good reduction stability, which is beneficial to further improving the conductivity and oxidation resistance of lithium-ion batteries.

[0067] Furthermore, when the total mass percentage of the first solvent and the second solvent, F+L, satisfies 50≤F+L≤70, the ion conduction performance and interfacial stability of the non-aqueous electrolyte can be better balanced, thereby obtaining a high-voltage lithium-ion battery that combines high conductivity and high oxidation resistance.

[0068] Table 3 shows the impedance growth rate, capacity retention rate, and lithium plating test results of the lithium-ion batteries prepared in Examples 1, 22 to 28 after 500 cycles at 45°C. The differences between Examples 22 to 28 and Example 1 lie in the relevant parameters in Table 3; the remaining parameters and preparation steps are the same as those described in Example 1. Specifically, the second solvent is DMC+EMC, and the type of the first solvent is different.

[0069] Table 3

[0070]

[0071] Note: In the table, "FEMC" represents methyltrifluoroethyl carbonate; "FDEC" represents di(2,2,2-trifluoroethyl) carbonate; "DFEA" represents 2,2-difluoroethyl acetate; "HFE458" represents 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether; when there are multiple types of first and second solvents, the contents are evenly distributed.

[0072] As shown in Table 3, when the mass percentage F of the first solvent in the non-aqueous electrolyte, the mass percentage L of the second solvent in the non-aqueous electrolyte, and the relationship 100E×(F / L) meet the corresponding conditions, using different types of first solvents is beneficial to improving the ion conduction performance and interface stability of the non-aqueous electrolyte. This indicates that the lithium-ion battery system provided by this invention has universality for different types of first solvents.

[0073] Table 4 shows the impedance growth rate, capacity retention rate, and lithium plating test results of the lithium-ion batteries prepared in Examples 1, 29 to 31 after 500 cycles at 45°C. The differences between Examples 29 to 31 and Example 1 lie in the relevant parameters in Table 4; the remaining parameters and preparation steps are the same as those described in Example 1. The specific difference is the type of the second solvent.

[0074] Table 4

[0075]

[0076] Note: In the table, "DMC" represents dimethyl carbonate; "EMC" represents ethyl methyl carbonate.

[0077] As shown in Table 4, when the mass percentage F of the first solvent in the non-aqueous electrolyte, the mass percentage L of the second solvent in the non-aqueous electrolyte, and the relationship 100E×(F / L) meet the corresponding conditions, different types of second solvents can be used to construct a stable fluorine-rich interface and achieve a balance with the electrolyte ion transport performance, thereby optimizing the performance of the high-voltage lithium-ion battery system. This indicates that the lithium-ion battery system provided by this invention has universality for different types of second solvents.

[0078] Table 5 shows the impedance growth rate, capacity retention rate, and lithium plating test results of the lithium-ion batteries prepared in Examples 1, 32 to 43 after 500 cycles at 45°C. The differences between Examples 32 to 43 and Example 1 lie in the relevant parameters in Table 5; the remaining parameters and preparation steps are the same as those described in Example 1. Specifically, Examples 32 to 43 contain a second additive, and the type and amount of the second additive are different.

[0079] Table 5

[0080]

[0081] Note: " / " in the table indicates that the item is not present; "PS" represents 1,3-propanesulfonyl lactone; "PST" represents propenyl-1,3-sulfonyl lactone; "BS" represents 1,4-butanesulfonyl lactone.

[0082] As shown in Table 5, when the mass percentage F of the first solvent in the non-aqueous electrolyte, the mass percentage L of the second solvent in the non-aqueous electrolyte, and the relationship 100E×(F / L) meet the corresponding conditions, the addition of different types of second additives within a certain range results in the formation of an elastic cross-linked network on the surface of the second additive. This effectively constructs the positive electrode interface film, inhibits the destruction of the positive electrode structure, and is beneficial for further improving high-temperature performance while maintaining stable low-temperature performance. This demonstrates that the lithium-ion battery system provided by this invention is universally applicable to different types of second additives.

[0083] Furthermore, when the mass percentage B% of the second additive satisfies 3≤B≤8, the interfacial film formed on the positive electrode surface has higher thermal stability, which is beneficial to further improve high-temperature performance and maintain stable low-temperature performance.

[0084] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte. The positive electrode comprises a positive electrode material layer comprising a positive electrode active material, the positive electrode active material comprising a lithium nickel manganese oxide material doped and / or coated with a phosphorus-containing compound, and a mass ratio of phosphorus element to nickel element in the positive electrode material layer is E; The non-aqueous electrolyte comprises a non-aqueous organic solvent and a lithium salt, the non-aqueous organic solvent comprising a first solvent and a second solvent; The first solvent comprises at least one of methyl trifluoroethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether; The second solvent comprises one or both of dimethyl carbonate or ethyl methyl carbonate; A mass percentage content of the first solvent is F% and a mass percentage content of the second solvent is L% based on a mass of the non-aqueous electrolyte; The lithium ion battery satisfies 0.1≤100E×(F / L)≤12 and 0.005≤E≤0.045, 5≤F≤50 and 10≤L≤60.

2. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies 0.13≤100E×(F / L)≤3.

5.

3. The lithium-ion battery of claim 1, wherein, The mass ratio E of phosphorus element to nickel element in the positive electrode material layer satisfies 0.008≤E≤0.

03.

4. The lithium-ion battery of claim 1, wherein, The mass percentage content F% of the first solvent satisfies 7≤F≤25 based on a mass of the non-aqueous electrolyte.

5. The lithium-ion battery of claim 1, wherein, The mass percentage content L% of the second solvent satisfies 20≤L≤50 based on a mass of the non-aqueous electrolyte.

6. The lithium-ion battery of claim 1, wherein, A total mass percentage content of the first solvent and the second solvent satisfies 50≤F+L≤70 based on a mass of the non-aqueous electrolyte.

7. The lithium-ion battery of claim 1, wherein, The non-aqueous electrolyte further comprises a first additive, the first additive comprising at least one of fluoroethylene carbonate or difluoroethylene carbonate, a mass percentage content A% of the first additive satisfies 1≤A≤8 based on a mass of the non-aqueous electrolyte; and / or, The non-aqueous electrolyte further comprises a second additive, the second additive comprising at least one of 1,3-propane sultone, 1,4-butane sultone or propenyl-1,3-sulfonic acid lactone, a mass percentage content B% of the second additive satisfies 1≤B≤10 based on a mass of the non-aqueous electrolyte.

8. The lithium-ion battery of claim 7, wherein, The mass percentage content A% of the first additive satisfies 1.5≤A≤7 based on a mass of the non-aqueous electrolyte; and / or, The mass percentage content B% of the second additive satisfies 3≤B≤8 based on a mass of the non-aqueous electrolyte.

9. The lithium-ion battery of claim 1, wherein, The lithium ion battery has a charge cut-off voltage of 4.6-5 V.

10. The lithium-ion battery of claim 1, wherein, The non-aqueous electrolyte has an electrical conductivity of 6.5 mS / cm or more at 25°C.

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