Lithium battery

Abstract

The present disclosure provides a lithium battery. Specifically, the lithium battery comprises an electrolyte, the electrolyte comprises a fluorinated ether solvent; wherein the fluorinated ether solvent comprises at least one compound of formula (I): wherein R2 and R3 are each independently selected from alkylene or fluorinated alkylene, and the total number of carbon atoms of R2 and R3 is 4, and the total number of fluorine atoms is ≤1; R1 and R4 are each independently methyl or fluorinated methyl, and the total number of fluorine atoms in R1 and R4 is 1-4. Such electrolyte can improve the cycle performance of medium-nickel high-voltage lithium battery, reduce the direct current resistance growth rate under high temperature storage conditions, and is beneficial to the long-term stable operation of lithium battery.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and more particularly to a lithium battery. Background Technology

[0002] Ternary cathode materials are a new type of cathode material for lithium-ion batteries, such as nickel-cobalt-manganese (NiCoMn) and nickel-cobalt-aluminum (NiCoA). NiCoMn, comprising nickel, cobalt, and manganese salts, stands out among many lithium-ion battery cathode materials due to its higher operating voltage and greater energy density. Based on the nickel content in NiCoMn, ternary cathode materials include low-nickel, medium-nickel, and high-nickel cathode materials. Among them, medium-nickel cathode materials not only have similar energy density performance to high-nickel cathode materials but also offer higher safety and lower cost, making them considered one of the mainstream solutions to address range anxiety in automotive batteries. However, under high-voltage conditions, unstable substances in the electrolyte are prone to decomposition, resulting in poor cycle performance of medium-nickel high-voltage batteries. Summary of the Invention

[0003] In view of this, the purpose of this disclosure is to provide a lithium battery.

[0004] To achieve the above objectives, a first aspect of this disclosure provides an electrolyte comprising a fluorinated ether solvent; wherein the fluorinated ether solvent comprises at least one compound of formula (I):

[0005]

[0006] in,

[0007] R2 and R3 are each independently selected from alkylene or fluoroalkylene, and the total number of carbon atoms in R2 and R3 is 4, and the total number of fluorine atoms is ≤1.

[0008] R1 and R4 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R4 is 1 to 4.

[0009] In some embodiments, the fluorinated ether solvent accounts for 10% to 50% of the total mass of the electrolyte, and optionally 15% to 25%.

[0010] In some embodiments, R2 and R3 are each independently selected from -CH2-, -CH2-CH2-, -CH2-CH2-CH2-, -CHF-, -CHF-CH2-, -CHF-CH2-CH2-, or -CH2-CHF-CH2-.

[0011] In some embodiments, the solvent further includes a non-fluorinated ether solvent; optionally, the non-fluorinated ether solvent includes at least one of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and carbonate, more preferably ethylene glycol dimethyl ether.

[0012] In some embodiments, based on the total mass of the electrolyte, the mass proportion of ethylene glycol dimethyl ether is 35% to 75%, optionally 50% to 70%.

[0013] In some embodiments, the electrolyte further includes a lithium salt; optionally, based on the total mass of the electrolyte, the mass proportion of the lithium salt is 11% to 15%, optionally 13% to 14%.

[0014] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiClO4, LiCF3SO3, LiBOB, LiODFB, and LiN(SO2CF3)2; optionally, the lithium salt is LiPF6.

[0015] In some embodiments, the electrolyte further includes at least one of lithium bis(fluorosulfonyl)imide and vinylene sulfate; optionally, based on the total mass of the electrolyte, the mass proportion of lithium bis(fluorosulfonyl)imide is 0.1% to 5%, more optionally 0.2% to 1%; optionally, the mass proportion of vinylene sulfate is 0.1% to 10%, more optionally 0.5% to 2%.

[0016] In some embodiments, the compound of formula (I) is selected from at least one of the following compounds:

[0017]

[0018]

[0019] Based on the same inventive concept, the second aspect of the present disclosure further provides a lithium battery, including the electrolyte described in any one of the foregoing; wherein, the positive electrode active material of the lithium battery includes Li a Ni x Mn y Co z O2; wherein, 0.9 < a < 1.1, 0.5 < x < 0.7, 0.1 < z ≤ 0.2 and x + y + z = 1.

[0020] As can be seen from the above, a lithium battery provided by the present disclosure, the lithium battery includes an electrolyte, and the electrolyte includes a fluorinated ether solvent; wherein, the fluorinated ether solvent includes at least one compound of formula (I): In this electrolyte, R2 and R3 are each independently selected from alkylene or fluoroalkylene groups, and the total number of carbon atoms in R2 and R3 is 4, while the total number of fluorine atoms is ≤1. R1 and R4 are each independently methyl or fluoromethyl groups, and the total number of fluorine atoms in R1 and R4 is 1 to 4. This electrolyte can improve the cycle performance of medium-nickel high-voltage lithium batteries, reduce the rate of increase of DC internal resistance under high-temperature storage conditions, and is beneficial to the long-term stable operation of lithium batteries. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0022] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this disclosure should have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure pertains.

[0023] In this disclosure, the term "range" is used to define a range in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–130 and 70–120 are listed for a specific parameter, it is expected that ranges of 60–120 and 70–130 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this disclosure, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0024] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0025] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this disclosure can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0027] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B".

[0028] In related technologies, common lithium-ion battery electrolyte solvent systems mainly consist of a mixture of cyclic and chain carbonates. Compared to ether solvents, cyclic and chain carbonates offer better oxidation resistance, but they still pose a risk of decomposition under high-voltage conditions. Therefore, developing more diverse solvent molecular structures to provide lithium-ion battery electrolyte solvent systems is a research hotspot.

[0029] Fluorinated ether solvents combine the high solubility of lithium salts found in ether solvents with a more stable chemical structure after fluorine modification, making them a strong candidate for high-voltage battery electrolytes. However, their high viscosity and cost limit their application as a single solvent system in lithium-ion batteries. Furthermore, the long carbon chains of fluorinated ethers somewhat affect their solubility in common lithium salts.

[0030] To achieve the objectives of this disclosure, embodiments of this disclosure provide an electrolyte comprising a novel fluorinated ether solvent, which advantageously broadens the electrochemical operating window of the electrolyte and improves the cycle performance of medium-nickel high-voltage cells.

[0031] electrolyte

[0032] This disclosure provides an electrolyte comprising a fluorinated ether solvent; wherein the fluorinated ether solvent comprises at least one compound of formula (I):

[0033]

[0034] in,

[0035] R2 and R3 are each independently selected from alkylene or fluoroalkylene groups, and the total number of carbon atoms in R2 and R3 is 4, while the total number of fluorine atoms is ≤1. Here, "alkylene" refers to a saturated, branched, straight-chain, or cyclic hydrocarbon residue with 1 to 18 carbon atoms, and having two monovalent residue centers derived from the same carbon atom or two different carbon atoms of the parent alkane by removing two hydrogen atoms. Typical alkylene residues include, but are not limited to, methylene (-CH2-), 1,2-ethyl (-CH2CH2-), 1,3-propyl (CH2CH2CH2-), and 1,4-butyl (-CH2CH2CH2CH2-).

[0036] R1 and R4 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R4 is 1 to 4.

[0037] The electrolyte provided in this disclosure can improve the cycle performance of medium-nickel high-voltage lithium batteries and contribute to their long-term stable operation. Here, the lithium battery can be a primary lithium battery or a secondary lithium battery; this disclosure does not limit it.

[0038] In the electrolyte disclosed herein, the compound of formula (I) is an ether with a long carbon chain and containing at least one fluorine atom. After the fluorine atom is substituted, the charge density distribution of the compound itself is changed. The more dispersed charge density distribution improves the oxidation resistance of the molecule, thereby improving the overall oxidation resistance of the electrolyte and exhibiting higher stability under high-temperature cycling conditions.

[0039] In some embodiments, R2 and R3 are each independently selected from -CH2-, -CH2-CH2-, -CH2-CH2-CH2-, -CHF-, -CHF-CH2-, -CHF-CH2-CH2-, or -CH2-CHF-CH2-. For example, R2 is -CH2-CH2- and R3 is -CHF-CH2-; or R2 is -CH2- and R3 is -CH2-CHF-CH2-; or R2 is -CHF- and R3 is -CH2-CH2-CH2-, etc.

[0040] In some embodiments, the compound of formula (I) is selected from at least one of the following compounds:

[0041]

[0042] In some embodiments, the compound of formula (I) is selected from at least one of I-7, I-8, I-1, I-10, I-9, I-15, I-11, I-2, I-3, I-4, and I-5. In some embodiments, optionally, the compound of formula (I) is selected from at least one of I-7, I-8, I-1, and I-6.

[0043] Regarding the aforementioned compounds, the inventors discovered that although fluoroethers exhibit high oxidative stability, differences in the number and sites of fluorine substitution result in variations in the uniformity of charge distribution across the overall compound structure, leading to differences in their chemical stability. A more uniform overall charge distribution correlates with higher oxidative stability, resulting in superior room-temperature cycling performance in electrolytes mixed with ether solvents. Furthermore, changes in the structure of fluoroethers affect the solvation structure of lithium ions in the electrolyte, further increasing the stability of the electrolyte itself.

[0044] In some embodiments, the mass percentage of the fluoroether solvent is 10% to 50%, for example, 10%, 14%, 18%, 20%, 25%, 31%, 35%, 40%, or 45%; optionally, it is 15% to 25%. During cycling, the addition of fluoroethers improves the thermal stability of the electrolyte, but this is accompanied by an increase in electrolyte viscosity. High thermal stability helps improve cell performance, while high viscosity leads to a decrease in cell performance. When the mass percentage of the fluoroether solvent is less than 10%, the solvent's antioxidant stability is insufficient, making it difficult to improve the stability of the electrolyte. Although the increase in fluoroethers results in better stability under high-temperature storage conditions due to their stronger thermal stability, the growth rate of the direct current resistance (DCR) in the 60-day high-temperature storage test (HTS) is relatively low. However, if the mass of fluorinated ether solvents exceeds 50%, the electrolyte viscosity will be too high, and the number of cycles at room temperature will decrease. This may be because the DC internal resistance gradually increases during the cycling process, the internal polarization of the cell increases, and thus the cell's performance in terms of the number of cycles at room temperature deteriorates.

[0045] In some embodiments, the electrolyte further includes a non-fluorinated ether solvent. Optionally, the non-fluorinated ether solvent includes at least one of tetrahydrofuran (THF), diethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (G2), triethylene glycol dimethyl ether (G3), tetraethylene glycol dimethyl ether (G4), and carbonates, more preferably diethylene glycol dimethyl ether.

[0046] It should be noted that carbonates include cyclic carbonates and chain carbonates. For example, cyclic carbonate solvents include at least one of propylene carbonate (PC) and ethylene carbonate (EC). Optionally, the cyclic carbonate solvent is ethylene carbonate. Cyclic carbonate solvents have a high dielectric constant, which helps dissolve lithium salts and ensures their uniform distribution in the electrolyte, thereby guaranteeing normal battery operation. In addition to increasing the solubility of lithium salts, ethylene carbonate can also form a stable solvation configuration with lithium ions, improving the stability and conductivity of the electrolyte, thus enhancing the performance of the lithium battery. For example, the chain carbonate solvent includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The inclusion of chain carbonate solvents in the electrolyte can reduce the overall viscosity, which helps improve the conductivity, cycle life, and energy density of the lithium battery.

[0047] In some embodiments, the electrolyte comprises ethylene carbonate and ethyl methyl carbonate. Further, based on the total mass of the electrolyte, the ethylene carbonate comprises 15% to 25% by mass, and the ethyl methyl carbonate comprises 40% to 60% by mass. The combination of ethylene carbonate and ethyl methyl carbonate helps to ensure the solubility of the lithium salt in the solvent while controlling the viscosity of the electrolyte, thereby enabling the production of high-performance lithium batteries.

[0048] In some embodiments, the ethylene glycol dimethyl ether comprises 35% to 75% of the total mass of the electrolyte, optionally 50% to 70%. The inclusion of ethylene glycol dimethyl ether within the above range and the compound shown in formula (I) in the electrolyte helps improve room temperature cycling performance and high temperature storage performance, and is particularly suitable for use with medium-nickel cathode active materials.

[0049] In some embodiments, the electrolyte further includes lithium salt; optionally, the lithium salt accounts for 11% to 15% of the total mass of the electrolyte, and optionally 13% to 14%.

[0050] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiClO4, LiCF3SO3, LiBOB, LiODFB, and LiN(SO2CF3)2.

[0051] Optionally, the lithium salt is LiPF6. LiPF6 has good solubility in mixtures of non-fluorinated ether solvents and fluorinated ether solvents, avoiding the degradation of battery performance caused by insufficient solubility of lithium salt.

[0052] In some embodiments, the electrolyte further includes additives, optionally selected from at least one of lithium fluorosulfonylimide (LiFSI) and vinyl sulfate (DTD); optionally, the additives include lithium fluorosulfonylimide (LiFSI) and vinyl sulfate (DTD). Lithium fluorosulfonylimide helps increase lithium ions in the electrolyte, thereby improving the overall battery performance; vinyl sulfate (DTD), as a sulfide-based additive, participates in the initial film formation of the cell, and during cycling, the solid electrolyte interphase (SEI and CEI) can be used to stabilize the interfacial phase between the positive and negative electrode materials and the electrolyte, enhancing the cycle performance of the cell.

[0053] In some embodiments, the lithium bis(fluorosulfonyl)imide comprises 0.1% to 5% of the total mass of the electrolyte, more preferably 0.2% to 1%; optionally, the vinyl sulfate comprises 0.1% to 10% of the total mass of the electrolyte, more preferably 0.5% to 2%.

[0054] lithium batteries

[0055] A second aspect of this disclosure provides a lithium battery, including the electrolyte provided above.

[0056] In some embodiments, a lithium battery includes a positive electrode, a negative electrode, a separator located between the positive and negative electrodes, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0057] Positive electrode sheet

[0058] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0059] For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0060] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0061] In some embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide, such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which may also be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may also be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which may also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may also be abbreviated as NCM811).

[0062] Optionally, the positive electrode active material of the lithium battery includes Li a Ni x Mn y Co z O2; wherein, 0.9 < a < 1.1, 0.5 < x < 0.7, 0.1 < z ≤ 0.2 and x + y + z = 1. When 0.5 < x < 0.7, the electrochemical performance of the positive electrode active material is excellent; when x > 0.7, the stability of the positive electrode active material is poor, and there may be oxidation of the fluorinated ether solvent on the surface of the positive electrode during charge and discharge. The unstable solvent system makes it difficult to operate stably for a long time due to a significant decrease in the number of cycles in the later stage at 25°C. This may be because a film layer is formed on the surface of the positive electrode after the fluorinated ether undergoes an oxidation reaction, and the film layer has poor conductivity, resulting in an increase in the DC internal resistance, which can be corroborated by the increase rate of the DC internal resistance in the high-temperature storage test.

[0063] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0064] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0066] Negative electrode sheet

[0067] The negative electrode includes a negative current collector and a film layer optionally disposed on at least one surface of the negative current collector.

[0068] For example, the film layer may include a negative electrode active material (e.g., artificial graphite), a conductive agent, a thickener, and a binder.

[0069] In some embodiments, the negative electrode sheet can be prepared by dispersing the negative electrode active material, conductive agent, thickener, binder and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0070] Separating membrane

[0071] In some embodiments, the secondary battery also includes a separator. This disclosure does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0072] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0073] Example

[0074] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0075] Examples 1 to 15

[0076] Examples 1-15 of this disclosure are secondary lithium batteries, wherein the positive electrode active material is a medium-nickel high-voltage positive electrode material, and its specific preparation method is as follows:

[0077] (1)LiNi 0.6 Mn 0.3 Co 0.1 Preparation of O2 cathode:

[0078] LiNi, the positive electrode active material 0.6 Mn 0.3 Co 0.1 O2, polyvinylidene fluoride as a binder, and conductive carbon black (Super P) as a conductive agent are mixed in a weight ratio of 98:1:1. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until the system is homogeneous and transparent to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto aluminum foil. After the aluminum foil is dried at room temperature, it is transferred to an oven for drying. Then, it is cold-pressed and slit to obtain the positive electrode (positive electrode sheet).

[0079] (2) Preparation of graphite anode:

[0080] Artificial graphite was used as the negative electrode active material, Super P as the conductive agent, sodium carboxymethyl cellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the binder. They were mixed in a mass ratio of 96:1:1:2, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil current collector. The copper foil was dried at room temperature and then transferred to an oven for drying. After cold pressing and slitting, the negative electrode (electrode sheet) was obtained.

[0081] (3) Preparation of electrolyte:

[0082] In an argon atmosphere glove box with a water content of <10 ppm, battery-grade fluorinated ether I-8, dimethyl ethylene glycol (DME), tetraethylene glycol dimethyl ether (G4), triethylene glycol dimethyl ether (G3), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed in the proportions specified in Examples 1-15 to form the total organic solvent. LiPF6 and DTD were then mixed thoroughly with the aforementioned organic solvent in the proportions specified in Examples 1-13 to obtain the electrolyte.

[0083] The proportions of each component in Examples 1-15 are shown in Table 1. It should be noted that the content of each component in Table 1 is a mass percentage calculated based on the total mass of the electrolyte.

[0084] (4) Preparation of the separating membrane:

[0085] Polypropylene film is used as the separator.

[0086] (5) Preparation of secondary batteries:

[0087] Using a 12μm thick polypropylene film as the separator, the prepared positive electrode, separator, and negative electrode were stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film was wrapped around the separator, and the mixture was dried in a vacuum oven at 120°C. After injecting 3.0 g / Ah of the prepared electrolyte, the mixture was sealed and liquefied to obtain a 1Ah soft-pack battery (i.e., a lithium-ion battery).

[0088] Comparative Examples 1 to 4

[0089] The difference between Comparative Examples 1-4 and Example 1 lies in the composition of the organic solvent in step (3). The components and proportions of the organic solvents in Comparative Examples 1-4 are shown in Tables 1 and 2. In Table 2, A represents the compound represented by formula A. B represents the compound shown in formula B.

[0090] Example 16, Comparative Example 5

[0091] Compared with Example 16, Comparative Example 5, and Example 1, the difference lies in step (1): the positive electrode active material is replaced with LiNi. 0.9 Mn 0.05 Co 0.05 For details on the composition and proportion of O2 and organic solvents in step (3), please refer to Table 2.

[0092] Test methods

[0093] The secondary batteries prepared in the above embodiments and comparative examples can be tested using the following methods:

[0094] (1) High-temperature storage test of secondary batteries

[0095] In an oven at a specified temperature (high temperature 45℃), the cells were cyclically charged with a current of 0.2C within a specified potential range (2.0V~3.8V), and cyclically discharged with a current of 1C within the same potential range (2.8V~4.35V). After three charge-discharge cycles, the initial volume of the cell was measured and recorded as V0. The cells were then stored in an oven at a specified temperature (high temperature 60℃) for fixed time intervals (60 days). The discharge coefficient (DCR) was measured at each time interval, and the high-temperature storage DCR growth rate was calculated by the difference between DCR at 0 days and DCR at 60 days. The test results are detailed in Tables 1 and 2.

[0096] (2) Secondary battery room temperature cycle test

[0097] In an oven at a specified temperature (25℃), the battery was cyclically charged and discharged within a specified potential range (2.0~3.8V) at a current of 1C. The discharge capacity of each cycle was recorded. The test ended when the battery capacity reached 80% of the capacity of the first cycle. The test results are detailed in Tables 1 and 2.

[0098] Table 1

[0099]

[0100]

[0101] Table 2

[0102]

[0103] Comparing Comparative Examples 1-4 and Example 5, it can be seen that adding fluorinated ether solvents to the electrolyte can improve the stability of the battery cell during room temperature cycling and reduce the DC internal resistance growth rate under high-temperature storage conditions. Comparing Comparative Examples 1-3 and Example 5, it can be seen that different fluorinated ether solvents have significantly different effects on improving the stability of the battery cell during room temperature cycling and the DC internal resistance growth rate. The fluorinated ether I-8 provided in this disclosure has a significantly better effect on improving the stability of the battery cell during room temperature cycling than octafluoropentyl-tetrafluoroethyl ether, Formula A, and Formula B, especially octafluoropentyl-tetrafluoroethyl ether. This may be because octafluoropentyl-tetrafluoroethyl ether has a high fluorine content but a short chain length, resulting in lower thermal stability compared to fluorinated ether I-8.

[0104] Comparison of Comparative Example 1, Examples 1-5, and Examples 7-8 shows that adding fluorinated ether I-8 to the electrolyte can improve the cycle stability of the battery cell and reduce the DC internal resistance growth rate under high-temperature storage conditions. In particular, when the mass percentage of fluorinated ether I-8 is within the range of 15% to 35%, the addition of fluorinated ether I-8 significantly improves the cycle stability of the battery cell and reduces the DC internal resistance growth rate.

[0105] Comparing Example 5 with Examples 9 to 11, it can be found that G3, G4, carbonate, DME, and fluoroether I-8 can all improve the cycle stability to varying degrees and reduce the growth rate of DC internal resistance under high-temperature storage conditions. Compared with the combinations of G4, G3, carbonate, and fluoroether I-8, the combination of DME and fluoroether I-8 is more conducive to improving the cycle stability of the battery cell. Compared with the combinations of G3, G4, and fluoroether I-8, the electrolyte containing both DME and fluoroether I-8 has good chemical stability and solubility for lithium salts, thus improving the performance of the battery cell. It should be noted that except for fluoroether I-8, when the compounds of formula (I) are combined with G3, G4, and carbonate, similar results are shown and will not be elaborated.

[0106] Comparing Example 16, Comparative Example 5, and Example 5, it can be seen that fluoroether I-8 can also improve the cycle stability of the battery cell prepared with high-nickel cathode active material and reduce the growth rate of DC internal resistance. In addition, the cathode active material also has a relatively large impact on the cycle stability of the battery cell. Compared with the high-nickel cathode active material (Examples 16 and Comparative Example 5), the battery cell with the combination of fluoroether I-8 and medium-nickel cathode active material (Ni6 in Example 5) has better performance. This may be because the material stability of the high-nickel cathode is poor, and there may be a situation where fluoroether is oxidized on the surface of the cathode during charge and discharge, resulting in a dive in the later stage of room-temperature cycling of the battery cell. After the fluoroether undergoes an oxidation reaction, a film-forming substance is generated on the surface of the cathode, and the ionic conductivity of this layer of substance itself is poor, resulting in a high growth rate of HTS-DCR 60d.

[0107] Except for fluoroether I-8, when the compounds of formula (I) are combined with the materials of high-nickel cathodes, similar results are shown and will not be elaborated.

[0108] It should be noted that the cathode active materials in Examples 1 to 15 are only representatives of medium-nickel cathode active materials, rather than limitations. The medium-nickel cathode active material of the present disclosure refers to Li a Ni x Mn y Co z O2; where 0.9 < a < 1.1, 0.5 < x < 0.7, 0.1 < z ≤ 0.2, and x + y + z = 1.

[0109] Comparing Example 5, Example 6, and Example 12, it can be seen that adding the combination of LiFSI and DTD to the electrolyte can improve the cycle performance of the battery cell and reduce the growth rate of DC internal resistance. Among them, DTD generates a relatively dense SEI and CEI on the surfaces of the positive and negative electrodes, which plays a protective role for the positive and negative electrode materials during the cycle and is conducive to improving the cycle performance of the battery cell.

[0110] Examples 17 to 25

[0111] Examples 17 to 25 are prepared in a similar manner to Examples 1 to 8 and Example 12, except that fluoroether I-8 is replaced with fluoroether I-9. The detailed composition and test results of the electrolyte are shown in Table 3.

[0112] Table 3

[0113]

[0114]

[0115] Examples 26 to 34

[0116] Examples 26 to 34 are prepared in a similar manner to Examples 1 to 8 and Example 12, except that fluoroether I-8 is replaced with fluoroether I-6. The detailed composition and test results of the electrolyte are shown in Table 4.

[0117] Table 4

[0118] category DME Fluoroether I-6 <![CDATA[LiPF6]]> LiFSI DTD HTS-DCR60d growth rate Number of cycles at 25℃ Example 26 77.85 8.65 13 0.5 —— 0.138 1126 Example 27 43.25 43.25 13 0.5 —— 0.122 1291 Example 28 51.90 34.60 13 0.5 —— 0.115 1357 Example 29 69.20 17.30 13 0.5 —— 0.105 1462 Example 30 60.55 25.95 13 0.5 —— 0.094 1746 Example 31 60.06 25.44 13 0.5 1 0.084 2024 Example 32 76.50 10.00 13 0.5 —— 0.122 1198 Example 33 36.50 50.00 13 0.5 —— 0.135 1105 Example 34 61.05 25.95 13 —— —— 0.125 1216

[0119] Examples 35 to 43

[0120] Examples 35 to 43 are prepared in a similar manner to Examples 1 to 8 and Example 12, except that fluoroether I-8 is replaced with fluoroether I-15. The detailed composition and test results of the electrolyte are shown in Table 5.

[0121] Table 5

[0122] category DME Fluorinated ether I-15 <![CDATA[LiPF6]]> LiFSI DTD HTS-DCR60d growth rate Number of cycles at 25℃ Example 35 77.85 8.65 13 0.5 —— 0.136 1103 Example 36 43.25 43.25 13 0.5 —— 0.121 1265 Example 37 51.90 34.60 13 0.5 —— 0.114 1329 Example 38 69.20 17.30 13 0.5 —— 0.104 1432 Example 39 60.55 25.95 13 0.5 —— 0.093 1711 Example 40 60.06 25.44 13 0.5 1 0.084 1983 Example 41 76.50 10.00 13 0.5 —— 0.120 1187 Example 42 36.50 50.00 13 0.5 —— 0.133 1172 Example 43 61.05 25.95 13 —— —— 0.124 1191

[0123] Examples 44 to 52

[0124] Examples 44 to 52 are prepared in a similar manner to Examples 1 to 8 and Example 12, except that fluoroether I-8 is replaced with fluoroether I-10. The detailed composition and test results of the electrolyte are shown in Table 6.

[0125] Table 6

[0126] category DME Fluorinated ether I-10 <![CDATA[LiPF6]]> LiFSI DTD HTS-DCR60d growth rate Number of cycles at 25℃ Example 44 77.85 8.65 13 0.5 —— 0.125 1080 Example 45 43.25 43.25 13 0.5 —— 0.119 1239 Example 46 51.90 34.60 13 0.5 —— 0.112 1302 Example 47 69.20 17.30 13 0.5 —— 0.103 1403 Example 48 60.55 25.95 13 0.5 —— 0.092 1676 Example 49 60.06 25.44 13 0.5 1 0.083 1943 Example 50 76.50 10.00 13 0.5 —— 0.124 1106 Example 51 36.50 50.00 13 0.5 —— 0.122 1140 Example 52 61.05 25.95 13 —— —— 0.122 1167

[0127] Examples 53 to 61

[0128] Examples 53 to 61 are prepared in a similar manner to Examples 1 to 8 and Example 12, except that fluoroether I-8 is replaced with fluoroether I-1. The detailed composition and test results of the electrolyte are shown in Table 7.

[0129] Table 7

[0130] category DME Fluoroether I-1 <![CDATA[LiPF6]]> LiFSI DTD HTS-DCR60d growth rate Number of cycles at 25℃ Example 53 77.85 8.65 13 0.5 —— 0.131 1036 Example 54 43.25 43.25 13 0.5 —— 0.116 1189 Example 55 51.90 34.60 13 0.5 —— 0.110 1249 Example 56 69.20 17.30 13 0.5 —— 0.101 1346 Example 57 60.55 25.95 13 0.5 —— 0.090 1609 Example 58 60.06 25.44 13 0.5 1 0.081 1865 Example 59 76.50 10.00 13 0.5 —— 0.112 1165 Example 60 36.50 50.00 13 0.5 —— 0.123 1078 Example 61 61.05 25.95 13 —— —— 0.119 1120

[0131] Examples 62 to 70

[0132] Examples 62 to 70 are prepared in a similar manner to Examples 1 to 8 and Example 12, except that fluoroether I-8 is replaced with fluoroether I-3. The detailed composition and test results of the electrolyte are shown in Table 8.

[0133] Table 8

[0134] category DME Fluoroether I-3 <![CDATA[LiPF6]]> LiFSI DTD HTS-DCR60d growth rate Number of cycles at 25℃ Example 62 77.85 8.65 13 0.5 —— 0.127 1027 Example 63 43.25 43.25 13 0.5 —— 0.113 1180 Example 64 51.90 34.60 13 0.5 —— 0.107 1240 Example 65 69.20 17.30 13 0.5 —— 0.099 1336 Example 66 60.55 25.95 13 0.5 —— 0.089 1597 Example 67 60.06 25.44 13 0.5 1 0.081 1851 Example 68 76.50 10.00 13 0.5 —— 0.108 1324 Example 69 36.50 50.00 13 0.5 —— 0.118 1100 Example 70 61.05 25.95 13 —— —— 0.116 1111

[0135] Examples 71 to 79

[0136] Examples 71 to 79 are prepared in a similar manner to Examples 1 to 8 and Example 12, except that fluoroether I-8 is replaced with fluoroether I-5. The detailed composition and test results of the electrolyte are shown in Table 9.

[0137] Table 9

[0138] category DME Fluorinated ether I-5 <![CDATA[LiPF6]]> LiFSI DTD HTS-DCR60d growth rate Number of cycles at 25℃ Example 71 77.85 8.65 13 0.5 —— 0.123 1026 Example 72 43.25 43.25 13 0.5 —— 0.110 1179 Example 73 51.90 34.60 13 0.5 —— 0.105 1239 Example 74 69.20 17.30 13 0.5 —— 0.097 1337 Example 75 60.55 25.95 13 0.5 —— 0.088 1598 Example 76 60.06 25.44 13 0.5 1 0.080 1851 Example 77 76.50 10.00 13 0.5 —— 0.110 1107 Example 78 36.50 50.00 13 0.5 —— 0.136 1017 Example 79 61.05 25.95 13 —— —— 0.113 1112

[0139] As can be seen from the test results in Tables 1 to 9, adding the compound of formula (I) provided in the embodiments of this disclosure to the electrolyte can improve the cycle stability of the battery cell and reduce the rate of increase in DC internal resistance under high-temperature storage conditions. Adding LiFSI and DTD to the electrolyte can further improve the cycle stability of the battery cell.

[0140] Furthermore, the electrolyte provided in this disclosure is particularly suitable for medium-nickel high-voltage positive electrode active materials, facilitating the preparation of lithium batteries with high energy density, good safety, and low cost.

[0141] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this disclosure as described above, which are not provided in detail for the sake of brevity.

[0142] This disclosure is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A lithium battery, characterized in that, It includes a positive electrode active material and an electrolyte; wherein the electrolyte includes a fluorinated ether solvent; wherein the fluorinated ether solvent includes at least one compound of formula (I): in, R2 and R3 are each independently selected from alkylene or fluoroalkylene, and the total number of carbon atoms in R2 and R3 is 4, and the total number of fluorine atoms is ≤1. R1 and R4 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R4 is 1 to 4. The positive electrode active material includes Li a Ni x Mn y Co z O2; where, 0.9 < a < 1.1, 0.5 < x < 0.7, 0.1 < z ≤ 0.2 and x + y + z = 1.

2. The lithium battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the fluorinated ether solvent accounts for 10% to 50% by mass, and optionally 15% to 25%.

3. The lithium battery according to claim 1 or 2, characterized in that, R2 and R3 are each independently selected from -CH2-, -CH2-CH2-, -CH2-CH2-CH2-, -CHF-, -CHF-CH2-, -CHF-CH2-CH2-, or -CH2-CHF-CH2-.

4. The lithium battery according to any one of claims 1 to 3, characterized in that, It also includes non-fluorinated ether solvents; the non-fluorinated ether solvents include at least one of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and carbonates.

5. The lithium battery according to claim 4, characterized in that, The non-fluorinated ether solvents include ethylene glycol dimethyl ether; Based on the total mass of the electrolyte, the mass percentage of ethylene glycol dimethyl ether is 35% to 75%.

6. The lithium battery according to claim 5, characterized in that, Based on the total mass of the electrolyte, the mass percentage of ethylene glycol dimethyl ether is 50% to 70%.

7. The lithium battery according to any one of claims 1 to 6, characterized in that, The electrolyte also includes lithium salt; the lithium salt accounts for 11% to 15% of the total mass of the electrolyte. The lithium salt includes at least one of LiPF6, LiBF4, LiClO4, LiCF3SO3, LiBOB, LiODFB and LiN(SO2CF3)2.

8. The lithium battery according to any one of claims 1 to 7, characterized in that, The electrolyte also includes at least one of lithium difluorosulfonylimide and vinyl sulfate.

9. The lithium battery according to claim 8, characterized in that, Based on the total mass of the electrolyte, the lithium difluorosulfonamide accounts for 0.1% to 5% by mass, more preferably 0.2% to 1% by mass; optionally, the vinyl sulfate accounts for 0.1% to 10% by mass, more preferably 0.5% to 2% by mass.

10. The lithium battery according to any one of claims 1 to 9, characterized in that, The compound of formula (I) is selected from at least one of the following compounds:

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