Electrolyte and lithium battery

Abstract

The electrolyte comprises a cyclic carbonate solvent and a fluoroether solvent; wherein the fluoroether solvent comprises at least one compound of formula (I): wherein R2 is a C4 alkylene or a C4 fluoroalkylene, wherein the number of fluorine atoms in the C4 fluoroalkylene is 1; R1 and R3 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R3 is 1-4; such an electrolyte can improve the cycle performance of a medium-nickel high-voltage lithium battery, and is conducive to long-term stable operation of the lithium battery.

Description

Technical Field

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

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

[0005]

[0006] in,

[0007] R2 is a C4 alkylene or a C4 fluoroalkylene, wherein the number of fluorine atoms in the C4 fluoroalkylene is 1;

[0008] R1 and R3 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R3 is 1 to 4.

[0009] In some embodiments, the cyclic carbonate solvent includes at least one of propylene carbonate and ethylene carbonate.

[0010] In some embodiments, R2 is a C4 chain alkylene or a C4 fluorochain alkylene, optionally a C4 straight-chain alkylene or a C4 fluorostraight-chain alkylene.

[0011] In some embodiments, based on the total mass of the electrolyte, the sum of the masses of the cyclic carbonate solvent and the fluoroether solvent is 15% to 60%, optionally 25% to 60%, and more preferably 35% to 50%; the mass of the fluoroether solvent is 4% to 45%, optionally 15% to 35%.

[0012] In some embodiments, it further includes chain carbonate solvents; optionally, the chain carbonate solvents include at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0013] In some embodiments, based on the total mass of the electrolyte, the mass percentage of ethylene carbonate is 15% - 25%; the mass percentage of ethyl methyl carbonate is 40% - 60%.

[0014] In some embodiments, the electrolyte further includes a lithium salt; optionally, based on the total mass of the electrolyte, the mass percentage of the lithium salt is 11% - 15%, optionally 13% - 14%; optionally, the lithium salt includes LiPF6.

[0015] In some embodiments, the electrolyte further includes at least one of lithium bis(fluorosulfonyl)imide, vinylene carbonate, and 1,3 - propane sultone; optionally, based on the total mass of the electrolyte, the mass percentage of lithium bis(fluorosulfonyl)imide is 0.1% - 5%, more optionally 0.2% - 1%; optionally, the mass percentage of vinylene carbonate is 0.1% - 10%, more optionally 0.2% - 1%; optionally, the mass percentage of 1,3 - propane sultone is 0.1% - 10%, more optionally 0.2% - 1%.

[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, the electrolyte and the lithium battery provided by the present disclosure, the electrolyte includes cyclic carbonate solvents and fluorinated ether solvents; wherein, the fluorinated ether solvents include at least one compound of formula (I): R2 is a C4 alkylene or C4 fluoroalkylene, wherein the number of fluorine atoms in the C4 fluoroalkylene is 1; R1 and R3 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R3 is 1 to 4. Such an electrolyte can improve the cycle performance of medium-nickel high-voltage lithium batteries 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 working window of the electrolyte and improves the cycle performance of medium-nickel high-voltage cells; at the same time, by forming a mixed system with cyclic carbonates, it improves the solubility of lithium salts and ensures that the lithium battery can operate stably for a long time.

[0031] electrolyte

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

[0033]

[0034] in,

[0035] R2 is a C4 alkylene or C4 fluoroalkylene, wherein the number of fluorine atoms in the C4 fluoroalkylene is 1; here, alkylene refers to a saturated, branched or straight-chain or cyclic hydrocarbon residue of 1 to 18 carbon atoms, and has two monovalent residue centers derived from the removal of two hydrogen atoms from the same carbon atom or two different carbon atoms of the parent alkane, such as 1,4-butyl (-CH2CH2CH2CH2-).

[0036] R1 and R3 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R3 is 1 to 4.

[0037] The electrolyte provided in this disclosure can improve the cycle performance of medium-nickel high-voltage lithium batteries and ensure 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] The electrolyte disclosed herein includes cyclic carbonate solvents, which have a high dielectric constant, helping to dissolve lithium salts and distribute them uniformly in the electrolyte, thereby ensuring the normal operation of the battery.

[0039] In the electrolyte disclosed herein, the compound of formula (I) is an ether with a relatively long carbon chain and containing at least one fluorine atom. The substitution of the fluorine atom alters the charge density distribution of the compound itself. This more dispersed charge density distribution enhances the oxidation resistance of the molecules, thereby improving the overall oxidation resistance of the electrolyte and exhibiting higher stability under high-temperature cycling conditions. Furthermore, since the main chain of compound (I) contains two relatively symmetrical oxygen atoms, this relatively long main chain solvent does not participate in the first solvent shell of lithium ions. Therefore, it does not participate in film formation during charge-discharge processes. However, the addition of this type of fluorinated ether solvent still alters the composition of the solvated structure of lithium ions, resulting in a significant improvement in high-temperature cycling stability compared to cells without fluorinated ether solvents.

[0040] In some embodiments, the cyclic carbonate solvent includes at least one of propylene carbonate (PC) and ethylene carbonate (EC). Optionally, the cyclic carbonate solvent is ethylene carbonate. 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, thereby enhancing the performance of the lithium battery.

[0041] In some embodiments, R2 is a C4 chain alkylene or a C4 fluorochain alkylene, optionally a C4 straight-chain alkylene or a C4 fluorostraight-chain alkylene.

[0042] In some embodiments, the compound of formula (I) is selected from at least one of the following compounds:

[0043]

[0044]

[0045] In some embodiments, the compound of formula (I) is selected from at least one of I-11, I-12, I-14, I-15, I-17, I-2, I-7, I-8, and I-10. In some embodiments, optionally, the compound of formula (I) is selected from at least one of I-11, I-12, I-14, I-15, and I-17; more preferably, it is at least one of I-11, I-15, and I-17.

[0046] 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 varying degrees of charge distribution uniformity in the overall structure, leading to differences in their chemical stability. A more uniform charge distribution in the overall structure correlates with higher oxidative stability and better high-temperature cycling performance in mixed electrolytes with carbonate solvents. For example, I-11 and I-15 exhibit relatively uniform charge distribution in their overall structures, resulting in superior high-temperature cycling performance.

[0047] In some embodiments, based on the total mass of the electrolyte, the sum of the mass of the cyclic carbonate solvent and the fluoroether solvent accounts for 15% to 60%, optionally 25% to 60%, and more preferably 35% to 50%. The cyclic carbonate solvent and the fluoroether solvent have high viscosity. Using cyclic carbonate solvents and fluoroether solvents within the above-mentioned mass range can improve the stability of the electrolyte and the solubility of lithium salts, without affecting the conductivity, cycle life, and energy density of the lithium battery due to viscosity.

[0048] In some embodiments, the mass percentage of the fluorinated ether solvent is 4% to 45%, for example 4%, 10%, 14%, 18%, 20%, 25%, 31%, 35%, 40%, or 45%; optionally, it is 15% to 35%. A mass percentage of less than 4% for the fluorinated ether solvent is insufficient to improve electrolyte stability, while a mass percentage greater than 45% will result in excessively high electrolyte viscosity and a decrease in the number of cycles at room temperature and high temperature. This may be because the direct current resistance (DCR) gradually increases during cycling, leading to increased internal polarization of the cell and consequently deteriorating the cell's performance in terms of both room temperature and high temperature cycling cycles.

[0049] In some embodiments, the electrolyte further includes a chain carbonate solvent; optionally, the chain carbonate solvent includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The inclusion of a chain carbonate solvent in the electrolyte can reduce the overall viscosity, which helps to improve the conductivity, cycle life, and energy density of the lithium battery.

[0050] 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.

[0051] In some embodiments, the electrolyte further includes a lithium salt; optionally, the lithium salt accounts for 11-15% of the total mass of the electrolyte, and optionally 13-14%; optionally, the lithium salt is LiPF6. LiPF6 has good solubility in cyclic carbonate solvents and fluorinated ether solvents, avoiding the battery performance degradation 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), vinylene carbonate (VC), and 1,3-propanesulfonate lactone (PS); optionally, the additive includes lithium fluorosulfonylimide (LiFSI), vinylene carbonate (VC), and 1,3-propanesulfonate lactone (PS); more preferably, the additive includes vinylene carbonate (VC) and 1,3-propanesulfonate lactone (PS). Lithium fluorosulfonylimide helps increase lithium ions in the electrolyte, thereby improving the overall battery performance; the combined use of vinylene carbonate and 1,3-propanesulfonate lactone generates a relatively dense solid electrolyte interphase (SEI) and CEI film layer on the positive and negative electrode surfaces, which protects the positive and negative electrode materials during cycling and is beneficial for improving the cycle performance of the cell.

[0053] In some embodiments, the lithium difluorosulfonylimide comprises 0.1% to 5% of the total mass of the electrolyte, more preferably 0.2% to 1%; optionally, the vinylene carbonate comprises 0.1% to 10% of the mass, more preferably 0.2% to 1%; optionally, the 1,3-propanesulfonate lactone comprises 0.1% to 10% of the mass, more preferably 0.2% to 1%.

[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] Exemplarily, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode 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 base layer and a metal layer formed on at least one surface of the polymer material base layer. 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; where 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 causes a dive in the cycle number in the later stage of cycling at 25°C and 45°C, making it difficult to operate stably for a long time.

[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 10

[0076] Examples 1-10 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-11, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed in the proportions specified in Examples 1-10 to form a total organic solvent. VC, PS, LiPF6, and LiFSI were then mixed uniformly with the aforementioned organic solvent in the proportions specified in Examples 1-10 to obtain the electrolyte.

[0083] The proportions of each component in Examples 1-10 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 1-3, Comparative Examples 5-7

[0089] The difference between Comparative Examples 1-3, 5-7 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 1-3, 5-7 are shown in Table 2. In Table 2, G4 represents tetraethylene glycol dimethyl ether; A represents the compound shown in formula A. B represents the compound shown in formula B.

[0090] Example 11, Comparative Example 4

[0091] The difference between Example 11 and Example 7 lies in step (1): replacing the positive electrode active material with LiNi. 0.9 Mn 0.05 Co 0.05 O2.

[0092] Compared with Comparative Example 4 and Example 11, the difference lies in the organic solvent in step (3) being a fluorinated ether, and the ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) is shown in Table 2.

[0093] Test methods

[0094] The secondary batteries prepared in the above embodiments and comparative examples can be tested using the following methods:

[0095] (1) High-temperature cycle test of secondary battery

[0096] In an oven at a specified temperature (45℃), 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.

[0097] (2) Secondary battery room temperature cycle test

[0098] 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.

[0099] Table 1. Details and test results of Examples 1 to 10

[0100]

[0101]

[0102] Table 2. Details and test results of Comparative Examples 1 to 6 and Example 11.

[0103]

[0104] Comparing Comparative Examples 1, 3, 5, 6, and 7, it can be seen that adding fluorinated ether solvents to the electrolyte, whether fluorinated ether I-11, octafluoropentyl-tetrafluoroethyl ether, formula A, or formula B, can improve the high-temperature cycling stability of the battery cell. Comparing Comparative Examples 3, 5, 6, and 7, it can be seen that different fluorinated ether solvents have significantly different effects on improving the cycling stability of the battery cell at room temperature and high temperature. The improvement effect of fluorinated ether I-11 provided in this disclosure is significantly better than that of octafluoropentyl-tetrafluoroethyl ether, formula A, and formula B. This may be because when the fluorinated ether compounds provided in this application are combined with carbonate compounds as organic solvents, the electrolyte, while possessing good stability, can also provide good lithium salt dissolution performance, thereby improving the battery's cycling performance under room temperature and high-temperature conditions.

[0105] Comparison of Comparative Example 1 and Examples 1-3 and 6-8 shows that adding fluorinated ether I-11 to the electrolyte can improve the cycle stability of the battery cell. In particular, when the mass percentage of fluorinated ether I-11 is in the range of 15% to 35%, the addition of fluorinated ether I-11 significantly improves the cycle stability of the battery cell, and in some ranges it is close to doubled, for example, 25.95%.

[0106] Comparing Comparative Example 2 and Example 7, it can be found that, compared with the combination of tetraethylene glycol dimethyl ether (G4) and fluoroether I-11, the combination of EC and fluoroether I-11 is more conducive to improving the cycle stability of the battery cell. This may be because the fluoroether of the present application combined with cyclic carbonate can inhibit the side reactions of each component of the solvent in the electrolyte during the cycle and form a stable solvation configuration with lithium ions, thereby improving the cycle stability of the battery cell.

[0107] Comparing Example 11, Comparative Example 4 and Example 7, it can be seen that fluoroether I-11 can also improve the cycle stability of the battery cell prepared with high-nickel cathode active material. 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 (Example 11 and Comparative Example 4), the battery cell performance of the combination of fluoroether I-11 and medium-nickel cathode active material (Ni6 in Example 7) is better. This may be because the combined solvent formed by the fluoroether compound of the present application and cyclic carbonate has a relatively high consistency between its stable electrochemical window and the working potential of the medium-nickel cathode active material. During the cycle, while reducing the multiphase side reactions caused by the dissolution of transition metals in the cathode active material, it greatly avoids the erosion of the cathode active material by the electrolyte side reactions under high voltage, and significantly improves the cycle stability of the battery cell under normal temperature and high temperature conditions.

[0108] It should be noted that the cathode active materials of Examples 1 to 10 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; wherein, 0.9 < a < 1.1, 0.5 < x < 0.7, 0.1 < z ≤ 0.2 and x + y + z = 1.

[0109] Comparing Example 4, Example 5, Example 7, Example 9 and Example 10, it can be seen that adding one or more of LiFSI, VC, and PS to the electrolyte can improve the cycle performance of the battery cell. The combination of LiFSI and VC, the combination of LiFSI and PS, or the combination of LiFSI, VC and PS can greatly improve the cycle performance of the battery cell. In particular, the combination of VC and PS will generate a relatively dense SEI and CEI on the surfaces of the positive and negative electrodes, which will play 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 12 to 21

[0111] Example 12 is similar to Example 11, except that fluoroether I-11 is replaced with fluoroether I-15; Examples 13 to 21 are prepared in a similar manner to Examples 1 to 9, except that fluoroether I-11 is replaced with fluoroether I-15; The detailed composition and test results of the electrolyte are shown in Table 3.

[0112] Table 3

[0113]

[0114]

[0115] Examples 22 to 31

[0116] Example 22 is similar to Example 11, except that fluoroether I-11 is replaced with fluoroether I-1; Examples 23 to 31 are similar to the preparation methods of Examples 1 to 9, except that fluoroether I-11 is replaced with fluoroether I-1. The detailed composition and test results of the electrolyte are shown in Table 4.

[0117] Table 4

[0118]

[0119] Examples 32 to 41

[0120] Example 32 is similar to Example 11, except that fluoroether I-11 is replaced with fluoroether I-6; Examples 33 to 41 are prepared in a similar manner to Examples 1 to 9, except that fluoroether I-11 is replaced with fluoroether I-6. The detailed composition and test results of the electrolyte are shown in Table 5.

[0121] Table 5

[0122]

[0123]

[0124] Examples 42 to 51

[0125] Example 42 is similar to Example 11, except that fluoroether I-11 is replaced with fluoroether I-2; Examples 43 to 51 are similar to the preparation methods of Examples 1 to 9, except that fluoroether I-11 is replaced with fluoroether I-2. The detailed composition and test results of the electrolyte are shown in Table 6.

[0126] Table 6

[0127]

[0128] Examples 52 to 61

[0129] Example 52 is similar to Example 11, except that fluoroether I-11 is replaced with fluoroether I-7; Examples 53 to 61 are similar to Examples 1 to 9 in preparation method, except that fluoroether I-11 is replaced with fluoroether I-7. The detailed composition and test results of the electrolyte are shown in Table 7.

[0130] Table 7

[0131]

[0132]

[0133] As can be seen from the test results in Tables 1 to 7, adding the compound of formula (I) and EC provided in the embodiments of this disclosure to the electrolyte can improve the cycle stability of the battery cell. Among them, I-11 and I-15 show better improvement in the high-temperature cycle performance of the battery cell. Adding LiFSI, VC and PS to the electrolyte can further improve the cycle stability of the battery cell.

[0134] 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.

[0135] 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.

[0136] 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, Includes positive electrode active material and electrolyte; among which, The positive electrode active material 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; The electrolyte comprises cyclic carbonate solvents, fluoroether solvents, and chain carbonate solvents; wherein the fluoroether solvents comprise at least one compound of formula (I): I in, R2 is a C4 alkylene or a C4 fluoroalkylene, wherein the number of fluorine atoms in the C4 fluoroalkylene is 1; R1 and R3 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R3 is 1 to 4. Based on the total mass of the electrolyte, the sum of the mass of the cyclic carbonate solvent and the fluoroether solvent accounts for 25% to 60%; the mass of the fluoroether solvent accounts for 15% to 35%.

2. The lithium battery according to claim 1, characterized in that, The cyclic carbonate solvents include at least one of propylene carbonate and ethylene carbonate.

3. The lithium battery according to claim 1 or 2, characterized in that, R2 is a C4 chain alkylene or a C4 fluorochain alkylene.

4. The lithium battery according to claim 3, characterized in that, R2 is a C4 straight-chain alkylene or a C4 fluoro-straight-chain alkylene.

5. The lithium battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the sum of the mass of the cyclic carbonate solvent and the fluoroether solvent accounts for 35% to 50%.

6. The lithium battery according to claim 1, characterized in that, The chain carbonate solvents include at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

7. The lithium battery according to claim 6, characterized in that, Based on the total mass of the electrolyte, the mass percentage of methyl ethyl carbonate is 40% to 60%.

8. The lithium battery according to claim 2, characterized in that, Based on the total mass of the electrolyte, the mass percentage of ethylene carbonate is 15% to 25%.

9. The lithium battery according to claim 1, characterized in that, The electrolyte also includes lithium salt; the lithium salt accounts for 11% to 15% of the total mass of the electrolyte.

10. The lithium battery according to claim 9, characterized in that, The lithium salt accounts for 13% to 14% of the total mass of the electrolyte; and / or The lithium salt includes LiPF6.

11. The lithium battery according to claim 1, characterized in that, The electrolyte further includes at least one of lithium difluorosulfonylimide, vinylene carbonate, and 1,3-propanesulfonate lactone.

12. The lithium battery according to claim 11, characterized in that, The lithium difluorosulfonamide accounts for 0.1% to 5% of the total mass of the electrolyte; and / or The vinylene carbonate accounts for 0.1% to 10% of the total mass; and / or The mass percentage of the 1,3-propanesulfonic acid lactone is 0.1% to 10%.

13. The lithium battery according to claim 11, characterized in that, The lithium difluorosulfonamide accounts for 0.2% to 1% of the total mass of the electrolyte; and / or The vinylene carbonate accounts for 0.2% to 1% of the total mass; and / or The mass percentage of the 1,3-propanesulfonic acid lactone is 0.2% to 1%.

14. The lithium battery according to claim 1, characterized in that, The compound of formula (I) is selected from at least one of the following compounds: 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 。

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