Lithium battery

Abstract

The present disclosure provides a lithium battery. Specifically, the lithium battery comprises an electrolyte, the electrolyte comprises a fluorinated ether solvent and a cyclic carbonate solvent; wherein the fluorinated ether solvent comprises at least one compound of formula (I): wherein R2 and R3 are each independently selected from an alkylene group or a fluorinated alkylene group, 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 a methyl group or a fluorinated methyl group, and the total number of fluorine atoms in R1 and R4 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] The present disclosure relates to the technical field of batteries, and particularly to a lithium battery. Background Art

[0002] The ternary cathode material is a new type of cathode material for lithium batteries, such as nickel cobalt manganese, nickel cobalt aluminum, etc. Nickel cobalt manganese includes nickel salts, cobalt salts and manganese salts, and stands out from the cathode materials of many lithium batteries with its higher working voltage and larger energy density. Based on the proportion of nickel in nickel cobalt manganese, the nickel cobalt manganese ternary cathode material includes low-nickel cathode materials, medium-nickel cathode materials and high-nickel cathode materials. Among them, the medium-nickel cathode material not only has an energy density effect similar to that of the high-nickel cathode material, but also has higher safety and lower cost, and is regarded as one of the mainstream solutions to solve the range anxiety of vehicle-mounted batteries. However, under high-voltage conditions, unstable substances in the electrolyte are extremely likely to decompose, resulting in poor cycle performance of medium-nickel high-voltage batteries. Summary of the Invention

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

[0004] Based on the above purpose, the present disclosure provides a lithium battery, including an electrolyte and a positive electrode active material; the electrolyte includes a fluorinated ether solvent and a cyclic carbonate solvent; wherein, the fluorinated ether solvent includes at least one compound of formula (I):

[0005]

[0006] Wherein,

[0007] 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 ≤ 1;

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

[0009] 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.

[0010] In some embodiments, based on the total mass of the electrolyte, the mass ratio of the fluorinated ether solvent is 4% - 35%, optionally 15% - 25%; and / or

[0011] The total mass percentage of the fluoroether solvent and the cyclic carbonate solvent is 15% to 65%, optionally 25% to 60%, and more preferably 35% to 50%.

[0012] 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-.

[0013] In some embodiments, the solvent further includes a chain carbonate solvent; optionally, the chain carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; optionally, the cyclic carbonate solvent includes at least one of propylene carbonate and ethylene carbonate.

[0014] In some embodiments, the chain carbonate solvent is ethyl methyl carbonate and dimethyl carbonate, and the cyclic carbonate solvent is ethylene carbonate; wherein...

[0015] Based on the total mass of the electrolyte, the mass percentage of methyl ethyl carbonate is 35% to 45%; the mass percentage of dimethyl carbonate is 5% to 7%; and the mass percentage of ethylene carbonate is 15% to 25%.

[0016] 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%.

[0017] In some embodiments, the lithium salt includes at least one of LiPF6, LiClO4, LiCF3SO3, LiBOB, LiODFB, and LiN(SO2CF3)2; optionally, the lithium salt is LiPF6.

[0018] In some embodiments, the electrolyte further includes at least one of lithium bis(fluorosulfonyl)imide, fluoroethylene carbonate, and LiBF4; optionally, the lithium bis(fluorosulfonyl)imide accounts for 0.1% to 5% of the total mass of the electrolyte, more preferably 0.2% to 1%; optionally, the fluoroethylene carbonate accounts for 0.1% to 10% of the mass, more preferably 0.3% to 1%; and the LiBF4 accounts for 0.1% to 2% of the mass, more preferably 0.1% to 0.3%.

[0019] In some embodiments, the compound of formula (I) is selected from at least one of the following compounds:

[0020]

[0021]

[0022] As can be seen from the above, the lithium battery provided in this disclosure includes an electrolyte and a positive electrode active material, wherein the electrolyte includes fluorinated ether solvents and cyclic carbonate solvents; wherein the fluorinated ether solvents include 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 and is beneficial for the long-term stable operation of lithium batteries. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0024] 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.

[0025] 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.

[0026] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0027] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0028] 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.

[0029] 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".

[0030] 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.

[0031] 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.

[0032] 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.

[0033] electrolyte

[0034] This disclosure provides an electrolyte comprising a fluoroether solvent and a cyclic carbonate solvent; wherein the fluoroether solvent comprises at least one compound of formula (I):

[0035]

[0036] in,

[0037] 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-).

[0038] R1 and R4 are each independently methyl or fluoromethyl, and the total number of fluorine atoms in R1 and R4 is 1 to 4.

[0039] 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.

[0040] The electrolyte disclosed herein includes cyclic carbonate solvents, which have a high dielectric constant, helping to dissolve lithium salts and compensating for the insufficient solubility of fluorinated ethers in lithium salts, allowing them to be evenly distributed in the electrolyte, thereby ensuring the normal operation of the battery.

[0041] 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.

[0042] 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.

[0043] In some embodiments, the compound of formula (I) is selected from at least one of the following compounds:

[0044]

[0045]

[0046] In some embodiments, the compound of formula (I) is selected from at least one of I-4, I-5, I-8, I-10, I-13, I-15, I-16, and I-19. In some embodiments, optionally, the compound of formula (I) is selected from at least one of I-5, I-10, I-13, I-15, and I-16.

[0047] 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.

[0048] In some embodiments, the total mass percentage of the fluoroether solvent and the cyclic carbonate solvent is 15% to 65%, optionally 25% to 60%, and more preferably 35% to 50%.

[0049] In some embodiments, the fluorinated ether solvent accounts for 4% to 35% of the total mass of the electrolyte, for example, 10%, 14%, 18%, 20%, 25%, or 31%; optionally, 15% to 25%. During cycling, the addition of fluorinated ethers 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. If the mass range of the fluorinated ether solvent is less than 10%, the solvent's antioxidant stability is insufficient, making it difficult to improve the stability of the electrolyte. If the mass range of the fluorinated ether solvent is greater than 50%, the electrolyte viscosity will be too high, resulting in a decrease in the number of cycles at room temperature. This may be because the DC internal resistance gradually increases during cycling, increasing the internal polarization of the cell and thus deteriorating the cell's performance in terms of the number of cycles at room temperature.

[0050] In some embodiments, the cyclic carbonate solvent includes at least one of propylene carbonate (PC) and ethylene carbonate (EC). 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. 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.

[0051] In some embodiments, the electrolyte further includes chain carbonates. Exemplarily, the chain carbonate solvent includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Because fluorinated ether solvents have relatively long main chains and high overall viscosity, including 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. Furthermore, DMC can improve the overall wettability of the electrolyte, which is beneficial for improving the overall cycle performance of the cell. Simultaneously, the addition of carboxylic acid esters alters the solvation structure of lithium ions and changes the film-forming material during charge and discharge, also contributing to improved overall cell cycle performance.

[0052] In some embodiments, the electrolyte comprises ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. Further, 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 35%–45%; and the mass percentage of dimethyl carbonate is 5%–7%. The combination of ethylene carbonate, ethyl methyl carbonate, and dimethyl 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.

[0053] 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%.

[0054] In some embodiments, the lithium salt includes at least one of LiPF6, LiClO4, LiCF3SO3, LiBOB, LiODFB, and LiN(SO2CF3)2.

[0055] Optionally, the lithium salt is LiPF6. LiPF6 has good solubility in mixtures of carbonate solvents and fluorinated ether solvents, avoiding the battery performance degradation caused by insufficient solubility of lithium salt.

[0056] In some embodiments, the electrolyte further includes additives, optionally including at least one of lithium bis(fluorosulfonyl)imide (LiFSI), fluoroethylene carbonate (FEC), and LiBF4. LiFSI helps increase lithium ions in the electrolyte, thereby improving overall battery performance; FEC participates in film formation during initialization, and the inorganic component of LiF can reduce the electronic conductivity of SEI and CEI, thus enhancing the stability of SEI and CEI during both high-temperature and room-temperature cycling. The addition of LiBF4 increases the overall conductivity of the electrolyte, and when used in combination with fluoroethers, it compensates for some of the conductivity decrease caused by high-viscosity solvents, thereby improving cycle performance.

[0057] 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 fluoroethylene carbonate comprises 0.1% to 10% of the total mass, more preferably 0.3% to 1%; and the LiBF4 comprises 0.1% to 2% of the total mass, more preferably 0.1% to 0.3%.

[0058] lithium batteries

[0059] A second aspect of this disclosure provides a lithium battery, including the electrolyte provided above.

[0060] 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.

[0061] Positive electrode sheet

[0062] 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.

[0063] 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.

[0064] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (e.g., polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0065] 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 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM811).

[0066] 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 makes it difficult to operate stably for a long time due to the diving in the later stage of the cycle 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 poor conductivity of this film layer leads to 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.

[0067] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0068] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0069] In some embodiments, the positive electrode plate can be prepared by the following method: Dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0070] Negative electrode sheet

[0071] The negative electrode includes a negative current collector and a film layer optionally disposed on at least one surface of the negative current collector.

[0072] For example, the film layer may include a negative electrode active material (e.g., artificial graphite), a conductive agent, a thickener, and a binder.

[0073] 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.

[0074] Separating membrane

[0075] 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.

[0076] 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.

[0077] Example

[0078] 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.

[0079] Examples 1 to 15, Comparative Example 1

[0080] Examples 1-15 and Comparative Example 1 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:

[0081] (1)LiNi 0.6 Mn 0.3 Co 0.1 Preparation of O2 cathode:

[0082] LiNi, the positive electrode active material 0.6 Mn 0.3 Co 0.1O2, 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).

[0083] (2) Preparation of graphite anode:

[0084] 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.

[0085] (3) Preparation of electrolyte:

[0086] In an argon atmosphere glove box with a water content of <10 ppm, battery-grade fluorinated ether I-5, dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed according to the proportions in Comparative Example 1 and Examples 1-15 to form a total organic solvent. LiPF6, LiFSI, LiBF4, and FEC were then mixed evenly with the aforementioned organic solvent according to the proportions in Comparative Example 1 and Examples 1-15 to obtain the electrolyte.

[0087] The proportions of each component in Examples 1-15 and Comparative Example 1 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.

[0088] (4) Preparation of the separating membrane:

[0089] Polypropylene film is used as the separator.

[0090] (5) Preparation of secondary batteries:

[0091] 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).

[0092] Comparative Examples 2 to 5

[0093] The difference between Comparative Examples 2-5 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 2-5 are shown in Table 1. In Table 2, A represents the compound represented by formula A. B represents the compound shown in formula B.

[0094] Example 16, Comparative Example 6

[0095] Compared with Example 16, Comparative Example 6, 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.

[0096] Test methods

[0097] The secondary batteries prepared in the above embodiments and comparative examples can be tested using the following methods:

[0098] (1) High-temperature cycle test of secondary battery

[0099] In an oven at a specified temperature (45℃), the battery was cyclically charged and discharged within a specified potential range (2.0V~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.

[0100] (2) Secondary battery room temperature cycle test

[0101] In an oven at a specified temperature (25℃), the battery was cyclically charged and discharged within a specified potential range (2.0V~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.

[0102] Table 1

[0103]

[0104]

[0105] Table 2

[0106]

[0107] Comparing Comparative Examples 1, 2, 3, 5, and 4, it can be seen that adding fluorinated ether I-5 to the electrolyte can significantly improve the room temperature cycling stability and high temperature cycling stability of the battery cell. Comparing Comparative Examples 2, 3, 5, and 4, it can be seen that different fluorinated ether compounds have significantly different effects on improving the cycling stability of the battery cell. The fluorinated ether I-5 provided in this disclosure has a significantly better effect on improving the cycling stability of the battery cell 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 than fluorinated ether I-5.

[0108] A comparison of Examples 1 to 5 shows that adding fluorinated ether I-5 to the electrolyte can improve the cycle stability of the battery cell. In particular, when the mass percentage of fluorinated ether I-5 is within the range of 15% to 25%, the addition of fluorinated ether I-5 significantly improves the cycle stability of the battery cell.

[0109] Comparing Comparative Example 4, Example 4, and Example 10 reveals that EC and EMC (or EC, EMC, and DMC) combined with fluorinated ether I-5 is more beneficial for improving the cycle stability of the battery cell than tetraethylene glycol dimethyl ether (G4) combined with fluorinated ether I-5. The combination of EC, EMC, and DMC is even better than that of EC and EMC. G4, which is not substituted with fluorine atoms, has a long chain, and a large number of ether bonds, making it thermodynamically unstable. During cycling, it decomposes into film-forming substances on the negative electrode that are detrimental to lithium-ion conduction, resulting in poor battery cell performance, including G4. It should be noted that, except for fluorinated ether I-5, all compounds of formula (I) exhibit similar results and will not be listed in detail further.

[0110] Comparing Example 16 and Comparative Example 6, it can be seen that compared with the significant improvement in cycle stability of the battery cell prepared by adding fluorinated ether I-5 to the medium-nickel cathode active material, the improvement in cycle stability of the battery cell prepared by fluorinated ether I-5 to the high-nickel cathode active material is not obvious. This may be because the stable electrochemical window of the high-nickel cathode material is inconsistent with that of the electrolyte containing fluorinated ether in this application. During the charge and discharge process, after the fluorinated ether undergoes an oxidation reaction at the cathode interface, a film-forming substance is formed on the cathode surface. The ionic conductivity of this substance itself is poor, and the battery cell experiences a drop in performance in the later stages of cycling.

[0111] Apart from fluorinated ether I-5, the compounds of formula (I) all showed similar results when paired with high-nickel cathode materials, which will not be elaborated further.

[0112] It should be noted that the positive electrode active materials in Examples 1 to 15 are merely representative of medium-nickel positive electrode active materials, and not limiting. The medium-nickel positive electrode active material disclosed herein 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.

[0113] Comparing Examples 4, Examples 6 - 9, it can be seen that adding one or more of LiFSI, LiBF4, and FEC to the electrolyte can improve the cycling performance of the battery cell. Among them, FEC forms a relatively dense SEI and CEI on the surfaces of the positive and negative electrodes, which can protect the positive and negative electrode materials during the cycling process and is beneficial to improving the cycling performance of the battery cell.

[0114] Examples 17 to 20

[0115] The preparation methods of Examples 17 - 20 are similar to that of Example 3, the difference being that the structures of the fluoroethers are different. The detailed compositions and test results of the electrolytes are shown in Table 3.

[0116] Table 3

[0117]

[0118] From the test results in Tables 1 - 3, it can be seen that adding the compound of formula (I) provided in the embodiments of the present disclosure to the electrolyte can improve the cycling stability of the battery cell. Among them, I-5, I-8, and I-10 have a more significant improvement in the cycling stability of the battery cell. Adding DMC, LiFSI, LiBF4, and FEC to the electrolyte can further improve the cycling stability of the battery cell.

[0119] In addition, the electrolyte provided in the embodiments of the present 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.

[0120] Those of ordinary skill in the art should understand that: the discussion of any above embodiment is only exemplary, and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples; under the idea of the present disclosure, the technical features between the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the embodiments of the present disclosure as described above, which are not provided in detail for the sake of brevity.

[0121] The embodiments of the present disclosure aim to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims. Therefore, any omission, modification, equivalent substitution, improvement, etc. made within the spirit and principle of the embodiments of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

1. A lithium battery, characterized in that, It includes an electrolyte and a positive electrode active material; wherein the electrolyte includes fluorinated ether solvents and cyclic carbonate solvents; wherein the fluorinated ether solvent includes at least one compound of formula (I): 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; wherein, 0.9 < a < 1.1, 0.5 < x < 0.7, 0.1 < z ≤ 0.2 and x + y + z = 1; Based on the total mass of the electrolyte, the fluorinated ether solvent accounts for 4% to 35% of the total mass; the total mass percentage of the fluorinated ether solvent and the cyclic carbonate solvent is 15% to 65%.

2. The lithium battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the fluorinated ether solvent is 15% to 25%.

3. The lithium battery according to claim 2, characterized in that, The total mass percentage of the fluoroether solvent and the cyclic carbonate solvent is 25% to 60%.

4. The lithium battery according to claim 3, characterized in that, The total mass percentage of the fluoroether solvent and the cyclic carbonate solvent is 35% to 50%.

5. The lithium battery according to claim 1, 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-.

6. The lithium battery according to claim 1, characterized in that, It also includes chain carbonate solvents.

7. The lithium battery according to claim 6, characterized in that, The chain carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and / or The cyclic carbonate solvents include at least one of propylene carbonate and ethylene carbonate.

8. The lithium battery according to claim 6, characterized in that, The total mass ratio of the fluorinated ether solvent and the cyclic carbonate solvent is 35% to 50%; the chain carbonate solvent includes ethyl methyl carbonate and dimethyl carbonate, and the cyclic carbonate solvent includes ethylene carbonate; wherein... Based on the total mass of the electrolyte, the mass percentage of methyl ethyl carbonate is 35% to 45%; the mass percentage of dimethyl carbonate is 5% to 7%; and 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.

11. The lithium battery according to claim 9, characterized in that, The lithium salt includes at least one of LiPF6, LiClO4, LiCF3SO3, LiBOB, LiODFB, and LiN(SO2CF3)2.

12. The lithium battery according to claim 1, characterized in that, The electrolyte further includes at least one of lithium bis(fluorosulfonyl)imide, fluoroethylene carbonate, and LiBF4; based on the total mass of the electrolyte, the mass percentage of lithium bis(fluorosulfonyl)imide is 0.1% to 5%; the mass percentage of fluoroethylene carbonate is 0.1% to 10%; and the mass percentage of LiBF4 is 0.1% to 2%.

13. The lithium battery according to claim 12, characterized in that, The lithium difluorosulfonamide accounts for 0.2% to 1% of the total mass of the electrolyte; and / or The fluoroethylene carbonate has a mass percentage of 0.3% to 1%; and / or The mass percentage of LiBF4 is 0.1% to 0.3%.

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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