Electrolyte, battery, and power consuming device

Abstract

This application relates to electrolytes, batteries, and electrical devices, belonging to the field of battery technology. By adding specific cyclic sulfate compounds to the electrolyte and controlling their mass percentage in the electrolyte, the NMR shift value of the central carbon atom in the electrolyte, and the geometric mean of the electrolyte's ionic conductivity at 40°C and at -10°C satisfying a specific relationship, this application ensures that the cyclic sulfate compounds rapidly form a film, providing good protection for the positive and negative electrodes and improving battery cycle performance. Simultaneously, it reduces the adverse effects of their addition on battery impedance and electrolyte conductivity, reduces polarization during charging, and improves fast-charging performance. Thus, the battery can achieve a balance between good cycle performance and fast-charging performance, especially high-temperature cycle performance and low-temperature fast-charging performance, exhibiting excellent overall electrochemical performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to electrolytes, batteries, and electrical devices. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that use lithium-ion intercalation compounds as the positive electrode material. They are widely used in various electrical devices such as mobile devices and electric vehicles, serving as core energy storage devices and providing crucial support for the stable operation of end products. With the continuous expansion of application scenarios, the market's performance requirements for lithium-ion batteries are becoming increasingly stringent, especially regarding the dual demands for high-temperature cycle life and low-temperature fast-charging performance. The electrolyte plays a vital role in lithium-ion batteries, acting like the "blood" of the battery, responsible for the efficient transport of lithium ions and the stable protection of the electrode interfaces. Therefore, how to optimize the electrolyte system to simultaneously improve the high-temperature cycle life and low-temperature fast-charging performance of lithium-ion batteries has become a crucial research topic urgently needing to be addressed in the field of lithium-ion batteries. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the prior art and provide electrolytes, batteries and electrical devices so that the batteries have both good cycle performance and fast charging performance, especially high temperature cycle performance and low temperature fast charging performance.

[0004] To achieve the above objectives, in a first aspect, this application provides an electrolyte comprising a lithium salt, a cyclic sulfate compound, and a solvent; The cyclic sulfate compound is at least one of the compounds shown in Formula I. , In Formula I, R1, R2, R3, and R4 each independently include a group as shown in Formula II, a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. In Formula II, R5 and R6 each independently include the group shown in Formula III, a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. In Formula III, R7 and R8 each independently include a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. The cyclic sulfate ester compound has a mass percentage of S% in the electrolyte, the central carbon atom nuclear magnetic shift value of the electrolyte is N ppm, and the ionic conductivity of the electrolyte at 40℃ and -10℃ is σ1mS / cm and σ2mS / cm, respectively, where σ = (σ1 × σ2). 0.5 , The electrolyte satisfies: 0.82 ≤ (σ × N) 0.5 ) / (σ+10S)≤12.5.

[0005] Secondly, this application provides a battery including the electrolyte.

[0006] Thirdly, this application provides an electrical device including the battery.

[0007] Compared to existing technologies, the advantages of this application are as follows: By adding specific cyclic sulfate compounds to the electrolyte and controlling their mass percentage in the electrolyte, the nuclear magnetic shift value of the central carbon atom in the electrolyte, and the geometric mean of the ionic conductivity of the electrolyte at 40℃ and at -10℃ satisfying a specific relationship, this application can ensure that the cyclic sulfate compounds form a film quickly, providing good protection for the positive and negative electrodes (especially the negative electrode), and improving the battery cycle performance. At the same time, it can reduce the adverse effects of their addition on battery impedance and electrolyte conductivity, reduce polarization during charging, and improve battery fast charging performance. Thus, the battery can achieve both good cycle performance and fast charging performance, especially high-temperature cycle performance and low-temperature fast charging performance, and possess excellent comprehensive electrochemical performance. Detailed Implementation

[0008] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0009] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0010] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0011] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0012] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0013] In this application, terms such as "first time" and "second time" are not used to limit the number of times.

[0014] In this application, the positive electrode material includes positive electrode active material, conductive agent, binder, etc.; the negative electrode material includes negative electrode active material, conductive agent, binder, etc.

[0015] According to a first aspect of this application, a battery is provided, comprising a lithium salt, a cyclic sulfate compound, and a solvent; The cyclic sulfate compound is at least one of the compounds shown in Formula I. , In Formula I, R1, R2, R3, and R4 each independently include a group as shown in Formula II, a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. In Formula II, R5 and R6 each independently include the group shown in Formula III, a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. In Formula III, R7 and R8 each independently include a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. The cyclic sulfate ester compound has a mass percentage of S% in the electrolyte, the central carbon atom nuclear magnetic shift value of the electrolyte is N ppm, and the ionic conductivity of the electrolyte at 40℃ and -10℃ is σ1mS / cm and σ2mS / cm, respectively, where σ = (σ1 × σ2). 0.5 , The electrolyte satisfies: 0.82 ≤ (σ × N) 0.5 ) / (σ+10S)≤12.5.

[0016] Cyclic sulfate compounds possess high reduction potentials, allowing them to preferentially form a protective film on the negative electrode surface, suppressing side reactions between the negative electrode and the electrolyte, and improving battery cycle performance. The aforementioned cyclic sulfate compounds with specific structures exhibit even higher reduction potentials; their addition to the electrolyte allows them to preferentially participate in the formation of the interfacial protective film on the negative electrode surface, even before active lithium. While increasing the amount of these cyclic sulfate compounds improves battery cycle performance, it also introduces impurities, increasing battery impedance and reducing electrolyte conductivity, leading to increased polarization during charging and consequently affecting fast-charging performance.

[0017] The central carbon atom in an electrolyte refers to the α-carbon directly bonded to the main functional group in the solvent molecule structure, or a carbon atom within the main functional group, or a substituent attached to the central carbon atom. This carbon atom can influence the electrochemical performance of the molecule. The main functional group is the highest priority functional group in a multifunctional molecule, determined according to the well-known functional group priority order in the art. This functional group determines the main chemical properties of the compound, usually possessing the highest reactivity or the most prominent structural features, and is used as a "surname" (i.e., suffix) in the systematic nomenclature of the compound. If a molecule has only one functional group, that group is itself the main functional group. In this application, when the solvent includes carbonate or carboxylic ester solvents, the central carbon atom in the electrolyte refers to the carbonyl carbon (C=O). The NMR chemical shift of the central carbon atom is closely related to its surrounding electron cloud environment; an increase in the NMR shift value indicates a decrease in the electron cloud density around the central carbon atom. A higher NMR shift value of the central carbon atom in the electrolyte indicates a lower electron cloud density and a weaker coordination ability of the solvent for lithium ions. This results in a stronger coordination ability of the aforementioned cyclic sulfate compounds for lithium ions, promoting faster film formation, particularly at the negative electrode, leading to higher film formation efficiency. Simultaneously, the reduced coordination ability of the solvent for lithium ions lowers the desolvation energy barrier, increasing the lithium ion mass transfer rate. Lithium ion transport can be completed in a shorter reaction time or with less side reaction, reducing the consumption of active lithium and electrolyte. However, if the NMR shift value of the central carbon atom in the electrolyte is too high, it can lead to high film formation efficiency but insufficient film formation, or a high proportion of organic components in the formed interfacial film, resulting in poor stability. This can negatively impact the long-term cycle performance of the battery, especially its high-temperature cycle performance.

[0018] σ is the geometric mean of the ionic conductivity of the electrolyte measured under high temperature (40℃) and low temperature (-10℃) conditions. It can reflect, to a certain extent, the overall ion transport capability of the electrolyte across temperature ranges (i.e., overall) under operating conditions and low temperature environments. When σ is high, it indicates that the electrolyte can maintain a certain ion transport capability across different temperature ranges, balancing fast charging and long-term cycle performance. However, if σ is too high, it may mean that the ion transport capability is too strong, especially under high temperature conditions, which may accelerate the side reactions at the positive / negative electrode interface, leading to a deterioration in cycle life. If σ is too low, it indicates that the overall ion transport capability of the electrolyte is insufficient, especially under low temperature conditions, which limits ion transport. This causes a significant increase in interfacial polarization and impedance during low-temperature startup or early low-temperature cycling, resulting in a decrease in the battery's fast charging capability.

[0019] By controlling the values ​​of S, N, and σ, the condition 0.82 ≤ (σ × N) is met. 0.5With a ratio of σ / (σ+10S)≤12.5, the cyclic sulfate ester compound can be rapidly film-formed, providing good protection for the positive and negative electrodes (especially the negative electrode) and improving battery cycle performance. At the same time, it can reduce the adverse effects of its addition on battery impedance and electrolyte conductivity, reduce polarization during charging, and improve battery fast-charging performance. Thus, the battery can achieve both good cycle performance and fast-charging performance, especially high-temperature cycle performance and low-temperature fast-charging performance, and has excellent comprehensive electrochemical performance.

[0020] σ×N 0.5 This study primarily reflects the comprehensive kinetics of the electrolyte in transporting lithium ions to the interface and participating in film formation. It also comprehensively demonstrates the accuracy of the parameters involved in characterizing actual battery performance. Among them, σ is obtained by geometrically averaging the ionic conductivity under high and low temperature conditions, reflecting the overall comprehensive performance of ion transport capability across the temperature range. N represents the guiding and coordination ability of the central carbon atom for lithium ions. By adjusting the weight of N's influence on the above comprehensive performance indicators, it is made to maintain a reasonable match with σ in terms of order of magnitude and intensity. This avoids the formula results being mainly dominated by solvent electronic structure factors, which would weaken the regulatory role of the content of the cyclic sulfate ester compound in the electrolyte and the ionic conductivity of the electrolyte on film quality and cycle performance. Instead, it can better reflect the influence of N on the lithium ion coordination environment and interfacial reaction kinetics. σ+10S is mainly related to cycling performance. Excessively high σ may increase the risk of side reactions, thus deteriorating cycling performance, especially at high temperatures. By adjusting the weight of S's influence on the aforementioned comprehensive performance indicators, it can be made reasonably matched with σ in terms of magnitude and intensity, preventing the impact of S on cycling performance from being masked by σ and thus failing to be effectively reflected. (σ×N) 0.5 If the value of σ / (σ+10S) is too low, it means that S is excessive or the overall power is insufficient, resulting in poor fast charging performance (especially low temperature fast charging performance); if the value is too high, the film formation rate and ion transport rate are mismatched, resulting in poor cycle stability (especially high temperature stability).

[0021] For example, (σ×N) 0.5 ) / (σ+10S) is a range formed by any two values ​​of 0.82, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 12.5 or higher. In some embodiments, the electrolyte satisfies: 1.8 ≤ (σ×N) / (σ+10S) 0.5 The ratio of σ / (σ+10S) ≤ 6.5 is used to achieve better film formation of the cyclic sulfate ester compound, providing better protection for the negative electrode and thus more effectively improving the cycle performance of the battery. At the same time, it can better reduce the adverse effects of its addition on battery impedance and electrolyte conductivity, reduce polarization during charging, and improve battery fast charging performance, thereby being more conducive to the balance between high-temperature cycle performance and low-temperature fast charging performance.

[0022] In some embodiments, S% is 0.3% to 3%, such as a range formed by any two values ​​of 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or higher. In some embodiments, S% is 1% to 2.5%.

[0023] When S% is in the range of 0.3% to 3%, especially in the range of 1% to 2.5%, the cyclic sulfate ester compounds can participate better in the formation of films on the positive and negative electrodes, and the olefin content in the formed film is higher, which is conducive to the formation of more polyolefins, thus making the protective effect of the interfacial film stronger, better reducing the side reactions between the electrolyte and the negative electrode, improving cycle performance, and avoiding the introduction of too many impurities that would lead to increased impedance, thereby being more conducive to the balance between fast charging performance and cycle performance.

[0024] This application does not limit the detection method for the value of S; it can be detected using conventional methods in the art. For example, the following detection method can be used: The electrolyte solution of the sample to be tested was injected into an Agilent Intuvo 9000 gas chromatograph-mass spectrometer using a microsyringe to obtain GC-MS chromatograms. A standard solution of a certain concentration was prepared by dissolving cyclic sulfate compounds in EMC solvent, and the mass percentage of cyclic sulfate compounds in the standard solution was recorded as w%. The electrolyte solution to be tested and the standard solution were then injected into the Agilent Intuvo 9000 gas chromatograph-mass spectrometer to obtain standard GC-MS chromatograms. The GC-MS spectrum of the electrolyte to be tested was compared with the standard GC-MS spectrum to confirm whether the corresponding components were present (the matching degree between the standard curve and the electrolyte sample curve was ≥98%). The electrolyte sample to be tested and the standard solution were subjected to GC testing to obtain the peak area X1 of the cyclic sulfate ester compound in the GC test spectrum of the sample to be tested and the peak area X2 of the cyclic sulfate ester compound in the GC test spectrum of the standard solution. The mass percentage of the cyclic sulfate ester compound in the electrolyte was calculated according to the following formula: S=(X1 / X2)×w.

[0025] In some embodiments, the number of sulfate groups in Formula I is an integer from 2 to 4, such as 4, 3 or 2, to reduce the molecular weight of the compound shown in Formula I, reduce its film-forming resistance, promote its participation in the formation of the protective film at the positive and negative electrode interfaces, reduce side reactions between the electrolyte and the positive and negative electrodes, thereby improving cycle performance.

[0026] In some embodiments, at least one of R1 to R4 is a hydrogen atom to reduce the steric hindrance of the compound shown in Formula I, which helps it participate in the formation of the protective film at the positive and negative electrode interface, weakens the side reactions between the electrolyte and the positive and negative electrodes, and thus improves cycle performance.

[0027] In some embodiments, R1 and R3 are the same to make cyclic sulfate compounds easier to synthesize and easier to process.

[0028] In some embodiments, R1 and R3 are selected from the groups shown in Formula II, hydrogen atoms, alkyl groups of 1 to 6 carbon atoms, halogen atoms, haloalkyl groups of 1 to 3 carbon atoms, alkoxy groups of 1 to 3 carbon atoms, haloalkoxy groups of 1 to 3 carbon atoms, alkenyl groups of 2 to 6 carbon atoms, alkynyl groups of 2 to 6 carbon atoms, aromatic groups, ester groups, cyano groups, or sulfonic acid groups, in order to reduce the molecular weight of the compound shown in Formula I, reduce its film-forming resistance, facilitate its participation in the formation of the protective film at the positive and negative electrode interfaces, reduce side reactions between the electrolyte and the positive and negative electrodes, and thereby improve cycle performance.

[0029] In some embodiments, the cyclic sulfate compound includes at least one of the following compounds: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , .

[0030] In some embodiments, σ ​​is 2 to 15.5, such as a range formed by any two values ​​of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 15.5 or more. In some embodiments, σ ​​is 4 to 9.

[0031] When σ is in the range of 2 to 15.5, especially in the range of 4 to 9, the electrolyte’s ion transport capacity across the temperature range (i.e., overall) is more suitable. This not only helps to reduce the rise in interfacial polarization and impedance during low-temperature start-up or early low-temperature cycling and improves low-temperature fast charging capability, but also weakens the side reactions at the positive / negative electrode interface under high-temperature conditions and improves high-temperature cycling capability.

[0032] The magnitude of the σ value is affected by a variety of factors, including but not limited to: the composition of the electrolyte, including the type and content of lithium salts, solvents and additives, as well as the preparation process of the electrolyte.

[0033] The σ value can be controlled by the following process parameters and component characteristics: The content and type ratio of lithium salts in the electrolyte: such as the ratio of LiFSI to lithium hexafluorophosphate (LiPF6). Increasing this ratio can significantly improve the conductivity across the entire temperature range (especially in low-temperature environments). Content of cyclic sulfate compounds; The content of small molecule solvents in the electrolyte, such as the content of carboxylic acid ester solvents (e.g., the content of carboxylic acid ester solvents such as methyl acetate (MA), methyl propionate (MP), or ethyl propionate (EP); Other additives in the electrolyte include vinylene carbonate (VC), fluoroethylene carbonate (FEC), lithium difluorooxalate borate (LiODFB), lithium difluorooxalate borate (LiBOB), and lithium difluorooxalate difluorophosphate (LiODFP). These additives affect the conductivity at different electrolyte temperatures by changing the solvation sheath structure of lithium ions and the degree of ion pair association, thereby fine-tuning the σ value. The electrolyte preparation process, including the order of feeding, stirring speed, and settling / maturation, affects the solubility of lithium salts, the uniformity of the solvation structure, and the impurity content in the system, thus influencing the σ value. Different feeding sequences and batch feeding of lithium salts alter the initial solvent environment in which the lithium salts initially contact. Lithium salts preferentially dissolve in solvents with higher dielectric constants, which generally improves the degree of lithium salt dissociation, reduces the formation of ion pairs or ion clusters, and thus increases the electrolyte conductivity. After the electrolyte is mixed, a period of settling or maturation allows the solvation structure of lithium ions to gradually stabilize, and the ion pairs or ion aggregates in the system to redistribute, affecting the electrolyte conductivity, especially at low temperatures. Prolonged settling time may also affect electrolyte performance due to the reaction of trace impurities or the slow decomposition of lithium salts. This application does not limit the detection method for the value of σ; it can be obtained using conventional methods in the art. For example, a Mettler conductivity meter (model: S230) is used for testing under normal pressure conditions. The conductivity meter consists of conductivity electrodes and an electronic unit. It uses high-frequency alternating current to measure the resistance of the solution between two parallel electrodes. The electronic unit uses an AC signal of appropriate frequency to amplify and process the signal before converting it into conductivity. The testing steps are as follows: (1) Electrode calibration Take approximately 10 mL of standard solution (12.88 mS / cm standard solution, specifically 0.1 mol / L potassium chloride solution) and place it in a centrifuge tube. Incubate the tube in a water bath at 25°C for 30 min. When the temperature of the standard solution measured by the temperature electrode is 25 ± 0.2°C, calibration begins. If the conductivity of the standard solution is ± 0.15 mS / cm relative to the standard conductivity, the calibration is successful.

[0034] (2) Electrolyte sample determination (2.1) σ1 test (2.1.1) Sample preparation Take approximately 100 mL of electrolyte sample into a dry, clean fluorinated bottle and seal it. Place the sample in a constant temperature water bath at 40 ± 0.2 °C for 30 min.

[0035] (2.1.2) Test Install the conductivity electrode and clean it with ethanol, then wipe it dry with filter paper. Open the sampling bottle, immerse the conductivity electrode in the sample to be tested, select "automatic measurement mode", click the "measure" button to start the measurement, and after hearing a "beep" sound, the value remains unchanged. Record the current value, which is the conductivity σ1.

[0036] (2.2) σ² test (2.2.1) Sample preparation Take approximately 100 mL of electrolyte sample into a dry, clean fluorinated bottle and seal it. Place the sample in a constant temperature liquid bath at -10±0.2℃ for 30 min.

[0037] (2.2.2) Test Install the conductivity electrode and clean it with ethanol, then wipe it dry with filter paper. Open the sampling bottle, immerse the conductivity electrode in the sample to be tested, select "automatic measurement mode", click the "measure" button to start the measurement, and after hearing a "beep" sound, the value remains unchanged. Record the current value, which is the conductivity σ2.

[0038] (2.3) Calculate σ according to the following formula: σ = (σ1 × σ2) 0.5 .

[0039] In some embodiments, σ1mS / cm is 8~25mS / cm, such as 8 mS / cm, 10 mS / cm, 12 mS / cm, 14 mS / cm, 16 mS / cm, 18 mS / cm, 20 mS / cm, 22 mS / cm, 25 mS / cm, or any two of the above values. Controlling σ1 within this range makes the high-temperature ionic conductivity of the electrolyte more suitable, which on the one hand is beneficial to improve fast charging capability, and on the other hand can reduce the side reactions at the positive / negative electrode interface under high-temperature conditions, thereby improving high-temperature cycling capability.

[0040] In some embodiments, σ²mS / cm is 0.5~10 mS / cm, such as 0.5 mS / cm, 1 mS / cm, 2 mS / cm, 4 mS / cm, 6 mS / cm, 8 mS / cm, 10 mS / cm, or any two of the above values ​​forming a range. Controlling σ² within this range makes the low-temperature ionic conductivity of the electrolyte more suitable. On the one hand, this helps to suppress the rise of interfacial polarization and impedance during low-temperature start-up or early low-temperature cycling, improving the low-temperature fast-charging capability. On the other hand, it reduces the side reactions at the positive / negative electrode interface under low-temperature conditions, enhancing the low-temperature cycling capability.

[0041] In some embodiments, N ppm is 140~250 ppm, such as 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm, 210 ppm, 220 ppm, 230 ppm, 240 ppm, 250 ppm, or any two of the above values. In some embodiments, N is 160~200.

[0042] When N ppm is in the range of 140~250ppm, especially in the range of 160~200ppm, the electron cloud density around the central carbon atom is more suitable. This not only makes the coordination ability of the cyclic sulfate ester compound for lithium ions more suitable, ensuring that it can participate in film formation quickly and fully, but also makes the film more stable and improves the protection of the positive and negative electrode plates. It also better suppresses the side reactions between the positive and negative electrode plates and the electrolyte under high temperature conditions, and improves cycle performance. Moreover, the coordination ability of the solvent for lithium ions is reduced, the desolvation energy barrier of lithium ions is reduced, and the lithium ion mass transfer rate is increased. This helps to complete lithium ion transport in a shorter reaction time or with a lower degree of side reaction, thereby reducing the consumption of active lithium and electrolyte, and thus contributing to the balance between high temperature cycle performance and low temperature fast charging performance.

[0043] The value of N is influenced by various factors, such as the electrolyte composition, including the type and content of lithium salts, solvents, and additives. Furthermore, the N value is also related to the feeding process during electrolyte preparation. The order of batch addition of lithium salts and cyclic sulfate compounds, as well as the preparation temperature, affect the initial coordination structure distribution of lithium ions between the solvent and additives. This alters the relative proportions of different components in the solvation sheath (the first coordination layer formed by solvent molecules, anions, and additive molecules surrounding lithium ions in the electrolyte, and its surrounding local microstructure), thereby changing the NMR shift of the central carbon atom in the electrolyte. Although the intrinsic value of N is mainly determined by the molecular structure of the electrolyte composition, different preparation process conditions may lead to differences in the dynamic coordination state and solvation equilibrium of lithium ions, solvents, and additives in the final electrolyte system. Different coordination structure ratios will change the local electronic environment of the central carbon atom, resulting in different measured N values. Specifically, the N value can be controlled through the following process parameters: Lithium salt content in the electrolyte; Types of lithium salts and the ratios of different lithium salts, such as the ratio of lithium hexafluorophosphate (LiPF6) to lithium bis(fluorosulfonyl)imide (LiFSI). The content of small molecule solvents in the electrolyte, such as the content of carboxylic acid ester solvents in the electrolyte; In electrolyte preparation, the order of batch addition is crucial, such as the batch addition and temperature control of lithium salts. Lithium salt dissolution is typically exothermic; adding it all at once or improper temperature control can lead to localized temperature increases, affecting the coordination structure between lithium ions and solvent molecules. By adding lithium salts in batches and controlling the temperature during dissolution, the lithium salts can gradually dissolve and form a more stable solvated structure, thereby altering the electronic environment around the solvent molecules.

[0044] Furthermore, the temperature control conditions for different batches can be set differently as needed, such as adding lithium salt in different batches, using a relatively low dissolution temperature in some batches and appropriately increasing the temperature in subsequent batches, or other settings.

[0045] Different temperature combinations may alter the solvation structure formation pathway during lithium salt dissolution. Under different temperature control conditions, the NMR chemical shift value N of the central carbon atom may exhibit varying degrees of change, thereby achieving regulation of the NMR chemical shift value N of the central carbon atom in the electrolyte.

[0046] This application does not limit the detection method for the value of N; it can be detected using conventional methods in the art. For example, the following method is used to measure it: (1) Confirmation of electrolyte composition The collected electrolyte samples were injected into an Agilent Intuvo 9000 gas chromatograph-mass spectrometer using a microsyringe for testing. GC-MS spectra were obtained, and the solvents in the electrolyte were identified by spectral library search and labeled as component 1, component 2, ..., component n.

[0047] (2) NMR spectrum test of each component corresponding to pure substances The pure substances corresponding to components 1, 2, ..., n identified by GC testing are used as samples for NMR testing. The shift values ​​of the central carbon atoms of each component's corresponding pure substance are tested according to the following steps.

[0048] (2.1) Take 5 mg to 10 mg of the sample to be tested in the glove box and put it into the NMR tube. Add 0.6 mL of deuterated solvent (commonly CDCl3 or DMSO-d6) to dissolve it completely, and then cap the NMR tube. (2.2) Place the sample tube into a nuclear magnetic resonance spectrometer (BRUKER AVANCE 400, BRUKER AVANCE III HD500, Bruker Avance NEO 600, etc.) equipped with a broadband probe, lock the deuterium signal and optimize the shimming; (2.3) Set the observation kernel to 13C, use a proton decoupled pulse sequence, adjust the spectral width (usually 0~250 ppm, relaxation delay 2~5s), and perform hundreds to thousands of scans to improve the signal-to-noise ratio; (2.4) After the acquisition is completed, the free induction attenuation signal is subjected to Fourier transform to obtain the spectrum, and then corrected for phase and baseline. (2.5) Using the peak position of TMS (tetramethylsilane) as the NMR zero point for chemical shift calibration, the NMR shift values ​​of carbon atoms of each sample can be read. (2.6) In the NMR shift spectra of carbon atoms of each pure substance sample, the peak with the latest elution position is the shift value of the central carbon atom of the corresponding pure substance sample. Record the corresponding shift values ​​of each pure substance sample as M1, M2...M n (n is the number of solvent types in the electrolyte).

[0049] (3) Electrolyte NMR spectrum test (3.1) Perform NMR carbon spectroscopy on the electrolyte sample according to the steps in (2.1) to (2.5) to obtain the NMR shift values ​​of carbon atoms in the electrolyte; (3.2) By reading the nuclear magnetic shift spectrum of carbon atoms in the electrolyte, the shift values ​​of the central carbon atoms of each component solvent in the electrolyte, N1, N2...N, can be obtained. n , where |N i -M i | / M i ≤5% (i is a positive integer between 1 and n. That is, the deviation between the displacement value of the central carbon atom of a certain component solvent in the electrolyte and the displacement value of the central carbon atom of the corresponding pure substance sample of that component is within 5%).

[0050] Calculate the average displacement value using the following formula: N = (N1 + N2 + ... + N) n ) / n.

[0051] In some embodiments, the solvent includes at least one of carboxylic acid ester solvents and carbonate solvents.

[0052] In some embodiments, the carboxylic acid ester solvent includes at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP).

[0053] In some embodiments, the carbonate solvent includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), ethyl methyl carbonate (EMC), trimethylene carbonate (TMC), and butenyl carbonate (BC).

[0054] In some embodiments, the mass percentage of the carboxylic acid ester solvent is 0-59.5% based on the total mass of the electrolyte, such as a range formed by any two values ​​of 0, 10%, 20%, 30%, 40%, 50%, 59.5% or above.

[0055] In some embodiments, the solvent in the electrolyte has a mass percentage of 75% to 87%, such as 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, or any two of the above values ​​forming a range.

[0056] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), and lithium difluorooxalate borate (LiODFB).

[0057] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

[0058] In some embodiments, based on the total mass of the lithium salt, the mass percentage of lithium difluorosulfonylimide is 0-60% (e.g., a range formed by any two values ​​of 0, 10%, 20%, 30%, 40%, 50%, 60% or more), and the mass percentage of lithium hexafluorophosphate is 40%-100% (e.g., a range formed by any two values ​​of 40%, 50%, 60%, 70%, 80%, 90%, 100% or more).

[0059] In some embodiments, the lithium salt accounts for 10% to 20% of the mass of the electrolyte, such as a range formed by any two values ​​of 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or more.

[0060] In some embodiments, the electrolyte further comprises a first additive selected from at least one of methyl methane disulfonate (MMDS), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), propylene sulfonate lactone (PST), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate (TMSB), and hexamethylene diisocyanate (HDI). Adding the first additive to the electrolyte can optimize the structure of the positive and negative electrode interface films and improve ion transport efficiency.

[0061] In some embodiments, the mass percentage of the first additive in the electrolyte is 0.2% to 2.5%. Controlling the mass percentage of the first additive in the electrolyte within the above range (e.g., 0.2%, 0.4%, 0.6%, 0.8%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.5%, or any two of the above values) is beneficial in two ways: firstly, it optimizes the structure of the positive and negative electrode interface film and improves ion transport efficiency; secondly, it suppresses the increase in electrolyte viscosity and enhances ion transport in the electrolyte, thereby improving fast charging performance and cycle performance.

[0062] The electrolyte can be prepared using conventional methods. In some embodiments, the preparation method of the electrolyte includes the following steps: The solvent is cooled to 0-10°C, and lithium salt is added in batches to dissolve it. Then, the cyclic sulfate compound is added in batches to dissolve it, thus obtaining the electrolyte.

[0063] In some embodiments, during the process of adding lithium salt in batches for dissolution, the temperature of the system is controlled to not exceed 20°C, for example, by adjusting the stirring speed.

[0064] In some embodiments, during the batch addition and dissolution of the cyclic sulfate compound, the temperature of the system is controlled to not exceed 20°C, for example, by adjusting the stirring speed.

[0065] In some embodiments, after all raw materials have been completely dissolved during the preparation of the electrolyte, a settling process is performed. According to a second aspect of this application, a battery is provided that includes the electrolyte.

[0066] In some embodiments, the battery further includes a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material comprising a positive electrode active material, and the positive electrode active material comprising at least one of ternary materials and lithium iron phosphate.

[0067] In some embodiments, the chemical formula of the ternary material is Li. a Ni x Co y Mn 1-x-yO2, where 0.9 ≤ a ≤ 1.1; 0 < x < 1; 0 < y < 1; x + y < 1. For example, a is 0.9, 1, 1.1 or the range formed by any two of the above values; x is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or the range formed by any two of the above values; y is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.35 or the range formed by any two of the above values; x + y is 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or the range formed by any two of the above values.

[0068] The ternary material may either contain no doping elements or contain doping elements, and the present application places no limitation on the types of doping elements in the ternary material. In some embodiments, the doping elements in the ternary material include, but are not limited to, at least one of Zr, Mo, B, Al, W, Sr, Mg, Ca, Ta, Ti, Nb, Y, Ta, Sb, S, Na. The present application places no limitation on the content of the doping elements in the ternary material. In some embodiments, the mass content of the doping elements in the ternary material is selected to be 300 - 30000 ppm, such as 300 ppm, 500 ppm, 1000 ppm, 5000 ppm, 10000 ppm, 12000 ppm, 15000 ppm, 17000 ppm, 20000 ppm, 22000 ppm, 25000 ppm, 27000 ppm, 30000 ppm or the range formed by any two of the above values.

[0069] The ternary material may either contain no coating material or be coated with a coating material on some or all of its surfaces. In some embodiments, the coating material includes at least one of alumina, zirconia, titanium dioxide, zinc oxide, magnesium oxide, aluminum fluoride, lithium fluoride, polypyrrole, tungsten oxide, boron oxide to form a dense and stable physical barrier layer, reduce the side reactions between the ternary material and the electrolyte, and improve the battery cycle life. In some embodiments, the thickness of the coating layer formed by the coating material is 10 - 100 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm or the range formed by any two of the above values.

[0070] In some embodiments, the chemical formula of the lithium iron phosphate is Li bFePO4, wherein 0.9 ≤ b ≤ 1.1 (e.g., b is 0.9, 1, 1.1, or any range formed by two of the above values). Lithium iron phosphate may or may not contain doping elements; this application does not limit the types of doping elements in lithium iron phosphate. In some embodiments, the doping elements in lithium iron phosphate include, but are not limited to, at least one of V, Zr, Al, Sr, Mg, Ti, Nb, Mn, Ni, Co, Cr, Cu, Bi, Sb, F, N, and Cl. This application does not limit the content of doping elements in lithium iron phosphate. In some embodiments, the mass content of the doping element in the lithium iron phosphate is selected to be 300-30000 ppm, such as 300 ppm, 500 ppm, 1000 ppm, 5000 ppm, 10000 ppm, 12000 ppm, 15000 ppm, 17000 ppm, 20000 ppm, 22000 ppm, 25000 ppm, 27000 ppm, 30000 ppm or any two of the above values ​​forming a range.

[0071] The lithium iron phosphate may be free of coating material or coated with coating material on part or all of its surface. In some embodiments, the lithium iron phosphate is coated with a carbon layer to improve its electronic conductivity and ion transport efficiency, reduce electrode polarization, and suppress the aggregation and grain growth of lithium iron phosphate particles during charge and discharge, thereby improving the battery's rate performance and cycle stability. In some embodiments, based on the total mass of the lithium iron phosphate (including the mass of the carbon layer), the mass content of the carbon layer is selected to be 1% to 3%, such as 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or any two of the above ranges.

[0072] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode material is 95%-99%, such as the range formed by any two values ​​of 95%, 96%, 97%, 98%, 99% or above.

[0073] In some embodiments, the positive electrode material further includes a conductive agent. The conductive agent in the positive electrode material is used to provide conductivity, and any conductive agent can be used without particular limitation as long as it has appropriate electron conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent includes but is not limited to at least one of carbon nanotubes, carbon black, graphite, activated carbon, carbon fiber, mesoporous carbon, fullerenes, etc. Among them, carbon fiber such as carbon nanofiber, etc.; carbon black such as acetylene black, SP, Ketjen black, etc. In some embodiments, in the positive electrode material, the mass percentage content of the conductive agent is 0.3% - 3%, such as 0.3%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.5%, 2%, 2.5%, 3% or any range formed by any two of the above values.

[0074] In some embodiments, the positive electrode material further includes a binder. The binder in the positive electrode material is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector, and any binder can be used without particular limitation as long as it has appropriate binding property and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder includes but is not limited to fluorinated polyolefin binders, and fluorinated polyolefin binders include but are not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers or their modified (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives, etc. In some embodiments, in the positive electrode material, the mass percentage content of the binder is 0.5% - 3%, such as 0.5%, 0.7%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 2%, 2.5%, 3% or any range formed by any two of the above values.

[0075] In some embodiments, the positive electrode sheet includes a positive electrode current collector. The present application has no particular limitation on the positive electrode current collector as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, aluminum, nickel, titanium, stainless steel, fired carbon can be used; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.

[0076] The positive electrode material can be located on one side of the positive electrode current collector or on both sides of the positive electrode current collector.

[0077] In some embodiments, the battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes at least one of graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon-based materials. Among them, graphite includes at least one of natural graphite and artificial graphite. The silicon-based materials include but are not limited to silicon, SiO f (0 < f < 2, such as f = 1), silicon carbide, Li4Ti5O12 At least one of them.

[0078] In some embodiments, the mass percentage of the negative electrode active material in the negative electrode material is 95%-99%, such as the range formed by any two values ​​of 95%, 96%, 97%, 98%, 99% or above.

[0079] In some embodiments, the negative electrode material further includes a conductive agent. The conductive agent in the negative electrode material is used to provide conductivity, and any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. Exemplarily, the conductive agent in the negative electrode material includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; carbon black is, for example, SP (Super P), acetylene black, Ketjen black, etc. In some embodiments, the mass percentage of the conductive agent in the negative electrode material is 0.3%-3%, such as 0.3%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.5%, 2%, 2.5%, 3%, or any two of the above ranges.

[0080] In some embodiments, the negative electrode material further includes a binder. The binder in the negative electrode material is used to improve the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. Exemplarily, the binder in the negative electrode material includes, but is not limited to, at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, and aqueous acrylic resin. In some embodiments, the mass percentage of the binder in the negative electrode material is 0.5%-4%, such as 0.5%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.7%, 4%, or any two of the above values ​​within a range.

[0081] In some embodiments, the negative electrode sheet includes a negative current collector. This application does not impose any particular limitation on the negative current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can use, for example: copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with at least one of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys.

[0082] The negative electrode material can be located on one side of the negative electrode current collector or on both sides of the negative electrode current collector.

[0083] The battery may further include a separator located between the positive and negative electrode plates to separate them and prevent short circuits caused by contact. The separator can be any of the battery-compatible membrane materials available in the art.

[0084] In some embodiments, the diaphragm includes a substrate layer comprising at least one of polyethylene, polypropylene, polyamide, and aramid.

[0085] Optionally, the diaphragm may further include an adhesive layer and / or a ceramic layer. The adhesive layer may be made of at least one of polyvinylidene fluoride, polymethyl methacrylate, aramid, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene copolymer, or polyaniline; the ceramic layer may be made of at least one of boehmite, alumina, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, magnesium oxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, and magnesium nitride.

[0086] According to a third aspect of this application, an electrical device is also provided, comprising the battery. The battery serves as a power source for the electrical device.

[0087] The term "electrical device" refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other energy forms, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, and e-cigarettes; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0088] The present invention is further illustrated below with specific embodiments: Examples 1-21 and Comparative Examples 1-2 These embodiments and comparative examples each provide a battery, including the following steps: (1) Preparation of positive electrode (1.1) Preparation of positive electrode active material The types of positive electrode active materials are shown in Table 1.

[0089] If the positive electrode active material is a ternary material, its preparation method is as follows: Nickel sulfate, cobalt sulfate, and manganese sulfate are mixed according to the molar ratio in the chemical formula of the ternary material (see Table 1), dissolved in deionized water, dispersed, and a mixed solution is prepared; the obtained mixed solution, precipitant sodium hydroxide, and complexing agent ammonia water (concentration 0.8 mol / L) are mixed and subjected to a co-precipitation reaction at a reaction temperature of 120℃, a reaction time of 25 h, a pH value of 7, and the molar amount of NH3 in the ammonia water is 1 times the total molar amount of nickel sulfate, cobalt sulfate, and manganese sulfate. After drying, a precursor is obtained; the lithium source and the obtained precursor are mixed and sintered in an oxygen-containing atmosphere at a sintering temperature of 850℃ for 8 h, and then pulverized to obtain the ternary material.

[0090] If the positive electrode active material is lithium iron phosphate (LFP), its preparation method is as follows: Lithium carbonate, iron phosphate, titanium dioxide, zirconium oxide, and sucrose are mixed and dispersed, then wet-milled in water for 3 hours at a speed of 1100 r / min; followed by spray drying at a pressure of 0.5 MPa, an atomizer speed of 11000 r / min, an inlet temperature of 200℃, and an outlet temperature of 80℃; the spray-dried powder is then subjected to a first calcination under a nitrogen atmosphere at a first sintering temperature of 800℃, a heating rate of 6℃ / min, and a holding time of 10 hours; after pulverization, it is then subjected to a nitrogen atmosphere... The material was then subjected to a second calcination at 780℃, with a heating rate of 5℃ / min and a holding time of 6h. It was then pulverized to obtain lithium iron phosphate. All pulverization was performed using air jet milling at a pressure of 1MPa. The ratio of Li to Fe in the lithium carbonate and iron phosphate was 1.05:1 (molar ratio). The molar ratio of Ti to Zr in the titanium oxide and zirconium oxide was 2:1. Based on the total mass of the obtained lithium iron phosphate material, the total mass percentage of Ti and Zr was 6000ppm. Based on the total mass of the obtained lithium iron phosphate material, the mass percentage of carbon in the sucrose was 1%.

[0091] (1.2) Preparation of positive electrode sheet According to the mass ratio of positive electrode active material: SP:PVDF = 98:1:1, the positive electrode active material, conductive carbon black SP, and binder PVDF were mixed, and N-methylpyrrolidone (NMP) was added and dispersed evenly to obtain a positive electrode slurry. The obtained positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil, dried, cold-pressed, and cut to obtain an areal density of 200 g / m³. 2 The positive electrode plate.

[0092] (2) Preparation of negative electrode According to the mass ratio of graphite:SP:SBR = 96.5:2:1.5, the negative electrode active material graphite, conductive carbon black SP, and binder SBR were mixed, deionized water was added, and the mixture was dispersed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on both sides of the negative electrode current collector copper foil, dried, cold-pressed, and cut to obtain a surface density of 140 g / m³. 2 The negative electrode plate.

[0093] (3) Preparation of electrolyte Operate in a glove box (moisture content less than 10 ppm), as follows: Ethylene carbonate (EC) was heated to 45°C to melt, then dimethyl carbonate (DMC) and carboxylic acid esters were added, dispersed, and cooled to 10°C. The lithium salt was added in batches (each batch had the same amount of lithium salt added), and the temperature of the electrolyte system was monitored in real time. The highest temperature of the electrolyte system after each batch was added was controlled as shown in Table 1 (as shown in Table 1, "the highest temperature that the electrolyte system can reach after each batch of lithium salt was added". Taking Example 1 as an example, the five temperature values ​​listed correspond to the addition of lithium salt in five batches with equal mass, and the highest temperature of the electrolyte system during the addition of each batch was controlled as 19°C, 18°C, 18°C, 17°C and 16°C respectively). After all the lithium salts were added, cyclic sulfate compounds were added. The electrolyte system was then allowed to stand at 20°C for a period of time, as shown in Table 1, to obtain the electrolyte used for battery preparation. Based on the total mass of the electrolyte, the contents of carboxylic acid esters, lithium salts, and cyclic sulfate compounds are shown in Table 1. The remainder is the total content of EC and DMC, thus reaching a total of 100%. The mass ratio of EC to DMC is shown in Table 1. The carboxylic acid ester is ethyl acetate. The lithium salt is a mixture of LiFSI and LiPF6. The proportion of LiFSI based on the total mass of the lithium salt is shown in Table 1. Table 1 lists the types of cyclic sulfate compounds, with compounds 1-6 listed below: (4) Preparation of the diaphragm The membrane material is a PE base membrane with alumina ceramic layers on both sides. The membrane thickness is 9.5 μm and the ceramic layer thickness is 1.5 μm.

[0094] (5) Assembly and formation The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the battery is obtained.

[0095] If the positive electrode active material is a ternary material, then the formation process is as follows: After standing at 25℃ for 24 hours, place the glass in a glass clamp with a clamping pressure of 0.5MPa; then proceed with steps 1) to 5) at 45℃. 1) Let stand at 45℃ for 10 minutes; 2) Charge at a rate of 0.02C, with a cutoff voltage of 3.4V; 3) Let it stand for 10 minutes; 4) Charge at a rate of 0.05C, with a cutoff voltage of 3.75V; 5) End.

[0096] If the positive electrode active material is lithium iron phosphate, the formation process is as follows: after being placed at 45°C for 24 hours, it is placed in a glass fixture with a fixture pressure of 0.5MPa; then the following treatment is performed at 45°C: stand for 10 minutes, charge at 0.05C for 120 minutes, stand for 10 minutes, charge at 0.33C for 120 minutes to complete the formation.

[0097] Table 1 Continued from Table 1 Using the methods described above, the σ1, σ2, σ, and N values ​​of the electrolytes in each embodiment and comparative example were tested. Simultaneously, the performance of the batteries in each embodiment and comparative example was tested as follows: (1) High-temperature cycling performance test The test subject was placed in a 25℃ incubator for 4 hours, and the following operations were performed on the test subject: Charge the battery at 0.33C to the upper limit voltage, then charge it at a constant voltage until the cutoff current is 0.05C; let it stand for 30 minutes, then discharge it at 0.33C to the lower limit voltage. Repeat this operation 3 times. Use the discharge capacity of the third cycle as the battery's rated capacity Q0. Then place the battery in a 45℃ incubator for 4 hours. At 45℃, perform a cycle test according to the following procedure: 1) Charge at a constant current rate of 1C to the upper limit voltage, and then charge at a constant voltage until the current drops to 0.05C; 2) Let it stand for 30 minutes; 3) Discharge at a 1C rate to the lower limit voltage; 4) Let it stand for 30 minutes. Perform cycle tests according to steps 1)-4) until the capacity of the lithium-ion battery is less than 80% of the fixed capacity Q0, and record the number of cycles.

[0098] Different positive electrode active material systems require corresponding adjustments to the upper and lower limit voltages: LFP - upper limit voltage 3.65V, lower limit voltage 2.5V; ternary - upper limit voltage 4.25V, lower limit voltage 2.5V.

[0099] (2) Low-temperature fast charging performance test Using copper wire as a reference electrode, after forming and stabilizing (steps as above), the battery was charged to 0% SOC. Then, lithium plating was performed on the copper wire in the three-electrode system at a rate of 0.01C on the positive electrode side for 10 hours. After lithium plating, the following fast charging test was performed. The prepared lithium-ion battery was placed at -10℃ for 4 hours until thermal equilibrium was reached. The battery is charged at a constant current of 0.1C to the upper limit voltage, then charged at a constant voltage until the current is less than or equal to 0.05C, and then discharged at 0.1C to the lower limit voltage. The above steps are repeated 3 times, and the capacity discharged in the third cycle is taken as the battery discharge capacity. Let stand for 10 minutes, discharge at 0.1C to 2.5V, let stand for 10 minutes, and charge at 0.1C to 10% SOC; Charge the battery at 1C until the upper limit voltage or auxiliary voltage 0mV, and record the charging time t0 for this stage. Then, the battery is charged at a constant current in increments of 0.8C, 0.6C, 0.4C, and 0.1C (each increment being 0.2C). The cutoff condition for each charge is that the battery is charged to the upper limit voltage or the auxiliary voltage is 0mV. The total charging time t1 is recorded, and the difference between t1 and t0 (t1-t0) is taken as the fast charging time of the battery.

[0100] Different positive electrode active material systems require corresponding adjustments to the upper and lower limit voltages: LFP - upper limit voltage 3.65V, lower limit voltage 2.5V; ternary - upper limit voltage 4.25V, lower limit voltage 2.5V.

[0101] The test results are shown in Table 2.

[0102] Table 2 The batteries prepared in the various embodiments of this application have a charging time of less than 200 minutes and a cycle count of more than 800 cycles, which shows that the batteries containing this application have both excellent low-temperature fast charging performance and high-temperature cycling performance.

[0103] Comparing Examples 1-5 with Examples 6-10, and Examples 11-12 with Examples 13-19, it can be seen that when the values ​​of σ, N, and S meet the preferred range described in this application, it is more conducive to balancing the low-temperature fast charging performance and high-temperature cycling performance of the battery.

[0104] Comparing Examples 1-5 with Examples 11-12, and Examples 6-10 with Examples 13-19, it can be seen that when the battery satisfies 1.8 ≤ (σ × N) 0.5 When ) / (σ+10S)≤6.5, it is more conducive to balancing low-temperature fast charging performance and high-temperature cycling performance.

[0105] As shown in Comparative Examples 1 and 2, even if the values ​​of σ, N, and S are all within a suitable range, when (σ × N) 0.5 When the value of σ / (σ+10S) exceeds the range of 0.82~12.5, the low-temperature fast charging performance or high-temperature cycling performance is poor, and it is impossible to achieve a balance between low-temperature fast charging performance and high-temperature cycling performance.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this article without departing from the essence and scope of the technical solutions of this article.

Claims

1. An electrolyte, characterized in that, Including lithium salts, cyclic sulfate compounds, and solvents; The cyclic sulfate compound is at least one of the compounds shown in Formula I. ， In Formula I, R1, R2, R3, and R4 each independently include a group as shown in Formula II, a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. In Formula II, R5 and R6 each independently include the group shown in Formula III, a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. In Formula III, R7 and R8 each independently include a hydrogen atom, an alkyl group of 1 to 6 carbon atoms, a halogen atom, a haloalkyl group of 1 to 3 carbon atoms, an alkoxy group of 1 to 3 carbon atoms, a haloalkoxy group of 1 to 3 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, an aromatic group, an ester group, a cyano group, or a sulfonic acid group. The cyclic sulfate ester compound has a mass percentage of S% in the electrolyte, the central carbon atom nuclear magnetic shift value of the electrolyte is N ppm, and the ionic conductivity of the electrolyte at 40℃ and -10℃ is σ1mS / cm and σ2mS / cm, respectively, where σ = (σ1 × σ2). 0.5 , The electrolyte satisfies: 0.82 ≤ (σ × N) 0.5 ) / (σ+10S)≤12.

5.

2. The electrolyte as described in claim 1, characterized in that, 1.8≤(σ×N 0.5 ) / (σ+10S)≤6.5。 3. The electrolyte as described in claim 1, characterized in that, The S% is 0.3% to 3%.

4. The electrolyte as described in claim 3, characterized in that, The S% is 1% to 2.5%.

5. The electrolyte as described in claim 1, characterized in that, In Formula I, the number of sulfate groups is an integer from 2 to 4.

6. The electrolyte as described in claim 1, characterized in that, At least one of R1 to R4 is a hydrogen atom.

7. The electrolyte as described in claim 1, characterized in that, R1 and R3 are the same.

8. The electrolyte as described in claim 7, characterized in that, R1 and R3 are selected from the groups shown in Formula II, hydrogen atoms, alkyl groups of 1 to 6 carbon atoms, halogen atoms, haloalkyl groups of 1 to 3 carbon atoms, alkoxy groups of 1 to 3 carbon atoms, haloalkoxy groups of 1 to 3 carbon atoms, alkenyl groups of 2 to 6 carbon atoms, alkynyl groups of 2 to 6 carbon atoms, aromatic groups, ester groups, cyano groups, or sulfonic acid groups.

9. The electrolyte as described in claim 1, characterized in that, The value of σ is 2 to 15.

5.

10. The electrolyte as described in claim 9, characterized in that, The value of σ is 4 to 9.

11. The electrolyte as described in claim 1, characterized in that, The σ1mS / cm is 8~25mS / cm.

12. The electrolyte as described in claim 1, characterized in that, The σ²mS / cm is 0.5~10mS / cm.

13. The electrolyte as described in claim 1, characterized in that, The N ppm is 140~250 ppm.

14. The electrolyte as described in claim 11, characterized in that, The N ppm is 160~200ppm.

15. The electrolyte as described in claim 1, characterized in that, The solvent includes at least one of carboxylic acid ester solvents and carbonate solvents.

16. The electrolyte as described in claim 15, characterized in that, The carboxylic acid ester solvent includes at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, and propyl propionate. And / or, the carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, vinylene carbonate, propylene carbonate, methyl ethyl carbonate, trimethylene carbonate, and butene carbonate.

17. The electrolyte as described in claim 1, characterized in that, The solvent has a mass percentage content of 75% to 87% in the electrolyte.

18. The electrolyte as described in claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium difluorooxalate borate.

19. The electrolyte as described in claim 18, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate and lithium difluorosulfonylimide.

20. The electrolyte as described in claim 19, characterized in that, Based on the total mass of the lithium salt, the mass percentage of lithium difluorosulfonylimide is 0-60%, and the mass percentage of lithium hexafluorophosphate is 40%-100%.

21. A battery, characterized in that, Includes the electrolyte as described in any one of claims 1 to 20.

22. The battery as claimed in claim 21, characterized in that, The battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, the positive electrode material includes a positive electrode active material, and the positive electrode active material includes at least one of ternary materials and lithium iron phosphate.

23. The battery as claimed in claim 21, characterized in that, The battery further includes a negative electrode sheet, which includes a negative electrode material. The negative electrode material includes a negative electrode active material, which includes at least one of graphite, mesophase micro carbon spheres, hard carbon, soft carbon, and silicon-based materials.

24. An electrical appliance, characterized in that, It includes the battery as described in any one of claims 21 to 23.

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