Electrolyte, secondary battery, and electric device

Abstract

This application discloses an electrolyte, a secondary battery, and an electrical device. The secondary battery includes an electrolyte; the electrolyte includes additives, including isocyanate compounds and phosphate ester compounds; the isocyanate compounds have the structure shown in Formula 1: OCN—R1—NCO, Formula 1; in Formula 1: R1 is selected from one of substituted or unsubstituted C1-C10 saturated alkyl groups and substituted or unsubstituted C2-C10 unsaturated alkyl groups; the phosphate ester compounds have the structure shown in Formula 2: in Formula 2: R2 to R4 are each independently selected from one or more of substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, phenyl, silane, carbonyl, carboxyl, ester, nitrile, and isocyanate groups. This application is beneficial for improving the cycle performance of batteries.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to an electrolyte, a secondary battery, and an electrical device. Background Technology

[0002] Batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles and electric cars, as well as in military equipment and aerospace and other fields.

[0003] The development of rechargeable batteries has not only driven technological progress but also provided support for development in various fields. In particular, improving the lifespan of rechargeable batteries is not only crucial for enhancing the performance of the batteries themselves but also has a profound impact on the development of related industries, technological innovation, and sustainable development. Summary of the Invention

[0004] The first aspect of this application provides a secondary battery, including an electrolyte;

[0005] The electrolyte includes additives, which include isocyanate compounds and phosphate ester compounds;

[0006] Isocyanate compounds have the structure shown in Formula 1:

[0007] OCN—R1—NCO

[0008] Formula 1;

[0009] In Formula 1: R1 is selected from one of substituted or unsubstituted C1-C10 saturated alkyl groups and substituted or unsubstituted C2-C10 unsaturated alkyl groups; the phosphate ester compound has the structure shown in Formula 2:

[0010]

[0011] In Formula 2: R2 to R4 are each independently selected from one or more of the following: substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, phenyl groups, silyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and isocyanate groups.

[0012] This application utilizes the synergistic effect of the aforementioned isocyanate compounds and phosphate compounds to improve the corrosion of the negative electrode active material or its components (such as silicon-based materials) by the acidic electrolyte, thereby improving the ion transport efficiency of the battery, reducing impedance, and enhancing the battery's cycle performance.

[0013] In some embodiments of this application, in Formula 1, R1 is selected from one of unsubstituted C3-C8 saturated alkyl groups. The selection of R1 from unsubstituted C3-C8 saturated alkyl groups, with an appropriate carbon chain length, helps maintain the high reactivity of isocyanate compounds, improving acid removal and film formation effects. Using unsubstituted saturated alkyl groups facilitates the formation of an interface film with low impedance, improving lithium-ion transport and further enhancing the battery's cycle performance.

[0014] In some embodiments of this application, in Formula 2, R2-R4 are each independently selected from one or more unsubstituted C1-C4 saturated alkyl, silane, and phenyl groups. The independent selection of R2-R4 from these groups is beneficial for further improving the cycle performance of the battery.

[0015] In some embodiments of this application, the silane shown includes silane. Silanes have less steric hindrance, better reactivity, and better film formation and acid removal effects, which is beneficial for further improving the cycle performance of the battery.

[0016] In some embodiments of this application, in Formula 2, at least two of R2-R4 are selected from silane groups.

[0017] Phosphate esters containing two or more silane groups have high reactivity, which is beneficial for forming an interfacial film with low impedance and high lithium-ion transport. In addition, they can provide more silicon-oxygen bonds to participate in the deacidification reaction, reduce the side reactions between the electrolyte and the negative electrode active material or the negative electrode active material (such as silicon-based materials), and thus further improve the cycle performance of the battery.

[0018] In some embodiments of this application, the additive satisfies at least one of the following (a) and (b):

[0019] (a) Isocyanate compounds include one or more of Formula 1-1 and Formula 1-2:

[0020] Equation 1-1 Formula 1-2

[0021] (b) Phosphate esters include one or more of Formula 2-1, Formula 2-2, and Formula 2-3:

[0022] Equation 2-1 Equation 2-2

[0023] Equation 2-3

[0024] This application may use any one or a combination of two of the isocyanate compounds shown in Formula 1-1 and Formula 1-2 as additives for the electrolyte, which have high reactivity and exhibit good deacidification and film-forming effects, thus helping to further improve the cycle performance of the battery.

[0025] This application can use any one or more of the phosphate ester compounds shown in Formulas 2-1, 2-2, and 2-3 as additives for the electrolyte, which exhibits good film-forming effect, facilitates acid removal, and further improves the cycle performance of the battery.

[0026] In some embodiments of this application, the content of isocyanate compounds is 0.005 wt% to 1 wt% based on the mass of the electrolyte.

[0027] When the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, it is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and enhance the cycle performance of the battery.

[0028] In some embodiments of this application, the content of isocyanate compounds is 0.1 wt% to 0.5 wt% based on the mass of the electrolyte.

[0029] When the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, it is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and further improve the cycle performance of the battery.

[0030] In some embodiments of this application, the content of phosphate ester compounds is 0.005wt%-3wt% based on the mass of the electrolyte.

[0031] When the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, it is beneficial to form an interface film with low impedance, improve ion transport efficiency, and enhance the cycle performance of the battery.

[0032] In some embodiments of this application, the content of phosphate ester compounds is 0.1 wt% to 1.5 wt% based on the mass of the electrolyte.

[0033] When the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, it is beneficial to form an interface film with low impedance, which can better improve ion transport efficiency and further enhance the cycle performance of the battery.

[0034] In some embodiments of this application, the mass ratio of phosphate esters to isocyanates is 1.5-5.

[0035] By controlling the mass ratio of phosphate esters and isocyanates to meet the above conditions, it is beneficial to fully utilize the synergistic effect between phosphate esters and isocyanates, thereby further improving the cycle performance of the battery.

[0036] In some embodiments of this application, the mass ratio of phosphate ester compound to isocyanate compound is 2-3.

[0037] By controlling the mass ratio of phosphate esters and isocyanates to meet the above conditions, it is beneficial to fully utilize the synergistic effect between phosphate esters and isocyanates, thereby further improving the cycle performance of the battery.

[0038] In some embodiments of this application, the additive also includes fluoroethylene carbonate.

[0039] Using FEC (fluoroethylene carbonate) as an electrolyte additive can serve as a repair agent for the SEI interface during battery charging and discharging; it can help repair the interface film of the silicon-based negative electrode, improve the stability of the negative electrode, and thus improve the cycle performance of the battery.

[0040] In some embodiments of this application, the content of fluoroethylene carbonate is 0.5 wt% to 20 wt% based on the mass of the electrolyte.

[0041] When the mass content of fluoroethylene carbonate in the electrolyte meets the above conditions, it is beneficial to repair the SEI interface film, improve the stability of the negative electrode, and improve the cycle performance of the battery.

[0042] In some embodiments of this application, the secondary battery further includes a negative electrode sheet, which includes a negative electrode active material, and the negative electrode active material includes a silicon-based material and graphite; the silicon-based material includes one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

[0043] One or more of elemental silicon (such as nano-silicon, micron-silicon, etc.), silicon-oxygen materials, and silicon-carbon materials can be used as silicon-based materials. These silicon-based materials can be mixed with graphite, such as through physical mixing, and then used as negative electrode active materials.

[0044] In some embodiments of this application, the silicon-carbon material includes porous carbon and nano-silicon located inside the porous carbon; and / or, in the silicon-carbon material, the mass ratio of silicon to carbon is 6:4 to 4:6.

[0045] Silicon-carbon materials can be selected where silicon is deposited in porous carbon, thus inhibiting silicon expansion to some extent. In silicon-carbon materials, carbon acts as an insulator to isolate the electrolyte, reducing the contact between acid byproducts and silicon; moreover, silicon-carbon materials have less expansion and a more stable structure, which is beneficial for improving the cycle performance of the battery.

[0046] In silicon-carbon materials, the mass ratio of silicon to carbon is 6:4 to 4:6, which helps to mitigate the side reactions between silicon and acid, reduce the volume expansion of the negative electrode, and improve the cycle performance of the battery.

[0047] In some embodiments of this application, the content of silicon-based material is 1wt%-90wt% and the content of graphite is 10wt%-99wt%, depending on the mass of the negative electrode active material.

[0048] If the content of silicon-based material meets the above conditions, a mixed system of silicon-based material and graphite is adopted. Graphite will dilute part of the silicon-based material, which will slow down the corrosion of the acidic environment of the electrolyte and improve the cycle performance of the battery compared with the silicon-based material itself.

[0049] In some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0050] In some embodiments of this application, the electrolyte salt includes one or both of lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0051] In some embodiments of this application, the content of lithium bis(fluorosulfonyl)imide is 0.05 M / L to 0.4 M / L, based on the mass of the electrolyte.

[0052] A second aspect of this application provides an electrolyte comprising additives, including isocyanate compounds and phosphate ester compounds; the isocyanate compounds having a structure as shown in Formula 1:

[0053] OCN—R1—NCO

[0054] Formula 1;

[0055] In Formula 1: R1 is selected from one of substituted or unsubstituted C1-C10 saturated alkyl groups and substituted or unsubstituted C2-C10 unsaturated alkyl groups; the phosphate ester compound has the structure shown in Formula 2:

[0056]

[0057] In Formula 2: R2 to R4 are each independently selected from one or more of the following: substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, phenyl groups, silyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and isocyanate groups.

[0058] This application uses the aforementioned isocyanate compounds and phosphate compounds in secondary batteries. The two work together to improve the corrosion of the negative electrode active material or its components (such as silicon-based materials) by the acidic electrolyte, improve the ion transport efficiency of the battery, reduce impedance, and improve the cycle performance of the battery.

[0059] In some embodiments of this application, in Formula 1, R1 is selected from one of unsubstituted C3-C8 saturated alkyl groups. The selection of R1 from unsubstituted C3-C8 saturated alkyl groups, with an appropriate carbon chain length, helps maintain the high reactivity of isocyanate compounds, improving acid removal and film formation effects. Using unsubstituted saturated alkyl groups facilitates the formation of an interface film with low impedance, improving lithium-ion transport and further enhancing the battery's cycle performance.

[0060] In some embodiments of this application, in Formula 2, R2-R4 are each independently selected from one or more unsubstituted C1-C4 saturated alkyl, silane, and phenyl groups. The independent selection of R2-R4 from these groups is beneficial for further improving the cycle performance of the battery.

[0061] In some embodiments of this application, the silane shown includes silane. Silanes have less steric hindrance, better reactivity, and better film formation and acid removal effects, which is beneficial for further improving the cycle performance of the battery.

[0062] In some embodiments of this application, in Formula 2, at least two of R2-R4 are selected from silane groups.

[0063] Phosphate esters containing two or more silane groups have high reactivity, which is beneficial for forming an interfacial film with low impedance and high lithium-ion transport. In addition, they can provide more silicon-oxygen bonds to participate in the deacidification reaction, reduce the side reactions between the electrolyte and the negative electrode active material or the negative electrode active material (such as silicon-based materials), and thus further improve the cycle performance of the battery.

[0064] In some embodiments of this application, the additive satisfies at least one of the following (a) and (b):

[0065] (a) Isocyanate compounds include one or more of Formula 1-1 and Formula 1-2:

[0066] Equation 1-1 Formula 1-2

[0067] (b) Phosphate esters include one or more of Formula 2-1, Formula 2-2, and Formula 2-3:

[0068] Equation 2-1 Equation 2-2

[0069] Equation 2-3

[0070] This application may use any one or a combination of two of the isocyanate compounds shown in Formula 1-1 and Formula 1-2 as additives for the electrolyte, which have high reactivity and exhibit good deacidification and film-forming effects, thus helping to further improve the cycle performance of the battery.

[0071] This application can use any one or more of the phosphate ester compounds shown in Formulas 2-1, 2-2, and 2-3 as additives for the electrolyte, which exhibits good film-forming effect, facilitates acid removal, and further improves the cycle performance of the battery.

[0072] In some embodiments of this application, the content of isocyanate compounds is 0.005 wt% to 1 wt% based on the mass of the electrolyte.

[0073] When the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, it is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and enhance the cycle performance of the battery.

[0074] In some embodiments of this application, the content of isocyanate compounds is 0.1 wt% to 0.5 wt% based on the mass of the electrolyte.

[0075] When the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, it is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and further improve the cycle performance of the battery.

[0076] In some embodiments of this application, the content of phosphate ester compounds is 0.005wt%-3wt% based on the mass of the electrolyte.

[0077] When the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, it is beneficial to form an interface film with low impedance, improve ion transport efficiency, and enhance the cycle performance of the battery.

[0078] In some embodiments of this application, the content of phosphate ester compounds is 0.1 wt% to 1.5 wt% based on the mass of the electrolyte.

[0079] When the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, it is beneficial to form an interface film with low impedance, which can better improve ion transport efficiency and further enhance the cycle performance of the battery.

[0080] In some embodiments of this application, the mass ratio of phosphate esters to isocyanates is 1.5-5.

[0081] By controlling the mass ratio of phosphate esters and isocyanates to meet the above conditions, it is beneficial to fully utilize the synergistic effect between phosphate esters and isocyanates, thereby further improving the cycle performance of the battery.

[0082] In some embodiments of this application, the mass ratio of phosphate ester compound to isocyanate compound is 2-3.

[0083] By controlling the mass ratio of phosphate esters and isocyanates to meet the above conditions, it is beneficial to fully utilize the synergistic effect between phosphate esters and isocyanates, thereby further improving the cycle performance of the battery.

[0084] In some embodiments of this application, the additive also includes fluoroethylene carbonate.

[0085] Using FEC (fluoroethylene carbonate) as an electrolyte additive can serve as a repair agent for the SEI interface during battery charging and discharging; it can help repair the interface film of the silicon-based negative electrode, improve the stability of the negative electrode, and thus improve the cycle performance of the battery.

[0086] In some embodiments of this application, the content of fluoroethylene carbonate is 0.5 wt% to 20 wt% based on the mass of the electrolyte.

[0087] When the mass content of fluoroethylene carbonate in the electrolyte meets the above conditions, it is beneficial to repair the SEI interface film, improve the stability of the negative electrode, and improve the cycle performance of the battery.

[0088] The third aspect of this application provides an electrical device, which includes the secondary battery proposed in the first aspect of this application.

[0089] The electrical equipment provided in this application includes the secondary battery described above, and has the advantages of the secondary battery described above, which will not be repeated here.

[0090] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0091] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0092] Figure 1This is a schematic diagram of a battery according to one embodiment of this application.

[0093] Figure 2 yes Figure 1 An exploded view of a battery according to one embodiment of this application is shown.

[0094] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0095] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0096] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0097] Figure 6 This is a schematic diagram of an electrical device in which a battery is used as a power source according to one embodiment of this application.

[0098] Explanation of reference numerals in the attached figures:

[0099] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0100] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0101] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0102] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0103] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0104] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0105] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing. Taking silicon-based rechargeable batteries as an example, battery life presents a significant bottleneck. For silicon-based rechargeable batteries, their cycle life and storage performance are significantly worse compared to graphite-based rechargeable batteries, making improving lifespan a crucial indicator for this type of battery.

[0106] Taking lithium-ion batteries as an example, the electrolyte is a weakly acidic solution. This is because lithium salts in the electrolyte (such as lithium hexafluorophosphate, LiPF6) undergo hydrolysis when they encounter trace amounts of water, producing hydrofluoric acid (HF), a strong acid. Furthermore, some additives may also produce acidic substances upon thermal decomposition. For example, fluorocarbonate additives (such as FEC (fluoroethylene carbonate) and DFEC (difluoroethylene carbonate)) decompose to generate hydrofluoric acid. Some anode materials, such as silicon-based materials, can react directly with HF to produce SiF4 and hydrogen gas, compared to graphite materials. Even nano-silicon can react directly with water. Therefore, protonated hydrogen is more sensitive to silicon-based materials, and acidic substances in the electrolyte have a significant corrosive effect on them. Moreover, the lithium storage process in silicon-based materials involves alloying / dealloying. When lithium ions are intercalated into silicon, a series of lithium-silicon alloy phases are formed. This alloying process is accompanied by complex phase transitions, which cause the volume of silicon to expand significantly during lithium intercalation. Therefore, silicon-based materials have a large volume effect, which causes the SEI (Solid Electrolyte Interphase) to rupture during charging and discharging. The electrolyte undergoes interface repair, which is accompanied by the consumption of active lithium, thereby reducing the reversible lithium content and exposing new silicon surfaces. This, in turn, intensifies the reaction with acidic substances, thus deteriorating battery life.

[0107] Currently, commonly used deacidifying additives, such as those containing silicon oxide and silicon nitrogen, achieve deacidification through chemical consumption with HF. However, when the reaction efficiency of these substances is low, the deacidification effect is not significant. Isocyanates are effective proton scavengers that can react with water, but these substances can degrade the kinetics of the battery cell.

[0108] Therefore, the first aspect of the embodiments of this application proposes a secondary battery, including an electrolyte;

[0109] The electrolyte includes additives, which include isocyanate compounds and phosphate ester compounds;

[0110] Isocyanate compounds have the structure shown in Formula 1:

[0111] OCN—R1—NCO

[0112] Formula 1;

[0113] In Formula 1: R1 is selected from one of substituted or unsubstituted C1-C10 saturated alkyl groups and substituted or unsubstituted C2-C10 unsaturated alkyl groups; the phosphate ester compound has the structure shown in Formula 2:

[0114]

[0115] In Formula 2: R2 to R4 are each independently selected from one or more of the following: substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, phenyl groups, silyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and isocyanate groups.

[0116] In this embodiment of the application, the negative electrode active material comprises a mixed system of silicon-based material and graphite, that is, the silicon-based material and graphite are mixed and then used as the negative electrode active material.

[0117] In this application, the types and contents of isocyanate and phosphate compounds in the electrolyte are well-known in the art and can be detected using well-known equipment and methods. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents". In this application, freshly prepared electrolyte can be used as a sample, or a fully discharged battery (discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0118] In Formula 1, the C2-C10 unsaturated alkyl group can be either a C2-C10 alkenyl group or a C2-C10 alkynyl group.

[0119] In Formula 2, the C3-C10 unsaturated alkyl group can be either a C3-C10 alkenyl group or a C3-C10 alkynyl group.

[0120] In this embodiment, isocyanate compounds as shown in Formula 1 are used as proton scavengers. These compounds can react directly with water to block the formation of acidic substances, thereby reducing side reactions between acidic substances and silicon-based materials, mitigating corrosion of silicon-based materials, and improving battery cycle performance. However, isocyanate compounds can also participate in interfacial film formation. Due to their high reactivity, isocyanate compounds may react chemically with solvents in the electrolyte (such as carbonate solvents) to generate insoluble substances (such as polycarbonate). These substances deposit on the electrode surface, forming a passivation layer that hinders lithium-ion and electron transport, thus increasing interfacial resistance. The solid electrolyte interphase (SEI) film is a passivation layer formed on the electrode surface, helping to prevent direct reactions between the electrolyte and electrode materials. Isocyanate compounds may alter the structure and thickness of the SEI film, making it denser or thicker. This change restricts lithium-ion diffusion on the electrode surface, increases battery impedance, and deteriorates kinetic performance. In the embodiments of this application, phosphate ester compounds as shown in Formula 2 above are used as interface optimization additives. The phosphorus-containing SEI generated by these compounds is beneficial for ion transfer at the interface. For example, phosphate interface products are generated. These phosphate interface products facilitate the formation of a stable SEI film, improve lithium-ion diffusion channels, reduce interfacial impedance, prevent electrolyte decomposition, promote uniform lithium-ion deposition, enhance the stability of electrode materials, and optimize electrochemical reaction kinetics, thereby improving the ion transport efficiency at the battery interface. Furthermore, the generated PLi3 may possess superior interfacial kinetics, increasing ionic conductivity and improving the battery's low-temperature cycling performance.

[0121] In addition, isocyanate compounds only contain N and C in the interfacial components, while phosphate compounds introduce P elements, and silicon-based phosphate compounds can further introduce Si elements. The interfacial components formed by multiple elements are similar to the principle of entropy increase, which is more conducive to improving the stability of the interface and the battery cycle performance.

[0122] In summary, in the embodiments of this application, the synergistic effect of the above-mentioned isocyanate compounds and phosphate compounds is beneficial to improve the corrosion of negative electrode materials (such as silicon-based materials) by acidic electrolytes, improve the ion transport efficiency of the battery, reduce impedance, and improve the cycle performance of the battery.

[0123] In some embodiments of this application, in Formula 1, R1 is selected from one of unsubstituted C3-C8 saturated alkyl groups.

[0124] In the isocyanate compounds shown in Formula 1, R1 can be selected from any one of substituted C1-C10 saturated alkyl groups, unsubstituted C1-C10 saturated alkyl groups, substituted C1-C10 unsaturated alkyl groups, and unsubstituted C1-C10 unsaturated alkyl groups. For substituted C1-C10 unsaturated alkyl groups, the substituent can be a halogen, such as F. Among the above-mentioned alkyl groups, the length of the carbon chain, the degree of alkyl saturation, and the substitution status will affect the reactivity of the isocyanate compounds in the electrolyte. For example, substituted alkyl groups (such as F-substituted alkyl groups) and unsaturated alkyl groups will cause a large number of isocyanate compounds to participate in the film-forming reaction, which will lead to a decrease in the acid removal and film-forming effects.

[0125] In this embodiment, R1 can be selected from unsubstituted C3-C8 saturated alkyl groups. An appropriate carbon chain length is beneficial for maintaining the high reactivity of isocyanate compounds and improving the deacidification and film formation effects. Using unsubstituted saturated alkyl groups is beneficial for forming an interface film with low impedance, improving the lithium-ion transport effect, and further improving the cycle performance of the battery.

[0126] In some embodiments of this application, in Formula 2, R2-R4 are each independently selected from one or more of unsubstituted C1-C4 saturated alkyl, silyl, and phenyl groups.

[0127] In this embodiment, R2-R4 can each be independently selected from unsubstituted C1-C4 saturated alkyl groups. Unsubstituted saturated alkyl groups with shorter carbon chain lengths have less steric hindrance and higher reactivity, which is beneficial to improving the efficiency of phosphate ester compounds participating in the film-forming reaction, forming an SEI film with lower impedance, improving lithium-ion transport efficiency, and improving the cycle performance of the battery.

[0128] R2-R4 can each be independently selected from silane groups. Silane groups have high reactivity, which is beneficial to improving the efficiency of film formation reaction. In addition, silane-containing phosphate ester compounds contain silicon-oxygen bonds, which can participate in the acid removal reaction, further improve the acidic environment of the electrolyte, reduce the acid corrosion of silicon-based materials, and further improve the cycle performance of the battery.

[0129] R2-R4 can each be independently selected from phenyl groups. Phosphate compounds containing phenyl groups have high reactivity, which is beneficial to improving the efficiency of film formation reaction and further improving the cycle performance of the battery.

[0130] In some embodiments of this application, silane includes methylsilane.

[0131] In this embodiment, the silane includes silane, i.e., SiH3-. Siane has less steric hindrance and better reactivity, which is beneficial to improving the efficiency of film formation reaction. In addition, silane-containing phosphate ester compounds contain silicon-oxygen bonds, which can participate in the acid removal reaction, further improve the acidic environment of the electrolyte, reduce the acid corrosion of silicon-based materials, and further improve the cycle performance of the battery.

[0132] In some embodiments of this application, in Formula 2, at least two of R2-R4 are selected from silane groups.

[0133] In this embodiment, at least two of R2-R4 are selected from silane groups. It can be any two of R2, R3, and R4 selected from silane groups, or all three of R2, R3, and R4 can be selected from silane groups. Phosphate ester compounds containing two or more silane groups have high reactivity, which is beneficial for forming a low-resistance, high-lithium-ion transport interfacial film. Furthermore, they can provide more silicon-oxygen bonds, participate in the acid removal reaction, reduce side reactions between the electrolyte and silicon-based materials, and thus further improve the cycle performance of the battery.

[0134] The aforementioned phosphate ester compounds, as additives, can serve two purposes. First, compared to carbon- or sulfur-containing substances, the phosphorus-containing interfacial products of phosphate ester compounds have lower lithium-ion desolvation energy, resulting in better lithium-ion interfacial charge transfer capability. Second, phosphate ester compounds containing groups such as TMS (trimethylsilyl) also have a mild proton scavenging effect, which can remove proton hydrogen generated during battery use, thereby inhibiting its corrosion of active materials.

[0135] In some embodiments of this application, the additive satisfies at least one of the following (a) and (b):

[0136] (a) Isocyanate compounds include one or more of Formula 1-1 and Formula 1-2:

[0137] Equation 1-1 Formula 1-2

[0138] (b) Phosphate esters include one or more of Formula 2-1, Formula 2-2, and Formula 2-3:

[0139] Equation 2-1 Equation 2-2

[0140] Equation 2-3

[0141] In this embodiment, any one or a combination of two of the isocyanate compounds shown in Formula 1-1 and Formula 1-2 can be used as an additive for the electrolyte. These compounds have high reactivity and exhibit good deacidification and film-forming effects, which are beneficial for further improving the cycle performance of the battery.

[0142] In the embodiments of this application, any one or more of the phosphate ester compounds shown in Formula 2-1, Formula 2-2, and Formula 2-3 can be used as additives for the electrolyte, exhibiting good film-forming effect, facilitating acid removal, and further improving the cycle performance of the battery.

[0143] In some embodiments of this application, the content of isocyanate compounds is 0.005 wt% to 1 wt% based on the mass of the electrolyte.

[0144] The content of isocyanate compounds in the electrolyte is related to the acid removal effect and the ion transport efficiency of the battery. As the content of isocyanate compounds in the electrolyte decreases, the acid removal effect tends to decline, leading to a decline in the cycle performance of the battery. As the content of isocyanate compounds in the electrolyte increases, the acid removal effect exhibits the above trend, the impedance increases, and the ion transport efficiency tends to decline, which in turn affects the cycle performance of the battery, such as low-temperature cycle performance.

[0145] In the embodiments of this application, the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, which is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and improve the cycle performance of the battery.

[0146] As an example, based on the mass of the electrolyte, the content of isocyanate compounds is 0.005 wt%, 0.006 wt%, 0.007 wt%, 0.008 wt%, 0.009 wt%, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, etc.

[0147] In some embodiments of this application, the content of isocyanate compounds is 0.1 wt% to 0.5 wt% based on the mass of the electrolyte.

[0148] In this embodiment, the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, which is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and further improve the cycle performance of the battery.

[0149] In some embodiments of this application, the content of phosphate ester compounds is 0.005wt%-3wt% based on the mass of the electrolyte.

[0150] The content of phosphate esters in the electrolyte is related to the improvement of battery kinetic performance and high-temperature cycle performance. As the content of phosphate esters in the electrolyte decreases, the effect of isocyanates on improving the deteriorating kinetic performance tends to decline, and lithium-ion transport efficiency tends to decrease, thus affecting the low-temperature cycle performance of the battery. As the content of phosphate esters in the electrolyte increases, the effect of isocyanates on improving the deteriorating kinetic performance tends to increase, and lithium-ion transport efficiency tends to increase. However, phosphate esters have poor high-temperature stability and can decompose at high temperatures, which leads to a decline in the high-temperature cycle performance of the battery.

[0151] In this embodiment, the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, which is beneficial for forming an interface film with low impedance, improving ion transport efficiency, and enhancing the cycle performance of the battery.

[0152] As an example, based on the mass of the electrolyte, the content of phosphate ester compounds is 0.005 wt%, 0.006 wt%, 0.007 wt%, 0.008 wt%, 0.009 wt%, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, etc.

[0153] In some embodiments of this application, the content of phosphate ester compounds is 0.1 wt% to 1.5 wt% based on the mass of the electrolyte.

[0154] In this embodiment, the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, which is beneficial for forming an interface film with low impedance, thereby improving ion transport efficiency and further enhancing the cycle performance of the battery.

[0155] In some embodiments of this application, the mass ratio of phosphate esters to isocyanates is 1.5-5.

[0156] The design of the mass ratio of isocyanate compounds to phosphate compounds can be based on a balance between proton scavenging and interfacial impedance. Isocyanate compounds have superior proton scavenging capabilities, but their interfacial products exhibit higher impedance, which can degrade the battery's kinetic performance. Phosphate compounds, by optimizing desolvation energy, can improve ion transport at the interface. Since isocyanate compounds contain two cyano groups while phosphate compounds have only one, a higher dosage of phosphate compounds is needed to balance kinetics and proton scavenging. By controlling the mass ratio of phosphate compounds to isocyanate compounds to meet the above conditions, the synergistic effect between the two compounds can be fully utilized, further improving the battery's cycle performance.

[0157] As examples, the mass ratios of phosphate esters to isocyanates are 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, and 5.

[0158] In some embodiments of this application, the mass ratio of phosphate ester compound to isocyanate compound is 2-3.

[0159] Controlling the mass ratio of phosphate esters to isocyanates to meet the above conditions helps to fully utilize the synergistic effect between phosphate esters and isocyanates, thereby further improving the cycle performance of the battery.

[0160] In some embodiments of this application, the additive also includes fluoroethylene carbonate.

[0161] Because silicon-based materials have a large volume effect, they are prone to SEI (Sediment Interlayer) rupture during charge and discharge, exposing new silicon surfaces and thus exacerbating reactions with acidic substances, thereby deteriorating battery life. In this embodiment, FEC (fluoroethylene carbonate) is used as an additive for the silicon-based negative electrode. During battery charge and discharge, it can perform interface repair functions, facilitating the repair of the interface film of the silicon-based negative electrode, improving negative electrode stability, and thus enhancing battery cycle performance.

[0162] In some embodiments of this application, the content of fluoroethylene carbonate is 0.5 wt% to 20 wt% based on the mass of the electrolyte.

[0163] As the content of fluoroethylene carbonate in the electrolyte decreases, the repair effect on the SEI interface film tends to decline, which will affect the cycle performance of the battery. As the content of fluoroethylene carbonate in the electrolyte increases, the repair effect on the SEI interface film tends to improve. However, fluoroethylene carbonate is prone to decomposition to form acidic substances, which will have an adverse effect on the silicon-based anode material, and may actually hinder further improvement of the battery cycle performance.

[0164] In this embodiment, the mass content of fluoroethylene carbonate in the electrolyte meets the above conditions, which is beneficial for repairing the SEI interface film, improving the stability of the silicon-based negative electrode, and improving the cycle performance of the battery.

[0165] As an example, based on the mass of the electrolyte, the content of fluoroethylene carbonate is 0.5wt%, 0.5wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, etc.

[0166] In some embodiments of this application, the content of fluoroethylene carbonate is 5wt%-15wt% based on the mass of the electrolyte.

[0167] In this embodiment, the mass content of fluoroethylene carbonate in the electrolyte meets the above conditions, which is beneficial for further repairing the SEI interface film, improving the stability of the silicon-based negative electrode, and better improving the cycle performance of the battery.

[0168] In some embodiments of this application, the secondary battery further includes a negative electrode sheet, which comprises a negative electrode active material, including a silicon-based material and graphite; the silicon-based material includes one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. Further, elemental silicon includes one or more of nano-silicon and micron-silicon.

[0169] In the embodiments of this application, the above-mentioned isocyanate compounds and phosphate compounds are used in combination in a battery system of silicon-based materials and graphite to improve the corrosion of silicon-based materials by acidic electrolytes, improve the ion transport efficiency of the battery, reduce impedance, and improve the cycle performance of the battery. This is of great significance for solving the lifespan bottleneck problem of silicon-based secondary batteries.

[0170] In addition, graphite materials have higher acid resistance than silicon-based materials and can maintain higher stability in acidic electrolytes. By using a mixture of silicon-based materials and graphite as the negative electrode active material, it is beneficial to improve the overall stability of the negative electrode active material in the electrolyte, which is conducive to improving the cycle performance of the battery.

[0171] Silicon-based materials have a high specific capacity, which is helpful for the fabrication of high-energy-density batteries. In the embodiments of this application, one or more of nano-silicon, micron-silicon, silicon-oxygen materials, and silicon-carbon materials can be used as silicon-based materials. These silicon-based materials are mixed with graphite, and can be used as negative electrode active materials after physical mixing.

[0172] In some embodiments of this application, the silicon-carbon material includes porous carbon and nano-silicon located inside the porous carbon; and / or, in the silicon-carbon material, the mass ratio of silicon to carbon is 6:4 to 4:6.

[0173] In silicon-carbon materials, the mass ratio of silicon to carbon is obtained by calculating the ratio of silicon content to carbon content. Methods known in the art can be used to determine the silicon and carbon content in silicon-carbon materials. As an example,

[0174] The silicon content test in silicon-carbon materials includes: determining the silicon content using inductively coupled plasma (ICP), specifically as follows: taking silicon-carbon material as a sample, digesting the sample with aqua regia and hydrofluoric acid HF, and detecting the silicon content after complete digestion.

[0175] Carbon content testing in silicon-carbon materials: Infrared absorption method for carbon-sulfur content analysis, according to GB / T20123-2006 testing standard, specifically as follows: take silicon-carbon material as a sample, completely digest it and measure the carbon content.

[0176] Based on the volume effect verification of silicon-based materials, the destruction and recombination of the interface structure during battery charging and discharging can affect the battery's cycle performance. Therefore, silicon-carbon materials, in which silicon is deposited in porous carbon, can be selected to suppress silicon expansion to a certain extent. In silicon-carbon materials, carbon acts as an insulator to isolate the electrolyte contact, reducing the contact between acid byproducts and silicon; moreover, silicon-carbon materials have less expansion and a more stable structure, which is beneficial to improving the battery's cycle performance.

[0177] In silicon-carbon materials, a silicon to carbon mass ratio of 6:4 to 4:6 helps mitigate side reactions between silicon and acid, reduces negative electrode volume expansion, and improves battery cycle performance. For example, silicon to carbon mass ratios of 6:4, 5:5, and 4:6 satisfy the condition that the sum of the first and second terms of the mass ratio is 10. Furthermore, a silicon to carbon mass ratio of 5:5 further improves battery cycle performance.

[0178] In some embodiments of this application, the silicon-carbon material includes porous carbon and nano-silicon located inside the porous carbon. For the porous carbon, the proportion of mesopores is greater than 50%, and the proportion of micropores is less than 50%.

[0179] Mesopores and micropores have meanings known in the art. For example, mesopores refer to pores with an average pore size of 2 nm to 10 nm, and micropores refer to pores with an average pore size of 0.2 nm to 2 nm.

[0180] Mesopores and micropores can be determined using methods known in the art. As an example, the method for determining the proportion of mesopores involves using conventional testing instruments to measure the distribution of each pore and statistically obtaining the specific quantity. For instance, using an ASAP2460 physical adsorption analyzer, the porous carbon material sample after drying and degassing is placed in liquid nitrogen, and different test pressures are adjusted to measure the amount of nitrogen adsorbed, and adsorption and desorption isotherms are plotted. The pore shape is determined based on the shape of the hysteresis loop, and the pore distribution is calculated according to different pore models. The BJH model is used to fit the pore size distribution curves of mesopores and macropores, and the DFT model is used to fit the pore size distribution curve of micropores. Particle size distribution, i.e., the particle size-volume distribution map of carbon particles, can be measured using conventional methods in the art, such as using a particle size analyzer to determine the particle size distribution map and then obtaining it statistically. In this application embodiment, laser diffraction particle size analysis is selected for determination, specifically referring to standard GB / T19077-2016 to obtain the particle size distribution map, which is then calculated.

[0181] The number of micropores and mesopores in this porous structure can be controlled to form a porous carbon material with a relatively high specific surface area. This porous carbon material not only allows for easy control of the silicon content formed within the porous structure, but also reserves some volume space to buffer the expansion of silicon material. By limiting the volume expansion of silicon material during lithium insertion / extraction, the cycle performance of the battery can be improved.

[0182] As an example, the proportion of mesopores in porous carbon is greater than 50% and less than 100%, while the proportion of micropores is less than 50% and greater than 0. More specifically, the proportion of mesopores in porous carbon is 51%, 60%, 70%, 80%, 90%, 95%, etc., and the corresponding proportion of micropores in porous carbon is 49%, 40%, 30%, 20%, 10%, 5%, etc.

[0183] In some embodiments of this application, the content of silicon-based material is 1wt%-90wt% and the content of graphite is 10wt%-99wt%, depending on the mass of the negative electrode active material.

[0184] As an example, the content of silicon-carbon materials and graphite in the negative electrode active material can be detected using the following method: First, cut the negative electrode sheet into 6mm×6mm pieces and attach them to an ion polishing machine. Cut the sheet at 7.5kV for 30 minutes, perpendicular to the large surface of the electrode. Then, according to the JY / T010-1996 testing standard, use a Sigma300 scanning electron microscope and energy dispersive spectroscopy (EDS) for testing and observation. Specifically: the image shows dark particles as graphite and bright particles as silicon. Select a single silicon particle to detect the elemental content ratio of silicon and carbon. Then, select a large area (defining the selection area size) for whole-area elemental testing to obtain the ratio of (graphite + carbon) to silicon. The percentage content of graphite and silicon-based materials can be obtained through final calculation.

[0185] In negative electrode active materials, an increased content of silicon-based materials is beneficial for achieving higher energy density in the battery, but the volume expansion effect becomes more pronounced, and the battery's cycle performance tends to decline. In the embodiments of this application, the content of silicon-based materials meets the above conditions, and a mixed system of silicon-based materials and graphite is used. Graphite dilutes some of the silicon-based materials, mitigating the corrosive effect of the acidic electrolyte environment, which is beneficial for improving the battery's cycle performance relative to the silicon-based materials themselves.

[0186] As an example, based on the mass of the negative electrode active material, the content of silicon-based material is 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, etc., and correspondingly, the content of graphite is 99%wt%, 95%wt%, 90%wt%, 85%wt%, 80%wt%, 75%wt%, 70%wt%, 65%wt%, 60%wt%, 55%wt%, 50%wt%, 45%wt%, 40%wt%, 35%wt%, 30%wt%, 25%wt%, 20%wt%, 15%wt%, 10%wt%, etc.

[0187] In some embodiments of this application, the content of silicon-based material is 2wt%-50wt% and the content of graphite is 50%wt-98wt%, depending on the mass of the negative electrode active material.

[0188] In this embodiment of the application, the content of silicon-based material meets the above conditions, which is beneficial to further improve the cycle performance of the battery.

[0189] As an example, based on the mass of the negative electrode active material, the silicon-based material content is 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, 42wt%, 44wt%, 4 6wt%, 48wt%, 50wt%, etc., corresponding to graphite contents of 98wt%, 96wt%, 94wt%, 92wt%, 90wt%, 88wt%, 86wt%, 84wt%, 82wt%, 80wt%, 78wt%, 76wt%, 74wt%, 72wt%, 70wt%, 68wt%, 66wt%, 64wt%, 62wt%, 60wt%, 50wt%, etc.

[0190] In some embodiments of this application, the content of silicon-based material is 3wt%-30wt% and the content of graphite is 70%wt-97wt%, depending on the mass of the negative electrode active material.

[0191] In this embodiment of the application, the content of silicon-based material meets the above conditions, which is beneficial to further improve the cycle performance of the battery.

[0192] In some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0193] The embodiments of this application do not specifically limit the type of electrolyte salt, and can be selected according to needs. As an example, one or more combinations of the electrolyte salts given above can be selected.

[0194] In some embodiments of this application, the electrolyte salt includes one or both of lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0195] In the embodiments of this application, lithium hexafluorophosphate, lithium bisfluorosulfonylimide, or a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide can be used as the electrolyte salt.

[0196] Furthermore, the electrolyte salts include lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0197] In this embodiment, lithium bisfluorosulfonylimide (LiFSI) can be used to participate in film formation to improve the high-temperature performance of the battery and reduce the acidic substances generated by the decomposition of lithium hexafluorophosphate (LiPF6). In addition, LiFSI has better dissociation ability than LiPF6, which is beneficial to improve the liquid phase ionic conductivity.

[0198] In some embodiments of this application, the content of lithium bis(fluorosulfonyl)imide is 0.05 M / L to 0.4 M / L, based on the mass of the electrolyte.

[0199] In the embodiments of this application, the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte meets the above conditions, which is beneficial to improve the high-temperature stability of the interface film, reduce the generation of acidic substances, improve ionic conductivity, and improve battery cycle performance.

[0200] As an example, based on the mass of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 0.05 M / L, 0.07 M / L, 0.09 M / L, 0.1 M / L, 0.2 M / L, 0.3 M / L, 0.4 M / L, etc.

[0201] Furthermore, based on the mass of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 0.1 M / L-0.2 M / L.

[0202] In the embodiments of this application, the molar concentration of lithium bisfluorosulfonylimide in the electrolyte meets the above conditions, which is beneficial to further improve the battery cycle performance.

[0203] Furthermore, the electrolyte salts include lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, with lithium hexafluorophosphate serving as the main salt and lithium bis(fluorosulfonyl)imide as the auxiliary salt. As an example, based on the mass of the electrolyte, the lithium hexafluorophosphate content can be 0.8 M / L to 1.2 M / L, and more specifically, the lithium hexafluorophosphate content can be 1 M / L.

[0204] In some embodiments of this application, the electrolyte also includes a solvent. Further, the solvent includes organic solvents.

[0205] In this application, the type of organic solvent is not particularly limited and can be selected according to actual needs. As an example, the organic solvent may also include one or more of the following: chain carbonates, cyclic carbonates, carboxylic acid esters, and ethers. The types of chain carbonates, cyclic carbonates, carboxylic acid esters, and ethers are not specifically limited and can be selected according to actual needs.

[0206] Furthermore, the organic solvent may also include one or more of the following: diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, dimethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butenyl carbonate, γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, tetrahydrofuran, dimethyl ether, diethyl ether, and ethylene glycol dimethyl ether.

[0207] In some embodiments of this application, the additive also includes one or more of the following: saturated or unsaturated cyclic carbonates, sulfite compounds, acid anhydrides, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, phosphite compounds, phosphate compounds, and borate compounds.

[0208] The secondary battery proposed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0209] In one embodiment of this application, a secondary battery is provided. Typically, it also includes a positive electrode, a negative electrode, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. An electrolyte (such as a liquid electrolyte solution) acts as a conductor of ions between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0210] [Positive electrode tablets]

[0211] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including the positive active material of the first aspect of this application.

[0212] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0213] 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 (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0214] In some embodiments, when the battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0215] In some implementations, such as when the battery is a sodium-ion battery, the positive electrode active material may, as an example, include, but is not limited to, at least one of layered transition metal oxides, polyanionic compounds, and Prussian blue analogues.

[0216] Examples of the aforementioned layered transition metal oxides include:

[0217] Na 1-x Cu h Fe k Mn l M 1 m O 2-y M 1 It is one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0218] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 It is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0219] Na a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0220] Examples of the aforementioned polyanionic compounds include:

[0221] A 1 f M 3 g (PO4)i O j X 1 3-j , wherein A 1 is one or more selected from the group consisting of H, Li, Na, K and NH4, M 3 is one or more selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, X 1 is one or more selected from the group consisting of F, Cl and Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2;

[0222] Na n M 4 PO4X 2 , wherein M 4 is one or more selected from the group consisting of Mn, Fe, Co, Ni, Cu and Zn, X 2 is one or more selected from the group consisting of F, Cl and Br, 0 < n ≤ 2;

[0223] Na p M 5 q (SO4)3, wherein M 5 is one or more selected from the group consisting of Mn, Fe, Co, Ni, Cu and Zn, 0 < p ≤ 2, 0 < q ≤ 2;

[0224] Na s Mn t Fe 3-t (PO4)2(P2O7), wherein 0 < s ≤ 4, 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2 or 3.

[0225] As examples of the above Prussian blue analogs, there can be mentioned, for example:

[0226] A u M 6 v [M 7 (CN)6] w ·xH2O, wherein A is H + , NH4 + , one or more selected from the group consisting of alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more selected from transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr+ Be 2+ Mg 2+ Ca 2+ 、Sr 2+ Ba 2+ and Ra 2+ One or more of them, M 6 and M 7 Each is an independent cation of one or more transition metal elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, and W.

[0227] The modified compounds for the above materials can be used to modify the materials by doping and / or by surface coating.

[0228] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0229] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0230] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0231] [Negative electrode plate]

[0232] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, such as the negative electrode active material proposed in the first aspect of the embodiments of this application.

[0233] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0234] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0235] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0236] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0237] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0238] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, 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.

[0239] [Isolation membrane]

[0240] In some embodiments, the battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0241] 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.

[0242] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0243] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0244] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0245] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The battery 5 is a square structure, which serves as an example.

[0246] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0247] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0248] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple batteries 5 can be fixed in place using fasteners.

[0249] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of batteries 5 are received.

[0250] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0251] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0252] A second aspect of this application provides an electrolyte comprising additives, including isocyanate compounds and phosphate ester compounds; the isocyanate compounds have a structure as shown in Formula 1:

[0253] OCN—R1—NCO

[0254] Formula 1;

[0255] In Formula 1: R1 is selected from one of substituted or unsubstituted C1-C10 saturated alkyl groups and substituted or unsubstituted C2-C10 unsaturated alkyl groups; the phosphate ester compound has the structure shown in Formula 2:

[0256]

[0257] In Formula 2: R2 to R4 are each independently selected from one or more of the following: substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, phenyl groups, silyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and isocyanate groups.

[0258] This application employs the aforementioned isocyanate compounds and phosphate compounds in a secondary battery. The combined effect of these compounds helps to mitigate the corrosive effects of acidic electrolytes on the negative electrode active material or its components (such as silicon-based materials), thereby improving the battery's ion transport efficiency, reducing impedance, and enhancing cycle performance. The electrolyte provided in this application has the beneficial effects of the electrolyte described in the first aspect above, which will not be repeated here.

[0259] In some embodiments of this application, in Formula 1, R1 is selected from one of unsubstituted C3-C8 saturated alkyl groups. The selection of R1 from unsubstituted C3-C8 saturated alkyl groups, with an appropriate carbon chain length, helps maintain the high reactivity of isocyanate compounds, improving acid removal and film formation effects. Using unsubstituted saturated alkyl groups facilitates the formation of an interface film with low impedance, improving lithium-ion transport and further enhancing the battery's cycle performance.

[0260] In some embodiments of this application, in Formula 2, R2-R4 are each independently selected from one or more unsubstituted C1-C4 saturated alkyl, silane, and phenyl groups. The independent selection of R2-R4 from these groups is beneficial for further improving the cycle performance of the battery.

[0261] In some embodiments of this application, the silane shown includes silane. Silanes have less steric hindrance, better reactivity, and better film formation and acid removal effects, which is beneficial for further improving the cycle performance of the battery.

[0262] In some embodiments of this application, in Formula 2, at least two of R2-R4 are selected from silane groups.

[0263] Phosphate esters containing two or more silane groups have high reactivity, which is beneficial for forming an interfacial film with low impedance and high lithium-ion transport. In addition, they can provide more silicon-oxygen bonds to participate in the deacidification reaction, reduce the side reactions between the electrolyte and the negative electrode active material or the negative electrode active material (such as silicon-based materials), and thus further improve the cycle performance of the battery.

[0264] In some embodiments of this application, the additive satisfies at least one of the following (a) and (b):

[0265] (a) Isocyanate compounds include one or more of Formula 1-1 and Formula 1-2:

[0266] Equation 1-1 Formula 1-2

[0267] (b) Phosphate esters include one or more of Formula 2-1, Formula 2-2, and Formula 2-3:

[0268] Equation 2-1 Equation 2-2

[0269] Equation 2-3

[0270] In the embodiments of this application, any one or a combination of two of the isocyanate compounds shown in Formula 1-1 and Formula 1-2 can be used as additives for the electrolyte. These additives have high reactivity and exhibit good deacidification and film-forming effects, which are beneficial for further improving the cycle performance of the battery.

[0271] In the embodiments of this application, any one or more combinations of the phosphate ester compounds shown in Formulas 2-1, 2-2, and 2-3 above can be used as additives for the electrolyte, exhibiting good film-forming effects and facilitating acid removal, which is beneficial for further improving the cycle performance of the battery.

[0272] In some embodiments of this application, the content of isocyanate compounds is 0.005 wt% to 1 wt% based on the mass of the electrolyte.

[0273] When the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, it is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and enhance the cycle performance of the battery.

[0274] In some embodiments of this application, the content of isocyanate compounds is 0.1 wt% to 0.5 wt% based on the mass of the electrolyte.

[0275] When the mass percentage of isocyanate compounds in the electrolyte meets the above conditions, it is beneficial to obtain a higher acid removal effect, form an interface film with low impedance, improve ion transport efficiency, and further improve the cycle performance of the battery.

[0276] In some embodiments of this application, the content of phosphate ester compounds is 0.005wt%-3wt% based on the mass of the electrolyte.

[0277] When the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, it is beneficial to form an interface film with low impedance, improve ion transport efficiency, and enhance the cycle performance of the battery.

[0278] In some embodiments of this application, the content of phosphate ester compounds is 0.1 wt% to 1.5 wt% based on the mass of the electrolyte.

[0279] When the mass percentage of phosphate ester compounds in the electrolyte meets the above conditions, it is beneficial to form an interface film with low impedance, which can better improve ion transport efficiency and further enhance the cycle performance of the battery.

[0280] In some embodiments of this application, the mass ratio of phosphate esters to isocyanates is 1.5-5.

[0281] By controlling the mass ratio of phosphate esters and isocyanates to meet the above conditions, it is beneficial to fully utilize the synergistic effect between phosphate esters and isocyanates, thereby further improving the cycle performance of the battery.

[0282] In some embodiments of this application, the mass ratio of phosphate ester compound to isocyanate compound is 2-3.

[0283] By controlling the mass ratio of phosphate esters and isocyanates to meet the above conditions, it is beneficial to fully utilize the synergistic effect between phosphate esters and isocyanates, thereby further improving the cycle performance of the battery.

[0284] In some embodiments of this application, the additive also includes fluoroethylene carbonate.

[0285] Using FEC (fluoroethylene carbonate) as an electrolyte additive can serve as a repair agent for the SEI interface during battery charging and discharging; it can help repair the interface film of the silicon-based negative electrode, improve the stability of the negative electrode, and thus improve the cycle performance of the battery.

[0286] In some embodiments of this application, the content of fluoroethylene carbonate is 0.5 wt% to 20 wt% based on the mass of the electrolyte.

[0287] When the mass content of fluoroethylene carbonate in the electrolyte meets the above conditions, it is beneficial to repair the SEI interface film, improve the stability of the negative electrode, and improve the cycle performance of the battery.

[0288] The third aspect of this application provides an electrical device, which includes the secondary battery proposed in the first aspect of this application.

[0289] The electrical equipment provided in this application includes at least one of the following: the battery provided in this application, the battery module assembled from the battery, or the battery pack. The battery, battery module, or battery pack can be used as a power source for the electrical equipment or as an energy storage unit for the electrical equipment. The electrical equipment may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0290] As electrical equipment, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0291] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density batteries, a battery pack or battery module can be used.

[0292] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0293] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0294] [Battery Manufacturing]

[0295] Example 1

[0296] (1) Preparation of positive electrode:

[0297] An 8μm thick aluminum foil was used as the positive electrode current collector. The positive electrode active material, LiNi, was used. 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in solvent N-methylpyrrolidone (NMP) at a weight ratio of 93:2:5. After thorough stirring and mixing, a positive electrode slurry is obtained. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0298] (2) Preparation of negative electrode sheet:

[0299] Silicon carbon material, graphite, conductive carbon black, and binder polyacrylic acid are mixed in a mass ratio of 2:6:1:1. Deionized water is added and the mixture is stirred thoroughly to form a negative electrode slurry. The silicon carbon material is composed of porous carbon and nano-silicon deposited inside. The number of mesopores (2nm-10nm) in the porous carbon accounts for 50%-60%, and the number of micropores (0.2nm-2nm) accounts for 40%-50%. The mass ratio of silicon to carbon in the silicon carbon material is 5:5. The negative electrode slurry is uniformly coated on one surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0300] (3) Separating membrane:

[0301] A 12μm thick polyethylene film was used as the separator.

[0302] (4) Preparation of electrolyte:

[0303] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, thoroughly dried electrolyte salts were dissolved in the mixed organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L. Additives were added according to the mass ratio of the electrolyte solution.

[0304] (5) Assemble the battery:

[0305] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. They are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0306] Examples 2-30

[0307] Examples 2-30 used the same method as in Example 1 to prepare batteries, with specific parameter differences shown in Table 1.

[0308] Comparative Example 1

[0309] Comparative Example 1 used the same method as in Example 1 to prepare a battery, except that no additives were added in the electrolyte preparation step. Specific parameter differences are shown in Table 1.

[0310] Comparative Example 2

[0311] Comparative Example 2 used the same method as in Example 1 to prepare a battery, except that a phosphate ester compound of Formula 2-1 was added as an additive in the electrolyte preparation step. Specific parameter differences are shown in Table 1.

[0312] Comparative Example 3

[0313] Comparative Example 3 used the same method as in Example 1 to prepare a battery, except that an isocyanate compound of Formula 1-1 was added as an additive in the electrolyte preparation step. Specific parameter differences are shown in Table 1.

[0314] Comparative Example 4

[0315] Comparative Example 4 used the same method as in Example 1 to prepare a battery, except that FEC was added as an additive in the electrolyte preparation step. Specific parameter differences are shown in Table 1.

[0316] Table 1

[0317]

[0318] Note: The specific structural formulas of the isocyanate and phosphate compounds in Table 1 are shown below: Formula 1-1: Equation 1-2:

[0319] Equation 2-1:

[0320] Equation 2-2:

[0321] Equation 2-3:

[0322]

Parameters and Performance Testing

[0323] I. Testing Methods

[0324] 1. Testing of additive content in electrolyte:

[0325] Referring to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents", the organic components in the electrolyte were qualitatively and quantitatively analyzed by gas chromatography. Batteries that had been completely discharged (discharged to the lower cutoff voltage so that the battery's state of charge was approximately 0% SOC) were disassembled in reverse. The free electrolyte obtained from the battery was used as a sample and analyzed by ion chromatography.

[0326] 2. Testing of silicon-carbon materials and graphite content:

[0327] First, the negative electrode sheet was cut into 6mm × 6mm pieces and attached to an ion polishing machine. It was then cut at 7.5kV for 30 minutes, perpendicular to the large surface of the electrode sheet. Following the JY / T010-1996 testing standard, a Sigma300 scanning electron microscope and energy dispersive spectroscopy (EDS) were used for testing and observation. The images showed dark particles as graphite and bright particles as silicon. A single silicon particle was selected for analysis to determine the silicon-carbon elemental content ratio. Then, a large area was selected (the selection area size was defined) for whole-area elemental analysis to obtain the ratio of (graphite + carbon) to silicon. Finally, the mass ratio of graphite / silicon-carbon material was calculated, thus obtaining the percentage content of graphite and silicon-carbon materials.

[0328] 3. Internal resistance test:

[0329] At 25°C, the shipped lithium-ion batteries and lithium-ion batteries that have undergone 800 cycles at 25°C are charged to 4.3V at a constant current of 1C. Then, they are charged at a constant voltage of 4.3V until the current is less than 0.05C, and then discharged at 1C for 30 minutes, adjusting the battery capacity to 50% SOC. Next, the positive and negative probes of a TH2523A AC internal resistance tester are connected to the positive and negative terminals of the battery, respectively, and the battery's internal resistance value is read using the tester. This value is recorded as the initial battery internal resistance (mΩ) and the battery internal resistance (mΩ) after 800 cycles.

[0330] 4. Low-temperature cycling performance:

[0331] 25℃ Cycling: At 25℃, the prepared secondary battery (full cell) is charged to 4.25V at 0.5C, and then discharged to 2.5V at 1C. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as the initial discharge capacity. The secondary battery is then subjected to the same charge-discharge cycle test as described above, and the discharge capacity after each cycle is recorded until the discharge capacity of the secondary battery decreases to 80% of the initial discharge capacity. The number of cycles at this point is recorded.

[0332] 5. High-temperature cycling performance:

[0333] 45℃ Cycling: At 45℃, the prepared secondary battery (full cell) is charged at 1C to 4.25V, and then discharged at 1C to 2.5V. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as the initial discharge capacity. The secondary battery is then subjected to the same charge-discharge cycle test as described above. The discharge capacity after each cycle is recorded until the discharge capacity of the secondary battery decreases to 80% of the initial discharge capacity. The number of cycles at this point is recorded.

[0334] II. Test Results

[0335] The test results for the examples and comparative examples are shown in Table 2.

[0336] Table 2

[0337]

[0338] As shown in Table 2, the test results indicate that, compared to Comparative Example 1 (without additives), Comparative Example 2 (with only phosphate ester compounds), Comparative Example 3 (with only isocyanate compounds), and Comparative Example 4 (with only FEC additives), the batteries provided in Examples 1-30 of this application, through the combined action of phosphate ester compounds and isocyanate compounds, better improve the high and low temperature cycle performance of the battery. Furthermore, the cycle performance of the battery can be further improved by adjusting various parameters, such as the amount of phosphate ester compounds and isocyanate compounds.

[0339] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, Including electrolyte; The electrolyte includes additives, which include isocyanate compounds and phosphate ester compounds; The isocyanate compounds have the structure shown in Formula 1: OCN—R1—NCO Formula 1; In Formula 1: R1 is selected from one of substituted or unsubstituted C1-C10 saturated alkyl groups and substituted or unsubstituted C2-C10 unsaturated alkyl groups; The phosphate ester compound has the structure shown in Formula 2: In Formula 2: R2 to R4 are each independently selected from one or more of the following: substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, phenyl groups, silyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and isocyanate groups.

2. The secondary battery according to claim 1, characterized in that, In Formula 1, R1 is selected from one of unsubstituted C3-C8 saturated alkyl groups.

3. The secondary battery according to claim 1 or 2, characterized in that, In Formula 2, R2-R4 are each independently selected from one or more of unsubstituted C1-C4 saturated alkyl, silyl, and phenyl groups.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The silanes shown include methylsilanes.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, In Equation 2, at least two of R2-R4 are selected from silane groups.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The additive satisfies at least one of the following (a) and (b): (a) The isocyanate compounds include one or more of Formula 1-1 and Formula 1-2: (b) The phosphate ester compounds include one or more of Formula 2-1, Formula 2-2, and Formula 2-3:

7. The secondary battery according to any one of claims 1 to 6, characterized in that, Based on the mass of the electrolyte, the content of the isocyanate compound is 0.005wt%-1wt%.

8. The secondary battery according to any one of claims 1 to 6, characterized in that, Based on the mass of the electrolyte, the content of the isocyanate compound is 0.1wt%-0.5wt%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, Based on the mass of the electrolyte, the content of the phosphate ester compound is 0.005wt%-3wt%.

10. The secondary battery according to any one of claims 1 to 8, characterized in that, Based on the mass of the electrolyte, the content of the phosphate ester compound is 0.1 wt% to 1.5 wt%.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The mass ratio of the phosphate ester compound to the isocyanate compound is 1.5-5.

12. The secondary battery according to any one of claims 1 to 10, characterized in that, The mass ratio of the phosphate ester compound to the isocyanate compound is 2-3.

13. The secondary battery according to any one of claims 1 to 12, characterized in that, The additives also include fluoroethylene carbonate.

14. The secondary battery according to claim 13, characterized in that, Based on the mass of the electrolyte, the content of the fluoroethylene carbonate is 0.5 wt% to 20 wt%.

15. The secondary battery according to any one of claims 1 to 14, characterized in that, The secondary battery also includes a negative electrode sheet, which includes a negative electrode active material. The negative electrode active material includes silicon-based materials and graphite. The silicon-based material includes one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

16. The secondary battery according to claim 15, characterized in that, The silicon-carbon material comprises porous carbon and nano-silicon located inside the porous carbon; and / or, in the silicon-carbon material, the mass ratio of silicon to carbon is 6:4 to 4:

6.

17. The secondary battery according to any one of claims 15 or 16, characterized in that, Based on the mass of the negative electrode active material The content of the silicon-based material is 1wt%-90wt%, and the content of the graphite is 10%wt-99wt%.

18. The secondary battery according to any one of claims 1 to 17, characterized in that, The electrolyte further includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

19. The secondary battery according to claim 18, characterized in that, The electrolyte salt includes one or both of lithium hexafluorophosphate and lithium difluorosulfonylimide.

20. The secondary battery according to claim 18 or 19, characterized in that, Based on the mass of the electrolyte, the content of lithium bis(fluorosulfonyl)imide is 0.05 M / L to 0.4 M / L.

21. An electrolyte, characterized in that, The electrolyte includes additives, which include isocyanate compounds and phosphate ester compounds; the isocyanate compounds have the structure shown in Formula 1: OCN—R1—NCO Formula 1; In Formula 1: R1 is selected from one of substituted or unsubstituted C1-C10 saturated alkyl groups and substituted or unsubstituted C2-C10 unsaturated alkyl groups; The phosphate ester compound has the structure shown in Formula 2: In Formula 2: R2 to R4 are each independently selected from one or more of the following: substituted or unsubstituted C1-C10 saturated alkyl groups, substituted or unsubstituted C3-C10 unsaturated alkyl groups, phenyl groups, silyl groups, carbonyl groups, carboxyl groups, ester groups, nitrile groups, and isocyanate groups.

22. The electrolyte according to claim 21, characterized in that, In Formula 1, R1 is selected from one of unsubstituted C3-C8 saturated alkyl groups.

23. The electrolyte according to claim 21 or 22, characterized in that, In Formula 2, R2-R4 are each independently selected from one or more of unsubstituted C1-C4 saturated alkyl, silyl, and phenyl groups.

24. The electrolyte according to any one of claims 21 to 23, characterized in that, The silanes shown include methylsilanes.

25. The electrolyte according to any one of claims 21 to 24, characterized in that, In Equation 2, at least two of R2-R4 are selected from silane groups.

26. The electrolyte according to any one of claims 21 to 25, characterized in that, The additive satisfies at least one of the following (a) and (b): (a) The isocyanate compounds include one or more of Formula 1-1 and Formula 1-2: (b) The phosphate ester compounds include one or more of Formula 2-1, Formula 2-2, and Formula 2-3:

27. The electrolyte according to any one of claims 21 to 26, characterized in that, Based on the mass of the electrolyte, the content of the isocyanate compound is 0.005wt%-1wt%.

28. The electrolyte according to any one of claims 21 to 26, characterized in that, Based on the mass of the electrolyte, the content of the isocyanate compound is 0.1wt%-0.5wt%.

29. The electrolyte according to any one of claims 21 to 28, characterized in that, Based on the mass of the electrolyte, the content of the phosphate ester compound is 0.005wt%-3wt%.

30. The electrolyte according to any one of claims 21 to 28, characterized in that, Based on the mass of the electrolyte, the content of the phosphate ester compound is 0.1 wt% to 1.5 wt%.

31. The electrolyte according to any one of claims 21 to 30, characterized in that, The mass ratio of the phosphate ester compound to the isocyanate compound is 1.5-5.

32. The electrolyte according to any one of claims 21 to 30, characterized in that, The mass ratio of the phosphate ester compound to the isocyanate compound is 2-3.

33. The electrolyte according to any one of claims 21 to 32, characterized in that, The additives also include fluoroethylene carbonate.

34. The electrolyte according to claim 33, characterized in that, Based on the mass of the electrolyte, the content of the fluoroethylene carbonate is 0.5 wt% to 20 wt%.

35. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 20.

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