Lithium-ion secondary battery and preparation method therefor, and electrical device

Abstract

A lithium-ion secondary battery and a preparation method therefor, and an electrical device. The lithium-ion secondary battery comprises an electrolyte. The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and an additive. The non-aqueous solvent comprises a cyclic carbonate and a linear carbonate. The linear carbonate comprises dimethyl carbonate, and further comprises a linear carbonate different from dimethyl carbonate. The electrolyte comprises lithium bis(fluorosulfonyl)imide. The mass percentage of dimethyl carbonate in the non-aqueous solvent is denoted as FDMC, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is denoted as CLiFSI mol / L, and (CLiFSI×FDMC) is relatively low.

Description

Lithium-ion secondary batteries, their preparation methods and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on March 26, 2025, with application number CN2025103650936 and entitled "Lithium-ion secondary battery and preparation method thereof and power device thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of lithium-ion battery technology, and further to a lithium-ion secondary battery, its preparation method, and an electrical device thereof. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] With the continuous expansion of the application fields and regions of lithium-ion rechargeable batteries, the operating temperature range of lithium-ion rechargeable batteries has significantly broadened, and the demand for high-temperature applications is constantly increasing. Conventional lithium-ion rechargeable batteries are usually used at room temperature and contain chain carbonates (such as dimethyl carbonate (DMC)) in the electrolyte. When this battery system is applied to a high-temperature environment, the cell will generate more gas during high-temperature use, which will deteriorate the long-term reliability at high temperatures.

[0006] Therefore, it is necessary to further improve the long-term reliability of lithium-ion secondary batteries at high temperatures. Summary of the Invention

[0007] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, a method for preparing the same, and an electrical device thereof. The long-term reliability of this lithium-ion secondary battery at high temperatures is significantly improved.

[0008] In one embodiment of the first aspect of this application, a lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive electrode and the negative electrode; the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises cyclic carbonates and chain carbonates; the chain carbonates comprise dimethyl carbonate, and further comprise chain carbonates different from dimethyl carbonate; the electrolyte comprises lithium bis(fluorosulfonyl)imide.

[0009] The mass percentage of dimethyl carbonate in the non-aqueous solvent is denoted as F. DMC The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is denoted as C. LiFSI mol / L; the electrolyte satisfies 0 < (C LiFSI ×F DMC)≤0.05.

[0010] By introducing lithium bisfluorosulfonylimide (LiFSI) into the electrolyte, LiFSI can participate in the formation of the interfacial film between the positive and negative electrodes and has a high thermal decomposition temperature. Theoretically, the introduction of LiFSI is beneficial for suppressing interfacial side reactions at high temperatures, reducing or delaying lithium consumption, and extending the battery's high-temperature lifespan. However, in the presence of dimethyl carbonate (DMC) in the electrolyte, LiFSI in the electrolyte accelerates the decomposition of DMC at high temperatures, leading to the generation of more gases (such as hydrogen). This severely limits the effect of LiFSI on improving the battery's high-temperature lifespan, posing a significant challenge to the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0011] By simultaneously introducing DMC (which can be denoted as the first chain carbonate), a chain carbonate different from DMC (which can be denoted as the second chain carbonate), and LiFSI into the electrolyte, and controlling the molar volume concentration (C) of LiFSI in the electrolyte... LiFSI ) and the mass percentage of DMC in non-aqueous solvents (F DMC The product of (C) LiFSI ×F DMC With a relatively low value, the superposition effect of LiFSI and DMC can be synergistically controlled, effectively suppressing the accelerated decomposition of DMC by LiFSI, better controlling high-temperature gas generation, and forming a robust solid electrolyte interphase (SEI) film based on the film-forming effect of LiFSI, giving the SEI film excellent high-temperature stability, significantly suppressing interfacial side reactions, and achieving better high-temperature lifetime. Furthermore, a second-chain carbonate with better stability is introduced to synergistically control the high-temperature gas generation of DMC. Based on the aforementioned synergistic effect, but not limited to the aforementioned theory, the long-term reliability of lithium-ion secondary batteries at high temperatures can be significantly improved.

[0012] In some implementations, 0.0002 ≤ (C LiFSI ×F DMC )≤0.05.

[0013] In some implementations, 0.0005 ≤ (C LiFSI ×F DMC )≤0.04.

[0014] By (C LiFSI ×F DMC Controlling the temperature within the aforementioned range helps to better and more persistently suppress high-temperature gas generation, and more significantly improves the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0015] In some embodiments, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than or equal to 0.2 mol / L, and may be selected as 0.2 mol / L to 1 mol / L.

[0016] By varying the molar volume concentration (C) of LiFSI in the electrolyte LiFSI Keeping the concentration of LiFSI (mol / L) within the aforementioned range helps to better leverage its role in extending the high-temperature lifespan of batteries.

[0017] In some embodiments, the mass percentage of dimethyl carbonate in the non-aqueous solvent satisfies 0. <F DMC ≤20%.

[0018] In some implementations, 0 <F DMC ≤10%.

[0019] By measuring the mass percentage of DMC in a non-aqueous solvent (F... DMC Controlling the gas production at high temperatures within the aforementioned range is beneficial for reducing the high-temperature gas production of DMC.

[0020] In some embodiments, the molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 1 mol / L, and 0.1% ≤ F DMC ≤20%;

[0021] Optionally, 0.3 mol / L to 1 mol / L, 0.1% ≤ F DMC ≤10%.

[0022] By varying the molar volume concentration (C) of LiFSI in the electrolyte LiFSI (mol / L) and the mass percentage of DMC in non-aqueous solvents (F DMC By controlling these parameters within the aforementioned range, it is beneficial to better and more persistently suppress high-temperature gas generation at high temperatures, and to more significantly improve the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0023] In some embodiments, the electrolyte salt further includes lithium hexafluorophosphate; wherein the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate in the electrolyte salt is greater than or equal to 0.05.

[0024] In some embodiments, the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate in the electrolyte salt is greater than or equal to 0.1.

[0025] LiFSI can function not only as a film-forming additive but also as an electrolyte salt. LiFSI exhibits better thermal stability and higher conductivity than lithium hexafluorophosphate (LiPF6), but the introduction of LiFSI into the battery system leads to more gas production compared to a pure LiPF6 system. When the electrolyte salt includes both LiFSI and LiPF6 (referred to as a "LiFSI+LiPF6" battery system), controlling the molar ratio of LiFSI to LiPF6 within the aforementioned range improves the long-term reliability of the "LiFSI+LiPF6" battery system at high temperatures; for example, it helps suppress accelerated capacity decay and rapid capacity drops at low state of equilibrium (SOH).

[0026] In some embodiments, the molar percentage of lithium difluorosulfonylimide in the electrolyte salt is 20% to 100%.

[0027] In some embodiments, the molar percentage of lithium difluorosulfonylimide in the electrolyte salt is 50% to 100%.

[0028] By controlling the molar percentage of LiFSI in the electrolyte salt within the aforementioned range, it is beneficial to improve the long-term reliability of the "LiFSI+LiPF6" battery system at high temperatures.

[0029] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0030] (a1) The chain carbonate includes one or both of diethyl carbonate (DEC) and ethyl methyl carbonate (EMC); optionally, the mass percentage of diethyl carbonate in the chain carbonate is denoted as L. DEC L DEC ≥40%;

[0031] (a2) The cyclic carbonate includes one or both of ethylene carbonate (EC) and propylene carbonate (PC); optionally, the mass percentage of ethylene carbonate in the cyclic carbonate is denoted as H. EC 50% ≤ H EC ≤100%;

[0032] (a3) The mass percentage of dimethyl carbonate in the chain carbonate is denoted as L. DMC 0 <L DMC ≤25%;

[0033] (a4) The cyclic carbonate includes ethylene carbonate; the mass ratio of diethyl carbonate and ethylene carbonate in the electrolyte is denoted as R. DEC / EC R DEC / EC ≥0.8, optionally, 0.8≤R DEC / EC ≤3.5.

[0034] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0035] (a1')50%≤L DEC ≤75%;

[0036] (a2')60%≤H EC ≤100%;

[0037] (a3')0 <L DMC ≤16%, optionally, 5% ≤L DMC ≤10%;

[0038] (a4')1≤R DEC / EC ≤2.5.

[0039] Second-chain carbonates (such as DEC, EMC, etc.) and cyclic carbonates (such as EC, PC, etc.) exhibit better stability at high temperatures than DMC. This can be achieved by controlling the mass percentage (L) of diethyl carbonate in the chain carbonates. DEC ), the mass percentage of ethylene carbonate in cyclic carbonates (H EC ), the mass percentage of dimethyl carbonate in chain carbonates (L) DMC One or more parameters in the above range are beneficial to improving the high-temperature performance of the battery and to significantly improving the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0040] By controlling R DEC / EC Within the aforementioned range, it is beneficial to control the increase in system viscosity caused by EC, and to take into account the room temperature performance of the battery.

[0041] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0042] (b1) The mass percentage of diethyl carbonate in the non-aqueous solvent is 20% to 65%;

[0043] (b2) The mass percentage of ethylene carbonate in the non-aqueous solvent is 15% to 50%;

[0044] (b3) The chain carbonate in the non-aqueous solvent is 50% to 75% by mass;

[0045] (b4) The cyclic carbonate in the non-aqueous solvent is 25% to 50% by mass;

[0046] (b5) The chain carbonates also include ethyl methyl carbonate.

[0047] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0048] (b1') The mass percentage of diethyl carbonate in the non-aqueous solvent is 25% to 50%;

[0049] (b2') The mass percentage of ethylene carbonate in the non-aqueous solvent is 25% to 40%;

[0050] (b3') The chain carbonate in the non-aqueous solvent is 55% to 75% by mass;

[0051] (b4') The cyclic carbonate in the non-aqueous solvent is 25% to 45% by mass.

[0052] By controlling the mass percentage (F) of diethyl carbonate in a non-aqueous solvent DEC ), the mass percentage of ethylene carbonate in non-aqueous solvents (F EC ), the mass percentage of chain carbonates in non-aqueous solvents (F LC ), the mass percentage of cyclic carbonates in non-aqueous solvents (F CC Controlling one or more parameters in the electrolyte within the aforementioned range helps to better control the high-temperature gas generation of non-aqueous solvents in the electrolyte, and more significantly improves the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0053] In some embodiments, the additive includes vinylene carbonate; the mass percentage of vinylene carbonate in the electrolyte is denoted as F. VC F VC ≥2%.

[0054] Ethylene carbonate (VC) can participate in the formation of a stable interfacial film at the negative electrode and can be consumed earlier than the solvent. By introducing VC into the electrolyte, it is beneficial to suppress high-temperature interfacial side reactions, suppress high-temperature gas generation, slow down capacity decay at high temperatures, and improve the long-term reliability of the battery at high temperatures.

[0055] By controlling the mass percentage of VC in the electrolyte (F VC Within the aforementioned range, it can effectively suppress high-temperature gas generation and extend high-temperature lifespan, thereby improving the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0056] In some implementations, 2% ≤ F VC ≤12%.

[0057] In some implementations, 2.5% ≤ F VC ≤10%.

[0058] In some implementations, 3% ≤ FVC ≤10%.

[0059] By controlling the mass percentage of VC in the electrolyte (F VC Within the aforementioned range, while better suppressing high-temperature interface side reactions and high-temperature gas generation, it also helps to better control the internal resistance of the cell, which is beneficial to improving the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0060] In some embodiments, the positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes a lithium iron phosphate-based positive electrode material;

[0061] Optionally, the lithium iron phosphate cathode material constitutes 80% to 100% of the cathode active material by mass.

[0062] By incorporating lithium iron phosphate (LFP) cathode materials into the positive electrode active material, the structural stability of the positive electrode active material can be improved, thus extending the high-temperature lifespan of lithium-ion secondary batteries. Furthermore, controlling the mass percentage of LFP cathode materials within the aforementioned range further enhances the ability to extend the high-temperature lifespan of lithium-ion secondary batteries.

[0063] In some embodiments, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode active material; the negative electrode active material includes one or more of graphite and coated graphite materials; wherein, the coated graphite material includes a graphite body and a hard carbon coating layer located on at least a portion of the surface of the graphite body.

[0064] In some embodiments, the coated graphite material constitutes 80% to 100% of the negative electrode active material by mass.

[0065] By controlling one or more of the negative electrode active materials, including graphite and coated graphite materials, it is beneficial to better control the volume expansion and contraction changes of the negative electrode active materials, and to ensure that the negative electrode active materials still have good structural stability during long-term cycling and / or storage at high temperatures.

[0066] Negative electrode active materials containing graphite components in their particle bulk are denoted as "graphite-based materials". When the graphite-based material in the negative electrode active material includes coated graphite material, the hard carbon coating layer is beneficial to improving the long-term structural stability of the graphite-based material at high temperatures.

[0067] By controlling the mass percentage of coated graphite material in the negative electrode active material within the aforementioned range, it is beneficial to improve the long-term structural stability of the negative electrode active material at high temperatures and to better improve the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0068] In some embodiments of the second aspect of this application, a method for preparing a lithium-ion secondary battery is provided, comprising the following steps:

[0069] An electrode assembly comprising a positive electrode, a separator, and a negative electrode is placed inside a battery casing; wherein the separator is disposed between the positive electrode and the negative electrode.

[0070] An electrolyte is injected into the battery casing; wherein the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises cyclic carbonates and chain carbonates; the chain carbonates comprise dimethyl carbonate, and further comprise chain carbonates different from dimethyl carbonate; the electrolyte comprises lithium bis(fluorosulfonyl)imide; the mass percentage of dimethyl carbonate in the non-aqueous solvent is denoted as F. DMC The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is denoted as C. LiFSI mol / L; the electrolyte satisfies 0 < (C LiFSI ×F DMC ≤0.05;

[0071] Let it stand and soak; and

[0072] formed.

[0073] In some embodiments, the lithium-ion secondary battery described in the first aspect of this application is prepared.

[0074] In a third aspect of this application, an electrical device is provided, which includes the lithium-ion secondary battery described in the first aspect of this application.

[0075] Details of one or more embodiments or examples of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0076] To better describe and illustrate the embodiments, examples, or models provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments, examples, or models, or the best mode of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. It should also be noted that the drawings are drawn in a simplified form and are only intended to facilitate and clarify the illustration of this application. The various dimensions of each part shown in the drawings are arbitrarily shown and may be precise or not drawn to scale. For example, the dimensions of parts are appropriately exaggerated in some places in the drawings to make the illustration clearer. Unless otherwise specified, the parts in the drawings are not drawn to scale. This application does not limit every dimension of every part. In the drawings:

[0077] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application.

[0078] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0079] Figure 3 is a schematic diagram of a battery device according to an embodiment of this application.

[0080] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0081] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0082] Figure 6 is a schematic diagram of an electrical device using a lithium-ion secondary battery as a power source according to an embodiment of this application.

[0083] Explanation of reference numerals in the attached drawings: 1, battery pack; 2, upper casing; 3, lower casing; 4, battery assembly; 5, individual battery cell; 51, battery casing; 52, electrode assembly; 53, cover plate; 6, electrical device. Detailed Implementation

[0084] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments and examples of the lithium-ion secondary battery, its preparation method, and its power application. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0085] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0086] In this application, the term "numerical value" includes the number itself and its reasonable approximations. The definition of "numerical value" can apply to discrete numerical points or to the endpoints of a numerical range. Unless otherwise specified, the term "approximation" covers a numerical interval based on a reasonable range of fluctuations of the number itself. This reasonable range of fluctuations can vary depending on the type and magnitude of the number. This reasonable range of fluctuations can be reasonably determined based on the accuracy of the testing or measurement method. Therefore, when referring to a numerical value or a numerical range, unless otherwise specified, it should be understood that the numerical value includes its reasonable approximation, and the numerical range includes reasonable approximations at both endpoints. Those skilled in the art will understand that acceptable fluctuation ranges of the relevant approximations can be included within the definition of the numerical value or the numerical range. In this application, unless otherwise specified, "N1" can be reasonably understood as "about N1," and "N1~N2" can be reasonably understood as "about N1 to about N2," where N1 and N2 are two unequal numerical values.

[0087] In this application, unless otherwise specified, "about" means within a reasonable range above and below the stated number, and the range of fluctuation may vary depending on the type and value of the stated number. For example, a range of ±10%, ±5%, ±2%, ±1%, etc., may be allowed. For example, taking "about 20°C" and its approximation as ±1°C, approximate values ​​such as 19°C, 19.5°C, etc., within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0088] In this application, the terms "multiple," "multi-item," or "multiple items" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one item or two or more (greater than or equal to) items. It can be understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0089] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0090] 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 or implementation 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. The term "implementation" as used herein has a similar understanding.

[0091] Those skilled in the art will understand that, unless otherwise specified, the order in which the steps are written in the various embodiments or methods of this application does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but are preferably performed sequentially. For example, if method M includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, method M may also include step (c), meaning that step (c) can be added to method M in any order. For example, method M 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.

[0092] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if 'a' includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both features or solutions where "a consists of a1, a2, and a3" or "a is selected from a1, a2, and a3," and features or solutions where "a includes not only a1, a2, and a3, but also other members."

[0093] In this application, unless otherwise specified, M (e.g., m1) means that m1 is a non-limiting example of M, and it is understood that M is not limited to m1.

[0094] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0095] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. Any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" represents the group consisting of M, N, and "a combination of M and N". "Containing M and / or N" can mean "containing M, containing N, and containing both M and N", or "containing M, containing N, or containing both M and N", and can be appropriately understood according to the context.

[0096] In this document, the word "suitable" in "suitable combination", "suitable method", etc., refers to the technical solution that can implement this application.

[0097] In this document, terms such as "preferred," "better," and "good" are merely descriptions of implementation methods or embodiments that achieve better results and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0098] In this application, terms such as "further," "even more," "especially," "for example," "as," "example," and "exemplary" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0099] In this application, the terms "first aspect," "second aspect," "third aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0100] In this application, unless otherwise expressly specified and limited, terms such as "connected" and "joined" in relation to mechanical structures should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral part. Those skilled in the art can understand the meaning of the above terms in this application according to the circumstances.

[0101] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0102] In this application, the term "room temperature" generally refers to 4℃ to 35℃, and may refer to 20℃ ± 5℃. In some embodiments or examples of this application, room temperature refers to 20℃ to 30℃.

[0103] In this application, when a unit is specified for a data range, if it is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5μm or 3-5μm both mean that the units for the left endpoint "3" and the right endpoint "5" are both μm (micrometers), and have the same meaning as 3μm~5μm. Furthermore, similar descriptions of other parameters such as temperature, concentration, and size are interpreted in the same way.

[0104] In this application, "greater than or equal to", "greater than or equal to", and "≥" have the same meaning and can be used interchangeably; "less than or equal to", "less than or equal to", and "≤" have the same meaning and can be used interchangeably; "greater than" can be equivalently represented as ">", and "less than" can be equivalently represented as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be considered as providing two additional solutions: "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be considered as providing two additional solutions: "less than" and "equal to".

[0105] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0106] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0107] Conventional lithium-ion secondary batteries are typically used in applications at room temperature and contain chain carbonates (such as dimethyl carbonate (DMC)) in the electrolyte. When this battery system is applied to a high-temperature environment, the cells will generate more gas during high-temperature use, which will deteriorate the long-term reliability at high temperatures.

[0108] By introducing lithium bisfluorosulfonylimide (LiFSI) into the electrolyte, LiFSI can participate in the formation of the interfacial film between the positive and negative electrodes and has a high thermal decomposition temperature. Theoretically, the introduction of LiFSI is beneficial for suppressing interfacial side reactions at high temperatures, reducing or delaying lithium consumption, and extending the battery's high-temperature lifespan. However, in the presence of dimethyl carbonate (DMC) in the electrolyte, LiFSI in the electrolyte accelerates the decomposition of DMC at high temperatures, leading to the generation of more gases (such as hydrogen). This severely limits the effect of LiFSI on improving the battery's high-temperature lifespan, posing a significant challenge to the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0109] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, a method for preparing the same, and an electrical device thereof. The long-term reliability of this lithium-ion secondary battery at high temperatures is significantly improved.

[0110] In some embodiments, a lithium-ion secondary battery is provided, comprising an electrolyte; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes cyclic carbonates and chain carbonates; the chain carbonate includes dimethyl carbonate (DMC); the electrolyte includes lithium bis(fluorosulfonyl)imide (LiFSI); the mass percentage of dimethyl carbonate in the non-aqueous solvent is denoted as F. DMCThe molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is denoted as C. LiFSI mol / L; (C LiFSI ×F DMC The value is relatively low; for example, the electrolyte satisfies 0 < (C). LiFSI ×F DMC )≤0.05.

[0111] By simultaneously adding DMC and LiFSI to the electrolyte and controlling the molar volume concentration (C) of LiFSI in the electrolyte, the method was successfully developed. LiFSI ) and the mass percentage of DMC in non-aqueous solvents (F DMC The product of (C) LiFSI ×F DMC With a relatively low value, the superposition effect of LiFSI and DMC can be synergistically controlled, which can better suppress the accelerated decomposition of DMC by LiFSI, which is conducive to better control of high-temperature gas generation. It can also play the role of LiFSI in participating in high-temperature film formation and suppressing interfacial side reactions, which is conducive to extending the high-temperature life of the battery. Based on the aforementioned synergistic effect, but not limited to the aforementioned theory, the long-term reliability of lithium-ion secondary batteries at high temperatures can be significantly improved.

[0112] In some embodiments, the chain carbonate includes dimethyl carbonate (DMC) and a second chain carbonate.

[0113] In this application, DMC is referred to as "first chain carbonate" and other types of chain carbonates other than DMC are referred to as "second chain carbonate".

[0114] In some embodiments, a lithium-ion secondary battery is provided, comprising an electrolyte; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes cyclic carbonates and chain carbonates; the chain carbonates include dimethyl carbonate (DMC), and further include a second chain carbonate; the electrolyte includes lithium bis(fluorosulfonyl)imide (LiFSI); further, (C LiFSI ×F DMC The value is relatively low; for example, the electrolyte satisfies 0 < (C). LiFSI ×F DMC )≤0.05.

[0115] Second-chain carbonates (such as DEC, EMC, etc.) have better high-temperature stability than DMC, and their high-temperature gas production is lower than that of DMC.

[0116] By simultaneously introducing DMC, second-chain carbonate, and LiFSI into the electrolyte, and controlling (C LiFSI ×F DMCWith a relatively low value, the superposition effect of LiFSI and DMC can be synergistically controlled, which can better suppress the accelerated decomposition of DMC by LiFSI, which is conducive to better control of high-temperature gas generation. It can also give full play to the role of LiFSI in high-temperature film formation and suppress interfacial side reactions, which is conducive to extending the high-temperature life of the battery. Furthermore, the introduction of a second chain carbonate with better stability can synergistically control the high-temperature gas generation of DMC. Based on the aforementioned synergistic effect, but not limited to the aforementioned theory, the long-term reliability of lithium-ion secondary batteries at high temperatures can be significantly improved.

[0117] In some embodiments, a lithium-ion secondary battery is provided, comprising an electrolyte; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes cyclic carbonates and chain carbonates; the chain carbonate includes dimethyl carbonate (DMC), 0 <L DMC ≤16%; the electrolyte includes lithium bis(fluorosulfonyl)imide (LiFSI); further, the electrolyte satisfies 0 < (C LiFSI ×F DMC )≤0.05. Where, L DMC This represents the mass percentage of dimethyl carbonate in the chain carbonate.

[0118] By simultaneously adding DMC and LiFSI to the electrolyte, the DMC content is controlled to be below a certain level, and the (C) content is controlled... LiFSI ×F DMC With a relatively low value, it can effectively suppress high-temperature gas production under the combined effect of LiFSI and DMC.

[0119] In some embodiments, the electrolyte includes LiFSI and vinylene carbonate (VC).

[0120] Ethylene carbonate (VC) can participate in the formation of a stable interfacial film at the negative electrode and is consumed earlier than the solvent. Utilizing the synergistic film-forming effect of LiFSI and VC, a more robust solid electrolyte interphase (SEI) film can be formed on the negative electrode surface, significantly improving the high-temperature performance of the battery and suppressing high-temperature gas generation.

[0121] In some embodiments, the chain carbonate includes DMC, the electrolyte includes LiFSI and vinylene carbonate (VC), and the electrolyte satisfies 0 < (C LiFSI ×F DMC )≤0.05.

[0122] In some embodiments, a lithium-ion secondary battery is provided, comprising an electrolyte; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive; the non-aqueous solvent includes cyclic carbonates and chain carbonates; the chain carbonate includes dimethyl carbonate (DMC); the electrolyte includes lithium bis(fluorosulfonyl)imide (LiFSI); the additive includes vinylene carbonate (VC); further, the electrolyte satisfies 0 < (C LiFSI ×F DMC )≤0.05.

[0123] It can synergistically control the superposition effect of LiFSI and DMC, effectively suppress the accelerated decomposition of DMC by LiFSI, and better control high-temperature gas generation. Furthermore, based on the synergistic film-forming effect of LiFSI and VC, it forms a robust solid electrolyte interphase (SEI) film, endowing the SEI film with excellent high-temperature stability, significantly suppressing interfacial side reactions, and achieving superior high-temperature lifetime. Based on the aforementioned synergistic effect, but not limited to the aforementioned theory, it can significantly improve the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0124] In some embodiments, a lithium-ion secondary battery is provided, comprising an electrolyte; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes cyclic carbonates and chain carbonates; the chain carbonates include dimethyl methacrylate (DMC), and further include chain carbonates different from DMC (i.e., also include a second chain carbonate); the electrolyte includes lithium bis(fluorosulfonyl)imide (LiFSI); the additives include vinylene carbonate (VC); furthermore, (C LiFSI ×F DMC The value is relatively low; for example, the electrolyte satisfies 0 < (C). LiFSI ×F DMC )≤0.05.

[0125] By simultaneously adding DMC, second-chain carbonate, LiFSI, and VC to the electrolyte, and controlling (C... LiFSI ×F DMC With relatively low values, the superposition effect of LiFSI and DMC can be synergistically controlled, effectively suppressing the accelerated decomposition of DMC by LiFSI and controlling high-temperature gas generation. Furthermore, based on the synergistic film-forming effect of LiFSI and VC, a robust solid electrolyte interphase (SEI) film is formed, endowing the SEI film with excellent high-temperature stability, significantly suppressing interfacial side reactions, and achieving better high-temperature lifetime. It also utilizes the characteristic that VC is preferentially consumed compared to the solvent and the more stable second-chain carbonate to synergistically suppress high-temperature gas generation of DMC. Based on the aforementioned synergistic effect, but not limited to the aforementioned theory, the long-term reliability of lithium-ion secondary batteries at high temperatures can be significantly improved.

[0126] In this application, unless otherwise specified, "high temperature" relating to battery application and / or performance can be greater than 30°C and less than or equal to 60°C, optionally greater than 30°C and less than or equal to 55°C, further optionally 35°C to 55°C, further optionally 40°C to 60°C, and even further optionally 45°C to 60°C, but is not limited thereto. "High temperature" relating to battery fast charging, storage, or cycling can also be any of the following temperatures or a range selected from any two of the following temperatures: 36°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc.

[0127] Unless otherwise specified in this application, "normal temperature" in relation to battery application and / or performance can be 20°C to 30°C, or optionally 20°C to 28°C, but is not limited to these. "High temperature" in relation to battery fast charging, storage, or cycling can also be any of the following temperatures or a range selected from any two of the following temperatures: 20°C, 22°C, 24°C, 25°C, 26°C, 28°C, 30°C, etc.

[0128] In some embodiments, a lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte, with a separator disposed between the positive and negative electrodes.

[0129] In this application, unless otherwise specified, the term "lithium-ion secondary battery" refers to a secondary battery in which the active ions include lithium ions, and "lithium-ion battery cell" refers to a battery cell in which the active ions include lithium ions. Typically, a lithium-ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. A separator is disposed between the positive and negative electrodes; the separator primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0130] In this application, unless otherwise specified, "electrode active material layer" includes at least one of the positive active material layer of the positive electrode sheet and the negative active material layer of the negative electrode sheet. Depending on the specific circumstances, the electrode active material layer may refer to either the positive active material layer or the negative active material layer. It is understood that the positive active material layer contains positive active material, and the negative active material layer contains negative active material. In this application, "electrode active material layer" may also be referred to as "active material layer," "positive active material layer" may also be referred to as "positive active layer," and "negative active material layer" may also be referred to as "negative active layer."

[0131] In this application, the terms "electrode sheet" and "electrode plate" have the same meaning and can be used interchangeably. An electrode sheet can be a positive electrode sheet or a negative electrode sheet, and the "active material" or "active substance" in the electrode sheet has the ability to reversibly insert and extract active ions.

[0132] In this application, the term "positive electrode sheet" includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material. The term "positive electrode active material" refers to a material used in a positive electrode sheet that is capable of reversibly extracting and inserting active ions.

[0133] In this application, unless otherwise specified, "positive electrode sheet" includes a positive current collector. A "positive current collector" refers to a structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive active layer is located on at least one side of the positive current collector, and may be located on one or both sides of the positive current collector.

[0134] In this application, the term "negative electrode sheet" includes a negative electrode active layer, which includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that is capable of reversibly inserting and de-inserting active ions.

[0135] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. A "negative electrode current collector" refers to a structure responsible for collecting and conducting electrons at the negative electrode. In the negative electrode sheet, the negative electrode active layer is located on at least one side of the negative electrode current collector, and may be located on one or both sides of the negative electrode current collector.

[0136] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0137] In a first aspect of this application, a lithium-ion secondary battery is provided, wherein the long-term reliability of the lithium-ion secondary battery at high temperatures is significantly improved.

[0138] In some embodiments of the first aspect of this application, a lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive and negative electrodes; the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises cyclic carbonates and chain carbonates; the chain carbonate comprises dimethyl carbonate (DMC, denoted as "first chain carbonate"), and further comprises a second chain carbonate, the second chain carbonate being a chain carbonate different from DMC; the electrolyte comprises lithium bis(fluorosulfonyl)imide (LiFSI); the electrolyte satisfies 0 < (C LiFSI ×F DMC )≤0.05; where the mass percentage of dimethyl carbonate in a non-aqueous solvent is denoted as F. DMC The molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is denoted as C. LiFSI mol / L.

[0139] In this application, DMC is referred to as "first chain carbonate" and other types of chain carbonates besides DMC are referred to as "second chain carbonate". In this application, the terms "first", "second", etc., in "first chain carbonate", "second chain carbonate", etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0140] In the lithium-ion secondary battery provided in this application, it is understood that the positive electrode and the negative electrode are wetted by the electrolyte.

[0141] In this application, unless otherwise specified, "non-aqueous solvent" means a solvent that is not water.

[0142] In this application, unless otherwise specified, "chain carbonate" refers to a chain compound having a *-OC(=O)-O-* structure, where each * independently represents a bonding site with a carbon atom.

[0143] In this application, unless otherwise specified, "cyclic carbonate" refers to a cyclic compound having a cyclic skeleton including a *-OC(=O)-O-* structure, where each * independently represents a bonding site with a cyclic carbon atom.

[0144] Unless otherwise stated in this application, "C" LiFSI "" refers to the numerical value of the molar volume concentration of LiFSI in the electrolyte, expressed in "mol / L".

[0145] In this application, “(C LiFSI ×F DMC The value of "( )" reflects the combined effect of LiFSI and DMC on the high-temperature performance of the battery. The higher the value, the stronger the combined effect.

[0146] By simultaneously introducing DMC (which can be denoted as the first chain carbonate), a chain carbonate different from DMC (which can be denoted as the second chain carbonate), and LiFSI into the electrolyte, and controlling (C... LiFSI ×F DMC With a relatively low value, the superposition effect of LiFSI and DMC can be synergistically controlled, effectively suppressing the accelerated decomposition of DMC by LiFSI, better controlling high-temperature gas generation, and forming a robust solid electrolyte interphase (SEI) film based on the film-forming effect of LiFSI, giving the SEI film excellent high-temperature stability, significantly suppressing interfacial side reactions, and achieving better high-temperature lifetime. Furthermore, a second-chain carbonate with better stability is introduced to synergistically control the high-temperature gas generation of DMC. Based on the aforementioned synergistic effect, but not limited to the aforementioned theory, the long-term reliability of lithium-ion secondary batteries at high temperatures can be significantly improved.

[0147] The types and concentrations of inorganic components in the electrolyte (which may include electrolyte salts and inorganic additives, and further may include LiFSI) can be tested with reference to relevant standards such as GB / T 34672-2017 General Rules for Determination of Chemical Reagents by Ion Chromatography, JY / T020-1996 General Rules for Ion Chromatographic Analysis, and GB / T6040-2019 General Rules for Infrared Spectroscopic Analysis, and the latest version of the standard method may be preferred. The types and contents of organic components in the electrolyte (including non-aqueous solvents and organic additives) can be tested with reference to relevant standards such as GB / T 9722-2023 General Rules for Gas Chromatography of Chemical Reagents.

[0148] Those skilled in the art can also identify the components of the electrolyte in a lithium-ion secondary battery using one or more of the following detection methods, including but not limited to: 1H NMR (1H NMR) spectroscopy. 1 Methods such as ¹H NMR, high-performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet spectroscopy are available. The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the characteristics of the sample. As a non-limiting example, FT-IR, ultraviolet spectroscopy, etc., can be used. 1 One or more of the following methods may be used to detect the types and contents of electrolyte components: ¹H NMR, mass spectrometry, MADI-TOF, etc., but not limited to these.

[0149] Without restriction, (C LiFSI ×F DMC The ) can be any of the following values ​​or a range selected from any two of the following values: 0.0002, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0. 012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.032, 0.034, 0.035, 0.036, 0.038, 0.04, 0.042, 0.044, 0.045, 0.046, 0.048, 0.05, etc. (C) LiFSI ×F DMCIt can also be selected from any of the following ranges: 0.0002~0.05, 0.0005~0.05, 0.001~0.05, 0.0025~0.05, 0.01~0.05, 0.0002~0.04, 0.0005~0.04, 0.001~0.04, 0.0025~0.04, 0.01~0.04, etc.

[0150] In some implementations, 0.0002 ≤ (C LiFSI ×F DMC )≤0.05.

[0151] In some implementations, 0.0005 ≤ (C LiFSI ×F DMC )≤0.04.

[0152] By (C LiFSI ×F DMC Controlling the temperature within the aforementioned range helps to better and more persistently suppress high-temperature gas generation, and more significantly improves the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0153] In some embodiments, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can be greater than or equal to 0.2 mol / L. In some embodiments, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can be less than or equal to 1 mol / L. In some embodiments, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.2 mol / L to 1 mol / L. Non-limitingly, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can also be any of the following values ​​or a range selected from any two of the following values: 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc. Non-limitingly, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can also be selected from any of the following ranges: 0.2 mol / L to 1 mol / L, 0.3 mol / L to 1 mol / L, 0.4 mol / L to 1 mol / L, 0.5 mol / L to 1 mol / L, 0.2 mol / L to 0.9 mol / L, 0.3 mol / L to 0.9 mol / L, 0.4 mol / L to 0.9 mol / L, 0.5 mol / L to 0.9 mol / L, 0.2 mol / L to 0.8 mol / L, 0.3 mol / L to 0.8 mol / L, 0.4 mol / L to 0.8 mol / L, 0.5 mol / L to 0.8 mol / L, etc.

[0154] By varying the molar volume concentration (C) of LiFSI in the electrolyte LiFSI Keeping the concentration of LiFSI (mol / L) within the aforementioned range helps to better leverage its role in extending the high-temperature lifespan of batteries.

[0155] In some embodiments, the mass percentage (F) of dimethyl carbonate in a non-aqueous solvent is... DMC Satisfy 0 <F DMC ≤20%.

[0156] In some implementations, 0 <F DMC ≤10%.

[0157] Without limitation, F DMC It can also be any of the following percentages or a range composed of any two of the following percentages: 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.25%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc. F DMC It can also be selected from any of the following ranges: 0.1%–20%, 0.1%–16%, 0.1%–15%, 0.1%–10%, 0.1%–6.25%, 0.1%–6%, 0.1%–5%, 0.5%–20%, 0.5%–16%, 0.5%–15%, 0.5%–10%, 0.5%–6.25%, 0.5%–6%, 0.5%–5%, 1%–20%, 1%–16%, 1%–15%, 1%–10%, 1%–6.25%, 1%–6%, 1%–5%, etc.

[0158] By measuring the mass percentage of DMC in a non-aqueous solvent (F... DMC Controlling the gas production at high temperatures within the aforementioned range is beneficial for reducing the high-temperature gas production of DMC.

[0159] In some embodiments, the second chain carbonate includes at least one of diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0160] In some embodiments, the chain carbonate includes DMC, and also includes at least one of DEC and EMC.

[0161] In some embodiments, the chain carbonate includes DEC and DMC. Non-limitingly, the sum of the mass percentages of DEC and DMC in a non-aqueous solvent can be 35% to 75%, optionally 35% to 60%, further optionally 38% to 60%, and can also be any of the following percentages or a range selected from any two of the following percentages: 35%, 38%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, etc.

[0162] In some embodiments, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than or equal to 0.2 mol / L. <F DMC ≤20%. C LiFSI and F DMC You can further select any suitable value or range described in the context.

[0163] In some exemplary embodiments, the molar volume concentration (Cl) of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.2 mol / L to 1 mol / L, and 0% ≤ F DMC ≤20%; optionally, Cl is 0.2mol / L to 1mol / L, and F is 0.1% ≤20%. DMC ≤16%; further optionally, Cl is 0.3mol / L to 1mol / L, and 1% ≤F DMC ≤20%.

[0164] In some exemplary embodiments, C1 is 0.2 mol / L to 1 mol / L, and F is 0.1% ≤ F. DMC ≤20%.

[0165] In some exemplary embodiments, C1 is 0.3 mol / L to 1 mol / L, and 1% ≤ F DMC ≤16%.

[0166] In some exemplary embodiments, C1 is 0.3 mol / L to 1 mol / L, and F is 0.1% ≤ F. DMC ≤16%.

[0167] In some exemplary embodiments, Cl is 0.3 mol / L to 0.8 mol / L, and 1% ≤ F DMC ≤10%.

[0168] In some exemplary embodiments, C1 is 0.3 mol / L to 1 mol / L, 0% <F DMC ≤5%.

[0169] By varying the molar volume concentration (C) of LiFSI in the electrolyte LiFSI (mol / L) and the mass percentage of DMC in non-aqueous solvents (F DMCBy controlling these parameters within the aforementioned range, it is beneficial to better and more persistently suppress high-temperature gas generation at high temperatures, and to more significantly improve the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0170] In some embodiments, the electrolyte salt further includes lithium hexafluorophosphate. Non-limitingly, the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate in the electrolyte salt may be greater than or equal to 0.05. In some embodiments, the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate in the electrolyte salt is greater than or equal to 0.1.

[0171] Non-limitingly, in the electrolyte salt, the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate can also be any of the following values, can be greater than or equal to any of the following values, and can be selected from a range consisting of any two of the following values: 0.05, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.75, 0.8, 1, 1.1, 1.2, 1.25, 1.3, 1.4, 1.5, 1.6, 1.75, 1.8, 1.9, 2, 2.25, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, etc. In the electrolyte salt, the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate can also be selected from any of the following ranges: 0.05–30, 0.1–20, etc.

[0172] LiFSI can function not only as a film-forming additive but also as an electrolyte salt. LiFSI exhibits better thermal stability and higher conductivity than lithium hexafluorophosphate (LiPF6), but the introduction of LiFSI into the battery system leads to more gas production compared to a pure LiPF6 system. When the electrolyte salt includes both LiFSI and LiPF6 (referred to as a "LiFSI+LiPF6" battery system), controlling the molar ratio of LiFSI to LiPF6 within the aforementioned range improves the long-term reliability of the "LiFSI+LiPF6" battery system at high temperatures; for example, it helps suppress accelerated capacity decay and rapid capacity drops at low state of equilibrium (SOH).

[0173] In some embodiments, the molar percentage of lithium bis(fluorosulfonyl)imide in the electrolyte salt can be 20% to 100%, optionally 50% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc.

[0174] By controlling the molar percentage of LiFSI in the electrolyte salt within the aforementioned range, it is beneficial to improve the long-term reliability of the "LiFSI+LiPF6" battery system at high temperatures.

[0175] In some embodiments, the chain carbonate includes DMC, and also includes one or both of diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0176] In this application, the mass percentage of diethyl carbonate (DEC) in the chain carbonate is denoted as L. DEC The mass percentage of dimethyl carbonate (DMC) in chain carbonates is denoted as L. DMC When the cyclic carbonate includes ethylene carbonate (EC), the mass percentage of ethylene carbonate (EC) in the cyclic carbonate is denoted as H. EC When the chain carbonate includes DEC and the cyclic carbonate includes EC, the mass ratio of diethyl carbonate to ethylene carbonate in the electrolyte is denoted as R. DEC / EC .

[0177] In some implementations, L DEC ≥40%, optionally, 40% ≤L DEC ≤75%, and optionally, 50% ≤L DEC ≤75%. L DEC It can also be any of the following percentages, or greater than or equal to any of the following percentages, or a range consisting of any two of the following percentages: 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, etc.

[0178] In some embodiments, the chain carbonate includes DEC and DMC. Non-limitingly, the sum of the mass percentages of DEC and DMC in the chain carbonate may be greater than or equal to 50%, optionally between 50% and 90%, and may also be any of the following percentages or a range selected from any two of the following percentages: 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc.

[0179] In some embodiments, the chain carbonate includes EMC. Without limitation, the mass percentage of EMC in the chain carbonate can be from 10% to 50%, and can also be any of the following percentages or a range selected from any two of the following percentages: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0180] In some embodiments, the chain carbonates include DEC, EMC, and DMC. Non-limitingly, the sum of the mass percentages of the chain carbonates can be 90% to 100%, optionally 95% to 100%.

[0181] In some embodiments, the cyclic carbonate includes one or both of ethylene carbonate (EC) and propylene carbonate (PC).

[0182] In some embodiments, cyclic carbonates include ethylene carbonate.

[0183] Without limitation, 50% ≤ H EC ≤100%, optionally, 60% ≤H EC ≤100%, and optionally, 80% ≤H EC ≤100%. H EC It can also be any of the following percentages or a range consisting of any two of the following percentages: 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc.

[0184] Without limitation, R DEC / EC ≥0.8, optionally, 0.8≤R DEC / EC ≤3.5, and further optionally, 1≤R DEC / EC ≤2.5; alternatively, 0.8≤R DEC / EC ≤2, and further optionally, 1≤R DEC / EC ≤2. R DEC / EC It can also be any of the following values ​​or a range consisting of any two of the following values: 0.8, 0.825, 0.85, 0.9, 0.95, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.1, 3.2, 3.3, 10 / 3, 3.4, 3.5, etc.

[0185] In some implementations, 0 <L DMC ≤25%, optionally, 0 <L DMC ≤20%, and optionally, 0 <L DMC ≤16%, and optionally, 1% ≤L DMC ≤10%, and optionally, 5% ≤L DMC ≤10%.

[0186] Without limitation, L DMC It can also be any of the following percentages, or less than or equal to any of the following percentages, or a range consisting of any two of the following percentages: 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 25%, etc.

[0187] In some embodiments, the chain carbonates include diethyl carbonate (DEC) and dimethyl carbonate (DMC), further, L DEC ≥40%, optionally, 40% ≤L DEC ≤75%, optionally, 50% ≤L DEC ≤75%.

[0188] In some embodiments, the chain carbonates include diethyl carbonate (DEC) and dimethyl carbonate (DMC), further, 0 <L DMC ≤25%, optionally, 0 <L DMC ≤20%, and optionally, 0 <L DMC ≤16%, and optionally, 5% ≤L DMC ≤10%.

[0189] In some implementations, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0190] (a1) Chain carbonates include one or both of diethyl carbonate (DEC) and ethyl methyl carbonate (EMC); without limitation, L DEC ≥40%, optionally, 40% ≤L DEC ≤75%, further, optionally, 50% ≤L DEC ≤75%;

[0191] (a2) Cyclic carbonates include one or both of ethylene carbonate (EC) and propylene carbonate (PC); non-limitingly, 50% ≤ H EC ≤100%, optionally, 60% ≤H EC ≤100%;

[0192] (a3)0 <L DMC ≤25%, optionally, 0 <L DMC ≤20%, and optionally, 0 <L DMC ≤16%, and optionally, 1% ≤L DMC ≤10%, and optionally, 5% ≤L DMC ≤10%;

[0193] (a4) Cyclic carbonates include ethylene carbonate; without limitation, R DEC / EC ≥0.8, optionally, 0.8≤R DEC / EC ≤3.5, and further optionally, 1≤R DEC / EC ≤2.5.

[0194] In some implementations, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0195] (a1')50%≤L DEC ≤75%;

[0196] (a2')60%≤H EC ≤100%;

[0197] (a3')0 <L DMC ≤16%, optionally, 5% ≤L DMC ≤10%;

[0198] (a4')1≤R DEC / EC ≤2.

[0199] Second-chain carbonates (such as DEC, EC, etc.) and cyclic carbonates (such as EC, PC, etc.) exhibit better stability at high temperatures than DMC.

[0200] By controlling the mass percentage (L) of diethyl carbonate in the chain carbonate... DEC ), the mass percentage of ethylene carbonate in cyclic carbonates (H EC ), the mass percentage of dimethyl carbonate in chain carbonates (L) DMC One or more parameters in the above range are beneficial to improving the high-temperature performance of the battery and to significantly improving the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0201] By controlling R DEC / EC Within the aforementioned range, it is beneficial to control the increase in system viscosity caused by EC, and to take into account the room temperature performance of the battery.

[0202] In some implementations, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0203] (b1) The mass percentage of diethyl carbonate in a non-aqueous solvent is 20% to 65%, optionally 25% to 50%, and may also be any of the following percentages or a range selected from any two of the following percentages: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc.

[0204] (b2) The mass percentage of ethylene carbonate in a non-aqueous solvent is 15% to 50%, optionally 25% to 40%, and may also be any of the following percentages or a range selected from any two of the following percentages: 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0205] (b3) The chain carbonate in a non-aqueous solvent is 50% to 75% by mass, optionally 55% to 75%, and may also be any of the following percentages or a range selected from any two of the following percentages: 50%, 55%, 60%, 65%, 70%, 75%, etc.

[0206] (b4) The cyclic carbonate in a non-aqueous solvent is 25% to 50% by mass, optionally 25% to 45%, and may also be any of the following percentages or a range selected from any two of the following percentages: 25%, 30%, 35%, 40%, 45%, 50%, 55%;

[0207] (b5) The chain carbonates also include ethyl methyl carbonate; without limitation, the mass percentage of ethyl methyl carbonate in a non-aqueous solvent may be 15% to 35%, optionally 15% to 30%, or any of the following percentages or a range consisting of any two of the following percentages: 15%, 20%, 25%, 30%, 35%, etc.

[0208] In some embodiments, the chain carbonate also includes ethyl methyl carbonate.

[0209] In some embodiments, the chain carbonate includes diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate. Non-limitingly, the sum of the mass percentages of diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate in a non-aqueous solvent can be 50% to 75%, optionally 55% to 75%, or any of the following percentages or a range selected from any two of the following percentages: 50%, 55%, 60%, 65%, 70%, 75%, etc.

[0210] In some implementations, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0211] (b1') The mass percentage of diethyl carbonate in a non-aqueous solvent is 25% to 50%;

[0212] (b2') The mass percentage of ethylene carbonate in a non-aqueous solvent is 25% to 40%;

[0213] (b3') The mass percentage of the chain carbonate in a non-aqueous solvent is 55% to 75%;

[0214] (b4') The mass percentage of cyclic carbonates in non-aqueous solvents is 25% to 45%.

[0215] By controlling the mass percentage (F) of diethyl carbonate in a non-aqueous solvent DEC ), the mass percentage of ethylene carbonate in non-aqueous solvents (FEC ), the mass percentage of chain carbonates in non-aqueous solvents (F LC ), the mass percentage of cyclic carbonates in non-aqueous solvents (F CC Controlling one or more parameters in the electrolyte within the aforementioned range helps to better control the high-temperature gas generation of non-aqueous solvents in the electrolyte, and more significantly improves the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0216] In some embodiments, the additive includes vinylene carbonate (VC). The mass percentage of vinylene carbonate in the electrolyte is denoted as F. VC In some of these implementations, F VC ≥2%.

[0217] Ethylene carbonate (VC) can participate in the formation of a stable interfacial film at the negative electrode and can be consumed earlier than the solvent. By introducing VC into the electrolyte, it is beneficial to suppress high-temperature interfacial side reactions, suppress high-temperature gas generation, slow down capacity decay at high temperatures, and improve the long-term reliability of the battery at high temperatures.

[0218] By controlling the mass percentage of VC in the electrolyte (F VC Within the aforementioned range, it can effectively suppress high-temperature gas generation and extend high-temperature lifespan, thereby improving the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0219] In some implementations, F VC ≤12%.

[0220] Without limitation, F VC It can also be any of the following percentages or a range composed of any two of the following percentages: 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, etc. F VC It can also be selected from any of the following ranges: 2%–12%, 2%–10%, 2%–8%, 2.5%–12%, 2.5%–10%, 2.5%–8%, 3%–12%, 3%–10%, 3%–8%, etc.

[0221] The mass percentage of vinylene carbonate (VC) in the electrolyte can be controlled by the amount of solution injected before formation, and can also be selectively replenished after formation to adjust the mass percentage of VC in the electrolyte.

[0222] In some implementations, 2% ≤ F VC ≤12%.

[0223] In some implementations, 2.5% ≤ FVC ≤10%.

[0224] In some implementations, 3% ≤ F VC ≤10%.

[0225] By controlling the mass percentage of VC in the electrolyte (F VC Within the aforementioned range, while better suppressing high-temperature interface side reactions and high-temperature gas generation, it also helps to better control the internal resistance of the cell, which is beneficial to improving the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0226] In some embodiments, the positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, and the positive electrode active material includes a lithium iron phosphate (LFP) positive electrode material. Non-limitingly, the mass percentage of the LFP positive electrode material in the positive electrode active material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0227] In this application, unless otherwise specified, "lithium iron phosphate cathode material" refers to a class of cathode active materials containing lithium iron phosphate. Unless otherwise specified, "lithium iron phosphate cathode material" may have an olivine structure.

[0228] By incorporating lithium iron phosphate (LFP) cathode materials into the positive electrode active material, the structural stability of the positive electrode active material can be improved, thus extending the high-temperature lifespan of lithium-ion secondary batteries. Furthermore, controlling the mass percentage of LFP cathode materials within the aforementioned range further enhances the ability to extend the high-temperature lifespan of lithium-ion secondary batteries.

[0229] Without limitation, lithium iron phosphate cathode materials may include at least one of lithium iron phosphate and lithium iron phosphate-carbon composites.

[0230] In some embodiments, the composite material of lithium iron phosphate and carbon is carbon-coated lithium iron phosphate.

[0231] In this application, the term "carbon-coated lithium iron phosphate" includes lithium iron phosphate and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate.

[0232] In some embodiments, lithium iron phosphate cathode materials include carbon-coated lithium iron phosphate cathode materials.

[0233] Non-limitingly, the mass percentage of carbon-coated lithium iron phosphate cathode material in lithium iron phosphate cathode material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0234] Non-limitingly, the mass percentage of carbon-coated lithium iron phosphate cathode material in the cathode active material can be 80% to 100%, optionally 90% to 100%, or any of the following percentages or a range selected from any two of the following percentages: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0235] Unless otherwise specified, "carbon-coated lithium iron phosphate cathode material" includes a cathode active body and a carbon coating layer located on at least a portion of the surface of the cathode active body, wherein the cathode active body includes lithium iron phosphate. When the cathode active body is lithium iron phosphate, the carbon-coated lithium iron phosphate cathode material is carbon-coated lithium iron phosphate.

[0236] In some embodiments, the lithium iron phosphate cathode material includes a cathode active body and a carbon coating layer located on at least a portion of the surface of the cathode active body, wherein the cathode active body includes lithium iron phosphate. In this case, the lithium iron phosphate cathode material is a carbon-coated lithium iron phosphate cathode material.

[0237] Applying a carbon coating to the surface of lithium iron phosphate cathode materials can improve the conductivity and lithium-ion diffusion capacity of the material surface, thereby reducing the internal resistance of the battery.

[0238] Non-limitingly, in carbon-coated lithium iron phosphate cathode materials, the carbon coating layer may include one or more of amorphous carbon, soft carbon, and hard carbon. Non-limitingly, in carbon-coated lithium iron phosphate cathode materials, the carbon coating layer may be a soft carbon coating layer. "Soft carbon coating layer" refers to a coating layer mainly composed of soft carbon, where the mass percentage of soft carbon in the soft carbon coating layer can be close to 100%.

[0239] "Soft carbon" and "hard carbon" have well-known meanings in the art. Soft carbon can be graphitized by further high-temperature treatment, while hard carbon is difficult to graphitize even with further high-temperature treatment. In this application, unless otherwise specified, "amorphous carbon" refers to transitional carbon materials with a very low degree of graphitization and crystallization, which are approximately amorphous (or have no fixed shape and periodic structural regularity).

[0240] In some embodiments, the carbon coating layer in carbon-coated lithium iron phosphate includes soft carbon. In some embodiments, the carbon coating layer in carbon-coated lithium iron phosphate is a soft carbon coating layer, in which case the carbon-coated lithium iron phosphate may be referred to as soft carbon-coated lithium iron phosphate. The mass percentage of the soft carbon coating layer or the soft carbon in the soft carbon coating layer in the carbon-coated lithium iron phosphate may be 1% to 1.5%, optionally 1.4% to 1.5%, but is not limited thereto.

[0241] The elemental composition of the positive electrode active material in the positive electrode active layer can be analyzed using methods known in the art, including but not limited to the following: inductively coupled plasma atomic emission spectrometry (ICP), X-ray diffraction (XRD), single-crystal X-ray diffraction (SCXRD), and energy dispersive spectroscopy (EDS). The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the sample characteristics. ICP can be used for quantitative analysis of the component content in the positive electrode active material.

[0242] The detection of positive electrode active material in the positive electrode active layer can be carried out by disassembling the battery after it is fully discharged, removing the positive electrode plate, scraping off the material of the positive electrode active layer, and using elemental analysis methods such as inductively coupled plasma (ICP) spectroscopy to test and analyze the types and proportions of elements, thereby confirming the elemental composition and chemical formula of the positive electrode active material.

[0243] In some embodiments, the negative electrode sheet includes a negative electrode active layer, which includes a negative electrode active material; the negative electrode active material includes one or more of graphite (referring to uncoated graphite) and coated graphite materials; wherein, the coated graphite material includes a graphite body and a hard carbon coating layer located on at least a portion of the surface of the graphite body.

[0244] Graphite can include one or more of natural graphite and synthetic graphite.

[0245] In some embodiments, the sum of the mass percentages of graphite and coated graphite materials in the negative electrode active material is 80% to 100%, optionally 90% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0246] In this application, "coated graphite material" includes an ink body and a coating layer located on at least a portion of the surface of the graphite body. The coating layer may include a carbon coating layer (which may also be referred to as "coated graphite material"), and further, the coating layer may include a hard carbon coating layer (which may also be referred to as "hard carbon coated graphite material"). The "graphite body" is composed of graphite. The "hard carbon coating layer" mainly comprises hard carbon. "Hard carbon" has a well-known meaning in the art. Unless otherwise specified, the mass percentage of hard carbon in the hard carbon coating layer may be greater than or equal to 80%, and may be greater than or equal to any of the following percentages, or selected from any of the following percentages and 100%, or selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, etc. It is understood that "coated graphite material" is a graphite-based material. In this application, negative electrode active materials containing graphite components in the particle body are referred to as "graphite-based materials". It can be understood that coated graphite materials and hard carbon coated graphite materials both belong to graphite-based materials.

[0247] Unless otherwise stated in this application, "hard carbon coated graphite material" includes a graphite body and a hard carbon coating layer located on at least a portion of the surface of the graphite body.

[0248] By controlling one or more of the negative electrode active materials, including graphite and coated graphite materials, it is beneficial to better control the volume expansion and contraction changes of the negative electrode active materials, and to ensure that the negative electrode active materials still have good structural stability during long-term cycling and / or storage at high temperatures.

[0249] When the graphite-based material in the negative electrode active material includes coated graphite material, the hard carbon coating layer is beneficial to improving the long-term structural stability of the graphite-based material at high temperatures.

[0250] By controlling the mass percentage of coated graphite material in the negative electrode active material within the aforementioned range, it is beneficial to improve the long-term structural stability of the negative electrode active material at high temperatures and to better improve the long-term reliability of lithium-ion secondary batteries at high temperatures.

[0251] In some embodiments, the mass percentage of hard carbon-coated graphite material in the negative electrode active material is 80% to 100%, optionally 90% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0252] In this application, the test sample of the "negative electrode active material" in the negative electrode sheet of a lithium-ion secondary battery can be obtained by disassembling the battery, removing the negative electrode sheet, and extracting the negative electrode active material from the negative electrode active layer of the negative electrode sheet using methods such as solvent washing (e.g., soaking and cleaning with dimethyl carbonate), ultrasonic dispersion, centrifugation, and fractional sedimentation. The extracted powder sample is then dried to obtain a powder sample. The obtained powder sample can be used for laser particle size analysis or other tests.

[0253] In some embodiments, the positive electrode active material includes a positive electrode active body and a coating layer located on the positive electrode active body.

[0254] In this application, for negative or positive electrode active materials including a coating layer (examples of which include a carbon coating layer), particle cross-sections can be obtained by particle cutting using methods such as FIB (Focused Ion Beam) or CP (Ion Beam Cross-Section Polishing). The cross-sectional morphology of the particles is then observed under TEM (Transmission Electron Microscopy, such as JEM-F200, Thermo Scientific-Talos F200S G2, etc.). A clear boundary can be observed at the coating interface. Based on the TEM image, the coating layer thickness and average thickness at multiple locations within a single particle can be analyzed and calculated. The average thickness of the coating layer in the coated material is then calculated based on the average coating layer thickness of multiple particles. For a single particle, the number of sampling points for analyzing its average coating layer thickness can be greater than or equal to 5, and further greater than or equal to 10; the number of particles being counted can be greater than or equal to 3, and further greater than or equal to 5. By combining one or more methods such as energy dispersive spectroscopy (EDS) analysis and Raman spectroscopy, the types of substances in the coating layer and the negative electrode active body can be identified, or the types of substances in the coating layer and the positive electrode active body can be identified.

[0255] In this application, taking a "hard carbon coating" as an example, the chemical composition of the hard carbon coating can be confirmed using conventional methods in the art for testing the crystalline morphology of carbon materials. For example, Raman spectroscopy can be used for testing and analysis, based on the characteristic peak information of the carbon composition in the spectrum (such as the intensity ratio of the D peak to the G peak, I...). D / G The analysis determined whether the coating layer contained hard carbon. The D and G peaks are Raman characteristic peaks of carbon atom crystals. The D peak represents defects in the carbon atom crystal; the more defects, the greater the intensity of the D peak. The G peak represents the in-plane stretching vibration of carbon atom sp2 hybridization; the intensity of the G peak reflects the content of graphitized (layered structure) regions. As the degree of carbon atom disorder increases, the intensity ratio of the D peak to the G peak also increases. The Raman spectra of specific structural layers of the tested particle can also be compared. D / G Standard Raman spectrum of graphite I D / G The differences between them are used to determine whether the structural layer contains hard carbon.

[0256] The following is a description of the positive electrode sheet.

[0257] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0258] Without limitation, the weight percentage of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80 wt%, further greater than or equal to 90 wt%, and even further greater than or equal to 92 wt%.

[0259] As a non-limiting example, the positive current collector has two surfaces that are opposite to each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0260] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. In the positive electrode current collector, 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. In the positive electrode current collector, the composite current collector may be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limitingly, in the positive electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0261] The types of positive electrode active materials in the positive electrode sheet can be referred to the description in the context of this application. Non-limitingly, other types of positive electrode active materials may also be introduced. The positive electrode active material may include lithium transition metal oxide (LiMe) positive electrode materials, wherein the mass percentage of LiMe in the positive electrode active material may be less than or equal to 20%, optionally less than or equal to 10%. "LiMe" refers to a positive electrode active material containing lithium, transition metal, and oxygen. Therefore, LiMe includes non-lithium metal elements, and the non-lithium metal elements include transition metal elements. Non-limitingly, in LiMe, the molar percentage of transition metal elements relative to non-lithium metal elements may be 90% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc. Unless otherwise specified, “non-lithium metal element” refers to a metal element that is not lithium (Li).

[0262] Non-limiting examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include 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 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.80 Co 0.15 Al 0.05 O2.

[0263] In some embodiments, the lithium transition metal oxide cathode material includes a ternary cathode material, which may be selected as a ternary cathode material. In this application, the "ternary cathode material" is composed of Li, nickel, cobalt, M2, and oxygen; wherein, M2 can be manganese or aluminum. When M2 is manganese (Mn), the ternary cathode material is lithium nickel cobalt manganese oxide, which can be denoted as NCM; when M2 is aluminum (Al), the ternary cathode material is lithium nickel cobalt aluminum oxide, which can be denoted as NCA.

[0264] In some embodiments, examples of lithium transition metal oxides may include, but are not limited to, one or more of the following: NCM ternary cathode materials, lithium cobalt oxide (LCO), Li2O2, lithium-rich materials (such as lithium-rich nickel oxide), lithium manganese oxide (LMO), lithium nickel oxide (LNO), and lithium vanadate (LVO).

[0265] Other types of positive electrode active materials may also include other types of lithium phosphates with an olivine structure. Non-limiting examples include, but are not limited to, one or more of lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. An example of lithium manganese phosphate is LiMnPO4.

[0266] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the Li content can be the initial state of the material or a non-initial state after charge-discharge cycles. When the positive electrode active material is applied to the positive electrode in a battery system, the Li content in the positive electrode active material at the positive electrode will usually change after charge-discharge cycles. The Li content can be measured in atomic molar content, but is not limited to this. Regarding "Li content is the initial state of the material," the initial state of the material refers to the state before it is formed into the positive electrode active layer. It is understood that new materials or substances obtained by appropriately modifying the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to an acceptable modification method for the positive electrode active material, and non-limiting examples include one or more of coating modification and doping modification.

[0267] In the exemplary description of the positive electrode active material in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the atomic molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in atomic molar content, but is not limited to this.

[0268] In some embodiments, the positive electrode active layer optionally includes a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Typically, the binder may constitute 0–10 wt% of the weight of the positive electrode active layer, more commonly 0–8 wt%, and even more commonly 1 wt%–5 wt%, based on the total weight of the positive electrode active layer.

[0269] In some embodiments, the positive electrode active layer optionally includes a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typically, the weight percentage of the conductive agent in the positive electrode active layer can be 0–10 wt%, more commonly 0–8 wt%, and even more commonly 0–5 wt%, based on the total weight of the positive electrode active layer.

[0270] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated onto at least one surface of the positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The solvent in the positive electrode slurry can be, but is not limited to, any of the solvents described in the foregoing embodiments, for example, it can include N-methylpyrrolidone (NMP), and more specifically, NMP. The surface of the positive current collector coated with the positive electrode slurry can be a single surface of the positive current collector or both surfaces of the positive current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating areal density (based on dry weight, minus solvent) can also be (0.1~0.5) g / 1540.25mm. 2 The optional value is (0.2~0.4)g / 1540.25mm. 2 However, this is not the only possibility. The compaction density of the positive electrode sheet can be 2.0 g / cm³. 3 ~2.8g / cm 3 2.3g / cm³ is an option. 3 ~2.75g / cm 3 .

[0271] The term "compacted density" as used in this application has a meaning well-known in the art and is one of the reference indicators for material energy density. In this application, unless otherwise specified, the compacted density of an electrode sheet refers to the ratio of the mass of the electrode active layer to its volume. The compacted density of a positive electrode sheet refers to the ratio of the mass of the positive active layer to its volume, and the compacted density of a negative electrode sheet refers to the ratio of the mass of the negative active layer to its volume.

[0272] The following is a description of the negative electrode plate.

[0273] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0274] Without limitation, the weight percentage of the negative electrode active material in the negative electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0275] As a non-limiting example, the negative electrode current collector has two surfaces that are opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0276] 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. In the negative electrode current collector, 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. In the negative electrode current collector, the composite current collector may be formed by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limitingly, in the negative electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0277] The types of negative electrode active materials in the negative electrode sheet can be found in the description within the context of this application. Non-limitingly, other types of negative electrode active materials may also be introduced into the negative electrode active material. These negative electrode active materials may be used alone or in combination of two or more, as long as it does not affect the achievement of long-term reliability at high temperatures. Exemplarily, the negative electrode active material may include silicon-based materials. Non-limitingly, silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. In some embodiments, the mass percentage of silicon-based materials in the negative electrode active material is 0% to 10%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0278] In some embodiments, the negative electrode active layer optionally includes a binder. Non-limitingly, the binder may include one or more 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). Non-limitingly, the weight percentage of the binder in the negative electrode active layer may be 0 wt% to 20 wt%, more further 0 wt% to 10 wt%, even further 0 to 5 wt%, even further 1 wt% to 5 wt%, and even more preferably 1 wt% to 3 wt%.

[0279] In some embodiments, the negative electrode active layer optionally includes a conductive agent. Non-limitingly, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Non-limitingly, the weight percentage of the conductive agent in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, and even more preferably 0 wt% to 5 wt%.

[0280] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the weight percentage of other additives in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, even more preferably 0 wt% to 5 wt%, even more preferably 0 wt% to 3 wt%, and even more preferably 0 wt% to 2 wt%.

[0281] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry. Further, the negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30wt% to 70wt%, optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, optionally 3000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating surface density (excluding solvent) can be 75 g / m² on a dry weight basis. 2 ~220g / m 2 The optional value is (0.12~0.2)g / 1540.25mm. 2 Based on the surface density of the coating on one side, the compacted density of the negative electrode sheet can be 1.0 g / cm³. 3 ~2.0g / cm 3 1.0g / cm can be selected. 3 ~1.85g / cm 3 .

[0282] The electrolyte is described below as an example.

[0283] The electrolyte serves to conduct ions between the positive and negative electrodes. The electrolyte is a non-aqueous electrolyte. It includes electrolyte salts and non-aqueous solvents.

[0284] In some embodiments, the electrolyte salt includes an electrolyte lithium salt, and more particularly, it can be an electrolyte lithium salt. The types of electrolyte salts can be seen in the context of this application. Non-limitingly, other types of electrolyte salts may also be introduced into the electrolyte.

[0285] In addition, other types of electrolyte lithium salts may include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0286] In some embodiments, the molar volume concentration of the electrolyte salt in the electrolyte is typically 0.2 mol / L to 2 mol / L, optionally 0.5 mol / L to 1.5 mol / L, and further optionally 0.7 mol / L to 1.2 mol / L. It can also be any of the following concentrations or a range selected from any two of the following concentrations: 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, etc.

[0287] The types and amounts of non-aqueous solvents in the electrolyte can be found in the context of this application.

[0288] The electrolyte includes additives. The types of additives are described in the context of this application. Other types of additives may also be included. Examples of other types of additives may include, but are not limited to, one or more of the following: FEC (fluoroethylene carbonate), MMDS (methylene disulfonate), TMP (trimethyl phosphate), ethylene sulfate (DTD), tris(trimethylsilyl) phosphite (TMSP), propylene sulfonate lactone (PST), butyl sulfonate lactone (BS), propylene sulfite (PS), vinyl ethylene carbonate (VEC), trithio(trimethylsilane) phosphate, tris(trimethylsilane) borate, adiponitrile, succinic anhydride, and 1,3,6-hexamethylenetrionitrile.

[0289] The following is an exemplary description of the separator membrane.

[0290] In some embodiments, the lithium-ion secondary 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.

[0291] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0292] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 6 μm to 20 μm.

[0293] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0294] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0295] In some embodiments, the outer packaging of the lithium-ion secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion secondary battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0296] A lithium-ion secondary battery includes at least one battery cell. A lithium-ion secondary battery may include one or more battery cells.

[0297] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy. Typically, a cell battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator is positioned between the positive and negative electrodes; its primary function is to prevent short circuits between the positive and negative electrodes while allowing ions to pass through.

[0298] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0299] In some embodiments, referring to FIG2, the outer packaging may include a battery casing 51 and a cover plate 53. The battery casing 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 battery casing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into electrode assemblies 52 by a winding process or a stacking process. The electrode assemblies 52 are encapsulated within the receiving cavity. The electrode assemblies 52 are immersed in an electrolyte. The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs. In some embodiments, the electrolyte injection coefficient is greater than or equal to 1.6 g / Ah.

[0300] The lithium-ion secondary battery can be a battery device 4 or a battery pack 1.

[0301] The battery device includes at least one battery cell. The number of battery cells in the battery device can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery device.

[0302] Figure 3 shows a battery device 4 as an example. Referring to Figure 3, in the battery device 4, multiple battery cells 5 can be arranged sequentially along the length of the battery device 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple battery cells 5 can be fixed in place by fasteners.

[0303] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0304] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0305] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery compartment and multiple battery devices 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, the upper compartment 2 covering the lower compartment 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery compartment.

[0306] In a second aspect of this application, a method for preparing a lithium-ion secondary battery is provided, which can be used to prepare the lithium-ion secondary battery of the first aspect of this application.

[0307] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps: placing an electrode assembly including a positive electrode, a separator and a negative electrode in a battery casing, injecting an electrolyte into the battery casing, and allowing it to stand to allow the electrolyte to wet the electrode assembly, thereby forming the battery.

[0308] The definitions of positive electrode, negative electrode, and electrolyte can be found in the context of this application.

[0309] In some embodiments of the second aspect of this application, a method for preparing a lithium-ion secondary battery is provided, comprising the following steps:

[0310] S100: An electrode assembly including a positive electrode, a separator, and a negative electrode is placed inside a battery casing; wherein a separator is provided between the positive electrode and the negative electrode.

[0311] S200: Injecting an electrolyte into the battery casing; wherein the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent includes cyclic carbonates and chain carbonates; the chain carbonates include dimethyl carbonate, and also include chain carbonates different from dimethyl carbonate; the electrolyte includes lithium bis(fluorosulfonyl)imide; the mass percentage of dimethyl carbonate in the non-aqueous solvent is denoted as F. DMC The molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is denoted as C. LiFSI mol / L; the electrolyte solution satisfies 0 < (C LiFSI ×F DMC ≤0.05;

[0312] S300: Static soaking; and

[0313] S400: Formation.

[0314] In some embodiments, in step 200, after injecting electrolyte into the battery casing, a lithium-ion secondary battery assembly is obtained.

[0315] In this application, the concentrations of additives and electrolyte salts involved in "injecting electrolyte into the battery casing" correspond to the "initial concentration," which can be interpreted as the initial mass percentage of the additives in the electrolyte and the initial molar volume concentration of the electrolyte salts in the electrolyte, respectively. For the types of electrolyte salts in the electrolyte of lithium-ion secondary battery components, please refer to the first aspect of this application. After formation treatment, the mass percentage of electrolyte salts in the electrolyte may change.

[0316] Non-limiting, the formation temperature can be 45°C, but is not limited to this. In some embodiments, the formation can be carried out by a method including, but not limited to, the following steps: charging at 0.05C for 5 hours, letting stand for 10 minutes; formation complete.

[0317] In lithium-ion secondary battery modules, the material composition and dimensions of the positive electrode, negative electrode, and separator can be found in the first aspect of this application. The dimensions of the positive electrode, negative electrode, and separator in the lithium-ion secondary battery module may differ somewhat from those in the lithium-ion secondary battery of the first aspect.

[0318] In some embodiments, the lithium-ion secondary battery described in the first aspect of this application is prepared.

[0319] Those skilled in the art will understand that the content of some additive components in the electrolyte may change after formation treatment. As a non-limiting example, for instance, the content of some film-forming additive components may decrease due to their participation in the formation of the solid electrolyte interface film of the positive and / or negative electrodes. As a non-limiting example, the content of VC in the electrolyte is typically reduced after formation treatment compared to the electrolyte before formation treatment. Optionally, replenishment may be performed after formation to adjust the additive content in the electrolyte.

[0320] In some embodiments, the types and amounts of electrolyte salts and additives in the electrolyte of the prepared lithium-ion secondary battery can be as described in the first aspect of this application.

[0321] In some embodiments of the third aspect of this application, an electrical device is provided, which includes the lithium-ion secondary battery described in the first aspect of this application.

[0322] Electrical devices that include the aforementioned lithium-ion secondary batteries can have the advantages and benefits of the aforementioned lithium-ion secondary batteries.

[0323] In some embodiments, the electrical device includes a lithium-ion secondary battery according to any of the embodiments provided in this application.

[0324] Lithium-ion secondary batteries can be used as a power source for electrical devices or as an energy storage unit for electrical devices. Electrical devices can include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can include, for example, mobile phones and laptops; electric vehicles can include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, power tools, etc., but are not limited to these. This type of electrical device can also be applied to military equipment, aerospace, and other fields, as well as to energy storage power systems such as hydroelectric, thermal, wind, and solar power plants.

[0325] As an electrical device, lithium-ion rechargeable batteries can be selected according to its usage requirements.

[0326] Figure 6 shows an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the lithium-ion secondary battery for this electrical device, a battery device or battery pack can be used.

[0327] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a lithium-ion rechargeable battery as their power source.

[0328] The following describes some embodiments of this application. The described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application and its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0329] Unless otherwise specified in the examples, the procedures described above, or those described in the literature in this field, or those described in the product instructions, shall be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, or products that can be synthesized using conventional methods from commercially available products.

[0330] In the following examples, room temperature refers to 20°C to 30°C.

[0331] I. Preparation of Lithium-ion Secondary Batteries

[0332] In Table 1, the initial mass percentages of DEC, EMC, DMC, EC, and PC in non-aqueous solvents are respectively compared with the corresponding concentrations F in the resulting lithium-ion secondary batteries. DEC F EMC F DMC F EC and F PC The initial concentration of LiFSI is close to that of C in the resulting lithium-ion secondary battery. LiFSI The mol / L values ​​are close.

[0333] Example 1.

[0334] (1) Positive electrode plate

[0335] A positive electrode slurry with a solid content of 65 wt% was prepared by mixing the positive electrode active material (carbon-coated LiFePO4, denoted as carbon-coated LFP), the conductive agent (acetylene black), and the binder (polyvinylidene fluoride) in a weight ratio of 97:2:1. The mixture was then uniformly dispersed in the solvent N-methylpyrrolidone (NMP). The positive electrode slurry was then coated onto both sides of the positive electrode current collector aluminum foil. After drying, the foil underwent cold pressing, edge trimming, cutting, and slitting to obtain the positive electrode sheet. When coating the positive electrode slurry, the coating surface density on one side of the positive electrode current collector, based on dry weight (excluding solvent), was 0.33 g / 1540.25 mm². 2 The compaction density of the positive electrode sheet is 2.6 g / cm³. 3 .

[0336] In this example, the lithium iron phosphate cathode material is carbon-coated lithium iron phosphate, the carbon coating layer is a soft carbon coating layer, and the mass percentage of the carbon coating layer in the carbon-coated lithium iron phosphate is approximately 1%.

[0337] (2) Negative electrode plate

[0338] A negative electrode slurry was prepared by mixing hard carbon-coated graphite (artificial graphite as the graphite body), conductive carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) in a weight ratio of 96:2:1:1. The mixture was then uniformly dispersed in deionized water (dispersed under vacuum stirring) to form a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was then coated onto both sides of the copper foil current collector. After drying, the coating was cold-pressed, trimmed, cut, and slit to obtain the negative electrode sheet. When coating the negative electrode slurry, the areal density per unit area on one side of the negative electrode current collector (after deducting solvent) was 0.160 g / 1540.25 mm². 2 The compaction density of the negative electrode sheet is 1.55 g / cm³. 3 .

[0339] In this example, the negative electrode active material is a coated graphite material, with a hard carbon coating layer on the surface of the graphite body (artificial graphite), and the thickness of the hard carbon coating layer is about 0.28 μm.

[0340] (3) Negative electrode plate

[0341] A polypropylene (PP) separator membrane with a thickness of 12μm is used.

[0342] (4) Electrolyte

[0343] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 30%:35%:30%:5% to obtain a non-aqueous solvent. Additives were added to the non-aqueous solvent, and then lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte was added and allowed to dissolve completely to prepare an electrolyte with a LiFSI molar volume concentration of 0.8 mol / L.

[0344] In this example, the molar percentage of LiFSI in the electrolyte salt is 100%, and the additive is vinylene carbonate (VC), with an initial mass percentage of VC in the electrolyte of 4%.

[0345] (5) Assemble and prepare lithium-ion secondary batteries

[0346] Following the sequence of "separator-negative electrode sheet-separator-positive electrode sheet," the positive electrode sheet, negative electrode sheet, and two separators are fixed at one end to the discharge roller, and the other ends are stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft, winding the positive electrode sheet, negative electrode sheet, and two separators to obtain a wound electrode assembly (denoted as the core). After assembly with mechanical components, the core is dried, injected with electrolyte, and then subjected to vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion secondary battery.

[0347] In this example, the formation parameters are as follows: formation temperature is 45℃, and the formation steps are: charging at 0.05C for 6 hours, standing for 10 minutes, and the formation is completed. After formation, an electrolyte containing VC is added to make the mass percentage of VC in the electrolyte 5%; the concentrations of non-aqueous solvents and electrolyte salts in the added electrolyte are basically the same as those during the initial injection (see Table 1).

[0348] Examples 2-16 and Comparative Examples 1-3 were prepared using essentially the same method as in Example 1, except that one or more parameters of the following were changed: the amount of DEC, EMC, DMC, EC, propylene carbonate (PC), and the composition of the electrolyte salt (LiFSI and / or LiPF6). See Table 1 for details.

[0349] In Example 15, the electrolyte salts used were 0.8 mol / L LiFSI and 0.2 mol / L lithium hexafluorophosphate (LiPF6).

[0350] In Example 15, the electrolyte salts used were 0.2 mol / L LiFSI and 0.8 mol / L lithium hexafluorophosphate (LiPF6).

[0351] Example 17. A lithium-ion secondary battery was prepared using a method essentially the same as that in Example 1, except that the hard carbon coating layer of lithium iron phosphate cathode material was omitted during the preparation of the positive electrode sheet, and uncoated artificial graphite was used instead. The remaining operation steps were the same as in Example 1.

[0352] Comparative Examples 4-6. Lithium-ion secondary batteries were prepared using essentially the same methods as Comparative Examples 1-3, except that the hard carbon coating layer of lithium iron phosphate cathode material was omitted during the preparation of the positive electrode, and uncoated artificial graphite was used instead. The remaining operational steps were the same as those in Comparative Examples 1-3.

[0353] The preparation parameters for each embodiment and comparative example can also be found in Table 1. Based on the summary and conversion of Table 1, the parameters in Table 2 can be obtained.

[0354] In each embodiment and comparative example, the initial mass percentage of VC in the electrolyte was controlled to be 4%. After formation, an electrolyte containing VC was added to make the VC content in the prepared lithium-ion secondary battery as shown in Table 1.

[0355] Table 1.

[0356] Table 2.

[0357] Table 2 defines the parameters as follows: mass percentage of diethyl carbonate in chain carbonates (L). DEC ), the mass percentage of dimethyl carbonate in chain carbonates (L) DMC ), the mass percentage of ethylene carbonate in cyclic carbonates (H EC ), the mass percentage of chain carbonates in non-aqueous solvents (F LC The mass ratio of DEC to EC in the electrolyte (R) DEC / EC ); the mass percentage of dimethyl carbonate in a non-aqueous solvent (F DMC The molar volume concentration (C2) of lithium difluorosulfonylimide in the electrolyte. LiFSI (mol / L).

[0358] II. Testing and Analysis

[0359] (I) Testing and Analysis Methods

[0360] 1. Determination of the types and contents of electrolyte components

[0361] The testing of electrolyte solvent types and contents shall be conducted in accordance with relevant standards or specifications such as GB / T 9722-2023 General Rules for Gas Chromatography of Chemical Reagents.

[0362] The types and concentrations of electrolyte salts were tested in accordance with relevant standards or specifications such as GB / T 34672-2017 General Rules for Determination of Chemical Reagents by Ion Chromatography and GB / T 6040-2019 General Rules for Infrared Spectroscopy Analysis.

[0363] Using proton nuclear magnetic resonance spectroscopy (NMR spectroscopy) 1 H NMR was used to detect the types and contents of organic additives (including vitamin C) in the electrolyte.

[0364] 2. Battery performance test

[0365] (1) High-temperature cycle life and high-temperature gas production test

[0366] The single-cell cycle test was conducted in accordance with the procedure in GBT36276-2024. The test temperature was 45℃, the test rate was 0.5C / 0.5C, and the voltage range was 2.5V-3.65V. The number of cycles when the capacity retention rate decayed to 80% SOH was recorded, and the gas production pressure of the cell when the capacity retention rate decayed to 80% SOH was detected.

[0367] High-temperature cycle life test: At 45℃, the battery under test is charged to 3.65V at a constant current of 0.5C, rested for 10 minutes, and then discharged to 2.5V at a constant current of 0.5C, rested for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as C0. This charge-discharge cycle process is repeated for the same battery under test, and the discharge capacity C of the 1st cycle, 2nd cycle, ..., nth cycle is recorded. n The battery's cycle capacity retention rate Pn = C after n cycles n / C0×100%, the number of cycles when the capacity retention rate Pn decays to 80% is recorded as "45℃ 80% SOH cycle count". The higher the test value, the better the high-temperature cycle life.

[0368] High-temperature gas generation test: Based on the high-temperature cycle life test, when the capacity retention rate Pn decays to 80%, the gas generation pressure inside the cell is recorded and denoted as "45℃ gas generation pressure". The lower the test value, the better the improvement in high-temperature gas generation.

[0369] The internal pressure can be tested using a needle with a pressure sensor (CDK pressure gauge, model PPX-R10NH-6M-KA). Specifically, after the battery cell has been circulated to 80% SOH, it should be fully discharged and allowed to stand at room temperature. Then, the explosion-proof valve should be punctured using a pressure testing device for testing. To ensure the reliability of the test results, a rubber nail should be placed on the surface of the explosion-proof valve and fixed with glue to prevent deformation of the explosion-proof valve from causing inaccurate testing.

[0370] The test results can be found in Table 3.

[0371] (2) Cyclic life at ambient temperature

[0372] Test procedure: 25℃, 0.5C / 0.5C cycle, voltage range 2.5V~3.65V, capacity retention is measured after 600 cycles.

[0373] Detailed steps: At 25℃, charge the battery under test with a constant current of 1C to 3.65V, then charge it with a constant voltage of 3.65V to the cutoff current of 0.05C, let it rest for 10 minutes, and then discharge it with a constant current of 0.5C to 2.5V, let it rest for 5 minutes. This constitutes one charge-discharge cycle. Record the discharge capacity at this point as C0. Repeat this charge-discharge cycle for the same battery, and record the discharge capacity C of the 1st cycle, 2nd cycle, ..., nth cycle. n Wherein, the cycle capacity retention rate of the battery after n cycles is recorded as Pn = C. n / C0×100%. The number of cycles when the capacity retention rate Pn decays to 80% is recorded as "25℃ 80% SOH cycle number".

[0374] The higher the test value, the better the cycle life at room temperature.

[0375] (II) Test Result Analysis

[0376] The lithium-ion secondary batteries prepared in each embodiment all exhibit significantly improved long-term reliability at high temperatures. Compared to Comparative Examples 1-3, Examples 1-16 show superior high-temperature cycling performance while significantly suppressing gas generation after long-term cycling at high temperatures. For example, in Examples 1-16, the number of cycles at 45°C and 80% SOH is all above 3000, with some examples exceeding 4000 cycles. The gas generation pressure at 45°C is below 0.15 MPa, while in Comparative Examples 1-3, the gas generation pressure at 45°C is above 0.15 MPa. Furthermore, compared to Comparative Examples 1-3, the embodiments including Example 1 not only significantly improved high-temperature gas generation but also showed varying degrees of improvement in high-temperature cycle life. See Table 3 for details.

[0377] Compared with Comparative Examples 4-6, Example 17 significantly improved high-temperature gas production while maintaining a better high-temperature cycle life. The gas production pressure at 45°C in Example 17 was significantly reduced, and the number of cycles at 80% SOH at 45°C was significantly increased.

[0378] The lithium-ion secondary batteries prepared in Examples 1-16 not only significantly improve long-term reliability at high temperatures but also exhibit good room-temperature cycling performance. For example, the test results for Example 1 show 8045 cycles at 25°C and 80% SOH, while the test results for Example 16 show 5413 cycles at 25°C and 80% SOH.

[0379] Table 3.

[0380] The descriptions of the various implementation methods and embodiments above tend to emphasize the differences between them. Similarities or resemblances can be referenced interchangeably, and for the sake of brevity, they will not be repeated here. The technical features of the implementation methods and embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combinations of these technical features do not contradict each other, they should be considered within the scope of this specification.

[0381] It should be noted that this application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and any embodiments and examples that have the same structure and achieve the same effect as the technical concept within the scope of this application are included in the technical scope of this application. The embodiments and examples described above only illustrate several embodiments and examples of this application, and although the descriptions are relatively detailed, they should not be construed as limiting the scope of the patent. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments or examples, and other ways of constructing embodiments or examples by combining some of the constituent elements of the embodiments or examples, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A lithium-ion secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive electrode and the negative electrode; the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises cyclic carbonates and chain carbonates; the chain carbonates comprise dimethyl carbonate, and further comprise chain carbonates different from dimethyl carbonate; the electrolyte comprises lithium bis(fluorosulfonyl)imide. The mass percentage of dimethyl carbonate in the non-aqueous solvent is denoted as F. DMC The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is denoted as C. LiFSI mol / L; the electrolyte satisfies 0 < (C LiFSI ×F DMC )≤0.

05.

2. The lithium-ion secondary battery according to claim 1, wherein, 0.0002≤(C LiFSI ×F DMC )≤0.05。 3. The lithium-ion secondary battery according to claim 1, wherein, 0.0005≤(C LiFSI ×F DMC )≤0.04。 4. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein, The molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than or equal to 0.2 mol / L, and can be selected from 0.2 mol / L to 1 mol / L.

5. The lithium-ion secondary battery according to any one of claims 1 to 4, wherein, The mass percentage of dimethyl carbonate in the non-aqueous solvent is 0. <F DMC ≤20%.

6. The lithium-ion secondary battery according to claim 5, wherein, 0<F DMC ≤10％。 7. The lithium-ion secondary battery according to any one of claims 1 to 6, wherein, The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is 0.2 mol / L to 1 mol / L, and 0.1% ≤ F DMC ≤20%; Optionally, 0.3 mol / L to 1 mol / L, 0.1% ≤ F DMC ≤10%.

8. The lithium-ion secondary battery according to any one of claims 1 to 7, wherein, The electrolyte salt further includes lithium hexafluorophosphate; in the electrolyte salt, the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate is greater than or equal to 0.

05.

9. The lithium-ion secondary battery according to claim 8, wherein, In the electrolyte salt, the molar ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate is greater than or equal to 0.

1.

10. The lithium-ion secondary battery according to claim 8 or 9, wherein, The molar percentage of lithium bis(fluorosulfonyl)imide in the electrolyte salt is 20% to 100%.

11. The lithium-ion secondary battery according to claim 10, wherein, The molar percentage of lithium bis(fluorosulfonyl)imide in the electrolyte salt is 50% to 100%.

12. The lithium-ion secondary battery according to any one of claims 1 to 11, wherein, The electrolyte satisfies one or more of the following characteristics: (a1) The chain carbonate includes one or both of diethyl carbonate and methyl ethyl carbonate; optionally, the mass percentage of diethyl carbonate in the chain carbonate is denoted as L. DEC L DEC ≥40%; (a2) The cyclic carbonate includes one or both of ethylene carbonate and propylene carbonate; optionally, the mass percentage of ethylene carbonate in the cyclic carbonate is denoted as H. EC 50% ≤ H EC ≤100%; (a3) The mass percentage of dimethyl carbonate in the chain carbonate is denoted as L. DMC 0 <L DMC ≤25%; (a4) The cyclic carbonate includes ethylene carbonate; the mass ratio of diethyl carbonate and ethylene carbonate in the electrolyte is denoted as R. DEC / EC R DEC / EC ≥0.8, optionally, 0.8≤R DEC / EC ≤3.

5.

13. The lithium-ion secondary battery according to claim 12, wherein, The electrolyte satisfies one or more of the following characteristics: (a1')50%≤L DEC ≤75%; (a2')60%≤H EC ≤100%; (a3')0 <L DMC ≤16%, optionally, 5% ≤L DMC ≤10%; (a4')1≤R DEC / EC ≤2.5。 14. The lithium-ion secondary battery according to claim 12 or 13, wherein, The electrolyte satisfies one or more of the following characteristics: (b1) The mass percentage of diethyl carbonate in the non-aqueous solvent is 20% to 65%; (b2) The mass percentage of ethylene carbonate in the non-aqueous solvent is 15% to 50%; (b3) The chain carbonate in the non-aqueous solvent is 50% to 75% by mass; (b4) The cyclic carbonate in the non-aqueous solvent is 25% to 50% by mass; (b5) The chain carbonates also include ethyl methyl carbonate.

15. The lithium-ion secondary battery according to claim 14, wherein, The electrolyte satisfies one or more of the following characteristics: (b1') The mass percentage of diethyl carbonate in the non-aqueous solvent is 25% to 50%; (b2') The mass percentage of ethylene carbonate in the non-aqueous solvent is 25% to 40%; (b3') The chain carbonate in the non-aqueous solvent is 55% to 75% by mass; (b4') The cyclic carbonate in the non-aqueous solvent is 25% to 45% by mass.

16. The lithium-ion secondary battery according to any one of claims 1 to 15, wherein, The additive includes vinylene carbonate; its mass percentage in the electrolyte is denoted as F. VC F VC ≥2%, optionally, 2% ≤ F VC ≤12%.

17. The lithium-ion secondary battery according to claim 16, wherein, 2.5％≤F VC ≤10％。 18. The lithium-ion secondary battery according to claim 16, wherein, 3％≤F VC ≤10％。 19. The lithium-ion secondary battery according to any one of claims 1 to 17, wherein, The positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material, including a lithium iron phosphate-based positive electrode material; Optionally, the lithium iron phosphate cathode material constitutes 80% to 100% of the cathode active material by mass.

20. The lithium-ion secondary battery according to any one of claims 1 to 19, wherein, The negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material; the negative electrode active material includes one or more of graphite and coated graphite materials; wherein, the coated graphite material includes a graphite body and a hard carbon coating layer located on at least a portion of the surface of the graphite body.

21. The lithium-ion secondary battery according to claim 20, wherein, The coated graphite material constitutes 80% to 100% of the negative electrode active material by mass.

22. A method for preparing a lithium-ion secondary battery, comprising the following steps: An electrode assembly, including a positive electrode, a separator, and a negative electrode, is placed inside the battery casing; wherein, The separator is provided between the positive electrode and the negative electrode; An electrolyte is injected into the battery casing; wherein the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the non-aqueous solvent comprises cyclic carbonates and chain carbonates; the chain carbonates comprise dimethyl carbonate, and further comprise chain carbonates different from dimethyl carbonate; the electrolyte comprises lithium bis(fluorosulfonyl)imide; the mass percentage of dimethyl carbonate in the non-aqueous solvent is denoted as F. DMC The molar volume concentration of lithium difluorosulfonylimide in the electrolyte is denoted as C. LiFSI mol / L; the electrolyte satisfies 0 < (C LiFSI ×F DMC ≤0.05; Let it stand and soak; and formed.

23. The method for preparing a lithium-ion secondary battery according to claim 22, wherein the lithium-ion secondary battery according to any one of claims 1 to 21 is prepared.

24. An electrical device comprising a lithium-ion secondary battery as described in any one of claims 1 to 21.

Images