Lithium-ion secondary battery, method for manufacturing the same, and electric device

Abstract

This application relates to lithium-ion secondary batteries, their preparation methods, and electrical devices. The lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte, with a separator between the positive and negative electrodes. The positive electrode includes a positive active layer comprising a positive active material. The electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The positive active material includes a lithium phosphate-based positive electrode material, with the average particle size of the primary particles in the positive active material being 100 nm to 500 nm. The additives include basic alkyne additives containing Lewis base nitrogen heterocycles. This lithium-ion secondary battery exhibits significantly improved high-temperature performance while also maintaining good room-temperature performance.

Description

Technical Field

[0001] This application relates to the field of lithium-ion secondary battery technology, and further to lithium-ion secondary batteries, their preparation methods and electrical devices. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] With the technological development of lithium-ion rechargeable batteries, they are increasingly widely used in smartphones, tablets, laptops, power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and other fields. They are also widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants. Among these, lithium-ion rechargeable batteries using positive electrode active materials such as lithium iron phosphate (LFP) have outstanding advantages in safety and battery life due to their excellent structural stability. However, these positive electrode active materials inevitably introduce moisture, which easily generates acid byproducts that damage the solid electrolyte interphase (SEI) film, exacerbating interfacial side reactions and limiting the lifespan advantage of this battery system. This is especially true at high temperatures, where water-involved side reactions are more severe, resulting in less than ideal high-temperature performance. For lithium-ion rechargeable batteries with positive electrode active materials including lithium phosphate-based positive electrode materials, although theoretically high-temperature performance can be improved by optimizing the negative electrode SEI film using high-temperature additives such as alkyne additives, this leads to increased interfacial impedance, affecting performance at room temperature. Summary of the Invention

[0004] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, its preparation method, and an electrical device thereof. This lithium-ion secondary battery exhibits significantly improved high-temperature performance while also maintaining good room-temperature performance.

[0005] 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 electrode and the negative electrode; the positive electrode includes a positive active layer, the positive active layer comprising a positive active material; the electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives; the positive active material comprises a lithium phosphate-based positive electrode material, wherein the average particle size of the primary particles in the positive active material is 100 nm to 500 nm; the additives comprise basic alkyne additives, wherein the basic alkyne additives contain Lewis base nitrogen heterocycles.

[0006] For lithium-ion secondary batteries with positive electrode active materials including lithium phosphate-based positive electrode materials, introducing alkaline alkyne additives (also referred to as additive A) containing carbon-carbon triple bonds and Lewis base nitrogen heterocycles with high-temperature stability into the electrolyte can utilize the Lewis base nitrogen heterocycles to absorb water and acid byproducts, reducing free acid byproducts in the electrolyte at high temperatures and suppressing the aggravating effect of acid byproducts on battery capacity decay at high temperatures. Furthermore, the carbon-carbon triple bonds form a highly stable solid electrolyte interphase (SEI) film at the negative electrode, reducing interfacial side reactions at high temperatures. Utilizing these multiple effects, the high-temperature performance of the battery can be significantly improved; further... Controlling the average particle size of primary particles in the positive electrode active material within a relatively moderate range can reduce the content of water and acid byproducts in the system and inhibit the damage of acid byproducts to the SEI film of the negative electrode. It can also suppress the increase in interfacial impedance at room temperature caused by the participation of alkaline alkyne additives in the film formation of the negative electrode. Furthermore, it can control the positive electrode active material to have a more suitable lithium-ion transport path, thereby regulating the internal resistance of the battery. This is beneficial for lithium-ion secondary batteries to achieve good room temperature performance. Based on the aforementioned multiple effects, but not limited to the aforementioned theories, it is possible to significantly improve the high-temperature performance of battery systems containing lithium phosphate positive electrode materials while also taking into account good room temperature performance.

[0007] In some embodiments, the average particle size of the primary particles in the positive electrode active material is 150nm~450nm, optionally 200nm~450nm, and further optionally 250nm~450nm.

[0008] By controlling the average particle size (D1) of the primary particles in the positive electrode active material within the aforementioned range, it is beneficial to better balance the increase in negative electrode interface impedance caused by water in the positive electrode active material and the influence of lithium-ion transport path on the battery internal resistance. This is beneficial to significantly improve the high-temperature performance of the battery while also better taking into account the room-temperature performance.

[0009] In some embodiments, the lithium phosphate cathode material includes a carbon-coated lithium phosphate cathode material, wherein the carbon-coated lithium phosphate cathode material includes a lithium phosphate matrix and a carbon coating layer located on at least a portion of the surface of the lithium phosphate matrix.

[0010] By setting a carbon coating layer on the surface of lithium phosphate cathode materials, the specific surface area of ​​the material may be increased, which in turn leads to an increase in the water absorption rate of the material surface. At this time, by controlling the average particle size (D1) of the primary particles in the cathode active material and the synergistic effect of introducing alkaline alkyne additives, the high-temperature performance of the battery can be significantly improved while also taking into account good room-temperature performance.

[0011] In some embodiments, the specific surface area of ​​the positive electrode active material is 5 m². 2 / g~18m 2 / g, optional 5m2 / g~15m 2 / g.

[0012] For lithium-ion secondary batteries, exemplarily including lithium-ion secondary batteries with positive electrode active materials including carbon-coated lithium phosphate positive electrode materials, by controlling the specific surface area (BET1) of the positive electrode active material within the aforementioned range, it is beneficial to better control the water absorption rate of the positive electrode active material, while also better suppressing high-temperature interface side reactions, which is beneficial to better improve the high-temperature performance of the battery while also taking into account good room-temperature performance.

[0013] In some embodiments, the carbon-coated lithium phosphate cathode material satisfies one or more of the following characteristics:

[0014] (a1) The degree of graphitization of the carbon coating is 28%~95%;

[0015] (a2) The carbon coating layer accounts for 0.5% to 2.5% of the mass of the carbon-coated lithium phosphate cathode material;

[0016] (a3) The average thickness of the carbon coating layer is 1 nm to 8 nm;

[0017] (a4) The maximum thickness of the carbon coating layer is less than or equal to 12 nm.

[0018] In some embodiments, the carbon-coated lithium phosphate cathode material satisfies one or more of the following characteristics:

[0019] (a1') The degree of graphitization of the carbon coating layer is 40%~90%, and can be selected as 40%~85%;

[0020] (a2') The carbon coating layer accounts for 0.8% to 2% of the mass of the carbon-coated lithium phosphate cathode material;

[0021] (a3') The average thickness of the carbon coating layer is 1 nm to 5 nm;

[0022] (a4') The maximum thickness of the carbon coating layer is less than or equal to 10 nm.

[0023] For lithium-ion secondary batteries with positive electrode active materials including carbon-coated lithium phosphate-containing positive electrode materials, the graphitization degree of the carbon coating layer can be controlled to be relatively high (G1), or the mass ratio of the carbon coating layer in the carbon-coated lithium phosphate-containing positive electrode material can be controlled (F). B ), average thickness of carbon coating (D) B ) and the maximum thickness of the carbon coating (D) maxHaving one or more parameters with relatively low values ​​is beneficial for reducing the water absorption rate of the positive electrode active material, reducing or delaying the consumption of the negative electrode interface by alkaline alkyne additives, reducing the growth rate of the negative electrode interface impedance, and better balancing room temperature performance.

[0024] For lithium-ion secondary batteries with positive electrode active materials including carbon-coated lithium phosphate positive electrode materials, by controlling the graphitization degree of the carbon coating layer within the aforementioned range, it is possible to better coordinate the water absorption rate of the material surface, the conductivity of the carbon coating layer, and the ion diffusion resistance of the carbon coating layer. This will better balance the influence of the carbon coating layer on the battery's internal resistance and the suppression effect of the carbon coating layer on the positive electrode interface side reactions, thereby better improving the battery's high-temperature performance while also ensuring good room-temperature performance.

[0025] For example, controlling a relatively high degree of graphitization within the aforementioned range is beneficial for reducing the water absorption rate on the material surface and improving the conductivity of the carbon coating layer, while also better controlling the ion diffusion resistance.

[0026] For example, controlling a relatively low degree of graphitization within the aforementioned range is beneficial for reducing the ion diffusion resistance of the carbon coating layer while also better controlling conductivity and water absorption rate.

[0027] By controlling the mass ratio of the carbon coating layer in the carbon-coated lithium phosphate cathode material (F... B ), average thickness of carbon coating (D) B ) and the maximum thickness of the carbon coating (D) max One, two, or three of the above-mentioned factors are beneficial for controlling the positive electrode active material to have a lower water absorption rate, and also beneficial for reducing the influence of ion diffusion impedance on the battery internal resistance, and for better balancing the battery's room temperature performance.

[0028] In some embodiments, the D of the positive electrode active material v 50 is 1μm~5μm, can be selected as 1μm~4μm, and can be further selected as 1.5μm~4μm.

[0029] By using the D of the positive electrode active material vBy controlling the concentration of 50 within the aforementioned range, the agglomeration degree of primary particles can be adjusted by combining the control of the average particle size (D1) of the primary particles. This allows for better control of the specific surface area and water absorption rate, and also better control of the overall ion transport path of the positive electrode active material particles. Based on the synergistic effects of the aforementioned factors, but not limited to the aforementioned theories, it is beneficial to better control the battery's internal resistance and to better balance the battery's high-temperature performance with its room-temperature performance. In some examples, for lithium-ion secondary batteries with positive electrode active materials including carbon-coated lithium phosphate-containing positive electrode materials, it can also better balance the effects of the carbon coating layer on the specific surface area, water absorption rate, conductivity, ion diffusion resistance, and positive electrode interface side reactions, thus significantly improving the battery's high-temperature performance while also maintaining good room-temperature performance.

[0030] In some embodiments, 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 at least one of carbon-based materials and silicon-based materials;

[0031] Optionally, the negative electrode sheet satisfies one or more of the following characteristics:

[0032] (b1) The silicon-based material accounts for 0-20% of the mass of the negative electrode active material, and may be selected as 0-10%;

[0033] (b2) The silicon-based material includes a silicon-carbon composite material, which includes a porous carbon matrix and elemental silicon located within the pores of the porous carbon matrix; the silicon-carbon composite material accounts for 80% to 100% of the mass of the silicon-based material.

[0034] (b3) The carbon-based material includes graphite-based material, and the graphite-based material accounts for 80% to 100% of the mass of the negative electrode active material;

[0035] (b4) The negative electrode active material includes a coated negative electrode material, which includes a negative electrode active body and a carbon coating layer located on the negative electrode active body, including at least a portion thereof; the mass percentage of the coated negative electrode material in the negative electrode active material is 80% to 100%.

[0036] By controlling the content of silicon-based materials in the negative electrode active material and / or the type of positive electrode active material within the aforementioned range, the expansion and contraction changes of the negative electrode can be better controlled, the generation of fresh interfaces can be reduced, and side reactions at the negative electrode interface can be suppressed. This is beneficial for reducing the consumption rate of alkaline alkyne additives, reducing the rate of increase in battery internal resistance, and better balancing the battery's performance at room temperature. For example, in silicon-based materials, the volume expansion and contraction changes of silicon-carbon composite materials are relatively low.

[0037] By incorporating a carbon-coated anode material into the anode active material, the lithium-ion transport channels on the surface of the anode active material can be optimized, promoting lithium-ion transport. This also helps to suppress side reactions at the anode interface and inhibit the increase in interfacial impedance caused by the participation of alkaline alkyne additives in film formation, which is beneficial for better control of battery internal resistance and battery performance at room temperature.

[0038] In some embodiments, the basic alkaline alkyne additive has a mass percentage of less than or equal to 3.5% in the electrolyte, preferably 0.01% to 3.5%, further preferably 0.1% to 2.5%, and even more preferably 0.2% to 2.5%.

[0039] By controlling the mass percentage (C) of the alkaline acetylene additive (additive A) in the electrolyte... A Within the aforementioned range, alkaline alkyne additives can continuously play a role in repairing the SEI film during cycling and / or storage, which is more conducive to significantly improving high-temperature performance while also maintaining good room-temperature performance.

[0040] In some embodiments, the additive includes a negative electrode film-forming additive that is different from the basic acetylene additive.

[0041] Unlike basic alkyne additives, negative electrode film-forming additives can competitively participate in negative electrode film formation, which can reduce or delay the consumption of basic alkyne additives in negative electrode film formation. They can also suppress the increase in negative electrode interface resistance caused by the participation of basic alkyne additives in negative electrode film formation, which is beneficial to improve the high-temperature performance of the battery while also better taking into account the room temperature performance.

[0042] In some embodiments, the additive further includes one or more of additive B, additive C, and additive D;

[0043] Wherein, additive B is one or more of silane additives and siloxane additives;

[0044] The additive C is one or more of isocyanate additives and acid anhydride additives;

[0045] The additive D is one or more of lithium salt additives and phosphate ester additives.

[0046] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0047] (c1) The mass ratio of the additive B to the alkaline acetylene additive is 0.1~50, and can be selected as 0.1~1;

[0048] (c2) The mass ratio of the additive C to the alkaline acetylene additive is 0.02~50, and can be selected as 0.02~1;

[0049] (c3) The mass ratio of the additive D to the alkaline acetylene additive is 0.1 to 100, and can be selected as 0.1 to 2.

[0050] In some embodiments, the mass ratio of additive B, additive C, additive D and alkaline acetylene additive in the electrolyte is (0~0.5):(0~0.5):(0~1):1.

[0051] Additives B, C, and D can all be used as negative electrode film-forming additives. Additive B is a type of additive with low negative electrode film-forming impedance and a certain degree of acid removal effect, although its acid removal effect is lower than that of basic alkyne additives, and its negative electrode film-forming impedance is also lower than that of basic alkyne additives. Additive C is a type of additive with good acid removal effect, which is better than that of basic alkyne additives, but its negative electrode film-forming impedance is higher than that of basic alkyne additives. Additive D has very low negative electrode film-forming impedance, far lower than that of basic alkyne additives.

[0052] By utilizing the synergistic effect of basic alkyne additives with one or more of additives B, C, and D, it is beneficial to achieve a significant improvement in high-temperature performance while also maintaining good room-temperature performance.

[0053] In some embodiments, the basic alkyne additive satisfies one or more of the following characteristics:

[0054] (d1) The molecular weight of the alkaline alkyne additive is less than or equal to 500 Da;

[0055] (d2) The molecules of the alkaline acetylene additives contain 1 to 4 carbon-carbon triple bonds;

[0056] (d3) The carbon-carbon triple bond is CH≡C-;

[0057] (d4) The molecules of the alkaline alkyne additives contain 1 to 4 Lewis base nitrogen heterocycles;

[0058] (d5) The Lewis base nitrogen heterocycle includes an imidazole ring;

[0059] (d6) In the molecule of the basic alkyne additive, the carbon-carbon triple bond and the Lewis base nitrogen heterocycle are connected by a linker L1, wherein the linker L1 contains a C-type carbon bond covalently bonded to the carbon-carbon triple bond. 1-3 Alkyl groups or those containing fluorinated C atoms covalently bonded to a carbon-carbon triple bond 1-3 Alkylene.

[0060] In some embodiments, the basic alkyne additive satisfies one or more of the following characteristics:

[0061] (e1) The molecular weight of the alkaline acetylene additive is less than or equal to 300 Da;

[0062] (e2) The basic alkyne additive contains 1 to 4 imidazole rings in its molecule;

[0063] (e3) The Lewis base nitrogen heterocycle includes an imidazole ring; the imidazole ring in the Lewis base nitrogen heterocycle is substituted by 0, 1, or more substituents Q2, wherein each substituent Q2 in the substituted imidazole group is independently C. 1-3 Alkyl, cyano, or fluorine atom;

[0064] (e4) The alkaline yne additive consists of carbon-carbon triple bonds, C 1-3 Alkylene and -OC(=O)-R 10 It is formed by sequential covalent bonds, R 10 It is a Lewis base nitrogen heterocycle.

[0065] In some embodiments, the basic alkyne additive comprises compound II with the structure shown in formula (II): ; among which, L 11 C 1-3 Alkylene, Q2 is independently C 1-3 Alkyl, cyano, or fluorine atom, p2 is 0, 1, 2, or 3;

[0066] The mass percentage of compound II in the basic alkyne additive is 80% to 100%.

[0067] By controlling the molecular weight of alkaline alkyne additives within the aforementioned lower range, the alkaline alkyne additives can have a smaller molecular size, which is beneficial for better control of the low viscosity characteristics of the electrolyte, resulting in higher conductivity of the electrolyte and better control of the battery's internal resistance.

[0068] By controlling the number of carbon-carbon triple bonds in alkaline alkyne additives within the aforementioned range, it is beneficial to suppress the increase in negative electrode interface impedance caused by alkaline alkyne additives participating in the formation and repair of the SEI film, and it is also beneficial to control the influence of alkaline alkyne additives on liquid phase impedance; thus, the increase in battery internal resistance can be better suppressed.

[0069] By controlling the number of Lewis base nitrogen heterocycles in the basic alkyne additives within the aforementioned range, it is beneficial to better absorb acid byproducts in the electrolyte, and at the same time, it is also beneficial to control the steric hindrance effect of Lewis base nitrogen heterocycles on carbon-carbon triple bonds.

[0070] Examples of Lewis base nitrogen heterocycles include the imidazole ring in compound II.

[0071] Introducing fluorine atom substituents into Lewis base nitrogen heterocycles (such as imidazole rings) is beneficial for inducing the formation of inorganic lithium fluoride phases at the negative electrode, which is beneficial for improving the stability of the SEI film and reducing the interfacial impedance, and for better improving the high-temperature performance of the battery while taking into account the room-temperature performance.

[0072] In some embodiments, the lithium-ion secondary battery satisfies one or more of the following characteristics:

[0073] (f1) The lithium phosphate-containing cathode material accounts for 80% to 100% of the mass of the cathode active material;

[0074] (f2) The lithium phosphate cathode material includes carbon-coated lithium iron phosphate, and the carbon-coated lithium iron phosphate accounts for 80% to 100% of the mass of the lithium phosphate cathode material.

[0075] 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:

[0076] An electrode assembly comprising a positive electrode, a separator, and a negative electrode is placed inside a battery casing, with the separator positioned between the positive and negative electrode. The positive electrode includes a positive active layer comprising a positive active material. The positive active material comprises a lithium phosphate-based positive electrode material, wherein the average particle size of the primary particles in the lithium phosphate-based positive electrode material is 100 nm to 500 nm.

[0077] A first electrolyte is injected into the battery casing, and the casing is left to stand to allow the first electrolyte to wet the positive electrode and the negative electrode, thus forming the electrolyte. The first electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive. The additive includes a basic alkyne additive, which contains a Lewis base nitrogen heterocycle.

[0078] In some embodiments, after formation, a second electrolyte comprising the alkaline alkyne additive is injected into the battery casing.

[0079] In some embodiments, the lithium-ion secondary battery described in the first aspect of this application is prepared.

[0080] 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.

[0081] 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

[0082] 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 conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0083] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0084] Figure 2 for Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0085] Figure 3 This is a schematic diagram of a battery device according to one embodiment of this application.

[0086] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0087] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0088] Figure 6 This is a schematic diagram of an electrical device that uses a lithium-ion secondary battery as a power source according to an embodiment of this application.

[0089] Explanation of reference numerals in the attached figures:

[0090] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery assembly; 5. Individual battery cell; 51. Battery housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0091] 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 the power supply device of this application. However, some unnecessary detailed descriptions 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0092] 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.

[0093] 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.

[0094] 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% is permissible. For instance, taking "about 20°C" as an example, where the approximation is ±1°C, approximate values ​​such as 19°C and 19.5°C within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0095] In this application, the terms "multiple," "various," 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.

[0096] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0097] 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.

[0098] 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.

[0099] 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."

[0100] 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.

[0101] 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."

[0102] 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.

[0103] In this document, the term "suitable" in "suitable combination method" or "suitable method" refers to the technical solution that enables the implementation of this application.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] In this application, the term "room temperature" generally refers to 4℃~35℃, and may refer to 20℃±5℃. In some embodiments or examples of this application, room temperature refers to 20℃~30℃.

[0110] 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 and size are interpreted in the same way.

[0111] In this application, unless otherwise stated, "molecular weight" refers to molecular mass measured in Daltons (Da), where 1 Dalton equals 12 One-twelfth of the mass of a carbon atom.

[0112] In this application, "greater than or equal to" and "≥" have the same meaning and can be used interchangeably; "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".

[0113] 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.

[0114] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0115] Lithium-ion secondary batteries using positive electrode active materials such as lithium iron phosphate (LFP) have outstanding advantages in safety and battery life due to their excellent structural stability. However, these positive electrode active materials usually inevitably introduce moisture, which can easily generate acid byproducts that damage the solid electrolyte interphase (SEI) film of the negative electrode, aggravate the interfacial side reactions of the negative electrode, and lead to capacity decay and affect battery life. In particular, the side reactions involving water are more intense at high temperatures, resulting in less than ideal high-temperature performance of the battery.

[0116] Although theoretically, high-temperature additives such as acetylene additives can be used to improve the high-temperature performance of the battery by optimizing the negative electrode SEI film, this will lead to an increase in the negative electrode interface impedance, affecting the performance at room temperature.

[0117] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery, its preparation method, and an electrical device thereof. This lithium-ion secondary battery exhibits significantly improved high-temperature performance while also maintaining good room-temperature performance.

[0118] In this application, unless otherwise specified, the "high temperature" referring to battery cycling and / or storage can be greater than 35°C and less than or equal to 80°C, optionally greater than 35°C and less than or equal to 60°C, further optionally 37°C to 60°C, further optionally 40°C to 60°C, and even more optionally 45°C to 60°C, but is not limited thereto. The "high temperature" referring to battery cycling or storage 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, 65°C, 70°C, 75°C, 80°C, etc.

[0119] In this application, unless otherwise specified, the "normal temperature" referring to battery cycling and / or storage can be 20℃~35℃, or optionally 20℃~30℃, but is not limited to this. The "normal temperature" referring to battery cycling or storage can also be any of the following temperatures or a range selected from any two of the following temperatures: 20℃, 22℃, 24℃, 25℃, 26℃, 28℃, 30℃, 32℃, 34℃, 35℃, etc.

[0120] In some embodiments, a lithium-ion secondary battery is provided, comprising a positive electrode and an electrolyte. The positive electrode includes a positive active layer, which includes a positive active material. The electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The positive active material includes a lithium phosphate-based positive electrode material, wherein the average particle size of the primary particles in the positive active material is moderate (e.g., 100 nm to 500 nm). The additives include basic alkyne additives, which contain Lewis base nitrogen heterocycles.

[0121] 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.

[0122] 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.

[0123] 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."

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0130] In a first aspect of this application, a lithium-ion secondary battery is provided, which has significantly improved high-temperature performance while also maintaining good room-temperature performance.

[0131] 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 electrode; the positive electrode includes a positive active layer, which includes a positive active material; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the positive active material includes a lithium phosphate-based positive electrode material, wherein the average particle size of the primary particles in the positive active material is 100 nm to 500 nm; the additives include basic alkyne additives, wherein the basic alkyne additives contain Lewis base nitrogen heterocycles.

[0132] In this application, unless otherwise specified, "lithium phosphate-containing cathode material" refers to a class of cathode active materials that include lithium phosphate components, and more specifically, materials that include lithium, transition metal elements, and phosphate ions (PO4). 3- The positive electrode active material is a lithium phosphate-containing cathode material. Unless otherwise specified, the lithium phosphate-containing cathode material may have an olivine structure.

[0133] In this application, the "average particle size of primary particles in the positive electrode active material" can be denoted as D1.

[0134] In this application, unless otherwise specified, the "average particle size of primary particles" in the positive electrode active material refers to the average particle size of all primary particles in the positive electrode active material. The "particle size of primary particles" refers to the maximum diameter of the primary particles in each direction.

[0135] In this application, unless otherwise specified, "primary particles" in the positive electrode active material refer to the basic particle unit in the positive electrode active material. It is understood that primary particles exist in the positive electrode active material. In the positive electrode active material, primary particles can exist in a non-agglomerated state, or multiple primary particles can form aggregates. Non-agglomerated primary particles can be called "non-agglomerated primary particles," and aggregates formed by multiple primary particles can be called "secondary particles."

[0136] In this application, unless otherwise specified, "non-aqueous solvent" means a solvent that is not water.

[0137] In this application, unless otherwise specified, "Lewis base nitrogen heterocycle" refers to a nitrogen heterocycle possessing Lewis base properties. This concept is based on the Lewis acid-base theory. Lewis base nitrogen heterocycles can donate electron pairs and are electron-rich. Therefore, Lewis base nitrogen heterocycles can attract and bind acidic substances. Furthermore, Lewis base nitrogen heterocycles can also form hydrogen bonds with water. Non-limiting examples of Lewis base nitrogen heterocycles include imidazole rings, but are not limited to these.

[0138] In this application, unless otherwise specified, "nitrogen heterocyclic structure" refers to a ring structure in which the cyclic atoms include nitrogen atoms. The term "cyclic atom" refers to the constituent atom of the ring skeleton. As a non-limiting example, the three carbon atoms and two nitrogen atoms in an imidazole ring are cyclic atoms, and the imidazole ring is a 5-membered ring. "Ringed nitrogen atom" refers to the nitrogen atom in the cyclic atom.

[0139] In this application, unless otherwise specified, "basic alkyne additives" refers to alkyne-based additives containing Lewis base nitrogen heterocycles; it is understood that basic alkyne additives contain carbon-carbon triple bonds "C≡C". Unless otherwise specified, "basic alkyne additives" as used herein refers to nonionic alkyne organic additives; it is understood that metal salt additives are not within the scope of the meaning of basic alkyne additives as used herein. It is understood that basic alkyne additives can attract and bind acidic substances, such as acid byproducts in the electrolyte (e.g., hydrofluoric acid). Basic alkyne additives can participate in the formation of the negative electrode solid electrolyte interphase (SEI) film. Basic alkyne additives can significantly improve the high-temperature performance of batteries, including extending high-temperature cycle performance and high-temperature storage performance, and can be used as high-temperature additives; however, the introduction of basic alkyne additives can easily lead to high negative electrode interfacial impedance at room temperature.

[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] For lithium-ion secondary batteries with positive electrode active materials including lithium phosphate-based positive electrode materials, introducing alkaline alkyne additives (also referred to as additive A) containing carbon-carbon triple bonds and Lewis base nitrogen heterocycles with high-temperature stability into the electrolyte can utilize the Lewis base nitrogen heterocycles to absorb water and acid byproducts, reducing free acid byproducts in the electrolyte at high temperatures and suppressing the aggravating effect of acid byproducts on battery capacity decay at high temperatures. Furthermore, the carbon-carbon triple bonds form a highly stable solid electrolyte interphase (SEI) film at the negative electrode, reducing interfacial side reactions at high temperatures. Utilizing these multiple effects, the high-temperature performance of the battery can be significantly improved; further... Controlling the average particle size of primary particles in the positive electrode active material within a relatively moderate range can reduce the content of water and acid byproducts in the system and inhibit the damage of acid byproducts to the SEI film of the negative electrode. It can also suppress the increase in interfacial impedance at room temperature caused by the participation of alkaline alkyne additives in the film formation of the negative electrode. Furthermore, it can control the positive electrode active material to have a more suitable lithium-ion transport path, thereby regulating the internal resistance of the battery. This is beneficial for lithium-ion secondary batteries to achieve good room temperature performance. Based on the aforementioned multiple effects, but not limited to the aforementioned theories, it is possible to significantly improve the high-temperature performance of battery systems containing lithium phosphate positive electrode materials while also taking into account good room temperature performance.

[0142] In this application, the Lewis base nitrogen heterocycles may absorb water and / or acid byproducts through means including but not limited to hydrogen bonding.

[0143] The types and concentrations of inorganic components (including electrolyte salts and inorganic additives) in the electrolyte 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 / T 6040-2019 General Rules for Infrared Spectroscopic Analysis, and the latest or current version of the standard method can be preferred. The types and contents of organic components (including non-aqueous solvents and organic additives) in the electrolyte can be tested with reference to relevant standards such as GB / T 9722-2023 General Rules for Gas Chromatography of Chemical Reagents.

[0144] In addition, 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: nuclear magnetic resonance hydrogen spectroscopy (NMR spectroscopy). 1Methods such as 1H NMR, high-performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), Fourier transform infrared spectroscopy (FT-IR), ultraviolet spectroscopy, and gas chromatography (GC) 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, and other methods 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, GC, etc., but not limited to these.

[0145] The electrolyte sample can be obtained by disassembling the battery cell.

[0146] In this application, the test sample of the "positive electrode active material" in the positive electrode sheet of a lithium-ion secondary battery can be obtained by disassembling the battery, removing the positive electrode sheet, and extracting the positive electrode active material from the positive electrode active layer of the positive electrode sheet using methods such as solvent washing, ultrasonic dispersion, centrifugation, fractionation sedimentation, and sintering. 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. Furthermore, the powder material extracted from the positive electrode active layer can be sintered to remove organic components, thereby obtaining a powder sample of the positive electrode active material.

[0147] For example, the preparation of powder samples of positive electrode active materials can be carried out by the following method: disassemble the battery, take out the positive electrode sheet, soak and clean it with a solvent such as dimethyl carbonate to remove residual electrolyte; scrape the powder material of the positive electrode active layer, soak the powder material extracted from the positive electrode active layer with a solvent (such as N-methylpyrrolidone (NMP) etc.) to dissolve organic components such as binders in the solvent (ultrasonic dispersion and other methods can also be combined to promote dissolution), wash and filter, collect the solid phase, and then use density difference to centrifuge to separate the relatively low-density conductive agent from the suspension, collect the centrifuged precipitate to obtain the test powder of positive electrode active material.

[0148] 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.

[0149] 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.

[0150] The particle morphology of the positive electrode active material can be used to statistically determine the particle size of the primary particles in the positive electrode active material, thereby obtaining the average particle size of the primary particles in the positive electrode active material. The particle morphology of the positive electrode active material can be obtained using scanning electron microscopy (SEM) results (e.g., ZEISS Sigma 300, JEOL SEM, Axia Chemi SEM, etc.). The sample to be tested can be obtained by laying a powder sample of the positive electrode active material on conductive adhesive, or by performing SEM testing on the cross-section of the positive electrode sheet. Non-limitingly, SEM testing can refer to JY / T(001)-1996. One or more regions are randomly selected in the sample to be tested for scanning, and based on the SEM image at a certain magnification, the particle size of each primary particle in the scanned region and the frequency of occurrence of different particle sizes are statistically analyzed, thereby calculating the average particle size of each statistically analyzed primary particle. Non-limitingly, the magnification of a single scanned region can be, for example, 1500X, or further, 1000X, but is not limited to this. To improve the accuracy of statistical results, multiple areas can be randomly selected for scanning. The number of particles counted in a single operation can be several hundred, or even greater than or equal to 1000, or greater than or equal to 2000. Increasing the number of particles counted in a single operation helps improve the accuracy of the statistical results.

[0151] In this application, unless otherwise specified, the maximum diameter of the primary particles in each direction in the SEM morphology image of the positive electrode active material is denoted as "the particle size of the primary particles in the positive electrode active material".

[0152] In some embodiments, the average particle size (D1) of the primary particles in the positive electrode active material can be 100 nm to 500 nm, optionally 150 nm to 500 nm, further optionally 150 nm to 450 nm, and even more preferably 200 nm to 450 nm. It can also be any of the following values ​​or a range selected from any two of the following values: 100 nm, 110 nm, 120 nm, 140 nm, 150 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 250 nm, 260 nm, 280 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc.

[0153] By controlling the "average particle size (D1) of primary particles in the positive electrode active material" within the aforementioned range, it is beneficial to better balance the increase in negative electrode interface impedance caused by water in the positive electrode active material and the influence of lithium-ion transport path on battery internal resistance. This is beneficial to significantly improve the high-temperature performance of the battery while also better taking into account its room-temperature performance.

[0154] In some embodiments, the water absorption rate of the positive electrode active material is 50 ppm / h to 85 ppm / h, and may also be any of the following values ​​or a range selected from any two of the following values: 50 ppm / h, 55 ppm / h, 60 ppm / h, 65 ppm / h, 70 ppm / h, 75 ppm / h, 80 ppm / h, 85 ppm / h, etc. The unit of "water absorption rate of the positive electrode active material" represents the increase in water content per unit time, and "water content" refers to the mass percentage of water in the sample. Tests can be performed using methods already available in the art, including but not limited to the Karl Fischer method for moisture content testing. Unless otherwise specified, the test methods described in the following examples can be used for testing.

[0155] In some embodiments, the lithium phosphate cathode material includes a carbon-coated lithium phosphate cathode material, which includes a lithium phosphate matrix and a carbon coating layer located on at least a portion of the surface of the lithium phosphate matrix.

[0156] In this application, unless otherwise stated, "coated positive electrode active material" includes a positive electrode active body and a coating layer located on at least a portion of the surface of the positive electrode active body.

[0157] In this application, unless otherwise specified, "carbon-coated lithium phosphate cathode material" is a coated cathode active material, wherein the cathode active body includes a lithium phosphate matrix, and the coating layer includes a carbon coating layer. Further, the carbon coating layer may include one or more of soft carbon, hard carbon, and amorphous carbon. "Soft carbon" and "hard carbon" have well-known meanings in the art; soft carbon can be graphitized through 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 a transitional carbon material with a very low degree of graphitization and crystallization, approximating an amorphous morphology (or lacking a fixed shape and periodic structural regularity).

[0158] By setting a carbon coating layer on the surface of lithium phosphate cathode materials, the specific surface area of ​​the material may be increased, which in turn leads to an increase in the water absorption rate of the material surface. At this time, by controlling the average particle size (D1) of the primary particles in the cathode active material and the synergistic effect of introducing alkaline alkyne additives, the high-temperature performance of the battery can be significantly improved while also taking into account good room-temperature performance.

[0159] In some embodiments, the specific surface area (BET1) of the positive electrode active material can be 5 m². 2 / g~18m 2 / g, optional 5m 2 / g~16m 2 / g, further optional to 5m 2 / g~15m 2 / g, or even more specifically 5.5m 2 / g~12m 2 / g, or even more specifically 5.5m 2 / g~10m 2 / g, can also be any of the following values ​​or a range selected from any two of the following values: 5 m 2 / g, 5.5 m 2 / g、6 m 2 / g, 6.5 m 2 / g、7 m 2 / g, 7.5 m 2 / g、8 m 2 / g, 8.5 m 2 / g、9 m 2 / g, 9.5 m 2 / g、10 m 2 / g, 10.5 m 2 / g、11 m 2 / g、12 m 2 / g、13 m 2 / g、14 m 2 / g、15 m 2 / g、16 m 2 / g etc.

[0160] In this application, unless otherwise specified, the "specific surface area" of the positive electrode active material has a commonly known meaning in the art. It can be tested using nitrogen adsorption specific surface area analysis and calculated using the BET (Brunauer Emmett Teller) method. Nitrogen adsorption specific surface area analysis can be performed using a Tri Star II specific surface area and porosity analyzer from Micromeritics, USA. The test procedures can refer to GB / T 19587-2004. Detailed steps are as follows: Using nitrogen as the adsorbent gas, calculate the specific surface area of ​​the material using the BET method; add the sample to be tested into a BET test tube until it reaches 2 / 3 of the bottom bulb, degas the sample, and heat it; after cooling to room temperature, refill with nitrogen to remove the vacuum, and plug the sample tube opening with a stopper, recording the sample weight; remove the stopper, add a filling rod, install the sample tube onto the instrument analysis station, input the sample weight, and begin the test. Before testing, the sample can be dried.

[0161] For lithium-ion secondary batteries, exemplarily including lithium-ion secondary batteries with positive electrode active materials including carbon-coated lithium phosphate positive electrode materials, by controlling the "specific surface area (BET1) of the positive electrode active material" within the aforementioned range, it is beneficial to better control the water absorption rate of the positive electrode active material, while also better suppressing high-temperature interface side reactions, which is beneficial to better improve the high-temperature performance of the battery while also taking into account good room-temperature performance.

[0162] In some embodiments, the carbon-coated lithium phosphate cathode material satisfies one or more of the following characteristics:

[0163] (a1) The graphitization degree (G1) of the carbon coating layer can be greater than or equal to 28%, further can be 28%~95%, even further can be 40%~95%, even further can be 40%~90%, even further can be 40%~85%, even further can be 50%~70%, and can also be any of the following values ​​or a range selected from any two of the following values: 28%, 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, 46%, 48%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.; the graphitization degree (G1) of the carbon coating layer can also be selected from any of the following ranges: 28%~90%, 40%~90%, 50%~90%, 28%~85%, 50%~85%, 28%~70%, 40%~70%, etc.;

[0164] (a2) Mass percentage of carbon coating in carbon-coated lithium phosphate cathode materials (F) B The percentage can be 0.5% to 2.5%, or optionally 0.8% to 2%, or any of the following percentages or a range composed of any two of the following percentages: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, etc.

[0165] (a3) Average thickness of carbon coating (D) B The thickness can be less than or equal to 8 nm, and can be selected from 1 nm to 8 nm; it can also be less than or equal to 6 nm, and can be selected from 1 nm to 6 nm; further, it can be selected from 1 nm to 5 nm; it can also be any of the following values ​​or a range selected from any two of the following values: 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 7 nm, 8 nm, etc.; non-limitingly, the average thickness (D) of the carbon coating layer... BThe average thickness (D) of the carbon coating can also be less than or equal to any of the following values: 5 nm, 5.5 nm, 6.5 nm, 7 nm, etc.; non-limitingly, the average thickness (D) of the carbon coating layer can also be less than or equal to any of the following values: 5 nm, 5.5 nm, 6.5 nm, 7 nm, etc. B It can also be smaller than any of the following values: 5.5 nm, 6 nm, 7 nm, 8 nm, etc.;

[0166] (a4) Maximum thickness of carbon coating (D) max The nm wavelength can be less than or equal to 12 nm, further less than or equal to 10 nm, even further less than or equal to 8 nm, even further less than or equal to 6 nm, and even further selectable as 1 nm to 5 nm. It can also be any of the following values ​​or a range selected from any two of the following values: 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 9 nm, 10 nm, 12 nm, etc. It can also be less than any of the following values, less than or equal to any of the following values, or greater than or equal to 1 nm and less than or equal to any of the following values: 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 9 nm, 10 nm, 12 nm, etc.

[0167] In some embodiments, the carbon-coated lithium phosphate cathode material 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):

[0168] (a1') The graphitization degree (G1) of the carbon coating layer is 40%~90%, and can be selected as 40%~85%;

[0169] (a2') Mass percentage of carbon coating in carbon-coated lithium phosphate cathode materials (F) B The percentage is 0.8% to 2%;

[0170] (a3') Average thickness of the carbon coating (D) B The range is 1nm to 5nm;

[0171] (a4') Maximum thickness of carbon coating (D) max The wavelength is less than or equal to 10 nm, and optionally less than or equal to 8 nm.

[0172] In this application, unless otherwise specified, "degree of graphitization" has a well-known meaning in the art and can be used to measure the degree to which the crystals of a carbon material approximate perfect graphite. The degree of graphitization can be tested using instruments and methods known in the art. As a non-limiting example, an X-ray diffractometer can be used for testing. X-ray diffractometers can be models such as the Bruker D8 Discover and Bruker D8 Advance, but are not limited to these. Testing can be performed in accordance with JIS K 0131-1996 and JB / T4220-2011. First, the interlayer spacing d of the (002) crystal plane of the carbon material is measured. 002 The interlayer spacing of the (002) crystal plane can be calculated using the Bragg equation; then, G = (0.3440 - d) can be calculated using the Mering-Maire formula. 002 The graphitization degree is calculated by dividing G by (0.3440 - 0.3354) and calculating 100%, where G is the graphitization degree (%), 0.3440 is the interlayer spacing of non-graphitized carbon (nm), 0.3354 is the interlayer spacing of ideal graphite crystals (half the c-axis lattice constant of hexagonal graphite, nm), and d. 002 This refers to the interlayer spacing of the (002) crystal plane of a carbon material, expressed in nanometers (nm). It should be noted that, in order to obtain more accurate d... 002 The diffraction angle can be corrected by adding Si powder to reduce errors. The degree of graphitization of the carbon coating layer in carbon-coated lithium phosphate cathode materials can be denoted as G1. The higher the degree of graphitization, the closer the carbon material crystal is to perfect graphite.

[0173] For lithium-ion secondary batteries with positive electrode active materials including carbon-coated lithium phosphate-containing positive electrode materials, the following can be used to control the degree of graphitization of the carbon coating layer (G1) or the mass ratio of the carbon coating layer in the carbon-coated lithium phosphate-containing positive electrode material (F1). B "The average thickness of the carbon coating (D)" B ")" and "maximum thickness of carbon coating (D)" max One or more parameters in “)” have relatively low values, which is beneficial to reduce the water absorption rate of the positive electrode active material, reduce or delay the consumption of the negative electrode interface of alkaline alkyne additives, reduce the growth rate of the negative electrode interface impedance, and better balance the room temperature performance.

[0174] For lithium-ion secondary batteries with positive electrode active materials including carbon-coated lithium phosphate positive electrode materials, by controlling the graphitization degree of the carbon coating layer within the aforementioned range, it is possible to better coordinate the water absorption rate of the material surface, the conductivity of the carbon coating layer, and the ion diffusion resistance of the carbon coating layer. This will better balance the influence of the carbon coating layer on the battery's internal resistance and the suppression effect of the carbon coating layer on the positive electrode interface side reactions, thereby better improving the battery's high-temperature performance while also ensuring good room-temperature performance.

[0175] For example, controlling a relatively high degree of graphitization within the aforementioned range is beneficial for reducing the water absorption rate on the material surface and improving the conductivity of the carbon coating layer, while also better controlling the ion diffusion resistance.

[0176] For example, controlling a relatively low degree of graphitization within the aforementioned range is beneficial for reducing the ion diffusion resistance of the carbon coating layer while also better controlling conductivity and water absorption rate.

[0177] By controlling the mass percentage (F) of the carbon coating layer in the carbon-coated lithium phosphate cathode material B "The average thickness of the carbon coating (D)" B ")" and "maximum thickness of carbon coating (D)" max One, two, or three of the above-mentioned factors are beneficial for controlling the positive electrode active material to have a lower water absorption rate, and also beneficial for reducing the influence of ion diffusion impedance on the battery internal resistance, and for better balancing the battery's room temperature performance.

[0178] For positive or negative electrode active materials that include a coating layer (examples of which include carbon coating layers), particle cutting can be performed using methods such as FIB (Focused Ion Beam) or CP (Ion Beam Cross-Section Polishing) to obtain a cross-section. The particle cross-sectional morphology can then be 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, average thickness, and maximum thickness at multiple locations within a single particle can be analyzed and calculated. The average thickness of the coating layer in the coated material can be calculated based on the average thickness of the coating layer in multiple particles, and the maximum thickness of the coating layer in the coated material can be calculated based on the maximum thickness of the coating layer in 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) and Raman spectroscopy, the types and contents of substances in the coating layer and the positive electrode active body can be identified, or the types and contents of substances in the coating layer and the negative electrode active body can be identified.

[0179] In some embodiments, the D of the positive electrode active material v 50 (denoted as D) v501) can be 1μm to 5μm, optionally 1μm to 4μm, further optionally 1.5μm to 4μm, and even further optionally 1.5μm to 3.5μm, or any of the following values ​​or a range selected from any two of the following values: 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc. Non-limitingly, the D of the positive electrode active material... v 50 can also be selected from any suitable range of the following: 1μm~3μm, 1.5μm~3μm, 2μm~5μm, 2μm~4.5μm, 2μm~3.5μm, etc.

[0180] Unless otherwise stated in this application, D v 50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. This parameter indicates that the particle size of 50% of the material's volume is less than or equal to D. v 50, and particles accounting for 50% of the material volume have a particle size greater than D. v 50. Those skilled in the art will understand D v The meaning of 50 can be determined using instruments and methods known in the field. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer or the LS-909 laser particle size analyzer from Malvern Instruments Ltd. (UK). Furthermore, for equipment models such as the Malvern 2000 laser particle size analyzer, the standard procedure GB / T19077-2016 / ISO 13320:2009 can be referenced for testing.

[0181] By using the D of the positive electrode active material v 50 (denoted as D) v By controlling the primary particle size (D1) within the aforementioned range (501), the agglomeration degree of the primary particles can be adjusted by combining the control of the average particle size (D1), thus better controlling the specific surface area and water absorption rate. It can also better control the overall ion transport path of the positive electrode active material particles. Based on the synergistic effects of the aforementioned factors, but not limited to the aforementioned theories, it is beneficial to better control the battery's internal resistance and to better balance the battery's high-temperature performance with its room-temperature performance. In some examples, for lithium-ion secondary batteries where the positive electrode active material includes carbon-coated lithium phosphate-containing positive electrode materials, it can also better balance the effects of the carbon coating layer on the specific surface area, water absorption rate, conductivity, ion diffusion resistance, and positive electrode interface side reactions, thus significantly improving the battery's high-temperature performance while also better balancing its room-temperature performance.

[0182] In some implementations, the D of the positive electrode active material can be tested using the following method. v 50, etc. A Malvern 2000 (MasterSizer 2000) laser particle size analyzer was used, following the standard procedure: GB / T19077-2016 / ISO 13320:2009. The detailed test procedure included: taking an appropriate amount of the sample to be tested, adding a solvent (the solvent can be deionized water, and the sample concentration can be controlled at 8%~12% opacity), sonicating for 5 min (53KHz / 120W) to fully disperse the sample, and then measuring the sample according to GB / T19077-2016 / ISO 13320:2009. Non-limiting examples of solvents include deionized water. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light. Based on the test data, a particle size volume distribution map is plotted, and D is obtained from the distribution map. v Parameters such as 50. To avoid agglomeration during the drying process affecting particle size testing, a dispersion test was performed on the washed and moistened sample. The washing reagent can be anhydrous ethanol, but is not limited to it.

[0183] In some embodiments, the negative electrode includes a negative electrode active layer, which includes a negative electrode active material; the negative electrode active material includes at least one of carbon-based materials and silicon-based materials.

[0184] In some embodiments, the negative electrode active material includes a carbon-based material. Non-limitingly, the carbon-based material may include one or more of graphite-based materials, soft carbon, and hard carbon; further, the carbon-based material may include one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Non-limitingly, the mass percentage of the carbon-based material in the negative electrode active material may be 80% to 100%, optionally 90% to 100%, further optionally 95% to 100%, and even more optionally 97% to 100%, or may be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0185] In some embodiments, the negative electrode active material includes a graphite-based material, and may further be a graphite-based material.

[0186] In this application, "graphite-based material" refers to a negative electrode active material containing a graphite bulk. Non-limitingly, graphite-based materials may include one or more of coated graphite-based materials and uncoated graphite. Coated graphite-based materials include a graphite bulk and a coating layer located on at least a portion of the surface of the graphite bulk; it is understood that the coating layer is different from the material in the graphite bulk. Non-limitingly, the mass percentage of the graphite bulk in the graphite-based material 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%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%. Graphite-based materials may include, but are not limited to, one or more of artificial graphite and natural graphite. In some embodiments, the carbon-based material is a graphite-based material. In some embodiments, the negative electrode active material is a graphite-based material.

[0187] In this application, the “graphite body” is composed of graphite.

[0188] In some embodiments, the graphite-based material accounts for 80% to 100% of the mass of the negative electrode active material, optionally 90% to 100%, further optionally 95% to 100%, and even more preferably 97% to 100%. It can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0189] In some embodiments, the negative electrode active material includes graphite, and further, the graphite may include one or more of artificial graphite and natural graphite.

[0190] Non-limitingly, the mass percentage of silicon-based material in the negative electrode active material can be 0% to 20%, optionally 0% to 10%, or any of the following percentages or a range selected from any two of the following percentages: 0, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.

[0191] Non-limitingly, the mass percentage of silicon-based material in the negative electrode active material can also be 1% to 20%, optionally 1% to 10%, or any of the following percentages or a range selected from any two of the following percentages: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.

[0192] In some embodiments, the negative electrode active material includes a silicon-based material. Without limitation, the silicon-based material may include one or more of elemental silicon, silicon-oxygen materials, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0193] "Silicon-carbon composite material" is a silicon-based material comprising a porous carbon matrix and elemental silicon located within the pores of the porous carbon matrix. Silicon-carbon composite materials can be obtained using vapor deposition methods. Those skilled in the art can prepare silicon-carbon composite materials using conventional methods in the field.

[0194] In some implementations, the negative electrode sheet 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] (b1) The mass percentage of silicon-based material in the negative electrode active material is 0-20%, which can be selected as 1%-20%, and further selected as 1%-10%. It can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.

[0196] (b2) Silicon-based materials include silicon-carbon composite materials, which include a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix; without limitation, the mass percentage of silicon-carbon composite materials in silicon-based materials may be 80% to 100%, optionally 90% to 100%, further optionally 95% to 100%, even further optionally 97% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 100%, etc.

[0197] (b3) Carbon-based materials include graphite-based materials; without limitation, the mass percentage of graphite-based materials in the negative electrode active material may be 80% to 100%, optionally 90% to 100%, further optionally 95% to 100%, and even further optionally 97% to 100%, and may also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 100%, etc.

[0198] (b4) The negative electrode active material includes a coated negative electrode material, which includes a negative electrode active body and a carbon coating layer located on the negative electrode active body, including at least a portion thereof; without limitation, the mass percentage of the coated negative electrode material in the negative 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%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 100%, etc.

[0199] By controlling the content of silicon-based materials in the negative electrode active material and / or the type of positive electrode active material within the aforementioned range, the expansion and contraction changes of the negative electrode can be better controlled, the generation of fresh interfaces can be reduced, and side reactions at the negative electrode interface can be suppressed. This is beneficial for reducing the consumption rate of alkaline alkyne additives, reducing the rate of increase in battery internal resistance, and better balancing the battery's performance at room temperature. For example, in silicon-based materials, the volume expansion and contraction changes of silicon-carbon composite materials are relatively low.

[0200] In some embodiments, the negative electrode active material includes a coated negative electrode material, which includes a negative electrode active body and a carbon coating layer located on at least a portion of the negative electrode active body. It is understood that the carbon coating layer and the negative electrode active body have different chemical compositions. The negative electrode active body can be selected from at least one material known in the art suitable for negative electrode active materials. Non-limitingly, the negative electrode active body can include one or more of graphite and silicon-based materials; non-limitingly, graphite can include one or more of natural graphite and artificial graphite; non-limitingly, the silicon-based material can include one or more of elemental silicon, silicon-oxygen materials, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon alloys. Non-limitingly, the carbon coating layer in the coated negative electrode material can include one or more of soft carbon, hard carbon, and amorphous carbon. Non-limitingly, the average thickness of the carbon coating in the coated negative electrode material can be 1 nm to 500 nm, optionally 50 nm to 500 nm, further optionally 100 nm to 500 nm, and even more preferably 100 nm to 200 nm. Non-limitingly, the mass percentage of the coating layer in the coated active material is 0.2% to 5%, optionally 0.5% to 3%. Non-limitingly, the mass percentage of the coated negative electrode material in the negative electrode active material can be 80% to 100%, optionally 90% to 100%, further optionally 92% to 100%, even further optionally 95% to 100%, even further optionally 95% to 98%, and can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0201] In some embodiments, the carbon coating layer in the coated negative electrode material is one of a soft carbon coating layer, a hard carbon coating layer, and an amorphous carbon coating layer. It can be understood that the material composition of the soft carbon coating layer is mainly soft carbon, the material composition of the hard carbon coating layer is mainly hard carbon, and the material composition of the amorphous carbon coating layer is mainly amorphous carbon.

[0202] In some embodiments, the coated negative electrode material includes coated graphite, and the negative electrode active body in the coated graphite includes a graphite body. Non-limitingly, the mass percentage of coated graphite in the negative electrode active material can be 80% to 100%, optionally 90% to 100%, further optionally 92% to 100%, even further optionally 95% to 100%, even further optionally 95% to 98%, and can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0203] In this application, "coated graphite" is a coated anode material, wherein the anode active body in coated graphite includes a graphite body; coated graphite includes a graphite body and a carbon coating layer located on at least a portion of the surface of the graphite body.

[0204] By incorporating a coated anode material (such as coated graphite) with a carbon coating layer into the anode active material, the lithium-ion transport channels on the surface of the anode active material can be optimized, promoting lithium-ion transport. It also helps to suppress side reactions at the anode interface and inhibit the increase in interfacial impedance caused by the participation of alkaline alkyne additives in film formation, which is beneficial for better control of battery internal resistance and battery performance at room temperature.

[0205] In some embodiments, the coated negative electrode material is coated graphite, in which case the active negative electrode body is the graphite body.

[0206] Those skilled in the art can identify the components in the positive and negative active layers using one or more of the following detection methods known in the art, including but not limited to: Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, and proton nuclear magnetic resonance (NMR) spectroscopy. 1 Methods include 1H NMR, gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), mass spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, single crystal X-ray diffraction (SCXRD), inductively coupled plasma optical emission spectrometry (ICP), 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 structure of the material or substance and the characteristics of the sample.

[0207] As a non-limiting example, EDS can be used to distinguish between carbon and silicon, and thus between carbon-based and silicon-based materials. Similarly, EDS can be used to detect the type and content of conductive agents, but is not limited to this.

[0208] Using natural graphite and artificial graphite as non-limiting examples, the negative electrode active materials can be distinguished by the appearance and morphology of the particles. Further X-ray diffraction (XRD) analysis can be performed. In the XRD pattern, if the characteristic peak near 2θ 26.5° is very sharp and has high intensity, it is natural graphite; if the characteristic peak near 2θ 26.5° is relatively broad and has weak intensity, it is artificial graphite.

[0209] 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, ultrasonic dispersion, centrifugation, and fractional sedimentation. The extracted material is then dried to obtain a powder sample. The obtained powder sample can be used for chemical composition analysis and other tests.

[0210] In some embodiments, in lithium-ion secondary batteries, the mass percentage (C) of alkaline acetylene additives in the electrolyte is... A The percentage can be less than or equal to 3.5%, and can be selected from 0.01% to 3.5%, further selected from 0.05% to 2.5%, even further selected from 0.1% to 2.5%, and even further selected from 0.2% to 2.5%. It can also be any of the following percentages or a range selected from any two of the following percentages: 0.01%, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.5%, 2%, 2.5%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.5%, etc. Non-restrictive, C A It can also be selected from the following ranges: 0.1%~3.5%, 0.1%~3%, 0.1%~2.5%, 0.05%~2%, 0.2%~3.5%, 0.2%~3%, 0.05%~4%, 0.1%~4%, 0.2%~4%, 0.3%~4%, etc.

[0211] By controlling the mass percentage (C) of alkaline acetylene additives in the electrolyte... A Within the aforementioned range, alkaline alkyne additives can continuously play a role in repairing the SEI film during cycling and / or storage, which is more conducive to significantly improving high-temperature performance while also maintaining good room-temperature performance.

[0212] In some embodiments, the additives include negative electrode film-forming additives that are different from basic acetylene additives.

[0213] "Negative electrode film-forming additives" refer to additives that can decompose at the negative electrode working potential and participate in the formation of the negative electrode SEI film. The higher the reduction potential of the negative electrode film-forming additive, that is, the more positive the potential value relative to Li / Li⁺, the earlier the negative electrode film-forming additive decomposes and thus participates in the formation of the negative electrode SEI film. It is understood that some negative electrode film-forming additives can also participate in the formation of the interface film (CEI film) at the positive electrode. Generally, those skilled in the art can determine whether an additive can participate in the formation of the negative electrode SEI film based on reduction potential analysis, analysis of decomposition products and SEI film composition, and electrochemical performance verification. For example, the reduction potential of the additive can be measured by cyclic voltammetry in a simulated battery environment (such as lithium metal-pair working electrode). For example, the composition of the SEI film can be analyzed by chemical composition analysis methods including but not limited to X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). For example, the change in performance indicators such as the initial coulombic efficiency, cycle stability, and impedance spectrum when the additive is introduced can be used to determine whether the introduced additive can participate in the formation of the negative electrode SEI film.

[0214] Unlike basic alkyne additives, negative electrode film-forming additives can competitively participate in negative electrode film formation, which can reduce or delay the consumption of basic alkyne additives in negative electrode film formation. They can also suppress the increase in negative electrode interface resistance caused by the participation of basic alkyne additives in negative electrode film formation, which is beneficial to improve the high-temperature performance of the battery while also better taking into account the room temperature performance.

[0215] In some embodiments, the additives also include one or more of additives B, C, and D;

[0216] Among them, additive B is one or more of silane additives and siloxane additives;

[0217] Additive C is one or more of isocyanate additives and acid anhydride additives;

[0218] Additive D is one or more of lithium salt additives and phosphate ester additives.

[0219] Additives B, C, and D can all be used as negative electrode film-forming additives. Additive B is a type of additive with low negative electrode film-forming impedance and a certain degree of acid removal effect, although its acid removal effect is lower than that of basic alkyne additives, and its negative electrode film-forming impedance is also lower than that of basic alkyne additives. Additive C is a type of additive with good acid removal effect, which is better than that of basic alkyne additives, but its negative electrode film-forming impedance is higher than that of basic alkyne additives. Additive D has very low negative electrode film-forming impedance, far lower than that of basic alkyne additives.

[0220] By utilizing the synergistic effect of basic alkyne additives with one or more of additives B, C, and D, it is beneficial to achieve a significant improvement in high-temperature performance while also maintaining good room-temperature performance.

[0221] Non-limitingly, in lithium-ion secondary batteries, the sum of the mass percentages of additives B, C, and D in the electrolyte can be greater than or equal to 0.02%, optionally 0.02% to 5%, further optionally 0.02% to 3%, further optionally 0.02% to 1.5%, also optionally 0.1% to 5%, further optionally 0.1% to 3%, even further optionally 0.1% to 1.5%, even further optionally 0.1% to 1%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0222] Without limitation, silane additives may include tris(trimethylsilane)borate (TMSB).

[0223] Without limitation, isocyanate additives may include, but are not limited to, toluene diisocyanate.

[0224] Without limitation, acid anhydride additives may include one or more of maleic anhydride, citrate anhydride, trifluoromethyl maleic anhydride, succinic anhydride, glutaric anhydride, succinic anhydride, etc.

[0225] Non-limitingly, in lithium-ion secondary batteries, the mass percentage of anhydride additives in the electrolyte can be 0% to 1%, optionally 0.01% to 1%, further optionally 0.1% to 1%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, etc.

[0226] Non-limitingly, lithium salt additives may include one or more of lithium oxalate, lithium tetrafluoroborate, lithium difluorophosphate, and fluorosulfonic acid lithium salts; non-limitingly, lithium oxalate may include one or more of lithium difluorooxalateborate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate; non-limitingly, fluorosulfonic acid lithium salts may include one or more of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide (LiFSI).

[0227] Non-limitingly, phosphate ester additives may include silicon-based phosphate ester additives; non-limitingly, silicon-based phosphate ester additives may include one or more of tris(trimethylsilane) phosphate, tris(trimethylsilyl) phosphite, etc.

[0228] In some implementations, the additives include lithium salt additives.

[0229] Non-limitingly, in lithium-ion secondary batteries, the mass percentage of lithium salt additives in the electrolyte can be 0 to 3%, greater than 0 and less than or equal to 3%, further optionally 0.05% to 3%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, etc.

[0230] In this application, when the mass percentage of lithium salt additives (such as LiFSI) in the electrolyte is greater than 3%, it can usually also play the role of electrolyte salt. Unless otherwise specified, the mass percentage of lithium salt additives (such as LiFSI) in the electrolyte in additive B is recorded as 3%.

[0231] In some implementations, the additives include phosphate esters.

[0232] Non-limitingly, in lithium-ion secondary batteries, the mass percentage of phosphate ester additives in the electrolyte can be 0 to 2%, greater than 0 and less than or equal to 2%, further optionally 0.1% to 2%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.5%, 2%, etc.

[0233] In some embodiments, in lithium-ion secondary batteries, the mass percentage (C) of additive B in the electrolyte is... BThe percentage can be 0% to 1%, or 0.1% to 1%, or any of the following percentages or a range of any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, etc.

[0234] Non-limitingly, in the electrolyte of a lithium-ion secondary battery, the mass ratio of additive B to the basic alkyne additive can be any of the following values ​​or a range selected from any two of the following values: 0, 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, etc. In some embodiments, in the electrolyte of a lithium-ion secondary battery, the mass ratio of additive B to the basic alkyne additive can be 0.1 to 50, optionally 0.1 to 1, and further optionally 0.2 to 1.

[0235] In some embodiments, in the lithium-ion secondary battery, the mass percentage of additive C in the electrolyte is 0% to 1%, optionally 0.1% to 1%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.01%, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, etc.

[0236] Non-limiting, in the electrolyte of a lithium-ion secondary battery, the mass ratio of additive C to alkaline acetylene additive (C0) is... C The value can be any of the following values ​​or a range selected from any two of the following values: 0, 0.01, 0.02, 0.04, 0.05, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, etc. In some embodiments, the mass ratio of additive C to alkaline alkyne additive in the electrolyte of a lithium-ion secondary battery can be 0.01 to 50, optionally 0.1 to 50, further optionally 0.1 to 20, even further optionally 0.1 to 1, and may also be 0.02 to 1.

[0237] In some embodiments, in the lithium-ion secondary battery, the mass percentage of additive D in the electrolyte is 0% to 2%, optionally 0.1% to 2%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.5%, 2%, etc.

[0238] Non-limitingly, in the electrolyte of a lithium-ion secondary battery, the mass ratio of additive D to alkaline acetylene additive (C) D The additive D can be any of the following values ​​or a range selected from any two of the following values: 0, 0.05, 0.08, 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, etc. In some embodiments, the mass ratio of additive D to alkaline alkyne additive in the electrolyte of a lithium-ion secondary battery is 0.1 to 100, optionally 0.1 to 50, further optionally 0.1 to 20, even further optionally 0.1 to 2, and may also be 0.2 to 1, etc.

[0239] In some embodiments, the mass ratio of additive B, additive C, additive D, and basic acetylene additive in the electrolyte of a lithium-ion secondary battery is (0~20):(0~20):(0:50):1, and may be combined with features of any suitable embodiment in the context. For example, the mass ratio of additive B, additive C, additive D, and basic acetylene additive in the electrolyte of a lithium-ion secondary battery may be (0.1~20):(0~20):(0:50):1, (0~20):(0.02~20):(0:50):1, (0~20):(0~20):(0.1:50):1, (0~0.5):(0~0.5):(0~1):1, (0.05~0.5):(0.02~0.5):(0.1~1):1, etc.

[0240] In some embodiments, in lithium-ion secondary batteries, 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):

[0241] (c1) The mass ratio of additive B to basic acetylene additive is 0.1~50, and can be selected as 0.1~1;

[0242] (c2) The mass ratio of additive C to basic acetylene additive is 0.02~50, and can be selected as 0.02~1;

[0243] (c3) The mass ratio of additive D to alkaline acetylene additive is 0.1~100, and can be selected as 0.1~2.

[0244] In some embodiments, the mass ratio of additive B, additive C, additive D and basic acetylene additive in the electrolyte of a lithium-ion secondary battery is (0~0.5):(0~0.5):(0~1):1.

[0245] In some embodiments, the basic alkyne additives satisfy one or more of the following characteristics:

[0246] (d1) The molecular weight of alkaline acetylene additives is less than or equal to 500 Da;

[0247] (d2) The molecules of basic alkyne additives contain 1 to 4 carbon-carbon triple bonds; not limited thereto, the number of carbon-carbon triple bonds in the molecules of basic alkyne additives can be 1, 2, 3 or 4.

[0248] (d3) The carbon-carbon triple bond is CH≡C-;

[0249] (d4) The molecules of basic alkyne additives contain 1 to 4 Lewis base nitrogen heterocycles; not limited thereto, the number of Lewis base nitrogen heterocycles in basic alkyne additives can be 1, 2, 3 or 4.

[0250] (d5) Lewis base nitrogen heterocycles include imidazole rings;

[0251] (d6) In the molecule of basic alkyne additives, the carbon-carbon triple bond and the Lewis base nitrogen heterocycle are linked by a linker L1, which contains a C-type carbon bond covalently bonded to the carbon-carbon triple bond. 1-3 Alkyl groups or those containing fluorinated C atoms covalently bonded to a carbon-carbon triple bond 1-3 Alkylene.

[0252] In some embodiments, the basic alkyne additives satisfy one or more of the following characteristics:

[0253] (e1) The molecular weight of alkaline acetylene additives is less than or equal to 300 Da;

[0254] (e2) The molecules of basic alkyne additives contain 1 to 4 imidazole rings; not limited thereto, the number of imidazole rings in basic alkyne additives can be 1, 2, 3 or 4.

[0255] (e3) Lewis base nitrogen heterocycles include imidazole rings; the imidazole ring in a Lewis base nitrogen heterocycle is substituted by 0, 1, or more substituents Q2, and each substituent Q2 in the substituted imidazole group is independently C.1-3 Alkyl, cyano, or fluorine atom;

[0256] (e4) Basic acetylene additives consist of carbon-carbon triple bonds, C 1-3 Alkylene and -OC(=O)-R 10 It is formed by sequential covalent bonds, R 10 It is a Lewis base nitrogen heterocycle.

[0257] In some embodiments, the basic alkyne additive includes compound II with the structure shown in formula (II): ; among which, L 11 C 1-3 Alkylene, Q2 is independently C 1-3 Alkyl, cyano, or fluorine atom, p2 is 0, 1, 2, or 3.

[0258] In a non-limiting sense, in a lithium-ion secondary battery, the mass percentage of compound II in the alkaline alkyne additive 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%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0259] In this application, "C" is involved. 1-3 "alkylene" can be methylene, ethylene, or propylene unless otherwise specified, and can further be methylene, 1,2-ethylene, or 1,3-propylene.

[0260] In this application, "C" is involved. 1-3 "alkyl" can be methyl, ethyl, or propyl unless otherwise specified, and may further be methyl, ethyl, n-propyl, or isopropyl.

[0261] In some implementations, L 11 It is a methylene group.

[0262] In some implementations, p2 is 0.

[0263] In some embodiments, compound II is (Compound IIa).

[0264] Non-limitingly, in lithium-ion secondary batteries, the mass percentage of compound IIa in the alkaline alkyne additive 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%, 82%, 84%, 85%, 86%, 88%, 90%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0265] By controlling the molecular weight of alkaline alkyne additives within the aforementioned lower range, the alkaline alkyne additives can have a smaller molecular size, which is beneficial for better control of the low viscosity characteristics of the electrolyte, resulting in higher conductivity of the electrolyte and better control of the battery's internal resistance.

[0266] By controlling the number of carbon-carbon triple bonds in alkaline alkyne additives within the aforementioned range, it is beneficial to suppress the increase in negative electrode interface impedance caused by alkaline alkyne additives participating in the formation and repair of the SEI film, and it is also beneficial to control the influence of alkaline alkyne additives on liquid phase impedance; thus, the increase in battery internal resistance can be better suppressed.

[0267] By controlling the number of Lewis base nitrogen heterocycles in the basic alkyne additives within the aforementioned range, it is beneficial to better absorb acid byproducts in the electrolyte, and at the same time, it is also beneficial to control the steric hindrance effect of Lewis base nitrogen heterocycles on carbon-carbon triple bonds.

[0268] Examples of Lewis base nitrogen heterocycles include the imidazole ring in compound II.

[0269] Introducing fluorine atom substituents into Lewis base nitrogen heterocycles (such as imidazole rings) is beneficial for inducing the formation of inorganic lithium fluoride phases at the negative electrode, which is beneficial for improving the stability of the SEI film and reducing the interfacial impedance, and for better improving the high-temperature performance of the battery while taking into account the room-temperature performance.

[0270] In some embodiments, the additives in the electrolyte include cyclic sulfates.

[0271] In a non-limiting sense, in a lithium-ion secondary battery, the mass percentage of cyclic sulfate esters in the electrolyte can be 0 to 3%, preferably 0.1% to 3%.

[0272] In this application, "cyclic sulfate" contains one or more monocyclic sulfate units, and "monocyclic sulfate unit" contains *-OS(=O)2-O-*, where each * independently represents a bonding site with a carbon atom.

[0273] In some embodiments, the additive includes a polycyclic sulfate ester, which contains a plurality of monocyclic sulfate ester units.

[0274] In some embodiments, the multiple monocyclic sulfate units in the polycyclic sulfate ester are linked in a chain-like manner.

[0275] In some embodiments, the number of monocyclic sulfate units in the polycyclic sulfate ester is 2 to 4, and may further be 2, 3 or 4.

[0276] In some embodiments, the monocyclic sulfate unit is a 5- to 7-membered monocyclic ring, which can be a 5-membered ring, a 6-membered ring, or a 7-membered ring, and more specifically, a 5-membered ring or a 6-membered ring.

[0277] In some embodiments, the monocyclic ring in the monocyclic sulfate unit is replaced by 0, 1, or more substituents Q3, each of which is independently a halogen, C, or C. 1-3 Alkyl or C 1-3 Alkoxy group. Optionally, the substituent Q3 in the monocyclic sulfate unit is each independently a fluorine atom, a methyl group, or a methoxy group.

[0278] By introducing cyclic sulfates into the electrolyte, the negative electrode interface film can be optimized, the stability of the negative electrode SEI film can be improved, the negative electrode interface side reactions can be reduced, and the negative electrode interface impedance and battery internal resistance can be better controlled.

[0279] In some embodiments, the additives in the electrolyte include vinyl sulfate (DTD).

[0280] In some embodiments, the additives in the electrolyte include vinylene carbonate (VC). Vinylene carbonate (VC) can optimize the SEI film. By introducing VC into the electrolyte, it is beneficial to reduce or delay the consumption of the negative electrode film by basic alkyne additives, better control the negative electrode interface impedance and battery internal resistance, and improve room temperature performance.

[0281] Non-limiting, in lithium-ion secondary batteries, the mass percentage of VC in the electrolyte can be 0 to 5%, further can be 0 to 3%, can also be 0.1% to 3%, and can also be any of the following percentages or a range selected from any two of the following percentages: 0, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, etc.

[0282] In some embodiments, the additives in the electrolyte include fluorocarbonate additives.

[0283] In a non-limiting sense, in lithium-ion secondary batteries, the mass percentage of fluorocarbonate additives in the electrolyte can be 0 to 10%, preferably 0.1% to 10%.

[0284] In some embodiments, fluorocarbonate additives may include fluoroethylene carbonate (FEC). Non-limitingly, in lithium-ion secondary batteries, the mass percentage of FEC in the electrolyte may be 0-10%, optionally 0-5%, and further optionally 0.1%-10%, and even more preferably 0.1%-5%.

[0285] Fluorinated ethylene carbonate (FEC) can form a robust interfacial film with low ion transport impedance on the negative electrode surface at room temperature. By introducing fluorocarbonate additives (such as FEC) into the electrolyte, it is beneficial to reduce or delay the consumption of basic alkyne additives in the negative electrode film formation, and better control the negative electrode interfacial impedance and battery internal resistance.

[0286] In some embodiments, the electrolyte includes one or both of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and in some of these embodiments, the electrolyte includes at least lithium hexafluorophosphate.

[0287] In some embodiments, in a lithium-ion secondary battery, the molar volume concentration of lithium hexafluorophosphate in the electrolyte can be 0.5 mol / L to 1.2 mol / L, optionally 0.6 mol / L to 1.2 mol / L, optionally 0.7 mol / L to 1.2 mol / L, or 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, etc.

[0288] In some embodiments, the electrolyte includes lithium bis(fluorosulfonyl)imide (LiFSI). Lithium bis(fluorosulfonyl)imide can function as both a film-forming additive and an electrolyte salt in the electrolyte. Non-limitingly, in lithium-ion secondary batteries, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can be 0.01 mol / L to 0.5 mol / L, optionally 0.01 mol / L to 0.3 mol / L, or any of the following concentrations or a range selected from any two of the following concentrations: 0.01 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.075 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L. mol / L, 0.35 mol / L, 0.4mol / L, 0.45 mol / L, 0.5 mol / L, etc.

[0289] In some embodiments, the electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Non-limitingly, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte may be greater than 0 mol / L and less than or equal to 0.5 mol / L, optionally from 0.01 mol / L to 0.5 mol / L, or may be selected from suitable ranges or values ​​in any of the embodiments described above.

[0290] Lithium bisfluorosulfonylimide (LiFSI) can participate in the formation of a stable solid electrolyte interfacial film at both the positive and negative electrodes. On the one hand, the stability of the positive and negative electrode interfacial film can be improved by introducing LiFSI into the electrolyte; on the other hand, LiFSI has a better ability to dissociate lithium ions than lithium hexafluorophosphate (LiPF6), so the addition of LiFSI is also beneficial to improving the liquid phase conductivity.

[0291] In some embodiments, the non-aqueous solvent includes chain carbonates.

[0292] 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.

[0293] In some embodiments, the structure of the chain carbonate is R 21 -OC(=O)-OR 22 R 21 and R 22 Each is independently an alkyl group having 1 to 3 (which can be 1, 2, or 3) carbon atoms. In some embodiments, R 21 and R 22 Each is independently methyl, ethyl, or propyl. In some embodiments, R 21 and R 22 Each can be methyl or ethyl.

[0294] In some embodiments, the non-aqueous solvent includes chain-like carboxylic acid ester compounds. Without limitation, in lithium-ion secondary batteries, the mass percentage of chain-like carboxylic acid ester compounds in the non-aqueous solvent can be 0% to 40%.

[0295] In this application, unless otherwise specified, "chain carboxylic acid ester" refers to a chain compound having a *-C(=O)-O-* structure, where each * independently represents a bonding site with a carbon atom. Chain carboxylic acid esters used in electrolytes for lithium-ion secondary batteries typically have low viscosity, which is beneficial for improving the lithium-ion conductivity of the electrolyte.

[0296] In some embodiments, in the lithium-ion secondary battery, the ionic conductivity of the electrolyte at 25°C is greater than or equal to 8 mS / cm, and can be selected from 8 mS / cm to 20 mS / cm, further selected from 9 mS / cm to 18 mS / cm, or can be any of the following conductivity values ​​or a range selected from any two of the following conductivity values: 8 mS / cm, 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 18 mS / cm, 20 mS / cm, etc.

[0297] In this application, unless otherwise specified, the term "ionic conductivity" of the electrolyte has a commonly known meaning in the art and can be tested and analyzed using existing methods in the field. Ionic conductivity can be obtained using a conductivity meter, such as the DDSJ-318 conductivity meter. The testing temperature can be 25±0.1℃. The testing method can be performed according to HG / T 4067-2015. Unless otherwise specified, the unit of ionic conductivity of the electrolyte is millisiemens per centimeter (mS / cm).

[0298] In some embodiments, the positive electrode active material includes a lithium phosphate-based positive electrode material with an olivine structure. Non-limiting examples of lithium phosphate-based positive electrode materials with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium iron phosphate include LiFePO4. Examples of lithium manganese phosphate include LiMnPO4.

[0299] Non-limiting examples of lithium phosphate cathode materials include lithium iron phosphate cathode materials.

[0300] In this application, unless otherwise specified, "lithium iron phosphate cathode material" refers to a class of cathode active materials containing lithium iron phosphate components. Unless otherwise specified, "lithium iron phosphate cathode material" may have an olivine structure.

[0301] In some embodiments, the positive electrode active material includes lithium iron phosphate-based positive electrode materials. Further, the lithium iron phosphate-based positive electrode material may include at least one of lithium iron phosphate and a composite material of lithium iron phosphate and carbon.

[0302] In some embodiments, the composite material of lithium iron phosphate and carbon is carbon-coated lithium iron phosphate.

[0303] In some implementations, lithium iron phosphate cathode materials include carbon-coated lithium iron phosphate.

[0304] In this application, the term "carbon-coated lithium iron phosphate" includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body, wherein the lithium iron phosphate body comprises lithium iron phosphate. Non-limitingly, the carbon coating layer in the carbon-coated lithium iron phosphate may include one or more of soft carbon, hard carbon, and amorphous carbon. Non-limitingly, the mass percentage of the carbon coating layer in the lithium iron phosphate cathode material may be 0.5% to 2.5%, optionally 0.8% to 2%.

[0305] In some embodiments, lithium iron phosphate cathode materials include lithium iron phosphate-based cathode materials. Lithium iron phosphate-based cathode materials refer to a class of cathode active materials containing lithium iron phosphate.

[0306] In some implementations, the lithium iron phosphate body includes lithium iron phosphate.

[0307] In some embodiments, the lithium iron phosphate-based cathode material includes carbon-coated lithium iron phosphate. In this case, the carbon-coated lithium iron phosphate comprises carbon-coated lithium iron phosphate.

[0308] 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. Further, the carbon coating layer in carbon-coated lithium iron phosphate may include one or more of soft carbon, hard carbon, and amorphous carbon.

[0309] In some implementations, the lithium-ion secondary battery 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):

[0310] (f1) The mass percentage of lithium phosphate-containing cathode material in cathode active material can be 80%~100%, or can be 90%~100%, or can be any of the following percentages or a range selected from any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0311] (f2) Lithium-containing phosphate cathode materials include carbon-coated lithium iron phosphate; without limitation, the mass percentage of carbon-coated lithium iron phosphate in lithium-containing phosphate cathode materials 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%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0312] The following is a description of the positive electrode sheet.

[0313] 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.

[0314] 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%, and may further be greater than or equal to 90 wt%.

[0315] Unless otherwise stated, “wt%” in this application means weight percentage.

[0316] 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.

[0317] 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).

[0318] The types of positive electrode active materials in the positive electrode sheet can be found in the description in the context of this application. Without limitation, other types of positive electrode active materials may also be introduced, as long as the solution provided in the first aspect of this application can significantly improve the high-temperature performance of the battery while also maintaining good room-temperature performance.

[0319] 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.

[0320] 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.

[0321] 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.

[0322] 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.

[0323] 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 electrode 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 electrode 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 electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. 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 / 1540.25 mm. 2 The optional value is (0.2~0.4) g / 1540.25 mm. 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 ~2.6g / cm 3 .

[0324] The term "compacted density" as used in this application has a meaning known in the art and is one of the reference indicators for the energy density of materials. In this application, unless otherwise specified, the compacted density of the positive electrode refers to the ratio of the mass of the positive electrode active layer to its volume, and the compacted density of the negative electrode refers to the ratio of the mass of the negative electrode active layer to its volume.

[0325] The following are some other descriptions of the negative electrode plate.

[0326] 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.

[0327] 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%.

[0328] 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.

[0329] 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).

[0330] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon-oxygen materials, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials or substances, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0331] 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%.

[0332] For further information on the types of negative electrode active materials, please refer to the context of this application.

[0333] 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%.

[0334] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Without limitation, 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%.

[0335] 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 optional 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 surface density of the coating on one side of the negative electrode current collector, based on dry weight (excluding solvent), can be 7.5 mg / cm³. 2 ~22mg / cm 2 The optional value is (0.12~0.2) g / 1540.25 mm. 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~2.0g / cm 3 1.0g / cm can be selected. 3 ~1.8g / cm 3 .

[0336] The electrolyte is described below as an example.

[0337] The electrolyte serves to conduct ions between the positive and negative electrodes. The electrolyte consists of an electrolyte salt and a solvent.

[0338] In some embodiments, the electrolyte is a non-aqueous electrolyte. A non-aqueous electrolyte may include an electrolyte salt and a non-aqueous solvent.

[0339] In some embodiments, the molar volume concentration of the electrolyte salt in the electrolyte is typically 0.5 mol / L to 5 mol / L, optionally 0.5 mol / L to 2 mol / L, further optionally 0.6 mol / L to 1.8 mol / L, and even more preferably 0.7 mol / L to 1.2 mol / L.

[0340] In some embodiments, the electrolyte salt includes an electrolyte lithium salt, and more particularly, it can be an electrolyte lithium salt. Non-limitingly, other types of electrolyte salts may also be introduced into the electrolyte.

[0341] In some embodiments, the electrolyte salt includes an electrolyte lithium salt. Non-limitingly, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), 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).

[0342] Non-limitingly, the non-aqueous solvent in the electrolyte may include one or more of carbonate solvents, carboxylic acid ester solvents, and sulfone solvents. Carbonate solvents may include one or more of cyclic carbonates and linear carbonates. Cyclic carbonates may include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), and fluoroethylene carbonate (FEC). Linear carbonates may include, but are not limited to, one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Non-limitingly, the number of carbon atoms in the linear carbonate may be 3 to 9, optionally 3 to 7, and may also be 3, 4, 5, 6, 7, 8, or 9, or selected from any range of two of the aforementioned values. Carboxylic acid ester solvents may include one or more of linear carboxylic acid esters and cyclic lactones. The chain carboxylic acid ester may include, but is not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. Non-limitingly, the chain carboxylic acid ester may have 2 to 8 carbon atoms, optionally 3 to 8, or 2, 3, 4, 5, 6, 7, or 8, or selected from any range of two of the aforementioned numbers. The cyclic lactone may include, but is not limited to, 1,4-butyrolactone. The sulfone solvent may include, but is not limited to, one or more of sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0343] The electrolyte includes additives, including at least basic alkyne additives. The types and amounts of additives can also be found in the context description. Non-limitingly, other types of additives may also be introduced into the electrolyte. These other types of additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance characteristics, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0344] The following is an exemplary description of the separator membrane.

[0345] 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.

[0346] 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.

[0347] In some embodiments, the thickness of the separator is 6μm to 40μm, and optionally 6μm to 20μm.

[0348] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0349] 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.

[0350] 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 flexible package, such as a pouch. The material of the flexible package can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate. Non-limitingly, the outer packaging can be a composite packaging material, such as an aluminum-plastic bag (which includes both aluminum foil and plastic).

[0351] A lithium-ion secondary battery includes at least one battery cell. A lithium-ion secondary battery may include one or more battery cells.

[0352] 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 The example shown is a square-structured battery cell 5.

[0353] In some of these implementations, reference is made to... Figure 2 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. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The electrode assembly 52 is 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, but is not limited thereto.

[0354] The lithium-ion secondary battery can be a battery device 4 or a battery pack 1.

[0355] 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.

[0356] Figure 3This is battery device 4, used as an example. (See reference...) Figure 3 In the battery assembly 4, multiple battery cells 5 can be arranged sequentially along the length of the battery assembly 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0357] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0358] 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.

[0359] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery devices 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery box.

[0360] 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.

[0361] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, comprising the following steps: immersing an electrode assembly including a positive electrode, a separator, and a negative electrode in an electrolyte for static wetting and formation, thereby obtaining a lithium-ion secondary battery. It is understood that after formation, other steps for preparing the lithium-ion secondary battery may also be included, such as aging.

[0362] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, comprising the following steps: immersing an electrode assembly including a positive electrode, a separator, and a negative electrode in a first electrolyte for formation; adding a second electrolyte to obtain a lithium-ion secondary battery. It is understood that after adding the second electrolyte, other steps for preparing the lithium-ion secondary battery may also be included, such as aging.

[0363] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps:

[0364] 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.

[0365] S200: Inject the first electrolyte into the battery casing, and let it stand to allow the first electrolyte to wet the positive and negative electrode plates, thus forming the battery. The first electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives. The additives include basic alkyne additives, which contain Lewis base nitrogen heterocycles.

[0366] In some embodiments, a second electrolyte comprising alkaline alkyne additives may be optionally injected into the battery casing after formation.

[0367] The definitions of the positive electrode and additives can be found in the context of this application.

[0368] Step S220 after formation: "Optionally, a second electrolyte including alkaline alkyne additives can be injected into the battery casing after formation," is optional. It can be determined based on the target amount of alkaline alkyne additives in the prepared lithium-ion secondary battery.

[0369] In some embodiments, the positive electrode sheet includes a positive active layer, which includes a positive active material; the positive active material includes a lithium phosphate-based positive electrode material, wherein the average particle size of the primary particles in the lithium phosphate-based positive electrode material is 100 nm to 500 nm.

[0370] The prepared lithium-ion secondary battery has the advantages of the lithium-ion secondary battery described in the first aspect of this application.

[0371] The formation temperature can be 45°C, but is not limited to this.

[0372] In some embodiments, the formation can be performed at 45°C using a method comprising the following steps (steps S1, S2, and S3 are performed sequentially):

[0373] S1) Charge at 0.05C to 6% SOC, then let stand for 5 minutes;

[0374] S2) Charge to 20% SOC at 0.1C, then let stand for 5 minutes;

[0375] S3) Charge to 30% SOC using 0.2C;

[0376] The transformation ends.

[0377] SOC (State of Charge) indicates the state of charge. When "SOC=0", it means that the battery is fully discharged, and when "SOC=100%", it means that the battery is fully charged.

[0378] 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 decreases 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 basic alkyne additives in the electrolyte typically decreases after formation treatment compared to the electrolyte before formation treatment.

[0379] The electrolyte injected before formation can be referred to as the first electrolyte; when electrolyte is added after formation, the electrolyte added after formation can be referred to as the second electrolyte. In this application, the terms "first" and "second" in "first electrolyte" and "second electrolyte" 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.

[0380] In some embodiments, in the step of injecting electrolyte (referred to as the first electrolyte) into the battery casing, the mass percentage of the alkaline alkyne additive in the first electrolyte can be 0-3%, optionally 0-2.5%, further optionally 0-2%, even more optionally 0.1%-2%, even more optionally 0.1%-1.5%, even more optionally 0.1%-1%, or can be any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0. The percentages of alkaline alkyne additives in the electrolyte can be 12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.75%, 0.8%, 0.9%, 1%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, etc. After formation, a second electrolyte containing alkaline alkyne additives can optionally be injected into the battery casing to adjust the mass percentage of the alkaline alkyne additives in the electrolyte to the desired concentration. For example, in the prepared lithium-ion secondary battery, the mass percentage of alkaline alkyne additives in the electrolyte can be, but is not limited to, 0.01%~3.5%, 0.1%~3.5%, 0.2%~3.5%, etc.

[0381] By controlling the mass percentage of basic alkyne additives in the first electrolyte within the aforementioned range, the consumption of basic alkyne additives during the negative electrode film formation stage can be controlled, which is beneficial for reducing the initial interfacial impedance of the negative electrode. Furthermore, the mass percentage of basic alkyne additives in the first electrolyte can be controlled to be greater than 0. In this case, the initial interfacial impedance of the negative electrode can be better controlled, and the initial stability of the negative electrode solid electrolyte interphase (SEI) film can be significantly improved. Based on the aforementioned multiple effects, but not limited to the aforementioned theory, this is beneficial for better improving room temperature performance and extending room temperature cycle life and / or room temperature storage life.

[0382] In some embodiments, a second electrolyte containing alkaline alkyne additives is injected after formation.

[0383] In other embodiments, a second electrolyte containing alkaline alkyne additives is not injected after formation.

[0384] It is understandable that after formation or after the injection of a second electrolyte, but before the lithium-ion secondary battery is prepared, other steps, such as aging, may be included. In some non-limiting examples, aging is carried out at 45°C for 48 hours, but it is not limited to this.

[0385] The basic alkyne additives involved in this application are commercially available or synthesized using existing methods in the field of organic chemical synthesis. Given the selected chemical structure of the basic alkyne additive, those skilled in the art can choose a suitable organic synthesis method to prepare the target compound; furthermore, those skilled in the art can also perform structural identification of the prepared basic alkyne additives using one or more of the following detection methods, including but not limited to: 1H NMR spectroscopy (…). 1 Methods include 1H NMR, high performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), and Fourier transform infrared spectroscopy (FT-IR).

[0386] In some embodiments, the content of each additive in the prepared lithium-ion secondary battery can be referred to the first aspect of this application.

[0387] This relates to carbon coating layers in positive and negative electrode active materials. Exemplarily, the carbon coating layer may include one or more of soft carbon, hard carbon, and amorphous carbon. Those skilled in the art can use existing carbon coating methods to achieve carbon coating on the surfaces of positive and negative electrode active materials.

[0388] Taking the deposition of a carbon coating layer on the surface of a positive electrode active material as an example, those skilled in the art can use existing methods in the art (such as co-precipitation) to obtain a positive electrode active bulk precursor, mix the positive electrode active bulk precursor with a carbon source, and then sinter it to form a positive electrode active bulk and achieve surface carbon coating. The graphitization degree of the carbon coating layer can be controlled by adjusting one or more parameters such as sintering temperature and sintering time. Non-limiting examples of positive electrode active bulk materials include lithium iron phosphate. Non-limiting examples of carbon sources include organic materials such as glucose. Non-limiting examples of sintering temperatures include 550℃~900℃.

[0389] Taking carbon coating on the surface of lithium phosphate-based cathode materials (such as lithium iron phosphate) as an example, the carbon coating can be performed non-limitingly using a sol-gel method. The carbon source can be an organic compound, and non-limiting examples of organic compounds include one or more of glucose, sucrose, and organic resins. The carbonization temperature can be non-limitingly 550℃~900℃, optionally 600℃~800℃, and a metal catalyst (such as Fe, Ni, or Co type catalysts) can be optionally added to catalyze graphitization. Soluble metal salts (such as nitrates, chlorides, etc.) can be added to the sol-gel method to generate corresponding metal nanoparticles during carbonization, thereby achieving catalytic graphitization. The degree of graphitization of the carbon coating layer can be adjusted by modifying the carbonization temperature, carbonization time, or selectively adding metal catalysts.

[0390] In addition, other methods known in the art can be used to adjust the graphitization degree of the carbon coating layer on the surface of the positive electrode active material. For example, chemical vapor deposition, high-temperature instantaneous annealing and other methods can be used to achieve a higher graphitization degree, but are not limited to these.

[0391] When preparing coated anode materials by carbon coating the surface of the anode active body, the carbon source can be asphalt, phenolic resin, etc., but is not limited to these. In some embodiments, taking asphalt for amorphous carbon coating as an example: the asphalt (softening point of asphalt, such as 70℃~150℃) is carbonized at 400℃~700℃ for 1h~3h. The heating rate for carbonization can be 1℃ / min~3℃ / min.

[0392] In some embodiments, the lithium-ion secondary battery described in the first aspect of this application is prepared.

[0393] In some embodiments of the third aspect of this application, an electrical device is provided, which includes at least one of the lithium-ion secondary batteries described in the first aspect of this application and lithium-ion secondary batteries prepared by the preparation method of the lithium-ion secondary batteries described in the second aspect of this application.

[0394] Electrical devices that include the aforementioned lithium-ion secondary batteries can have the advantages and benefits of the aforementioned lithium-ion secondary batteries.

[0395] In some embodiments, the electrical device includes a lithium-ion secondary battery according to any of the embodiments provided in this application.

[0396] 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 in aerospace and other fields, and can also be used in energy storage power systems such as hydroelectric, thermal, wind, and solar power plants.

[0397] As an electrical device, lithium-ion rechargeable batteries can be selected according to its usage requirements.

[0398] Figure 6 Here is 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 this electrical device for lithium-ion secondary batteries, a battery device or battery pack can be used.

[0399] 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.

[0400] 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.

[0401] 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.

[0402] In the following examples, room temperature refers to 20 ℃ ~ 30 ℃.

[0403] In the following examples, unless otherwise specified, the parameters involved can be confirmed by referring to the test methods described above. For example, regarding the average particle size of primary particles in the positive electrode active material, the particle morphology of the positive electrode active material can be obtained by scanning electron microscopy (e.g., ZEISS Sigma 300, JEOL scanning electron microscope, Axia ChemiSEM scanning electron microscope, etc.) and then statistically analyzed. Regarding the D of the positive electrode active material... v 50 can be tested using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Regarding the specific surface area of ​​the positive electrode active material, a nitrogen adsorption specific surface area analysis method can be used. Nitrogen adsorption specific surface area analysis is performed using a Micromeritics Tri Star II specific surface area and porosity analyzer, and the specific surface area is calculated using the BET (Brunauer Emmett Teller) method. Regarding the carbon coating layer, it can be tested and analyzed using a JEM-F200 transmission electron microscope combined with an EDS (Energy Dispersive Spectrometer) to determine the mass percentage (e.g., F). B ), average thickness (e.g., D) B ), maximum thickness (e.g., D) max Parameters such as the degree of graphitization of the carbon coating can be measured and calculated using X-ray diffraction. For example, the ionic conductivity of the electrolyte can be tested using a DDSJ-318 conductivity meter, referring to the detection method in HG-T 4067-2015. The organic and inorganic components in the prepared lithium-ion secondary battery can be tested with reference to relevant standards such as GB / T 9722-2023 General Rules for Gas Chromatography of Chemical Reagents.

[0404] Among them, compound IIa ( Taking 2-propyn-1-yl 1H-imidazol-1-carboxylic acid ester as an example, the structure can be identified and quantitatively analyzed by the following methods:

[0405] In the 1H NMR spectrum, the H in the methylene group linked to the triple bond has a characteristic peak around 4.677 ppm; the hydrogen between the two nitrogen atoms in the imidazole ring has a characteristic peak around 8.095 ppm. By calculating the integrated area of ​​each characteristic peak and comparing it with the integrated area of ​​the internal standard trifluoromethylbenzene, the content of compound IIa can be quantitatively calculated.

[0406] The mass fraction of additives in electrolytes can be determined using nuclear magnetic resonance (NMR) spectroscopy. The testing procedure is as follows: Add 500 μL of deuterated reagent to an NMR tube in a nitrogen-filled glove box. Add 100 μL of the non-aqueous electrolyte sample to the NMR tube. Shake the NMR tube to dissolve the non-aqueous electrolyte in the deuterated reagent. Perform the test using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because the non-aqueous electrolyte is highly sensitive to moisture, both the proton NMR test and sample preparation are conducted under a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831 KF coulometric moisture analyzer was used for moisture testing. Then, 10 mL of dried DMSO-d6 and 300 μL of dried trifluoromethylbenzene (internal standard) were mixed thoroughly in a nitrogen-filled glove box to obtain the first solution. 10 mL of dried deuterated acetonitrile and 300 μL of dried trifluoromethylbenzene (internal standard) were then mixed thoroughly to obtain the second solution. Finally, the first and second solutions were mixed thoroughly to obtain the deuterated reagent.

[0407] In the following embodiments, the electrolyte salt is an example of an electrolyte lithium salt, and compound IIa is a basic alkyne additive as a non-limiting example.

[0408] In the following examples, the positive electrode active material is a lithium phosphate-based positive electrode material, further, a lithium iron phosphate-based positive electrode material, and even further, a carbon-coated lithium iron phosphate (which can be referred to as carbon-coated LFP) as an example.

[0409] In the following examples involving carbon-coated lithium iron phosphate, carbon coating can be performed under the following conditions: A lithium iron phosphate precursor prepared by co-precipitation is mixed with a carbon source, glucose, and subjected to sintering heat treatment at 550°C to 900°C to form lithium iron phosphate (the positive electrode active material) and a carbon-carbon coating on the surface of the lithium iron phosphate, thus preparing carbon-coated lithium iron phosphate. The graphitization degree of the carbon coating layer can be controlled by adjusting one or more parameters such as sintering temperature and sintering time. Those skilled in the art can also combine or use other known carbon coating methods (such as chemical vapor deposition, high-temperature instantaneous annealing, etc.) to achieve a higher graphitization degree, such as approximately 90%, for example, by using the same average primary particle size and D as the positive electrode active material in Example 1. vThe positive electrode active body with similar properties was prepared, and the graphitization degree of the carbon coating layer in the carbon-coated lithium iron phosphate was adjusted to 88%. The lithium-ion secondary battery was prepared using a method basically the same as in Example 1. At this time, it is also possible to achieve good room temperature performance while significantly improving the high temperature performance of the battery.

[0410] In the carbon-coated lithium iron phosphate used in Examples 1-14 below, the mass percentage of the carbon coating layer in the carbon-coated lithium iron phosphate is in the range of 0.5% to 2.5%, and further in the range of 0.8% to 2%; the average thickness of the carbon coating layer is in the range of 1 nm to 8 nm, and further in the range of 1 nm to 5 nm; the maximum thickness of the carbon coating layer is ≤12 nm, and in most examples, the maximum thickness of the carbon coating layer is ≤10 nm. It can be understood that the specific surface area of ​​the positive electrode active material can be adjusted by adjusting the amount of carbon coating.

[0411] The positive electrode active material D used in the following Examples 1-14 v All 50 are within the range of 1μm to 5μm. For example, the D of the positive electrode active material in Example 1 v 50 is approximately 3μm.

[0412] In the lithium-ion secondary batteries prepared in Examples 1-14 below, the ionic conductivity of the electrolyte at 25°C was controlled within the range of 8 mS / cm to 20 mS / cm. For example, the ionic conductivity of the electrolyte in Example 1 at 25°C was approximately 11 mS / cm.

[0413] In the following examples, based on the total mass of the first electrolyte and the second electrolyte, the mass percentage of the first electrolyte can be 80% to 100%. In Example 1, the mass percentage of the first electrolyte is 80%.

[0414] I. Preparation of Lithium-ion Secondary Batteries

[0415] Example 1.

[0416] (1) Positive electrode plate:

[0417] The positive electrode active material (carbon-coated lithium iron phosphate), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were mixed uniformly in the solvent N-methylpyrrolidone (NMP) at a weight ratio of 97.2:0.7:2.1 to obtain a positive electrode slurry with a solid content of 60 wt%. The positive electrode slurry was coated on both sides of the positive electrode current collector aluminum foil, with a coating density of 0.35 g / 1540.25 mm² on each side. 2 The positive electrode sheet is prepared by drying and cold pressing. After cold pressing, the compacted density of the positive electrode sheet is approximately 2.5 g / cm³. 3 .

[0418] The average particle size (D1) of the primary particles in the positive electrode active material is approximately 250 nm (251 nm), and the specific surface area (BET1) of the positive electrode active material is 9.6 m². 2 / g.

[0419] (2) Negative electrode plate:

[0420] The negative electrode active material (coated graphite), conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were mixed evenly in deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry was then coated on both sides of the negative electrode current collector copper foil, with a coating surface density of 0.16 g / 1540.25 mm² on each side. 2 The negative electrode sheet was prepared by drying and cold pressing. The compacted density of the negative electrode sheet was 1.6 g / cm³. 3 .

[0421] In this example, the negative electrode active material is a carbon-based material, and further, it is coated graphite (the negative electrode active body is artificial graphite with an amorphous carbon coating layer on its surface).

[0422] (3) Separation membrane: Polypropylene membrane is used as the separation membrane.

[0423] (4) Electrolyte:

[0424] Additives were added to a non-aqueous solvent and mixed thoroughly. Then, fully dried lithium electrolyte was added and mixed thoroughly to ensure complete dissolution of the lithium electrolyte, thus preparing the first and second electrolytes. The concentration of the lithium electrolyte was approximately the same in both the first and second electrolytes. The concentrations of additives, except for the basic alkyne additive, were also approximately the same in both electrolytes. The mass percentage of the basic alkyne additive in the first electrolyte was 1.5%, and the mass percentage of the basic alkyne additive in the second electrolyte was determined based on the target concentration in the electrolyte of the lithium-ion secondary battery prepared in Table 1.

[0425] The electrolyte salt in the electrolyte is a lithium electrolyte salt, specifically lithium hexafluorophosphate (LiPF6), with a concentration of 1 mol / L in both the first and second electrolytes. The non-aqueous solvents are ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 30:60:10. The additives are 2-propynyl-1-yl1H-imidazolium-1-carboxylic acid ester (as a basic alkyne additive) and vinylene carbonate (VC). The structure of the basic alkyne additive is shown in formula (IIa), also denoted as compound IIa. Compound IIa has a mass percentage of 1.5 wt% in the first electrolyte, and VC has a mass percentage of 2% in both the first and second electrolytes. In the prepared lithium-ion secondary battery, compound IIa has a mass percentage of 2% in the electrolyte.

[0426]

[0427] (5) Preparation of lithium-ion secondary battery: The positive electrode, separator and negative electrode are stacked in sequence to obtain bare cell (electrode assembly); the bare cell is welded with tabs and put into aluminum-plastic bag, and baked at 80°C to remove water. Then the first electrolyte is injected and sealed. Then the battery goes through the following processes in sequence: standing, hot and cold pressing, formation, injection of second electrolyte, aging, shaping and capacity testing to obtain lithium-ion secondary battery.

[0428] The formation process includes the following steps performed sequentially: charging at 0.05C to 6% SOC and letting stand for 5 minutes; charging at 0.1C to 20% SOC and letting stand for 5 minutes; charging at 0.2C to 30% SOC; formation complete.

[0429] Examples 2-4 used essentially the same method as Example 1 to prepare lithium-ion secondary batteries, the difference being that the positive electrode active material used in the positive electrode preparation step was different. The main changes involved altering at least one parameter among the primary particle average size (D1), the graphitization degree of the carbon coating (G1), and the specific surface area (BET1). Relevant parameters of the positive electrode active material can be found in Table 1. The remaining operational steps were the same as in Example 1. In the prepared lithium-ion secondary batteries, the mass percentage of the alkaline alkyne additive compound IIa in the electrolyte was approximately 2%.

[0430] Examples 2-3 mainly change the average particle size (D1) of the primary particles, as shown in Table 1.

[0431] Example 4 mainly changes the graphitization degree (G1) of the carbon coating layer, as shown in Table 1.

[0432] Examples 5-12 prepared lithium-ion secondary batteries using essentially the same method as Example 1, the difference being that the types and / or amounts of additives in the electrolyte of the prepared lithium-ion secondary batteries were different; Example 5 also omitted the step of supplementing with a second electrolyte. The remaining operating steps were the same as in Example 1.

[0433] Example 5 omits the step of supplementing the second electrolyte, but changes the amount of alkaline alkyne additive in the first electrolyte and changes the amount of first electrolyte injected to keep the total injected mass of the electrolyte basically the same as in Example 1; in the prepared lithium-ion secondary battery, the mass percentage of alkaline alkyne additive compound IIa in the electrolyte is about 0.4%.

[0434] In Example 6, the amount of alkaline alkyne additive in the second electrolyte was changed, and the mass percentage of alkaline alkyne additive compound IIa in the electrolyte of the prepared lithium-ion secondary battery was 3.4%.

[0435] The additives in the electrolyte of the lithium-ion secondary battery prepared in Example 7 are compound IIa, VC and TMSB (tris(trimethylsilane)borate); the first electrolyte and the second electrolyte contain 1.5% VC and 0.3% TMSB by mass, respectively. The mass percentage of compound IIa in the electrolyte of the prepared lithium-ion secondary battery is basically the same as that in Example 1.

[0436] The additives in the electrolyte of the lithium-ion secondary battery prepared in Example 8 are compound IIa, VC and TDI (toluene diisocyanate); the first electrolyte and the second electrolyte contain 1.5% VC and 0.3% TDI by mass, respectively. The mass percentage of compound IIa in the electrolyte of the prepared lithium-ion secondary battery is basically the same as that in Example 1.

[0437] The additives in the electrolyte of the lithium-ion secondary battery prepared in Example 9 are compound IIa, VC and LiDFOB (lithium difluorooxalate borate); the first electrolyte and the second electrolyte contain 1.5% VC and 0.5% LiDFOB by mass, respectively. The mass percentage of compound IIa in the electrolyte of the prepared lithium-ion secondary battery is basically the same as that in Example 1.

[0438] The additives in the electrolyte of the lithium-ion secondary battery prepared in Example 10 are compound IIa, VC and TMSP (tris(trimethylsilane)phosphate); the first electrolyte and the second electrolyte contain 1.5% VC and 0.3% TMSP by mass, respectively. The mass percentage of compound IIa in the electrolyte of the prepared lithium-ion secondary battery is basically the same as that in Example 1.

[0439] The additives in the electrolyte of the lithium-ion secondary battery prepared in Example 11 are compound IIa, VC and DTD (ethylene sulfate); the first electrolyte and the second electrolyte contain 1.5% VC and 1% DTD by mass, respectively. The mass percentage of compound IIa in the electrolyte of the prepared lithium-ion secondary battery is basically the same as that in Example 1.

[0440] The additives in the electrolyte of the lithium-ion secondary battery prepared in Example 12 are compound IIa, VC, TMSP and fluoroethylene carbonate (FEC); both the first electrolyte and the second electrolyte contain 1.5% VC, 0.3% TMSP (tris(trimethylsilane) phosphate) and 2% FEC by mass. The mass percentage of compound IIa in the electrolyte of the prepared lithium-ion secondary battery is basically the same as that in Example 1.

[0441] Example 13 prepared a lithium-ion secondary battery using essentially the same method as Example 12, except that the composition of the electrolyte salts in the first and second electrolytes was different. Both the first and second electrolytes used 0.3 mol / L LiFSI and 0.7 mol / L LiPF6. The remaining operating steps were essentially the same as in Example 1.

[0442] Example 14 uses essentially the same method as Example 1 to prepare a lithium-ion secondary battery, the difference being that the negative electrode active material is different in the negative electrode preparation step, while the other operation steps are the same as in Example 1. In Example 14, the negative electrode active material is a carbon-based material and a silicon-based material in a mass ratio of 94:6, that is, the mass proportion of silicon-based material in the negative electrode active material is 6%. The carbon-based material is the same as in Example 1; the silicon-based material is a silicon-carbon composite material, including a porous carbon matrix and elemental silicon deposited in the pores of the porous carbon matrix, with a silicon to carbon element mass ratio of 1:1.

[0443] Comparative Example 1. A lithium-ion secondary battery was prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was different, the alkaline alkyne additive was omitted from the first and second electrolytes, and the concentrations of the remaining components in the first and second electrolytes remained unchanged. The remaining operating steps were the same as in Example 1.

[0444] Comparative Example 2. A lithium-ion secondary battery was prepared using essentially the same method as in Example 14, except that the composition of the electrolyte was different, the alkaline alkyne additive was omitted from the first and second electrolytes, and the concentrations of the remaining components in the first and second electrolytes remained unchanged. The remaining operating steps were the same as in Example 14.

[0445] Comparative Example 3. A lithium-ion secondary battery was prepared using essentially the same method as in Example 1, except that the composition of the electrolyte was different, and the alkaline alkyne additive compound IIa in the first and second electrolytes was replaced with methylcarboxylic acid-2-propynyl ester (Methylcarboxylic acid-2-propynyl ester). The concentrations of the remaining components in the electrolyte remain unchanged in both the first and second electrolytes. The remaining operating steps are the same as in Example 1.

[0446] Comparative Examples 4-5. Lithium-ion secondary batteries were prepared using essentially the same method as in Example 1, except that the positive electrode active material was different in the positive electrode preparation step, mainly by changing the average particle size (D1) of the primary particles. The remaining operational steps were the same as in Example 1. In Comparative Examples 4 and 5, the specific surface area (BET1) of the positive electrode active material was approximately 23 m². 2 / g and approximately 5.7m 2 / g.

[0447] The relevant preparation parameters for Examples 1-14 and Comparative Examples 1-5 can also be found in Tables 1 and 2.

[0448] II. Test and Analysis Methods

[0449] 1. Testing the water absorption rate of the positive electrode active material

[0450] The test temperature is 25℃±0.5℃. A dry sample of the powder to be tested is taken, and the initial test value of the moisture content is recorded as A1ppm. The sample is placed in a 90%RH humidity environment for 12h, and the moisture content of the powder is tested. The moisture content value after 12h is recorded as B2ppm. The water absorption rate of the sample is calculated by the following formula: Water absorption rate = (B2-A1)ppm / 12h.

[0451] The moisture content was tested using a Karl Fischer moisture analyzer with a testing accuracy of ppm (parts per million). The moisture content test results were based on the mass ratio of the powder being tested.

[0452] The test results for some embodiments can be found in Table 1.

[0453] 2. Normal temperature cycling performance (25℃)

[0454] At 25℃, the battery under test was charged at a constant current of 0.5C to 3.65V, then charged at a constant voltage of 3.65V to the cutoff current of 0.05C, left to rest for 10 minutes, and then discharged at a constant current of 0.5C to 2.5V, left to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as C0. This charge-discharge cycle is repeated for the same battery, and the discharge capacity C of the first, second, ..., nth cycle is recorded. n The number of cycles must be at least 300.

[0455] Record the battery's cycle capacity retention rate P300 = C after 300 cycles. 300 / C0×100%.

[0456] Test results can be found in "Capacity Retention Rate After 300 Cycles at Room Temperature". A higher test value indicates a better cycle life at room temperature.

[0457] 3. Initial DC internal resistance (DCR) test after room temperature cycling:

[0458] The batteries that have undergone cycle testing using the "2. Room temperature cycle performance (25℃) method" will be subjected to DCR testing.

[0459] At 25℃, the battery under test was charged to 3.65V at a constant current of 0.5C, and then charged at a constant voltage until the current was 0.05C. The battery was then discharged at a constant current of 0.5C for 30 minutes to adjust the battery to 50% SOC. The voltage of the battery at this time is recorded as U1. The battery was then discharged at a constant current of 4C for 30 seconds, and the voltage at the end of the discharge was recorded as U2, using a sampling time of 0.1 seconds. The initial DCR of the battery is represented by the discharge DCR at 50% SOC. The initial DCR of the battery is calculated as (U1-U2) / I, where I is the current value corresponding to 4C.

[0460] The test results can be found in Table 3, "Battery DCR after room temperature cycling".

[0461] The same method can also be used to test the initial DCR (DCR0) of the prepared lithium-ion secondary battery.

[0462] 4. High-temperature cycling performance (60℃)

[0463] At 60℃, the battery under test is charged to 3.65V with a constant current of 1C, then charged to 0.05C with a constant voltage of 3.65V. After resting for 5 minutes, it is discharged to 2.5V with a constant current of 1C. This is the first charge / discharge cycle of the battery, and the discharge capacity of this cycle is recorded as the discharge capacity (C1) of the battery in the first cycle. The above steps are repeated for the same battery. The process capacity (Cn) of the battery after the nth cycle is recorded. The capacity retention rate after n cycles is calculated as Cn / C1 × 100%. The capacity retention rate is recorded when the number of cycles is 600.

[0464] The test results can be found in "Capacity Retention Rate after 600 Cycles at 60℃".

[0465] The more cycles a product has, the better its high-temperature cycle life.

[0466] III. Test Analysis Results

[0467] The water absorption rate of the positive electrode active materials used in Examples 1-14 is in the range of 50 ppm / h to 85 ppm / h.

[0468] Table 1.

[0469]

[0470] In the process of preparing lithium-ion secondary batteries, the mass percentages of alkaline alkyne additives, other negative electrode film-forming additives, and electrolyte salts in the electrolyte can be found in Table 2.

[0471] Table 2.

[0472]

[0473] In the prepared lithium-ion secondary batteries, the electrolyte composition was tested by disassembling the cells: In Example 7, the mass ratio of additive B to basic acetylene additive was in the range of 0.1 to 50, and the mass percentage of additive B in the electrolyte was in the range of 0.1% to 1%, further in the range of 0.1% to 0.3%; In Example 8, the mass ratio of additive C to basic acetylene additive was in the range of 0.02 to 50, and the mass percentage of additive C in the electrolyte was in the range of 0.1% to 1%, further in the range of 0.1% to 0.3%; In Examples 9-10, the mass ratio of additive D to basic acetylene additive was in the range of 0.1 to 100, and the mass percentage of additive D in the electrolyte was in the range of 0.1% to 2%, further in the range of 0.1% to 0.5%.

[0474] The battery performance test results of Examples 1-14 and Comparative Examples 1-5 can be found in Table 3.

[0475] The lithium-ion secondary batteries prepared in Examples 1-14 all exhibited significantly improved high-temperature performance as well as good room-temperature performance.

[0476] Compared to Example 1, Comparative Example 1 omitted the basic alkyne additive, resulting in a significant deterioration in both its high-temperature and room-temperature performance. Similarly, compared to Example 14, Comparative Example 2 omitted the basic alkyne additive, resulting in a significant deterioration in both its high-temperature and room-temperature performance.

[0477] In Comparative Example 3, the basic alkyne additive in Example 1 was replaced with an alkyne additive that does not contain Lewis base nitrogen heterocycles. The high-temperature performance and room-temperature performance of Comparative Example 3 were significantly deteriorated.

[0478] Comparative Examples 4-5 adjusted the average particle size D1 of the primary particles of the positive electrode active material based on Examples 2 and 3, respectively. The high-temperature performance and room-temperature performance of Comparative Examples 4-5 deteriorated compared to Examples 2 and 3, respectively.

[0479] The initial DCR (DCR0) of the lithium-ion secondary battery prepared in Comparative Example 4 was lower than that of Examples 1-2. However, the positive electrode active material in Comparative Example 4 had a large specific surface area, which led to a high water absorption rate of the positive electrode active material. The DCR of the battery after cycling at room temperature was significantly higher than that of Examples 1-2.

[0480] The average particle size of the primary particles of the positive electrode active material in the lithium-ion secondary battery prepared in Comparative Example 5 is larger than that in Example 1, and the initial DCR of the battery is higher than that in Example 1.

[0481] Table 3.

[0482]

[0483] Furthermore, even with VC omitted in both the first and second electrolytes of Example 1 and Comparative Example 1, Example 1 still significantly improves high-temperature performance while maintaining good room-temperature performance compared to Comparative Example 1.

[0484] 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.

[0485] 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, characterized in that, The device includes a positive electrode, a negative electrode, and an electrolyte, with a separator between the positive and negative electrode. The positive electrode includes a positive active layer comprising a positive active material. The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives. The negative electrode includes a negative active layer comprising a negative active material, which is a carbon-based material, and the carbon-based material constitutes 92% to 100% of the total negative active material by mass. The positive electrode active material includes a lithium phosphate-based positive electrode material, which is a lithium iron phosphate-based positive electrode material; the lithium phosphate-based positive electrode material accounts for 80% to 100% of the total mass of the positive electrode active material; the lithium phosphate-based positive electrode material includes a carbon-coated lithium phosphate-based positive electrode material, which includes a lithium phosphate matrix and a carbon coating layer located on at least a portion of the surface of the lithium phosphate matrix; the average particle size of the primary particles in the positive electrode active material is 100 nm to 500 nm; the D of the positive electrode active material... v 50 is 2.5μm~5μm; the additives include basic alkyne additives and additive C, the basic alkyne additives contain Lewis base nitrogen heterocycles, and additive C is one or more of isocyanate additives and acid anhydride additives; the isocyanate additives include toluene diisocyanate; the acid anhydride additives include one or more of maleic anhydride, citrate anhydride, trifluoromethyl maleic anhydride, succinic anhydride, glutaric anhydride, and succinic anhydride.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The average particle size of the primary particles in the positive electrode active material is 150 nm to 450 nm.

3. The lithium-ion secondary battery according to claim 1, characterized in that, The average particle size of the primary particles in the positive electrode active material is 200 nm to 450 nm.

4. The lithium-ion secondary battery according to claim 1, characterized in that, The average particle size of the primary particles in the positive electrode active material is 350 nm to 450 nm.

5. The lithium-ion secondary battery according to claim 4, characterized in that, The specific surface area of ​​the positive electrode active material is 5m². 2 / g~18m 2 / g.

6. The lithium-ion secondary battery according to claim 5, characterized in that, The specific surface area of ​​the positive electrode active material is 5m². 2 / g~15m 2 / g.

7. The lithium-ion secondary battery according to claim 4, characterized in that, The carbon-coated lithium phosphate cathode material satisfies one or more of the following characteristics: (a1) The degree of graphitization of the carbon coating is 28%~95%; (a2) The carbon coating layer accounts for 0.5% to 2.5% of the mass of the carbon-coated lithium phosphate cathode material; (a3) The average thickness of the carbon coating layer is 1 nm to 8 nm; (a4) The maximum thickness of the carbon coating layer is less than or equal to 12 nm.

8. The lithium-ion secondary battery according to claim 7, characterized in that, The carbon-coated lithium phosphate cathode material satisfies one or more of the following characteristics: (a1') The degree of graphitization of the carbon coating is 40%~90%; (a2') The carbon coating layer accounts for 0.8% to 2% of the mass of the carbon-coated lithium phosphate cathode material; (a3') The average thickness of the carbon coating layer is 1 nm to 5 nm; (a4') The maximum thickness of the carbon coating layer is less than or equal to 10 nm.

9. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The positive electrode active material D v 50 is 2.5μm~4.5μm.

10. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The positive electrode active material D v 50 is 2.5μm~4μm.

11. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The negative electrode sheet satisfies one or more of the following characteristics: (b1) The mass percentage of silicon-based materials in the negative electrode active material is 0-8%; (b2) The negative electrode active material includes a silicon-based material; the silicon-based material includes a silicon-carbon composite material, the silicon-carbon composite material includes a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix; the silicon-carbon composite material accounts for 80% to 100% of the mass of the silicon-based material; (b3) The carbon-based material includes graphite-based material, and the graphite-based material accounts for 80% to 100% of the mass of the negative electrode active material; (b4) The negative electrode active material includes a coated negative electrode material, which includes a negative electrode active body and a carbon coating layer located on the negative electrode active body, including at least a portion thereof; the mass percentage of the coated negative electrode material in the negative electrode active material is 80% to 100%.

12. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The basic alkaline alkyne additive is present in the electrolyte at a mass percentage of 0.01% to 3.5%.

13. The lithium-ion secondary battery according to claim 12, characterized in that, The basic alkaline alkyne additive is present in the electrolyte at a mass percentage of 0.1% to 3.5%.

14. The lithium-ion secondary battery according to claim 12, characterized in that, The basic alkaline alkyne additive is present in the electrolyte at a mass percentage of 1.5% to 3.5%.

15. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The additive C has a mass percentage of 0.1% to 1% in the electrolyte, and the acid anhydride additive has a mass percentage of 0.01% to 1% in the electrolyte.

16. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The additives include negative electrode film-forming additives that are different from the basic acetylene additives; the additives include one or more of additives B, C, and D; Wherein, additive B is one or more of silane additives and siloxane additives; The additive C is one or more of isocyanate additives and acid anhydride additives; The additive D is one or more of lithium salt additives and phosphate ester additives.

17. The lithium-ion secondary battery according to claim 16, characterized in that, The electrolyte satisfies one or more of the following characteristics: (c1) The mass ratio of additive B to the basic acetylene additive is 0.1~5; (c2) The mass ratio of the additive C to the alkaline acetylene additive is 0.02~5; (c3) The mass ratio of the additive D to the alkaline acetylene additive is 0.1 to 10.

18. The lithium-ion secondary battery according to claim 16, characterized in that, In the electrolyte, the mass ratio of additive B, additive C, additive D and alkaline acetylene additive is (0~0.5):(0~0.5):(0~1):

1.

19. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The alkaline alkyne additive satisfies one or more of the following characteristics: (d1) The molecular weight of the alkaline alkyne additive is less than or equal to 500 Da; (d2) The molecules of the alkaline acetylene additives contain 1 to 4 carbon-carbon triple bonds; (d3) The carbon-carbon triple bond is CH≡C-; (d4) The molecules of the alkaline alkyne additives contain 1 to 4 Lewis base nitrogen heterocycles; (d5) The Lewis base nitrogen heterocycle includes an imidazole ring; (d6) In the molecule of the basic alkyne additive, the carbon-carbon triple bond and the Lewis base nitrogen heterocycle are connected by a linker L1, wherein the linker L1 contains a C-type carbon bond covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene or containing fluorinated C atoms covalently bonded to a carbon-carbon triple bond 1-3 Alkylene.

20. The lithium-ion secondary battery according to claim 19, characterized in that, The alkaline alkyne additive satisfies one or more of the following characteristics: (e1) The molecular weight of the alkaline acetylene additive is less than or equal to 300 Da; (e2) The basic alkyne additive contains 1 to 4 imidazole rings in its molecule; (e3) The Lewis base nitrogen heterocycle includes an imidazole ring; the imidazole ring in the Lewis base nitrogen heterocycle is substituted by 0, 1, or more substituents Q2, wherein each substituent Q2 in the substituted imidazole group is independently C. 1-3 Alkyl, cyano, or fluorine atom; (e4) The alkaline yne additive consists of carbon-carbon triple bonds, C 1-3 Alkylene and -OC(=O)-R 10 It is formed by sequential covalent bonds, R 10 It is a Lewis base nitrogen heterocycle.

21. The lithium-ion secondary battery according to claim 20, characterized in that, The basic alkyne additive includes compound II with the structure shown in formula (II): Among them, L 11 C 1-3 Alkylene, Q2 is independently C 1-3 Alkyl, cyano, or fluorine atom, p2 is 0, 1, 2, or 3; The mass percentage of compound II in the basic alkyne additive is 80% to 100%.

22. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, It meets one or more of the following characteristics: (f1) The water absorption rate of the positive electrode active material is 50ppm / h~85ppm / h; (f2) The lithium phosphate cathode material includes carbon-coated lithium iron phosphate, and the carbon-coated lithium iron phosphate accounts for 80% to 100% of the mass of the lithium phosphate cathode material.

23. A method for preparing a lithium-ion secondary battery, characterized in that, Includes the following steps: An electrode assembly comprising a positive electrode, a separator, and a negative electrode is placed inside a battery casing, with the separator positioned between the positive and negative electrode. The positive electrode includes a positive active layer comprising a positive active material. The positive active material comprises a lithium phosphate-based positive electrode material, specifically a lithium iron phosphate-based positive electrode material. The lithium phosphate-based positive electrode material constitutes 80%–100% of the total positive active material by mass. The lithium phosphate-based positive electrode material includes a carbon-coated lithium phosphate-based positive electrode material, comprising a lithium phosphate matrix and a carbon coating layer located on at least a portion of the surface of the lithium phosphate matrix. The average particle size of the primary particles in the lithium phosphate-based positive electrode material is 100 nm–500 nm. The positive active material has a D... v 50 is 2.5μm~5μm; 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 a carbon-based material, and the mass percentage of the carbon-based material in the negative electrode active material is 92%~100%; A first electrolyte is injected into the battery casing, and the casing is left to stand to allow the first electrolyte to wet the positive electrode and the negative electrode, thus forming the battery. The first electrolyte comprises an electrolyte salt, a non-aqueous solvent, and additives. The additives include a basic alkyne additive and additive C. The basic alkyne additive contains a Lewis base nitrogen heterocycle, and additive C is one or more of isocyanate additives and acid anhydride additives. The isocyanate additive includes toluene diisocyanate. The acid anhydride additive includes one or more of maleic anhydride, citrate anhydride, trifluoromethyl maleic anhydride, succinic anhydride, glutaric anhydride, and succinic anhydride.

24. The method for preparing a lithium-ion secondary battery according to claim 23, characterized in that, After formation, a second electrolyte, including the alkaline alkyne additive, is injected into the battery casing.

25. The method for preparing a lithium-ion secondary battery according to claim 23 or 24, characterized in that, The lithium-ion secondary battery according to any one of claims 2 to 22 is prepared.

26. An electrical appliance, characterized in that, Includes the lithium-ion secondary battery according to any one of claims 1 to 22.

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