Lithium ion secondary battery, preparation method thereof and electric device

Abstract

The invention relates to a lithium ion secondary battery, a preparation method thereof and an electric device. The lithium ion secondary battery comprises a positive pole piece, a negative pole piece and electrolyte, wherein an isolating membrane is arranged between the positive pole piece and the negative pole piece; the positive pole piece comprises a positive active layer, and the positive active layer comprises a positive active material; the electrolyte comprises electrolyte salt, a non-aqueous solvent and an additive; the positive electrode active material comprises a lithium-containing phosphate positive electrode material, and the average particle size of primary particles in the positive electrode active material is 100-500 nm; the additive comprises an alkaline alkyne additive, and the alkaline alkyne additive contains Lewis base nitrogen heterocyclic rings. The lithium ion secondary battery has remarkably improved high-temperature performance and also has good normal-temperature performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion secondary batteries, and further relates to lithium-ion secondary batteries, their preparation methods, and electrical devices. Background Art

[0002] The statements herein only provide background information related to the present application and do not necessarily constitute prior art.

[0003] With the development of lithium-ion secondary battery technology, lithium-ion secondary batteries are increasingly widely used in many fields such as smart phones, tablet computers, laptop computers, power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc., and are also widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations. Among them, lithium-ion secondary batteries using cathode active materials such as lithium iron phosphate (LFP) have outstanding advantages in terms of safety and battery life due to their excellent structural stability. However, such cathode active materials usually inevitably introduce moisture, easily generate acid by-products, which damage the solid electrolyte interface (SEI) film of the anode, aggravate the interfacial side reactions of the anode, and limit the exertion of the life advantages of such battery systems. Especially, the side reactions involving water at high temperatures are more intense, resulting in less than ideal high-temperature performance of the battery. For lithium-ion secondary batteries with cathode active materials including lithium-containing phosphate cathode materials, although in theory, high-temperature additives such as alkynyl additives can improve the high-temperature performance of the battery by optimizing the anode SEI film, it will increase the interfacial impedance of the anode and affect the performance at room temperature. Summary of the Invention

[0004] According to various embodiments and examples of the present application, the present application provides a lithium-ion secondary battery, its preparation method, and an electrical device. The lithium-ion secondary battery has significantly improved high-temperature performance while also taking into account good room-temperature performance.

[0005] In some embodiments of the first aspect of the present application, a lithium-ion secondary battery is provided, which includes a positive electrode plate, a negative electrode plate, and an electrolyte solution. A separator is provided between the positive electrode plate and the negative electrode plate; the positive electrode plate includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; the electrolyte solution includes an electrolyte salt, a non-aqueous solvent, and an additive; the positive electrode active material includes a lithium-containing phosphate cathode material, and the average particle size of the primary particles in the positive electrode active material is 100 nm to 500 nm; the additive includes an alkaline alkynyl additive, and the alkaline alkynyl additive contains a Lewis base nitrogen heterocycle.

[0006] For a lithium-ion secondary battery whose positive electrode active material includes a lithium-containing phosphate positive electrode material, by introducing an alkaline alkyne additive (which can also be denoted as additive A) with a carbon-carbon triple bond and a Lewis base nitrogen heterocycle and having high-temperature stability into the electrolyte, the Lewis base nitrogen heterocycle can absorb water and acid by-products, reduce the free acid by-products in the electrolyte at high temperatures, inhibit the exacerbating effect of the acid by-products on the battery capacity attenuation at high temperatures, and then use the carbon-carbon triple bond to form a solid electrolyte interface (SEI) film with high stability on the negative electrode, reduce the interfacial side reactions at high temperatures. By utilizing the aforementioned multiple effects, the high-temperature performance of the battery can be significantly improved; further controlling the average particle size of the primary particles in the positive electrode active material within a relatively moderate range can not only reduce the content of water and acid by-products in the system and inhibit the damage of the acid by-products to the negative electrode SEI film, inhibit the increase in interfacial impedance at room temperature caused by the participation of the alkaline alkyne additive in the negative electrode film formation, but also control the positive electrode active material to have a more suitable lithium-ion transmission path and then regulate the internal resistance of the battery, thereby facilitating the lithium-ion secondary battery to also achieve good room-temperature performance; based on the aforementioned multiple effects, but not limited to the aforementioned theory, the high-temperature performance of the lithium-containing phosphate positive electrode material battery system can be significantly improved 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 150 nm to 450 nm, optionally 200 nm to 450 nm, and further optionally 250 nm to 450 nm.

[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 the interfacial impedance of the negative electrode indirectly caused by water in the positive electrode active material and the influence of the lithium-ion transmission path on the internal resistance of the battery, and it 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-containing phosphate positive electrode material includes a carbon-coated lithium-containing phosphate positive electrode material, and the carbon-coated lithium-containing phosphate positive electrode material includes a lithium-containing phosphate matrix and a carbon coating layer covering at least a part of the surface of the lithium-containing phosphate matrix.

[0010] By providing a carbon coating layer on the surface of the lithium-containing phosphate positive electrode material, the specific surface area of the material may be increased, and as a result, the water absorption rate on the surface of the material may increase. At this time, through the synergistic effect of controlling the average particle size (D1) of the primary particles in the positive electrode active material and introducing the alkaline alkyne additive, the high-temperature performance of the battery can be significantly improved while also taking into account better room-temperature performance.

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

[0012] For a lithium-ion secondary battery, exemplarily including a lithium-ion secondary battery in which a positive electrode active material includes a carbon-coated lithium-containing phosphate-based positive electrode material, by controlling the specific surface area (BET 1 ) within the aforementioned range, it is beneficial to better control the water absorption rate of the positive electrode active material, while also better suppressing the side reactions at the high-temperature interface, which is beneficial to better improving the high-temperature performance of the battery while also taking into account good room-temperature performance.

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

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

[0015] (a2) The mass ratio of the carbon coating layer in the carbon-coated lithium-containing phosphate-based positive electrode material is 0.5% - 2.5%;

[0016] (a3) The average thickness of the carbon coating layer is 1 nm - 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-containing phosphate-based positive electrode material satisfies one or more of the following characteristics:

[0019] (a1') The graphitization degree of the carbon coating layer is 40% - 90%, and optionally 40% - 85%;

[0020] (a2') The mass ratio of the carbon coating layer in the carbon-coated lithium-containing phosphate-based positive electrode material is 0.8% - 2%;

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

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

[0023] For a lithium-ion secondary battery in which a positive electrode active material includes a carbon-coated lithium-containing phosphate-based positive electrode material, by controlling the carbon coating layer to have a relatively high graphitization degree (G 1 ), or by controlling the mass ratio (F B ) of the carbon coating layer in the carbon-coated lithium-containing phosphate-based positive electrode material, the average thickness (D B ) of the carbon coating layer, and the maximum thickness (D maxOne or more of the parameters in ) have relatively low values, which is beneficial to reducing the water absorption rate of the positive electrode active material, reducing or delaying the consumption of the negative electrode interface of the alkaline alkyne additive, reducing the growth rate of the negative electrode interface impedance, and is beneficial to better balancing the normal temperature performance.

[0024] For a lithium-ion secondary battery in which the positive electrode active material includes a carbon-coated lithium-containing phosphate-based positive electrode material, by controlling the graphitization degree of the carbon coating layer within the foregoing range, it is possible to better coordinate the water absorption rate on the material surface, the conductivity of the carbon coating layer, and the ion diffusion impedance of the carbon coating layer, and better balance the influence of the carbon coating layer on the battery internal resistance and the inhibitory effect of the carbon coating layer on the side reactions at the positive electrode interface, so as to better balance good normal temperature performance while improving the high temperature performance of the battery.

[0025] Exemplarily, controlling a relatively high graphitization degree within the foregoing range of graphitization degrees is beneficial to reducing the water absorption rate on the material surface and increasing the conductivity of the carbon coating layer while also better controlling the ion diffusion impedance.

[0026] Exemplarily, controlling a relatively low graphitization degree within the foregoing range of graphitization degrees is beneficial to reducing the ion diffusion impedance of the carbon coating layer while also better controlling the conductivity and the water absorption rate.

[0027] By controlling the mass ratio (F of the carbon coating layer in the carbon-coated lithium-containing phosphate-based positive electrode material B ), the average thickness (D of the carbon coating layer B ), and the maximum thickness (D of the carbon coating layer max ) to be within the foregoing range for one or two or all three of them, it is beneficial to control the positive electrode active material to have a relatively low water absorption rate, and is also beneficial to reducing the influence of the ion diffusion impedance on the battery internal resistance, and is beneficial to better balancing the normal temperature performance of the battery.

[0028] In some embodiments, the D of the positive electrode active material v 50 is 1 μm to 5 μm, optionally 1 μm to 4 μm, and further optionally 1.5 μm to 4 μm.

[0029] By making the D of the positive electrode active material vWhen the 50 control is within the aforementioned range, the degree of agglomeration of the primary particles can be adjusted by combining the joint control of the average particle size (D1) of the primary particles, the specific surface area and the water absorption rate can be better controlled, and the ion transport path of the overall positive electrode active material particles can also be better controlled. Based on the synergy of the aforementioned effects, but not limited to the aforementioned theory, it is beneficial to better control the internal resistance of the battery and to better balance the normal temperature performance of the battery while significantly improving the high temperature performance of the battery. In some examples, for a lithium ion secondary battery in which the positive electrode active material includes a carbon-coated lithium-containing phosphate-based positive electrode material, the influence of the carbon coating layer on the specific surface area, the water absorption rate, the conductivity, the ion diffusion impedance, and the side reaction at the positive electrode interface can be better balanced, and the normal temperature performance of the battery can be better balanced while significantly improving the high temperature performance of the battery.

[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 a carbon-based material and a silicon-based material;

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

[0032] (b1) The mass ratio of the silicon-based material in the negative electrode active material is 0 to 20%, and may be 0 to 10%;

[0033] (b2) The silicon-based material includes a silicon-carbon composite material, and the silicon-carbon composite material includes a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix; the mass ratio of the silicon-carbon composite material in the silicon-based material is 80% to 100%;

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

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

[0036] By controlling the content of the silicon-based material in the negative electrode active material and / or the type of the 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, the side reaction at the negative electrode interface can be inhibited, which is beneficial to reducing the consumption rate of the alkaline alkyne additive, reducing the growth rate of the battery internal resistance, and is beneficial to better balancing the normal temperature performance of the battery. Exemplarily, among the silicon-based materials, the volume expansion and contraction changes of the silicon-carbon composite material are relatively low.

[0037] By providing a coated anode material including a carbon coating layer in the anode active material, the lithium ion transport channels on the surface of the anode active material can be optimized to promote lithium ion transport. It is also beneficial to suppress side reactions at the anode interface and inhibit the increase in interface impedance caused by the participation of alkaline alkyne additives in film formation, which is conducive to better controlling the internal resistance of the battery and the room temperature performance of the battery.

[0038] In some embodiments, the mass percentage of the alkaline alkyne additive in the electrolyte is less than or equal to 3.5%, optionally 0.01% - 3.5%, further optionally 0.1% - 2.5%, and still further optionally 0.2% - 2.5%.

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

[0040] In some embodiments, the additive includes a cathode film-forming additive different from the alkaline alkyne additive.

[0041] The cathode film-forming additive different from the alkaline alkyne additive can competitively participate in cathode film formation, reduce or delay the consumption of the alkaline alkyne additive in cathode film formation, and inhibit the increase in cathode interface impedance caused by the participation of the alkaline alkyne additive in cathode film formation, which is beneficial to improving the high temperature performance of the battery while 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, the additive B is one or more of silane additives and siloxane additives;

[0044] the additive C is one or more of isocyanate additives and 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 alkyne additive is 0.1 - 50, optionally 0.1 - 1;

[0048] (c2) The mass ratio of the additive C to the alkaline alkyne additive is 0.02 - 50, optionally 0.02 - 1;

[0049] The mass ratio of the additive D to the alkaline alkyne additive is 0.1 to 100, and may be optionally 0.1 to 2.

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

[0051] Additive B, additive C, and additive D can all be used as anode film-forming additives. Additive B is a type of anode film-forming additive with low impedance and a certain acid-removing effect. Its acid-removing effect is lower than that of the alkaline alkyne additive, and its anode film-forming impedance is lower than that of the alkaline alkyne additive. Additive C is a type of additive with a good acid-removing effect. Its acid-removing effect is better than that of the alkaline alkyne additive, but its anode film-forming impedance is higher than that of the alkaline alkyne additive. The anode film-forming impedance of additive D is very low, far lower than that of the alkaline alkyne additive.

[0052] Utilizing the synergistic effect of the alkaline alkyne additive and one or more of additive B, additive C, and additive D is beneficial to better significantly improve the high-temperature performance while also taking into account good room-temperature performance.

[0053] In some embodiments, the alkaline 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 molecule of the alkaline alkyne additive contains 1 to 4 carbon-carbon triple bonds;

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

[0057] (d4) The molecule of the alkaline alkyne additive contains 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 alkaline alkyne additive, the carbon-carbon triple bond and the Lewis base nitrogen heterocycle are connected by a linking group L 1 which is 1 contains a C 1-3 alkylene covalently bonded to the carbon-carbon triple bond or a fluoro C 1-3 alkylene covalently bonded to the carbon-carbon triple bond.

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

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

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

[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 Q 2 and the substituents Q in the substituted imidazole group 2 are each independently C 1-3 alkyl, cyano or fluorine atom;

[0064] (e4) The basic alkyne additive is composed of a carbon-carbon triple bond, C 1-3 alkylene and -O-C(=O)-R 10 covalently bonded in sequence, and R 10 is a Lewis base nitrogen heterocycle.

[0065] In some embodiments, the basic alkyne additive includes Compound II having a structure as shown in Formula (II): ; wherein, L 11 is C 1-3 alkylene, Q 2 is independently C 1-3 alkyl, cyano or fluorine atom, and 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 the basic alkyne additive within the aforementioned lower range, the basic alkyne additive can have a smaller molecular size, which is beneficial to better control the low-viscosity characteristics of the electrolyte, make the electrolyte have a higher conductivity, and better control the internal resistance of the battery.

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

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

[0070] An example of the Lewis base nitrogen heterocycle is the imidazole ring in Compound II.

[0071] By introducing fluorine atom substituents on a Lewis base nitrogen heterocycle (such as an imidazole ring), it is beneficial to induce the formation of inorganic lithium fluoride on the negative electrode, which is beneficial to improving the stability of the SEI film and reducing the interfacial impedance, and is beneficial to better improving the high-temperature performance of the battery and 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 mass ratio of the lithium-containing phosphate cathode material in the cathode active material is 80% - 100%;

[0074] (f2) The lithium-containing phosphate cathode material includes carbon-coated lithium iron phosphate, and the mass ratio of the carbon-coated lithium iron phosphate in the lithium-containing phosphate cathode material is 80% - 100%.

[0075] In some embodiments of the second aspect of the present application, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps:

[0076] Place an electrode assembly including a positive electrode sheet, a separator, and a negative electrode sheet in a battery case, with the separator disposed between the positive electrode sheet and the negative electrode sheet; wherein, the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; the positive electrode active material includes a lithium-containing phosphate cathode material, and the average particle size of the primary particles in the lithium-containing phosphate cathode material is 100nm - 500nm;

[0077] Inject a first electrolyte into the battery case, let it stand to allow the first electrolyte to infiltrate the positive electrode sheet and the negative electrode sheet, and then carry out formation; wherein, the first electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive; the additive includes an alkaline alkyne additive, and the alkaline alkyne additive contains a Lewis base nitrogen heterocycle.

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

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

[0080] In some embodiments of the third aspect of the present application, an electrical device is provided, which includes the lithium-ion secondary battery described in the first aspect of the present application.

[0081] Details of one or more embodiments or examples of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] To better describe and illustrate the embodiments, examples or instances provided by this application, one or more drawings may be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed application, the currently described embodiments, examples or instances, and the best mode of these applications currently understood. Moreover, in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

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

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

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

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

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

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

[0089] Description of reference numerals:

[0090] 1, battery pack; 2, upper box body; 3, lower box body; 4, battery device; 5, battery cell; 51, battery housing; 52, electrode assembly; 53, cover plate; 6, electrical device. Specific embodiments

[0091] Hereinafter, some embodiments and some examples of the lithium-ion secondary battery, its preparation method and electrical device of this application are described in detail with appropriate reference to the drawings. However, there may be cases where non-essential details are omitted. For example, there are cases where the detailed description of well-known matters and the repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter recited in 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, and the selected lower limit and upper limit define the boundaries of a specific range. The range defined in this way can include or exclude the end values. Any end value can be independently included or excluded, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60-120 and 80-110 are listed for a specific parameter, it is understood that the ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4, and 5 are also listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed in this article, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when expressing that a certain parameter is an integer ≥2, it is equivalent to listing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when expressing that a certain parameter is 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, when referring to a "numerical value", its meaning includes the present number and its reasonable divisors. The definition of this "numerical value" can be applied to discrete numerical points and can also be applied to the endpoints of a numerical range. Unless otherwise specified, when referring to a "divisor", it covers a numerical interval within a reasonable fluctuation range based on the present number, and the reasonable fluctuation range may vary depending on the type and magnitude of the present number. This reasonable fluctuation range can be reasonably confirmed according to the accuracy of the test 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 covers its reasonable divisors, and the numerical range covers the reasonable divisors of the two endpoints. Those skilled in the art can understand that the acceptable fluctuation ranges of the relevant divisors can all be incorporated into the definition of this numerical value or this 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 given number, and the fluctuation range may vary depending on the type and value of the number. For example, fluctuations within the ranges of ±10%, ±5%, ±2%, ±1%, etc. are allowed. For example, taking "about 20°C" with an approximate value of ±1°C as an example, approximate values such as 19°C and 19.5°C within the approximate value range indicated by "about 20°C" should also be included within the range indicated by "about 20°C".

[0095] In this application, when referring to "a plurality of", "a variety of", "multiple items", etc., unless otherwise specified, it means greater than or equal to 2 in quantity. For example, "one or more" means one or ≥ (greater than or equal to) two. It can be understood that when referring to "any number of" items, it means any suitable combination of multiple items, that is, the combination of "any number of" items is carried out in a non-conflicting and implementable manner of this application.

[0096] If there is no special description, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0097] Referring to "embodiment" in this text means that the specific features, structures, or characteristics described in combination with the embodiment can be included in at least one embodiment or implementation manner of this application. The appearance of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments. The same understanding applies to the "implementation manner" mentioned in this text.

[0098] Those skilled in the art can understand that in the methods of each embodiment or implementation manner of this application, unless otherwise restricted, the written order of each step does not mean a strict execution order that constitutes any limitation to the implementation process, and the detailed execution order of each step should be determined by its function and possible internal logic. If there is no special description, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, method M includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, method M may further include step (c), which means that step (c) can be added to method M in any order. For example, method M can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0099] In this application, in an open technical feature or technical solution described by words such as "containing", "including", and "comprising", without other specifications, additional members other than the listed members are not excluded. It can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution that also includes additional members outside the listed members. For example, if a includes a1, a2, and a3, without other specifications, it may also include other members or may not include additional members. It can be regarded as providing both a feature or solution of "a consists of a1, a2, and a3" or "a is selected from a1, a2, and a3", and a feature or solution of "a not only includes a1, a2, and a3, but also includes other members".

[0100] In this application, without other specifications, M (such as m1) indicates that m1 is a non-limiting example in M, and it can be understood that M is not limited to m1.

[0101] In this application, "optionally", "optional", and "option" mean that it can be either present or absent, that is, it refers to any one of two parallel options of "present" or "absent". If "optional" appears multiple times in a technical solution, without special specifications and without contradictions or mutual restrictions, each "optional" is independent. Without other specifications, descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or may not include".

[0102] In this application, without other specifications, the feature or solution corresponding to "and / or" includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. Among them, any and all combinations include combinations of any two related listed items, any more related listed items, or all related listed items. For example, "M and / or N" represents the group composed of M, N, and "the combination of M and N". Among them, "containing M and / or N" can mean "containing M, containing N, and containing the combination of M and N", or it can also mean "containing M, containing N, or containing the combination of M and N", which can be appropriately understood according to the context of the sentence.

[0103] In this text, "suitable combination method", "suitable method", etc., the "suitable" is subject to being able to implement the technical solution of this application.

[0104] In this text, "preferred", "better", and "more preferable" only describe implementation manners or embodiments with better effects. It should be understood that they do not constitute a limitation on the protection scope of this application. If "preferred" appears multiple times in a technical solution, without special specifications and without contradictions or mutual restrictions, each "preferred" is independent.

[0105] In this application, terms such as "further", "even further", "especially", "for example", "such as", "example", "exemplification" are used for descriptive purposes, indicating differences in content, but should not be construed as limiting the scope of protection of this application.

[0106] In this application, in "the first aspect", "the second aspect", "the third aspect", etc., the terms "first", "second", "third", etc. are only used for descriptive purposes 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. only serve the purpose of non-exhaustive enumerative description and should be understood not to constitute a closed limitation on quantity.

[0107] In this application, unless otherwise clearly specified and defined, terms such as "connected" and "joined" related to mechanical structures should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated. For those of ordinary skill in the art, the meanings of the above terms in this application can be understood according to the circumstances.

[0108] In this application, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature can mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature can represent the mutual positional relationship of horizontal height, or can only represent the existence of an attachment relationship without limiting the mutual positional relationship of horizontal height.

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

[0110] In this application, for units related to data ranges, if the unit is only attached after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, both 3~5μm and 3-5μm mean that the units of the left endpoint "3" and the right endpoint "5" are both μm (micrometers), and both have the same meaning as 3μm~5μm. In addition, similar descriptions of other parameters such as temperature and size are understood in the same way.

[0111] In this application, unless otherwise stated, "molecular weight" refers to the molecular mass measured in daltons (Da), and 1 dalton is equal to 12 one-twelfth of the mass of a C 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 expressed as ">", and "less than" can be equivalently expressed as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be regarded as also providing two options of "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be regarded as also providing two options of "less than" and "equal to".

[0113] In this application, for exemplary descriptions such as "in some embodiments" or "in one embodiment", etc., the following meanings can be covered but are not limited to: These solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0114] The improvement effects described in this application, unless otherwise specified, are not intended to be limited by any theoretical restrictions.

[0115] Lithium-ion secondary batteries using cathode active materials such as lithium iron phosphate (LFP) have outstanding advantages in terms of safety and battery life due to their excellent structural stability. However, such cathode active materials usually inevitably introduce moisture, easily generate acid by-products, which can damage the solid electrolyte interface (SEI) film of the anode, exacerbate the interfacial side reactions of the anode, lead to capacity attenuation and affect the battery life. Especially, the side reactions involving water at high temperatures are more intense, resulting in less than ideal high-temperature performance of the battery.

[0116] Although theoretically, high-temperature additives such as alkyne additives can improve the high-temperature performance of the battery by optimizing the anode SEI film, it will increase the interfacial impedance of the anode and affect the performance at room temperature.

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

[0118] In this application, unless otherwise specified, "high temperature" when referring to battery cycling and / or storage can be greater than 35°C and less than or equal to 80°C. Optionally, it is greater than 35°C and less than or equal to 60°C. Further optionally, it is 37°C to 60°C. Further optionally, it is 40°C to 60°C. Still further optionally, it is 45°C to 60°C, but not limited thereto. "High temperature" when referring to battery cycling or storage can also be any one of the following temperatures or a range composed of 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, "room temperature" when referring to battery cycling and / or storage can be 20°C to 35°C, optionally 20°C to 30°C, but not limited thereto. "Room temperature" when referring to battery cycling or storage can also be any one of the following temperatures or a range composed of any two of the following temperatures: 20°C, 22°C, 24°C, 25°C, 26°C, 28°C, 30°C, 32°C, 34°C, 35°C, etc.

[0120] In some embodiments, a lithium-ion secondary battery is provided, which includes a positive electrode sheet and an electrolyte. The positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive; the positive electrode active material includes a lithium-containing phosphate-based positive electrode material, and the average particle size of the primary particles in the positive electrode active material is moderate (such as 100 nm to 500 nm); the additive includes an alkaline alkyne additive, and the alkaline alkyne additive contains a Lewis base nitrogen heterocycle.

[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. Generally, a lithium-ion secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, the active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. A separator is provided between the positive electrode sheet and the negative electrode sheet, and the separator mainly plays a role in preventing short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0122] In some embodiments, a lithium-ion secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, and a separator is provided between the positive electrode sheet and the negative electrode sheet.

[0123] In this application, unless otherwise specified, the "electrode active material layer" includes at least one of the positive electrode active material layer of the positive electrode sheet and the negative electrode active material layer of the negative electrode sheet. According to the specific situation, the electrode active material layer can refer to the positive electrode active material layer or the negative electrode active material layer. It can be understood that the positive electrode active material layer contains a positive electrode active material, and the negative electrode active material layer contains a negative electrode active material. In this application, the "electrode active material layer" can also be denoted as the "active material layer", the "positive electrode active material layer" can also be denoted as the "positive electrode active layer", and the "negative electrode active material layer" can also be denoted as the "negative electrode active layer".

[0124] In this application, the terms "sheet" and "electrode sheet" have the same meaning and can be used interchangeably. The 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 embed and extract active ions.

[0125] In the present application, the term "negative electrode sheet" includes a negative electrode active layer, and the negative electrode active layer includes a negative electrode active material. The term "negative electrode active material" refers to a material used for the negative electrode sheet that can reversibly insert and extract active ions.

[0126] In the present application, unless otherwise specified, the "negative electrode sheet" includes a negative electrode current collector. The "negative electrode current collector" refers to a structure that is 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 can be located on one or both sides of the negative electrode current collector.

[0127] In the present 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 for the positive electrode sheet that can reversibly extract and insert active ions.

[0128] In the present application, unless otherwise specified, the "positive electrode sheet" includes a positive electrode current collector. The "positive electrode current collector" refers to a structure that is responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive electrode active layer is located on at least one side of the positive electrode current collector, and can be located on one or both sides of the positive electrode current collector.

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

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

[0131] In some embodiments of the first aspect of the present application, a lithium-ion secondary battery is provided, which includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. A separator is disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive; the positive electrode active material includes a lithium-containing phosphate-based positive electrode material, and the average particle size of the primary particles in the positive electrode active material is 100 nm to 500 nm; the additive includes an alkaline alkyne additive, and the alkaline alkyne additive contains a Lewis base nitrogen heterocycle.

[0132] In the present application, unless otherwise specified, the "lithium-containing phosphate-based positive electrode material" refers to a type of positive electrode active material that includes a lithium-containing phosphate component, and further refers to a positive electrode active material that includes lithium element, transition metal element, and phosphate ion (PO 4 3- ). Unless otherwise specified, the "lithium-containing phosphate-based positive electrode material" may have an olivine structure.

[0133] In the present application, the "average particle size of the primary particles in the positive electrode active material" can be denoted as D 1 .

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

[0135] In this application, unless otherwise specified, the "primary particles" in the positive electrode active material are the basic particle units in the positive electrode active material. It can be understood that there are primary particles in the positive electrode active material. In the positive electrode active material, the primary particles can exist in a non-agglomerated state, or multiple primary particles can form an aggregate. The non-agglomerated primary particles can be called "non-agglomerated primary particles", and the aggregate formed by multiple primary particles can be called "secondary particles".

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

[0137] In this application, unless otherwise specified, the "Lewis base nitrogen heterocycle" refers to a nitrogen heterocycle with Lewis base properties. This concept is based on the Lewis acid-base theory (Lewis acids and bases). The Lewis base nitrogen heterocycle can provide an electron pair and has the characteristic of being electron-rich. Therefore, the Lewis base nitrogen heterocycle can attract and combine with acidic substances. In addition, the Lewis base nitrogen heterocycle can also form hydrogen bonds with water. Non-limiting examples of the Lewis base nitrogen heterocycle include, but are not limited to, the imidazole ring.

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

[0139] In this application, unless otherwise specified, the "alkynyl basic additive" refers to an alkynyl base additive containing a Lewis base nitrogen heterocycle; it can be understood that the alkynyl basic additive contains a carbon-carbon triple bond "C≡C". Unless otherwise specified, the "alkynyl basic additive" used herein is a non-ionic alkynyl organic additive; it can be understood that metal salt additives are not within the meaning scope of the alkynyl basic additives used herein. It can be understood that the alkynyl basic additive can attract and combine with acidic substances, such as acid by-products (such as hydrofluoric acid) in the electrolyte. The alkynyl basic additive can participate in the formation of the solid electrolyte interface (SEI) film on the negative electrode. The alkynyl basic additive can significantly improve the high-temperature performance of the battery, including extending the high-temperature cycle performance and high-temperature storage performance, and can be used as a high-temperature additive. However, the introduction of the alkynyl basic additive easily leads to a large interfacial impedance of the negative electrode at room temperature.

[0140] In the lithium-ion secondary battery provided by the present application, it can be understood that the positive electrode sheet and the negative electrode sheet are wetted by the electrolyte solution.

[0141] For a lithium-ion secondary battery in which the positive electrode active material includes a lithium-containing phosphate positive electrode material, by introducing an alkaline alkyne additive (which can also be denoted as additive A) having a carbon-carbon triple bond and a Lewis base nitrogen heterocycle and having high temperature stability into the electrolyte solution, the Lewis base nitrogen heterocycle can be used to absorb water and acid by-products, reduce the free acid by-products in the electrolyte solution at high temperature, inhibit the aggravating effect of the acid by-products on the battery capacity attenuation at high temperature, and then use the carbon-carbon triple bond to form a solid electrolyte interface (SEI) film with high stability on the negative electrode, reduce the interfacial side reactions at high temperature, and utilize the foregoing multiple effects to significantly improve the high temperature performance of the battery; further control the average particle size of the primary particles in the positive electrode active material within a relatively moderate range, which can not only reduce the content of water and acid by-products in the system and inhibit the damage of the acid by-products to the negative electrode SEI film, inhibit the increase of the interfacial impedance at room temperature caused by the participation of the alkaline alkyne additive in the negative electrode film formation, but also control the positive electrode active material to have a more suitable lithium ion transmission path and then regulate the internal resistance of the battery, so as to be beneficial to enabling the lithium-ion secondary battery to also achieve good room temperature performance; based on the foregoing multiple effects, but not limited to the foregoing theory, the high temperature performance of the battery system containing the lithium-containing phosphate positive electrode material can be significantly improved while also taking into account good room temperature performance.

[0142] In the present application, the manner in which the Lewis base nitrogen heterocycle absorbs water and / or acid by-products may include, but is not limited to, hydrogen bond interaction.

[0143] The types and concentrations of the inorganic components (which may include electrolyte salts and inorganic additives) in the electrolyte solution can be tested with reference to relevant standards such as "General Rules for the Determination of Chemical Reagents by Ion Chromatography (GB / T 34672-2017)", "General Rules for Ion Chromatographic Analysis Methods (JY / T 020-1996)", "General Rules for Infrared Spectral Analysis Methods (GB / T 6040-2019)", etc., and the standard methods of the updated version or the current version can be preferably used. The testing of the types and contents of the organic components (including non-aqueous solvents and organic additives) in the electrolyte solution can be tested with reference to relevant standards such as "General Rules for Gas Chromatography of Chemical Reagents (GB / T 9722-2023)".

[0144] In addition, those skilled in the art can also identify the components contained in the electrolyte solution in the lithium-ion secondary battery through one or more of the following detection methods, including but not limited to: nuclear magnetic resonance hydrogen spectrum ( 11H NMR), high performance liquid chromatography (HPLC), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MADI-TOF), Fourier transform infrared spectroscopy (FT-IR), ultraviolet spectroscopy, gas chromatography (GC), etc. The sample preparation methods and test methods of these test 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 sample characteristics. As a non-limiting example, FT-IR, ultraviolet spectroscopy, 1 1H NMR, mass spectrometry, MADI-TOF, GC and other methods can be used to detect the types and contents of the components of the electrolyte, but are not limited thereto.

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

[0146] In this application, the sample to be tested of the "positive active material" in the positive electrode sheet of the lithium-ion secondary battery can be obtained by disassembling the battery, taking out the positive electrode sheet, and using methods such as solvent washing, ultrasonic dispersion, centrifugal separation, fractional sedimentation, and sintering to extract the positive active material from the positive active layer of the positive electrode sheet, and drying to obtain a powder sample. The obtained powder sample can be used for laser particle size analyzer analysis and testing, or for other tests. In addition, the powder material extracted from the positive active layer can be sintered to remove organic components, thereby obtaining a powder sample of the positive active material.

[0147] Exemplarily, the powder sample of the positive active material can be prepared 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 the residual electrolyte; scrape the powder material of the positive active layer, and use a solvent (such as N-methylpyrrolidone (NMP), etc.) to fully soak the powder material extracted from the positive active layer 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 the density difference to centrifuge to separate the relatively low-density conductive agent from the suspension, and collect the centrifuged precipitate to obtain the powder to be tested of the positive active material.

[0148] The elemental composition of the positive active material in the positive active layer can be analyzed by methods well known in the art, including but not limited to the following methods: inductively coupled plasma spectroscopy (ICP), X-ray diffraction (XRD), single crystal X-ray diffraction (SCXRD), energy dispersive spectrometer (EDS), etc. The sample preparation methods and test methods of these test methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the sample characteristics. The ICP method can be used for quantitative test analysis of the component content in the positive active material.

[0149] The detection of the cathode active material in the cathode active layer can be carried out by disassembling the battery cell after full discharge, taking out the cathode electrode, scraping the material of the cathode active layer, and using elemental analysis methods such as inductively coupled plasma (ICP) spectrometry to test and analyze the types and proportions of elements, so as to confirm the elemental composition and chemical formula of the cathode active material.

[0150] The particle size of the primary particles in the cathode active material can be counted by using the particle morphology map of the cathode active material, and then the average particle size of the primary particles in the cathode active material can be obtained. The particle morphology map of the cathode active material can adopt the test results of a scanning electron microscope (such as ZEISS Sigma 300, JEOL scanning electron microscope, Axia ChemiSEM scanning electron microscope, etc.). The sample to be tested can be obtained by laying and sticking the powder sample of the cathode active material on the conductive adhesive, or the cross-section of the cathode electrode can be used for SEM testing. Without limitation, the SEM test can refer to JY / T(001)-1996. Randomly select one or more regions in the sample to be tested for scanning test, and based on the SEM images at a certain magnification, count the particle sizes of each primary particle and the occurrence frequencies of different particle sizes in the scanned region, and then calculate the average particle size of each primary particle counted. Without limitation, the magnification of a single scanning region can be, for example, 1500X, further, for example, 1000X, but not limited thereto. To improve the accuracy of the statistical results, multiple regions can be randomly selected for scanning. The statistical quantity of the primary particles can be several hundred, or greater than or equal to 1000, or greater than or equal to 2000. Increasing the statistical quantity of the primary particles is beneficial to improving 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 map of the cathode active material is denoted as "the particle size of the primary particles in the cathode active material".

[0152] In some embodiments, the average particle size (D1) of the primary particles in the cathode active material can be 100nm - 500nm, optionally 150nm - 500nm, further optionally 150nm - 450nm, still further optionally 200nm - 450nm, and can also be any one of the following values or a range composed of any two of the following values: 100 nm, 110 nm, 120 nm, 140nm, 150 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 250 nm, 260 nm, 280 nm, 300 nm, 350nm, 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 the negative electrode interface impedance indirectly caused by water in the positive electrode active material and the influence of the lithium ion transport path on the internal resistance of the battery, and it is beneficial to better take into account the normal temperature performance while significantly improving the high temperature performance of the battery.

[0154] In some embodiments, the water absorption rate of the positive electrode active material is 50 ppm / h to 85 ppm / h, and it can also be any one of the following values or a range composed of 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 the "water absorption rate of the positive electrode active material" represents the increase in the water content per unit time, and the "water content" refers to the mass ratio of water in the sample; existing methods in the art can be used for testing, which can include but are not limited to the Karl Fischer method for testing the water content. Unless otherwise specified, the testing method in the following example part can be used for testing.

[0155] In some embodiments, the lithium-containing phosphate-based positive electrode material includes a carbon-coated lithium-containing phosphate-based positive electrode material, and the carbon-coated lithium-containing phosphate-based positive electrode material includes a lithium-containing phosphate matrix and a carbon coating layer located on at least a part of the surface of the lithium-containing phosphate matrix.

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

[0157] In this application, unless otherwise specified, the "carbon-coated lithium-containing phosphate-based positive electrode material" is a coated positive electrode active material, the positive electrode active body includes a lithium-containing phosphate matrix, and the coating layer includes a carbon coating layer. Further, the carbon coating layer can 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 after further high-temperature treatment, while hard carbon is difficult to graphitize even after further high-temperature treatment. In this application, unless otherwise specified, "amorphous carbon" refers to a transition carbon material with a very low degree of graphitization crystallization, approximately in an amorphous form (or without a fixed shape and periodic structural rules).

[0158] By providing a carbon coating layer on the surface of the lithium-containing phosphate-based positive electrode material, the specific surface area of the material may be increased, and then the water absorption rate of the material surface may be increased. At this time, through the synergistic effect of controlling the average particle size (D1) of primary particles in the positive electrode active material and introducing an alkaline alkyne additive, it is possible to take into account better normal temperature performance while significantly improving the high temperature performance of the battery.

[0159] In some embodiments, the specific surface area (BET 1 ) of the positive electrode active material can be 5 m 2 / g to 18 m 2 / g, optionally 5 m 2 / g to 16 m 2 / g, further optionally 5 m 2 / g to 15 m 2 / g, still further optionally 5.5 m 2 / g to 12 m 2 / g, still further optionally 5.5 m 2 / g to 10 m 2 / g, or can also be any of the following values or a range composed of 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 the well-known meaning in the art. It can be tested by the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis test can be carried out by the Tri Star II specific surface area and pore size analyzer of Micromeritics Company in the United States, and the test steps can refer to GB / T 19587-2004. The detailed steps are as follows: Use nitrogen as the adsorption gas, and calculate the specific surface area of the material by the BET method; Take the sample to be tested and add it to the BET test tube until it reaches 2 / 3 of the bottom bulb, and heat the sample for degassing; After cooling to room temperature, backfill nitrogen to remove the vacuum and block the sample tube mouth with a stopper, and record the sample weight; Remove the stopper, add a filling rod, install the sample tube to the instrument analysis station, and start the test after inputting the sample weight. Before the test, the sample to be tested can be dried first.

[0161] For a lithium-ion secondary battery, exemplarily, a lithium-ion secondary battery including a positive electrode active material comprising a carbon-coated lithium-containing phosphate-based positive electrode material, by controlling the "specific surface area (BET 1 )" within the aforementioned range, it is beneficial to better control the water absorption rate of the positive electrode active material, and at the same time, it can better inhibit the side reactions at the high-temperature interface, which is beneficial to better improving the high-temperature performance of the battery while also taking into account good room-temperature performance.

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

[0163] (a1) The graphitization degree (G 1 ) of the carbon coating layer can be greater than or equal to 28%, further can be 28% - 95%, still further can be optionally 40% - 95%, still further can be optionally 40% - 90%, still further can be optionally 40% - 85%, still further can be optionally 50% - 70%, and can also be any one of the following values or a range composed of 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 (G 1 ) of the carbon coating layer can also be selected from any one of the following ranges: 28% - 90%, 40% - 90%, 50% - 90%, 28% - 85%, 50% - 85%, 28% - 70%, 40% - 70%, etc.;

[0164] (a2) The mass ratio (F B ) of the carbon coating layer in the carbon-coated lithium-containing phosphate-based positive electrode material can be 0.5% - 2.5%, optionally 0.8% - 2%, and can also be any one 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) The average thickness (D Bcan be less than or equal to 8 nm, optionally 1 nm to 8 nm, can also be less than or equal to 6 nm, optionally 1 nm to 6 nm, further optionally 1 nm to 5 nm, can also be any of the following values or a range composed of 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.; without limitation, the average thickness (D B can also be less than or equal to any of the following values: 5 nm, 5.5 nm, 6.5 nm, 7 nm, etc.; without limitation, the average thickness (D B can also be less than any of the following values: 5.5 nm, 6 nm, 7 nm, 8 nm, etc.;

[0166] (a4) The maximum thickness (D max ) can be less than or equal to 12 nm, further can be less than or equal to 10 nm, further can be less than or equal to 8 nm, further less than or equal to 6 nm, further optionally 1 nm to 5 nm, can also be any of the following values or a range composed of 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., 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-containing phosphate cathode material satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable value or range in the context):

[0168] (a1’) The graphitization degree (G 1 ) of the carbon coating is 40% to 90%, optionally 40% to 85%;

[0169] (a2’) The mass ratio (F B ) of the carbon coating in the carbon-coated lithium-containing phosphate cathode material is 0.8% to 2%;

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

[0171] The maximum thickness (D max ) of the carbon coating layer is less than or equal to 10 nm, and optionally less than or equal to 8 nm.

[0172] In this application, unless otherwise specified, "graphitization degree" has its well-known meaning in the art and can be used to measure the degree to which the crystal of the carbon material approaches perfect graphite. The graphitization degree can be tested by using instruments and methods known in the art. As a non-limiting example, an X-ray diffractometer can be used for testing. The X-ray diffractometer can be of models such as Bruker D8 Discover, Bruker D8 advance, etc., but is not limited thereto. The test can refer to JIS K 0131-1996, JB / T4220-2011. First, measure the interlayer spacing d 002 of the (002) crystal plane of the carbon material, and the interlayer spacing of the (002) crystal plane can be calculated using the Bragg equation; then, according to the Franklin formula (Mering-Maire formula), calculate G = (0.3440 - d 002 ) / (0.3440 - 0.3354) × 100% to obtain the graphitization degree, where G is the graphitization degree (%), 0.3440 is the interlayer spacing of non-graphitized carbon (nm), 0.3354 is the interlayer spacing of an ideal graphite crystal (half of the lattice constant of the c-axis of hexagonal graphite, nm), and d 002 is the interlayer spacing of the (002) crystal plane of the carbon material expressed in nanometers (nm). It should be noted that in order to obtain a more accurate d 002 value, Si powder can be incorporated to correct the diffraction angle to reduce errors. The graphitization degree of the carbon coating layer in the carbon-coated lithium-containing phosphate cathode material can be denoted as G 1 . The higher the graphitization degree, the higher the degree to which the carbon material crystal approaches perfect graphite.

[0173] For a lithium-ion secondary battery whose positive electrode active material includes a carbon-coated lithium-containing phosphate cathode material, by controlling "the carbon coating layer has a relatively high graphitization degree (G 1 )", or controlling "the mass ratio (F B ) of the carbon coating layer in the carbon-coated lithium-containing phosphate cathode material", "the average thickness (D B ) of the carbon coating layer" and "the maximum thickness (D max ) of the carbon coating layer" to have relatively low values of one or more of these parameters, it 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 the alkaline alkyne additive, and reduce the growth rate of the negative electrode interface impedance, which is beneficial to better balance the room temperature performance.

[0174] For a lithium-ion secondary battery in which the positive electrode active material includes a carbon-coated lithium-containing phosphate positive electrode material, by controlling the graphitization degree of the carbon coating layer within the aforementioned range, it is possible to better coordinate the water absorption rate on the material surface, the conductivity of the carbon coating layer, and the ion diffusion impedance of the carbon coating layer, and better balance the influence of the carbon coating layer on the internal resistance of the battery and the inhibitory effect of the carbon coating layer on the side reactions at the positive electrode interface, so as to better improve the high-temperature performance of the battery while also taking into account good room-temperature performance.

[0175] Exemplarily, controlling a relatively high graphitization degree within the aforementioned range of graphitization degrees is beneficial to reducing the water absorption rate on the material surface and increasing the conductivity of the carbon coating layer while also better controlling the ion diffusion impedance.

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

[0177] By controlling one or two or all three of "the mass ratio of the carbon coating layer in the carbon-coated lithium-containing phosphate positive electrode material (F B )", "the average thickness of the carbon coating layer (D B )", and "the maximum thickness of the carbon coating layer (D max )" within the aforementioned range, it is beneficial to control the positive electrode active material to have a low water absorption rate, and it is also beneficial to reduce the influence of the ion diffusion impedance on the internal resistance of the battery, which is beneficial to better taking into account the room-temperature performance of the battery.

[0178] For the positive electrode active material or the negative electrode active material including a coating layer (examples of the coating layer such as a carbon coating layer), after using methods such as FIB (focused ion beam) and CP (ion beam cross-section polishing) to perform particle cutting to obtain a cross-section, the cross-sectional morphology of the particles can be observed under TEM (transmission electron microscope, such as JEM-F200, Thermo Scientific-Talos F200S G2, etc.). An obvious boundary can be observed at the coating interface. Based on the TEM images, the thickness, average thickness, and maximum thickness of the coating layer at multiple positions in 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 of 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 of multiple particles. For a single particle, the number of sampling positions for analyzing the average thickness of its coating layer can be greater than or equal to 5, and further can be greater than or equal to 10; the number of particles to be statistically analyzed can be greater than or equal to 3, and further can be greater than or equal to 5. Further, by combining one or more of methods such as energy dispersive spectroscopy (EDS) analysis and Raman spectroscopy, the types and contents of substances in the coating layer and the positive electrode active material body can be respectively confirmed, or the types and contents of substances in the coating layer and the negative electrode active material body can be respectively confirmed.

[0179] In some embodiments, the D v 50 (denoted as D v 50 1 ) of the positive electrode active material can be 1 μm to 5 μm, optionally 1 μm to 4 μm, further optionally 1.5 μm to 4 μm, still further optionally 1.5 μm to 3.5 μm, and can also be any of the following values or a range composed of any two of the following values: 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc. Without limitation, the D v 50 of the positive electrode active material can also be selected from any suitable range among the following ranges: 1 μm to 3 μm, 1.5 μm to 3 μm, 2 μm to 5 μm, 2 μm to 4.5 μm, 2 μm to 3.5 μm, etc.

[0180] In this application, unless otherwise specified, D v 50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%. This parameter indicates that the particle size of 50% of the material volume is less than or equal to D v 50, and the particle size of 50% of the material volume is greater than D v 50. Those skilled in the art can understand the meaning of D v 50, and can use the instruments and methods well-known in the art for measurement. For example, it can be conveniently measured with reference to GB / T 19077-2016 Laser diffraction method for particle size distribution, using a laser particle size analyzer, such as the Mastersizer 2000E type laser particle size analyzer of Malvern Instruments Limited in the UK, the LS-909 laser particle size analyzer (Omec). Further, for equipment models such as the Malvern 2000 (MasterSizer 2000) laser particle size analyzer, the test can be carried out with reference to the standard process GB / T19077-2016 / ISO 13320:2009.

[0181] By making the "D v 50 (denoted as D v 50 1When the control is within the foregoing range, the degree of aggregation of the primary particles can be adjusted by combining with the joint control of the average particle size (D1) of the primary particles, the specific surface area and the water absorption rate can be better controlled, and the ion transport path of the overall positive electrode active material particles can also be better controlled. Based on the synergy of the foregoing effects, but not limited to the foregoing theory, it is beneficial to better control the internal resistance of the battery, and it is beneficial to better balance the battery's normal temperature performance while significantly improving the battery's high-temperature performance. In some examples, for a lithium-ion secondary battery in which the positive electrode active material includes a carbon-coated lithium-containing phosphate-based positive electrode material, the influence of the carbon coating layer on the specific surface area, water absorption rate, conductivity, ion diffusion impedance, and side reactions at the positive electrode interface can also be better balanced, and the battery's normal temperature performance can be better balanced while significantly improving the battery's high-temperature performance.

[0182] In some embodiments, the following method can be used to measure D of the positive electrode active material v 50, etc. Using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer, referring to the standard process: GB / T19077-2016 / ISO 13320:2009, the detailed test process includes: 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% light obscuration), and performing ultrasonic treatment for 5 min (53KHz / 120W) to fully disperse the sample. Then, the sample is measured according to the GB / T19077-2016 / ISO 13320:2009 standard. Non-limiting examples of the solvent include deionized water, etc. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. When the particles are irradiated by the laser beam, the particle size distribution characteristics of the particles can be obtained by receiving and measuring the energy distribution of the scattered light. According to the test data, a particle size volume distribution diagram is drawn, and parameters such as D v 50, etc. can be obtained from the distribution diagram. To avoid the influence of aggregation during the drying process on the particle size measurement, the washed and wet sample is taken for dispersion testing. The washing reagent can be anhydrous ethanol, but is not limited thereto.

[0183] 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 a carbon-based material and a silicon-based material.

[0184] In some embodiments, the negative electrode active material includes a carbon-based material. Without limitation, 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. Without limitation, the mass percentage of the carbon-based material in the negative electrode active material may be 80% - 100%, optionally 90% - 100%, further optionally 95% - 100%, still further optionally 97% - 100%, and may also be any one of the following percentages or a range formed by 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 further may be a graphite-based material.

[0186] In the present application, the "graphite-based material" refers to the negative electrode active material containing a graphite body. Without limitation, the graphite-based material may include one or more of coated graphite-based materials and uncoated graphite. The coated graphite-based material includes a graphite body and a coating layer located on at least a part of the surface of the graphite body. It can be understood that the material in the coating layer is different from that in the graphite body. Without limitation, the mass percentage of the graphite body in the graphite-based material may be 90% - 100%, and may also be any one of the following percentages or a range formed by any two of the following percentages: 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%. The graphite-based material may include, but is 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 the present application, the "graphite body" is composed of graphite.

[0188] In some embodiments, the mass percentage of the graphite-based material in the negative electrode active material is 80% - 100%, optionally 90% - 100%, further optionally 95% - 100%, still further optionally 97% - 100%, and may also be any one of the following percentages or a range formed by 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. Further, the graphite may include one or more of artificial graphite and natural graphite.

[0190] Non - restrictively, the mass ratio of the silicon - based material in the negative electrode active material can be 0 to 20%, optionally 0% to 10%, and can also be any one of the following percentages or a range composed of 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 - restrictively, the mass ratio of the silicon - based material in the negative electrode active material can also be 1% to 20%, optionally 1% to 10%, and can also be any one of the following percentages or a range composed of 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. Non - restrictively, the silicon - based material can include one or more of elemental silicon, silicon - oxygen materials, silicon - carbon composites, silicon - nitrogen composites, and silicon alloys.

[0193] "Silicon - carbon composite" is a kind of silicon - based material. The silicon - carbon composite includes a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix. The silicon - carbon composite can be obtained by chemical vapor deposition. Those skilled in the art can prepare the silicon - carbon composite by conventional methods in the art.

[0194] In some embodiments, the negative electrode sheet satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable value or range in the context):

[0195] (b1) The mass ratio of the silicon - based material in the negative electrode active material is 0 to 20%, optionally 1% to 20%, further optionally 1% to 10%, and can also be any one of the following percentages or a range composed of 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) The silicon-based material includes a silicon-carbon composite material, and the silicon-carbon composite material includes a porous carbon matrix and elemental silicon located within the pores of the porous carbon matrix; without limitation, the mass percentage of the silicon-carbon composite material in the silicon-based material can be 80% - 100%, optionally 90% - 100%, further optionally 95% - 100%, still further optionally 97% - 100%, and can also be any one of the following percentages or a range composed of any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 100%, etc.;

[0197] (b3) The carbon-based material includes a graphite-based material; without limitation, the mass percentage of the graphite-based material in the negative electrode active material can be 80% - 100%, optionally 90% - 100%, further optionally 95% - 100%, still further optionally 97% - 100%, and can also be any one of the following percentages or a range composed of 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, and the coated negative electrode material includes a negative electrode active body and a carbon coating layer located on at least a part of the negative electrode active body; without limitation, the mass percentage of the coated negative electrode material in the negative electrode active material can be 80% - 100%, optionally 90% - 100%, and can also be any one of the following percentages or a range composed of 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 the silicon-based material in the negative electrode active material and / or the type of the positive electrode active material within the foregoing ranges, the expansion and contraction changes of the negative electrode can be better controlled, the generation of fresh interfaces can be reduced, the side reactions at the negative electrode interface can be inhibited, which is beneficial to reducing the consumption rate of the alkaline alkyne additives, reducing the growth rate of the battery internal resistance, and is conducive to better balancing the battery's room temperature performance. Exemplarily, among the silicon-based materials, the silicon-carbon composite material has relatively low volume expansion and contraction changes.

[0200] In some embodiments, the negative electrode active material includes a coated negative electrode material, and the coated negative electrode material includes a negative electrode active body and a carbon coating layer covering at least a part of the negative electrode active body. It can be understood that the chemical composition of the carbon coating layer is different from that of the negative electrode active body. The negative electrode active body can be selected from at least one material known in the art suitable for negative electrode active materials. Without limitation, the negative electrode active body can include one or more of graphite and silicon-based materials; without limitation, the graphite can include one or more of natural graphite and artificial graphite; without limitation, the silicon-based materials can include one or more of elemental silicon, silicon oxide materials, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon alloys. Without limitation, the carbon coating layer in the coated negative electrode material can include one or more of soft carbon, hard carbon, and amorphous carbon. Without limitation, 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 still further optionally 100 nm to 200 nm. Without limitation, the mass percentage of the coating layer in the coated active material is 0.2% to 5%, optionally 0.5% to 3%. Without limitation, the mass ratio 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%, still further optionally 95% to 100%, still further optionally 95% to 98%, and can also be any one of the following percentages or a range composed of 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. Without limitation, the mass ratio of the coated graphite in the negative electrode active material can be 80% to 100%, optionally 90% to 100%, further optionally 92% to 100%, still further optionally 95% to 100%, still further optionally 95% to 98%, and can also be any one of the following percentages or a range composed of any two of the following percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0203] In the present application, "coated graphite" is a coated anode material. The anode active body in the coated graphite includes a graphite body; the coated graphite includes a graphite body and a carbon coating layer covering at least a part of the surface of the graphite body.

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

[0205] In some embodiments, the coated anode material is coated graphite, and in this case, the anode active body is a graphite body.

[0206] Those skilled in the art can identify the components in the positive electrode active layer and the negative electrode active layer by 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, nuclear magnetic resonance hydrogen spectrum ( 1 1H NMR) method, gel permeation chromatography (GPC) method, high performance liquid chromatography (HPLC) method, mass spectrometry, X-ray photoelectron spectroscopy (XPS) method, X-ray diffraction (XRD) method, Raman spectroscopy method, single crystal X-ray diffraction (SCXRD) method, inductively coupled plasma spectroscopy (ICP) method, energy dispersive spectrometer (EDS) analysis, etc. The sample preparation methods and test methods of these test 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 carbon elements and silicon elements, and thus distinguish carbon-based materials and silicon-based materials. For another example, the type and content of the conductive agent can be detected by EDS, but not limited thereto.

[0208] Taking the anode active material including natural graphite and artificial graphite as a non-limiting example, natural graphite and artificial graphite can be distinguished by the appearance morphology of the particles; X-ray diffraction (XRD) analysis and testing can be further carried out. In the XRD pattern, if the characteristic peak near 2θ 26.5° is very sharp and has a high intensity, it is natural graphite; if the characteristic peak near 2θ 26.5° is relatively wide and has a weak intensity, it is artificial graphite.

[0209] In this application, a 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, taking out the negative electrode sheet, and using methods such as solvent washing, ultrasonic dispersion, centrifugal separation, and fractional sedimentation to extract the negative electrode active material from the negative electrode active layer of the negative electrode sheet, and then drying to obtain a powder sample. The obtained powder sample can be used for chemical composition analysis tests or other tests.

[0210] In some embodiments, in a lithium-ion secondary battery, the mass percentage of the alkaline alkyne additive in the electrolyte (C A ) can be less than or equal to 3.5%, optionally 0.01% - 3.5%, further optionally 0.05% - 2.5%, still further optionally 0.1% - 2.5%, still further optionally 0.2% - 2.5%, and can also be any one of the following percentages or a range composed of 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. Without limitation, C A 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 of the alkaline alkyne additive in the electrolyte (C A )" within the foregoing range, the alkaline alkyne additive can continuously play a role in repairing the SEI film during cycling and / or storage, which is more beneficial to significantly improving the high-temperature performance while also taking into account good room-temperature performance.

[0212] In some embodiments, the additive includes a negative electrode film-forming additive different from the alkaline alkyne additive.

[0213] "Negative electrode film-forming additive" refers to an additive that can decompose at the working potential of the negative electrode 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 the earlier it participates in the formation of the negative electrode SEI film. It can be 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 judge whether a certain additive can participate in the formation of the negative electrode SEI film through methods such as reduction potential analysis, decomposition product and SEI film composition analysis, and electrochemical performance verification; exemplarily, the reduction potential of the additive can be measured by cyclic voltammetry in a simulated battery environment (such as a lithium metal counter electrode); exemplarily, chemical composition analysis methods including but not limited to X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) can be used to analyze the composition of the SEI film; exemplarily, it can be judged whether a certain additive introduced can participate in the formation of the negative electrode SEI film according to the changes in performance indicators such as the initial Coulomb efficiency, cycle stability, and impedance spectrum when the additive is introduced or not.

[0214] The negative electrode film-forming additives different from the alkaline alkyne additives can competitively participate in the negative electrode film formation, can reduce or delay the consumption of the alkaline alkyne additives for negative electrode film formation, can inhibit the increase in the negative electrode interface impedance caused by the participation of the alkaline alkyne additives in the negative electrode film formation, and are beneficial to improving the high-temperature performance of the battery while better taking into account the room-temperature performance.

[0215] In some embodiments, the additive further includes one or more of additive B, additive C, and additive 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 anhydride additives;

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

[0219] Additive B, additive C, and additive D can all be used as negative electrode film-forming additives. Additive B is a type of negative electrode film-forming additive with low impedance and a certain acid-removing effect, and its acid-removing effect is lower than that of the alkaline alkyne additives, and the negative electrode film-forming impedance is lower than that of the alkaline alkyne additives. Additive C is a type of additive with a good acid-removing effect, and its acid-removing effect is better than that of the alkaline alkyne additives but the negative electrode film-forming impedance is higher than that of the alkaline alkyne additives. The negative electrode film-forming impedance of additive D is very low, much lower than that of the alkaline alkyne additives.

[0220] Utilizing the synergistic effect of alkaline alkyne additives with one or more of additive B, additive C, and additive D is beneficial for better simultaneously improving high-temperature performance while also taking into account good room-temperature performance.

[0221] Non-limitingly, in a lithium-ion secondary battery, the sum of the mass percentages of additive B, additive C, and additive D in the electrolyte can be greater than or equal to 0.02%, optionally 0.02% - 5%, further optionally 0.02% - 3%, further optionally 0.02% - 1.5%, can also be 0.1% - 5%, further optionally 0.1% - 3%, still further optionally 0.1% - 1.5%, still further optionally 0.1% - 1%, can also be any one of the following percentages or a range composed of 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] Non-limitingly, silane additives can include tris(trimethylsilyl) borate (TMSB).

[0223] Non-limitingly, isocyanate additives can include, but are not limited to, toluene diisocyanate.

[0224] Non-limitingly, acid anhydride additives can include one or more of maleic anhydride, citraconic anhydride, trifluoromethyl maleic anhydride, succinic anhydride, glutaric anhydride, butanedioic anhydride, etc.

[0225] Non-limitingly, in a lithium-ion secondary battery, the mass percentage of acid anhydride additives in the electrolyte can be 0% - 1%, optionally 0.01% - 1%, further optionally 0.1% - 1%, can also be any one of the following percentages or a range composed 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.

[0226] Non-limitingly, lithium salt additives can include one or more of oxalic acid lithium salts, lithium tetrafluoroborate, lithium difluorophosphate, fluorosulfonic acid lithium salts, etc.; non-limitingly, oxalic acid lithium salts can include one or more of lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, etc.; non-limitingly, fluorosulfonic acid lithium salts can include one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide (LiFSI), etc.

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

[0228] In some embodiments, the additive includes a lithium salt additive.

[0229] Non - restrictively, in a lithium - ion secondary battery, the mass percentage of the lithium salt additive in the electrolyte may be 0 - 3%, may be greater than 0 and less than or equal to 3%, further optionally 0.05% - 3%, and may also be any one of the following percentages or a range composed of 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 the present application, when the mass percentage of the lithium salt additive (such as LiFSI) in the electrolyte is greater than 3%, it can generally also play the role of an electrolyte salt. Without other instructions, at this time, the mass percentage of the lithium salt additive (such as LiFSI) in the additive B in the electrolyte is recorded as 3%.

[0231] In some embodiments, the additive includes phosphate ester additives.

[0232] Non - restrictively, in a lithium - ion secondary battery, the mass percentage of the phosphate ester additive in the electrolyte may be 0 - 2%, may be greater than 0 and less than or equal to 2%, further optionally 0.1% - 2%, and may also be any one of the following percentages or a range composed of 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 a lithium - ion secondary battery, the mass percentage (C B ) of the additive B in the electrolyte is 0% - 1%, optionally 0.1% - 1%, and may also be any one of the following percentages or a range composed 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 - restrictively, in the electrolyte of a lithium - ion secondary battery, the mass ratio of additive B to the alkaline alkyne additive can be any one of the following values or a range composed of 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 alkaline alkyne additive can be 0.1 - 50, optionally 0.1 - 1, and further optionally 0.2 - 1.

[0235] In some embodiments, in a lithium - ion secondary battery, the mass percentage of additive C in the electrolyte is 0% - 1%, optionally 0.1% - 1%, and can also be any one of the following percentages or a range composed 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.

[0236] Non - restrictively, in the electrolyte of a lithium - ion secondary battery, the mass ratio of additive C to the alkaline alkyne additive (C C ) can be any one of the following values or a range composed of 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, in the electrolyte of a lithium - ion secondary battery, the mass ratio of additive C to the alkaline alkyne additive can be 0.01 - 50, optionally 0.1 - 50, further optionally 0.1 - 20, still further optionally 0.1 - 1, and can also be 0.02 - 1.

[0237] In some embodiments, in a lithium - ion secondary battery, the mass percentage of additive D in the electrolyte is 0% - 2%, optionally 0.1% - 2%, and can also be any one of the following percentages or a range composed of 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 - restrictively, in the electrolyte of a lithium - ion secondary battery, the mass ratio of additive D to the alkaline alkyne additive (C D)(It) can be any of the following numerical values or a range composed of any two of the following numerical 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, in the electrolyte of the lithium-ion secondary battery, the mass ratio of additive D to the alkaline alkyne additive is 0.1 to 100, optionally 0.1 to 50, further optionally 0.1 to 20, still further optionally 0.1 to 2, and can also be 0.2 to 1, etc.

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

[0240] In some embodiments, in the lithium-ion secondary battery, the electrolyte satisfies one or more of the following features (any numerical parameter in the following features can also be selected from any suitable numerical value or range in the context):

[0241] (c1) The mass ratio of additive B to the alkaline alkyne additive is 0.1 to 50, optionally 0.1 to 1;

[0242] (c2) The mass ratio of additive C to the alkaline alkyne additive is 0.02 to 50, optionally 0.02 to 1;

[0243] (c3) The mass ratio of additive D to the alkaline alkyne additive is 0.1 to 100, optionally 0.1 to 2.

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

[0245] In some embodiments, the alkaline alkyne additive satisfies one or more of the following features:

[0246] (d1) the molecular weight of the basic acetylene additive is less than or equal to 500 Da;

[0247] (d2) the molecule of the basic acetylene additive contains 1 to 4 carbon-carbon triple bonds; without limitation, the number of carbon-carbon triple bonds in the molecule of the basic acetylene additive may be 1, 2, 3 or 4;

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

[0249] (d4) the molecule of the basic acetylene additive contains 1 to 4 Lewis base nitrogen heterocycles; without limitation, the number of Lewis base nitrogen heterocycles in the basic acetylene additive can be 1, 2, 3 or 4;

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

[0251] (d6) In the molecule of the basic acetylene additive, the carbon-carbon triple bond and the Lewis base nitrogen heterocycle are connected by a linker L 1 Connected, connecting base L 1 Contains C covalently bonded to a carbon-carbon triple bond 1-3 Alkylene or containing a fluorinated C covalently bonded to a carbon-carbon triple bond 1-3 Alkylene.

[0252] In some embodiments, the basic acetylenic additive satisfies one or more of the following characteristics:

[0253] (e1) the molecular weight of the basic acetylene additive is less than or equal to 300 Da;

[0254] (e2) the molecule of the basic acetylene additive contains 1 to 4 imidazole rings; without limitation, the number of imidazole rings in the basic acetylene additive may be 1, 2, 3 or 4;

[0255] (e3) Lewis base nitrogen heterocycles include imidazole rings; the imidazole rings in the Lewis base nitrogen heterocycles are substituted by 0, 1 or more substituent groups Q 2 Substituted, the substituent group Q in the substituted imidazole 2 Each independently is C 1-3 an alkyl group, a cyano group or a fluorine atom;

[0256] (e4) Basic acetylenic additives are composed of carbon-carbon triple bonds, C 1-3 Alkylene and -OC(=O)-R 10 Sequentially covalently bonded to form, R 10 It is a Lewis base nitrogen heterocycle.

[0257] In some embodiments, the basic acetylene additive includes a compound II having a structure as shown in formula (II): Among them, L11 is C 1-3 alkylene, Q 2 is independently C 1-3 alkyl, cyano or fluorine atom, and p2 is 0, 1, 2 or 3.

[0258] Non - restrictively, in a lithium - ion secondary battery, the mass ratio of Compound II in the alkaline alkyne additive can be 80% - 100%, optionally 90% - 100%, and can also be any of the following percentages or a range composed of 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, when referring to "C 1-3 alkylene", without other explanations, it can be methylene, ethylene or propylene, and further can be methylene, 1,2 - ethylene or 1,3 - propylene.

[0260] In this application, when referring to "C 1-3 alkyl", without other explanations, it can be methyl, ethyl or propyl, and further optionally can be methyl, ethyl, n - propyl or isopropyl.

[0261] In some embodiments, L 11 is methylene.

[0262] In some embodiments, p2 is 0.

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

[0264] Non - restrictively, in a lithium - ion secondary battery, the mass ratio of Compound IIa in the alkaline alkyne additive can be 80% - 100%, optionally 90% - 100%, and can also be any of the following percentages or a range composed of 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 the alkaline alkyne additive within the aforementioned lower range, the alkaline alkyne additive can have a smaller molecular size, which is beneficial to better control the low - viscosity characteristics of the electrolyte, make the electrolyte have a higher conductivity, and better control the internal resistance of the battery.

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

[0267] By controlling the number of Lewis base nitrogen heterocycles in the alkaline alkyne additive within the aforementioned range, it is beneficial to better absorb the acid by-products in the electrolyte, and at the same time, it is also beneficial to control the steric effect of the Lewis base nitrogen heterocycle on the carbon-carbon triple bond.

[0268] Examples of the Lewis base nitrogen heterocycle include the imidazole ring in Compound II.

[0269] By introducing fluorine atom substituents on the Lewis base nitrogen heterocycle (such as the imidazole ring), it is beneficial to induce the formation of inorganic lithium fluoride on the negative electrode, beneficial to improving the stability of the SEI film and reducing the interface impedance, and beneficial to better improving the high-temperature performance of the battery and taking into account the room-temperature performance.

[0270] In some embodiments, the additive in the electrolyte includes cyclic sulfate.

[0271] Non-limitingly, in the lithium-ion secondary battery, the mass percentage of the cyclic sulfate in the electrolyte can be 0-3%, and can be optionally 0.1%-3%.

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

[0273] In some embodiments, the additive includes polycyclic sulfate, and the polycyclic sulfate contains multiple monocyclic sulfate units.

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

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

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

[0277] In some embodiments, the monocyclic ring in the monocyclic sulfate unit is substituted by 0, 1 or more substituent groups Q 3 The substituent group Q in the monocyclic sulfate unit 3 Each independently is a halogen, C 1-3Alkyl or C 1-3 alkoxy group. Optionally, the substituent Q in the monocyclic sulfate unit 3 are each independently a fluorine atom, a methyl group or a methoxy group.

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

[0279] In some embodiments, the additive in the electrolyte includes vinylene sulfate (DTD).

[0280] In some embodiments, the additive in the electrolyte includes vinylene carbonate. 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 formation of alkaline alkyne additives, better control the negative electrode interface impedance and the battery internal resistance, and is beneficial to improving the room temperature performance.

[0281] Non-limitingly, in the lithium-ion secondary battery, the mass percentage of VC in the electrolyte can be 0-5%, further can be 0-3%, can also be 0.1%-3%, can also be any one of the following percentages or a range composed of 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 additive in the electrolyte includes fluorinated carbonate additives.

[0283] Non-limitingly, in the lithium-ion secondary battery, the mass percentage of the fluorinated carbonate additives in the electrolyte can be 0-10%, and can be optionally 0.1%-10%.

[0284] In some embodiments, the fluorinated carbonate additives can include fluoroethylene carbonate (FEC). Non-limitingly, in the lithium-ion secondary battery, the mass percentage of FEC in the electrolyte can be 0-10%, can be optionally 0-5%, can also be 0.1%-10%, and can be further optionally 0.1%-5%.

[0285] Fluoroethylene carbonate (FEC) can form a relatively firm interface film with a lower ion transport impedance on the surface of the negative electrode at room temperature. By introducing fluorinated carbonate additives (such as FEC) into the electrolyte, it is beneficial to reduce or delay the consumption of the negative electrode film formation of alkaline alkyne additives, and better control the negative electrode interface impedance and the battery internal resistance.

[0286] In some embodiments, the electrolyte includes one or both of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. In some of these embodiments, the electrolyte at least includes 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, and can also be any one of the following concentrations or a range composed of 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 act as a film-forming additive in the electrolyte and also play the role of an electrolyte salt. Without limitation, in a lithium-ion secondary battery, 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, and can also be any one of the following concentrations or a range composed of 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, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, etc.

[0289] In some embodiments, the electrolyte includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Without limitation, the molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can be greater than 0 mol / L and less than or equal to 0.5 mol / L, optionally 0.01 mol / L to 0.5 mol / L, and can also be selected from a suitable range or value in any of the embodiments described above.

[0290] Lithium bis(fluorosulfonyl)imide (LiFSI) can participate in the formation of a stable solid electrolyte interface film on both the positive and negative electrodes. On the one hand, by introducing LiFSI into the electrolyte, the stability of the interface films on the positive and negative electrodes can be improved; on the other hand, the ability of LiFSI to dissociate lithium ions is superior to that of lithium hexafluorophosphate (LiPF 6 6), therefore, 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 *-O-C(=O)-O-* structure, and each of the two * independently represents a bonding site to a carbon atom.

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

[0294] In some embodiments, the non-aqueous solvent includes chain carboxylate compounds. Without limitation, in a lithium-ion secondary battery, the mass percentage of the chain carboxylate compound in the non-aqueous solvent can be 0% to 40%.

[0295] In this application, unless otherwise specified, "chain carboxylate" refers to a chain compound having a *-C(=O)-O-* structure, and each of the two * independently represents a bonding site to a carbon atom. The chain carboxylate used in the electrolyte of a lithium-ion secondary battery generally has a low viscosity, which is beneficial to improving the lithium-ion conductivity of the electrolyte.

[0296] In some embodiments, in a lithium-ion secondary battery, the ionic conductivity of the electrolyte at 25 °C is greater than or equal to 8 mS / cm, optionally 8 mS / cm to 20 mS / cm, further optionally 9 mS / cm to 18 mS / cm, and can also be any one of the following conductivities or a range composed of any two of the following conductivities: 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 "ionic conductivity" of the electrolyte has the well-known meaning in the art and can be tested and analyzed by existing methods in the art. The ionic conductivity can be obtained by testing with a conductivity tester, such as a DDSJ-318 conductivity meter. The test temperature can be 25 ± 0.1 °C. The method of HG / T 4067-2015 can be referred to for testing. Unless otherwise specified, the unit of the ionic conductivity of the electrolyte is millisiemens per centimeter (mS / cm).

[0298] In some embodiments, the positive electrode active material includes a lithium-containing phosphate positive electrode material having an olivine structure. Non-limiting examples of the lithium-containing phosphate positive electrode material having an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. An example of lithium iron phosphate is LiFePO 4 . An example of lithium manganese phosphate is LiMnPO 4 .

[0299] Non-limiting examples of the lithium-containing phosphate positive electrode material include iron lithium phosphate-based positive electrode materials.

[0300] In this application, unless otherwise specified, the "iron lithium phosphate-based positive electrode material" refers to a type of positive electrode active material containing iron lithium phosphate components. Unless otherwise specified, the "iron lithium phosphate-based positive electrode material" may have an olivine structure.

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

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

[0303] In some embodiments, the iron lithium phosphate-based positive electrode material includes carbon-coated iron lithium phosphate.

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

[0305] In some embodiments, the lithium iron phosphate-based cathode material includes a lithium iron phosphate-based cathode material. The lithium iron phosphate-based cathode material refers to a type of cathode active material containing lithium iron phosphate components.

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

[0307] In some of these embodiments, the lithium iron phosphate-based cathode material includes carbon-coated lithium iron phosphate. At this time, the carbon-coated lithium iron phosphate includes carbon-coated lithium iron phosphate.

[0308] In the present application, the term "carbon-coated lithium iron phosphate" includes lithium iron phosphate and a carbon coating layer located on at least a part of the surface of lithium iron phosphate. Further, the carbon coating layer in the carbon-coated lithium iron phosphate may include one or more of soft carbon, hard carbon, and amorphous carbon.

[0309] In some embodiments, the lithium ion secondary battery satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable value or range in the context):

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

[0311] (f2) The lithium-containing phosphate-based cathode material includes carbon-coated lithium iron phosphate; non-limitingly, the mass ratio of the carbon-coated lithium iron phosphate in the lithium-containing phosphate-based cathode material can be 80% - 100%, optionally 90% - 100%, and can also be any of the following percentages or a range composed of 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 are some descriptions of the positive electrode tab.

[0313] The positive electrode tab includes a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material.

[0314] Non-limitingly, the weight percentage of the positive electrode active material in the positive electrode active layer can be greater than or equal to 80 wt%, and further can be greater than or equal to 90 wt%.

[0315] In the present application, unless otherwise specified, "wt%" represents weight percentage.

[0316] As a non-limiting example, the positive electrode current collector has two surfaces facing away from each other in its own thickness direction, and the positive electrode active layer is disposed on either or both of the two surfaces of the positive electrode current collector facing away from each other.

[0317] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. 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. In the positive electrode current collector, non-limiting examples of the metal material 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), polyethylene (PE), etc.

[0318] The type of the positive electrode active material in the positive electrode sheet may refer to the description in the context of this application. Non-limitingly, other types of positive electrode active materials may also be introduced into the positive electrode active material, as long as the scheme provided in the first aspect of this application can be used to significantly improve the high-temperature performance of the battery while also taking into account good room-temperature performance.

[0319] It can be understood that during the charge and discharge process of the battery, the insertion and extraction and consumption of lithium (Li) will occur, and the content of Li in the positive electrode sheet is different when the battery is discharged to different states. In the exemplary description of the positive electrode active material in this application, unless otherwise specified, the content of Li may be the initial state of the material or the non-initial state after charge and discharge cycles. When the positive electrode active material is applied to the positive electrode in the battery system, after charge and discharge cycles, the content of Li in the positive electrode active material at the positive electrode usually changes. Among them, the content of Li can be measured by atomic molar content, but is not limited thereto. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before it is made into the positive electrode active layer. It can be understood that the new materials or new substances obtained by appropriately modifying the listed positive electrode active materials are also within the scope of the positive electrode active material. The aforementioned appropriate modification refers to the acceptable modification methods 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 content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the atomic molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by atomic molar content, but is not limited thereto.

[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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. Generally, the weight percentage of the binder in the positive electrode active layer may be 0 to 10 wt%, further may be 0 to 8 wt%, and still further may be 1 wt% to 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. Generally, the weight percentage of the conductive agent in the positive electrode active layer may be 0 to 10 wt%, further may be 0 to 8 wt%, and still further may be 0 to 5 wt%, based on the total weight of the positive electrode active layer.

[0323] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated on at least one surface of the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained. Cold pressing can be carried out using a cold rolling mill. The types of solvents in the positive electrode slurry may include but are not limited to any one of the foregoing embodiments, for example, it may include N-methylpyrrolidone (NMP), and further may be NMP. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on two surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating surface density (calculated based on the single-sided coating surface density) in terms of dry weight (after deducting the solvent) can also be (0.1 to 0.5) g / 1540.25 mm 2 , optionally (0.2 to 0.4) g / 1540.25 mm 2 , but not limited thereto. The tap density of the positive electrode plate can be 2.0 g / cm 3 ~2.8 g / cm 3 , optionally 2.3 g / cm 3 ~2.6 g / cm 3 .

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

[0326] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector, and the negative electrode active layer includes a negative electrode active material.

[0327] Non-limitingly, the weight percentage of the negative electrode active material in the negative electrode active layer can be greater than or equal to 80 wt%, and further can be greater than or equal to 90 wt%.

[0328] As a non-limiting example, the negative electrode current collector has two surfaces facing away from each other in its own thickness direction, and the negative electrode active layer is provided on either or both of the two surfaces of the negative electrode current collector facing away from each other.

[0329] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. In the negative electrode current collector, the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. In the negative electrode current collector, the composite current collector can be formed by forming a metal material on the polymer material base layer. In the negative electrode current collector, non-limiting examples of the metal material can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. Non-limitingly, in the negative electrode current collector, the polymer material base layer can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0330] In some embodiments, the negative electrode active material can be a negative electrode active material well-known in the art for batteries. As a non-limiting example, the negative electrode active material can 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. The silicon-based materials can include one or more of elemental silicon, silicon oxide materials, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon alloys. The tin-based materials can include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials or substances, and other traditional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0331] In some embodiments, the negative electrode active layer optionally includes a binder. Non-limiting examples of 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%, further may be 0 wt% to 10 wt%, still further may be 0 to 5 wt%, still further may be 1 wt% to 5 wt%, and still further may be optionally 1 wt% to 3 wt%.

[0332] The types of the negative electrode active material can also be referred to in the context of this application.

[0333] In some embodiments, the negative electrode active layer optionally includes a conductive agent. Non-limiting examples of 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%, further may be optionally 0 wt% to 10 wt%, and still further may be optionally 0 wt% to 5 wt%.

[0334] In some embodiments, the negative electrode active layer optionally includes other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na), etc.). Non-limitingly, the weight percentage of the other additives in the negative electrode active layer may be 0 wt% to 15 wt%, further may be optionally 0 wt% to 10 wt%, still further may be optionally 0 wt% to 5 wt%, still further may be optionally 0 wt% to 3 wt%, and still further may be optionally 0 wt% to 2 wt%.

[0335] In some embodiments, the negative electrode sheet can be prepared by the following method: dispersing the above components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other optional components, in a solvent (non-limiting examples of the solvent such as deionized water) to form a negative electrode slurry. Further, the negative electrode slurry is coated on at least one surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained. Cold pressing can be carried out 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 two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30 wt% to 70 wt%, and can be optionally 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, and can be optionally 3000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, based on the dry weight (after deducting the solvent), the coating areal density on one side of the negative electrode current collector can be 7.5 mg / cm2 ~22 mg / cm 2 , optionally (0.12 - 0.2) g / 1540.25 mm 2 . The compaction density of the negative electrode sheet can be 1.0 g / cm 3 ~2.0 g / cm 3 , optionally 1.0 g / cm 3 ~1.8 g / cm 3 .

[0336] The following is an exemplary description of the electrolyte.

[0337] The electrolyte solution functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The electrolyte solution includes an electrolyte salt and a solvent.

[0338] In some embodiments, the electrolyte solution is a non-aqueous electrolyte. The 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 solution can generally be 0.5 mol / L - 5 mol / L, optionally 0.5 mol / L - 2 mol / L, further optionally 0.6 mol / L - 1.8 mol / L, and still further optionally 0.7 mol / L - 1.2 mol / L.

[0340] In some embodiments, the electrolyte salt includes an electrolyte lithium salt, and further can be an electrolyte lithium salt. Without limitation, other types of electrolyte salts can also be introduced into the electrolyte solution.

[0341] In some embodiments, the electrolyte salt includes an electrolyte lithium salt. Without limitation, the electrolyte lithium salt can include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP), or one or more of them.

[0342] Non - restrictively, the non - aqueous solvents in the electrolyte can include one or more of carbonate solvents, carboxylate solvents, and sulfone solvents. The carbonate solvents can include one or more of cyclic carbonates and linear carbonates. The cyclic carbonates can include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), etc. The linear carbonates can 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), ethyl propyl carbonate (EPC), etc. Non - restrictively, the number of carbon atoms in the linear carbonates can be 3 - 9, optionally 3 - 7, and can also be 3, 4, 5, 6, 7, 8, or 9, or selected from the range formed by any two of the foregoing numerical values. The carboxylate solvents can include one or more of linear carboxylates and cyclic lactones. The linear carboxylates can include, but are not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, etc. Non - restrictively, the number of carbon atoms in the linear carboxylates can be 2 - 8, optionally 3 - 8, and can also be 2, 3, 4, 5, 6, 7, or 8, or selected from the range formed by any two of the foregoing numerical values. The cyclic lactones can include, but are not limited to, 1,4 - butyrolactone. The sulfone solvents can include, but are not limited to, one or more of sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, etc.

[0343] The electrolyte includes additives, and the additives at least include alkaline alkyne additives. The types and contents of the additives can also refer to the descriptions in the context. Non - restrictively, other types of additives can also be introduced into the electrolyte. Other types of additives can include negative electrode film - forming additives, positive electrode film - forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the over - charge performance of the battery, additives for improving the high - temperature or low - temperature performance of the battery, etc.

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

[0345] In some embodiments, the lithium - ion secondary battery further includes a separator. The present application has no particular limitation on the type of the separator, and any well - known porous - structure separator with good chemical stability and mechanical stability can be selected.

[0346] In some embodiments, the material of the separator can include one or more of glass fiber, non - woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single - layer film or a multi - layer composite film, without particular limitation. When the separator is a multi - layer composite film, the materials of each layer can be the same or different, without particular limitation.

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

[0348] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0349] In some embodiments, the lithium-ion secondary battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0350] In some embodiments, the outer package of the lithium-ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the lithium-ion secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. Further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. Non-limitingly, the outer package can be a composite packaging material, such as an aluminum-plastic bag (the aluminum-plastic bag includes both aluminum foil and plastic).

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

[0352] The present application has no particular limitation on the shape of the battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0353] In some of these embodiments, referring to Figure 2 , the outer package may include a battery case 51 and a cover plate 53. Among them, the battery case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The battery case 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrode assembly 52 is immersed in the electrolyte. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs. In some embodiments, the injection coefficient of the electrolyte 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 included in the battery device can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery device.

[0356] Figure 3The battery device 4 is taken as an example. Refer to Figure 3 In the battery device 4, a plurality of battery cells 5 may be arranged in sequence along the length direction of the battery device 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0357] Optionally, the battery device 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0358] In some of the embodiments, the above battery device may also be assembled into a battery pack. The number of battery devices included in the battery pack may be one or more, and those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0359] Figure 4 and Figure 5 The battery pack 1 is taken as an example. Refer to Figure 4 and Figure 5 In the battery pack 1, a battery box and a plurality of battery devices 4 arranged in the battery box may be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery device 4. The plurality of battery devices 4 may be arranged in the battery box in any manner.

[0360] In the second aspect of the present application, a method for preparing a lithium-ion secondary battery is provided, which can be used to prepare the lithium-ion secondary battery in the first aspect of the present application.

[0361] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps: allowing an electrode assembly including a positive electrode plate, a separator, and a negative electrode plate to stand and soak in an electrolyte, and forming to obtain a lithium-ion secondary battery. It can be understood that after forming, other steps for preparing the lithium-ion secondary battery may also be included, such as aging, etc.

[0362] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps: allowing an electrode assembly including a positive electrode plate, a separator, and a negative electrode plate to stand and soak in a first electrolyte, forming, and supplementing a second electrolyte to obtain a lithium-ion secondary battery. It can be understood that after supplementing the second electrolyte, other steps for preparing the lithium-ion secondary battery may also be included, such as aging, etc.

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

[0364] S100: Placing an electrode assembly including a positive electrode plate, a separator, and a negative electrode plate in a battery housing; wherein, a separator is provided between the positive electrode plate and the negative electrode plate;

[0365] S200: Inject a first electrolyte solution into the battery housing, let it stand still to allow the first electrolyte solution to soak the positive electrode plate and the negative electrode plate, and then perform formation; wherein, the first electrolyte solution includes an electrolyte salt, a non-aqueous solvent, and an additive; the additive includes an alkaline alkyne additive, and the alkaline alkyne additive contains a Lewis base nitrogen heterocycle.

[0366] In some embodiments, after formation, it is also optionally possible to supplement and inject a second electrolyte solution including an alkaline alkyne additive into the battery housing.

[0367] The definitions of the positive electrode plate and the additive can be referred to in the context of this application.

[0368] Step S220 after formation: "After formation, it is also optionally possible to supplement and inject a second electrolyte solution including an alkaline alkyne additive into the battery housing" can be carried out or not. It can be determined according to the target amount of the alkaline alkyne additive in the prepared lithium-ion secondary battery.

[0369] In some embodiments, the positive electrode plate includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; the positive electrode active material includes a lithium-containing phosphate-based positive electrode material, and the average particle size of the primary particles in the lithium-containing 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] Non-limitingly, the formation temperature can be 45 °C, but is not limited thereto.

[0372] In some embodiments, the formation can be carried out at 45 °C by a method including the following steps (steps S1, S2, and S3 are carried out in sequence):

[0373] S1) Charge at 0.05C to 6% SOC, and let it stand still for 5 min;

[0374] S2) Charge at 0.1C to 20% SOC, and let it stand still for 5 min;

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

[0376] End the formation.

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

[0378] Those skilled in the art are aware that after formation treatment, the contents of some additive components in the electrolyte may change. As a non-limiting example, for some film-forming additive components, their contents decrease because they participate in the formation of the solid electrolyte interface film on the positive electrode and / or the negative electrode. As a non-limiting example, compared with the electrolyte before formation treatment, the content of alkaline alkyne additives in the electrolyte usually decreases after formation treatment.

[0379] The electrolyte injected before formation can be denoted as the first electrolyte; when the electrolyte is supplemented and injected after formation, the electrolyte supplemented and injected after formation can be denoted as the second electrolyte. In this application, the "first" and "second" in the "first electrolyte" and "second electrolyte" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0380] In some embodiments, in the step of injecting the electrolyte (denoted as the first electrolyte) into the battery housing, the mass percentage of the alkaline alkyne additive in the first electrolyte can be 0 to 3%, optionally 0 to 2.5%, further optionally 0 to 2%, still further optionally 0.1% to 2%, still further optionally 0.1% to 1.5%, still further optionally 0.1% to 1%, and can also be any one of the following percentages or a range composed of any two of the following percentages: 0.1%, 0.12%, 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, optionally, a second electrolyte containing alkaline alkyne additives can be supplemented and injected into the battery housing to adjust the mass percentage of the alkaline alkyne additive in the electrolyte to the desired concentration. For example, in the prepared lithium-ion secondary battery, the mass percentage of the alkaline alkyne additive in the electrolyte can be, but is not limited to, 0.01% to 3.5%, 0.1% to 3.5%, 0.2% to 3.5%, etc.

[0381] By controlling the mass percentage of the alkaline alkyne additive in the first electrolyte within the aforementioned range, the consumption of the alkaline alkyne additive for forming a film on the negative electrode during the formation stage can be controlled, which is beneficial to reducing the initial interfacial impedance of the negative electrode. Further, the mass percentage of the alkaline alkyne additive in the first electrolyte can be controlled to be greater than 0. At this time, the initial interfacial impedance of the negative electrode can be well controlled, and the initial stability of the solid electrolyte interface (SEI) film of the negative electrode can be significantly improved. Based on the aforementioned multiple effects, but not limited to the aforementioned theory, it is beneficial to better improve the room temperature performance and extend the room temperature cycle life and / or room temperature storage life.

[0382] In some embodiments, a second electrolyte containing an alkaline alkyne additive is supplemented and injected after formation.

[0383] In other embodiments, a second electrolyte containing an alkaline alkyne additive is not supplemented and injected after formation.

[0384] It can be understood that after formation or after supplementing and injecting the second electrolyte, before preparing the lithium-ion secondary battery, other steps can also be included, such as aging. In some non-limiting examples, aging is carried out at 45 °C for 48 h, but not limited thereto.

[0385] The alkaline alkyne additive involved in this application can be obtained commercially or synthesized by existing methods in the field of organic chemical synthesis. When the chemical structure of the alkaline alkyne additive is selected, those skilled in the art can select a suitable organic synthesis method to prepare the target compound; further, those skilled in the art can also identify the structure of the prepared alkaline alkyne additive by one or more of the following detection methods including but not limited to: nuclear magnetic resonance hydrogen spectrum ( 1 1H NMR) method, high performance liquid chromatography (HPLC) method, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MADI-TOF) method, Fourier transform infrared spectroscopy (FT-IR) method, etc.

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

[0387] Regarding the carbon coating layer in the positive electrode active material and the negative electrode active material, exemplarily, the carbon coating layer can include one or more of soft carbon, hard carbon, and amorphous carbon. Those skilled in the art can achieve carbon coating on the surfaces of the positive electrode active material and the negative electrode active material by using existing carbon coating methods in the art.

[0388] Taking the example of setting a carbon coating layer on the surface of the positive electrode active material, those skilled in the art can use existing methods in the art (such as the coprecipitation method, etc.) to obtain the precursor of the positive electrode active body, mix the precursor of the positive electrode active body with a carbon source, and then form the positive electrode active body through sintering treatment to achieve surface carbon coating. The graphitization degree of the carbon coating layer can be regulated by adjusting one or more of parameters such as the sintering temperature and the sintering time. Non-limiting examples of the positive electrode active body include lithium iron phosphate. Non-limiting examples of the carbon source include organic substances such as glucose. Non-limiting examples of the sintering temperature include 550°C to 900°C.

[0389] Taking the example of carbon coating on the surface of a lithium-containing phosphate positive electrode material (such as lithium iron phosphate), without limitation, the sol-gel method can be used for carbon coating; the carbon source can be an organic substance, and non-limiting examples of the organic substance can include one or more of glucose, sucrose, organic resin, etc. Without limitation, the temperature for carbonization treatment can be 550°C to 900°C, optionally 600°C to 800°C, and a metal catalyst (such as an Fe, Ni, or Co type catalyst) can also be optionally added to catalyze graphitization. Soluble salts of metals (such as nitrates, chlorides, etc.) can be added in the sol-gel method to generate corresponding metal nanoparticles during carbonization to achieve catalytic graphitization. Without limitation, the graphitization degree of the carbon coating layer can be adjusted by means such as adjusting the carbonization temperature, the carbonization time, and selectively adding a metal catalyst.

[0390] In addition, other methods known in the art can also be used to regulate the graphitization degree of the carbon coating layer on the surface of the positive electrode active material. For example, a higher graphitization degree can be achieved by using methods such as chemical vapor deposition and high-temperature instantaneous annealing, but not limited thereto.

[0391] When carbon coating is carried out on the surface of the negative electrode active body to prepare a coated negative electrode material, the carbon source can be pitch, phenolic resin, etc., but not limited thereto. In some embodiments, taking the example of using pitch for amorphous carbon coating: pitch (the softening point of pitch is such as 70°C to 150°C) is carbonized at 400°C to 700°C for 1 h to 3 h. The heating rate for carbonization treatment can be 1°C / min to 3°C / min.

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

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

[0394] The electrical device including the aforementioned lithium-ion secondary battery can have the advantageous effects of the aforementioned lithium-ion secondary battery.

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

[0396] The lithium-ion secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto. Among them, the mobile device can be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle can be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, an electric motorcycle, an electric tool, etc., but is not limited thereto. The electrical device can also be applied to fields such as aerospace, and can also be applied to energy storage power systems such as hydraulic, thermal, wind, and solar power stations.

[0397] As the electrical device, the lithium-ion secondary battery can be selected according to its usage requirements.

[0398] Figure 6 Shown as an example is the electrical device 6. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the lithium-ion secondary battery, a battery device or a battery pack can be adopted.

[0399] Shown as another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinning, and a lithium-ion secondary battery can be adopted as the power source.

[0400] Hereinafter, some embodiments of the present application will be described. The described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present application.

[0401] For those not specified in the embodiments in terms of techniques or conditions, they shall be carried out according to the descriptions above, or according to the techniques or conditions described in the literature in the art, or according to the product specifications. For those reagents or instruments not specified in terms of the manufacturer, they are all conventional products that can be obtained through commercial purchase, or can be synthesized from commercially available products in a conventional manner.

[0402] In the following embodiments, room temperature refers to 20 °C to 30 °C.

[0403] In the following examples, unless otherwise specified, the parameters involved can be confirmed with reference to the test methods described in the previous text. For example, regarding the average particle size of the primary particles in the positive electrode active material, after obtaining the particle morphology map of the positive electrode active material by using a scanning electron microscope (such as ZEISS Sigma 300, JEOL scanning electron microscope, Axia ChemiSEM scanning electron microscope, etc.), statistics can be carried out. Regarding the D v 50 of the positive electrode active material, it can be tested by using a Malvern 2000 (MasterSizer2000) laser particle size analyzer. Regarding the specific surface area of the positive electrode active material, it can be tested by using the nitrogen adsorption specific surface area analysis test method. The nitrogen adsorption specific surface area analysis test is carried out by using a Tri StarII type specific surface area and pore analyzer of Micromeritics Company in the United States, and the specific surface area is calculated by the BET (Brunauer Emmett Teller) method. Regarding the carbon coating layer, it can be tested and analyzed by using a transmission electron microscope JEM-F200 combined with EDS (Energy Dispersive Spectrometer), and the mass percentage (such as F B ), average thickness (such as D B ), maximum thickness (such as D max ), etc. of the parameters can be determined. Regarding the graphitization degree of the carbon coating layer, it can be tested and calculated by using an X-ray diffractometer. For another example, regarding the test of the ionic conductivity of the electrolyte, a DDSJ-318 conductivity meter is used, and the detection method of HG-T 4067-2015 is referred to. Regarding the various organic components and inorganic components in the prepared lithium-ion secondary battery, they can be tested with reference to relevant standards such as "General Rules for Gas Chromatography of Chemical Reagents GB / T 9722-2023".

[0404] Among them, taking compound IIa ( , 2-propyn-1-yl 1H-imidazole-1-carboxylate) as an example, the structure identification and quantitative analysis can be carried out by the following method:

[0405] In the nuclear magnetic resonance hydrogen spectrum, the H in the methylene group connected to the triple bond can have a characteristic peak near 4.677 ppm; the hydrogen between the two nitrogen atoms in the imidazole ring can have a characteristic peak near 8.095 ppm; calculate the integral area of each characteristic peak, and then compare it with the peak integral area of the internal standard trifluoromethylbenzene, and the content of compound IIa can be quantitatively calculated.

[0406] The mass fraction of the additive in the electrolyte can be detected by nuclear magnetic resonance spectroscopy (NMR). The test steps can be as follows: Add 500 μL of deuterated reagent into a nuclear magnetic tube in a glove box filled with nitrogen, take 100 μL of non-aqueous electrolyte sample and add it into the nuclear magnetic tube, shake the nuclear magnetic tube to dissolve the non-aqueous electrolyte into the deuterated reagent, and perform the test using the bench-top nuclear magnetic resonance spectrometer X-Pulse of Oxford Instruments. Since the non-aqueous electrolyte is very sensitive to moisture, the proton NMR test and sample preparation are both carried out in a nitrogen atmosphere (H 2 O content is less than 0.1 ppm, O 2 content is less than 0.1 ppm), and at the same time, the instruments related to the test also need to be washed with pure water in advance and dried in a vacuum environment at 60 °C for more than 48 hours. Among them, the deuterated reagent is prepared according to the following steps: Dry deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene with 4A molecular sieves at a temperature above 25 °C for more than 3 days to make the water content of all reagents less than 3 ppm. The moisture test instrument can be the 831 KF type coulometric moisture tester of Metrohm Ltd., Switzerland. Then, in a glove box filled with nitrogen, take 10 mL of the dried DMSO-d 6 and 300 μL of the dried internal standard trifluoromethylbenzene and mix them evenly to obtain the first solution. Take 10 mL of the dried deuterated acetonitrile and 300 μL of the dried internal standard trifluoromethylbenzene and mix them evenly to obtain the second solution. Mix the first solution and the second solution evenly to obtain the deuterated reagent.

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

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

[0409] In the following examples, regarding carbon-coated lithium iron phosphate, carbon coating can be carried out under the following conditions: Mix the lithium iron phosphate precursor prepared by the co-precipitation method with the carbon source glucose, and perform sintering heat treatment at 550 °C to 900 °C to form lithium iron phosphate (the positive electrode active body) and the carbon coating covering the surface of lithium iron phosphate, and obtain carbon-coated lithium iron phosphate. The graphitization degree of the carbon coating layer can be regulated by adjusting one or more of the parameters such as the sintering temperature and sintering time. Those skilled in the art can also combine or adopt other known carbon coating methods (such as chemical vapor deposition method, high-temperature instantaneous annealing method, etc., one or more of these methods) to achieve a relatively high graphitization degree, such as about 90%. For example, adopting the primary particle average diameter and D of the positive electrode active material in Example 1 vA cathode active body with a particle size D50 similar to that of Comparative Example 50 was used, and the graphitization degree of the carbon coating layer in the carbon-coated lithium iron phosphate was adjusted to 88%. A lithium ion secondary battery was also prepared by substantially the same method as in Example 1. At this time, it was also possible to significantly improve the high-temperature performance of the battery while achieving good room-temperature performance.

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

[0411] The D50 of the cathode active material used in the following Examples 1-14 v was in the range of 1 μm to 5 μm. Exemplarily, the D50 of the cathode active material in Example 1 v was about 3 μm.

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

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

[0414] I. Preparation of Lithium Ion Secondary Battery

[0415] Example 1.

[0416] (1) Positive electrode sheet:

[0417] The cathode active material (carbon-coated lithium iron phosphate), the conductive agent carbon black (Super P), and the 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 surfaces of the positive electrode current collector aluminum foil, and the coating surface density on one side was 0.35 g / 1540.25 mm 2 , dried and cold-pressed to prepare a positive electrode sheet. After cold pressing, the compaction density of the positive electrode sheet was about 2.5 g / cm 3 .

[0418] The average particle size (D1) of the primary particles in the positive electrode active material is about 250 nm (251 nm), and the specific surface area (BET 1 ) is 9.6 m 2 / g.

[0419] (2) Negative electrode sheet:

[0420] Mix 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) in deionized water as the solvent in a mass ratio of 96.4:0.7:1.8:1.1, and the solid content is 50 wt% to obtain a negative electrode slurry; coat the negative electrode slurry on both sides of the negative electrode current collector copper foil, and the coating surface density on one side is 0.16 g / 1540.25 mm 2 , and the negative electrode sheet is prepared by drying and cold pressing. The compaction density of the negative electrode sheet is 1.6 g / cm 3 .

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

[0422] (3) Separator: A polypropylene film is used as the separator.

[0423] (4) Electrolyte:

[0424] Add additives to the non-aqueous solvent, mix evenly, then add the fully dried electrolyte lithium salt, and mix well to make the electrolyte lithium salt fully dissolve, and the first electrolyte and the second electrolyte are respectively prepared. The concentration of the electrolyte lithium salt in the first electrolyte and the second electrolyte is basically the same; the concentration of the additives other than the alkaline alkyne additives in the first electrolyte and the second electrolyte is basically the same; the mass percentage of the alkaline alkyne additive in the first electrolyte is 1.5%, and the mass percentage of the alkaline alkyne additive in the second electrolyte is determined according to the target concentration in the electrolyte of the lithium ion secondary battery prepared in Table 1.

[0425] The electrolyte salt in the electrolyte is the electrolyte lithium salt. Further, the electrolyte lithium salt is lithium hexafluorophosphate (LiPF 6), the concentration of lithium hexafluorophosphate in the first electrolyte and the second electrolyte is 1 mol / L; the non-aqueous solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) with a mass ratio of 30:60:10; the additives are 2-propyn-1-yl 1H-imidazole-1-carboxylate (as a basic alkyne additive) and vinylene carbonate (VC). The structure of the basic alkyne additive is shown in formula (IIa), which is also denoted as compound IIa. The mass percentage of compound IIa in the first electrolyte is 1.5 wt%, and the mass percentage of VC in both the first electrolyte and the second electrolyte is 2%. In the prepared lithium-ion secondary battery, the mass percentage of compound IIa in the electrolyte is 2%.

[0426]

[0427] (5) Preparation of the lithium-ion secondary battery: Stack the positive electrode sheet, separator, and negative electrode sheet in sequence to obtain a bare battery cell (electrode assembly); weld the tabs to the bare battery cell, place the bare battery cell in an aluminum-plastic bag, bake it at 80 °C to remove water, then inject the first electrolyte and seal it. Subsequently, through processes such as standing, hot and cold pressing, formation, supplementary injection of the second electrolyte, aging, shaping, and capacity testing, a lithium-ion secondary battery is obtained.

[0428] The formation includes the following steps carried out in sequence: Charge at 0.05C to 6% SOC and stand for 5 min; charge at 0.1C to 20% SOC and stand for 5 min; charge at 0.2C to 30% SOC; the formation is completed.

[0429] In Examples 2-4, lithium-ion secondary batteries were prepared using substantially the same method as in Example 1, except that: in the step of preparing the positive electrode sheet, the positive active materials used were different, mainly changing at least one parameter among the average particle size (D1) of the primary particles, the graphitization degree (G 1 ) of the carbon coating layer, and the specific surface area (BET 1 ). The relevant parameters of the positive active materials can be referred to in Table 1. The remaining operating steps were the same as in Example 1. In the prepared lithium-ion secondary batteries, the mass percentage of the basic alkyne additive compound IIa in the electrolyte was approximately 2%.

[0430] In Examples 2-3, the average particle size (D1) of the primary particles was mainly changed, which can be referred to in Table 1.

[0431] In Example 4, the graphitization degree (G 1 ) of the carbon coating layer was mainly changed, which can be referred to in Table 1.

[0432] Examples 5 - 12 were prepared in substantially the same manner as Example 1, except that: the types and / or amounts of additives in the electrolyte of the prepared lithium - ion secondary battery were different; Example 5 also omitted the step of supplementary injection of the second electrolyte. The remaining operating steps were the same as those in Example 1.

[0433] In Example 5, the step of supplementary injection of the second electrolyte was omitted, the amount of the alkaline alkyne additive in the first electrolyte was changed, and the injection amount of the first electrolyte was changed to keep the total injection mass of the electrolyte substantially the same as that in Example 1; in the prepared lithium - ion secondary battery, the mass percentage of the alkaline alkyne additive compound IIa in the electrolyte was about 0.4%.

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

[0435] The additives in the electrolyte of the lithium - ion secondary battery prepared in Example 9 were compound IIa, VC, and TMSB (tris(trimethylsilyl) borate); the first electrolyte and the second electrolyte each contained 1.5% by mass of VC and 0.3% by mass of TMSB, and the mass percentage of compound IIa in the electrolyte of the prepared lithium - ion secondary battery was substantially the same as that in Example 1.

[0436] The additives in the electrolyte of the lithium - ion secondary battery prepared in Example 10 were compound IIa, VC, and TDI (toluene diisocyanate); the first electrolyte and the second electrolyte each contained 1.5% by mass of VC and 0.3% by mass of TDI, and the mass percentage of compound IIa in the electrolyte of the prepared lithium - ion secondary battery was substantially the same as that in Example 1.

[0437] The additives in the electrolyte of the lithium - ion secondary battery prepared in Example 11 were compound IIa, VC, and LiDFOB (lithium difluorooxalate borate); the first electrolyte and the second electrolyte each contained 1.5% by mass of VC and 0.5% by mass of LiDFOB, and the mass percentage of compound IIa in the electrolyte of the prepared lithium - ion secondary battery was substantially the same as that in Example 1.

[0438] The additives in the electrolyte of the lithium - ion secondary battery prepared in Example 12 were compound IIa, VC, and TMSP (tris(trimethylsilyl) phosphate); the first electrolyte and the second electrolyte each contained 1.5% by mass of VC and 0.3% by mass of TMSP, and the mass percentage of compound IIa in the electrolyte of the prepared lithium - ion secondary battery was substantially 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 (vinyl sulfite); the first electrolyte and the second electrolyte each contain 1.5% by mass of VC and 1% by mass of DTD, and 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% by mass of VC, 0.3% by mass of TMSP (tris(trimethylsilyl) phosphate), and 2% by mass of FEC, and 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. A lithium-ion secondary battery is prepared by a method substantially the same as that in Example 12, except that: the composition of the electrolyte salt in the first electrolyte and the second electrolyte is different, and both the first electrolyte and the second electrolyte use 0.3 mol / L of LiFSI and 0.7 mol / L of LiPF 6 . The remaining operation steps are basically the same as those in Example 1.

[0442] Example 14. A lithium-ion secondary battery is prepared by a method substantially the same as that in Example 1, except that: in the step of preparing the negative electrode sheet, the negative electrode active material is different, and the remaining operation steps are the same as those in Example 1. In Example 14, the negative electrode active material is a carbon-based material and a silicon-based material with a mass ratio of 94:6, that is, the mass proportion of the silicon-based material in the negative electrode active material is 6%. The carbon-based material is the same as that 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, and the mass ratio of silicon element to carbon element is 1:1.

[0443] Comparative Example 1. A lithium-ion secondary battery is prepared by a method substantially the same as that in Example 1, except that: the composition of the prepared electrolyte is different, the alkaline alkyne additive is omitted in the first electrolyte and the second electrolyte, and the concentrations of the remaining components in the electrolyte in the first electrolyte and the second electrolyte remain unchanged. The remaining operation steps are the same as those in Example 1.

[0444] Comparative Example 2. A lithium-ion secondary battery is prepared by a method substantially the same as that in Example 14, except that: the composition of the prepared electrolyte is different, the alkaline alkyne additive is omitted in the first electrolyte and the second electrolyte, and the concentrations of the remaining components in the electrolyte in the first electrolyte and the second electrolyte remain unchanged. The remaining operation steps are the same as those in Example 14.

[0445] Comparative Example 3. A lithium-ion secondary battery was prepared by substantially the same method as in Example 1, except that: the composition of the prepared electrolyte was different, and the alkaline alkyne additive compound IIa in the first electrolyte and the second electrolyte was replaced by 2-propynyl methylcarboxylate ( ), and the concentrations of the remaining components in the electrolyte remained unchanged in the first electrolyte and the second electrolyte. The remaining operation steps were the same as those in Example 1.

[0446] Comparative Examples 4-5. A lithium-ion secondary battery was prepared by substantially the same method as in Example 1, except that: in the step of preparing the positive electrode sheet, the positive electrode active material was different, and the average particle size (D1) of the primary particles was mainly changed. The remaining operation steps were the same as those in Example 1. In Comparative Example 4 and Comparative Example 5, the specific surface area (BET 1 ) of the positive electrode active material was about 23 m 2 / g and about 5.7 m 2 / g, respectively.

[0447] For the relevant preparation parameters of Examples 1-14 and Comparative Examples 1-5, reference can also be made to Table 1 and Table 2.

[0448] II. Test and analysis methods

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

[0450] The test temperature was 25°C ± 0.5°C. A dry powder sample to be tested was taken, and the initial test value of the water content was recorded as A 1 ppm. The sample to be tested was placed in a humidity environment of 90% RH for 12 h, and the water content of the powder was tested. The water content value after 12 h was recorded as B 2 ppm. Then, the water absorption rate of the sample to be tested was calculated by the following formula: water absorption rate = (B 2 -A 1 ) ppm / 12 h.

[0451] The test method for the water content was as follows: Karl Fischer moisture analyzer, and the test accuracy was ppm (one in a million); the test result of the water content was based on the mass ratio of the powder to be tested.

[0452] For the test results of some examples, reference can be made to Table 1.

[0453] 2. Room temperature cycling performance (25°C)

[0454] At 25°C, the battery to be tested was charged at a constant current of 0.5C to 3.65V, then charged at a constant voltage of 3.65V until the cut-off current was 0.05C, left standing for 10 minutes, and then discharged at a constant current of 0.5C to 2.5V, left standing for 5 minutes. This was one charge-discharge cycle. The discharge capacity at this time was recorded as C 0Repeat this charge-discharge cycle process for the same battery, and record the discharge capacity C of the 1st cycle, 2nd cycle, …, nth cycle. n , where the number of cycles is at least 300 cycles.

[0455] Record the cycle capacity retention rate P300 of the battery after 300 cycles = C 300 / C 0 ×100%.

[0456] The test results can be referred to "Capacity retention rate after 300 cycles at room temperature". The higher the test value, the better the room temperature cycle life.

[0457] 3. Test of initial DC internal resistance (DCR) after room temperature cycling:

[0458] Perform DCR test on the battery after cycle test using the method of "2. Room temperature cycle performance (25 °C) method".

[0459] At 25 °C, charge the battery under test at a constant current of 0.5C to 3.65V, then charge at a constant voltage until the current drops to 0.05C; discharge the battery at a constant current of 0.5C for 30 minutes to adjust the battery to 50% SOC, and record the voltage of the battery at this time as U1; discharge the battery at a constant current of 4C for 30 seconds, with a sampling point every 0.1 second, and record the voltage at the end of discharge as U2. Use the discharge DCR of the battery at 50% SOC to represent the initial DCR of the battery, and the initial DCR of the battery = (U1 - U2) / I, where I is the current value corresponding to 4C.

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

[0461] The initial DCR (DCR 0 ) of the fabricated lithium-ion secondary battery can also be tested using the same method.

[0462] 4. High temperature cycle performance (60 °C)

[0463] At 60 °C, charge the battery under test at a constant current of 1C to 3.65V, then charge at a constant voltage of 3.65V until the current drops to 0.05C, let it stand for 5 min, and then discharge at a constant current of 1C to 2.5 V. This is the first charge / discharge cycle of the battery, and the discharge capacity of this time is recorded as the discharge capacity (C1) of the first cycle of the battery; repeat the above steps for the same battery, the process capacity (Cn) of the battery after the nth cycle, and the capacity retention rate after n cycles = Cn / C1×100%. Record the capacity retention rate when the number of cycles is 600.

[0464] The test results can be referred to "Capacity retention rate after 600 cycles at 60 °C".

[0465] The more the number of cycles, the better the high-temperature cycle life represents.

[0466] III. Test analysis results

[0467] The water absorption rates of the cathode active materials used in Examples 1-14 are all in the range of 50 ppm / h to 85 ppm / h.

[0468] Table 1.

[0469]

[0470] In the process of preparing a lithium-ion secondary battery, the mass percentages of the alkaline alkyne additive, other anode film-forming additives, and electrolyte salts in the electrolyte can be referred to Table 2.

[0471] Table 2.

[0472]

[0473] In the prepared lithium-ion secondary battery, when disassembling the battery cell to test the electrolyte components: in Example 7, the mass ratio of additive B to the alkaline alkyne additive is in the range of 0.1 to 50, and the mass percentage of additive B in the electrolyte is in the range of 0.1% to 1%, and further in the range of 0.1% to 0.3%; in Example 8, the mass ratio of additive C to the alkaline alkyne additive is in the range of 0.02 to 50, and the mass percentage of additive C in the electrolyte is in the range of 0.1% to 1%, and further in the range of 0.1% to 0.3%; in Examples 9-10, the mass ratios of additive D to the alkaline alkyne additive are all in the range of 0.1 to 100, and the mass percentages of additive D in the electrolyte are all in the range of 0.1% to 2%, and further all 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 referred to Table 3.

[0475] The lithium-ion secondary batteries prepared in Examples 1-14 all have good room-temperature performance while having significantly improved high-temperature performance.

[0476] Comparative Example 1 omits the alkaline alkyne additive compared to Example 1, and the high-temperature performance and room-temperature performance of Comparative Example 1 both deteriorate significantly. Similarly, Comparative Example 2 omits the alkaline alkyne additive compared to Example 14, and the high-temperature performance and room-temperature performance of Comparative Example 2 both deteriorate significantly.

[0477] Comparative Example 3 replaces the alkaline alkyne additive in Example 1 with an alkyne additive without a Lewis base-containing nitrogen heterocycle, and the high-temperature performance and room-temperature performance of Comparative Example 3 both deteriorate significantly.

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

[0479] The initial DCR (DCR) of the lithium-ion secondary battery prepared in Comparative Example 4 0 ) is lower than that of Example 1-2. However, the specific surface area of ​​the positive electrode active material in Comparative Example 4 is large, resulting in a large water absorption rate of the positive electrode active material, and the battery DCR after room temperature cycling is significantly higher than that of Example 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] In addition, when VC is omitted from both the first electrolyte and the second electrolyte of Example 1 and Comparative Example 1, Example 1 can still significantly improve the high-temperature performance while also taking into account good room-temperature performance compared to Comparative Example 1.

[0484] The description of each embodiment and example above tends to emphasize the differences between each embodiment and example, and the same or similar parts can be referenced to each other. For the sake of brevity, this article will not repeat them. The technical features of the above-described embodiments and examples can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0485] It should be noted that the present application is not limited to the above-mentioned embodiments and examples. The above-mentioned embodiments and examples are only examples. Within the scope of the technical solution of the present application, the embodiments and examples that have the same structure as the technical idea and play the same effect are all included in the technical scope of the present application. The above-described embodiments and examples only express several embodiments and examples of the present application, and the description is relatively detailed, but it cannot be understood as a limitation on the scope of the patent. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be thought of by a person skilled in the art to the embodiments or examples, and other methods of combining some of the constituent elements in the embodiments or examples are also included in the scope of the present application.

Claims

1. A lithium ion secondary battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein a separator is arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material; the electrolyte comprises an electrolyte salt, a non-aqueous solvent and an additive; The positive electrode active material comprises a lithium-containing phosphate positive electrode material, and the average particle size of primary particles in the positive electrode active material is 100nm-500nm; the additive comprises an alkaline acetylene additive, and the alkaline acetylene additive contains a Lewis base nitrogen heterocycle.

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

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

4. The lithium-ion secondary battery according to claim 1, characterized in that: The lithium-containing phosphate positive electrode material includes a carbon-coated lithium-containing phosphate positive electrode material, and the carbon-coated lithium-containing phosphate positive electrode material includes a lithium-containing phosphate matrix and a carbon coating layer located on at least a portion of the surface of the lithium-containing phosphate matrix.

5. The lithium ion secondary battery according to claim 4, characterized in that: The specific surface area of ​​the positive electrode active material is 5 m 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 5 m 2 / g~15m 2 / g.

7. The lithium ion secondary battery according to claim 4, characterized in that: The carbon-coated lithium-containing phosphate positive electrode material meets one or more of the following characteristics: (a1) the graphitization degree of the carbon coating layer is 28% to 95%; (a2) the mass proportion of the carbon coating layer in the carbon-coated lithium-containing phosphate positive electrode material is 0.5% to 2.5%; (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-containing phosphate positive electrode material meets one or more of the following characteristics: (a1') The graphitization degree of the carbon coating layer is 40% to 90%; (a2') the mass proportion of the carbon coating layer in the carbon-coated lithium-containing phosphate positive electrode material is 0.8% to 2%; (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 1μm~5μm.

10. The lithium ion secondary battery according to claim 9, characterized in that: The positive electrode active material D v 50 is 1.5μm~4μm.

11. The lithium ion secondary battery according to any one of claims 1 to 8, characterized in that: The negative electrode plate comprises a negative electrode active layer, and the negative electrode active layer comprises a negative electrode active material; the negative electrode active material comprises at least one of a carbon-based material and a silicon-based material; The negative electrode plate meets one or more of the following characteristics: (b1) The mass proportion of the silicon-based material in the negative electrode active material is 0-20%; (b2) the silicon-based material comprises a silicon-carbon composite material, wherein the silicon-carbon composite material comprises a porous carbon matrix and elemental silicon located in the pores of the porous carbon matrix; the mass proportion of the silicon-carbon composite material in the silicon-based material is 80% to 100%; (b3) the carbon-based material includes a graphite-based material, and the mass proportion of the graphite-based material in the negative electrode active material is 80% to 100%; (b4) The negative electrode active material includes a coated negative electrode material, wherein the coated negative electrode material includes a negative electrode active body and a carbon coating layer located at at least a portion of the negative electrode active body; the mass proportion 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 mass percentage of the alkaline acetylene additive in the electrolyte is less than or equal to 3.5%.

13. The lithium ion secondary battery according to claim 12, characterized in that: The mass percentage of the alkaline acetylene additive in the electrolyte is 0.01% to 3.5%.

14. The lithium ion secondary battery according to claim 12, characterized in that: The mass percentage of the alkaline acetylene additive in the electrolyte is 0.1% to 2.5%.

15. The lithium ion secondary battery according to any one of claims 1 to 8, characterized in that: The additive includes a negative electrode film-forming additive different from the basic acetylenic additive.

16. The lithium ion secondary battery according to claim 15, characterized in that: The additives further include one or more of additive B, additive C and additive D; Wherein, the additive B is one or more of a silane additive and a siloxane additive; The additive C is one or more of an isocyanate additive and an acid anhydride additive; The additive D is one or more of a lithium salt additive and a phosphate ester additive.

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 the additive B to the alkaline acetylene additive is 0.1-50; (c2) the mass ratio of the additive C to the alkaline acetylene additive is 0.02-50; (c3) The mass ratio of the additive D to the basic acetylene additive is 0.1-100.

18. The lithium ion secondary battery according to claim 16, characterized in that: In the electrolyte, the mass ratio of the additive B, the additive C, the additive D and the 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 acetylene additive meets one or more of the following characteristics: (d1) the molecular weight of the alkaline acetylene additive is less than or equal to 500 Da; (d2) the molecule of the alkaline acetylene additive contains 1 to 4 carbon-carbon triple bonds; (d3) the carbon-carbon triple bond is CH≡C-; (d4) the basic acetylene additive contains 1 to 4 Lewis base nitrogen heterocycles in its molecule; (d5) the Lewis base nitrogen heterocycle includes an imidazole ring; (d6) In the molecule of the alkaline acetylene additive, the carbon-carbon triple bond and the Lewis base nitrogen heterocycle are connected via a linker L1, wherein the linker L1 contains a C covalently bonded to the carbon-carbon triple bond. 1-3 Alkylene or containing a fluorinated C 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 acetylene additive meets 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 alkaline acetylene 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 substituent groups Q2, and the substituent groups Q2 in the substituted imidazole group are each independently C 1-3 an alkyl group, a cyano group or a fluorine atom; (e4) The alkaline acetylene additive is composed of a carbon-carbon triple bond, a C 1-3 Alkylene and -OC(=O)-R 10 Sequentially covalently bonded to form, R 10 It is a Lewis base nitrogen heterocycle.

21. The lithium ion secondary battery according to claim 20, characterized in that: The alkaline acetylene additive includes a compound II having a structure as 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 proportion of the compound II in the alkaline acetylene additive is 80% to 100%.

22. The lithium ion secondary battery according to any one of claims 1 to 8, characterized in that: Meet one or more of the following characteristics: (f1) The mass proportion of the lithium phosphate positive electrode material in the positive electrode active material is 80% to 100%; (f2) The lithium-phosphate-containing positive electrode material comprises a carbon-coated lithium iron phosphate material, and the mass proportion of the carbon-coated lithium iron phosphate in the lithium-phosphate-containing positive electrode material is 80% to 100%.

23. A method for preparing a lithium ion secondary battery, characterized in that: The steps include: Placing an electrode assembly including a positive electrode sheet, a separator and a negative electrode sheet in a battery housing, so that the separator is disposed between the positive electrode sheet and the negative electrode sheet; wherein the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material; the positive electrode active material includes a lithium-containing phosphate positive electrode material, and the average particle size of primary particles in the lithium-containing phosphate positive electrode material is 100nm~500nm; A first electrolyte is injected into the battery housing, and the first electrolyte is allowed to soak the positive electrode sheet and the negative electrode sheet to form a battery; wherein the first electrolyte comprises an electrolyte salt, a non-aqueous solvent and an additive; the additive comprises an alkaline acetylene additive, and the alkaline acetylene additive contains a Lewis base nitrogen heterocycle.

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 acetylene additive is additionally injected into the battery housing.

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

26. An electrical device, characterized in that: A lithium ion secondary battery comprising any one of claims 1 to 22.

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