Lithium ion battery

Abstract

The invention discloses a lithium ion battery. The lithium ion battery comprises a positive pole piece and an electrolyte, the positive pole piece comprises a carbon-coated positive active material, the electrolyte comprises an additive, and the additive comprises vinylene carbonate; the lithium ion battery meets the relational expression that 0.15 < = C * theta / S < = 0.48, C is the mass percentage content of carbon coated by the carbon-coated positive electrode active material, and the unit is%; theta is the mass percentage content of vinylene carbonate, and the unit is%; s is the specific surface area of the carbon-coated positive electrode active material, and the unit is m < 2 > / g. When the lithium ion battery meets the relational expression, the cycle performance of the lithium ion battery can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a lithium ion battery and a secondary battery. Background Art

[0002] For consumers, long cycle performance is one of the key indicators to measure the quality of lithium-ion batteries. It is directly related to the service life and reliability of the battery. Lithium-ion batteries with long cycle life mean less replacement frequency and lower cost of use. In electric vehicles and large-scale energy storage systems, long cycle performance is even more important, which ensures the stability and economy of energy supply. With the advancement of technology, battery manufacturers are constantly improving the long cycle performance of batteries through innovative materials and optimized designs to meet the market demand for efficient and long-lasting energy storage solutions. Therefore, choosing a lithium-ion battery with excellent long cycle performance is choosing a sustainable future.

[0003] The long cycle performance of lithium-ion batteries can be improved through a variety of technological innovations. For example, the conductivity of the positive electrode active material lithium iron phosphate itself is poor, but it can be carbon-coated. The appropriate amount of carbon coating helps to improve the conductivity of the electrode material and increase the cycle life of the battery. At the same time, a certain amount of electrolyte additives can be added to the electrolyte. During the first charging process of the lithium-ion battery, the electrolyte additives help to generate products that are deposited on the surface of the negative electrode to form a passivation layer (SEI film). The SEI film can effectively inhibit the side reactions between the negative electrode and the electrolyte, thereby improving the cycle stability of the lithium battery. Therefore, it is necessary to fully understand these influencing factors and rationally optimize the battery parameters to effectively improve the battery cycle performance and extend the battery life. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art to a certain extent. To this end, the present invention provides a lithium ion battery having excellent cycle performance.

[0005] Therefore, in the first aspect of the present invention, the present invention proposes a lithium ion battery, the lithium ion battery comprises a positive electrode plate and an electrolyte; the positive electrode plate comprises a carbon-coated positive electrode active material, the electrolyte comprises an additive, and the additive comprises vinyl carbonate; the lithium ion battery satisfies the relationship: 0.15≤C×θ / S≤0.48, wherein C is the mass percentage of carbon coated by the carbon-coated positive electrode active material, in %; θ is the mass percentage of vinyl carbonate, in %; S is the specific surface area of ​​the carbon-coated positive electrode active material, in m 2 / g.

[0006] Therefore, the lithium ion battery of the present invention has excellent cycle performance.

[0007] In some embodiments, the mass percentage θ of vinylene carbonate is 2-4%.

[0008] In some embodiments, the mass percentage C of carbon coated by the carbon-coated positive electrode active material is 0.8-2.5%.

[0009] In some embodiments, the specific surface area S of the carbon-coated positive electrode active material is 9 to 14 m 2 / g.

[0010] In some embodiments, the positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0011] In some embodiments, the positive electrode plate further includes a positive electrode current collector, a conductive agent, and a binder; the mass percentage of carbon-coated positive electrode active material: conductive agent: binder is (94-97.5): (0.5-3): (1-3).

[0012] In some embodiments, the electrolyte further comprises a solvent and a lithium salt, and the electrolyte satisfies at least one of the following:

[0013] (1) The solvent includes at least two of cyclic carbonate, chain carbonate, and carboxylic acid ester;

[0014] (2) Lithium salts including fluorine-containing lithium salts;

[0015] (3) The additive includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfonic acid, methylene disulfonate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, and vinyl fluorosulfate.

[0016] In some embodiments, the lithium-ion battery further includes a negative electrode sheet and a separator.

[0017] In some embodiments, the negative electrode plate includes a negative electrode current collector, a negative electrode active material, a conductive agent, a binder, and a thickener; the mass percentage of the negative electrode active material: conductive agent: thickener: binder is (94-97): (0.5-3): (1-3): (1-3).

[0018] In a second aspect of the present invention, the present invention provides a secondary battery, comprising the lithium ion battery of the first aspect.

[0019] Therefore, the secondary battery of the present invention has excellent cycle performance.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The present invention controls the physical properties of the positive electrode material and the design parameters of the battery cell in the lithium ion battery to meet the following conditions: 0.15≤C×θ / S≤0.48, wherein C is the mass percentage of carbon coated by the carbon-coated positive electrode active material, in units of %; θ is the mass percentage of vinyl carbonate, in units of %; S is the specific surface area of ​​the carbon-coated positive electrode active material, in units of m 2 / g. Thereby improving the high temperature storage capacity and battery cycle performance of lithium-ion batteries.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0024] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0025] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0026] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0027] In a first aspect of an embodiment of the present invention, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode plate and an electrolyte; the positive electrode plate comprises a carbon-coated positive electrode active material, the electrolyte comprises an additive, and the additive comprises vinyl carbonate; the lithium-ion battery satisfies the relationship: 0.15≤C×θ / S≤0.48, wherein C is the mass percentage of carbon coated by the carbon-coated positive electrode active material, in %; θ is the mass percentage of vinyl carbonate, in %; S is the specific surface area of ​​the carbon-coated positive electrode active material, in m 2 / g.

[0028] During the battery charging and discharging process, the polarization phenomenon on the electrode surface will cause the battery capacity to be lost, and the carbon material has a high conductivity. Therefore, by carbon coating the positive electrode active material, a continuous conductive network is formed on the surface of the positive electrode active material. Even if the volume of the material changes during the battery charging and discharging process, this network can maintain the integrity of the structure and maintain a good electron transmission channel. At the same time, the carbon layer can act as a protective layer to reduce the side reactions between the positive electrode active material and the electrolyte, extend the service life of the electrode material, and improve the cycle stability of the battery. Therefore, the mass percentage of the carbon coated by the carbon-coated positive electrode active material and the specific surface area of ​​the carbon-coated positive electrode active material have an important influence on the battery cycle performance.

[0029] In addition, by adding a certain amount of vinylene carbonate (VC) to the electrolyte, during the first charging process of the lithium-ion battery, the negative electrode film-forming additive will undergo reduction and decomposition before the electrolyte solvent, and the generated product will be deposited on the negative electrode surface to form a passivation layer (SEI film). The SEI film only allows lithium ions to pass through, which can not only effectively inhibit the solvated lithium ions from being inserted into the graphite interlayer, thereby preventing the peeling of graphite, but also effectively inhibit the side reactions between the negative electrode and the electrolyte, thereby improving the cycle stability of the lithium battery.

[0030] Therefore, the present invention comprehensively designs the mass percentage of carbon coated by the carbon-coated positive electrode active material, the specific surface area of ​​the carbon-coated positive electrode active material, and the mass percentage of vinyl carbonate intrinsic parameters, and reasonably quantifies the correlation between the above parameters. Thus, when the lithium-ion battery satisfies the relationship of 0.15≤C×θ / S≤0.48, the battery cycle performance can be effectively improved.

[0031] In some embodiments of the present invention, the mass percentage θ of vinylene carbonate is 2-4%.

[0032] As an electrolyte additive for lithium-ion batteries, vinylene carbonate (VC) mainly participates in the process of forming a solid electrolyte interface (SEI) on the surface of the negative electrode, thereby improving battery performance and cycle life. The decomposition products of VC mainly include Li2CO3 and unsaturated bicarbonates. These decomposition products help to form a stable SEI film, which can inhibit the further decomposition of the electrolyte and prevent the co-embedding of solvent molecules and lithium ions, which has a positive effect on battery performance. However, the amount of VC added needs to be strictly controlled, because the graphite negative electrode will produce volume expansion during the lithium insertion process, which may cause the SEI film to be destroyed, and the exposed fresh negative electrode will promote the polymerization reaction of residual VC with the free radicals produced by decomposition, which may lead to an increase in battery impedance. Therefore, when the mass percentage θ of the electrolyte additive is 2-4%, excessive polymerization reaction and excessive thickening of the SEI film can be avoided. As a result, the cycle performance of the battery is further improved.

[0033] As examples, θ is 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, etc.

[0034] In some embodiments of the present invention, the mass percentage C of carbon coated in the carbon-coated positive electrode active material is 0.8-2.5%.

[0035] In the present invention, when the mass percentage of carbon coating C is 0.8-2.5%, the electronic conductivity of the positive electrode active material can be significantly improved, and the cycle stability can be enhanced, thereby further improving the cycle performance of the battery.

[0036] As an example, C is 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, etc.

[0037] In some embodiments of the present invention, the specific surface area S of the carbon-coated positive electrode active material is 9 to 14 m 2 / g.

[0038] The amount of carbon coating will also affect the specific surface area of ​​the positive electrode active material, which has an important impact on the battery cycle performance. A larger specific surface area usually means that the active material has more active sites and a shorter lithium ion diffusion path, which helps to improve the charge and discharge rate and reversible capacity of the battery. However, when the specific surface area is too large, it may increase the contact area with the electrolyte, which may lead to more side reactions and electrolyte consumption, thereby affecting the cycle life of the battery. In the present invention, when the specific surface area S of the carbon-coated positive electrode active material is 9 to 14 m 2 / g, the charge and discharge rate, cycle performance and storage performance of the battery can be significantly improved. Thus, the cycle performance of the battery can be further improved.

[0039] As an example, S is 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, etc.

[0040] In some embodiments of the present invention, the positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0041] When lithium iron phosphate and lithium iron manganese phosphate are selected as positive electrode active materials, their electronic conductivity and energy density are low, so they are often treated by modification methods such as carbon coating to further improve their performance.

[0042] In some embodiments of the present invention, the positive electrode plate further includes a positive electrode current collector, a conductive agent, and a binder; the mass percentage of carbon-coated positive electrode active material: conductive agent: binder is (94-97.5): (0.5-3): (1-3).

[0043] As an example, the conductive agent includes at least one of carbon black, graphite, or carbon fiber.

[0044] As an example, the binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyvinyl alcohol, polytetrafluoroethylene, polyolefins, modified SBR rubber, fluorinated rubber, polyurethane, or polymethacrylate.

[0045] In some embodiments of the present invention, the positive electrode current collector includes at least one of aluminum foil, carbon-coated aluminum foil, nickel foil and aluminum-plated polymer film.

[0046] In some embodiments of the present invention, the electrolyte further includes a solvent and a lithium salt, and the electrolyte satisfies at least one of the following:

[0047] (1) The solvent includes at least two of cyclic carbonate, chain carbonate, and carboxylic acid ester;

[0048] (2) Lithium salts including fluorine-containing lithium salts;

[0049] (3) The additive includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfonic acid, methylene disulfonate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(trimethylsilyl)borate, vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, and vinyl fluorosulfate.

[0050] As an example, cyclic carbonates include at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), and bisfluoroethylene carbonate (DFEC); chain carbonates include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC); carboxylates include at least one of methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), and ethyl butyrate (EB).

[0051] As an example, the fluorine-containing lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluoro(trifluoromethanesulfonyl)imide, and lithium difluorophosphate.

[0052] In some embodiments of the present invention, the lithium-ion battery further includes a negative electrode plate and a separator.

[0053] In some embodiments of the present invention, the negative electrode plate includes a negative electrode current collector, a negative electrode active material, a conductive agent, a binder, and a thickener; the mass percentage of the negative electrode active material: conductive agent: thickener: binder is (94-97): (0.5-3): (1-3): (1-3).

[0054] In some embodiments of the present invention, the negative electrode current collector includes at least one of copper foil, carbon-coated copper foil, carbon paper and copper-plated polymer film.

[0055] In some embodiments of the present invention, the negative electrode active material includes at least one of artificial graphite, natural graphite, mesophase carbon balls, soft carbon, and hard carbon.

[0056] In a second aspect of the embodiment of the present invention, the present invention provides a secondary battery, comprising the lithium ion battery of the first aspect. Therefore, the secondary battery of the present invention has excellent cycle performance.

[0057] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0058] Embodiment 1:

[0059] Carbon-coated lithium iron phosphate: carbon black: polyvinylidene fluoride = 96:2:2 is dissolved in N-methylpyrrolidone to prepare a positive electrode slurry, coated on the surface of aluminum foil, and dried and rolled to obtain a positive electrode sheet; artificial graphite negative electrode active material, conductive agent (SP), binder (SDR) and thickener (CMC) are dispersed in water according to a mass ratio of 96%:1%:1.8%:1.2%, coated on the surface of copper foil, and dried and rolled to obtain a negative electrode sheet. The positive electrode sheet, negative electrode sheet, and isolation membrane are prepared into a stacked core by a Z-shaped stacking machine, and then the lithium-ion soft-pack battery is obtained through processes such as pole ear welding, liquid injection, pre-sealing, formation, and capacity division. Among them, the electrolyte additive is vinylene carbonate (VC).

[0060] Test method for carbon coating mass percentage C of lithium iron phosphate: establish a linear fitting relationship y=y1+y2*x between the thermal weight loss rate of carbon-coated lithium iron phosphate and the proportion of coating agent added, and then quantitatively evaluate the coating content according to the thermal weight loss rate of the tested sample, and perform multi-region sampling tests on the material to evaluate the uniformity and consistency of the material. Or use physical indicators such as SEM and BET to characterize the material to detect the content of the carbon coating on the surface of the lithium iron phosphate material.

[0061] The test method for the specific surface area S of carbon-coated lithium iron phosphate is as follows: the surface area is tested in accordance with GB / T13390-2008 “Determination of specific surface area of ​​metal powders by nitrogen adsorption method”.

[0062] The carbon coating mass percentage C of the positive electrode active material lithium iron phosphate powder is 1.3%, and the specific surface area S of the carbon coated lithium iron phosphate is 13g / m 2 , the mass percentage content θ of the electrolyte additive VC is 3.2%.

[0063] Embodiment 2:

[0064] The difference between Example 2 and Example 1: The specific surface area S of the carbon-coated lithium iron phosphate in Example 2 is 9.2 m 2 / g.

[0065] Embodiment 3:

[0066] The difference between Example 3 and Example 1 is that the mass percentage content C of the carbon coating of the lithium iron phosphate in Example 3 is 1.1%.

[0067] Embodiment 4:

[0068] The difference between Example 4 and Example 1 is that the mass percentage content θ of the electrolyte additive VC in Example 4 is 2.4%.

[0069] Embodiment 5:

[0070] The difference between Example 5 and Example 1 is that the mass percentage content θ of the electrolyte additive VC in Example 5 is 4.0%.

[0071] Embodiment 6:

[0072] The difference between Example 6 and Example 1 is that the mass percentage content C of the carbon coating of the lithium iron phosphate in Example 6 is 0.8%, and the mass percentage content θ of the electrolyte additive VC is 2.5%.

[0073] Embodiment 7:

[0074] The difference between Example 7 and Example 1 is that the carbon coating mass percentage C of the lithium iron phosphate in Example 7 is 1.5%, and the specific surface area S of the carbon-coated lithium iron phosphate is 10m 2 / g.

[0075] Comparative Example 1:

[0076] The difference between Comparative Example 1 and Example 1 is that the mass percentage content C of the carbon coating of the lithium iron phosphate in Comparative Example 1 is 0.4%.

[0077] Comparative Example 2:

[0078] The difference between Comparative Example 2 and Example 1 is that the carbon coating mass percentage C of the lithium iron phosphate in Comparative Example 2 is 2.6%, and the specific surface area S of the carbon-coated lithium iron phosphate is 16 g / m 2 .

[0079] Comparative Example 3:

[0080] The difference between Comparative Example 3 and Example 1 is that the mass percentage content θ of the electrolyte additive VC in Comparative Example 3 is 1.0%.

[0081] Battery performance test:

[0082] 1. Battery cycle performance test: The battery cycle performance test is carried out in accordance with GB / T 31484-2015 "Cycle life requirements and test methods for power batteries for electric vehicles", and the capacity retention rate after 400 cycles is taken.

[0083] 2. Battery high temperature storage performance test: According to GB / T 31484-2015 "Storage life requirements and test methods for power batteries for electric vehicles" standard, the battery discharge capacity retention rate stored in an environment of 45C±2℃ for 30 days is tested.

[0084] The battery performance test results of the above embodiments and comparative examples are shown in Table 1.

[0085] Table 1 Battery performance test results of the embodiments and comparative examples

[0086]

[0087] It can be seen from Table 1 that the values ​​of C, S and θ of the embodiment are all within the specified range of the present invention. Compared with the comparative example, the high temperature storage rate and capacity retention rate of the battery of the embodiment are higher than those of the comparative example, indicating that the present invention effectively improves the cycle performance of the battery.

[0088] It can be seen from the comparison between Example 1 and Example 2 that Example 1 increases the specific surface area S, increases the contact area between the carbon-coated lithium iron phosphate active material and the electrolyte, shortens the transmission path of lithium ions, and reduces the electrochemical polarization and concentration polarization resistance, thereby effectively improving the cycle performance of the battery cell. In Example 3, the carbon coating amount of the lithium iron phosphate active material is relatively small, which reduces the contact area with the electrolyte, reduces the occurrence of side reactions and the loss of the electrolyte, thereby improving the cycle capacity of the lithium ion battery. In Example 4, the content of the electrolyte additive VC is reduced, and the negative electrode film-forming effect is slightly reduced, but at the same time, it also reduces the probability of later electrolyte decomposition, thereby improving the storage performance and cycle performance of the battery. In Example 5, the content of the electrolyte additive VC is increased, and the negative electrode film-forming effect is improved, but the excessive thickness of the SEI film will increase the battery impedance, which will have a negative impact on high temperature maintenance and cycle effects. In Example 6, the carbon coating amount of the lithium iron phosphate active material is too small, which reduces the contact area with the electrolyte, reduces the conductivity of the positive electrode, and has a large impedance, which has a negative impact on the battery. However, at the same time, the content of the electrolyte additive VC is reduced, and the negative electrode film-forming effect is slightly reduced, but at the same time, the probability of electrolyte decomposition in the later stage is also reduced, and the battery cycle is slightly improved. In Example 7, the carbon coating amount of the acid lithium iron active material is indicated, which increases the contact area with the electrolyte, improves the conductivity of the positive electrode, and reduces the specific surface area. The side reactions are reduced, and the cycle and capacity retention rate are improved to a certain extent. In Comparative Example 1, due to the small amount of carbon coating of the positive active material lithium iron phosphate, the conductivity of the pole piece is poor, and a continuous conductive network cannot be formed, which makes the electronic impedance of the pole piece too large, which seriously affects the high temperature storage performance and cycle performance of the battery cell. In Comparative Example 2, the carbon coating amount of the positive electrode active material lithium iron phosphate is too high, which also leads to an excessively high specific surface area S, and a significantly increased contact area with the electrolyte, resulting in excessive side reactions in the later stage of the battery, rapid loss of the electrolyte, and thus causing the battery to produce more gas and thicken, affecting the safety performance and cycle performance of the battery cell. In Comparative Example 3, the amount of VC added is too little, resulting in less SEI film formation during the initial charging process, an unstable structure, and easy co-embedding of solvent molecules and lithium ions during the electrochemical reaction, which increases polarization and is not conducive to the cycle performance of the battery cell. Therefore, it is shown that the present invention effectively improves the cycle performance and storage performance of the battery.

[0089] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0090] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode plate and an electrolyte; the positive electrode plate comprises a carbon-coated positive electrode active material, the electrolyte comprises an additive, and the additive comprises vinylene carbonate; the lithium-ion battery satisfies the relationship: 0.15≤C×θ / S≤0.48, Wherein, C is the mass percentage of carbon coated by the carbon-coated positive electrode active material, in %; θ is the mass percentage of vinylene carbonate, in %; S is the specific surface area of ​​the carbon-coated positive electrode active material, in m 2 / g.

2. The lithium-ion battery according to claim 1, characterized in that The mass percentage θ of the vinylene carbonate is 2-4%.

3. The lithium ion battery according to claim 1 or 2, characterized in that: The mass percentage C of the carbon coated in the carbon-coated positive electrode active material is 0.8-2.5%.

4. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The specific surface area S of the carbon-coated positive electrode active material is 9 to 14 m 2 / g.

5. The lithium ion battery according to any one of claims 1 to 4, characterized in that: The positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

6. The lithium ion battery according to any one of claims 1 to 5, characterized in that: The positive electrode plate also includes a positive electrode current collector, a conductive agent, and a binder; the mass percentage of the carbon-coated positive electrode active material: conductive agent: binder is (94-97.5): (0.5-3): (1-3).

7. The lithium ion battery according to any one of claims 1 to 6, characterized in that: The electrolyte further comprises a solvent and a lithium salt, and the electrolyte satisfies at least one of the following: (1) The solvent includes at least two of cyclic carbonate, chain carbonate, and carboxylic acid ester; (2) The lithium salt includes a fluorine-containing lithium salt; (3) The additive also includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfonic acid, methylene disulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, tris(trimethylsilane) borate, vinylene carbonate, vinyl ethylene carbonate, vinyl sulfate, vinyl sulfite, and vinyl fluorosulfate.

8. The lithium ion battery according to any one of claims 1 to 7, characterized in that: The lithium-ion battery also includes a negative electrode plate and a separator.

9. The lithium-ion battery according to claim 8, characterized in that: The negative electrode plate includes a negative electrode current collector, a negative electrode active material, a conductive agent, a binder, and a thickener; the mass percentage of the negative electrode active material: conductive agent: thickener: binder is (94-97): (0.5-3): (1-3): (1-3).

10. A secondary battery, characterized in that: A lithium ion battery comprising any one of claims 1 to 9.

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