Lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a lithium ion battery, in particular to a lithium ion battery considering impedance and rate cycle performance of the battery. The lithium ion battery comprises a positive plate, a negative plate, a diaphragm and a non-aqueous electrolyte, the positive plate comprises a positive electrode material layer containing a positive electrode material; the positive electrode material comprises a nickel-containing material and a phosphate material; the non-aqueous electrolyte comprises an additive, a lithium salt and an organic solvent; the additive comprises a first additive and difluorophosphate ions; the lithium ion battery meets the following conditions: # imgabs0 #, 0.01 < = a < = 0.8, 0.01 < = b < = 1, 0.5 < = c < = 200, 1.2 < = d < = 20. According to the lithium ion battery provided by the invention, a high-stability and high-toughness positive electrode interface film is formed by adjusting a positive electrode active material compounding system and the non-aqueous electrolyte, so that the battery has low impedance and high-rate cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium-ion battery that takes into account the impedance and rate cycling performance of the battery. Background Art

[0002] At present, lithium-ion power batteries are developing towards the direction of low cost, high cost performance, and high safety. Phosphate-based system materials take into account high energy density and high safety, and have become the focus of attention in the industry. However, the inherent problems of phosphate-based system materials, such as low tap density, low theoretical specific capacity, and low conductivity, limit their wide application. Blending nickel-containing materials into the phosphate-based system can make up for the above performance defects. Blending the phosphate-based system with the ternary system has effects such as energy density improvement, tap density increase, and low-temperature performance improvement, taking into account high energy density and high safety. At the same time, compared with the pure ternary system, it reduces the material cost and dependence on rare precious metal elements, and has strong application prospects.

[0003] In the phosphate-based system blended with the ternary system materials, if the nickel-containing materials account for the majority (>50%), phosphate-based materials with smaller particle sizes usually adsorb on the surface of the ternary to form a coating layer due to higher surface energy. The composite materials can achieve the mutual matching of large and small particle sizes between materials, and improve the tap density, volume energy density, cycle performance, conductivity, and electrochemical performance of the cathode material. However, the composite materials put forward higher requirements for the compatible electrolyte, especially for the high-rate cycling performance, which is the mainstream development trend of power batteries. Due to the rapid lithium-ion deintercalation / insertion, it may lead to the separation of the composite materials and deteriorate the overall performance of the battery. Therefore, the electrolyte is required to form a highly stable cathode interface / electrolyte interface film (CEI film) not only on the surface of the phosphate and nickel-containing materials, but also the cathode film formation should have good toughness. At the same time, a large number of studies have confirmed that although the increase in the Ni content in the nickel-containing materials is beneficial to the improvement of the energy density, it inevitably weakens the stability of the cathode structure. The change in the composite particle size due to the different blending ratios of the composite materials will also affect the stability and consistency of the cathode film formation. Therefore, developing a lithium-ion secondary battery electrolyte that has a good film-forming effect in the phosphate-based system blended with the ternary system materials is of great significance for taking into account the battery impedance and excellent rate cycling performance. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a lithium-ion battery that takes into account the impedance and rate cycling performance of the battery, so as to solve the problems of high impedance and poor high-rate cycling performance in the phosphate-based system blended with the ternary system materials in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solutions.

[0006] The present invention provides a lithium-ion battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator, and a non-aqueous electrolyte; The positive electrode sheet includes a positive electrode material layer containing a positive electrode material, and the positive electrode material includes a nickel-containing material and a phosphate material; The non-aqueous electrolyte includes an additive, a lithium salt, and an organic solvent; The additive includes a first additive and difluorophosphate ions; The first additive includes at least one of Compound 1 to Compound 5; ;

[0007] The lithium-ion battery satisfies the following conditions: ; and 0.01 ≤ a ≤ 0.8, 0.01 ≤ b ≤ 1, 0.5 ≤ c ≤ 200, 1.2 ≤ d ≤ 20; a is the mass percentage content of the first additive in the non-aqueous electrolyte, with the unit of %; b is the mass percentage content of difluorophosphate ions in the non-aqueous electrolyte, with the unit of %; c is the molar ratio of Ni and Fe in the positive electrode material layer; d is the D90 / D50 ratio of the positive electrode material.

[0008] For the positive electrode system of power batteries, the nickel-containing material is inferior to the phosphate material in terms of safety, long cycle life, and cost. Therefore, its proportion in the power market has been decreasing year by year. However, the excellent high energy density, rate performance, and low-temperature performance of ternary materials are also advantages that the phosphate system cannot match. In this context, a positive electrode system in which a nickel-containing material is compounded with a phosphate material is expected to have balanced performance without obvious shortcomings. Using a nickel-containing material as the main body and blending with a phosphate material can improve the thermal stability and compaction density of the positive electrode, etc., and reduce the cost of the positive electrode material. However, electrolytes that are simply adapted to the ternary system or the phosphate system cannot fully exert the electrochemical performance of the compounded system.

[0009] First, for the composite of nickel-containing materials and phosphate materials, the types, particle sizes, and blending ratios of the two materials have significant differences in battery performance and electrolyte compatibility. In nickel-containing materials, Ni, as a transition metal, its content is usually the key and most frequently adjusted parameter. High-nickel nickel-containing materials have higher energy density but at the cost of sacrificing structural stability. In phosphate materials, Fe is the most important transition metal element. The well-known lithium iron phosphate cathode is a phosphate material dominated by the Fe element, and the Fe element also plays an important role in improving the conductivity and stability of the emerging lithium iron manganese phosphate material. Therefore, the molar ratio of Ni and Fe in the cathode material layer is an important parameter that can represent the stability of the cathode material and the blending ratio of the composite materials. On the other hand, the D90 / D50 ratio of the cathode material is also a key parameter affecting the composite materials. Since phosphate materials are usually nanonized to reduce the particle size and improve the lithium ion migration rate, the particle size of phosphate materials is generally much lower than that of nickel-containing materials. The composite system dominated by the ternary system takes advantage of this to form a spatial distribution of phosphate materials coating nickel-containing materials, thereby increasing the tap density of the materials, reducing the contact area between nickel-containing materials and the electrolyte, and improving the overall conductivity of the cathode material, ultimately improving the impedance, rate performance, and cycle performance of the battery. D50 mainly reflects the particle size and blending ratio of small-particle-size phosphate materials, and D90 takes into account the particle sizes of both cathode materials. Therefore, D90 / D50 can reflect the particle size gap and distribution of the composite materials. The above parameters of the composite cathode will affect the applicable content and distribution of the additives. Difluorophosphate anions can increase the proportion of the inorganic component LiF in the membrane component and are more suitable for ternary cathodes with large phase changes and volume changes; while the first additive will decompose to form an S-containing organic membrane component and is more suitable for phosphate cathodes with low conductivity and large specific surface area. The combined use of difluorophosphate ions and the first additive will have a synergistic effect, but to fully exert their complementary effects, the compatibility of the cathode materials also needs to be considered.

[0010] Finally, through extensive research, the inventors found that when the first additive and difluorophosphate ions in the non-aqueous electrolyte are used as an additive combination, and the molar ratio of Ni and Fe in the positive electrode material layer and the ratio of D90 / D50 of the positive electrode material satisfy the above range and relationship, low impedance and excellent rate cycling performance can be achieved in the composite system of nickel-containing materials and phosphate materials with different blending ratios. This is because both additives can decompose on the positive electrode of the composite system to form an interface film with high stability and high toughness, and when used simultaneously, they can exert a synergistic effect, which is better in terms of stability and toughness than when they form films separately. In addition, the blending ratio in the composite system, the proportion of different transition metals in the positive electrode material, and the particle size distribution also have a strong correlation with the quality and uniformity of film formation, and have a significant impact on battery performance, which can be represented by the molar ratio of Ni and Fe in the positive electrode material layer and the ratio of D90 / D50 of the positive electrode material. The molar ratio of Ni and Fe is jointly affected by the blending ratio of the composite materials, the doping ratio of Ni content in the nickel-containing materials, and / or the proportion of Fe element in the phosphate materials, and can reflect the structural stability and thermal stability of the composite materials; while the ratio of D90 / D50 is mainly affected by the blending ratio and distribution of the composite materials, the particle size of the phosphate materials, and / or the particle size of the nickel-containing materials, and can represent the lithium-ion transport kinetics, the compatibility of the composite materials, and the particle size complementary effect of the composite materials.

[0011] In the present invention, the film-forming adaptability of the two additives in the nickel-containing material and phosphate material system is different. For example, difluorophosphate ions form a high-LiF inorganic film component, which has a better film-forming protection effect on high-nickel materials; while the first additive forms a sulfur-containing organic film component, which has a better film-forming effect on phosphate materials with a high specific surface area. Therefore, when the two additives are used in combination, the best effect can be achieved when the molar ratio of Ni and Fe in the positive electrode material layer and the ratio of D90 / D50 of the positive electrode material satisfy the above relationship. In summary, by using the two additives to form a film synergistically, a low-impedance, highly stable, and high-toughness positive electrode interface film is formed on a composite material system with good control of performance such as stability and lithium-ion kinetics and a reasonable particle size distribution, ultimately achieving both the impedance and rate cycling performance of the battery. Preferably, the lithium-ion battery satisfies: 。

[0012] In some embodiments of the present invention, the first additive can participate in the formation of a dense and uniform interfacial film on both the positive and negative electrodes of the lithium-ion battery. Moreover, whether in a ternary positive electrode system or a phosphate positive electrode system, it has an excellent improvement effect on the high-temperature cycling performance. When used in combination with difluorophosphate ions, it can further enhance the flexibility of the interfacial film. This is because the decomposition products of the first additive are mostly sulfur-containing organic components. These sulfur-containing organic components, as the main organic film components, act as corresponding high-toughness components in the outer and inner layers of the CEI film together with the LiF component, playing a skeletal role. Thereby, the stability of the film formation of the composite material positive electrode is significantly improved, effectively reducing the dissolution of metal ions and side reactions, thus improving the cycling performance at the battery level and improving the impedance growth situation. If the mass percentage value a% of the first additive is too high, although it is beneficial to form a positive electrode film with high stability and high toughness, the overly thick film formation results in too high impedance, which will not only exacerbate the polarization and heat generation of the battery, but also make the lithium-ion transport kinetics poor in the interfacial film. During rate cycling, the rapid migration of lithium ions is hindered, and lithium deposition is likely to occur, leading to the rapid reaction and consumption of the electrolyte and active lithium. If the mass percentage value a% of the first additive is too low, then it will be difficult to improve the stability and toughness of the positive electrode interfacial film, or it will be difficult to form an organic film component with high stability and high toughness, unable to play a synergistic role with difluorophosphate ions, and thus unable to improve the battery performance deterioration problem caused by the incompatibility of the composite material, ultimately resulting in the impedance growth of the battery and the decline of the high-rate cycling performance. Specifically, the mass percentage a% of the first additive is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.7%, 0.8% or the range composed of any two of these values. Preferably, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.1% - 0.45%.

[0013] In some embodiments of the present invention, the compound containing difluorophosphate ions is selected from at least one of lithium difluorophosphate, sodium difluorophosphate, potassium difluorophosphate, calcium difluorophosphate, and magnesium difluorophosphate. In the non-aqueous electrolyte of the present invention, as the counter ion of the difluorophosphate ion, monovalent cations and divalent cations can be used; preferably, the monovalent cation is preferably lithium ion, and the divalent cation is preferably magnesium ion. Other monovalent or divalent cations are also within the protection scope of the present invention and will not be elaborated here.

[0014] In the non-aqueous electrolyte of the lithium-ion battery of the present invention, the meaning of the mass percentage content of difluorophosphate ions is the same as the concentration of difluorophosphate ions; the present invention does not make special limitations on the measurement method of the mass percentage content of difluorophosphate ions, and the well-known test methods in the art can be used, such as ion chromatography, 19 19F NMR, etc.

[0015] Generally, difluorophosphate ions in the electrolyte will form a LiF film component on the surfaces of the positive and negative electrodes during the battery formation process. LiF not only has good high-temperature stability but also has good toughness. Therefore, it has a good film-forming effect on the ternary system with large changes in crystal structure during the cycling process. For the phosphate material system with stable positive electrodes itself, difluorophosphate ions will not have a deteriorating effect, and can also improve the film breakage problem caused by different volume changes of different materials in the ternary composite phosphate positive electrode system. If the mass percentage content b% value of the difluorophosphate ions is too high, then excessive difluorophosphate ions will precipitate as solids in the form of lithium difluorophosphate from the electrolyte or cannot be completely dissolved and eventually become solid impurities. These impurity foreign matters may cause poor film-forming consistency or battery virtual sealing, resulting in uneven internal stress of the battery and further deteriorating the battery interface performance. In addition, too high a content may cause too many film-forming components generated by the decomposition of LiF or other difluorophosphate ions in the interface film, thereby deteriorating the battery impedance. If the mass percentage content b% value of the difluorophosphate ions is too low, it is difficult to form an interface film with high stability and high toughness on the positive electrode; when the stability and toughness of the interface film are poor, the side reactions on the positive electrode side are difficult to be effectively suppressed, and finally the battery impedance and high-temperature performance cannot be improved. Specifically, the mass percentage content b% of the difluorophosphate ions is 0.01%, 0.03%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or the range composed of any two of these values. Preferably, the mass percentage content b% of the difluorophosphate ions is 0.1% - 0.5%.

[0016] In some embodiments of the present invention, the molar ratio of Ni to Fe in the positive electrode material layer depends on the blending ratio of the nickel-containing material and the phosphate material on the one hand, and on the proportion of Ni element in the nickel-containing material and the proportion of Fe element in the phosphate material on the other hand. If the c value of the molar ratio of Ni to Fe in the positive electrode material layer is too high, it indicates that there is too much Ni element or too little Fe element. Too much Ni element is actually an indication of too high a blending ratio of the nickel-containing material in the composite positive electrode or too high a proportion of Ni element in the nickel-containing material (ultra-high nickel ternary positive electrode). In both cases, the stability of the positive electrode is sacrificed to improve the energy density. At this time, the stability of the composite material positive electrode is mainly affected by the high-nickel nickel-containing material, and the stability of the positive electrode is very poor. Moreover, the blending ratio of the phosphate material is also low and cannot play an improvement role. These factors will deteriorate the electrochemical performance of the battery. Too little Fe element is also an indication of too low a blending ratio of the phosphate material in the composite positive electrode or too low a proportion of Fe element in the phosphate material. The structural stability and thermal stability of the phosphate-based positive electrode are significantly better than those of the ternary system. The reduction of its blending ratio in the composite material will significantly reduce the overall stability of the composite positive electrode. Moreover, too low a proportion of Fe element in the phosphate material will deteriorate the stability of the positive electrode, or reduce its low-cost commercial competitive advantage (doping too many other transition metal elements), or affect its practicality (for example, the charge-discharge platform of lithium nickel phosphate is about 5.2V, exceeding the upper limit of the tolerance voltage of the conventional electrolyte). Therefore, generally speaking, too high a c value usually means a significant decrease in the stability of the composite positive electrode or no commercial value. If the c value of the molar ratio of Ni to Fe in the positive electrode material layer is too low, that is, the blending ratio of the nickel-containing material is not high, and Ni accounts for a relatively low proportion as a transition metal, while Fe is the main transition metal in the phosphate material. At this time, the stability of the composite material positive electrode is excellent and the conductivity is also good, but the energy density of the composite material is too low, which means that the nickel-containing material in the composite system is not the main material and does not have commercial value. Specifically, the molar ratio c of Ni to Fe in the positive electrode material layer is 0.5, 1, 3, 5, 8, 10, 13, 15, 20, 30, 40, 50, 60, 100, 150, 200, 300 or the range composed of any two of these values. Preferably, the molar ratio c of Ni to Fe in the positive electrode material layer is 0.5 to 30.

[0017] In the present invention, D50 represents the particle size corresponding to when the cumulative particle size distribution number of a sample reaches 50%. Its physical meaning is that 50% of the particles have a particle size larger than it and 50% of the particles have a particle size smaller than it. D50 is also called the median particle size or the median diameter and is often used to represent the average particle size of the powder.

[0018] D90 represents the particle size corresponding to when the cumulative particle size distribution number of a sample reaches 90%. Its physical meaning is that 90% of the particles have a particle size larger than it.

[0019] In the present invention, the cathode material refers to all the materials included in the cathode material layer, including the cathode active material, the cathode conductive agent, and the cathode binder. Since the content of the cathode active material in the cathode material layer accounts for the majority, the D90 / D50 ratio of the cathode material actually mainly reflects the D90 / D50 ratio of the cathode active material.

[0020] The D90 / D50 ratio d of the cathode material is directly related to the particle size distribution of the cathode active material. The design of the cathode particle size distribution helps to improve the density and mechanical properties of the cathode sheet, reduce the appearance of pores and defects, and enhance the strength and toughness of the electrode sheet. The cathode particle size distribution can optimize the lithium ion transmission rate to a certain extent. More importantly, it also has a great impact on the film formation uniformity and the film formation component composition. For example, the decomposition and action of the first additive and the difluorophosphate ion on the surface of the cathode active material. When the D90 / D50 ratio d of the cathode material is too small, it means that the particle size difference is small (usually caused by uneven mixing), the gaps between particles are larger and more, the specific surface area of the active material is larger, and more additives are required to form the cathode surface interface film on the surface of the active material particles to form a stable CEI film, which easily leads to problems such as uneven film formation or premature excessive consumption of additives. When the D90 / D50 ratio d of the cathode material is too large, it means that the small particle phosphate material is densely filled in the pore space of the large nickel-containing material particles. Most of the additives form a film on the surface of the high specific energy phosphate material, while the film formation protection of the nickel-containing material particles is poor. At the same time, the large particles and the densely wrapped nickel-containing material cannot exert their higher lithium ion migration ability, which limits the capacity utilization and is not conducive to the improvement of the energy density of the lithium ion battery, nor is it conducive to the improvement of the film formation quality of the cathode surface interface film.

[0021] Normally, the particle size of a single positive electrode active material satisfies a normal distribution. However, for a composite positive electrode containing nickel materials and phosphate materials, it has additional distribution characteristics. This is because the phosphate material particles are much smaller than the nickel-containing materials, so as to improve the deficiency of the lower conductivity of the phosphate materials. Therefore, the D50 of the composite material obtained by statistics is necessarily mainly affected by the blending ratio of the phosphate materials and their particle size distribution, while D90 can take into account the particle size distribution of the nickel-containing materials and almost all of the phosphate material particles. In the ternary composite positive electrode material mainly composed of nickel-containing materials, the phosphate materials will adhere to the surface of the nickel-containing materials in the form of coating. On the one hand, this coating reduces the contact area between the nickel-containing materials with lower stability and the electrolyte. On the other hand, it improves the overall compaction density, conductivity and safety of the positive electrode. The particle size gap and blending ratio between the two materials have a great impact on the electrochemical performance of the battery. The D90 / D50 ratio of the composite material can be used as an indication of the degree of this impact. If the d value of the D90 / D50 ratio of the positive electrode material is too low, it means that the difference between the D90 and D50 values is extremely small. In the composite material, this usually indicates that the two positive electrode materials are not fully and evenly mixed, and thus the spatial structure in which the phosphate materials coat the nickel-containing materials cannot be formed, and the advantages of the composite material cannot be exerted. Moreover, the incompatibility problem between the materials will seriously deteriorate the electrochemical performance. In addition, it may also be that the particle sizes of the two materials are similar. Whether they are both small particle sizes or large particle sizes, they cannot effectively improve the compaction density and conductivity of the positive electrode. Not only that, it will also significantly exacerbate the detachment caused by the incompatibility of the composite materials, or lead to problems such as large differences in film formation. From the perspective of the battery, the specific manifestations are large initial impedance, extremely poor cycling performance, extremely poor rate performance, and extremely obvious impedance growth. If the d value of the D90 / D50 ratio of the positive electrode material is too high, it means that the blending ratio of the phosphate is relatively high and its particle size is small. This makes D50 basically reflect the particle size of the phosphate particles, and the value is very small. At the same time, the particle sizes of the nickel-containing materials are generally large, thus pulling up the value of D90, and finally making the difference between D90 / D50 extremely large, and the particle size gap between the two materials is huge. In this case, the nickel-containing materials with large particles and high coating rate have poor lithium ion migration performance. The large particle nickel-containing materials will further deteriorate the lithium ion migration kinetics, making the composite effect even worse than that of a single positive electrode material. And the small particle and high specific surface area phosphate materials will lead to an increase in side reactions, and thus the high temperature performance of the battery is poor. Moreover, the phosphate materials with high surface energy will preferentially consume the additives and form a film on their surfaces. Such a composite material is not only prone to detachment and incompatibility problems between the materials, but also due to the small and numerous characteristics of the phosphate materials, the specific surface area of the positive electrode is too high, which instead exacerbates the side reactions on the positive electrode side, making the battery impedance increase and the cycling performance deteriorate, and thus affecting the film formation quality of the nickel-containing materials.Finally, the battery has poor electrochemical performance in all aspects and cannot exert the complementary improvement effect of the composite materials. Specifically, the D90 / D50 ratio d of the positive electrode material is 1.2, 1.5, 2, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 14, 15, 16, 17, 18, 19, 20, or the range composed of any two of these values. Preferably, the D90 / D50 ratio d of the positive electrode material is 2 to 12.

[0022] The test methods for D50 and D90 of the positive electrode material of the present invention are as follows: Disassemble the battery, soak and clean the positive electrode sheet with dimethyl carbonate, place it in a glove box and dry it in vacuum for 24 h. Use a small spatula to scrape the powder of the material layer (excluding the current collector), about 2 g to 3 g. After pretreatment, place the sample in the injection chamber of a laser particle size analyzer. After ultrasonic dispersion is sufficient (≥20 min, no significant sedimentation) and the light shielding rate is stable, perform the test.

[0023] Specifically, in some embodiments of the present invention, the nickel-containing material includes a material with the chemical formula Li q Ni x Co y M 1-x-y O 2- g R g or a Li q Ni x Co y M 1-x-y O 2-g R g material with a coating layer provided on its surface. Among them, 0.9 ≤ q ≤ 1.2, 0.5 ≤ x ≤ 0.96, y > 0, 1 - x - y > 0, 0 ≤ g ≤ 1, M includes one or both of Mn and Al, and includes zero, one, or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, Ce, and R includes one or more of N, F, S, and Cl. The nickel-containing material may not contain doping elements or a coating layer, or may be a nickel-containing material modified by doping elements and / or a coating layer. The coating layer is preferably a metal oxide coating layer.

[0024] The phosphate material includes a material with the molecular formula Li r Mn α Fe β A 1-α-β PO 4-n G n or a Li r Mn α Feβ A 1-α-β PO 4-n G n At least one of the materials, where 0.9 ≤ r ≤ 1.1, 0 ≤ α ≤ 0.8, 0.2 ≤ β ≤ 1, 0 ≤ n ≤ 0.1, A is selected from one or more of Ti, Mg, V, Cr, Zr, Nb, Zn, Al, Na, K, Mo, W, Ni, Co, Ga, Sn, Sb, Ge, and W, and G includes one or more of N, F, S, and Cl. The phosphate material may not contain doping elements or a coating layer, or it may be a phosphate material modified by doping elements and / or a coating layer. The coating layer is preferably a carbon coating layer.

[0025] More specifically, in some embodiments of the present invention, the nickel-containing material includes: LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.65 Co 0.3 Mn 0.05 O 2 , LiNi 0.85 Co 0.1 Mn 0.05 O 2 , LiNi 0.92 Co 0.06 Mn 0.02 O 2 , LiNi 0.5 Co 0.4 Mn 0.1 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.5 Co 0.3 Mn 0.2 O 2 , LiNi 0.9 Co 0.06 Mn 0.04 O 2 , LiNi 0.95 Co 0.03 Mn 0.02 O 2 , LiNi 0.7 Co 0.2 Mn 0.1 O 2 , LiNi 0.87 Co 0.1 Mn 0.03 O 2 , LiNi 0.75 Co0.2 Mn 0.05 O 2 、LiNi 0.88 Co 0.1 Mn 0.02 O 2 、LiNi 0.6 Co 0.3 Mn 0.1 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.95 Co 0.04 Mn 0.01 O 2 、LiNi 0.7 Co 0.15 Mn 0.15 O 2 、LiNi 0.8 Co 0.1 Al 0.1 O 2 、LiNi 0.8 Co 0.1 Nb 0.1 O 2 、LiNi 0.8 Co 0.1 Mg 0.1 O 2 、LiNi 0.75 Co 0.15 Mn 0.05 O 2 、LiNi 0.96 Co 0.03 Mn 0.01 O 2 、LiNi 0.93 Co 0.04 Mn 0.03 O 2 。

[0026] The phosphate materials include: LiMn 0.6 Fe 0.4 PO 4 、LiMn 0.7 Fe 0.3 PO 4 、LiMn 0.65 Fe 0.35 PO 4 、LiMn 0.85 Fe 0.15 PO 4 、LiMn 0.5 Fe 0.5 PO 4, LiMn 0.8 Fe 0.2 PO 4 , LiMn 0.3 Fe 0.7 PO 4 , LiMn 0.56 Fe 0.44 PO 4 , LiMn 0.75 Fe 0.25 PO 4 , LiMn 0.82 Fe 0.18 PO 4 , LiMn 0.9 Fe 0.1 PO 4 , LiMn 0.62 Fe 0.38 PO 4 , LiMn 0.55 Fe 0.45 PO 4 , LiFePO 4 , LiMn 0.05 Fe 0.95 PO 4 , LiMn 0.5 Fe 0.4 Mg 0.1 PO 4 , LiMn 0.5 Fe 0.4 Na 0.1 PO 4 , LiMn 0.5 Fe 0.4 Al 0.1 PO 4 , LiMn 0.2 Fe 0.8 PO 4 .

[0027] In the preferred embodiment of the present invention, the molar ratio of the nickel-containing material in the positive electrode material layer to the total molar number of the nickel-containing material and the phosphate material is greater than or equal to 0.5, and this value reflects the blending ratio of the nickel-containing material in the composite material. When the above range is satisfied, the molar ratio of Ni / Fe in the positive electrode material layer can be adjusted within a set range by combining suitable raw materials and manufacturing processes, and the D90 / D50 of the positive electrode material can also be adjusted within a set range, improving the tap density, volumetric energy density, cycle performance, conductivity, and electrochemical performance of the positive electrode material.

[0028] In some embodiments of the present invention, the lithium salt includes LiPF 6 , lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, LiBF 4, LiBOB, LiSbF 6 , LiAsF 6 , LiCF 3 SO 3 , LiDFOB, LiDFOP, LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiN(SO 2 C 2 F 5 ) 2 , LiCl, LiBr, LiI, LiClO 4 , LiB 10 Cl 10 , LiAlCl 4 , at least one of lithium chloroborane and lithium tetraphenylborate.

[0029] In some embodiments of the present invention, the organic solvent is one or more of cyclic carbonates, linear carbonates, carboxylic acid esters, and ethers.

[0030] In some embodiments of the present invention, the cyclic carbonates include one or more of vinylene carbonate, propylene carbonate, ethylene carbonate, and butylene carbonate.

[0031] In some embodiments of the present invention, the linear carbonates include one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0032] In some embodiments of the present invention, the carboxylic acid esters include one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, isobutyl methyl acetate, methyl pivalate, and ethyl pivalate.

[0033] In some embodiments of the present invention, the ethers include one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0034] In some preferred embodiments of the present invention, the organic solvent is a mixture of ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0035] Specifically, in some embodiments of the present invention, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of cyclic sulfate compounds, sultone compounds, cyclic carbonate compounds, phosphate compounds, and borate compounds. Adding the auxiliary additive to the electrolyte can participate in the film-forming process together with the first additive and the second additive, further improving the stability of the protective film, and thus further improving the high-temperature storage performance and fast charge cycle performance of the battery.

[0036] In some preferred embodiments, the cyclic sulfate compounds include at least one of 4-methyl vinyl sulfate, vinyl sulfate, and allyl sulfate.

[0037] In some preferred embodiments, the sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, and allyl-1,3-sultone.

[0038] In some preferred embodiments, the cyclic carbonate compounds include at least one of vinylene carbonate, ethylene vinylene carbonate, methylene vinylene carbonate, fluoroethylene carbonate, trifluoromethyl carbonate, difluoroethylene carbonate, and the compound shown in the following structural formula 1: ; In the shown structural formula 1, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group.

[0039] In some preferred embodiments, the compound shown in the structural formula 1 includes at least one of the compounds shown in the following compounds 1-1 to 1-6: ;

[0040] In some preferred embodiments, the phosphate compounds include at least one of the compounds shown in the following structural formula 2: ;

[0041] In the structural formula 2, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, and -Si(C m H 2m+1 ) 3, m is a natural number from 1 to 3; more preferably, the compound shown in Structural Formula 2 includes at least one of tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tripropargyl phosphate, dipropargylmethyl phosphate, dipropargylethyl phosphate, dipropargylpropyl phosphate, dipropargyltrifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargylhexafluoroisopropyl phosphate, triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyltrifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate.

[0042] In some preferred embodiments, the borate compound includes at least one of tris(trimethylsilyl) borate and tris(triethylsilyl) borate.

[0043] Specifically, in some embodiments of the present invention, based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01% to 10%. Preferably, the content is 0.1% to 5%; more preferably, the content is 0.1% to 2%. Specifically, the content of any optional substance in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5% or the range composed of any two of these values.

[0044] In some embodiments of the present invention, the separator is located between the positive electrode sheet and the negative electrode sheet.

[0045] In some embodiments of the present invention, the separator can be an existing conventional separator, selected from one or more of ceramic separators, polymer separators, non-woven fabrics, and inorganic-organic composite separators. For example, single-layer polypropylene (PP) separators, single-layer polyethylene (PE) separators, double-layer PP / PE separators, double-layer PP / PP separators, and triple-layer PP / PE / PP separators.

[0046] In some embodiments of the present invention, the tap density of the positive electrode sheet is 2.0 g / cm 3 ~4.4 g / cm 3 , and the tap density of the negative electrode sheet is 1.0 g / cm 3 ~2.0 g / cm 3 .

[0047] In some preferred embodiments of the present invention, the tap density of the positive electrode sheet is 2.3 g / cm3 ~4.2 g / cm 3 The compaction density of the negative electrode sheet is 1.4 g / cm 3 ~1.8 g / cm 3 .

[0048] In some embodiments of the present invention, the double-sided density of the positive electrode sheet is 20 mg / cm 2 ~70 mg / cm 2 , and the double-sided density of the negative electrode sheet is 10 mg / cm 2 ~35 mg / cm 2 .

[0049] In some preferred embodiments of the present invention, the double-sided density of the positive electrode sheet is 30 mg / cm 2 ~50 mg / cm 2 , and the double-sided density of the negative electrode sheet is 15 mg / cm 2 ~30 mg / cm 2 .

[0050] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode material layer is located on both sides of the positive electrode current collector. The positive electrode current collector includes a metal material capable of conducting electrons. Preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0051] In some embodiments of the present invention, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0052] Based on the total mass of the positive electrode material layer being 100%, the mass percentage content of the positive electrode binder is 0.5% - 3%, and the mass percentage content of the positive electrode conductive agent is 0.5% - 3%.

[0053] In some embodiments of the present invention, the positive electrode binder includes one or more of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; sodium carboxymethyl cellulose; polyvinyl butyral; ethylene - vinyl acetate copolymer; polyvinyl alcohol; and styrene - butadiene rubber.

[0054] In some embodiments of the present invention, the positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0055] Specifically, in some embodiments of the present invention, the negative electrode sheet includes a negative electrode material layer containing a negative electrode active material, and the negative electrode active material includes one or more of a silicon-based negative electrode and a carbon-based negative electrode.

[0056] In some preferred embodiments of the present invention, the carbon-based negative electrode includes one or several of graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres. The graphite includes one or several of natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. The natural graphite is flaky graphite, scaly graphite, soil graphite, and / or graphite particles obtained by subjecting these graphites to treatments such as spheroidization and densification.

[0057] The artificial graphite is obtained by graphitizing organic substances such as coal tar pitch, heavy crude oil of coal type, atmospheric residue, heavy crude oil of petroleum type, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polystyrene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at high temperatures.

[0058] The amorphous carbon may be amorphous carbon particles obtained by heat-treating a graphitizable carbon precursor such as tar or asphalt as a raw material one or more times in a temperature range where graphitization does not occur (in the range of 400°C to 2200°C), or amorphous carbon particles obtained by heat-treating a non-graphitizable carbon precursor such as resin as a raw material.

[0059] The carbon-coated graphite may be obtained by mixing natural graphite and / or artificial graphite with a carbon precursor such as tar, asphalt, or resin and performing heat treatment one or more times in the range of 400°C to 2300°C. Using the obtained natural graphite and / or artificial graphite as core graphite, it is coated with amorphous carbon to obtain a carbon graphite composite. The carbon graphite composite may be in a form where the entire or part of the surface of the core graphite is coated with amorphous carbon, or in a form where multiple primary particles are compounded with carbon originating from the above carbon precursor as a binder. Additionally, a carbon graphite composite may be obtained by reacting hydrocarbon gases such as benzene, toluene, methane, propane, and volatile components of aromatic substances with natural graphite and / or artificial graphite at high temperatures to deposit carbon on the graphite surface.

[0060] The graphite-coated graphite can be obtained by mixing natural graphite and / or artificial graphite with carbon precursors of easily graphitizable organic compounds such as tar, asphalt, and resin, and performing heat treatment more than once in the range of about 2400 °C to 3200 °C. Using the obtained natural graphite and / or artificial graphite as the core graphite, and coating the whole or part of the surface of the core graphite with a graphitized material, graphite-coated graphite can be obtained.

[0061] The resin-coated graphite can be obtained by mixing natural graphite and / or artificial graphite with resin, etc., drying at a temperature below 400 °C, using the obtained natural graphite and / or artificial graphite as the core graphite, and coating the core graphite with resin, etc. The above-mentioned organic compounds such as tar, asphalt, and resin are selected from one or more of carbonizable organic compounds in coal-based heavy crude oil, straight-run heavy crude oil, cracked petroleum heavy crude oil, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenylene, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins.

[0062] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder, a negative electrode conductive agent, and a negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, which will not be elaborated here. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent respectively, which will not be elaborated here.

[0063] For the lithium-ion battery provided by the present invention, when the mass percentage content a% of the first additive in the non-aqueous electrolyte, the mass percentage content b% of the difluorophosphate ion in the non-aqueous electrolyte, the molar ratio c of Ni and Fe in the positive electrode material layer, and the D90 / D50 ratio d of the positive electrode material satisfy the following conditions: , and 0.01 ≤ a ≤ 0.8, 0.01 ≤ b ≤ 1, 0.5 ≤ c ≤ 200, 1.2 ≤ d ≤ 20, can the synergistic effect of the two additive film-forming components be fully exerted to form a highly stable and highly ductile positive electrode interface film, which matches the compounded ternary-dominated positive electrode material, so as to achieve both low impedance and high-rate cycling performance. Specific Embodiments

[0064] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0065] Example 1 The preparation method of the lithium-ion battery in this embodiment includes the following steps: 1. Preparation of the positive electrode sheet A mixture of a positive electrode active material (nickel-containing material LiNi 0.8 Co 0.1 Mn 0.1 O 2 and a phosphate material LiFePO 4 is mixed with an N-methylpyrrolidone (NMP) solvent, and polyvinylidene fluoride (PVDF) is added as a binder, and the mixture is stirred well to obtain a PVDF adhesive solution. In the PVDF adhesive solution, a composite system of super carbon black and carbon nanotubes (super P+CNT) is added as a conductive agent, and the mixture is stirred well. The mass ratio of the positive electrode active material, the binder, and the conductive agent is 94:3:3. The prepared positive electrode slurry is uniformly coated on an aluminum foil, and after drying, rolling, die-cutting or slitting, a positive electrode sheet is obtained. The molar ratio of Ni and Fe in the positive electrode material layer of the positive electrode sheet is 3.2, and the D90 / D50 ratio of the positive electrode material is 8.

[0066] 2. Preparation of negative electrode sheet (1) Weigh each substance according to the negative electrode sheet ratio of graphite (FSN-1): conductive carbon (super P): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 96.3:1.0:1.2:1.5 (mass ratio).

[0067] (2) First, add CMC according to a solid content of 1.5% to pure water, and stir well to prepare a transparent CMC adhesive solution.

[0068] (3) Add conductive carbon (super P) to the CMC adhesive solution, and stir well to prepare a conductive adhesive.

[0069] (4) Continuously add graphite and stir well to finally obtain the required negative electrode slurry.

[0070] (5) The prepared negative electrode slurry is uniformly coated on a copper foil, and after drying, rolling, die-cutting or slitting, a negative electrode sheet is obtained.

[0071] 3. Preparation of non-aqueous electrolyte Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are mixed according to a mass ratio of EC:DEC:EMC = 1:1:1, and compound 1 and lithium difluorophosphate are added as additives, and then lithium hexafluorophosphate (LiPF 6 ) is added until the molar concentration is 1 mol / L. In the non-aqueous electrolyte, the mass percentage content of compound 1 is 0.45%, and the mass percentage content of lithium difluorophosphate is 0.5%.

[0072] 4. Preparation of lithium-ion battery cell Assemble the prepared positive electrode sheet and the negative electrode sheet above into a laminated soft-pack battery cell.

[0073] 5. Liquid injection and formation of the battery cell In a glove box with the dew point controlled below -40°C, inject the electrolyte prepared above into the battery cell, perform vacuum packaging, and let it stand for 72 h. Then conduct the conventional formation for the first charge according to the following steps: constant current charge at 0.05C for 180 min, constant current charge at 0.1C for 120 min, constant current charge at 0.2C for 120 min, perform secondary vacuum sealing, and then further fully charge at a current of 0.2C (100% SOC). After standing at room temperature for 72 h, fully discharge at a current of 0.2C (0% SOC).

[0074] Examples 2 - 26 and Comparative Examples 1 - 22 This example and the comparative examples are used to comparatively illustrate the lithium-ion battery disclosed in the present invention, including most of the operation steps in Example 1 above. The differences lie in: the type of the positive active material, the doping molar ratio of the nickel-containing material in the positive active material, the molar ratio of Ni and Fe in the positive electrode material layer, the D90 / D50 ratio of the positive electrode material, and the content of the additive in the non-aqueous electrolyte, as shown in Table 1 specifically.

[0075] Perform the following performance tests on the lithium-ion batteries prepared in each example and comparative example: (1) High-temperature 3C / 3C cycle performance test At 45°C, charge the lithium-ion batteries prepared in the examples and comparative examples at a rate of 1C within the conventional voltage range (usually 2.5 - 4.2V) of the composite positive electrode battery system with constant current and constant voltage (cut-off current 0.05C), discharge at a rate of 1C for three cycles, and use the capacity of the last cycle as the initial 100% SOC capacity. After fully charging at a rate of 3C with constant current and constant voltage, discharge at a rate of 3C, and conduct a full charge and full discharge cycle test within the common charge and discharge cut-off voltages of the corresponding system. When the charge / discharge cycle reaches 500 cycles, calculate the impedance growth rate of the 500th cycle; then until the capacity of the lithium-ion battery decays to 80% of the initial capacity, record the number of cycles.

[0076] Impedance growth rate after the 500th cycle (%) = (Internal resistance after the 500th cycle - Initial internal resistance before cycling) / Initial internal resistance before cycling × 100%; The test procedure for the internal resistance is the same as that for the "Internal resistance test at 0°C" below, with the difference that the temperature is 45°C.

[0077] Internal resistance test at 0°C: Charge the battery at a constant current to 50% of the battery capacity at room temperature (25°C), then adjust the temperature to 0°C and keep it for 6 h.

[0078] After constant current charging at 0.1C for 10s, it is left to stand for 40s; after constant current discharging at 0.1C for 10s, it is left to stand for 40s, and record the cut-off voltage V1; After constant current charging at 0.2C for 10s, it is left to stand for 40s; after constant current discharging at 0.2C for 10s, it is left to stand for 40s, and record the cut-off voltage V2; After constant current charging at 0.5C for 10s, it is left to stand for 40s; after constant current discharging at 0.5C for 10s, it is left to stand for 40s, and record the cut-off voltage V3.

[0079] Taking current as the abscissa and voltage as the ordinate, draw a straight line, and the slope of the straight line is the impedance at 0°C.

[0080] Test results: As shown in Table 1 are the various parameters required for preparing the lithium-ion batteries in Examples 1 to 19 and Comparative Examples 1 to 19; the differences between Examples 2 to 19 and Comparative Examples 1 to 19 and Example 1 lie in the relevant parameters in Table 1. The specific differences are: the type of nickel-containing material, the type of phosphate material, the molar proportion of the nickel-containing material in the compounded cathode, the mass percentage content a (%) of the first additive, the mass percentage content b (%) of the difluorophosphate ion, the molar ratio c of Ni / Fe in the cathode material layer, the ratio d of D90 / D50 of the compounded material, and the calculation result, and the remaining parameters and preparation steps are the same as those described in Example 1.

[0081] Table 2 shows the performance test results of the lithium-ion batteries prepared in Examples 1 to 19 and Comparative Examples 1 to 19.

[0082] Table 1 Note: " / " in the table indicates that there is no such item.

[0083] Table 2

[0084] From the test results of Examples 1 to 19 and Comparative Examples 1 to 19, it can be seen that for the lithium-ion batteries provided in the present invention, a cathode system in which a nickel-containing material is compounded with a phosphate material is adopted, and a first additive and a difluorophosphate ion are used as additives in the non-aqueous electrolyte. At the same time, it is also defined that the mass percentage content a of the first additive, the mass percentage content b of the difluorophosphate ion, the molar ratio c of Ni and Fe in the cathode material layer, and the ratio d of D90 / D50 of the cathode material satisfy the relational expression ;When 0.01 ≤ a ≤ 0.8, 0.01 ≤ b ≤ 1, 0.5 ≤ c ≤ 200, and 1.2 ≤ d ≤ 20, a lithium-ion battery with both low impedance and high-rate cycling performance can be obtained.

[0085] From the test results of Example 1 and Comparative Examples 1-19, it can be seen that when any one of the parameters of the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of difluorophosphate ions, the molar ratio c of Ni and Fe in the positive electrode material layer, and the D90 / D50 ratio d of the positive electrode material does not meet the range or the relationship is too large or too small, the synergistic effect of the two additive film-forming components cannot be fully exerted, and a highly stable and highly ductile positive electrode interface film cannot be formed, resulting in the inability to achieve both low impedance and high-rate cycling performance of the lithium-ion battery.

[0086] When the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of difluorophosphate ions, the molar ratio c of Ni and Fe in the positive electrode material layer, and the D90 / D50 ratio d of the positive electrode material further satisfy , and 0.05 ≤ a ≤ 0.5, 0.05 ≤ b ≤ 0.5, 0.5 ≤ c ≤ 30, 2 ≤ d ≤ 12, the formation of a high LiF inorganic film component by difluorophosphate ions will have a better film-forming protection effect on high-nickel materials, and the first additive forms a sulfur-containing organic film component, which has a better film-forming effect on phosphate materials with a high specific surface area. When the two additives are used in combination, the best effect can be achieved only when the molar ratio of Ni and Fe in the positive electrode material layer and the D90 / D50 ratio of the positive electrode material satisfy the above relationship.

[0087] Table 3 shows the performance test results of the lithium-ion batteries prepared in Example 1 and Examples 20-23; the difference between Examples 20-23 and Example 1 lies in the type of the first additive shown in Table 3, and the remaining parameters and preparation steps are the same as those recorded in Example 1.

[0088] Table 3

[0089] From the measurement results in Table 3, it can be known that when the mass percentage content a of the first additive, the mass percentage content b of difluorophosphate ions, the molar ratio c of Ni and Fe in the positive electrode material layer, the D90 / D50 ratio d of the positive electrode material, and the relationship meet the relevant requirements, adding any one of Compounds 1-5 as the first additive can make the lithium-ion battery have both low impedance and high-rate cycling performance, indicating that the battery system of the present invention has universality for different types of first additives.

[0090] Table 4 shows the performance test results of the lithium-ion batteries prepared in Example 1, Examples 24 to 26, and Comparative Examples 20 to 22; the differences between Examples 24 to 26 and Comparative Examples 20 to 22 and Example 1 lie in the mass percentage (%) of the first additive, the mass percentage content b (%) of difluorophosphate ions, and the co-additive and its content shown in Table 4, and the remaining parameters and preparation steps are the same as those described in Example 1.

[0091] Table 4 Note: " / " in the table indicates that there is no such item.

[0092] From the measurement results in Table 4, it can be seen that when the mass percentage content a of the first additive, the mass percentage content b of difluorophosphate ions, the molar ratio c of Ni and Fe in the positive electrode material layer, the D90 / D50 ratio d of the positive electrode material, and the relational expression meet the relevant requirements, adding different types of co-additives can make the lithium-ion battery take into account both low impedance and high-rate cycling performance, indicating that the battery system of the present invention has universality for different co-additives.

[0093] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A lithium ion battery, characterized in that: include: Positive electrode sheet, negative electrode sheet, separator and non-aqueous electrolyte; The positive electrode sheet comprises a positive electrode material layer containing a positive electrode material, wherein the positive electrode material comprises a nickel-containing material and a phosphate material; The non-aqueous electrolyte comprises an additive, a lithium salt and an organic solvent; The additive includes a first additive and difluorophosphate ions; The first additive includes at least one of Compound 1 to Compound 5; ； The lithium-ion battery meets the following conditions: ; and 0.01≤a≤0.8, 0.01≤b≤1, 0.5≤c≤200, 1.2≤d≤20; a is the mass percentage of the first additive in the non-aqueous electrolyte, in %; b is the mass percentage of difluorophosphate ion in the non-aqueous electrolyte, unit is %; c is the molar ratio of Ni and Fe in the positive electrode material layer; d is the D90 / D50 ratio of the positive electrode material.

2. The lithium-ion battery according to claim 1, characterized in that The lithium-ion battery meets the following conditions: .

3. The lithium ion battery according to claim 1, characterized in that The mass percentage a% of the first additive in the non-aqueous electrolyte is 0.1%-0.45%.

4. The lithium ion battery according to claim 1, characterized in that The mass percentage b% of difluorophosphate ions in the non-aqueous electrolyte is 0.1%-0.5%.

5. The lithium ion battery according to claim 1, characterized in that The molar ratio c of Ni to Fe in the positive electrode material layer is 0.5-30.

6. The lithium ion battery according to claim 1, characterized in that The D90 / D50 ratio d of the positive electrode material is 2-12.

7. The lithium ion battery according to claim 1, characterized in that The nickel-containing material includes a chemical formula of Li q Ni x Co y M 1-x-y O 2-g R g The material or the surface of which is provided with a coating layer of Li q Ni x Co y M 1-x-y O 2-g R g At least one of the materials, wherein 0.9≤q≤1.2, 0.5≤x≤0.96, y>0, 1-xy>0, 0≤g≤1, M includes one or two of Mn and Al, and zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, Ce, and R includes one or more of N, F, S and Cl; and / or, The phosphate material includes a molecular formula of Li r Mn α Fe β A 1-α-β PO 4-n G n The material or the surface of which is provided with a coating layer of Li r Mn α Fe β A 1-α-β PO 4-n G n At least one of the materials, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0≤n≤0.1, A is selected from one or more of Ti, Mg, V, Cr, Zr, Nb, Zn, Al, Na, K, Mo, W, Ni, Co, Ga, Sn, Sb, Ge and W, and G includes one or more of N, F, S and Cl.

8. The lithium ion battery according to claim 1, characterized in that The molar ratio of the nickel-containing material in the positive electrode material layer to the total molar ratio of the nickel-containing material and the phosphate material is greater than or equal to 0.

5.

9. The lithium ion battery according to claim 1, characterized in that The lithium salts include LiPF6, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide), LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiN(SO2CF3)2, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10 , LiAlCl4, lithium chloroborane, and lithium tetraphenylborate.

10. The lithium ion battery according to claim 1, characterized in that The non-aqueous electrolyte further includes an auxiliary additive, wherein the auxiliary additive includes at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound and a borate compound; and / or, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01% to 10%; and / or, The cyclic sulfate ester compound includes at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone and propenyl-1,3-sultone; and / or, The cyclic carbonate compound includes at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound shown in the following structural formula 1: ； In the structural formula 1 shown, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, a C1-C5 group; and / or, The phosphate compound includes at least one of the compounds shown in the following structural formula 2: ； In the structural formula 2, R 31 , R 32 , R 33 Each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3; and / or, The borate ester compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

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