A lithium-ion battery

Abstract

The present invention belongs to the technical field of lithium-ion batteries and relates to a lithium-ion battery, specifically to a lithium-ion battery that takes into account both the impedance and rate cycling performance of the battery. The lithium-ion battery comprises: a positive electrode sheet, a negative electrode sheet, a separator, and a non-aqueous electrolyte; the positive electrode sheet comprises a positive electrode material layer comprising 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 satisfies the following conditions: 0.01≤a≤0.8, 0.01≤b≤1, 0.5≤c≤200, 1.2≤d≤20. The lithium-ion battery provided by the present invention forms a highly stable and highly tough positive electrode interface film by adjusting the positive electrode active material compound system and the non-aqueous electrolyte, so that the battery takes into account both low impedance and high rate cycling performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a lithium-ion battery that takes both battery impedance and rate cycle performance into consideration. Background Art

[0002] Currently, lithium-ion power batteries are developing in the direction of low cost, high cost performance, and high safety. Phosphate-based materials, which combine high energy density with high safety, have become a focus of industry attention. However, the inherent low compaction density, low theoretical gram capacity, and low electrical conductivity of phosphate-based materials limit their widespread application. The addition of nickel-containing materials to the phosphate system can compensate for these performance deficiencies. The addition of ternary systems to phosphate systems has the effects of increasing energy density, increasing compaction density, and improving low-temperature performance, while combining high energy density with high safety. Compared with pure ternary systems, it reduces material costs and dependence on rare precious metal elements, and has strong application prospects.

[0003] In ternary materials blended with phosphate systems, if nickel-containing materials account for the majority (>50%), the smaller-particle phosphate materials will typically adsorb onto the ternary surface due to their higher surface energy, forming a coating. The composite material allows for a balanced mix of large and small particle sizes, improving the cathode material's compaction density, volumetric energy density, cycling performance, conductivity, and electrochemical properties. However, composite materials place higher demands on compatible electrolytes, especially for high-rate cycling performance, a mainstream development trend in power batteries. Rapid lithium-ion deintercalation and insertion can cause the composite materials to segregate, degrading the overall battery performance. Therefore, the electrolyte must not only form a highly stable cathode / electrolyte interface (CEI) film on both the phosphate and nickel-containing material surfaces, but also exhibit good toughness. Numerous studies have confirmed that while increasing the Ni content in nickel-containing materials is beneficial for improving energy density, it inevitably weakens the stability of the cathode structure. Variations in the composite particle size due to varying blending ratios can also affect the stability and consistency of the cathode film. Therefore, the development of lithium-ion secondary battery electrolytes that can have good film-forming effects by mixing ternary system materials into the phosphate system is of great significance for taking into account both battery impedance and excellent rate cycle 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 both 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 system mixed with ternary system materials in the prior art.

[0005] To achieve the above-mentioned purpose, 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;

[0007] 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;

[0008] The non-aqueous electrolyte includes additives, lithium salt and organic solvent;

[0009] The additive includes a first additive and difluorophosphate ions;

[0010] The first additive includes at least one of Compound 1 to Compound 5;

[0011] ;

[0012] The lithium-ion battery meets the following conditions:

[0013] ; and 0.01≤a≤0.8, 0.01≤b≤1, 0.5≤c≤200, 1.2≤d≤20;

[0014] a is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0015] b is the mass percentage of difluorophosphate ions in the non-aqueous electrolyte, unit is %;

[0016] c is the molar ratio of Ni to Fe in the positive electrode material layer;

[0017] d is the D90 / D50 ratio of the positive electrode material.

[0018] For the positive electrode system of power batteries, nickel-containing materials are inferior to phosphate materials in terms of safety, long cycle life and cost, so their share in the power market has been declining year by year. However, the excellent high energy density, rate and low-temperature performance of ternary materials are also advantages that phosphate systems cannot achieve. In this context, the positive electrode system of nickel-containing materials and phosphate materials is expected to have balanced performance without obvious shortcomings. Using nickel-containing materials as the main body and mixing phosphate materials can improve the thermal stability and compaction density of the positive electrode 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 properties of the composite system.

[0019] First, when it comes to nickel-containing materials combined with phosphate materials, the type, particle size, and blending ratio of the two materials significantly impact battery performance and electrolyte compatibility. Ni, as a transition metal, is often a critical and frequently adjusted parameter in nickel-containing materials. High-nickel nickel-containing materials offer higher energy density, but at the expense of structural stability. Fe is the most important transition metal element in phosphate materials. The well-known lithium iron phosphate cathode is a phosphate material dominated by Fe, while the emerging lithium manganese iron phosphate material also plays a crucial role in improving material conductivity and stability. Therefore, the molar ratio of Ni to Fe in the cathode material layer is a key parameter that reflects the stability of the cathode material and the blending ratio of the composite materials. Furthermore, the D90 / D50 ratio of the cathode material is also a key parameter influencing the composite material. Since phosphate materials are often nanosized to reduce particle size and increase lithium ion mobility, the particle size of phosphate materials is generally much smaller than that of nickel-containing materials. A ternary-based composite system exploits this principle, creating a spatial distribution of phosphate-coated nickel-containing materials. This increases the material's compaction density, reduces the contact area between the nickel-containing material and the electrolyte, and improves the overall conductivity of the cathode material, ultimately enhancing the battery's impedance, rate, and cycling performance. While D50 primarily reflects the particle size and blend ratio of the small-particle phosphate material, D90 accounts for the particle size of both cathode materials. Therefore, D90 / D50 reflects the particle size difference and distribution of the composite materials. These composite cathode parameters influence the applicable additive content and distribution. Difluorophosphate anions increase the proportion of the inorganic LiF component in the membrane, making them more suitable for ternary cathodes with large phase transitions and volume changes. The first additive, on the other hand, decomposes to form an organic sulfur-containing membrane component, making it more suitable for phosphate cathodes with low conductivity and large specific surface area. The combined use of difluorophosphate and the first additive can produce a synergistic effect, but to fully leverage their complementary effects, the compatibility of the cathode materials must also be considered.

[0020] Finally, the inventors found through extensive research that when the first additive and difluorophosphate ions in the non-aqueous electrolyte are combined as additives 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 meet the range and relationship, the nickel-containing material and phosphate material composite system with different blending ratios can have low impedance and excellent rate cycling performance. This is due to the fact that both additives can decompose on the positive electrode of the composite system to form a highly stable and highly tough interface film, and can play a synergistic role when used at the same time, which is better than the stability and toughness of their individual film formations. 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 are also strongly correlated with the quality and uniformity of the 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 material, the doping ratio of Ni content in the nickel-containing material and / or the proportion of Fe element in the phosphate material, and can reflect the structural stability and thermal stability of the composite material; while the D90 / D50 ratio is mainly affected by the blending ratio and distribution of the composite material, the particle size of the phosphate material and / or the particle size of the nickel-containing material, and can represent the lithium ion transfer kinetics of the composite material, the compatibility of the composite material and the particle size complementary effect.

[0021] In the present invention, the two additives have different film-forming adaptability in nickel-containing materials and phosphate material systems. For example, difluorophosphate ions form high-LiF inorganic film components, which have better film-forming protection effects on high-nickel materials; and the first additive forms sulfur-containing organic film components, which have better film-forming effects on phosphate materials with high specific surface areas; so 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 meet the above relationship. In summary, the two additives are used to form a film in a coordinated manner to form a low-impedance, highly stable and tough positive electrode interface film on a composite material system with good control over properties such as stability and lithium ion dynamics and a reasonable particle size distribution, ultimately achieving both the impedance and rate cycle performance of the battery. Preferably, the lithium-ion battery meets: .

[0022] In some embodiments of the present invention, the first additive can participate in the formation of a dense and uniform interface film at both the positive and negative electrodes of the lithium-ion battery, and it has an excellent improvement effect on high-temperature cycle performance, whether in a ternary positive electrode system or a phosphate positive electrode system. When used in combination with difluorophosphate ions, the flexibility of the interface film can be further improved. 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 with the LiF component, respectively, and play a skeleton role. As a result, the stability of the composite material positive electrode film formation is significantly improved, and the dissolution of metal ions and side reactions are effectively reduced, thereby improving the cycle performance at the battery level and improving the impedance growth. If the mass percentage a% value of the first additive is too high, although it is conducive to forming a positive electrode film with high stability and high toughness, the film is too thick, resulting in excessive impedance, which not only aggravates the polarization and heat generation of the battery, but also causes poor transmission kinetics of lithium ions in the interface film. During rate cycling, the rapid migration of lithium ions is hindered, and lithium precipitation is likely to occur, which in turn leads to rapid reaction and consumption of the electrolyte and active lithium. If the mass percentage a% value of the first additive is too low, it will be difficult to improve the stability and toughness of the positive electrode interface film, or it will be difficult to form an organic film component with high stability and high toughness, and it will not be able to play a synergistic role with difluorophosphate ions, and it will not be able to improve the battery performance degradation problem caused by the incompatibility of the composite materials, which will eventually lead to an increase in the impedance of the battery and a decrease in the high rate cycle 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 a range consisting of any two of these values. Preferably, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.1% to 0.45%.

[0023] 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, monovalent and divalent cations can be used as counterions for the difluorophosphate ions; preferably, the monovalent cation is preferably a lithium ion, and the divalent cation is preferably a magnesium ion. Other monovalent or divalent cations are also within the scope of protection of the present invention and are not further described here.

[0024] In the non-aqueous electrolyte of the lithium ion battery of the present invention, the mass percentage of difluorophosphate ions has the same meaning as the concentration of difluorophosphate ions; the method for determining the mass percentage of difluorophosphate ions is not particularly limited in the present invention, and a test method known in the art can be used, such as ion chromatography, 19 F NMR, etc.

[0025] Typically, difluorophosphate ions in the electrolyte will form LiF film components on the positive and negative electrode surfaces 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 cycle. For phosphate material systems with stable positive electrodes, difluorophosphate ions will not have a deteriorating effect, and can improve the film damage problem caused by different volume changes of different materials in the ternary composite phosphate positive electrode system. If the mass percentage b% value of the difluorophosphate ions is too high, then too much difluorophosphate ions will precipitate into a solid from the electrolyte in the form of lithium difluorophosphate, or will not be able to dissolve completely, and will eventually become solid impurities. These impurities and foreign matter may cause poor film formation consistency or a virtual seal of the battery, causing uneven stress inside the battery, thereby degrading the battery interface performance. In addition, too high a content may cause too many film-forming components produced by the decomposition of LiF or other difluorophosphate ions in the interface film, thereby degrading the battery impedance. If the mass percentage b% of the difluorophosphate ion is too low, it is difficult to form a highly stable and tough interface film on the positive electrode; when the stability and toughness of the interface film are poor, the side reactions on the positive electrode are difficult to be effectively suppressed, and ultimately the battery impedance and high temperature performance cannot be improved. Specifically, the mass percentage b% of the difluorophosphate ion 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 a range consisting of any two of these values. Preferably, the mass percentage b% of the difluorophosphate ion is 0.1% to 0.5%.

[0026] In some embodiments of the present invention, the molar ratio of Ni and 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 ratio of the Ni element in the nickel-containing material and the ratio of the Fe element in the phosphate material on the other hand. If the molar ratio c value of Ni and Fe in the positive electrode material layer is too high, it means that there is too much Ni element or too little Fe element. Excessive Ni element is actually a manifestation of too high a blending ratio of nickel-containing materials in the composite positive electrode, or too high a Ni element ratio in the nickel-containing material (ultra-high nickel ternary positive electrode). In both cases, the positive electrode stability is sacrificed in order to increase the energy density. At this time, the stability of the composite material positive electrode is mainly affected by the high-nickel nickel-containing material, the positive electrode stability is very poor, and the blending ratio of the phosphate material is also low, which cannot play an improving role. These factors will deteriorate the electrochemical performance of the battery. Excessive Fe element is also a manifestation of too low a blending ratio of phosphate materials in the composite positive electrode, or too low a Fe element ratio in the phosphate material. The structural stability and thermal stability of the positive electrode of the phosphate system 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. In addition, the Fe element ratio in the phosphate material is too low, which will deteriorate the positive electrode stability, or reduce its low-cost commercial competitive advantage (doped with too many other transition metal elements), or affect its practicality (for example, the charge and discharge platform of lithium nickel phosphate is about 5.2V, which exceeds the upper limit of the withstand voltage of conventional electrolytes). Therefore, in summary, a high c value usually means that the stability of the composite positive electrode decreases significantly, or does not have commercial value. If the molar ratio c value of Ni and Fe in the positive electrode material layer is too low, that is, the nickel-containing material blending ratio is not high, and wherein Ni accounts for a low proportion as a transition metal, while Fe is the main transition metal in the phosphate material. At this point, the composite material positive electrode stability is excellent and the electrical 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 a range consisting of any two of these values. Preferably, the molar ratio c of Ni to Fe in the positive electrode material layer is 0.5-30.

[0027] In this application, D50 represents the particle size at which the cumulative particle size distribution of a sample reaches 50%. Physically, this means that 50% of the particles have a diameter greater than this value, and 50% of the particles have a diameter less than this value. D50, also known as the median particle size or median particle size, is often used to represent the average particle size of a powder.

[0028] 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.

[0029] In the present invention, the positive electrode material refers to all materials contained in the positive electrode material layer, including the positive electrode active material, the positive electrode conductor and the positive electrode binder. Since the positive electrode active material accounts for the majority of the content in the positive electrode material layer, the D90 / D50 ratio of the positive electrode material actually mainly reflects the D90 / D50 ratio of the positive electrode active material.

[0030] The D90 / D50 ratio d of the positive electrode material is directly related to the particle size distribution of the positive electrode active material. The design of the positive electrode particle size distribution helps to improve the density and mechanical properties of the positive electrode sheet, reduce the occurrence of pores and defects, and enhance the strength and toughness of the electrode sheet; the positive electrode particle size distribution can improve and optimize the lithium ion transmission rate to a certain extent. More importantly, it also has a great influence on the film formation uniformity and film formation component composition, such as the decomposition and action of the first additive and difluorophosphate ions on the surface of the positive electrode active material. When the D90 / D50 ratio d of the positive electrode material is too small, it means that the particle size difference is small (usually caused by uneven mixing), the gaps between the particles are larger and more, and the specific surface area of ​​the active material is larger. More additives are required to generate a positive electrode surface interface film based on the surface of the active material particles to form a stable CEI film, which can easily lead to uneven film formation or premature consumption of additives. When the D90 / D50 ratio d of the positive electrode material is too large, it means that small particles of phosphate material are densely filled in the pore space of large particles of nickel-containing material. Most of the additives form a film on the surface of the high-specific energy phosphate material, while the film protection of the nickel-containing material particles is poor. At the same time, the large and densely wrapped nickel-containing material cannot exert its higher lithium ion migration ability and limit its capacity, which is not conducive to the improvement of the energy density of lithium-ion batteries, and is also not conducive to the improvement of the film formation quality of the positive electrode surface interface film.

[0031] Normally, the particle size of a single cathode active material follows a normal distribution. However, composite cathodes containing nickel and phosphate materials exhibit additional distribution characteristics. This is because phosphate particles are much smaller than nickel, which mitigates the phosphate's lower conductivity. Therefore, the D50 of a composite material is primarily influenced by the phosphate's blend ratio and particle size distribution, while the D90 factor accounts for both the nickel-containing material's particle distribution and nearly all phosphate particles. In ternary composite cathode materials primarily based on nickel, the phosphate material adheres to the nickel-containing material as a coating. This coating reduces the contact area between the less stable nickel-containing material and the electrolyte, while also improving the overall cathode density, conductivity, and safety. The particle size difference and blend ratio between the two materials significantly impact the battery's electrochemical performance. The D90 / D50 ratio of a composite material provides an indicator of this influence. If the D90 / D50 ratio d value of the positive electrode material is too low, it means that the difference between the D90 and D50 values ​​is very small. This usually indicates that the two positive electrode materials are not fully and evenly mixed in the composite material, and thus the spatial structure of the phosphate material coating the nickel-containing material cannot be formed, and the advantages of the composite material cannot be brought into play. The incompatibility problem between the materials will seriously deteriorate the electrochemical performance. In addition, it may also be that the particle size of the two materials is similar. Whether they are small or large, the positive electrode compaction density and conductivity cannot be effectively improved. Not only that, it will also significantly aggravate the detachment caused by the incompatibility of the composite materials, or cause problems such as large film formation differences. From the battery level, it is specifically manifested as large initial impedance, extremely poor cycle performance, extremely poor rate performance, and extremely obvious impedance growth. If the D90 / D50 ratio d value of the positive electrode material is too high, it means that the phosphate blending ratio is 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 size of nickel-containing materials is generally large, which increases the value of D90, and ultimately makes the difference in 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 coverage have poor lithium ion migration performance. Large-particle nickel-containing materials will further deteriorate the lithium ion migration kinetics, making the compounding effect even worse than that of a single positive electrode material. Small-particle phosphate materials with high specific surface area will lead to aggravated side reactions, thereby making the high-temperature performance of the battery poor. In addition, phosphate materials with high surface energy will preferentially consume additives and form a film on their surface. Such compound materials are not only prone to separation and incompatibility problems between materials, but also due to the small and numerous characteristics of phosphate materials, the specific surface area of ​​the positive electrode is too high, which in turn aggravates the side reactions on the positive electrode side, increases the battery impedance and deteriorates the cycle performance, thereby affecting the film-forming quality of the nickel-containing material.Ultimately, the battery has poor electrochemical performance in all aspects, and the complementary improvement effect of the compound materials cannot be achieved. 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 a range consisting of any two of these values. Preferably, the D90 / D50 ratio d of the positive electrode material is 2 to 12.

[0032] The D50 and D90 test methods 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 vacuum dry it for 24 hours, use a small scraper to scrape about 2g~3g of the material layer (excluding the current collector) powder, and after pretreatment, place the sample in the sampling chamber of a laser particle size analyzer. After sufficient ultrasonic dispersion (≥20 minutes, no significant sedimentation), the test is performed after the shading rate stabilizes.

[0033] Specifically, in some embodiments of the present invention, 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 the 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, and Ce, and R includes one or more of N, F, S, and Cl. The nickel-containing material may not include a doping element or a coating layer, or may be a nickel-containing material modified by a doping element and / or a coating layer, and the coating layer is preferably a metal oxide coating layer.

[0034] 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 the Li r Mn α Feβ 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. The phosphate material may not contain a doping element or a coating layer, or may be a phosphate material modified by a doping element and / or a coating layer, and the coating layer is preferably a carbon coating layer.

[0035] More specifically, in some embodiments of the present invention, the nickel-containing material includes: LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.65 Co 0.3 Mn 0.05 O2、LiNi 0.85 Co 0.1 Mn 0.05 O2、LiNi 0.92 Co 0.06 Mn 0.02 O2、LiNi 0.5 Co 0.4 Mn 0.1 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.5 Co 0.3 Mn 0.2 O2、LiNi 0.9 Co 0.06 Mn 0.04 O2、LiNi 0.95 Co 0.03 Mn 0.02 O2、LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.87 Co 0.1 Mn 0.03 O2, LiNi 0.75 Co 0.2 Mn 0.05 O2、LiNi 0.88 Co 0.1 Mn 0.02 O2、LiNi 0.6 Co 0.3 Mn 0.1 O2、LiNi0.6 Co 0.2 Mn 0.2 O2, LiNi 0.95 Co 0.04 Mn 0.01 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi 0.8 Co 0.1 Nb 0.1 O2, LiNi 0.8 Co 0.1 Mg 0.1 O2, LiNi 0.75 Co 0.15 Mn 0.05 O2, LiNi 0.96 Co 0.03 Mn 0.01 O2, LiNi 0.93 Co 0.04 Mn 0.03 O2.

[0036] Comprehensive range of silicic acid silica materials: LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.65 Fe 0.35 PO4, LiMn 0.85 Fe 0.15 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.56 Fe 0.44 PO4, LiMn 0.75 Fe 0.25 PO4, LiMn 0.82 Fe 0.18 PO4, LiMn 0.9 Fe 0.1 PO4, LiMn 0.62 Fe 0.38 PO4, LiMn 0.55 Fe 0.45 PO4, LiFePO4, LiMn 0.05 Fe 0.95 PO4, LiMn0.5 Fe 0.4 Mg 0.1 PO4、LiMn 0.5 Fe 0.4 Na 0.1 PO4、LiMn 0.5 Fe 0.4 Al 0.1 PO4、LiMn 0.2 Fe 0.8 PO4.

[0037] In a preferred embodiment of the present invention, the molar ratio of the nickel-containing material in the positive electrode material layer relative to the total molar ratio of the nickel-containing material and the phosphate material is greater than or equal to 0.5, which reflects the mixing ratio of the nickel-containing material in the composite material. When the above range is met, combined with appropriate raw materials and production processes, the Ni / Fe molar ratio in the positive electrode material layer can be regulated within a set range, and the D90 / D50 of the positive electrode material can be regulated within a set range, thereby improving the positive electrode material's compaction density, volume energy density, cycle performance, conductivity, and electrochemical properties.

[0038] In some embodiments of the present invention, the lithium salt includes 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.

[0039] In some embodiments of the present invention, the organic solvent is one or more of cyclic carbonates, linear carbonates, carboxylates and ethers.

[0040] In some embodiments of the present invention, the cyclic carbonate includes one or more of vinylene carbonate, propylene carbonate, ethylene carbonate and butylene carbonate.

[0041] In some embodiments of the present invention, the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate.

[0042] In some embodiments of the present invention, the carboxylic acid ester includes one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate and ethyl trimethylacetate.

[0043] 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.

[0044] In some preferred embodiments of the present invention, the organic solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

[0045] Specifically, in some embodiments of the present invention, 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. Adding the auxiliary additive to the electrolyte can participate in the film formation process together with the first and second additives, further enhancing the stability of the protective film, thereby further improving the high-temperature storage performance and fast-charge cycle performance of the battery.

[0046] In some preferred embodiments, the cyclic sulfate ester compound includes at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate.

[0047] In some preferred embodiments, the sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone.

[0048] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound represented by the following structural formula 1:

[0049] ;

[0050] 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, and a C1-C5 group.

[0051] In some preferred embodiments, the compound represented by structural formula 1 includes at least one of the following compounds represented by compounds 1-1 to 1-6:

[0052] ;

[0053] In some preferred embodiments, the phosphate compound includes at least one of the compounds represented by the following structural formula 2:

[0054] ;

[0055] In the structural formula 2, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number of 1 to 3; more preferably, the compound shown in structural formula 2 includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0056] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0057] Specifically, in some embodiments of the present invention, based on the total mass of the non-aqueous electrolyte as 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 one of the optional substances 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 a range consisting of any two of these values.

[0058] In some embodiments of the present invention, the separator is located between the positive electrode sheet and the negative electrode sheet.

[0059] In some embodiments of the present invention, the separator can be a conventional separator selected from one or more of a ceramic separator, a polymer separator, a non-woven fabric, and an inorganic-organic composite separator. For example, a single-layer polypropylene (PP) separator, a single-layer polyethylene (PE) separator, a double-layer PP / PE separator, a double-layer PP / PP separator, and a triple-layer PP / PE / PP separator.

[0060] In some embodiments of the present invention, the compaction density of the positive electrode sheet is 2.0 g / cm 3 ~4.4g / cm 3 The compaction density of the negative electrode sheet is 1.0 g / cm 3 ~2.0g / cm 3 .

[0061] In some preferred embodiments of the present invention, the compaction density of the positive electrode sheet is 2.3 g / cm 3 ~4.2g / cm 3 The compaction density of the negative electrode sheet is 1.4 g / cm 3 ~1.8g / cm 3 .

[0062] In some embodiments of the present invention, the double-sided density of the positive electrode sheet is 20 mg / cm 2 ~70mg / cm 2 The double-sided density of the negative electrode sheet is 10 mg / cm 2 ~35mg / cm 2 .

[0063] In some preferred embodiments of the present invention, the double-sided density of the positive electrode sheet is 30 mg / cm 2 ~50mg / cm 2 The double-sided density of the negative electrode sheet is 15 mg / cm 2 ~30mg / cm 2 .

[0064] Specifically, in some embodiments of the present invention, the positive electrode sheet further includes a positive electrode current collector, the positive electrode material layer is located on both sides of the positive electrode current collector, and the positive electrode current collector includes an electron-conducting metal material. Preferably, the positive electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0065] In some embodiments of the present invention, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor, and the positive electrode active material, the positive electrode binder and the positive electrode conductor are blended to obtain the positive electrode material layer.

[0066] Based on the total mass of the positive electrode material layer being 100%, the mass percentage of the positive electrode binder is 0.5% to 3%, and the mass percentage of the positive electrode conductor is 0.5% to 3%.

[0067] In some embodiments of the present invention, the positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; sodium hydroxymethyl cellulose; polyvinyl butyral; an ethylene-vinyl acetate copolymer; polyvinyl alcohol; and one or more of styrene butadiene rubber.

[0068] In some embodiments of the present invention, the positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0069] 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.

[0070] In some preferred embodiments of the present invention, the carbon-based negative electrode comprises one or more of graphite, hard carbon, soft carbon, graphene, and mesocarbon microbeads. The graphite coating is selected from one or more of natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. The natural graphite is scaly graphite, flake graphite, soil graphite, and / or graphite particles obtained by using these graphites as raw materials and subjecting them to spheroidization, densification, and other treatments.

[0071] The artificial graphite is obtained by graphitizing organic substances such as coal tar pitch, coal-based heavy crude oil, atmospheric residue, petroleum-based heavy crude oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at high temperature.

[0072] The amorphous carbon may be amorphous carbon particles obtained by heat-treating a graphitizable carbon precursor such as tar or pitch at a temperature range where graphitization does not occur (400° C. to 2200° C.) or more, or amorphous carbon particles obtained by heat-treating a non-graphitizable carbon precursor such as resin.

[0073] The carbon-coated graphite can be a mixture of natural graphite and / or artificial graphite with a carbon precursor such as tar, pitch, or a resin, and subjected to heat treatment at a temperature of 400° C. to 2300° C. The obtained natural graphite and / or artificial graphite is used as core graphite and coated with amorphous carbon to obtain a carbon-graphite composite. The carbon-graphite composite can be a form in which the entire or partial surface of the core graphite is coated with amorphous carbon, or a form in which a plurality of primary particles are composited using carbon derived from the carbon precursor as a binder. In addition, a hydrocarbon gas such as benzene, toluene, methane, propane, or an aromatic volatile component can be reacted with natural graphite and / or artificial graphite at a high temperature to deposit carbon on the graphite surface to obtain a carbon-graphite composite.

[0074] The graphite-coated graphite can be obtained by mixing natural graphite and / or artificial graphite with a carbon precursor of an easily graphitizable organic compound such as tar, pitch, or resin, and subjecting the mixture to one or more heat treatments at a temperature of about 2400° C. to 3200° C. The obtained natural graphite and / or artificial graphite is used as core graphite, and the entire or partial surface of the core graphite is coated with a graphitized material to obtain the graphite-coated graphite.

[0075] The resin-coated graphite can be obtained by mixing natural graphite and / or artificial graphite with a resin, drying the mixture at a temperature below 400°C, and using the resulting natural graphite and / or artificial graphite as core graphite, which is then coated with a resin. The organic compounds such as tar and asphalt resin are selected from one or more carbonizable organic compounds selected from coal-based heavy crude oil, direct current heavy crude oil, decomposed petroleum heavy crude oil, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenylene, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins.

[0076] Specifically, in some embodiments of the present invention, the negative electrode material layer further includes a negative electrode binder, a negative electrode conductor, 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 and will not be described in detail here. The negative electrode binder and negative electrode conductor can be the same as those of the positive electrode binder and positive electrode conductor, respectively, and will not be described in detail here.

[0077] In the lithium-ion battery provided by the present invention, when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the difluorophosphate ion in the non-aqueous electrolyte, the molar ratio c of Ni to Fe in the positive electrode material layer, and the D90 / D50 ratio d of the positive electrode material meet the following conditions: , and 0.01≤a≤0.8, 0.01≤b≤1, 0.5≤c≤200, 1.2≤d≤20, can fully exert the synergistic effect of the two additive film-forming components to form a highly stable and tough positive electrode interface film, matching the compounded positive electrode material dominated by ternary, thereby achieving both low impedance and high rate cycle performance. DETAILED DESCRIPTION

[0078] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0079] Example 1

[0080] The method for preparing a lithium-ion battery in this embodiment includes the following steps:

[0081] 1. Preparation of positive electrode

[0082] The positive electrode active material (nickel-containing material LiNi 0.8 Co 0.1 Mn 0.1 A mixture of O2 and LiFePO4 (a phosphate material, wherein the ratio of the molar number of the nickel-containing material to the total molar number of the nickel-containing material and the phosphate material is 0.8) is mixed with N-methylpyrrolidone (NMP) solvent, and polyvinylidene fluoride (PVDF) is added as a binder. The mixture is thoroughly stirred to obtain a PVDF glue. A composite system of super carbon black and carbon nanotubes (super P+CNT) is added to the PVDF glue as a conductive agent and thoroughly stirred. The mass ratio of the positive electrode active material, binder, and conductive agent is 94:3:3. The prepared positive electrode slurry is evenly coated on aluminum foil and dried, rolled, die-cut, or slit to obtain a positive electrode sheet. The molar ratio of Ni to 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.

[0083] 2. Preparation of negative electrode sheet

[0084] (1) Weigh the materials 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).

[0085] (2) First, add CMC into pure water at a solid content of 1.5%, stir thoroughly, and prepare a transparent CMC glue.

[0086] (3) Add conductive carbon (super P) to the CMC glue solution and stir thoroughly to prepare the conductive glue.

[0087] (4) Continue to add graphite and stir thoroughly to obtain the required negative electrode slurry.

[0088] (5) The prepared negative electrode slurry is evenly coated on the copper foil, and the negative electrode sheet is obtained by drying, rolling, die-cutting or striping.

[0089] 3. Preparation of non-aqueous electrolyte

[0090] Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 1:1:1. Compound 1 and lithium difluorophosphate were added as additives, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. The mass percentage of Compound 1 in the non-aqueous electrolyte was 0.45%, and the mass percentage of lithium difluorophosphate was 0.5%.

[0091] 4. Lithium-ion battery cell preparation

[0092] The prepared positive electrode sheet and the negative electrode sheet are assembled into a laminated soft-pack battery cell.

[0093] 5. Battery injection and formation

[0094] In a glove box maintained at a dew point below -40°C, the prepared electrolyte was injected into the cell, vacuum-sealed, and left to rest for 72 hours. The cells were then subjected to conventional formation for the first charge, following the following steps: 180 minutes of constant-current charging at 0.05C, 120 minutes of constant-current charging at 0.1C, and 120 minutes of constant-current charging at 0.2C. The cells were then vacuum-sealed again, followed by a further full charge at 0.2C (100% SOC). After 72 hours of storage at room temperature, the cells were fully discharged at 0.2C (0% SOC).

[0095] Examples 2 to 26 and Comparative Examples 1 to 22

[0096] This embodiment and comparative example are used to compare and illustrate the lithium-ion battery disclosed in the present invention, including most of the operating steps in the above-mentioned embodiment 1. The differences are as follows: the type of positive electrode active material, the mixing molar ratio of the nickel-containing material in the positive electrode active material, the molar ratio of Ni to 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.

[0097] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to the following performance tests:

[0098] (1) High temperature 3C / 3C cycle performance test

[0099] At 45°C, the lithium-ion batteries prepared in the Examples and Comparative Examples were charged at a constant current and constant voltage rate of 1C (cut-off current 0.05C) within the conventional voltage range of the composite cathode battery system (usually 2.5-4.2V), and discharged at a rate of 1C for three cycles, with the capacity of the last cycle being used as the initial 100% SOC capacity. After being fully charged at a constant current and constant voltage rate of 3C, the battery was discharged at a rate of 3C. Full charge and discharge cycles were performed within the charge and discharge cut-off voltage commonly used for the corresponding system. After 500 charge / discharge cycles, the impedance growth rate at the 500th cycle was calculated. The number of cycles was then recorded until the capacity of the lithium-ion battery decayed to 80% of the initial capacity.

[0100] Impedance growth rate after the 500th cycle (%) = (internal resistance after the 500th cycle - initial internal resistance before the cycle) / initial internal resistance before the cycle × 100%; the test procedure for internal resistance is the same as the following "internal resistance test at 0°C", except that the temperature is 45°C.

[0101] Internal resistance test at 0℃:

[0102] At room temperature (25°C), charge the battery with constant current to 50% of the battery capacity, then adjust the temperature to 0°C and maintain it for 6 hours.

[0103] Charge at 0.1C constant current for 10s and then rest for 40s; discharge at 0.1C constant current for 10s and then rest for 40s, and record the end voltage V1;

[0104] Charge at 0.2C constant current for 10s and then rest for 40s; discharge at 0.2C constant current for 10s and then rest for 40s, and record the end voltage V2;

[0105] Charge at 0.5C constant current for 10s and then rest for 40s; discharge at 0.5C constant current for 10s and then rest for 40s, and record the termination voltage V3.

[0106] Draw a straight line with current as the horizontal axis and voltage as the vertical axis. The slope of the straight line is the 0°C impedance.

[0107] Test results:

[0108] As shown in Table 1, the parameters required for preparing lithium-ion batteries in Examples 1 to 19 and Comparative Examples 1 to 19 are shown; the differences between Examples 2 to 19 and Comparative Examples 1 to 19 and Example 1 are the relevant parameters in Table 1, specifically the following: nickel-containing material type, phosphate material type, molar ratio of nickel-containing material in the composite positive electrode, mass percentage a (%) of the first additive, mass percentage b (%) of difluorophosphate ions, molar ratio c of Ni / Fe in the positive electrode material layer, ratio d of D90 / D50 of the composite material, and The remaining parameters and preparation steps are the same as those described in Example 1.

[0109] Table 2 shows the performance test results of the lithium-ion batteries prepared in Examples 1 to 19 and Comparative Examples 1 to 19.

[0110] Table 1

[0111] ; ;

[0112] Note: “ / ” in the table means that there is no such item.

[0113] Table 2

[0114] ;

[0115] The test results of Examples 1 to 19 and Comparative Examples 1 to 19 show that the lithium-ion battery provided by the present invention adopts a positive electrode system comprising a nickel-containing material and a phosphate material, and uses a first additive and difluorophosphate ions as additives in a non-aqueous electrolyte. At the same time, the mass percentage a of the first additive, the mass percentage b of the 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 are limited to satisfy the relationship: ; and when 0.01≤a≤0.8, 0.01≤b≤1, 0.5≤c≤200, and 1.2≤d≤20, a lithium-ion battery having both low impedance and high rate cycle performance can be obtained.

[0116] From the test results of Example 1 and Comparative Examples 1 to 19, it can be seen that when any one of the parameters of the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the difluorophosphate ion, 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 relationship If the value 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 tough positive electrode interface film cannot be formed, resulting in the inability to achieve both low impedance and high rate cycle performance of lithium-ion batteries.

[0117] When the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the difluorophosphate ion, 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 when 0.05≤a≤0.5, 0.05≤b≤0.5, 0.5≤c≤30, and 2≤d≤12, the difluorophosphate ions form a high LiF inorganic film component, which has a better film-forming protection effect on high-nickel materials. 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 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 meet the above relationship.

[0118] Table 3 shows the performance test results of the lithium-ion batteries prepared in Example 1 and Examples 20 to 23. The difference between Examples 20 to 23 and Example 1 lies in the type of the first additive shown in Table 3. The remaining parameters and preparation steps are the same as those described in Example 1.

[0119] Table 3

[0120]

[0121] From the results of the measurement in Table 3, it can be seen that when the mass percentage of the first additive a, the mass percentage of the difluorophosphate ion b, the molar ratio of Ni and Fe in the positive electrode material layer c, the D90 / D50 ratio d of the positive electrode material and the relationship When the relevant requirements are met, adding any one of Compounds 1 to 5 as the first additive can enable the lithium-ion battery to have both low impedance and high-rate cycle performance, indicating that the battery system of the present invention is universal for different types of first additives.

[0122] 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 are the mass percentage (%) of the first additive, the mass percentage b (%) of difluorophosphate ions, and the auxiliary additives and their contents shown in Table 4. The remaining parameters and preparation steps are the same as those described in Example 1.

[0123] Table 4

[0124] ;

[0125] Note: “ / ” in the table means that there is no such item.

[0126] From the results of the measurement in Table 4, it can be seen that when the mass percentage of the first additive a, the mass percentage of the difluorophosphate ion b, the molar ratio of Ni and Fe in the positive electrode material layer c and the D90 / D50 ratio d of the positive electrode material and the relationship When relevant requirements are met, adding different types of auxiliary additives can enable lithium-ion batteries to have both low impedance and high-rate cycle performance, indicating that the battery system of the present invention is universal for different auxiliary additives.

[0127] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by 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 includes a positive electrode material layer containing a positive electrode material, wherein the positive electrode material refers to all materials contained in the positive electrode material layer, including a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; the positive electrode active material includes a mixture of a nickel-containing material and a phosphate material; 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; 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 the 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, and Ce, and R includes one or more of N, F, S, and Cl; 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 the 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; The non-aqueous electrolyte includes additives, lithium salt and 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, 0.1≤b≤0.5, 0.5≤c≤30, 5≤d≤12; a is the mass percentage of the first additive in the non-aqueous electrolyte, in %; b is the mass percentage of difluorophosphate ions in the non-aqueous electrolyte, unit is %; c is the molar ratio of Ni to 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, wherein The lithium-ion battery meets the following conditions: .

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

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

5. The lithium-ion battery according to claim 1, wherein The non-aqueous electrolyte further includes an auxiliary additive; 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.

6. The lithium-ion battery according to claim 5, wherein 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, vinyl ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound represented by the following structural formula 1: ； In the structural formula 1 shown, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 are each 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 C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, 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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