Lithium ion battery

Abstract

In order to solve the problems that Fe ions are dissolved out and battery performance is affected in an existing lithium iron phosphate / lithium iron manganese phosphate battery, the invention provides a lithium ion battery, the lithium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode comprises a positive electrode material layer containing a positive electrode active material, and the non-aqueous electrolyte is arranged in the thickness direction of the positive electrode material layer. The projection of the positive electrode material layer on the negative electrode is located in the coverage range of the negative electrode material layer, and the positive electrode active material comprises a phosphate material coated and / or doped with a Ti element; the non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt and an additive, the additive comprises a first additive, and the first additive comprises a compound as shown in a structural formula 1; the lithium ion battery meets the following conditions: 0.3 < = a < = 5, 1.2 < = b < = 2.8, 0.05 < = c < = 2, and 0.1 < = d < = 0.8.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic components, and particularly relates to a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have outstanding advantages such as high energy density, long cycle life, high working voltage, low self-discharge rate and environmental friendliness, and can be used as an ideal power supply for multiple purposes.

[0003] Lithium iron phosphate is widely used in power and energy storage batteries, and its high safety and long cycle stability are relatively outstanding among various positive electrode materials. Considering the ultra-long service life (8-10 years) of automobiles and energy storage batteries, higher demands for the service life (≥10000 cycles), energy density (≥180Wh / kg) and safety performance of lithium iron phosphate batteries have been put forward in recent years, but existing lithium iron phosphate batteries are difficult to meet these demands.

[0004] In particular, the dissolution of Fe ions in the lithium iron phosphate positive electrode during the charging and discharging cycle of the battery leads to the destruction of the crystal structure of the positive active material, the capacity of the battery decreases, and the dissolved Fe ions are deposited on the negative electrode to form metal dendrites, which causes the self-discharge problem of the battery. Due to the high electric field strength and lithium ion concentration change rate at the edge of the negative electrode, metal dendrites are more likely to occur, and serious metal dendrites can cause short circuit of the battery, thereby causing safety problems. It is difficult to balance the service life, energy density and safety performance by only optimizing the electrode plate design or electrolyte. SUMMARY

[0005] In view of the problem that the existing lithium iron phosphate / lithium iron manganese phosphate battery has Fe ion dissolution, which affects the performance of the battery, the application provides a lithium ion battery.

[0006] The technical scheme adopted by the application to solve the above technical problems is as follows: The application provides a lithium ion battery, which comprises a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive active material comprises a phosphate material coated and / or doped with Ti elements, and the mass percentage content of Ti elements in the positive electrode material layer is d%; The negative electrode comprises a negative electrode material layer containing a negative active material, and the ratio of the double-sided area density of the positive electrode material layer to the negative electrode material layer is b; Along the thickness direction of the positive electrode material layer, the projection of the positive electrode material layer on the negative electrode is located within the coverage range of the negative electrode material layer, and the distance between the edge of the negative electrode material layer and the edge of the positive electrode material layer is a mm; The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and an additive, the additive comprises a first additive, the first additive comprises a compound shown in structural formula 1: Structural formula 1 Wherein, X is selected from Or R1, R2 are each independently selected from H, Or R1 and R2 are not simultaneously selected from H, and at least one of X, R1 and R2 contains a sulfur atom; The mass percentage content of the first additive is c% based on the mass of the non-aqueous electrolyte; The lithium ion battery satisfies the following conditions: And 0.3≤a≤5, 1.2≤b≤2.8, 0.05≤c≤2, 0.1≤d≤0.8.

[0007] Optionally, the lithium ion battery satisfies the following conditions: 5.

[0008] Optionally, the distance a mm that the edge of the negative electrode material layer exceeds the edge of the positive electrode material layer satisfies: 1≤a≤3.5.

[0009] Optionally, the double-sided area density of the positive electrode material layer is 350~800g / m 2 ; and / or The double-sided area density of the negative electrode material layer is 150~350g / m 2 ; and / or The ratio b of the double-sided area density of the positive electrode material layer to the negative electrode material layer satisfies: 1.5≤b≤2.5.

[0010] Optionally, the mass percentage content c% of the first additive in the non-aqueous electrolyte satisfies: 0.1≤c≤1.

[0011] Optionally, the mass percentage content d% of Ti element in the positive electrode material layer satisfies: 0.2≤d≤0.6.

[0012] Optionally, the compound shown in structural formula 1 comprises at least one of the following compounds: .

[0013] Optionally, the additive further comprises a second additive, the second additive comprises at least one of vinyl sulfate, methane disulfonic acid methylene ester, 1,3-propane sulfolane, vinyl sulfite, and 1,4-butane sulfonic acid lactone; The mass percentage of the second additive is e% based on the mass of the nonaqueous electrolyte, and the lithium ion battery satisfies the following conditions: 0.1≤c+e≤3, 0.1≤d / (c+e)≤5, and 0.01≤e≤2.

[0014] Optionally, the lithium ion battery satisfies at least one of the following conditions: (1) 0.2≤c+e≤2 (2) 0.2≤d / (c+e)≤2.5 (3) 0.1≤e≤1 (4) 0.1≤c≤1 (5) 0.2≤d≤0.6.

[0015] Optionally, the phosphate material includes at least one of Li r Mn α Fe β A 1-α-β PO 4-n G n and Li r Mn α Fe β A’ 1-α-β PO 4-n G n coated with Ti-containing oxide on the surface, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0≤n≤0.1, A includes Ti and zero, one or more of Mg, V, Cr, Zr, Nb, Zn, Al, Na, K, Mo, W, Ni, Co, Ga, Sn, Sb, Ge and W, A’ includes zero, one or more of 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.

[0016] The lithium ion battery provided by the application uses a phosphate material coated and / or doped with Ti elements as a positive electrode active material, the negative electrode sheet is designed in excess, the double-face area density of the positive electrode material layer and the negative electrode material layer is matched, and a first additive is added to the nonaqueous electrolyte, and the inventors have found that when the distance a between the edge of the negative electrode material layer and the edge of the positive electrode material layer, the ratio b of the double-face area density of the positive electrode material layer and the negative electrode material layer, the mass percentage c of the first additive in the nonaqueous electrolyte, and the mass percentage d of Ti elements in the positive electrode material layer satisfy the conditions When the lithium ion battery is obtained, the long cycle life, the high energy density and the optimal safety performance can be considered, which is speculated to be due to the fact that the first additive is decomposed on the surface of the negative electrode under the electrochemical action during the battery formation process, and participates in the formation of the solid electrolyte interface film on the surface of the negative electrode. The stability of the solid electrolyte interface film at the edge position of the negative electrode has a great influence on the anti-metal dendrite effect. The excess control of the edge of the negative electrode material layer (the distance a between the edge of the negative electrode material layer and the edge of the positive electrode material layer) can affect the active lithium supply and the current density at the edge position of the negative electrode in the formation stage, and further affect the solid electrolyte interface film density at the position. Similarly, the ratio of the double surface density of the positive electrode material layer and the negative electrode material layer also affects the solid electrolyte interface film density and stability at the edge of the negative electrode. On this basis, the phosphate material coated or doped with Ti element can improve the stability and cycle life of the phosphate material, reduce the dissolution of Fe ions, and also can use a smaller excess design to make the battery have a high energy density. Therefore, by controlling the distance a between the edge of the negative electrode material layer and the edge of the positive electrode material layer, the ratio b of the double surface density of the positive electrode material layer and the negative electrode material layer, the mass percentage content c of the first additive in the non-aqueous electrolyte, and the mass percentage content d of Ti element in the positive electrode material layer under the synergistic condition, the film stability of the solid electrolyte interface film formed by the first additive on the surface of the negative electrode, especially at the edge thereof, can be improved, the metal dendrite probability at the edge of the negative electrode can be reduced, and the design of the electrode sheet can be better matched, so that the battery has good cycle performance, the safety performance of the battery is improved, and the energy density, the safety performance and the cycle performance of the lithium ion battery can be effectively considered. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0018] In the embodiments of the present application, the qualitative and quantitative detection of each substance or each element can be carried out by using suitable devices and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc., and those skilled in the art can also adaptively change certain detection steps / instrument parameters from the perspective of detection accuracy, in order to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used jointly for qualitative or quantitative determination.

[0019] In the embodiments of the present application, the detection method of the types and contents of the first additive and the second additive in the non-aqueous electrolyte is known in the art, and the known equipment and method in the art can be used for detection, for example, the qualitative and quantitative analysis of the organic components in the electrolyte can be performed by gas chromatography according to GB / T 9722-2006 "Chemical Reagents-General Gas Chromatography". In the embodiments of the present application, the newly prepared electrolyte can be taken as a sample, or the free electrolyte obtained from the battery after reverse disassembly of the battery with a charged state of about 0% SOC can be taken as a sample, and the gas chromatography analysis method is used for detection.

[0020] In the embodiments of the present application, the double-sided area density of the positive electrode material layer is the meaning known in the art, and the method known in the art can be used for testing. The positive electrode material layer comprises positive electrode active material, conductive agent, binder and other components. Double-sided area density = double-sided positive electrode material layer weight / positive electrode material layer coverage area, wherein the double-sided positive electrode material layer weight = average weight of the electrode sheet-average weight of the current collector, because the current collector has positive electrode material layer on both sides. The specific testing process is as follows: a double-sided coated and cold-pressed positive electrode sheet is cut into a small round sheet with an area of S1, and the weight is weighed and recorded as M1. Then, the positive electrode material layer of the above weighed positive electrode sheet is wiped off, the weight of the positive electrode current collector is weighed and recorded as M0, and the double-sided area density of the positive electrode material layer = (weight of the positive electrode sheet M1-weight of the positive electrode current collector M0) / S1. The testing process of the double-sided area density of the negative electrode material layer is the same as that of the double-sided area density of the positive electrode material layer, which is not described here. The "average" here can be the average value after 5 parallel tests.

[0021] In the embodiments of the present application, the content of each element (such as Ti element) in the positive electrode material layer can be tested by the method known in the art. For example, a newly prepared battery or a battery after reverse disassembly of the battery with a charged state of about 0% SOC can be taken, the positive electrode material layer coated on the positive electrode current collector is scraped as a sample, and then the sample is dissolved in aqua regia, and the element analysis is performed by inductively coupled plasma emission spectrometry (ICP, Thermo Fisher, model: iCAP 7400) to obtain the proportion of each element. Through the proportion of each element, the chemical formula of the phosphate material and the content of the Ti element are determined.

[0022] The embodiments of the present application provide a lithium ion battery, which comprises a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive electrode comprises a positive electrode material layer containing positive electrode active material, and the positive electrode active material comprises a phosphate material coated and / or doped with Ti element, and the mass percentage content of the Ti element in the positive electrode material layer is d%. The negative electrode includes a negative electrode material layer containing a negative electrode active material, and the ratio of the double-sided areal density of the positive electrode material layer to that of the negative electrode material layer is b. Along the thickness direction of the positive electrode material layer, the projection of the positive electrode material layer onto the negative electrode is located within the coverage area of ​​the negative electrode material layer, and the distance by which the edge of the negative electrode material layer extends beyond the edge of the positive electrode material layer is a mm; The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and additives, wherein the additives include a first additive, which comprises a compound shown in structural formula 1: Structural Formula 1 Where X is selected from or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; Based on the mass of the non-aqueous electrolyte, the mass percentage of the first additive is c%; The lithium-ion battery meets the following conditions: And 0.3≤a≤5, 1.2≤b≤2.8, 0.05≤c≤2, 0.1≤d≤0.8.

[0023] The inventors discovered that when the following conditions are met: a) the distance a from the edge of the negative electrode material layer to the edge of the positive electrode material layer; b) the ratio of the areal density of the positive electrode material layer to the negative electrode material layer; c) the mass percentage of the first additive in the non-aqueous electrolyte; and d) the mass percentage of Ti element in the positive electrode material layer, the following conditions are met: The resulting lithium-ion battery achieves a balance between long cycle life, high energy density, and superior thermal safety performance. This is presumably due to the first additive decomposing on the negative electrode surface during battery formation under electrochemical action, participating in the formation of a solid electrolyte interfacial film (SEIA) on the negative electrode surface. The stability of the SEIA at the negative electrode edge significantly impacts its resistance to metal dendrite formation. Excessive control over the edge of the negative electrode material layer (the distance *a* between the edge of the negative electrode material layer and the edge of the positive electrode material layer) affects the active lithium supply and current density at the negative electrode edge during formation, thus affecting the density of the SEIA at that location. Similarly, the ratio of the areal density of the positive electrode material layer to that of the negative electrode material layer also affects the density and stability of the SEIA at the negative electrode edge. Furthermore, the addition of Ti coating or doping further contributes to this effect. Phosphate materials containing elements can improve the stability and cycle life of phosphate materials, reduce the dissolution of Fe ions, and allow for a smaller excess design, resulting in higher energy density in the battery. Therefore, by controlling the distance (a) of the edge of the negative electrode material layer beyond the edge of the positive electrode material layer, the ratio of the areal density of the positive and negative electrode material layers (b), the mass percentage of the first additive in the non-aqueous electrolyte (c), and the mass percentage of Ti element in the positive electrode material layer (d) under synergistic conditions, the film-forming stability of the solid electrolyte interface film formed by the first additive on the negative electrode surface, especially at its edge, can be improved, the probability of metal dendrites at the negative electrode edge can be reduced, and the electrode design can be better matched, resulting in better cycle performance and improved battery safety. This effectively balances the energy density, safety, and cycle performance of lithium-ion batteries.

[0024] In a preferred embodiment, the lithium-ion battery satisfies the following conditions: .

[0025] When the following conditions are met: the distance a from the edge of the negative electrode material layer to the edge of the positive electrode material layer; the ratio b of the areal density of the positive electrode material layer to the negative electrode material layer; the mass percentage content c of the first additive in the non-aqueous electrolyte; and the mass percentage content d of Ti element in the positive electrode material layer, it is beneficial to further reduce the probability of metal dendrites at the edge of the negative electrode and improve the safety and cycle performance of lithium-ion batteries.

[0026] In a specific embodiment, the distance 'a' from the edge of the negative electrode material layer to the edge of the positive electrode material layer can be any two of the following: 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.3 mm, 2.5 mm, 2.8 mm, 3 mm, 3.2 mm, 3.5 mm, 3.8 mm, 4 mm, 4.2 mm, 4.5 mm, 4.8 mm, 5 mm, or more.

[0027] In a preferred embodiment, the distance a mm from the edge of the negative electrode material layer to the edge of the positive electrode material layer satisfies: 1 ≤ a ≤ 3.5.

[0028] In the description of this invention, it should be understood that "the distance a from the edge of the negative electrode material layer to the edge of the positive electrode material layer" is the absolute value of the distance between the edge of the projection of the positive electrode material layer onto the negative electrode and the edge of the negative electrode material layer along the thickness direction of the positive electrode material layer, and the distance between the edge of the projection of the positive electrode material layer onto the negative electrode and the edge of the negative electrode material layer is the shortest distance between the two.

[0029] To improve battery safety, the negative electrode is designed to extend beyond the edge of the positive electrode material layer in both length and width. When the distance *a* by which the edge of the negative electrode material layer extends beyond the edge of the positive electrode material layer is too small, the negative electrode lacks a suitable location to receive lithium and Fe ions. These ions easily precipitate on the surface of the negative electrode, forming metal dendrites. These dendrites may pierce the separator, causing an internal short circuit and posing a safety risk. However, when the distance *a* by which the edge of the negative electrode material layer extends beyond the edge of the positive electrode material layer is too large, the battery's energy density decreases. Furthermore, it leads to insufficient active lithium concentration at the edge of the negative electrode material layer during the formation stage, resulting in decreased density and stability of the solid electrolyte interface film at the edge.

[0030] In some embodiments, the double-sided areal density of the positive electrode material layer is 350~800 g / m³. 2 .

[0031] In a specific embodiment, the bifacial areal density of the positive electrode material layer can be 350 g / m². 2 380g / m 2 410g / m 2 440g / m 2 470g / m 2 500g / m 2 530g / m 2 560g / m 2 590g / m 2 620g / m 2 650g / m 2 680g / m 2 710g / m 2 740g / m 2 770g / m 2 800g / m 2 Or a range between any two of the above.

[0032] In some embodiments, the double-sided areal density of the negative electrode material layer is 150~350 g / m³. 2 .

[0033] In a specific embodiment, the double-sided areal density of the negative electrode material layer can be 150 g / m². 2 170g / m 2 190g / m 2 210g / m 2 230g / m 2 250g / m 2 270g / m 2 290g / m 2 310g / m 2 330g / m 2 350g / m 2 Or a range between any two of the above.

[0034] In a specific embodiment, the ratio b of the bifacial density of the positive electrode material layer and the negative electrode material layer can be any two of the following: 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8.

[0035] In a preferred embodiment, the ratio b of the bifacial areal density of the positive electrode material layer and the negative electrode material layer satisfies: 1.5 ≤ b ≤ 2.5.

[0036] The ratio 'b' of the bifacial areal density of the positive electrode material layer to the negative electrode material layer represents the relationship between the lithium ions that the negative electrode can accept and the lithium ions that are extracted from the positive electrode. During battery charging and discharging, active lithium ions from the positive electrode are extracted and inserted into the negative electrode, simultaneously participating in the formation of the solid electrolyte interface film at the negative electrode. If the bifacial areal density ratio of the positive electrode material layer to the negative electrode material layer is too large, on the one hand, the lithium ions extracted from the positive electrode material layer cannot be completely inserted into the negative electrode material layer, leading to metal dendrites and affecting battery safety performance; on the other hand, it leads to a longer lithium ion transport distance, resulting in poorer battery kinetic performance and affecting battery cycle life. If the bifacial areal density ratio of the positive electrode material layer to the negative electrode material layer is too small, on the one hand, there is too much excess negative electrode material, affecting the battery's energy density; and on the other hand, under the same conditions, the increased density of the negative electrode material layer is detrimental to the battery's fast charging performance.

[0037] In a specific embodiment, the mass percentage c% of the first additive in the non-aqueous electrolyte can be any two of the following: 0.05%, 0.08%, 0.1%, 0.2%, 0.4%, 0.5%, 0.7%, 0.8%, 1.0%, 1.1%, 1.3%, 1.5%, 1.8%, 2.0%.

[0038] In a preferred embodiment, the mass percentage c% of the first additive in the non-aqueous electrolyte satisfies: 0.1 ≤ c ≤ 1.

[0039] During the battery formation stage, the first additive, together with active lithium, forms a solid electrolyte interface film on the surfaces of the positive and negative electrodes. This film helps to suppress the dissolution of Fe ions from the positive electrode active material and the formation of metal dendrites on the negative electrode. If the mass percentage of the first additive in the non-aqueous electrolyte is too low, it is not conducive to the formation of a stable solid electrolyte interface film on the surfaces of the positive and negative electrodes, leading to the dissolution of elements such as Fe from the positive electrode active material and the formation of metal dendrites on the negative electrode. In addition, the dissolved Fe ions will migrate through the separator to the surface of the negative electrode, causing strong side reactions in the electrolyte, damaging the SEI of the negative electrode, and degrading the battery cycle life. If the mass percentage of the first additive in the non-aqueous electrolyte is too high, it will result in an excessively thick solid electrolyte interface film, increasing the battery impedance. Therefore, when the mass percentage of the first additive in the non-aqueous electrolyte is within the above-mentioned range, it is beneficial to form a stable solid electrolyte interface film on the surfaces of the positive and negative electrodes, improving the battery cycle performance.

[0040] In a specific embodiment, the mass percentage d% of Ti element coated or doped in the positive electrode material layer can be any two of the following: 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, or more.

[0041] In a preferred embodiment, the mass percentage d% of Ti element in the positive electrode material layer satisfies: 0.2≤d≤0.6.

[0042] Doping or coating phosphate materials with an appropriate amount of Ti can enhance the structural stability of phosphates, reduce the dissolution of Fe ions, significantly improve battery safety, and avoid risks such as spontaneous combustion and explosion. If the Ti content in the phosphate material is too low, it will not be conducive to suppressing the corrosion of lithium iron phosphate by hydrofluoric acid, causing Fe ion dissolution. At the same time, the accumulation of interfacial reaction byproducts such as lithium fluoride will increase the CEI thickness, negatively affecting the interfacial lithium ion insertion / extraction process, and thus causing gradual capacity decay. When the Ti content in the cathode material layer is too high, although it makes the structural stability of lithium iron phosphate better during charge and discharge, it will seriously affect the conductivity and ion diffusion rate of the material. On the one hand, it will affect the kinetic performance of the battery, and in severe cases, it may even lead to lithium plating during charge and discharge, affecting the battery's safety performance. On the other hand, it will affect the battery's energy density. Therefore, when the Ti content coated or doped in the cathode material layer is controlled within the above range, it is beneficial for the battery to balance energy density, cycle performance, and safety performance. This invention effectively reduces the adverse effects of Fe leaching from the cathode on the stability of the cathode active material and non-aqueous electrolyte by forming a highly stable interfacial film on the surface of the phosphate material with the synergistic effect of the first additive and the doping or coating of an appropriate amount of Ti element on the phosphate cathode material.

[0043] In some embodiments, in the compound represented by structural formula 1, X is selected from... or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom, and X, R1 and R2 do not contain sulfur atoms at the same time.

[0044] As an example, the first additive is selected from one or more of the following compounds: The first additive includes both sulfur-containing cyclic structures and carbonate-containing cyclic structures. The interfacial film component formed by the combination of carbonate cyclic structures and sulfur-containing cyclic structures is more stable and dense.

[0045] In some embodiments, in the compound represented by structural formula 1, X is selected from... R1 and R2 are each independently selected from H or R1 and R2 are not both selected from H.

[0046] As an example, the first additive is selected from one or more of the following compounds: The first additive has a polycyclic structure. Compared with the monocyclic structure of vinyl sulfate, the polycyclic structure allows each ring to open and participate in the formation of the interface film on the electrode surface. The resulting interface film is more stable and dense, which can improve the strength of the interface film structure and thus help improve its high-temperature stability.

[0047] In some embodiments, the additive further includes a second additive, the second additive comprising at least one of vinyl sulfate, methylene methane disulfonate, 1,3-propane sulpholactone, vinyl sulfite, and 1,4-butane sulpholactone. Based on the mass of the non-aqueous electrolyte, the mass percentage of the second additive is e%, and the lithium-ion battery meets the following conditions: 0.1≤c+e≤3, 0.1≤d / (c+e)≤5, and 0.01≤e≤2.

[0048] By further adding a second additive to the aforementioned non-aqueous electrolyte system, a solid electrolyte interface film can be formed on the surfaces of the positive and negative electrodes in synergy with the first additive. The second additive can decompose to form sulfur-containing lithium salt components, further enhancing the stability of the solid electrolyte interface film, inhibiting the dissolution of Fe elements in the positive electrode material layer, further reducing battery side reactions, and significantly suppressing the increase in DC internal resistance during battery cycling and storage. By controlling the content d of Ti elements coated or doped in the phosphate positive electrode material layer, and ensuring that the mass percentage content c of the first additive and the mass percentage content e of the second additive satisfy 0.1≤c+e≤3 and 0.1≤d / (c+e)≤5, the synergistic effect between the first additive, the second additive, and the Ti elements coated or doped in the lithium iron phosphate material layer can be fully utilized. This results in lithium iron phosphate materials exhibiting high structural stability, oxidation resistance, and safety performance, unexpectedly and significantly suppressing the decomposition reaction of the electrolyte after charging, improving battery cycle and safety performance while maintaining high battery energy density.

[0049] In a preferred embodiment, the lithium-ion battery satisfies at least one of the following conditions: (1) 0.2≤c+e≤2 (2) 0.2≤d / (c+e)≤2.5 (3) 0.1≤e≤1 (4) 0.1≤c≤1 (5) 0.2≤d≤0.6.

[0050] In a specific embodiment, the mass percentage e% of the second additive in the non-aqueous electrolyte can be any two of the following: 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.4%, 0.5%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%.

[0051] If the content of the second additive is too low, it will be difficult to form a stable solid electrolyte interface film on the surface of the positive and negative electrode active materials, thus degrading the safety and cycle performance of the battery. If the content of the second additive is too high, it will result in an excessively thick solid electrolyte interface film, increasing the battery impedance and degrading the cycle performance.

[0052] In some embodiments, the additive further includes at least one selected from boron-containing lithium salt compounds, fluorine-containing lithium salt compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds; Preferably, the content of the additive is 0.01% to 30% based on the mass of the non-aqueous electrolyte.

[0053] In some embodiments, the cyclic sulfate compounds include vinyl sulfate, propylene sulfate, and methyl vinyl sulfate. , At least one of them; The boron-containing lithium salt compound includes at least one of LiODFB, LiBOB, and LiBF4; The fluorinated lithium salt compound includes at least one of LiPO2F2, LiFSI, LiTFSI, and LiODFP; The cyclic carbonate compounds include at least one of vinylene carbonate, ethylene ethylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, or the compound shown in structural formula 2. Structural Formula 2 In structural formula 2, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group; The phosphate ester compound includes at least one of tris(trimethylsilane) phosphite or the compound shown in structural formula 3: Structural Formula 3 In structural formula 3, R 31R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, where m is a natural number from 1 to 3; In a preferred embodiment, the phosphate compound represented by structural formula 2 may be at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargyl phosphate, diargylmethyl phosphate, diargylethyl phosphate, diargylpropyl phosphate, diargyltrifluoromethyl phosphate, diargyl-2,2,2-trifluoroethyl phosphate, diargyl-3,3,3-trifluoropropyl phosphate, diargylhexafluoroisopropyl 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. The borate ester compounds include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; The nitrile compounds include at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptacyanide, octadionitrile, nonadionitrile, and sebaconitol.

[0054] In other embodiments, the additive may also include other additives that can improve battery performance: for example, additives that improve battery safety performance, such as flame retardant additives like fluorophosphates and cyclophosphonitriles, or overcharge prevention additives like tert-amylbenzene and tert-butylbenzene.

[0055] It should be noted that, unless otherwise specified, the content of any optional substance in the additive in the non-aqueous electrolyte is generally less than 10%, preferably 0.1%-5%, and more preferably 0.1%-2%. Specifically, the content of any optional substance in the additive can be 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%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0056] In some embodiments, when the auxiliary additive is selected from fluoroethylene carbonate, the content of the fluoroethylene carbonate is 0.05% to 30% based on the mass of the non-aqueous electrolyte.

[0057] In some embodiments, the non-aqueous organic solvent includes one or more of cyclic carbonates, linear carbonates, carboxylic acid esters, and ether solvents.

[0058] In some embodiments, the cyclic carbonate may be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate may be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited and is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of the present invention. However, when using only one type, its content is typically 3% or more, preferably 5% or more, by volume relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, making it easier to achieve good high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. Furthermore, the upper limit is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby contributing to enhanced stability during high-temperature storage. The content of the chain carbonate is not particularly limited, but relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 15% or more by volume, preferably 20% or more, and more preferably 25% or more. Furthermore, it is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less. By keeping the chain carbonate content within the above range, it is easier to achieve an appropriate viscosity for the non-aqueous electrolyte, suppressing the decrease in ionic conductivity, and thus contributing to achieving a good range of output characteristics for the non-aqueous electrolyte battery. When using two or more chain carbonates in combination, it is sufficient to ensure that the total amount of chain carbonate meets the above range.

[0059] In some embodiments, the carboxylic acid ester includes cyclic carboxylic acid esters and / or chain carbonates. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), butyl propionate, and ethyl fluoroacetate.

[0060] In some embodiments, the ether solvent includes cyclic ethers or chain ethers and their fluorinated derivatives, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. Specifically, the cyclic ether may be, but is not limited to, at least one of 1,3-dioxane (DOL), 1,4-dioxane (DD), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ether may be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. Ether compounds can be used alone or in any combination and ratio of two or more. The content of ether compounds is not particularly limited and is arbitrary as long as it does not significantly impair the high areal density lithium-ion battery effect of this invention. Typically, the volume ratio is 1% or more, preferably 2% or more, and more preferably 3% or more when the non-aqueous solvent volume ratio is 100%. Furthermore, the volume ratio is typically 30% or less, preferably 25% or less, and more preferably 20% or less. When using two or more ether compounds in combination, the total amount of ether compounds should meet the above-mentioned range. When the content of ether compounds is within the above-mentioned preferred range, it is easy to ensure the improved ionic conductivity effect resulting from the increased lithium-ion dissociation degree and reduced viscosity of the chain ethers. In addition, when the negative electrode active material is a carbon-based material, the phenomenon of co-intercalation between the chain ethers and lithium ions can be suppressed, thus enabling the input / output characteristics and charge / discharge rate characteristics to reach an appropriate range.

[0061] In some embodiments, the mass content of the non-aqueous organic solvent is 65% to 90% based on the mass of the non-aqueous electrolyte.

[0062] Specifically, based on the mass of the non-aqueous electrolyte, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, 90%, or any combination of these values.

[0063] In some embodiments, the electrolyte salt is selected from lithium salts, and the lithium salt is selected from LiPF6.

[0064] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 8 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or any combination of these values.

[0065] Specifically, in some preferred embodiments of the present invention, the lithium salt includes at least LiPF6. In the non-aqueous electrolyte, the concentration of the lithium salt is 0.1 mol / L to 2 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 1.5 mol / L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, or any combination of these values.

[0066] In some embodiments, the phosphate material includes Li r Mn α Fe β A 1-α-β PO 4-n G n and Li with Ti oxide coating on its surface r Mn α Fe β A' 1-α-β PO 4-n G n At least one of the following, wherein 0.9≤r≤1.1, 0≤α≤0.8, α+β≤1, 0.2≤β≤1, 0≤n≤0.1, A includes Ti, and zero or one or more of Mg, V, Cr, Zr, Nb, Zn, Al, Na, K, Mo, W, Ni, Co, Ga, Sn, Sb, Ge and W, A' includes zero or one or more of 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.

[0067] In some embodiments, 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.

[0068] The positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0069] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0070] In some embodiments, the positive current collector comprises a metallic material capable of conducting electrons. Preferably, the positive current collector comprises at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0071] In some embodiments, the negative electrode active material includes at least one of carbon-based, silicon-based, tin-based, and lithium-based negative electrodes. Carbon-based negative electrodes may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; silicon-based negative electrodes may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; tin-based negative electrodes may include tin, tin-carbon, tin-oxygen, and tin metal compounds; lithium-based negative electrodes may include metallic lithium or lithium alloys. Specifically, lithium alloys may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0072] In a more preferred embodiment, the negative electrode active material includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, mesophase microcarbon spheres, silicon, silicon oxide, silicon-carbon composites, or metallic lithium.

[0073] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0074] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector includes a metallic material capable of conducting electrons. Preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0075] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0076] The negative electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0077] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0078] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0079] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0080] The present invention will be further illustrated by the following examples.

[0081] Table 1 - Lithium-ion battery implementation conditions for Examples 1-26 and Comparative Examples 1-13 Continued from Table 1 Example 1 This embodiment illustrates the lithium-ion battery and its preparation method disclosed in this invention, including the following operations: 1) Preparation of non-aqueous electrolyte: Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:EMC = 3:7. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. Based on the total weight of the non-aqueous electrolyte (100%), the first and second additives shown in Table 1 were added.

[0082] 2) Preparation of the positive electrode plate: The positive electrode active material, conductive carbon black (Super-P), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2 and dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode active material is selected from lithium iron phosphate material, which is doped with Ti element. The positive electrode slurry is uniformly coated on both sides of carbon-coated aluminum foil, and after drying, rolling and vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain a positive electrode plate. The thickness of the electrode plate is between 100-150μm. The areal density of the positive electrode material layer is controlled by the amount of positive electrode slurry coating. 3) Preparation of the negative electrode plate: Artificial graphite (Shanghai Shanshan, FSN-1), conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5 and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, and after drying, calendering, and vacuum drying, copper leads were welded on using an ultrasonic welder to obtain a negative electrode plate. The thickness of the electrode plate was between 100-150 μm, and the areal density of the negative electrode material layer was controlled by the amount of negative electrode slurry applied.

[0083] 4) Cell fabrication: In an environment where the dew point is controlled below -30℃, a 20μm thick separator is placed between the positive and negative plates. Then, the sandwich structure consisting of the positive plate, negative plate, and separator is stacked. The distance by which the edge of the negative electrode material layer extends beyond the edge of the positive electrode material layer and the ratio of the surface density of the positive and negative electrode material layers are shown in Table 1. The stacked body is then flattened and placed in a square aluminum metal shell. The leads of the positive and negative electrodes are welded to the corresponding positions on the cover plate, and the cover plate and the metal shell are welded together using a laser welding machine to obtain the battery cell to be injected with electrolyte. The electrolyte prepared above is injected into the battery cell through the injection hole, and the amount of electrolyte should be sufficient to fill the gaps in the battery cell.

[0084] 5) Cell formation: The initial formation process is performed as follows: 0.05C constant current charging, voltage limit 3.65V, time limit 30min; rest for 5min; 0.15C constant current charging, voltage limit 3.65V, time limit 20min; rest for 5min; 0.3C constant current charging, voltage limit 3.65V, time limit 41min; after aging at 45℃, a second electrolyte replenishment is performed. After replenishment, the electrolyte inlet is welded, and then further charged at a constant current of 0.2C to the 3.65V cutoff voltage. After resting at room temperature for 24hr, it is discharged at a constant current of 0.2C to 2.5V to obtain a lithium iron phosphate / graphite lithium-ion battery.

[0085] Examples 2-26 Examples 2-26 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The types and contents of the first additive, the form of Ti in the positive electrode active material, the distance of the edge of the negative electrode material layer beyond the edge of the positive electrode material layer, and the ratio of the surface density of the positive electrode material layer to the negative electrode material layer are shown in Examples 2-26 of Table 1.

[0086] Comparative Examples 1-13 Comparative Examples 1-13 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, the difference being: The types and contents of the first additive, the form of Ti in the positive electrode active material, the distance of the edge of the negative electrode material layer beyond the edge of the positive electrode material layer, and the ratio of the surface density of the positive electrode material layer to the negative electrode material layer are shown in Comparative Examples 1 to 13 in Table 1.

[0087] Performance testing The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests: Room temperature cycling performance: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged at a rate of 1C and discharged at a rate of 1C. The battery capacity of the first charge and discharge (i.e., the initial capacity) was recorded. Full charge and discharge cycle tests were carried out within the charge and discharge cutoff voltage of 2.5V to 3.65V until the capacity of the lithium-ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0088] The battery was disassembled after being cycled at room temperature, and the electrolyte was sampled. The Fe ion content was detected and recorded by ICP.

[0089] Lithium plating test of batteries: At 25°C, the lithium-ion secondary batteries prepared in the examples and comparative examples were charged at a constant capacity of 1C to the nominal capacity and then discharged at 1C to 2.5V. This process was repeated 10 times. Afterward, the lithium-ion secondary batteries were fully charged at 1C to the nominal capacity, and the negative electrode was disassembled. The lithium plating on the surface of the negative electrode was then observed. Specifically, a lithium plating area of ​​less than 1% on the negative electrode surface was considered no lithium plating; a lithium plating area of ​​1% or more but less than 5% was considered slight lithium plating; a lithium plating area of ​​5% to 40% was considered moderate lithium plating; and a lithium plating area of ​​more than 40% was considered severe lithium plating.

[0090] (1) The test results obtained from Examples 1-22 and Comparative Examples 1-13 are filled in Table 2.

[0091] Table 2 - Test Results of Examples 1-22 and Comparative Examples 1-13 The test results from Examples 1-22 and Comparative Examples 1-13 show that when lithium iron phosphate coated and / or doped with Ti is used as the positive electrode active material, and the negative electrode sheet is over-designed, while matching the areal density of the positive and negative electrode material layers, and when a first additive is added to the non-aqueous electrolyte, the performance of lithium-ion batteries can be significantly improved. Specifically, when the distance a (0.3≤a≤5) of the edge of the negative electrode material layer extending beyond the edge of the positive electrode material layer, the ratio of the areal density of the positive and negative electrode material layers b (1.2≤b≤2.8), the mass percentage of the first additive in the non-aqueous electrolyte c (0.05≤c≤2), and the mass percentage of Ti in the positive electrode material layer d (0.1≤d≤0.8) meet specific conditions... The prepared lithium-ion battery can simultaneously achieve long cycle life, high energy density, and excellent safety performance. This superior performance is attributed to the synergistic effect of various parameters. During battery formation, the first additive decomposes on the negative electrode surface under electrochemical action, participating in the formation of the solid electrolyte interphase (SEI) film. The stability of the SEI film at the negative electrode edge is crucial for suppressing metal dendrite growth. By precisely controlling the excess amount (i.e., distance a) at the edge of the negative electrode material layer, the active lithium supply and current density at the negative electrode edge during the formation stage can be adjusted, thereby affecting the density of the SEI film at that location. Simultaneously, the ratio b of the areal density of the positive and negative electrode material layers also significantly affects the density and stability of the SEI film at the negative electrode edge. Furthermore, phosphate materials coated or doped with Ti not only improve the stability and cycle life of the positive electrode material and reduce Fe ion dissolution, but also reduce the excess design requirements of the negative electrode, contributing to increased battery energy density. By rationally adjusting the four key parameters a, b, c, and d, the stability of the SEI film formed by the first additive on the negative electrode surface (especially at the edge) can be synergistically improved, the risk of metal dendrites forming at the edge of the negative electrode can be reduced, and the electrode design matching degree can be optimized, thereby comprehensively improving the cycle performance, safety performance and energy density of lithium-ion batteries.

[0092] Based on the test results of Comparative Examples 1-8, if the first additive is added to the non-aqueous electrolyte, the inventors found that when the distance *a* between the edge of the negative electrode material layer and the edge of the positive electrode material layer, the ratio *b* of the areal density of the positive and negative electrode material layers, the mass percentage of the first additive in the non-aqueous electrolyte *c*, and the mass percentage of Ti in the positive electrode material layer *d* do not meet their respective defined ranges (0.3≤a≤5, 1.2≤b≤2.8, 0.05≤c≤2, 0.1≤d≤0.8), even if the conditions are met... Under these conditions, the lithium-ion batteries still suffer from Fe ion dissolution, indicating that whether the a, b, c, or d values ​​are too high or too low, it is not conducive to improving the cycle performance and safety performance of lithium-ion batteries.

[0093] The test results from Comparative Examples 9-13 show that when values ​​a, b, c, and d do not meet the requirements... Even if each of these factors meets its corresponding content range, the initial capacity and cycle count of the resulting lithium-ion battery will still decrease, while the amount of Fe ions dissolved will increase. This indicates that there is an interaction between the following factors: the distance (a) between the edge of the negative electrode material layer and the edge of the positive electrode material layer; the ratio (b) of the areal density of the positive and negative electrode material layers; the mass percentage (c) of the first additive in the non-aqueous electrolyte; and the mass percentage (d) of Ti in the positive electrode material layer. Only when these four factors reach a good balance can the performance of the lithium-ion battery be significantly improved.

[0094] (2) The test results obtained in Examples 1, 23 to 26 are filled in Table 3.

[0095] Table 3 - Test Results of Examples 1, 23-26 A comparison of the test results from Examples 1 and 23-26 shows that, in the battery system provided by this invention, under the condition that... Under the premise that 0.3≤a≤5, 1.2≤b≤2.8, 0.05≤c≤2, and 0.1≤d≤0.8, different first additives can improve the cycle performance and safety performance of lithium-ion batteries to a certain extent, indicating that the battery system provided by the present invention is applicable to different first additives.

[0096] Table 4 - Implementation conditions of lithium-ion batteries in Examples 29-41 Note: DTD - vinyl sulfate; MMDS - methylene disulfonate; PS - 1,3-propane sulpholactone; ESi - vinyl sulfite; BS - 1,4-butane sulpholactone; Examples 29-41 Examples 29-41 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The non-aqueous electrolyte also includes a second additive. The types and contents of the first additive, the types and contents of the second additive, the distance by which the edge of the negative electrode material layer extends beyond the edge of the positive electrode material layer, and the ratio of the surface density of the positive electrode material layer to the negative electrode material layer are shown in Examples 29-41 of Table 4.

[0097] Performance testing The lithium-ion batteries prepared in the above embodiments were subjected to the following performance tests: Room temperature cycling performance: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged at a rate of 1C and discharged at a rate of 1C. The battery capacity of the first charge and discharge (i.e., the initial capacity) was recorded. Full charge and discharge cycle tests were carried out within the charge and discharge cutoff voltage of 2.5V to 3.65V until the capacity of the lithium-ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0098] The battery was disassembled after being cycled at room temperature, and the electrolyte was sampled. The Fe ion content was detected and recorded by ICP.

[0099] Lithium plating test of batteries: At 25°C, the lithium-ion secondary batteries prepared in the examples and comparative examples were charged at a constant capacity of 1C to the nominal capacity and then discharged at 1C to 2.5V. This process was repeated 10 times. Afterward, the lithium-ion secondary batteries were fully charged at 1C to the nominal capacity, and the negative electrode was disassembled. The lithium plating on the surface of the negative electrode was then observed. Specifically, a lithium plating area of ​​less than 1% on the negative electrode surface was considered no lithium plating; a lithium plating area of ​​1% or more but less than 5% was considered slight lithium plating; a lithium plating area of ​​5% to 40% was considered moderate lithium plating; and a lithium plating area of ​​more than 40% was considered severe lithium plating.

[0100] (3) The test results obtained in Examples 1, 27 to 37 are filled in Table 5.

[0101] Table 5 - Test Results of Examples 1, 27-37 Comparison of the test results of Examples 1 and 27-37 shows that the addition of a second additive to the above-mentioned non-aqueous electrolyte system can synergistically interact with the first additive to jointly construct a solid electrolyte interface film on the positive and negative electrode surfaces. The second additive decomposes to generate sulfur-containing lithium salts, which effectively enhances the stability of the solid electrolyte interface film, thereby inhibiting the dissolution of Fe elements in the positive electrode material layer, further reducing battery side reactions, and significantly curbing the increasing trend of DC internal resistance during battery cycling and storage. When the distance *a* between the edge of the negative electrode material layer and the edge of the positive electrode material layer, the ratio *b* of the areal density of the positive and negative electrode material layers, the mass percentage *c* of the first additive in the non-aqueous electrolyte, and the mass percentage *d* of Ti elements in the positive electrode material layer satisfy the conditions 0.2 ≤ *c+e* ≤ 2 and 0.2 ≤ *d* / (*c+e*) ≤ 2.5, the synergistic effect between the first additive, the second additive, and the Ti elements coated or doped in the lithium iron phosphate material layer will be fully demonstrated. This gives lithium iron phosphate materials excellent structural stability, oxidation resistance, and safety performance. It can not only significantly suppress the decomposition reaction of the electrolyte after charging with unexpected results, but also greatly improve the cycle performance and safety performance of the battery while ensuring that the battery maintains a high energy density.

[0102] (4) The test results obtained in Examples 27, 38-41 are filled in Table 6.

[0103] Table 6 - Test Results of Examples 27, 38-41 A comparison of the test results of Examples 27 and 38-41 shows that, in the battery system provided by the present invention, under the conditions of 0.1≤c+e≤3, 0.1≤d / (c+e)≤5, and 0.01≤e≤2, 0.05≤c≤2, and 0.1≤d≤0.8, different second additives can improve the cycle performance and safety performance of lithium-ion batteries to a certain extent, indicating that the battery system provided by the present invention is suitable for different second additives.

[0104] Table 7 - Lithium-ion battery implementation conditions for Examples 42-64 and Comparative Examples 14-27 Continued from Table 7 Examples 42-64 Examples 42-64 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The types and contents of the first additive, the form of Ti in the positive electrode active material, the distance of the edge of the negative electrode material layer beyond the edge of the positive electrode material layer, and the ratio of the surface density of the positive electrode material layer to the negative electrode material layer are shown in Examples 42-64 in Table 7.

[0105] Comparative Examples 14-27 Comparative Examples 14-27 are used to illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, the difference being: The types and contents of the first additive, the form of Ti in the positive electrode active material, the distance of the edge of the negative electrode material layer beyond the edge of the positive electrode material layer, and the ratio of the surface density of the positive electrode material layer to the negative electrode material layer are shown in Comparative Examples 14-27 in Table 7.

[0106] Performance testing The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests: Room temperature cycling performance: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged at a rate of 1C and discharged at a rate of 1C. The battery capacity of the first charge and discharge (i.e., the initial capacity) was recorded. Full charge and discharge cycle tests were carried out within the charge and discharge cutoff voltage of 2.5V to 3.65V until the capacity of the lithium-ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0107] The battery was disassembled after being cycled at room temperature, and the electrolyte was sampled. The Fe ion content was detected and recorded by ICP.

[0108] Lithium plating test of batteries: At 25°C, the lithium-ion secondary batteries prepared in the examples and comparative examples were charged at a constant capacity of 1C to the nominal capacity and then discharged at 1C to 2.5V. This process was repeated 10 times. Afterward, the lithium-ion secondary batteries were fully charged at 1C to the nominal capacity, and the negative electrode was disassembled. The lithium plating on the surface of the negative electrode was then observed. Specifically, a lithium plating area of ​​less than 1% on the negative electrode surface was considered no lithium plating; a lithium plating area of ​​1% or more but less than 5% was considered slight lithium plating; a lithium plating area of ​​5% to 40% was considered moderate lithium plating; and a lithium plating area of ​​more than 40% was considered severe lithium plating.

[0109] (5) The test results obtained from Examples 42-64 and Comparative Examples 14-27 are filled in Table 8.

[0110] Table 8 - Test results of Examples 42-64 and Comparative Examples 14-27 The test results from Examples 42-64 and Comparative Examples 24-27 show that when lithium iron phosphate coated and / or doped with Ti is used as the positive electrode active material, and the negative electrode sheet is over-designed, while matching the areal density of the positive and negative electrode material layers, and when a first additive is added to the non-aqueous electrolyte, the performance of lithium-ion batteries can be significantly improved. Specifically, when the distance a (0.3≤a≤5) of the edge of the negative electrode material layer extending beyond the edge of the positive electrode material layer, the ratio of the areal density of the positive and negative electrode material layers b (1.2≤b≤2.8), the mass percentage of the first additive in the non-aqueous electrolyte c (0.05≤c≤2), and the mass percentage of Ti in the positive electrode material layer d (0.1≤d≤0.8) meet specific conditions... The prepared lithium-ion battery can simultaneously achieve long cycle life, high energy density, and excellent safety performance. This superior performance is attributed to the synergistic effect of various parameters. During battery formation, the first additive decomposes on the negative electrode surface under electrochemical action, participating in the formation of the solid electrolyte interphase (SEI) film. The stability of the SEI film at the negative electrode edge is crucial for suppressing metal dendrite growth. By precisely controlling the excess amount (i.e., distance a) at the edge of the negative electrode material layer, the active lithium supply and current density at the negative electrode edge during the formation stage can be adjusted, thereby affecting the density of the SEI film at that location. Simultaneously, the ratio b of the areal density of the positive and negative electrode material layers also significantly affects the density and stability of the SEI film at the negative electrode edge. Furthermore, phosphate materials coated or doped with Ti not only improve the stability and cycle life of the positive electrode material and reduce Fe ion dissolution, but also reduce the excess design requirements of the negative electrode, contributing to increased battery energy density. By rationally adjusting the four key parameters a, b, c, and d, the stability of the SEI film formed by the first additive on the negative electrode surface (especially at the edge) can be synergistically improved, the risk of metal dendrites forming at the edge of the negative electrode can be reduced, and the electrode design matching degree can be optimized, thereby comprehensively improving the cycle performance, safety performance and energy density of lithium-ion batteries.

[0111] A comparison of the test results from Examples 42 and 64 shows that, in the battery system provided by this invention, under the condition that... Under the premise that 0.3≤a≤5, 1.2≤b≤2.8, 0.05≤c≤2, and 0.1≤d≤0.8, different first additives can improve the cycle performance and safety performance of lithium-ion batteries to a certain extent, indicating that the battery system provided by the present invention is applicable to different first additives.

[0112] The test results of Example 42 and Comparative Example 14 show that replacing the first additive with vinyl sulfate does not achieve the same effect as the first additive in this battery system. This indicates that the first additive of this application has a more significant effect on improving battery performance than the monocyclic vinyl sulfate. This is because the multicyclic structure of the first additive of this application participates in the formation of the interface film on the electrode surface through its own ring opening. The resulting interface film components are more stable and dense, which can improve the strength of the interface film structure and thus help improve its high-temperature stability. In contrast, the monocyclic vinyl sulfate cannot form a good synergistic effect with other components, and its effect on improving the energy density and cycle performance of lithium-ion batteries is not good.

[0113] Based on the test results of Comparative Examples 15-22, if the first additive is added to the non-aqueous electrolyte, the inventors found that when the distance *a* between the edge of the negative electrode material layer and the edge of the positive electrode material layer, the ratio *b* of the areal density of the positive and negative electrode material layers, the mass percentage of the first additive in the non-aqueous electrolyte *c*, and the mass percentage of Ti in the positive electrode material layer *d* do not meet their respective defined ranges (0.3≤a≤5, 1.2≤b≤2.8, 0.05≤c≤2, 0.1≤d≤0.8), even if the conditions are met... Under these conditions, the lithium-ion batteries still suffer from Fe ion dissolution, indicating that whether the a, b, c, or d values ​​are too high or too low, it is not conducive to improving the rate performance and safety performance of lithium-ion batteries.

[0114] The test results from comparative examples 23-27 show that when the values ​​of a, b, c, and d do not meet the requirements... Even if each of these factors meets its corresponding content range, the initial capacity and cycle count of the resulting lithium-ion battery will still decrease, while the amount of Fe ions dissolved will increase. This indicates that there is an interaction between the following factors: the distance (a) between the edge of the negative electrode material layer and the edge of the positive electrode material layer; the ratio (b) of the areal density of the positive and negative electrode material layers; the mass percentage (c) of the first additive in the non-aqueous electrolyte; and the mass percentage (d) of Ti in the positive electrode material layer. Only when these four factors reach a good balance can the performance of the lithium-ion battery be significantly improved.

[0115] Table 9 - Implementation conditions of lithium-ion batteries in Examples 65-79 Note: DTD - vinyl sulfate; MMDS - methylene disulfonate; PS - 1,3-propane sulpholactone; ESi - vinyl sulfite; BS - 1,4-butane sulpholactone; Examples 65-79 Examples 65-79 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences: The non-aqueous electrolyte also includes a second additive. The types and contents of the first additive, the types and contents of the second additive, the distance by which the edge of the negative electrode material layer extends beyond the edge of the positive electrode material layer, and the ratio of the surface density of the positive electrode material layer to the negative electrode material layer are shown in Examples 65-79 of Table 9.

[0116] The lithium-ion batteries prepared in the above embodiments were subjected to the following performance tests: Room temperature cycling performance: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged at a rate of 1C and discharged at a rate of 1C. The battery capacity of the first charge and discharge (i.e., the initial capacity) was recorded. Full charge and discharge cycle tests were carried out within the charge and discharge cutoff voltage of 2.5V to 3.65V until the capacity of the lithium-ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0117] The battery was disassembled after being cycled at room temperature, and the electrolyte was sampled. The Fe ion content was detected and recorded by ICP.

[0118] Lithium plating test of batteries: At 25°C, the lithium-ion secondary batteries prepared in the examples and comparative examples were charged at a constant capacity of 1C to the nominal capacity and then discharged at 1C to 2.5V. This process was repeated 10 times. Afterward, the lithium-ion secondary batteries were fully charged at 1C to the nominal capacity, and the negative electrode was disassembled. The lithium plating on the surface of the negative electrode was then observed. Specifically, a lithium plating area of ​​less than 1% on the negative electrode surface was considered no lithium plating; a lithium plating area of ​​1% or more but less than 5% was considered slight lithium plating; a lithium plating area of ​​5% to 40% was considered moderate lithium plating; and a lithium plating area of ​​more than 40% was considered severe lithium plating.

[0119] (6) The test results obtained in Examples 42, 65~75 are filled in Table 10.

[0120] Table 10 - Test Results of Examples 42, 65~75 Comparison of the test results of Examples 42 and 65-75 shows that the addition of a second additive to the above-mentioned non-aqueous electrolyte system can synergistically interact with the first additive to jointly construct a solid electrolyte interface film on the positive and negative electrode surfaces. The second additive decomposes to generate sulfur-containing lithium salts, which effectively enhances the stability of the solid electrolyte interface film, thereby inhibiting the dissolution of Fe elements in the positive electrode material layer, further reducing battery side reactions, and significantly curbing the increasing trend of DC internal resistance during battery cycling and storage. When the distance *a* between the edge of the negative electrode material layer and the edge of the positive electrode material layer, the ratio *b* of the areal density of the positive and negative electrode material layers, the mass percentage *c* of the first additive in the non-aqueous electrolyte, and the mass percentage *d* of Ti elements in the positive electrode material layer satisfy the conditions 0.2 ≤ *c+e* ≤ 2 and 0.2 ≤ *d* / (*c+e*) ≤ 2.5, the synergistic effect between the first additive, the second additive, and the Ti elements coated or doped in the lithium iron phosphate material layer will be fully realized. This gives lithium iron phosphate materials excellent structural stability, oxidation resistance, and safety performance. It can not only significantly suppress the decomposition reaction of the electrolyte after charging with unexpected results, but also greatly improve the cycle performance and safety performance of the battery while ensuring that the battery maintains a high energy density.

[0121] (7) The test results obtained in Examples 65, 76-79 are filled in Table 11.

[0122] Table 11 - Test Results of Examples 65, 76-79 A comparison of the test results of Examples 65 and 76-79 shows that, in the battery system provided by the present invention, under the conditions of 0.1≤c+e≤3, 0.1≤d / (c+e)≤5, and 0.01≤e≤2, 0.05≤c≤2, and 0.1≤d≤0.8, different second additives can improve the cycle performance and safety performance of lithium-ion batteries to a certain extent, indicating that the battery system provided by the present invention is suitable for different second additives.

[0123] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, Includes positive electrode, negative electrode, and non-aqueous electrolyte; The positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material includes a phosphate material coated and / or doped with Ti, and the mass percentage of Ti in the positive electrode material layer is d%. The negative electrode includes a negative electrode material layer containing a negative electrode active material, and the ratio of the double-sided areal density of the positive electrode material layer to that of the negative electrode material layer is b. Along the thickness direction of the positive electrode material layer, the projection of the positive electrode material layer onto the negative electrode is located within the coverage area of ​​the negative electrode material layer, and the distance by which the edge of the negative electrode material layer extends beyond the edge of the positive electrode material layer is a mm; The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and an additive. The electrolyte salt is selected from lithium salts, and the lithium salt includes at least LiPF6. The concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 2 mol / L. The additive includes a first additive, which comprises a compound shown in structural formula 1. Structural Formula 1 Where X is selected from or R1 and R2 are each independently selected from H, ,or R1 and R2 are not both selected from H, and X, R1 and R2 contain at least one sulfur atom; Based on the mass of the non-aqueous electrolyte, the mass percentage of the first additive is c%; The lithium-ion battery meets the following conditions: And 0.3≤a≤5, 1.2≤b≤2.8, 0.05≤c≤2, 0.1≤d≤0.

8.

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 distance a mm from the edge of the negative electrode material layer to the edge of the positive electrode material layer satisfies: 1 ≤ a ≤ 3.

5.

4. The lithium-ion battery according to claim 1, characterized in that, The double-sided areal density of the positive electrode material layer is 350~800 g / m³. 2 ; and / or The areal density of the negative electrode material layer is 150~350 g / m³. 2 ; and / or The ratio b of the areal density of the positive electrode material layer and the negative electrode material layer satisfies: 1.5≤b≤2.

5.

5. The lithium-ion battery according to claim 1, characterized in that, The mass percentage (c%) of the first additive in the non-aqueous electrolyte satisfies: 0.1 ≤ c ≤ 1.

6. The lithium-ion battery according to claim 1, characterized in that, The mass percentage d% of Ti element in the cathode material layer satisfies: 0.2≤d≤0.

6.

7. The lithium-ion battery according to claim 1, characterized in that, The compound represented by structural formula 1 includes at least one of the following compounds: 。 8. The lithium-ion battery according to claim 1, characterized in that, The additive also includes a second additive, which includes at least one of vinyl sulfate, methylene disulfonate, 1,3-propane sulphol, vinyl sulfite, and 1,4-butane sulphol. Based on the mass of the non-aqueous electrolyte, the mass percentage of the second additive is e%, and the lithium-ion battery meets the following conditions: 0.1≤c+e≤3, 0.1≤d / (c+e)≤5, and 0.01≤e≤2.

9. The lithium-ion battery according to claim 8, characterized in that, The lithium-ion battery satisfies at least one of the following conditions: 0.2≤c+e≤2; 0.2≤d / (c+e)≤2.5; 0.1≤e≤1； 0.1≤c≤1； 0.2≤d≤0.6。 10. The lithium-ion battery according to claim 1, characterized in that, The phosphate material includes Li r Mn α Fe β A 1-α-β PO 4-n G n and Li with Ti oxide coating on its surface r Mn α Fe β A' 1-α-β PO 4-n G n At least one of the following, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0≤n≤0.1, A includes Ti, and zero or one or more of Mg, V, Cr, Zr, Nb, Zn, Al, Na, K, Mo, W, Ni, Co, Ga, Sn, Sb, Ge and W, A' includes zero or one or more of 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.

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