Non-aqueous electrolyte and lithium ion battery

Abstract

A non-aqueous electrolyte and a lithium ion battery. The non-aqueous electrolyte comprises an organic solvent, a lithium salt, a difluorophosphate ion, tris(trimethylsilyl) phosphate, and a first additive; the lithium salt comprises lithium hexafluorophosphate; the non-aqueous electrolyte satisfies the following conditions: 0.05 ≤ a / b ≤ 20, 0.03 ≤ a / c ≤ 15, 0.05 ≤ c x d / b ≤ 20, 0.01 ≤ a ≤ 1, 0.01 ≤ b ≤ 1.2, 0.01 ≤ c ≤ 0.8, 1.1 ≤ d ≤ 1.3, wherein a is a mass percentage of the first additive in the non-aqueous electrolyte, expressed in %; b is a mass percentage of the difluorophosphate ion in the non-aqueous electrolyte, expressed in %; c is a mass percentage of the tris(trimethylsilyl) phosphate in the non-aqueous electrolyte, expressed in %; and d is a density of the non-aqueous electrolyte, expressed in g / ml.

Description

A non-aqueous electrolyte and a lithium-ion battery

[0001] This application claims priority to Chinese Patent Application No. 202411864761.1, filed on December 18, 2024, entitled "A Non-Aqueous Electrolyte and a Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion battery technology, specifically to a non-aqueous electrolyte and lithium-ion battery with excellent high-temperature performance and low impedance. Background Technology

[0003] Lithium-ion batteries are widely used in personal electronics and electric vehicles. A lithium-ion battery mainly consists of four key components: the positive electrode, the negative electrode, the electrolyte, and the separator. The stability of the electrolyte not only limits the battery's potential window, but its continuous decomposition also leads to a significant degradation in battery performance. Therefore, studying the various chemical and electrochemical reactions of the electrolyte within the battery is an effective way to improve battery performance.

[0004] The most common electrolyte system is lithium hexafluorophosphate (LiPF6) dissolved in carbonate solvents. As the most commonly used lithium salt in lithium-ion batteries, LiPF6 suffers from two major drawbacks: poor thermal stability and sensitivity to water. In practical applications, it may undergo side reactions to generate PF5, POF3, and PF2O2. - The decomposition of LiPF6 produces byproducts such as HF. The decomposition mechanism of LiPF6 remains controversial. It is generally believed that the LiF generated from LiPF6 decomposition helps form a highly stable SEI film, while the resulting HF acid damages the positive and negative electrode materials and the interfacial film, thus degrading the battery's high-temperature performance. Tris(trimethylsilyl)phosphate (TMSP) is frequently used in fast-charging electrolyte formulations due to its ability to reduce impedance; however, TMSP catalyzes the decomposition of LiPF6 and generates gas, significantly increasing the impact of lithium salt decomposition on battery performance. Therefore, developing an electrolyte that can fully utilize the LiF-rich interfacial film formed by lithium salt decomposition and reduce the negative impact of HF generated by lithium salt decomposition on the battery is of great significance for batteries that balance impedance and high-temperature performance. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a non-aqueous electrolyte and lithium-ion battery that exhibit excellent high-temperature performance while maintaining low impedance.

[0006] The following technical solution is adopted in this application:

[0007] A non-aqueous electrolyte, the non-aqueous electrolyte comprising an organic solvent, a lithium salt, difluorophosphate ions, tris(trimethylsilyl)phosphate, and a first additive;

[0008] The lithium salt includes lithium hexafluorophosphate;

[0009] The first additive includes at least one of compounds 1-3:

[0010] The non-aqueous electrolyte meets the following conditions:

[0011] 0.05≤a / b≤20, 0.03≤a / c≤15, 0.05≤c×d / b≤20, 0.01≤a≤1, 0.01≤b≤1.2, 0.01≤c≤0.8, 1.1≤d≤1.3;

[0012] Where a is the mass percentage of the first additive in the non-aqueous electrolyte, in %;

[0013] b represents the mass percentage of difluorophosphate ions in the non-aqueous electrolyte, in %;

[0014] c represents the mass percentage of tris(trimethylsilyl)phosphate in the non-aqueous electrolyte, expressed as a percentage.

[0015] d represents the density of the non-aqueous electrolyte, in g / ml.

[0016] The non-aqueous electrolyte of this application uses lithium hexafluorophosphate as the lithium salt, and a first additive and tris(trimethylsilyl)phosphate as additives. Through extensive research, the inventors discovered that when the relationships between the mass percentages of the first additive (a), difluorophosphate ions (b), and tris(trimethylsilyl)phosphate in the non-aqueous electrolyte (c) satisfy 0.05≤a / b≤20, 0.03≤a / c≤15, 0.05≤c×d / b≤20, 0.01≤a≤1, 0.01≤b≤1.2, 0.01≤c≤0.8, and 1.1≤d≤1.3, both low initial impedance and excellent high-temperature fast-charge cycle performance can be achieved, while suppressing the problem of rapid impedance growth during high-temperature fast-charge cycles. It is speculated that this is because tris(trimethylsilyl)phosphate, as an additive, can reduce impedance. On the one hand, it can participate in film formation to create an interface film component containing phosphorus; on the other hand, it can react with the lithium salt to generate… The process involves the formation of byproducts such as lithium difluorophosphate. Lithium difluorophosphate participates in film formation, creating an interface film rich in lithium fluoride, thereby improving battery impedance. However, the reaction of tris(trimethylsilyl)phosphate with lithium salt has certain side effects. This is mainly due to the generation of other products from lithium salt decomposition, such as HF, which can severely degrade the quality of the electrolyte and battery performance. Even though tris(trimethylsilyl)phosphate can react with water and HF to remove water and acid, the reaction products are still acids or TMSF. The generated acids may still attack the interface film, and TMSF is a gas at room temperature, which can lead to poor electrode adhesion and uneven lithium intercalation. To address the negative impact of tris(trimethylsilyl)phosphate, a first additive was added. This first additive is more likely to combine with fluoride ions than tris(trimethylsilyl)phosphate, reducing the adverse products generated by the decomposition of tris(trimethylsilyl)phosphate and lithium salt, and significantly reducing the risk of tris(trimethylsilyl)phosphate degrading the high-temperature performance of the battery when used as an additive. The density change of the non-aqueous electrolyte reflects the change in its components or their proportions. This density change significantly affects the degree of reaction between tris(trimethylsilyl)phosphate and lithium salt, thus influencing the effectiveness of the first additive in maximizing the benefits of this reaction. When the mass percentages of the first additive (a), difluorophosphate ions (b), tris(trimethylsilyl)phosphate (c), and the non-aqueous electrolyte density (d) in the non-aqueous electrolyte are in a synergistic state, the battery can achieve both low initial impedance and excellent high-temperature fast-charge cycle performance. This suppresses the problem of rapid impedance growth during high-temperature fast-charge cycles, leverages the positive effect of tris(trimethylsilyl)phosphate as an additive in easily forming a LiF-rich interfacial film in the electrolyte, and suppresses the negative effect of HF generation on battery electrochemical performance.

[0017] When the mass percentage of the first additive (a) and the mass percentage of difluorophosphate ions (b) in the non-aqueous electrolyte are related by a / b < 0.05, it indicates that the first additive is insufficient or that there are too many difluorophosphate ions in the electrolyte. If the value of a is too small, it is difficult to decompose and form a highly stable and dense uniform film, and it is difficult to suppress the negative effects of the reaction between tris(trimethylsilyl)phosphate and LiPF6. If the value of b is too large, it usually indicates that too many compounds containing difluorophosphate ions have been added or that LiPF6 has undergone severe hydrolysis. As a result, it is easy for LiPO2F2 to be precipitated from the electrolyte, leading to uneven stress between the electrodes and uneven lithium insertion / extraction during cycling, which becomes a battery failure site. In addition, although excessive LiPO2F2 can easily form a LiF-rich interface film, it also makes the proportion of inorganic matter in the film composition too high, thereby affecting lithium ion transport and causing excessive battery impedance.

[0018] When the mass percentage of the first additive (a) and the mass percentage of difluorophosphate ions (b) in the non-aqueous electrolyte are greater than 20 (a / b), it indicates that there is too much of the first additive or too little difluorophosphate ions in the electrolyte. If the value of a is too large, although a highly stable and dense uniform film can be formed, the impedance of the positive and negative electrode films is too large, which intensifies the heat generation of the battery and results in poor lithium ion transport kinetics in the interface film. The battery is prone to "diving" (very rapid capacity decay during cycling) and has a high safety risk. If the value of b is too small, it usually means that the reaction degree between the trimethylsilyl group and LiPF6 is extremely low without the addition of a compound containing difluorophosphate ions. Although the hydrolysis of LiPF6 is well controlled and the HF acid content in the electrolyte is also low, it is impossible to form a LiF-rich interface film by using the LiPO2F2 product generated by the reaction of the trimethylsilyl group and LiPF6 to improve the battery impedance and high-temperature performance.

[0019] Preferably, the relationship between the mass percentage a of the first additive in the non-aqueous electrolyte and the mass percentage b of difluorophosphate ions satisfies 0.1 ≤ a / b ≤ 10.

[0020] When the mass percentage of the first additive (a) and the mass percentage of tris(trimethylsilyl)phosphate (c) in the non-aqueous electrolyte (a / c) are less than 0.03, it indicates that the first additive is insufficient or the tris(trimethylsilyl)phosphate is excessive. If the value of a is too small, it is difficult for the first additive to decompose and form a highly stable and dense uniform film, and it is difficult to suppress the negative effects of the reaction between tris(trimethylsilyl)phosphate and LiPF6. If the value of c is too large, it will lead to the decomposition of lithium salt and excessive acidity in the electrolyte. At high temperatures, the acidity will increase rapidly, thereby damaging the positive and negative electrode interface film. During cycling, more active lithium will be consumed for film repair, and the side reactions between the electrode and the electrolyte will be aggravated. Furthermore, HF can attack the positive and negative electrode active materials, causing transition metal ions to dissolve and the electrode structure to be damaged. Transition metal ions can also catalyze the decomposition of lithium salts and solvents, producing more HF and undesirable byproducts, forming a vicious cycle. At the battery level, this manifests as rapid capacity decay and impedance growth. In addition, the high content of tris(trimethylsilyl)phosphate, after reacting with LiPF6 at high temperatures, can even cause the precipitation of LiPO2F2, making it a solid impurity that degrades battery performance. At the same time, it can produce a small amount of gas containing TMSF, CO2, etc., which can cause poor adhesion of the cell electrodes and poor battery sealing.

[0021] When the mass percentage of the first additive (a) and the mass percentage of tris(trimethylsilyl)phosphate (c) in the non-aqueous electrolyte are related by a / c > 15, it indicates that there is too much of the first additive or too little of the tris(trimethylsilyl)phosphate. If the value of a is too large, although a highly stable and dense and uniform film can be formed, the impedance of the positive and negative electrode films is too large, which intensifies the heat generation of the battery and results in poor transport kinetics of lithium ions in the interface film. The battery is prone to "diving" (very rapid capacity decay during cycling) and has a high safety risk. If the value of c is too small, the battery impedance cannot be effectively reduced, making it difficult to meet the performance requirements of low impedance and high rate of the battery.

[0022] Preferably, the relationship between the mass percentage a of the first additive in the non-aqueous electrolyte and the mass percentage c of tris(trimethylsilyl)phosphate satisfies 0.1≤a / c≤10.

[0023] It is worth noting that the mass percentage b of difluorophosphate ions in the non-aqueous electrolyte is affected by the mass percentage c of tris(trimethylsilyl)phosphate, but there is no necessary correlation. The value of b can be directly controlled by adding compounds containing difluorophosphate ions. At the same time, the reaction between tris(trimethylsilyl)phosphate and LiPF6 is also affected by many factors, such as temperature, residual moisture in the electrolyte, product concentration, and the chemical properties of other components in the electrolyte.

[0024] When the relationship between the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) in the non-aqueous electrolyte (c×d / b) is less than 0.05, it indicates that the difluorophosphate ion content is too high, the tris(trimethylsilyl)phosphate content is too low, or the non-aqueous electrolyte density is too low. The former two will lead to the deterioration or failure of battery performance. The non-aqueous electrolyte density (d) being too low means that there is less lithium salt content or less of the denser cyclic carbonate component in the electrolyte. Although insufficient lithium salt can reduce the degree of its decomposition, it will significantly weaken the electrolyte's ability to transport lithium ions. If the proportion of cyclic carbonate as a solvent component is too small, the lithium salt cannot be fully dissociated. Although this also reduces the possibility of lithium salt decomposition, the undissociated lithium salt, as a large molecule, is difficult to migrate quickly. Therefore, although the non-aqueous electrolyte density weakens lithium salt decomposition and its effects, the sacrifice of lithium ion migration kinetics is too great, which will significantly reduce battery impedance and other performance characteristics.

[0025] When the relationship between the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) in the non-aqueous electrolyte (c×d / b) > 20, it indicates that the difluorophosphate ion content is too low, the tris(trimethylsilyl)phosphate content is too high, or the non-aqueous electrolyte density is too high. Too low a difluorophosphate ion content cannot effectively improve battery performance, while too high a tris(trimethylsilyl)phosphate content will lead to excessive side reactions with lithium salts, thus degrading battery performance. Too high a non-aqueous electrolyte density (d) means that there is too much lithium salt or too much denser cyclic carbonate. Excessive lithium salt leads to more vigorous decomposition, and the excess lithium salt, unable to dissociate, acts as a large molecule, hindering the migration of normally solvated lithium ions. Too high a proportion of cyclic carbonate as a solvent component will significantly increase electrolyte viscosity. At high viscosity, the lithium ion migration rate will be significantly affected. Therefore, too high a non-aqueous electrolyte density may exacerbate lithium salt decomposition and degrade kinetic performance, ultimately affecting all aspects of battery performance.

[0026] Preferably, the relationship between the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate ester (c), and the density of the non-aqueous electrolyte (d) satisfies 0.1 ≤ c × d / b ≤ 5.

[0027] The first additive can participate in the formation of a dense and uniform interfacial film at both the positive and negative electrodes, improving the stability of the interfacial film and its resistance to HF attack, thereby improving the high-temperature performance of the battery. In addition, it also has a stronger affinity for free HF than trimethylsilyl groups and proton H. -The binding ability allows different decomposition pathways of lithium salts to focus more on reacting with tris(trimethylsilyl)phosphate to form lithium difluorophosphate, thus suppressing the generation of byproducts with significant negative effects such as HF and TMSF. If the a value is too high, the battery impedance will be too large, and the battery charge-discharge polarization and heat generation will increase significantly, causing a series of negative effects such as thermal decomposition of lithium salt and impedance growth, and ultimately degrading the various electrochemical performances of the battery. If the a value is too low, it will be difficult to improve the high-temperature performance of the battery, and the reaction of tris(trimethylsilyl)phosphate in the electrolyte with lithium salt will degrade performance, and the risks of gas generation or impedance growth will increase significantly. Specifically, in some embodiments of this application, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination of these values; preferably, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.05% to 0.5%.

[0028] The first additive of this application has a tricyclic structure. Compared with a bicyclic or monocyclic structure, the bicyclic or monocyclic structure will significantly weaken its ability to bind with fluoride ions, thus failing to suppress the degradative effect of lithium salt and trimethylsilyl group decomposition byproducts on battery performance.

[0029] In some preferred embodiments of this application, the first additive includes at least one of compound 1 and compound 2. Compared to compound 3, compounds 1 and 2 have both cyclic structures of ethylene carbonate and ethylene sulfate, and have higher HOMO energies and lower LUMO energies than carbonate solvents. Therefore, they can preferentially undergo redox polymerization reactions at the positive and negative electrodes to form an interfacial film on the electrode surface. The formed interfacial film has better ionic conductivity, which can improve the lithium-ion transport rate and reduce the internal resistance of the battery, thereby giving the battery excellent high-temperature fast-charge cycle performance.

[0030] In this application, the difluorophosphate ions in the non-aqueous electrolyte originate from the hydrolysis of compounds containing difluorophosphate ions and / or lithium hexafluorophosphate. The content of difluorophosphate ions in the non-aqueous electrolyte can be controlled by adjusting the amount of compounds containing difluorophosphate ions added to the electrolyte or the degree of hydrolysis of lithium hexafluorophosphate. The specific control method is not limited in this application; as long as the content of difluorophosphate ions in the non-aqueous electrolyte meets the range defined in this application, it is within the scope of this application. Difluorophosphate ions can participate in the formation of the SEI film, increasing the LiF content in the film component, thereby improving the stability of the SEI film and reducing the film impedance. If the b value is too high, it is easy to precipitate from the electrolyte in the form of lithium difluorophosphate or it cannot be completely dissolved, acting as an impurity, causing uneven stress inside the battery and degrading battery performance. Furthermore, an excessively high content may result in an excessive amount of inorganic components in the interface film, degrading battery impedance. If the b value is too low, it is difficult to form a LiF-rich interface film, failing to improve battery impedance and high-temperature performance. Specifically, in some embodiments of this application, the mass percentage b% of difluorophosphate ions in the non-aqueous electrolyte is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, or any combination of these values; preferably, the mass percentage b% of difluorophosphate ions in the non-aqueous electrolyte is 0.05% to 0.8%. More preferably, the mass percentage b% of difluorophosphate ions in the non-aqueous electrolyte is 0.1% to 0.4%.

[0031] In the non-aqueous electrolyte of this application, 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 specifically limited in this application, and well-known testing methods in the art, such as ion chromatography, can be used. 19 F NMR, etc.

[0032] Tris(trimethylsilyl)phosphate can promote the hydrolysis of LiPF6, producing decomposition products such as LiPO2F2 and HF. The presence of LiPO2F2 can participate in the formation of the SEI film, increasing the LiF content in the film composition, thereby improving the stability of the SEI film and reducing the film impedance. On the other hand, the generation of HF acid can attack the positive and negative electrode interface film and even corrode the electrode material, causing a series of negative effects, such as a significant increase in film impedance. Therefore, the content of tris(trimethylsilyl)phosphate is relatively high. If the c value is too high, the decomposition of lithium salt in the electrolyte will be significantly accelerated, and the excessive acidity of the electrolyte will cause serious degradation of battery performance; if the c value is too low, the improvement on battery impedance will be very limited. Specifically, in some embodiments of this application, the mass percentage (c%) of tris(trimethylsilyl)phosphate in the non-aqueous electrolyte is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or any combination of these values; preferably, the mass percentage (c%) of tris(trimethylsilyl)phosphate in the non-aqueous electrolyte is 0.05% to 0.5%.

[0033] Specifically, in some embodiments of this application, the compound containing difluorophosphate ions includes lithium difluorophosphate.

[0034] Specifically, in some embodiments of this application, the lithium salt further includes lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiN(SO2CF3)2, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiCl, LiBr, LiI, LiClO4, and LiB 10 Cl 10 At least one of the following: LiAlCl4, lithium chloroborane, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, and lithium tetraphenylborate.

[0035] Specifically, in some embodiments of this application, the organic solvent includes at least one of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, and ether solvents.

[0036] In some preferred embodiments, the cyclic carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, and butene carbonate.

[0037] In some preferred embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0038] In some preferred embodiments, the carboxylic acid ester solvent includes at least one of ethyl acetate, ethyl propionate, propyl propionate, ethyl difluoroacetate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0039] In some preferred embodiments, the ether solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0040] Specifically, in some embodiments of this application, the density d of the non-aqueous electrolyte is 1.1–1.3 g / mL. By controlling the density of the non-aqueous electrolyte within the above range, the decomposition degree of lithium hexafluorophosphate can be reduced, the generation of HF acid can be decreased, and the battery can have good cycle performance. The density of the non-aqueous electrolyte is affected by the type and content of the solvent and lithium salt. If the electrolyte density is too low, it may be due to the low concentration of lithium salt or the low density of organic solvent. Although a low concentration of lithium salt can weaken the reaction between lithium salt and tris(trimethylsilyl)phosphate and the hydrolysis of lithium salt, it also severely weakens the lithium-ion migration ability of the electrolyte. Not only is it difficult to form easily lithium-conducting interfacial film components such as LiF and alkyl lithium carbonate during film formation, but it also cannot play a bridging role for the rapid passage of lithium ions between the positive and negative electrodes during battery cycling, ultimately leading to poor initial battery performance. Increased impedance and rapid capacity degradation during fast charging cycles (rapid capacity decay within a short number of cycles) are common problems. Low organic solvent density usually indicates insufficient addition of high-density cyclic carbonate solvents. Cyclic carbonates in the solvent typically play a role in dissociating lithium salts and forming solvation structures with lithium ions. Low density results in a low dielectric constant of the electrolyte, which cannot fully dissociate lithium salts. Although it suppresses lithium salt-related side reactions, it also severely weakens the lithium ion migration ability of the electrolyte, leading to battery performance degradation, i.e., poor impedance and rate performance at the battery level. Excessive electrolyte density may be due to excessive lithium salt concentration or excessive organic solvent density. Excessive lithium salt concentration, limited by the solvent's dissociation ability, cannot improve the lithium ion migration ability of the electrolyte. Instead, it may act as an undissociated component, hindering the normal solvation of lithium ions. Moreover, excessive lithium salt concentration will significantly exacerbate the side reactions with tris(trimethylsilyl)phosphate and the hydrolysis reaction of the lithium salt itself, generating byproducts such as HF, which degrades battery performance. Excessive organic solvent density usually means that there are too many high-viscosity components. The increase in electrolyte viscosity will hinder the rapid migration of lithium ions, ultimately causing high battery impedance and poor rate performance.More specifically, the densities of the non-aqueous electrolyte are 1.1 g / mL, 1.12 g / mL, 1.131 g / mL, 1.136 g / mL, 1.14 g / mL, 1.148 g / mL, 1.15 g / mL, 1.154 g / mL, 1.16 g / mL, 1.177 g / mL, 1.180 g / mL, 1.184 g / mL, 1.187 g / mL, 1.19 g / mL, 1.196 g / mL, 1.2 g / mL, 1.21 g / mL, 1.218 g / mL, and 1.22 g / mL. The concentration of the non-aqueous electrolyte is 1.225 g / mL, 1.23 g / mL, 1.233 g / mL, 1.24 g / mL, 1.246 g / mL, 1.25 g / mL, 1.256 g / mL, 1.26 g / mL, 1.264 g / mL, 1.27 g / mL, 1.275 g / mL, 1.28 g / mL, 1.286 g / mL, 1.291 g / mL, 1.296 g / mL, 1.3 g / mL, or any combination of these values; preferably, the density of the non-aqueous electrolyte is 1.14–1.26 g / mL. More preferably, the density of the non-aqueous electrolyte is 1.14–1.22 g / mL.

[0041] Specifically, in some embodiments of this application, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate ester compounds, and nitrile compounds.

[0042] In some preferred embodiments, the cyclic sulfate compound includes at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

[0043] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0044] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 1 below:

[0045] In the structural formula 1 shown, 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;

[0046] In some preferred embodiments, the compound of structural formula 1 includes at least one of the compounds shown in compounds 1-1 to 1-6 below:

[0047] In some preferred embodiments, the phosphate ester compound includes at least one of the compounds represented by structural formula 2:

[0048] In structural formula 2, R 31 R 32 R 33 Each is independently selected from saturated hydrocarbon groups, unsaturated hydrocarbon groups, and halogenated hydrocarbon groups of C1-C5; more preferably, the compound represented by structural formula 2 includes at least one of the following: triargyl 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, diallyl 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.

[0049] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0050] In some preferred embodiments, the nitrile compound includes at least one selected from succinic anhydride, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebacate.

[0051] In some embodiments, the content of the auxiliary additive is 0.01% to 10% based on 100% of the total mass of the non-aqueous electrolyte. Preferably, the content is 0.1% to 5%; more preferably, the content is 0.1% to 2%. Specifically, the content of any one optional substance in the auxiliary additive can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, or any combination of these values.

[0052] Secondly, this application also provides a lithium-ion battery, including a positive electrode, a negative electrode, and the aforementioned non-aqueous electrolyte.

[0053] The negative electrode includes a negative electrode material layer containing a negative electrode active material. Specifically, in some embodiments of this application, the negative electrode material is any one or more of silicon-based materials and carbon materials. The silicon-based material is selected from one or more of silicon materials, silicon oxide materials, silicon-carbon materials, and silicon alloy materials; preferably, the silicon material is nano-silicon material; preferably, the silicon oxide material is SiOx material, wherein 0≤x<2; preferably, the silicon-carbon material is: a silicon-based material containing silicon and carbon materials, and / or a silicon-based material containing SiOy and carbon materials, wherein 0≤y<2; preferably, the silicon alloy material is Mg2Si alloy material and / or Fe2Si alloy material. The carbon material is selected from one or more of artificial graphite, natural graphite, composite graphite, graphene, and hard carbon; preferably, the carbon material is artificial graphite material.

[0054] Specifically, in some embodiments of this application, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent.

[0055] The negative electrode binder includes one or more 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.

[0056] The negative electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0057] Specifically, in some embodiments of this application, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is disposed on 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 one or more of aluminum, nickel, tin, copper, and stainless steel.

[0058] Specifically, in some embodiments of this application, the positive electrode includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material may include LiFe. 1-x’ M' x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mnz M 1-x-y-z One or more of O2, wherein M' is selected from one or more of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, and M is selected from one or more of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1. The positive electrode active material may also include one or more of sulfides, selenides, and halides. More preferably, the positive electrode active material may include LiCoO2, LiFePO4, LiFe 0.4 Mn 0.6 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 One or more of O2.

[0059] Specifically, in some embodiments of this application, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector. The material of the positive electrode current collector may be the same as that of the positive electrode current collector, and will not be described in detail here.

[0060] Specifically, in some embodiments of this application, 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. The positive electrode binder and the positive electrode conductive agent can be the same as the negative electrode binder and the negative electrode conductive agent, respectively, and will not be described in detail here.

[0061] Specifically, in some embodiments of this application, the lithium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0062] 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.

[0063] The non-aqueous electrolyte of this application uses a first additive and tris(trimethylsilyl)phosphate as additives. The relationships between the mass percentage of the first additive (a), the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) in the non-aqueous electrolyte are defined as follows: 0.05≤a / b≤20, 0.03≤a / c≤15, 0.05≤c×d / b≤20, 0.01≤a≤1, 0.01≤b≤1.2, 0.01≤c≤0.8, 1.1≤d≤1.3. This allows the tris(trimethylsilyl)phosphate to fully leverage its advantages in reducing battery impedance and forming a highly stable LiF-rich interface film, while significantly suppressing its disadvantage of catalyzing lithium salt decomposition and generating undesirable byproducts. At the battery level, this achieves a balance between low initial impedance and excellent high-temperature fast-charge cycle performance, while also suppressing the problem of rapid impedance growth during high-temperature fast-charge cycles. Detailed Implementation

[0064] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments in this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this application.

[0065] In the embodiments and comparative examples of this application, one of the compounds shown in Table 1 is used as a non-aqueous electrolyte additive.

[0066] Table 1

[0067] Example 1

[0068] The method for preparing the lithium-ion battery in this embodiment includes the following steps:

[0069] 1) Preparation of the positive electrode sheet:

[0070] LiNi 0.5 Mn 0.3 Co 0.2O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are mixed uniformly at a mass ratio of 97:1.5:1.5, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, and after drying, calendering, and vacuum drying, a positive electrode material layer is obtained. Aluminum leads are then welded on using an ultrasonic welding machine to obtain the positive electrode sheet.

[0071] 2) Preparation of the negative electrode sheet:

[0072] The negative electrode active material graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 96.3:1.0:1.2:1.5, and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, rolled, and vacuum dried, and then nickel leads were soldered on using an ultrasonic welding machine to obtain the negative electrode sheet.

[0073] 3) Preparation of electrolyte:

[0074] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a certain mass ratio, additives were added, and then lithium hexafluorophosphate (LiPF6) was added and its content was controlled so that the density of the non-aqueous electrolyte met the set range. The density of each additive and the non-aqueous electrolyte is shown in Table 2.

[0075] 4) Preparation of the diaphragm:

[0076] A three-layer separator membrane made of polypropylene, polyethylene, and polypropylene is used, with a thickness of 20μm.

[0077] 5) Battery assembly:

[0078] The prepared positive electrode sheet and the prepared negative electrode sheet are assembled into a stacked soft-pack battery cell.

[0079] 6) Electrolyte injection and formation of battery cells

[0080] In a glove box with the dew point controlled below -40°C, the electrolyte prepared above was injected into the cell, vacuum sealed, and left to stand for 72 hours. Then, the first charge was performed according to the following steps: 0.05C constant current charging for 180 min, 0.1C constant current charging for 120 min, 0.2C constant current charging for 120 min, followed by a second vacuum sealing, and then a full charge at 0.2C (100% SOC). After resting at room temperature for 72 hours, a full discharge at 0.2C (0% SOC) was performed.

[0081] Examples 2-28 and Comparative Examples 1-31

[0082] This embodiment and comparative example are used to illustrate the lithium-ion battery disclosed in this application. They include most of the operating steps in the above embodiment 1. The difference is that the composition and content of solvent, lithium salt and additives in the non-aqueous electrolyte are as follows: the concentration of lithium salt and the composition of solvent are not shown. They need to be adjusted according to the actual situation so that the density of the electrolyte meets the set range. The types and contents of additives and the density of non-aqueous electrolyte are shown in Table 2.

[0083] Table 2

[0084] Continued from Table 2

[0085] Continued from Table 2

[0086] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to performance testing according to the following methods:

[0087] 1. Initial and post-cycle DCIR testing of the battery at 0°C

[0088] At room temperature (25℃), the battery is fully charged and discharged for 3 cycles at a 1C rate within the commonly used charge and discharge cutoff voltage of the corresponding system. The discharge capacity of the third cycle is taken as the capacity of the battery at 100% SOC.

[0089] At room temperature (25℃), the empty-state battery is charged with constant current to 50% of its current capacity, then the temperature is adjusted to 0℃ and maintained for 6 hours.

[0090] Charge at 0.1C constant current for 10 seconds and then let stand for 40 seconds; discharge at 0.1C constant current for 10 seconds and then let stand for 40 seconds, and record the termination voltage V1.

[0091] Charge at 0.2C constant current for 10s and then let stand for 40s; discharge at 0.2C constant current for 10s and then let stand for 40s, and record the termination voltage V2.

[0092] Charge at 0.5C constant current for 10 seconds and then let stand for 40 seconds; discharge at 0.5C constant current for 10 seconds and then let stand for 40 seconds, and record the termination voltage V3.

[0093] Plot a straight line with current as the x-axis and voltage as the y-axis. The slope of the line is the impedance at 0°C.

[0094] The battery was tested in its initial state and at 0℃ DCIR after 800 cycles.

[0095] 2. High-Temperature Fast Charging Cycle Performance Test

[0096] At 45°C, the lithium-ion batteries prepared in the examples and comparative examples were charged at a constant current and constant voltage of 3C (cutoff current 0.05C) and discharged at a 3C rate. Full charge and discharge cycle tests were conducted within the commonly used charge and discharge cutoff voltage range for the corresponding systems (e.g., 2.5-3.65V for lithium iron phosphate / artificial graphite system, and 3-4.25V for conventional ternary / artificial graphite system) until the capacity of the lithium-ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0097] (1) The test results of Examples 1-19 and Comparative Examples 5-25 are shown in Table 3.

[0098] Table 3

[0099] As can be seen from the test results in Table 3, the non-aqueous electrolyte of this application, using lithium hexafluorophosphate as the lithium salt, and the first additive and tris(trimethylsilyl)phosphate as additives, and further controlling the relationship between the mass percentage of the first additive (a), the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) in the non-aqueous electrolyte to satisfy 0.05≤a / b≤20, 0.03≤a / c≤15, 0.05≤c×d / b≤20, 0.01≤a≤1, 0.01≤b≤1.2, 0.01≤c≤0.8, and 1.1≤d≤1.3, can achieve both low initial impedance and excellent high-temperature fast-charge cycle performance in lithium-ion batteries, while suppressing the problem of rapid impedance growth during high-temperature fast-charge cycles.

[0100] As can be seen from the test results of Example 1 and Comparative Examples 5-25, when any one or more of the following parameters in the non-aqueous electrolyte—the mass percentage of the first additive (a), the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d)—do not meet the specified range, or when any one or more of the relationships a / b, a / c, and c×d / b are too large or too small, it is impossible to simultaneously achieve low impedance and high-temperature fast-charging cycle performance of the lithium-ion battery. This indicates that there is a strong correlation between the mass percentage of the first additive (a), the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) in reducing the impedance of the lithium-ion battery and optimizing its high-temperature performance.

[0101] (2) The test results of Examples 1, 20-21, and Comparative Examples 29-31 are shown in Table 4.

[0102] Table 4

[0103] As shown in Table 4, the test results of Examples 1 and 20-21 indicate that for the non-aqueous electrolyte of this application, when different first additives are used, the optimization of the impedance performance and high-temperature fast-charging cycle performance of lithium-ion batteries can be achieved when the mass percentage of the first additive (a), the mass percentage of difluorophosphate ions (b), the mass percentage of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) meet the corresponding conditions. This demonstrates that the battery system of this application has universality for different first additives.

[0104] The test results of Example 1 and Comparative Examples 29-31 show that when using compounds with monocyclic or bicyclic structures, it is impossible to suppress the deteriorating effect of lithium salt and tris(trimethylsilyl)phosphate decomposition byproducts on battery performance. The battery impedance and high-temperature fast-charging cycle performance cannot be improved, further illustrating the synergistic effect between the first additive and other additives.

[0105] (3) The test results of Examples 1, 22-25, and Comparative Examples 26-28 are shown in Table 5.

[0106] Table 5

[0107] As can be seen from the test results of Examples 1, 22-25, and Comparative Examples 26-28 in Table 5, for the lithium-ion battery of this application, when different positive electrode active materials are used, the impedance performance and high-temperature performance of the lithium-ion battery can be optimized when the mass percentage content of the first additive (a), the mass percentage content of difluorophosphate ions (b), the mass percentage content of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) meet the corresponding conditions. Under the same positive electrode active material, when any parameter among the mass percentage content of the first additive (a), the mass percentage content of difluorophosphate ions (b), the mass percentage content of tris(trimethylsilyl)phosphate (c), and the density of the non-aqueous electrolyte (d) does not meet the corresponding conditions, the battery performance will be affected. This shows that the battery system of this application has universality for different positive electrode active materials.

[0108] (4) The test results of Examples 1, 26-28, and Comparative Examples 1-4 are shown in Table 6.

[0109] Table 6

[0110] As shown in Table 6, the test results of Examples 1 and 26-28 indicate that the lithium-ion battery of this application, when used in combination with auxiliary additives in a non-aqueous electrolyte, still exhibits good improvement effects on the impedance performance and high-temperature performance of the lithium-ion battery. However, the test results of Examples 1, 26-28, and Comparative Examples 1-4 show that when different amounts of auxiliary additives are used to replace the first additive, the remaining additives do not form a good synergistic effect, resulting in poor suppression of lithium-ion battery impedance growth and improvement of high-temperature cycling performance.

[0111] The present application has been further described above with reference to specific embodiments. However, it should be understood that the specific descriptions herein should not be construed as limiting the substance and scope of the present application. Various modifications made by those skilled in the art to the above embodiments after reading this specification are all within the scope of protection of the present application.

Claims

1. A nonaqueous electrolyte, wherein, The non-aqueous electrolyte comprises an organic solvent, lithium salt, difluorophosphate ions, tris(trimethylsilyl)phosphate, and a first additive. The lithium salt includes lithium hexafluorophosphate; The first additive includes at least one of compounds 1-3: The non-aqueous electrolyte meets the following conditions: 0.05≤a / b≤20, 0.03≤a / c≤15, 0.05≤c×d / b≤20, 0.01≤a≤1, 0.01≤b≤1.2, 0.01≤c≤0.8, 1.1≤d≤1.3; Where a is the mass percentage of the first additive in the non-aqueous electrolyte, in %; b represents the mass percentage of difluorophosphate ions in the non-aqueous electrolyte, in %; c represents the mass percentage of tris(trimethylsilyl)phosphate in the non-aqueous electrolyte, in %; d represents the density of the non-aqueous electrolyte, in g / ml.

2. The nonaqueous electrolyte according to claim 1, wherein The non-aqueous electrolyte satisfies the following conditions: 0.1≤a / b≤10, 0.1≤a / c≤10, 0.1≤c×d / b≤5.

3. The nonaqueous electrolyte according to claim 1 or 2, wherein The mass percentage (a%) of the first additive in the non-aqueous electrolyte is 0.05% to 0.5%.

4. The nonaqueous electrolyte according to any one of claims 1 to 3, wherein The mass percentage (b%) of difluorophosphate ions in the non-aqueous electrolyte is 0.05% to 0.8%.

5. The nonaqueous electrolyte according to any one of claims 1 to 4, wherein The mass percentage (c%) of tris(trimethylsilyl)phosphate in the non-aqueous electrolyte is 0.05% to 0.5%.

6. The nonaqueous electrolyte according to any one of claims 1 to 5, wherein The density d of the non-aqueous electrolyte is 1.14 g / mL to 1.26 g / mL.

7. The nonaqueous electrolyte according to any one of claims 1 to 6, wherein The density d of the non-aqueous electrolyte is 1.14 g / mL to 1.22 g / mL.

8. The nonaqueous electrolyte according to any one of claims 1 to 7, wherein The non-aqueous electrolyte also includes auxiliary additives, which include at least one of cyclic sulfate compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and nitrile compounds.

9. The nonaqueous electrolyte according to any one of claim 8, wherein Based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additives is 0.01% to 10%.

10. The nonaqueous electrolyte according to any one of claim 8, wherein The cyclic sulfate compounds include at least one of 4-methyl vinyl sulfate, vinyl sulfate, and propylene sulfate.

11. The nonaqueous electrolyte according to any one of claim 8, wherein The sulfonyl lactone compounds include at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

12. The nonaqueous electrolyte according to any one of claim 8, wherein The cyclic carbonate compound includes at least one of vinylene carbonate, vinyl ethylene carbonate, methylene vinyl carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by Structural Formula 1 below: In Structural Formula 1, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from one of a hydrogen atom, a halogen atom, and a C1-C5 group.

13. The nonaqueous electrolyte of any one of claim 8, wherein, The phosphate ester compound includes at least one of the compounds represented by the following formula 2: In the structural formula 2, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group.

14. The nonaqueous electrolyte of any one of claim 8, wherein, The borate ester compounds include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; and / or, The nitrile compounds include at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitol.

15. A lithium-ion battery, wherein, It includes a positive electrode, a negative electrode, and the non-aqueous electrolyte according to any one of claims 1-14.

16. The lithium-ion battery of claim 15, wherein, The positive electrode includes a positive electrode material layer comprising a positive electrode active material, wherein the positive electrode active material includes LiFe. 1-x’ M' x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z One or more of O2, wherein M' is selected from one or more of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, and M is selected from one or more of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, Zr, W, V or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

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