Composite lithium iron phosphate, preparation method therefor and use thereof

Abstract

Disclosed in the present application are a composite lithium iron phosphate, a preparation method therefor and the use thereof. The composite lithium iron phosphate comprises high-tap-density lithium iron phosphate and high-power lithium iron phosphate, surfaces of the high-tap-density lithium iron phosphate and the high-power lithium iron phosphate both being coated with carbon, wherein the ratio of the carbon content of the surface of the high-tap-density lithium iron phosphate to the carbon content of the surface of the high-power lithium iron phosphate is a, and the particle strength of the high-power lithium iron phosphate is b, a and b respectively satisfying the following relational expressions: 0.5≤a≤1.1, and 40 MPa≤b≤150 MPa.

Description

A composite lithium iron phosphate, its preparation method and application

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410920751.9, filed on July 10, 2024, entitled “A Composite Lithium Iron Phosphate and Its Preparation Method and Application”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to, but is not limited to, the field of secondary battery technology, and in particular to a composite lithium iron phosphate, its preparation method, and its application. Background Technology

[0004] Driven by the urgent global demand for environmental protection and renewable energy, lithium-ion batteries have become a key component in electric vehicles, energy storage systems, and other fields due to their efficient and clean energy storage characteristics. In particular, lithium iron phosphate (LiFePO4, LFP) has become the mainstream choice in the market due to its significant advantages such as widely available raw materials, low cost, excellent safety performance, and long cycle life.

[0005] However, lithium iron phosphate (LFP) materials still face some technical challenges in practical applications. For example, their inherently low electronic conductivity and small lithium-ion diffusion coefficient lead to rapid capacity decay in batteries under high-current charge-discharge conditions and significant performance degradation at low temperatures, severely limiting their application in high-performance power batteries and extreme environments. To overcome these limitations, researchers have employed a series of techniques to improve the electrochemical performance of LFP. One effective method is to control the particle size and morphology of LFP, such as reducing particle size to shorten the diffusion path of lithium ions within the material. This facilitates rapid lithium-ion transport during charge-discharge, thereby improving the battery's rate performance and reducing polarization effects, thus enhancing cycle stability. Furthermore, carbon coating on the surface of LFP can effectively improve its electronic conductivity, thereby improving its performance at low temperatures.

[0006] While the aforementioned technologies have improved the electrochemical performance of lithium iron phosphate to some extent, several problems remain to be solved. For example, these technologies often only improve one specific performance characteristic of lithium iron phosphate, such as cycle performance or low-temperature performance, and cannot achieve comprehensive optimization of both. Furthermore, the lithium iron phosphate materials prepared using these methods still have significant room for improvement in terms of compaction density and energy density, which directly affects the energy density and power density of the battery.

[0007] Therefore, how to maintain the compaction density of lithium iron phosphate material powder at no less than 2.38 g / cm³ is a key challenge.3 Building upon this already high level of performance, significantly improving its low-temperature performance (especially achieving a substantial increase in 0.2C discharge retention rate at -20℃, compared to only 70% to 75% in current technologies) while maintaining its high-temperature storage and cycling performance has become a crucial research topic. This technological breakthrough will not only greatly enhance the overall performance of lithium iron phosphate materials but also promises to further expand the application scope of lithium-ion batteries in electric vehicles, energy storage systems, and other fields. Summary of the Invention

[0008] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0009] This application proposes a composite lithium iron phosphate that simultaneously possesses high compaction density, high low-temperature discharge retention rate, and good high-temperature cycling performance.

[0010] This application also proposes a method for preparing the aforementioned composite lithium iron phosphate.

[0011] This application also proposes applications of the aforementioned composite lithium iron phosphate.

[0012] According to one embodiment of this application, a composite lithium iron phosphate is proposed, comprising high-density lithium iron phosphate and high-power lithium iron phosphate, wherein both the high-density lithium iron phosphate and the high-power lithium iron phosphate are coated with carbon, wherein the ratio of the carbon content on the surface of the high-density lithium iron phosphate to the carbon content on the surface of the high-power lithium iron phosphate is a, and the particle strength of the high-power lithium iron phosphate is b, wherein a and b satisfy the following relationships: 0.5≤a≤1.1; 40MPa≤b≤150MPa.

[0013] According to one embodiment of this application, at least the following beneficial effects are achieved: The composite lithium iron phosphate proposed in this embodiment successfully optimizes both compaction performance and low-temperature performance by cleverly combining high-compaction lithium iron phosphate with high-power lithium iron phosphate with specific characteristics. Specifically, this embodiment cleverly controls the ratio of carbon coating rate on the surface of high-compaction and high-power lithium iron phosphate, and particularly strengthens the particle strength of high-power lithium iron phosphate. This strategy enhances the conductivity of the material, promotes efficient charge transport, and ensures that the material is not easily broken during compaction, thereby maintaining a high compaction density. More importantly, an appropriate carbon coating ratio further optimizes charge transport and ion diffusion inside the battery, and further enhances the battery's performance in low-temperature environments. At the same time, by controlling the particle strength within a certain range, the migration channels of lithium ions can be better optimized, improving the battery's charge and discharge efficiency, and avoiding excessively high particle strength from hindering the migration of lithium ions inside the material, which would lead to a decrease in its low-temperature performance.

[0014] This innovative composite material not only ensures the stability of the cell's energy density but also significantly improves the material's performance at low temperatures. Specifically, it maintains a powder compaction density of no less than 2.38 g / cm³. 3 Building upon its superior performance, the composite lithium iron phosphate material of this application, tested at a discharge rate of 0.2C at a low temperature of -20°C, still maintains a discharge retention rate of over 78%, far exceeding the performance level of similar products. Furthermore, after undergoing 500 charge-discharge cycles at a high temperature of 45°C, the capacity retention rate remains above 92%, fully demonstrating its excellent cycle stability and long lifespan. The composite material solution of this application also provides new possibilities for improving the performance and expanding the applications of lithium iron phosphate batteries.

[0015] In some embodiments of this application, the high-pressure lithium iron phosphate and high-power lithium iron phosphate are independently selected from primary particles, secondary particles formed by the aggregation of primary particles, or a mixture of primary and secondary particles.

[0016] In some embodiments of this application, the high-pressure lithium iron phosphate and the high-power lithium iron phosphate also satisfy at least one of the following conditions:

[0017] 1) The ratio of the average primary particle size of the high-pressure lithium iron phosphate and the high-power lithium iron phosphate is c, and c satisfies the following relationship: c>3;

[0018] 2) Both the high-pressure lithium iron phosphate and the high-power lithium iron phosphate include a secondary particle structure formed by primary particle agglomeration. The ratio of the secondary particle Dv50 of the high-pressure lithium iron phosphate and the high-power lithium iron phosphate is d, and d satisfies the following relationship: d < 0.15.

[0019] 3) The ratio of the tap density of the high-pressure lithium iron phosphate to that of the high-power lithium iron phosphate is e, where e satisfies the following relationship: e < 0.7.

[0020] In some embodiments of this application, a satisfies the following relationship: 0.8≤a≤1.

[0021] In some embodiments of this application, a satisfies the following relationship: 0.9≤a≤1.

[0022] In some embodiments of this application, a satisfies the following relationship: 0.92≤a≤0.99.

[0023] In some embodiments of this application, the carbon content on the surface of the high-pressure lithium iron phosphate is 0.8% to 1.4%.

[0024] In some embodiments of this application, the carbon content on the surface of the high-pressure lithium iron phosphate is 1.0% to 1.4%.

[0025] In some embodiments of this application, the carbon content on the surface of the high-pressure lithium iron phosphate is 1.15% to 1.25%.

[0026] In some embodiments of this application, the carbon content on the surface of the high-pressure lithium iron phosphate is 1.2%.

[0027] In some embodiments of this application, the carbon content on the surface of the high-power lithium iron phosphate is 0.9% to 1.6%.

[0028] In some embodiments of this application, the carbon content on the surface of the high-power lithium iron phosphate is 1.0% to 1.5%.

[0029] In some embodiments of this application, the carbon content on the surface of the high-power lithium iron phosphate is 1.2% to 1.4%.

[0030] In some embodiments of this application, the carbon content on the surface of the high-power lithium iron phosphate is 1.25% to 1.35%.

[0031] In some embodiments of this application, the carbon content on the surface of the high-power lithium iron phosphate is 1.3%.

[0032] By controlling the carbon coating rate to a specific level, the conductivity of lithium iron phosphate materials can be better guaranteed.

[0033] In some embodiments of this application, b satisfies the following relationship: 50MPa≤b≤100MPa.

[0034] In some embodiments of this application, b satisfies the following relationship: 60MPa≤b≤100MPa. For example, it can be 60MPa, 70MPa, 80MPa, 90MPa, etc.

[0035] Appropriate particle strength not only ensures the compaction density and low-temperature performance of the material, but also reduces the difficulty of the preparation process and improves production efficiency and cost.

[0036] In some embodiments of this application, c satisfies the following relationship: 3 < c < 6.

[0037] In some embodiments of this application, c satisfies the following relationship: 3.2≤c≤5.0.

[0038] In some embodiments of this application, c satisfies the following relationship: 3.5≤c≤4.5.

[0039] In some embodiments of this application, c satisfies the following relationship: 3.5≤c≤3.8.

[0040] In some embodiments of this application, the primary particle size of the high-pressure lithium iron phosphate is between 300 nm and 1000 nm.

[0041] In some embodiments of this application, the primary particle size of the high-pressure lithium iron phosphate is between 300 nm and 800 nm.

[0042] In some embodiments of this application, the average particle size of the primary particles of the high-pressure lithium iron phosphate is between 600 nm and 800 nm.

[0043] In some embodiments of this application, the average particle size of the primary particles of the high-pressure lithium iron phosphate is between 700 nm and 780 nm.

[0044] In some embodiments of this application, the primary particle size of the high-power lithium iron phosphate is between 50 nm and 250 nm.

[0045] In some embodiments of this application, the primary particle size of the high-power lithium iron phosphate is between 80 nm and 200 nm.

[0046] In some embodiments of this application, the average primary particle size of the high-power lithium iron phosphate is between 100 nm and 180 nm.

[0047] Controlling the primary particle size distribution of high-power and high-compaction lithium iron phosphate allows for better maintenance of compaction density within a specific range, while simultaneously improving the material's discharge rate performance.

[0048] In some embodiments of this application, d satisfies the following relationship: 0.05 < d < 0.15.

[0049] In some embodiments of this application, d satisfies the following relationship: 0.1≤d≤0.14.

[0050] In some embodiments of this application, d satisfies the following relationship: 0.12≤d≤0.13.

[0051] In some embodiments of this application, the secondary particle size (Dv50) of the high-pressure lithium iron phosphate is 0.5 μm to 1.5 μm.

[0052] In some embodiments of this application, the secondary particle Dv50 of the high-pressure lithium iron phosphate is 1.0 μm to 1.5 μm.

[0053] In some embodiments of this application, the secondary particle Dv50 of the high-pressure lithium iron phosphate is 1.1 μm to 1.2 μm.

[0054] In some embodiments of this application, the secondary particle Dv50 of the high-power lithium iron phosphate is 6 μm to 10 μm.

[0055] In some embodiments of this application, the secondary particle Dv50 of the high-power lithium iron phosphate is 7 μm to 9.5 μm.

[0056] In some embodiments of this application, the secondary particle Dv50 of the high-power lithium iron phosphate is 8 μm to 9.2 μm.

[0057] By controlling the secondary particle size distribution of high-power and high-pressure lithium iron phosphate, the packing density of the material can be increased within a specific range, thereby improving the volume and energy density of the battery. At the same time, the uniformity and stability of the electrode can also be improved.

[0058] In some embodiments of this application, 3 < c < 6 and 0.05 < d < 0.15.

[0059] By controlling the ratio of primary to secondary particle size, the microstructure of the material can be optimized, the lithium-ion diffusion rate and electronic conductivity can be improved, thereby synergistically improving the low-temperature performance of the battery.

[0060] In some embodiments of this application, e satisfies the following relationship: 0.2 < e < 0.7.

[0061] In some embodiments of this application, e satisfies the following relationship: 0.6 ≤ e < 0.7.

[0062] In some embodiments of this application, e satisfies the following relationship: 0.65≤e≤0.68.

[0063] In some embodiments of this application, the tap density of high-pressure lithium iron phosphate is <1.2 g / cm³. 3 .

[0064] In some embodiments of this application, 0.5 g / cm 3 <Pack density of high-pressure lithium iron phosphate <1.2 g / cm³ 3 .

[0065] In some embodiments of this application, 1.0 g / cm 3 ≤Phase-pressed lithium iron phosphate tap density <1.2 g / cm³ 3 .

[0066] In some embodiments of this application, 1.0 g / cm 3 The tap density of high-pressure lithium iron phosphate is ≤1.1 g / cm³. 3 .

[0067] In some embodiments of this application, the tap density of high-power lithium iron phosphate is >1.6 g / cm³. 3 .

[0068] In some embodiments of this application, 1.6 g / cm 3 The tap density of high-power lithium iron phosphate is <2.0 g / cm³. 3 .

[0069] In some embodiments of this application, 1.6 g / cm 3 The tap density of high-power lithium iron phosphate is ≤1.8 g / cm³. 3 .

[0070] In some embodiments of this application, 1.7 g / cm 3 The tap density of high-power lithium iron phosphate is ≤1.8 g / cm³. 3 .

[0071] The tap density of lithium iron phosphate materials depends mainly on the material's microstructure and properties. Measuring the tap density helps to better control the quality of the material and promotes standardized production.

[0072] In some embodiments of this application, the mass ratio of high-density lithium iron phosphate to high-power lithium iron phosphate is x:(10 to x), where x satisfies the following relationship: 5≤x<10. Examples include 6:4, 7:3, 8:2, or 9:1. A higher mass ratio of high-density lithium iron phosphate results in a higher energy density for the composite lithium iron phosphate. Other ratios can also be used as needed.

[0073] In some embodiments of this application, x satisfies the following relationship: 6≤x≤8.

[0074] In some embodiments of this application, the compacted density of the composite lithium iron phosphate powder is 2.38 g / cm³. 3 The discharge retention rate is above 78% at -20℃ and 0.2C.

[0075] In some embodiments of this application, the compacted density of the composite lithium iron phosphate powder is 2.45 g / cm³. 3 The discharge retention rate is above 78% at -20℃ and 0.2C.

[0076] In some embodiments of this application, the compacted density of the composite lithium iron phosphate powder is 2.5 g / cm³. 3 The discharge retention rate is above 85% at -20℃ and 0.2C.

[0077] According to another embodiment of this application, a method for preparing the above-mentioned composite lithium iron phosphate is provided, comprising the following steps:

[0078] The high-density lithium iron phosphate and high-power lithium iron phosphate are mixed to obtain the final product.

[0079] In some embodiments of this application, the preparation method includes the step of preparing high-pressure lithium iron phosphate, specifically including:

[0080] Fe source I, Li source I, P source I, and reducing carbon source I are mixed, ground, sprayed, and sintered under an inert atmosphere to obtain the product. The amount of carbon source I added is controlled so that the carbon content in the product is 0.8% to 1.4% of the product mass.

[0081] In some embodiments of this application, the Li:Fe molar ratio is approximately 1.03 to 1.05 and the Fe:P molar ratio is >96.5% during the preparation of the high-pressure lithium iron phosphate.

[0082] In some embodiments of this application, the preparation method includes the step of preparing high-power lithium iron phosphate, specifically including:

[0083] Fe source II, Li source II, P source II, and reducing carbon source II are mixed, ground, sprayed, and sintered under an inert atmosphere to obtain the product. The amount of carbon source II added is controlled so that the carbon content in the product is 0.9% to 1.6% of the product mass.

[0084] In some embodiments of this application, the Li:Fe molar ratio is approximately 1.03 to 1.05 and the Fe:P molar ratio is >97% during the preparation of the high-power lithium iron phosphate.

[0085] The preparation method according to one embodiment of this application has at least the following beneficial effects: the preparation method of the scheme of this application does not require complex preparation process and expensive equipment, thus saving production costs. At the same time, it is easy to operate and has good industrial application prospects.

[0086] In some embodiments of this application, the inert atmosphere used in the steps of preparing high-pressure lithium iron phosphate and high-power lithium iron phosphate is independently selected from nitrogen, helium, and argon. It can be an inert atmosphere formed by nitrogen or an inert gas.

[0087] In some embodiments of this application, the sintering temperature in the steps of preparing high-pressure lithium iron phosphate and preparing high-power lithium iron phosphate is independently selected from 750°C to 800°C.

[0088] The primary particle size can be controlled by adjusting the grinding particle size and sintering temperature; the tap density can be controlled by adjusting the grinding particle size, spraying, sintering, and pulverizing; the secondary particle size can be controlled by adjusting the pulverizing parameters; and the carbon content can be controlled by adjusting the amount of carbon source added. The particle strength can be controlled by controlling the solid content of the grinding slurry, the spray inlet air temperature, and the temperature rise curve during sintering, thereby controlling the particle density and moisture content after spray drying, as well as the rate of moisture and carbon dioxide emission during sintering. Through conventional adjustments, high-power lithium iron phosphate and high-pressure lithium iron phosphate meeting the above parameters can be obtained. Then, the two are mixed to obtain the composite lithium iron phosphate of the embodiment described in this application.

[0089] In some embodiments of this application, the Fe sources I and II are independently selected from at least one of FeSO4, FePO4, FeCl3, FeC2O4, and Fe2O3.

[0090] In some embodiments of this application, the Li sources I and II are independently selected from at least one of Li2CO3, LiH2PO4, and Li3PO4.

[0091] In some embodiments of this application, the reducing carbon sources I and II are independently selected from at least one of C2H2, CH4, glucose, polyethylene glycol, sucrose, starch, and CO.

[0092] According to another embodiment of this application, a positive electrode sheet is provided, wherein the raw materials for preparing the positive electrode sheet include a positive electrode active material, wherein the positive electrode active material includes the above-mentioned composite lithium iron phosphate or composite lithium iron phosphate prepared by the above method.

[0093] The positive electrode sheet according to one embodiment of this application has at least the following beneficial effects: the composite lithium iron phosphate of this application has high compaction density, excellent low-temperature resistance, and good thermodynamic stability. The positive electrode sheet made using this material exhibits superior performance in terms of energy density, low-temperature adaptability, cycle life, and thermal stability. The compaction density of the positive electrode sheet made using the above composite material can reach 2.65 g / cm³. 3 In summary, the high density of this electrode allows batteries made from this material to store more energy within the same volume. Furthermore, this electrode maintains stable performance under both high and low temperature conditions, remaining virtually unaffected by significant temperature changes. Therefore, batteries made from this electrode exhibit high stability and good safety, making them promising for a wide range of applications.

[0094] In some embodiments of this application, the raw materials for preparing the positive electrode sheet also include a positive electrode conductive agent and a positive electrode binder.

[0095] In some embodiments of this application, the positive electrode conductive agent can be a conventional conductive agent, such as conductive carbon black (e.g., acetylene black, Super P, Super S, 350G or Ketjen black), conductive graphite (e.g., KS-6, KS-15, SFG-6, SFG-15 or Ks-6), carbon fiber or carbon nanotubes.

[0096] Conductive agents are added during electrode fabrication to ensure good charge-discharge performance. These conductive materials collect microcurrents between active materials and between the active materials and the current collector, reducing electrode contact resistance and accelerating electron movement. They also effectively increase the migration rate of lithium ions within the electrode material, thereby improving charge-discharge efficiency. Conventional conductive agents used in this field can be added in standard amounts; no restrictive regulations are imposed.

[0097] In some embodiments of this application, the positive electrode binder may be a conventional binder, such as fluoropolymers and / or synthetic rubbers. In some examples, it may be selected from any one or a combination of at least two of polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, styrene-butadiene rubber, fluororubber, and ethylene propylene diene rubber.

[0098] Typical but non-limiting examples of the combinations include: combinations of polyvinylidene fluoride and polyvinylidene fluoride; combinations of polytetrafluoroethylene and styrene-butadiene rubber; combinations of styrene-butadiene rubber, fluorinated rubber, and ethylene propylene diene rubber; combinations of polytetrafluoroethylene, styrene-butadiene rubber, and fluorinated rubber; combinations of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, and styrene-butadiene rubber; combinations of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, fluorinated rubber, and ethylene propylene diene rubber, etc., with particular selection from polyvinylidene fluoride.

[0099] In some embodiments of this application, the raw materials for preparing the positive electrode sheet include positive electrode active material, positive electrode conductive agent, and positive electrode binder in a mass ratio of (89-96):(1-4):(3-7). The presence of a certain proportion of conductive agent and binder in the lithium-ion battery positive electrode material facilitates the adhesion of the active material to the current collector during electrode sheet fabrication, thereby improving the charge-discharge efficiency of the positive electrode. For example, ratios of 89:1:3, 90:2:4, 92:3:5, 94:1.5:3.5, 94:1:3, 94:2:4, 95:1:3, 95:2:5, or 96:2:5 are all possible, including but not limited to the listed values. Furthermore, other unlisted values ​​within the same range are also applicable.

[0100] According to another embodiment of this application, a secondary battery is proposed, comprising the above-described positive electrode sheet.

[0101] The secondary battery according to an embodiment of the present application has at least the following beneficial effects: The lithium iron phosphate positive electrode sheet compounded by the solution of the embodiment of the present application not only has a high energy density, but also the secondary battery made of this electrode sheet shows a higher energy output capacity. At the same time, this positive electrode sheet also has excellent low-temperature performance. Even under low-temperature conditions, it can maintain a high discharge efficiency and capacity retention rate, ensuring that the battery can still maintain a good working state in a cold environment. In addition, this material also has a long cycle life and excellent thermal stability, making the secondary battery made of it not only have a longer service life, but also is not prone to thermal runaway or combustion under extreme conditions. Therefore, it has extremely broad application prospects.

[0102] In some embodiments of the present application, the secondary battery is a lithium-ion battery.

[0103] In some embodiments of the present application, the secondary battery further includes a negative electrode sheet. The preparation raw materials of the negative electrode sheet include a negative electrode active material, and the active material includes at least one of graphite and hard carbon. A negative electrode sheet commonly used in the art can be used, including carbon materials (which can be mesocarbon microbead graphite, natural graphite, expanded graphite, glassy carbon, activated carbon, carbon-carbon composite materials, carbon fibers, hard carbon, porous carbon, highly oriented graphite, carbon black, carbon nanotubes or graphene, etc.) or non-carbon materials (which can be typically but not limited to SiO x / C composite materials. The " / " in the SiO x / C composite materials can be understood to mean "and", that is, a material composed of SiO x material and carbon material. x generally ranges between 0 and 2 (0 < x < 2). Specifically, such as SiO x / mesocarbon microbead graphite, SiO x / natural graphite, SiO x / expanded graphite, SiO x / glassy carbon, SiO x / activated carbon, SiO x / carbon fiber, SiO x / hard carbon, SiO x / highly oriented graphite, SiO x / carbon black, SiO x / carbon nanotubes or SiO x / graphene, etc., and any one or more of these materials can be selected. In some examples, the SiO x / C composite material is a SiO x / artificial graphite composite material) are all applicable.

[0104] In some embodiments of this application, the raw materials for preparing the negative electrode sheet also include a negative electrode conductive agent and a negative electrode binder.

[0105] In some embodiments of this application, the negative electrode conductive agent can be a conventional conductive agent. Typical but not limiting conductive agents include conductive carbon black (such as acetylene black, Super P, Super S, 350G, or Ketjen black), conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, or Ks-6), carbon fiber, or carbon nanotubes. The conductive agent is added during electrode fabrication to ensure good charge-discharge performance of the electrode. It collects microcurrents between active materials and between the active materials and the current collector, reducing electrode contact resistance and accelerating electron movement. It also effectively increases the migration rate of lithium ions in the electrode material, thereby improving the charge-discharge efficiency of the electrode.

[0106] In some embodiments of this application, the negative electrode binder includes any one or more of sodium alginate, lithium alginate, polyacrylic acid, sodium carboxymethyl cellulose, or styrene rubber, and may be selected from lithium alginate. Conventional negative electrode binders can be used; no particular limitation is made, and this is merely an exemplary example.

[0107] In some embodiments of this application, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is (89-96):(1-4):(3-7), for example, it can be 89:1:3, 90:2:4, 92:3:5, 94:1.5:3.5, 94:1:3, 94:2:4, 95:1:3, 95:2:5, or 96:2:5, etc., including but not limited to the listed values. Other unlisted values ​​within the range are also applicable. The presence of a certain proportion of conductive agent and binder in the lithium-ion battery negative electrode material is beneficial for the active material to adhere well to the current collector during electrode fabrication, thereby improving the charge and discharge efficiency of the negative electrode.

[0108] In some embodiments of this application, the secondary battery further includes an electrolyte comprising a lithium salt.

[0109] In some embodiments of this application, the lithium salt is selected from at least one of LiPF6, LiBF4, and LiTFSI. Any conventional lithium salt may be used. No particular limitation is made.

[0110] In some embodiments of this application, the solvent of the electrolyte includes any one or more of propylene carbonate, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, N,N-dimethylacetamide, fluoroethylene carbonate, methyl propionate, ethyl propionate, ethyl acetate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, dimethoxymethane, 1,2-dimethoxypropane, triethylene glycol dimethyl ether, dimethyl sulfone, dimethyl ether, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, and crown ether (12-crown-4).

[0111] In some embodiments of this application, the solvent is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC).

[0112] In some embodiments of this application, the volume ratio of EC, DEC and EMC in the solvent is (35 to 45): (25 to 35): 30.

[0113] In some embodiments of this application, the volume ratio of EC, DEC and EMC in the solvent is (38 to 42):(28 to 32):30.

[0114] In some embodiments of this application, the volume ratio of EC, DEC and EMC in the solvent is 4:3:3.

[0115] In some embodiments of this application, the electrolyte further contains additives; the mass fraction of the additives in the electrolyte is 0.1% to 20%, optionally from 5% to 15%. Typical, but not limiting, mass fractions of the additives in the electrolyte are 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, 18%, or 20%.

[0116] Understandably, there are no particular restrictions on electrolyte additives, and conventional electrolyte additives can be used.

[0117] Adding one or more additives to the electrolyte can further improve one or more properties of a secondary battery. Based on their function, additives include film-forming additives (such as carbon dioxide, sulfur dioxide, lithium carbonate, carbonates, thiolated organic solvents, halogenated organic film-forming additives, etc.), overcharge protection additives (with redox couples: ortho- and para-dimethoxy-substituted benzenes, polymerization increases internal resistance, blocking charging, such as biphenyl, cyclohexylbenzene, etc.), stabilizers, additives that improve high and low temperature performance, conductive additives, or flame retardant additives (organophosphorus compounds, organofluorine compounds, halogenated alkyl phosphates, etc.).

[0118] In some embodiments of this application, the additives include fluoroethylene carbonate (FEC), vinylene carbonate (VC), cyclohexylbenzene (CHB), ethylene carbonate, 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone, vinyl sulfate, propylene sulfate, ethylene sulfate, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, ethylene sulfite, methyl chloroformate, succinic anhydride (SA), dimethyl sulfoxide, anisole, acetamide, diazabenzene, and m-diazabenzene. The following are any one or more of the following: 12-crown ether-4, 18-crown ether-6, 4-fluoroanisole, fluorochain ether, difluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, chloroethylene carbonate, bromoethylene carbonate, trifluoroethylphosphonic acid, bromobutyrolactone, fluoroacetic acid ethane, phosphate ester, phosphite ester, phosphazene, ethanolamine, dimethyl carbide, cyclobutyl sulfone, 1,3-dioxocyclopentane, acetonitrile, long-chain olefins, aluminum oxide, magnesium oxide, barium oxide, potassium carbonate, calcium carbonate, carbon dioxide, sulfur dioxide, and lithium carbonate.

[0119] The additives can be used alone or in combination of two or more of the above-mentioned additives.

[0120] In some embodiments of this application, the electrolyte contains vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), and cyclohexylbenzene (CHB).

[0121] In some embodiments of this application, the mass ratio of VC, PS, FEC and CHB is 2 to 4: 1 to 3: 0.5 to 1.5: 1.

[0122] In some embodiments of this application, the mass ratio of VC, PS, FEC and CHB is 2.5 to 3.5: 1.5 to 2.5: 0.8 to 1.2: 1.

[0123] In some embodiments of this application, the mass ratio of VC, PS, FEC and CHB is 3:2:1:1.

[0124] In some embodiments of this application, the secondary battery further includes a separator. There are no particular limitations on the separator; any common separator in the art can be used. Examples include polyethylene (PE) separators, polypropylene (PP) separators, or PE / PP composite separators.

[0125] According to another aspect of this application, an electrical device is proposed, including the aforementioned secondary battery.

[0126] The electrical device according to one embodiment of this application has at least the following beneficial effects: the secondary battery of the solution of this application has a high energy density, which can support higher energy output. At the same time, it can maintain good working performance even in cold environments, meeting the usage needs of electric vehicles, smartphones and other electronic devices in winter; the secondary battery of the solution of this application has good thermal stability and chemical stability, reducing the safety accidents that may occur during the use of electrical devices.

[0127] In some embodiments of this application, the electrical device is an electric vehicle. It can also be other electrical devices such as energy storage systems, power tools, drones, mobile devices such as wearable products, laptops, and mobile phones.

[0128] In some embodiments of this application, the electrical device is an electric car or an electric bicycle. It can also be other electric vehicles, such as electric motorcycles, electric scooters, electric wheelchairs, etc.

[0129] In this application, "high-pressure compacted lithium iron phosphate" refers to a powder compaction density ≥ 2.38 g / cm³ under a pressure of 3 tons. 3 (can be ≥2.45g / cm) 3 The lithium iron phosphate material, referred to as "high-power lithium iron phosphate," means that the powder compaction density is <2.2 g / cm³ under 3 tons of pressure. 3 Furthermore, the lithium iron phosphate material has a 1C cladding capacity of >150mAh / g.

[0130] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing this application. Attached Figure Description

[0131] The above and / or additional aspects and advantages of this application will be described in conjunction with the following drawings, in which:

[0132] Figure 1 is a scanning electron microscope (SEM) image of the high-density lithium iron phosphate prepared in Example 1 of this application.

[0133] Figure 2 is a scanning electron microscope (SEM) image of the high-power lithium iron phosphate prepared in Example 1 of this application.

[0134] Figure 3 is a scanning electron microscope (SEM) image of the composite lithium iron phosphate prepared in Example 1 of this application.

[0135] Figure 4 is a flowchart of the preparation method of composite lithium iron phosphate according to an embodiment of this application.

[0136] Explanation of reference numerals in the attached figures:

[0137] In Figures 1 and 2: 1: Primary particles of high-pressure lithium iron phosphate; 2: Primary particles of high-power lithium iron phosphate; The markings in the figures are not particularly limiting and are only shown as illustrative examples of primary particle size for ease of understanding.

[0138] In Figure 4: S100 represents mixing carbon-coated high-density lithium iron phosphate and carbon-coated high-power lithium iron phosphate; S200 represents obtaining composite lithium iron phosphate. Detailed Implementation

[0139] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application. Unless otherwise specified, the experimental methods used in the embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available. Unless otherwise specified, the same parameter value is the same in each embodiment. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0140] In the description of this application, the terms "one embodiment," "some embodiments," "one example," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0141] In some embodiments of this application, the Fe, Li, P, and C sources that can be selected for preparing high-power or high-density lithium iron phosphate are as follows: Fe sources can be FeSO4, FePO4, FeCl3, FeC2O4, or Fe2O3; Li sources can be Li2CO3, LiH2PO4, or Li3PO4; reducing carbon sources can be C2H2, CH4, glucose, polyethylene glycol, sucrose, starch, or CO. When preparing high-density lithium iron phosphate, the amounts of Fe, Li, and P sources satisfy the following relationship: the Li:Fe molar ratio is approximately 1.03 to 1.05, and the Fe:P molar ratio is >96.5%. When preparing high-power lithium iron phosphate, the amounts of Fe, Li, and P sources satisfy the following relationship: the Li:Fe molar ratio is approximately 1.03 to 1.05, and the Fe:P molar ratio is >96.5%. The carbon content can be achieved by adjusting the amount of reducing carbon source added in the formula, based on common knowledge. Specifically, the carbon content mass ratio in high-pressure lithium iron phosphate is selected from 0.8% to 1.4%; and the carbon content mass ratio in high-power lithium iron phosphate is selected from 0.9% to 1.6%.

[0142] In some embodiments of this application, when preparing high-power or high-compact lithium iron phosphate, the primary particle size can be achieved by adjusting the milling particle size and sintering temperature according to common knowledge; the tap density can be achieved mainly by adjusting the milling particle size, spraying, sintering, and pulverizing parameters according to common knowledge; the secondary particle size can be achieved mainly by adjusting the pulverizing parameters according to common knowledge; and the particle strength is controlled by controlling the solid content of the grinding slurry, the spray inlet air temperature, and the temperature rise curve during the sintering process, thereby controlling the particle density and moisture content after spray drying and controlling the rate of moisture and carbon dioxide emission during sintering. The sintering temperature can be selected from 750℃ to 800℃.

[0143] In some embodiments of this application, when preparing high-power or high-pressure lithium iron phosphate, either nitrogen or an inert gas atmosphere can be used as the inert atmosphere.

[0144] In some embodiments of this application, when preparing a lithium-ion battery, the separator can be a commercially available PE, PP or PE / PP composite separator.

[0145] Examples 1 to 10 and Comparative Example 1

[0146] This example demonstrates the preparation of a composite lithium iron phosphate (LFP) consisting of high-power LFP and high-density LFP. The preparation process involves mixing the high-power LFP and high-density LFP, as shown in Figure 4. The characteristic parameters of the high-power LFP (referred to as "high-power" in the table) and the high-density LFP (referred to as "high-density") are shown in Table 1 below.

[0147] Table 1

[0148] The ratios mentioned in the table above are all for high-pressure lithium iron phosphate: high-power lithium iron phosphate.

[0149] The high-compact / high-power lithium iron phosphate in Table 1 can be obtained through the following preparation process: Fe source, Li source, P source raw materials and reducing carbon source (as reducing agent and carbon source) are mixed, ground and sprayed, and the resulting mixture is sintered under an inert atmosphere to obtain lithium iron phosphate substrate. After air jet milling, high-compact / high-power lithium iron phosphate material that meets the particle size requirements is obtained.

[0150] The methods for testing particle size and particle strength in the table above are as follows:

[0151] 1) Primary particle size test

[0152] The particle morphology of high-compact and high-power lithium iron phosphate materials was tested by SEM, and the average of 100 primary particle sizes was statistically measured to obtain the average primary particle size of the material.

[0153] 2) Secondary particle size test

[0154] Secondary particle size and carbon content tests were conducted in accordance with the test methods in GB / T 30835-2014 Carbon Composite Lithium Iron Phosphate Cathode Materials for Lithium-ion Batteries.

[0155] 3) Particle strength test

[0156] The MCT series micro compression testing machine uses an electromagnetic mechanism to apply a constantly increasing test force to the positive electrode particle, fixing it between the upper pressure bar (standard 50μm flat pressure head) and the lower pressure plate. The deformation of the sample is then automatically measured. The particle hardness is determined based on its compressive strength at the fracture point, calculated using the applied compressive force and particle diameter: H = 2.8P / (πr). 2 ), where H is the compressive breaking strength (mN / μm) 2 P is the applied compressive force (mN), and r is the particle diameter (μm). The calculated H value is proportional to 1 Pa = 1 N / m. 2 Convert to MPa units for easier and more concise writing.

[0157] The morphology of the high-compaction lithium iron phosphate and high-power lithium iron phosphate in each embodiment and comparative example was characterized by scanning electron microscopy (SEM). Figure 1 shows the morphology characterization results of the high-compaction lithium iron phosphate used in Example 1, which identifies primary particles 1 of high-compaction lithium iron phosphate with different particle sizes. As can be seen from the figure, the high-compaction lithium iron phosphate in this embodiment improves powder compaction density by combining large and small primary particle sizes.

[0158] The morphology characterization results of high-power lithium iron phosphate are shown in Figure 2, which identifies the primary particles 2 of the high-power lithium iron phosphate in the material. As can be seen from the figure, the high-power lithium iron phosphate in this embodiment consists of high-tap-density secondary agglomerates with small primary particle sizes. The primary particle size is uniform, improving power while also taking into account processing performance.

[0159] The morphological characterization results of the composite lithium iron phosphate prepared in Example 1 are shown in Figure 3. As can be seen from the figure, the secondary particles of high-power lithium iron phosphate are spherical or near-spherical, and the overall particle size of the composite lithium iron phosphate exhibits a mixture of large and small particles.

[0160] The morphological characterization results of other embodiments are similar, and to avoid redundancy, they are not shown one by one.

[0161] Application effect example

[0162] Using the composite lithium iron phosphate from the above examples and comparative examples as the positive electrode active material, a slurry was prepared according to conventional techniques and then coated onto the positive electrode current collector to obtain the positive electrode sheet. This positive electrode sheet, along with the negative electrode sheet, separator, and electrolyte, were then used to fabricate a lithium-ion battery using conventional techniques.

[0163] In the above embodiments, the positive electrode sheet prepared from the composite lithium iron phosphate has a compaction density of not less than 2.6 g / cm³. 3 The negative electrode used is a commercially available conventional lithium-ion battery negative electrode, with a compaction density of not less than 1.6 g / cm³. 3 The negative electrode active material in the negative electrode sheet is amorphous carbon-coated graphite, such as the Shanshan QCG-X9 negative electrode. The electrode sheets are baked in a 110℃ high-temperature oven for 7 hours to remove moisture. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. After being wound into a square bare cell, it is placed in an aluminum-plastic film, injected with the appropriate non-aqueous electrolyte, and sealed. Following processes such as settling, hot and cold pressing, formation, clamping, and capacity testing, a lithium-ion battery with a nominal capacity of 2Ah is obtained. The non-aqueous electrolyte has a composition of EC:DEC:EMC = 4:3:3, with additives accounting for 10% of the total mass. The additive composition is VC:PS:FEC:CHB = 3:2:1:1, and the concentration of lithium hexafluorophosphate in the electrolyte is 1mol / L.

[0164] The performance of the composite lithium iron phosphate batteries in the above embodiments and comparative examples, as well as the lithium-ion batteries prepared in the above application effect examples, was tested. The test process is as follows:

[0165] 1) Powder compaction density

[0166] Weigh 1g of the composite lithium iron phosphate from each of the examples and comparative examples, and add it to a cylindrical mold with a cross-sectional area of ​​S in the circular hole. Apply a pressure of 3t to the powder inside the mold and hold the pressure for 30s, recording the powder thickness as t. Then, calculate the compacted density ρ (g / cm³) of the lithium iron phosphate cathode active material corresponding to each of the examples and comparative examples. 3 The sample mass (g) can be calculated using the following formula: ρ = m / (S × t), where m is the sample mass and S is the cross-sectional area of ​​the mold hole (cm²). 2 ), where t is the thickness of the powder (cm).

[0167] 2) Low-temperature discharge capacity retention rate at -20℃

[0168] The lithium-ion batteries prepared with composite lithium iron phosphate in the above examples and comparative examples were subjected to charge-discharge tests. One charge-discharge cycle was as follows: constant current charging at 0.2C to 3.65V, followed by constant voltage charging until the charging current was less than 0.05C; pause for 5 minutes; constant current discharge at 0.2C to 2.5V; pause for 5 minutes. This constitutes one room temperature charge-discharge cycle of the battery. The battery was fully charged at room temperature and then placed in a -20℃ low-temperature chamber for 5 hours. It was then discharged at a constant current of 0.2C to 2.5V. The ratio of the low-temperature discharge capacity to the room-temperature discharge capacity was calculated.

[0169] 3) 45℃ Cyclic Performance Test

[0170] The lithium-ion batteries prepared with composite lithium iron phosphate in the above examples and comparative examples were placed in a 40°C oven and left to stand for 2 hours, followed by charge-discharge tests. One charge-discharge cycle was as follows: constant current charging at 1C to 3.65V, then constant voltage charging continued until the charging current was less than 0.05C; paused for 5 minutes; constant current discharging at 1C to 2.5V; paused for 5 minutes. This constituted one charge-discharge cycle of the battery. This process was repeated continuously until 500 cycles were completed, and the ratio of the battery capacity to its initial value was calculated.

[0171] The test results are shown in Table 2 below.

[0172] Table 2

[0173] As can be seen from Table 2, compared with Example 1, in Example 2, as the proportion of high-pressure lithium iron phosphate increases, the powder compaction is improved, but the low-temperature discharge capability decreases, while the high-temperature cycling capability is slightly improved.

[0174] Compared with Example 1, in Example 3, with the increase of the proportion of high-power lithium iron phosphate, the powder compaction is reduced, the low-temperature discharge capability is significantly improved, and the high-temperature cycling capability is slightly reduced.

[0175] Compared with Example 1, Example 4 increased the primary particle size of the high-pressure compacted phosphoric acid material (by raising the sintering temperature of the lithium iron phosphate material to 795°C). As the ratio of high-pressure compacted primary particle size to high-power primary particle size increased, the average primary particle size of the high-pressure compacted material became larger, and the powder compaction was significantly improved. However, the low-temperature discharge capability decreased, while the high-temperature cycling trend was slightly improved.

[0176] Compared with Example 1, Example 5 increases the secondary particle size Dv50 (achieved by adjusting the spraying parameters of the high-power material). As the high-power material Dv50 increases and the ratio of high-compacted Dv50 to high-power Dv50 decreases, the powder compaction remains unchanged, the lithium-ion migration distance increases, and the low-temperature discharge capability decreases.

[0177] Compared with Example 1, Example 6 increases the carbon coating on the surface of high-pressure lithium iron phosphate. As the high-pressure C content and high-power C content increase, the material compaction density shows a decreasing trend. The low-temperature discharge capability is basically the same, and the high-temperature cycling capability is slightly improved.

[0178] Compared to Example 1, Example 7 improved the strength of high-power material particles by reducing the solvent evaporation rate during the spraying process, lowering the spray inlet air temperature to 190°C, and extending the heating rate during sintering. With the increased strength of the high-power material particles, the material compaction density improved slightly, but the impedance of the lithium-ion intercalation cathode material increased slightly at low temperatures, resulting in a slight decrease in low-temperature discharge performance, while the high-temperature cycling performance remained essentially unchanged.

[0179] Compared to Example 1, in Example 8, although the low-temperature retention rate was significantly improved when the high-power material blending ratio was increased, the powder compaction decreased to 2.4 g / cm³. 3 .

[0180] Compared to Example 1, the high-power LFP material particles in Example 9 showed reduced strength, and the blended high-power LFP particles exhibited breakage after compaction, leading to a sharp decrease in powder compaction (2.4 g / cm³). 3 This does not meet the energy density requirements of battery cell design.

[0181] Compared with Example 1, Example 10 has a higher C content in high-power LFP materials, which increases to 1.1. The increased carbon content reduces powder compaction, which in turn leads to a decrease in powder compaction after mixing. Low-temperature discharge is slightly improved, but it does not meet the energy density requirements of cell design.

[0182] In Comparative Example 1, the high-compacted:high-power mass ratio was consistent with Example 1, at 8:2. The high-power material particles had higher strength, and the high-compacted and high-power material primary particle size design was too large, despite the powder compaction density increasing to 2.56 g / cm³. 3 However, compared with Example 1, the low-temperature discharge characteristics are significantly reduced, and it is impossible to simultaneously meet the requirements of energy density and low-temperature performance.

[0183] The embodiments of this application have been described in detail above, but this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application.

Claims

1. A composite lithium iron phosphate, comprising high-density lithium iron phosphate and high-power lithium iron phosphate, wherein both the high-density lithium iron phosphate and the high-power lithium iron phosphate are coated with carbon, wherein... The ratio of the carbon content on the surface of the high-pressure lithium iron phosphate to the carbon content on the surface of the high-power lithium iron phosphate is a, and the strength of the high-power lithium iron phosphate particles is b. Wherein, a and b satisfy the following relationships: 0.5≤a≤1.1; 40MPa≤b≤150MPa.

2. The composite lithium iron phosphate according to claim 1, wherein, The high-pressure lithium iron phosphate and high-power lithium iron phosphate also satisfy at least one of the following conditions: 1) The ratio of the average primary particle size of the high-pressure lithium iron phosphate and the high-power lithium iron phosphate is c, and c satisfies the following relationship: 3 < c < 6. 2) Both the high-pressure lithium iron phosphate and the high-power lithium iron phosphate include a secondary particle structure formed by primary particle agglomeration. The ratio of the secondary particle Dv50 of the high-pressure lithium iron phosphate and the high-power lithium iron phosphate is d, and d satisfies the following relationship: 0.05 < d < 0.

15. 3) The ratio of the tap density of the high-pressure lithium iron phosphate to that of the high-power lithium iron phosphate is e, where e satisfies the following relationship: 0.2 < e < 0.

7.

3. The composite lithium iron phosphate according to claim 1 or 2, wherein, a and b each satisfy at least one of the following relationships: 1) 0.8 ≤ a ≤ 1; 2) 50 MPa ≤ b ≤ 100 MPa.

4. The composite lithium iron phosphate according to claim 1 or 2, wherein, The high-pressure lithium iron phosphate also possesses at least one of the following characteristics: 1) The carbon content on the surface of the high-pressure lithium iron phosphate is 0.8% to 1.4%; 2) The primary particle size of the high-pressure lithium iron phosphate is between 300 nm and 1000 nm; 3) The secondary particle size (Dv50) of the high-pressure lithium iron phosphate is 0.5 μm to 1.5 μm; 4) The tap density of high-pressure lithium iron phosphate is <1.2 g / cm³. 3 .

5. The composite lithium iron phosphate according to claim 1 or 2, wherein, The high-pressure lithium iron phosphate also possesses at least one of the following characteristics: 1) The carbon content on the surface of the high-power lithium iron phosphate is 0.9% to 1.6%; 2) The primary particle size of the high-power lithium iron phosphate is between 50 nm and 250 nm; 3) The secondary particle Dv50 of the high-power lithium iron phosphate is 6μm to 10μm; 4) The tap density of high-power lithium iron phosphate is >1.6 g / cm³. 3 .

6. The composite lithium iron phosphate according to claim 1 or 2, wherein, The mass ratio of the high-pressure lithium iron phosphate to the high-power lithium iron phosphate is x:(10 to x), where x satisfies the following relationship: 5≤x<10.

7. The composite lithium iron phosphate according to claim 6, wherein, x satisfies the following relationship: 6≤x≤8.

8. A secondary battery, comprising a positive electrode sheet, wherein the raw materials for preparing the positive electrode sheet include a positive electrode active material, wherein the positive electrode active material includes a composite lithium iron phosphate as described in any one of claims 1 to 7.

9. The secondary battery according to claim 8, wherein, The secondary battery is a lithium-ion battery.

10. An electrical device comprising a secondary battery as described in claim 8 or 9.

11. The electrical appliance according to claim 10, wherein, The electrical device is an electric vehicle.

12. The electrical appliance according to claim 10, wherein, The electrical device is an electric car or an electric bicycle.

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