Positive electrode active material, secondary battery, and electric device

Abstract

The present invention relates to a positive electrode active material, a secondary battery and an electric device, the positive electrode active material comprising positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, the fluoride coating material comprising a compound represented by formula I: A7-(2n + 3m) MnM'mF7-xRx / y, wherein 0 < n < = 2, 0 < m < = 2, 0 < = x < = 2, and y is the absolute value of the valence state of R; a comprises Na and / or Li; m comprises at least one of Ca, Zn, Mg, Sr and Ba; m'comprises at least one of Ga, Al, La, Y, B, In, Sc, Bi and Sb; r comprises at least one of O, S, Se, Te, Cl, Br, I, CN, BF4 and BH4.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a fluoride coating material, a positive electrode active material comprising positive electrode active particles coated with the fluoride coating material, and a secondary battery. BACKGROUND

[0002] During the cycle process of the battery, electrochemical degradation phenomena such as voltage drop and capacity attenuation often occur. In addition, in the high charged state, the oxygen ions in the oxide positive electrode participate in the redox reaction, and the reaction between the generated oxygen and the organic electrolyte will release a large amount of heat, causing the battery to heat runaway, which has great safety hazards. SUMMARY The present application provides a positive electrode active material, a secondary battery comprising the same, and a power device, the positive electrode active material comprising positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, wherein the fluoride coating material has good corrosion resistance and air stability, and at the same time has high thermodynamic stability, wide electrochemical window, high ionic conductivity and excellent mechanical properties, which can be adapted to common high-voltage positive electrode materials, so that the positive electrode active particles coated with it can improve the cycle stability and heat runaway of the battery.

[0003] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material. The positive electrode active material comprises positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, the fluoride coating material comprising a compound represented by Formula I: Formula I; wherein 0 A comprises Na and / or Li; M comprises at least one of Ca, Zn, Mg, Sr, Ba; M' comprises at least one of Ga, Al, La, Y, B, In, Sc, Bi, Sb; R comprises at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, BH4.

[0004] The fluoride coating material of the present application has high thermodynamic stability, wide electrochemical window, high ionic conductivity and excellent mechanical properties at the same time, which can alleviate the side reaction between the positive electrode active particles and the electrolyte after coating the positive electrode active particles with it, so that the positive electrode active particles can work at a higher voltage, thereby improving the capacity and energy density of the battery, as well as the first cycle coulombic efficiency, cycle stability, safety and rate performance, and especially improving the battery heat runaway.

[0005] In terms of thermodynamic stability, the anion framework of the fluoride coating material is mainly composed of fluoride ions, and the electronegativity of fluorine element is very high (stronger than oxygen and chlorine), and the interaction between the cations in the structure is stronger, so the structure is more stable, so that the fluoride coating material is coated on at least part of the surface of the positive active particles, which can improve the structural stability of the positive active particles, thereby improving the cycle stability of the battery. In terms of electrochemical window, the fluoride coating material can have a working voltage range that can cover the high-voltage positive electrode and the electrolyte, and the high-voltage resistance is significantly stronger than that of the oxide. Due to the good electrochemical stability of the coating material, the electrochemical side reaction between the high-voltage positive electrode and the electrolyte can be avoided. In terms of ionic conductivity, the fluoride coating material has a Weberite configuration (also known as a magnesioice structure or a magnesioice-like structure), which has a three-dimensional ion transmission channel, and the alkali metal in the structure is in a higher octahedral environment. On the one hand, the high coordination environment forms a "alkali metal cage" with a larger space, and the migration barrier of alkali metal ions is reduced; on the other hand, the alkali metal-F bond in the structure is longer, and the binding ability of the alkali metal ion is weaker, so that the diffusion coefficient of the alkali metal ion is higher; therefore, the fluoride coating material has excellent ionic conductivity. Furthermore, M and M' in the fluoride coating material are in the octahedral coordination connected by the apex in the Weberite configuration structure, which plays a supporting role in the structure framework. The framework connected by the apex has a larger creep space, which can improve the mechanical properties. The application further selects M (at least one of Ca, Zn, Mg, Sr, and Ba) and M' (at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb) with suitable ionic radii, which can increase the crystal axis length and the lattice volume, thereby widening the lattice structure and increasing the ion transmission channel, and further improving the ionic conductivity. The ionic conductivity of the fluoride coating material in the application can be 3-7 orders of magnitude higher than that of Li2ZrF6, LiF, etc. This indicates that it has potential fast charging capability and does not affect the rate performance of the battery. In addition, in terms of mechanical properties, the fluoride coating material can have a smaller mechanical modulus than LiF, Li2ZrF6, LiNbO3, and Li3PO4, which indicates that the fluoride coating material is softer than other fluorides and oxides, and is easier to process, and is not easy to break during rolling and cycling, which does not adversely affect the efficiency and capacity of the positive electrode material.

[0006] In any embodiment, M further comprises not more than 10 mol% of a first transition metal element based on the total moles of M, wherein the first transition metal element comprises at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, and V.

[0007] In any embodiment, M' further includes not more than 10 mol% of a second transition metal element based on the total moles of M', wherein the second transition metal element includes at least one of Fe, Co, Ni, Mn, V, Ti, and Cr.

[0008] When the fluoride-coated material includes the above variable valence transition metal in a suitable amount, the electronic conductivity of the fluoride-coated material can be improved.

[0009] In any embodiment, A further includes not more than 20 mol% of K and / or Ag based on the total moles of A.

[0010] In any embodiment, M further includes not more than 10 mol% in total of at least one element of A and at least one element of M' based on the total moles of M.

[0011] In the crystal lattice of the fluoride-coated material, the M site can also be occupied by monovalent ions of at least one element of A (i.e., one or more of Li, Na, K, and Ag) and trivalent ions of at least one element of M' (i.e., one or more of Ga, Al, La, Y, B, In, Sc, Bi, and Sb). The monovalent ions occupy the M site because disordered mixing occurs during the synthesis of the fluoride-coated material, and ions at some of the A sites occupy the M site. In addition, allowing the trivalent ions to occupy the M site can cause alkali metal ion vacancies, thereby improving the alkali metal ion conductivity.

[0012] In any embodiment, M includes at least one of Ca, Zn, and Mg.

[0013] In any embodiment, M' includes at least one of Ga and Al.

[0014] When the fluoride-coated material includes one or more elements selected from Ca, Zn, and Mg and one or more elements selected from Ga and Al, the ion conduction ability and high voltage stability are further improved, so that the capacity, energy density, cycle stability, safety, and rate performance of the battery are improved.

[0015] In any embodiment, the positive electrode active material includes 0.01 to 10 wt% of the fluoride-coated material based on the total weight of the positive electrode active particles.

[0016] If the weight percentage of the coating material in the positive active material is less than 0.01, it will result in too small coating area on the surface of the positive active particles, uneven coating, and most of the positive active particles still directly contact with the electrolyte, so that the coating effect cannot be achieved. At high voltage, the positive active particles will still react violently with the electrolyte, thereby affecting the cycle performance and thermal stability of the battery. If the weight percentage of the coating material in the positive active material is greater than 10, it will result in too thick coating layer on the surface of the positive active particles, which will increase the impedance of the battery, thereby affecting the performance of the battery.

[0017] In any embodiment, the coating thickness of the fluoride coating material is 5 to 20 nm.

[0018] The oxide (such as Al2O3, MgO, etc.) and fluoride (such as AlF3, Li2ZrF6) coating layers commonly found on the surface of positive active particles are usually thin, for example, 2 to 10 nm, due to low ionic conductivity, in order to ensure high rate performance, and thin coating layers may degrade or fail during high temperature or long-term cycling, causing partial exposure of the positive electrode leading to thermal runaway. The fluoride coating material of the present application has high thermodynamic stability, wide electrochemical window, and high ionic conductivity, so that the thickness of the coating layer does not need to be precisely controlled to be thin, and a coating layer can be prepared on the surface of the corresponding high-voltage positive active particles by a simple coating process such as wet coating.

[0019] In any embodiment, the positive active particles include at least one of a layered oxide material, a spinel oxide material, and a fluoride material, wherein: The layered oxide material includes a compound represented by Formula II: Formula II In Formula II, 0 ≤ e ≤ 0.2, and f is the absolute value of the valence of R 1 , A 1 includes Li or Na, M a includes a transition metal element, R 1 includes at least one of F and Cl. The spinel oxide material includes a compound represented by Formula III: Formula III In Formula III, 0 ≤ g ≤ 0.4, and h is the absolute value of the valence of R 2 , A 2 includes Li or Na, M b includes a transition metal element, R 2 includes at least one of F and Cl. The fluoride material includes a compound shown in Formula IV: Formula IV In Formula IV, 0 < k ≤ 2, 0 < p ≤ 2, 0 ≤ i ≤ 2, j is the absolute value of the valence state of R 3 , A 3 includes Li or Na, M c includes a transition metal element having a divalent valence state, M d includes a transition metal element having a trivalent valence state, R 3 includes at least one of F and Cl.

[0020] The electrochemical window of the fluoride coating material of the present application can cover the working voltage range of common high-voltage positive electrode active materials. Coating the above-mentioned high-voltage positive electrode active material with a fluoride coating material can improve the capacity, energy density, cycle stability, safety and rate performance of the battery.

[0021] In any embodiment, the positive electrode active material has one or more of the following characteristics: (1) the Dv50 particle size of the positive electrode active material is in the range of 5 to 30 μm; (2) the BET specific surface area of the positive electrode active material is in the range of 0.1 to 14 m 2 / g; (3) the tap density of the positive electrode active material is in the range of 1.1 to 2.3 g / cm 3 ; (4) the hardness of the positive electrode active material is in the range of 6 to 12 GPa.

[0022] Controlling the Dv50 particle size, BET specific surface area, tap density and hardness of the positive electrode active particles in a suitable range can improve the processing performance of the positive electrode sheet, achieve improvement in electrochemical reaction kinetics, and improve cycle stability.

[0023] In any embodiment, the positive electrode sheet includes a current collector and a positive electrode film layer disposed on at least one surface of the current collector, wherein the positive electrode film layer includes 70% to 98% by weight of the positive electrode active material based on the total weight of the positive electrode film layer.

[0024] Controlling the proportion of the positive electrode active material in the positive electrode film layer in a suitable range can effectively improve the energy density of the battery.

[0025] In any embodiment, the positive electrode film layer further includes 2% to 30% by weight of a binder based on the total weight of the positive electrode film layer.

[0026] In any embodiment, the positive electrode has a strength of 2.3 to 3.7 g / cm³. 3 The compaction density within the range.

[0027] A second aspect of the present invention provides a positive electrode active material comprising positive electrode active particles and a fluoride coating material coating at least a portion of the surface of the positive electrode active particles. The fluoride coating material comprises a compound of formula I: Formula I; Where 0 < n ≤ 2, 0 < m ≤ 2, 0 ≤ x ≤ 2, and y is the absolute value of the valence state of R; A includes Na and / or Li; M includes at least one of Ca, Zn, Mg, Sr, and Ba; M' includes at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb; R includes at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4.

[0028] A third aspect of the present invention provides an electrical device comprising a secondary battery according to the first aspect or a positive electrode active material according to the second aspect. Attached Figure Description

[0029] Figure 1 The X-ray diffraction (XRD) patterns of the fluoride-coated materials of Examples 1 and 3 are shown, in which... Figure 1 (a) is the fluoride coating material of Example 1. The X-ray diffraction (XRD) pattern, Figure 1 (b) is the fluoride coating material of Example 3. The X-ray diffraction (XRD) pattern.

[0030] Figure 2 A schematic diagram of a secondary battery according to one embodiment of the present invention is shown.

[0031] Figure 3 It shows Figure 2 An exploded view of a secondary battery according to one embodiment of the present invention is shown.

[0032] Figure 4 A schematic diagram of a battery module according to one embodiment of the present invention is shown.

[0033] Figure 5 A schematic diagram of a battery pack according to one embodiment of the present invention is shown.

[0034] Figure 6 It shows Figure 5 An exploded view of a battery pack according to one embodiment of the present invention is shown.

[0035] Figure 7 A schematic diagram of a power consuming device using a secondary battery as a power source is shown.

[0036] BRIEF DESCRIPTION OF DRAWINGS 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the fluoride-coated material, the positive electrode sheet, and the secondary battery of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are already well known, and repeated description of actually identical structures, are omitted. This is in order to avoid the following description from becoming unnecessarily lengthy, and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided in order for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0038] The ranges disclosed herein are defined by their lower and upper limits. Ranges created by the upper and lower limits are inclusive of the endpoints. The ranges can be any combination of upper and lower limits. For example, if a range is stated as 60-120 and 80-110, it is understood that the range can be 60-110, 80-120, or 60-120 and 80-110. Further, if a range is stated as 1-2 and 3-5, it is understood that the range can be 1-5, 1-2, 3-5, 1-5 and 1-2, or 1-5 and 3-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand manner of describing a range associated with any and all sub-ranges between the upper value a and the lower value b, wherein a and b are both real numbers. For example, a numerical range of "0-5" means that all real numbers between 0 and 5 have been specifically listed in the present application, and "0-5" is merely a shorthand manner of describing the range of values. Additionally, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0039] All embodiments of the present application and optional embodiments can be combined with each other to form new technical solutions, if not otherwise specified.

[0040] All technical features of the present application and optional technical features can be combined with each other to form new technical solutions, if not otherwise specified.

[0041] If not specified otherwise, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0042] If not specified otherwise, the terms "comprising" and "including" as used herein are meant to be interpreted in an open way, i.e. they are meant not to exclude further components. For example, the terms "comprising" and "including" can mean that further components can be included or comprised, or they can mean that only the listed components are included or comprised.

[0043] If not specified otherwise, the term "or" as used herein is intended to mean an inclusive "or", i.e. the term "or" as used herein is intended to mean "and / or", unless explicitly indicated to mean an alternative "or" that is taken a part of a set of alternatives. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions can satisfy the condition "A or B": A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), or both A and B are true (or present).

[0044] One of the reasons for the electrochemical degradation phenomena such as voltage drop and capacity decay of the battery during cycling is that the positive electrode cycling stability cannot meet the requirements. Cracks are formed on the surface and inside of the particles after positive electrode cycling, leading to continuous occurrence of side reactions and increase of lithium consumption. The dissolved transition metal ions (such as ) in the positive electrode migrate to the negative electrode, catalyze the decomposition of the electrolyte, and make the SEI (solid electrolyte interface) layer thicker, consuming reversible lithium. The metal ions such as Li+ are reduced and deposited on the surface of the negative electrode, destroying the uniform nucleation of lithium, leading to an increase of lithium dendrites and "dead lithium" (i.e. lithium metal that loses electrochemical activity), and further reducing the coulombic efficiency. Moreover, the oxygen released from the oxide positive electrode promotes the further occurrence of side reactions between the positive electrode and the electrolyte.

[0045] A common way to improve the positive electrode cycling stability is to perform positive electrode active material doping modification / element concentration regulation. The use of cations such as Mg, Cu and Al for doping can inhibit the phase transition to some extent and improve the structural stability of the positive electrode active material. In addition, the design of the positive electrode active particle structure with a gradient distribution of element concentration, such as a center rich in nickel and a shell rich in manganese structure, can improve the capacity and surface stability of the positive electrode material. However, the aforementioned element doping strategies have limited improvement on the positive electrode cycling stability, and cannot completely solve the problem of side reactions between the positive electrode and the electrolyte. Moreover, the special positive electrode active particle structure process is complex and difficult to be popularized on a large scale.

[0046] Another way to improve the cycling stability of the positive electrode is to use a coating layer / interface modification. Coating the positive active particles with oxide (Al2O3, MgO, etc.), phosphate and silicate (AlPO4, MnSiO4, etc.), fluoride (AlF3, Li2ZrF6, etc.) materials can form a stable surface layer, reduce the direct contact between the positive active particles and the electrolyte, and inhibit the phase transition of the positive electrode. However, the ionic conductivity of most fluoride and oxide coating materials is low, and in order to ensure high rate performance, the thickness of the coating layer needs to be precisely controlled to be thin, and the process is complex. The uniformity of the thin coating layer is difficult to control, and it cannot completely prevent the positive electrode from contacting the electrolyte, while the uniform coating technology such as atomic layer deposition has a high cost.

[0047] In order to solve the problem of battery thermal runaway and improve the safety of the battery, solid-state electrolyte can be used to replace organic electrolyte. Although solid-state electrolyte can improve the safety of the battery to some extent, it cannot fundamentally solve the problem of thermal runaway. At about 200°C, the interface reaction between the oxide solid-state electrolyte and the electrode releases oxygen, leading to thermal runaway. At about 300°C, the sulfur ions in the sulfide solid-state electrolyte are reduced to sulfur vapor, which reacts with the oxygen released from the oxide positive electrode, leading to thermal runaway.

[0048] A common way to solve the problem of battery thermal runaway also includes using flame-retardant electrolyte additives. However, the solubility of flame-retardant additives is low, making it difficult to achieve high concentration addition, limiting their flame-retardant effect. Some flame retardants have poor compatibility with electrodes, and side reactions occur, affecting the cycle life of the battery.

[0049] Another solution is to use a coating layer to coat the positive active particles. The use of a coating layer reduces the side reactions between the positive active material and the electrolyte, and inhibits the structural changes and oxygen evolution at high temperatures. However, as mentioned earlier, the ionic conductivity of most coating layers is low, and the thickness of the coating layer needs to be reduced. Thin coating layers may degrade or fail during high-temperature or long-term cycling, losing their flame-retardant effect. It is difficult to ensure the uniformity of the thin coating layer, and the exposure of some positive electrodes leads to thermal runaway.

[0050] In addition, in terms of improving the cycle stability of the battery, fluorides have extremely strong corrosion resistance, can maintain structural stability in a longer voltage range, and do not release flammable gases, so fluorine-containing solvents, fluorine-containing lithium / sodium salts, and fluorine-containing additives are often used in the formulation of high-voltage electrolytes. During the formation stage or the first charge stage, an inorganic layer rich in lithium / sodium fluoride (LiF / NaF) is formed at the electrode / electrolyte interface, which inhibits the further decomposition of the electrolyte and improves the cycle stability of the battery. However, the ionic conductivity of fluorides is usually very low (<10 -6 S / cm), making it difficult for fluoride battery materials to be practically applied.

[0051] In terms of improving the stability of the positive electrode, the positive electrode cycle stability can be improved by positive electrode doping modification or element concentration regulation, but the problem of the side reaction between the positive electrode and the electrolyte cannot be completely solved. Using oxide, phosphate and silicate and fluoride materials to coat the positive electrode active particles can form a stable surface layer to reduce the direct contact between the positive electrode and the electrolyte, but the ionic conductivity of most fluoride and oxide coating materials is low, and the thickness of the coating layer needs to be precisely controlled to be thin to ensure high rate performance. In terms of improving battery thermal runaway, although the use of flame-retardant electrolyte additives can inhibit battery thermal runaway, the solubility of flame-retardant additives is low, and it is difficult to achieve high concentration addition, which limits its flame-retardant effect. In addition, the use of coating layers to reduce the side reaction between the positive electrode and the electrolyte, inhibit the structural change and oxygen evolution at high temperature, but the ionic conductivity of most coating layers is low, and the thickness of the coating layer needs to be reduced, and the thin coating layer may degrade or fail during high temperature or long-term cycling, losing the flame-retardant effect. In terms of improving the cycle stability of the battery, fluorine-containing solvents, fluorine-containing lithium / sodium salts, and fluorine-containing additives are often used in the formulation of high-voltage electrolytes, which can inhibit the further decomposition of the electrolyte and improve the cycle stability of the battery, but the ionic conductivity of common fluorides is low, which makes it difficult to be applied in practice.

[0052] [Positive electrode active material] Therefore, the present application provides a positive electrode active material, which comprises positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, wherein the fluoride coating material comprises a compound represented by Formula I: Formula I; wherein 0 < n < 2, 0 < m < 2, 0 < x < 2, and y is the absolute value of the valence of R; A comprises Na and / or Li; M comprises at least one of Ca, Zn, Mg, Sr, and Ba; M' comprises at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb; R comprises at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4.

[0053] The fluoride coating material of the present application has high thermodynamic stability, wide electrochemical window, high ionic conductivity, and excellent mechanical properties. After coating the positive electrode active particles with the fluoride coating material, the side reaction between the positive electrode active particles and the electrolyte can be alleviated, so that the positive electrode active particles can work at a higher voltage, thereby improving the capacity, energy density, cycle stability, safety, and rate performance of the battery, especially the battery thermal runaway.

[0054] In the present invention, the thermodynamic stability is characterized by the reaction energy of the coating material with the electrolyte. The reaction energy can be calculated as follows: wherein is the ground state energy of the coating material, is the ground state energy of the electrolyte, is the ground state energy of the reaction product of the coating material with the electrolyte, wherein the ground state energy of each material can be calculated according to density functional theory.

[0055] In the present invention, the term "electrochemical window" refers to the voltage range in which the fluoride coating material can exist stably on a specific electrode material, i.e. within this voltage interval the fluoride coating material does not undergo significant oxidative or reductive decomposition reactions. The electrochemical window of the fluoride coating material can be calculated, for example, by the grand potential phase diagram method, according to the following procedure: Under the influence of the electrode potential The chemical potential of the mobile ion A (Li or Na) is expressed as: wherein is the chemical potential of the A metal, e is the absolute value of the electronic charge. The redox behavior of a material is determined by its phase decomposition energy, which is expressed as wherein E is the energy of the material itself, is the energy of the equilibrium state, is the change in the mobile ion. The electrochemical window is defined as the range of corresponding to the range of in which the material is neither oxidized nor reduced.

[0056] In the present invention, the term "ionic conductivity" refers to the ratio of the current density contributed only by the migration of alkali metal ions to the applied electric field strength per unit cross-sectional area and per unit length of the fluoride coating material at a given temperature and under the action of an electric field, characterizing the ability of the fluoride coating material to conduct alkali metal ions. As an example, the ionic conductivity of the coating material can be determined using the alternating current impedance method. For example, the following procedure can be followed: 1. Sample preparation A dense, flat, and uniform sheet with a certain thickness (usually 0.5-2 mm) is prepared by pressing the coating material powder into a sheet (cold pressing or hot pressing sintering).

[0057] 2. Electrode preparation (blocking electrode): Common electrode materials: noble metals such as gold (Au), platinum (Pt), or stainless steel; A dense and uniform electrode layer is formed on both sides of the electrolyte sheet by magnetron sputtering, evaporation, or sintering after coating with conductive paste.

[0058] 3. Cell fixture: Place prepared electrolyte pellet into a dedicated test fixture, ensuring good contact between the electrodes and the metal probes of the fixture, with uniform and constant pressure (commonly spring-loaded or screw- tightened fixtures are used); 4. EIS test 4.1. Equipment: electrochemical workstation 4.2. Parameter settings: Frequency range: a wide range is usually set, for example 1 MHz to 0.1 Hz; AC perturbation voltage: a small amplitude, usually 10-100 mV; Test environment: depending on the sensitivity of the electrolyte to air / moisture, the test can be carried out in a glovebox (for air-sensitive materials such as sulfides, metal-organic frameworks, etc.) or in an atmospheric environment (for stable materials such as oxides, etc.); 5. Data processing and calculation 5.1. Obtain impedance spectrum: After testing, the Nyquist plot is obtained, i.e. the curve of the imaginary part of impedance (-Z'') vs. the real part (Z') 5.2. Fit equivalent circuit: Use ZView or similar software to fit the spectrum, thereby accurately obtaining the value of Rb (bulk electrolyte resistance).

[0059] 6. Calculate ionic conductivity :

[0060] : ionic conductivity (unit: S / cm) L: thickness of the electrolyte pellet (unit: cm). Accurately measured with a micrometer R: bulk resistance R obtained from the EIS spectrum (unit: Ω) b A: contact area of the electrode (unit: cm 2 ).

[0061] Further, the ionic diffusion coefficient of the coating material can be calculated using the obtained ionic conductivity by the following formula: Formula: ​where D is the ion diffusion coefficient, σ is the ionic conductivity, N is the number of diffusing ions (= the number of alkali metal ions contained in one mole of the coating material x the molar amount of the coating material), q is the charge of the ion (for alkali metal ions, q = 1), V is the volume of the coating material, k is the Boltzmann constant, and T is the temperature. In the present application, the mechanical properties of the fluoride coating material can be represented by the bulk modulus B, the shear modulus G, and the Young's modulus E. The term "bulk modulus" is a physical quantity that describes the ability of a material to resist volume compression under uniform pressure, and is defined as the ratio of the change in pressure to the relative change in volume. The term "shear modulus" is a physical quantity that describes the ability of a material to resist shear deformation, and is equal to the ratio of the shear stress to the shear strain. The term "Young's modulus" is a physical quantity that describes the ability of a solid material to resist deformation under elastic conditions, and is defined as the ratio of the stress to the strain, reflecting the stiffness characteristics of the material itself. The bulk modulus B, the shear modulus G, and the Young's modulus E of the fluoride coating material can be calculated as follows: First, the elastic matrix of the material is calculated, and the upper limit of the bulk modulus and the shear modulus are calculated according to Voigt approximation and Reuss approximation, respectively , and the lower limit . The bulk modulus formula , the shear modulus formula , and the Young's modulus formula .

[0062] In some embodiments, in the compound represented by formula I, M includes a total of not less than 90 mol% of elements selected from Ca, Zn, Mg, Sr, and Ba, based on the total moles of M. These elements are referred to as the main elements of M.

[0063] In some embodiments, in the compound represented by formula I, M' includes a total of not less than 90 mol% of elements selected from Ga, Al, La, Y, B, In, Sc, Bi, and Sb, based on the total moles of M'. These elements are referred to as the main elements of M'.

[0064] In some embodiments, in the compound represented by formula I, A is optionally Na. In this case, for the application of lithium batteries, the coating material can be directly used to coat the positive active particles of the lithium battery. During the charging and discharging process of the lithium battery, the Na ions in the coating material will be at least partially exchanged into Li ions.

[0065] In some embodiments, in the compound represented by formula I, A is optionally Na and Li. In this case, for the application of lithium batteries, the Na ions in the coating material can be at least partially exchanged into Li ions first, and then the coating material after ion exchange is used to coat the positive active particles of the lithium battery.

[0066] In some embodiments, the compound of Formula I optionally excludes anions other than fluoride, i.e., has the general formula .

[0067] In the structure of the fluoride coating material, the anion framework optionally consists entirely of fluoride ions. Fluorine has a very high electronegativity (stronger than oxygen, chlorine), and has a stronger interaction with the cations in the structure, thus the structure has better stability. Such a fluoride coating material has a low absolute value of reaction with lithium / sodium salts and solvents, and has good compatibility with electrolytes, which can greatly improve the cycle stability of the battery. The electrochemical window of the fluoride coating material is very wide, which can well match the high-voltage positive electrode material, reduce the occurrence of electrochemical side reactions, and inhibit the loss of oxygen from the positive electrode. In addition, the coating material has a special Weberite configuration, which can promote ion transport. Compared with Li2ZrF6, LiF, and other fluoride coating systems, the ion conductivity is 3-7 orders of magnitude higher, and is comparable to the ion conductivity of layered oxide positive electrodes. Moreover, the mechanical properties of the coating material are good, and the mechanical processing difficulty is lower than that of most fluorides and oxides, and the coating material is not easy to break.

[0068] In the present application, the fluoride coating material of Formula I can be characterized by using instruments and methods known in the art, for example, X-ray diffraction (XRD) patterns can be used. For characterization of the coating material in the coating layer of the positive electrode active material in the secondary battery, the positive electrode sheet can be disassembled to obtain the positive electrode active material after washing with electrolyte in a glove box and drying, scraping powder and collecting to obtain the positive electrode active material, and then the positive electrode active material is cut open, and XRD analysis is performed on the selected area (depending on the thickness of the coating layer), so that the phase of the coating material can be determined.

[0069] In some embodiments, M can further include not more than 10 mol% of a first transition metal element based on the total moles of M, wherein the first transition metal element includes at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, and V.

[0070] In some embodiments, M can further include 0 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, or a value within a range defined by any two of the values, of the first transition metal element based on the total moles of M.

[0071] In some embodiments, M' can further include not more than 10 mol% of a second transition metal element based on the total moles of M', wherein the second transition metal element includes at least one of Fe, Co, Ni, Mn, V, Ti, and Cr.

[0072] In some embodiments, M' further comprises 0 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, or a value within a range defined by any two of the values, of a second transition metal element, based on the total moles of M'.

[0073] When the fluoride-coated material comprises the above variable valence transition metal ions in a suitable amount, the electronic conductivity can be improved, and the overall performance of the positive electrode can be systematically improved.

[0074] In some embodiments, A further comprises no more than 20 mol%, for example, no more than 15 mol%, no more than 10 mol%, no more than 5 mol%, no more than 2.5 mol%, no more than 1 mol%, no more than 0.5 mol% of K and / or Ag, based on the total moles of A.

[0075] In some embodiments, M further comprises no more than 10 mol%, for example, no more than 9 mol%, no more than 8 mol%, no more than 7 mol%, no more than 6 mol%, no more than 5 mol%, no more than 4 mol%, no more than 3 mol%, no more than 2 mol%, no more than 1 mol%, no more than 0.5 mol% of at least one element of A and at least one element of M', based on the total moles of M.

[0076] In the crystal lattice of the fluoride-coated material, the M sites can be occupied by monovalent ions of at least one element of A (i.e., one or more of Li, Na, K, Ag) and trivalent ions of at least one element of M', in particular the host element of M' (i.e., one or more of Ga, Al, La, Y, B, In, Sc, Bi, Sb). The monovalent ions occupy the M sites because of the disordered arrangement that occurs during the synthesis of the fluoride-coated material, with ions from some A sites occupying the M sites. In addition, the occupation of the M sites by trivalent ions can cause alkali metal ion vacancies, thereby improving the alkali metal ion conductivity.

[0077] When the M sites are occupied by monovalent metal ions and trivalent metal ions, or other variable valence transition metal ions, the overall valence state is +2; when the M' sites are occupied by monovalent metal ions and trivalent metal ions, or other variable valence transition metal ions, the overall valence state is +3.

[0078] In the present disclosure, instruments and methods known in the art can be used to determine the elements occupying the various sites in the crystal lattice of the fluoride-coated material and the proportion of the element occupying the corresponding site, for example, the Rietveld refinement can be performed using the pattern obtained by neutron diffraction to determine the types and proportions of elements occupying the M and M' sites. Specifically, as an example, the following operations can be performed: 1 Sample preparation: 2 g of powder sample, vacuum dried, sealed and packaged in a V sample box 2 Experimental application: submit experimental application on CSNS website, communicate with experimental station scientists about experimental feasibility 3 Experiment: 3.1 Sample loading and replacement: load sample into sample box and seal, install to spectrometer sample position 3.2 Parameter setting: neutron source type: spallation source; wavelength: 1 Å; angle range: 10-80°; temperature: 300K 3.3 Collect diffraction data 4 Data processing 4.1 Background subtraction, normalization, absorption correction, angle correction 4.2 Use Mantid software for preliminary processing 4.3 Use TOPAS software for Rietveld refinement to determine cell parameters, atomic positions, element types and proportions at each site.

[0079] For the coating material in the coating layer of the positive active material in the secondary battery, the secondary battery can be disassembled to obtain the positive electrode sheet, the electrode sheet is washed with electrolyte and then dried in a glove box, the powder is scraped and collected to obtain the positive active material, and then the positive active material is cut open, and the selected region (depending on the thickness of the coating layer) is subjected to the spectrum analysis as described above, so that the elements at the lattice sites of the fluoride coating material and the proportion of the element at the corresponding site can be determined.

[0080] In some embodiments, the fluoride coating material has a general formula , wherein M is optionally composed of one or more elements selected from Ca, Zn and Mg; M' is optionally composed of one or more elements selected from Ga and Al. Such fluoride coating material has further improved stability with electrolyte and positive electrode, which can greatly improve the cycle stability of the battery; and the fluoride coating material has a wide electrochemical window of, for example, 2.33-6.23 V, which has significantly stronger high-voltage stability than oxide. Moreover, the room temperature alkali metal ion conductivity of the fluoride coating material is on the order of 10 -5 S / cm, which is significantly stronger than LiF (10 -13 S / cm) and Li2ZrF6 (10 -9 S / cm), and is comparable to layered oxide positive electrode (10 -5 S / cm).

[0081] In the present application, the term "room temperature" refers to 25 ± 5℃.

[0082] In some embodiments, the positive active material can include 0.01 to 10% by weight of the fluoride coating material based on the total weight of the positive active material.

[0083] If the weight percentage of the coating material in the positive active material is less than 0.01, it will result in too small coating area on the surface of the positive active particles, uneven coating, and most of the positive active particles still directly contact with the electrolyte, thus failing to achieve the effect of coating. At high voltage, the positive active particles will still react violently with the electrolyte, thereby affecting the cycle performance and thermal stability of the battery. If the weight percentage of the coating material in the positive active material is greater than 10, it will result in too thick coating layer on the surface of the positive active particles, which will increase the impedance of the battery, thereby affecting the performance of the battery.

[0084] In some embodiments, the fluoride coating material completely coats the positive active particles, and the coating layer formed by the fluoride coating material can have a thickness of 5-20 nm.

[0085] The oxide (e.g., Al2O3, MgO, etc.) and fluoride (e.g., AlF3, Li2ZrF6) coating layers commonly found on the surface of positive active particles are usually thin, e.g., 2-10 nm, due to low ionic conductivity, to ensure high rate performance, while thin coating layers can degrade or fail during high temperature or long-term cycling, exposing part of the positive electrode and leading to thermal runaway. The fluoride coating material of the present application has high thermodynamic stability, wide electrochemical window, and high ionic conductivity, thereby eliminating the need for precise control of the thickness of the coating layer, and enabling the preparation of a coating layer on the surface of the corresponding high-voltage positive active particles through a simple coating process, such as wet coating.

[0086] In the present application, instruments and methods known in the art can be used to characterize the fluoride coating layer, for example, scanning transmission electron microscopy and energy dispersive spectroscopy mapping (STEM-EDS Mapping) can be used to characterize the fluoride coating layer on the surface of the positive active particles. In addition, the thickness of the coating layer formed by the fluoride coating material can be determined using instruments and methods known in the art. For example, the composite particles are sliced, and the thickness of the coating layer is measured by the cross-section of the particles under a high-power electron microscope (TEM).

[0087] In some embodiments, the positive active particles can include at least one of a layered oxide material, a spinel oxide material, and a fluoride material, wherein: The layered oxide material includes a compound represented by Formula II: Formula II In Formula II, 0 ≤ e ≤ 0.2, and f is the absolute value of the valence state of R 1 A 1 includes Li or Na, M a ​comprising at least one of F, Cl; 1 comprising at least one of F, Cl; The spinel oxide material comprises a compound according to Formula III: Formula III In Formula III, 0 < g < 0.4, h is the absolute value of the valence state of R 2 comprising at least one of F, Cl; A 2 comprising Li or Na, M b comprising at least one of F, Cl; 2 comprising at least one of F, Cl; The fluoride material comprises a compound according to Formula IV: Formula IV In Formula IV, 0 < k < 2, 0 < p < 2, 0 < i < 2, j is the absolute value of the valence state of R 3 comprising at least one of F, Cl; A 3 comprising Li or Na, M c comprising a transition metal element having a divalent valence state, M d comprising a transition metal element having a trivalent valence state, R 3 comprising at least one of F, Cl.

[0088] In some embodiments, the positive active particles are optionally high-voltage positive active particles, which can comprise at least one of: 、

[0089] The electrochemical window of the fluoride coating material of the present application can very well cover the working voltage interval of the above-mentioned high-voltage positive active materials. Coating the above-mentioned high-voltage positive active materials with the fluoride coating material can effectively improve the capacity, energy density, cycle stability, safety and rate capability of the battery.

[0090] Furthermore, in principle, the present application is not limited by the size of the positive active material. Any common size of positive active material is suitable for the present application. In some embodiments, the positive active material can have a Dv50 particle size of 5 to 30 pm.

[0091] Dv50 particle size has the meaning well known in the art and can be determined using instruments and methods well known in the art. As an example, a laser particle size analyzer can be used according to the following procedure: take a clean beaker, add an appropriate amount of sample to be tested, add a dispersant after adding a surfactant, and ultrasonic for 5 min at 120 W to ensure that the sample is completely dispersed in the dispersant; the sample is poured into the sample tower and circulated to the test light path system with the solution, the particles are irradiated by the laser beam, and the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light (light shielding degree: 8-12%), and the Dv50 particle size can be obtained based on the particle size distribution curve.

[0092] In some embodiments, the positive electrode active material optionally has a BET specific surface area in the range of 0.1 to 14 m 2 / g.

[0093] BET specific surface area has the meaning well known in the art and can be measured using methods and equipment known in the art. As an example, referring to GB / T 19587-2017, using nitrogen adsorption specific surface area analysis test method, immerse the sample tube containing the porous carbon sample in liquid nitrogen at -196 ℃, measure the adsorption amount of nitrogen on the surface of the solid sample at different pressures under the relative pressure of 0.05-0.30 MPa, obtain the monolayer adsorption amount of the sample based on the BET multilayer adsorption theory and calculation formula, and further obtain the BET specific surface area, which can be performed, for example, by a Tri-Star 3020 type specific surface area and pore size analyzer of the American Micromeritics company.

[0094] In some embodiments, the positive electrode active material optionally has a tap density in the range of 1.1 to 2.3 g / cm 3 .

[0095] In the present application, the "tap density" refers to the mass per unit volume of a powder or particulate material when it is in the most compacted state under specific vibration or tapping conditions. The tap density can be measured using methods and equipment known in the art. As an example, the following operation can be performed: a certain amount of powder (usually ≥ 50 g) is loaded into a graduated cylinder, tapped gently to remove air bubbles, and then mechanically tapped at a frequency of 300 times / min and a height of 3 mm until the volume is constant, and the final volume is recorded. The tap density is obtained by dividing the weight by the volume, and the commonly used unit is g / cm 3 .

[0096] In some embodiments, the positive electrode active material optionally has a hardness in the range of 6 to 12 GPa.

[0097] In the present invention, "hardness" specifically refers to nanoindentation hardness, i.e., the ability of a material to resist local plastic deformation at the nanoscale. Hardness can be measured using methods and equipment known in the art. As an example, the following can be performed: using a single-particle compression method. A single particle of the positive electrode active material is placed under the indenter of a micro / nanomechanical testing machine, and loaded to fracture at a constant rate (e.g., 0.1 μm / s), the maximum load F and the particle diameter d are recorded, and the hardness H is calculated as Compressive strength i.e., the hardness of the particle.

[0098] [Positive electrode tab] The positive electrode tab includes a current collector and a positive electrode film layer disposed on at least one surface of the current collector, the positive electrode film layer including positive electrode active particles coated with a fluoride coating material in some embodiments.

[0099] As an example, the current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the current collector.

[0100] In some embodiments, the current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, the positive electrode active particles can include high-voltage layered oxide materials, spinel oxide materials, fluoride materials for batteries known in the art. As an example, the positive electrode active particles can include at least one of the following materials: 、

[0102] .

[0103] In some embodiments, the positive electrode film layer can include 70% to 98% by weight of the positive electrode active particles coated with the fluoride coating material, based on the total weight of the positive electrode film layer.

[0104] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0105] In some embodiments, the positive electrode film layer can further include 2% to 30% by weight of a binder, based on the total weight of the positive electrode film layer.

[0106] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In some embodiments, the positive electrode film layer can further include additional additives, such as dispersants, thickeners, stabilizers, flame retardants.

[0108] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methyl pyrrolidone (NMP)) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., obtaining the positive electrode tab.

[0109] In some embodiments, the positive electrode tab can have a compacted density in the range of 2.3 to 3.7 g / cm 3 .

[0110] In the present disclosure, the term “compacted density” refers to the mass per unit volume of the tab after or after pressing, and is usually expressed in grams per cubic centimeter (g / cm 3 ), and the calculation formula is: Compacted density = mass per unit area of the tab (g / cm 2 ) / thickness of the tab (cm).

[0111] The compacted density of the tab can be determined using instruments and methods known in the art, and as an example, the following operations can be performed in particular: 1. Sampling and pretreatment 1.1 Weigh the total tab mass m1 (including the current collector) 1.2 Wipe the coating with an electrolyte swab, rinse with deionized water, dry, and weigh the mass of the current collector m2 1.3 Coating mass

[0112] 2. Thickness test 2.2 Measure the thickness H of each point on the 3 selected points on the negative electrode tab using a micrometer 2.3 Measure the thickness h of the current collector at the same position 3. Data analysis 3.1 Coating thickness

[0113] 3.2 Coating volume

[0114] 3.3 Compaction density .

[0115] [Negative electrode tab] The negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material. As an example, the negative electrode current collector has two opposite surfaces in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0116] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0117] In some embodiments, the negative electrode active material can employ a negative electrode active material for a battery known in the art. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0118] In some embodiments, the negative electrode film layer further optionally comprises a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0119] In some embodiments, the negative electrode film layer further optionally comprises a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes (e.g., single-walled carbon nanotubes (SWCNTs)), graphene, and carbon nanofibers.

[0120] In some embodiments, the negative electrode film layer further optionally comprises other auxiliary agents, such as thickening agents (e.g., sodium hydroxymethyl cellulose (CMC-Na)) and the like.

[0121] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, and the like, obtaining the negative electrode sheet.

[0122] [Electrolyte] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not have specific limitations on the type of electrolyte, which can be selected according to the needs. For example, the electrolyte can be liquid, gel, or all-solid-state.

[0123] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0124] In some embodiments, the electrolyte salt can be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bisfluorosulfonylimide, sodium bis-trifluoromethylsulfonylimide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorobisoxalate borate, sodium bisoxalate borate, sodium difluorobisoxalate phosphate, and sodium tetrafluorobisoxalate phosphate; or at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0125] In some embodiments, the solvent can be selected from solvents with good high pressure stability. As examples, one can cite sulfolane, dimethyl sulfoxide, dimethyl sulfone, acetonitrile, propionitrile, butyronitrile, pentanenitrile, hexanenitrile, phenylacetonitrile, fluoroethylene carbonate, bisfluoroethylene carbonate, trifluoromethyl ethylene carbonate, 2,2,2-trifluoroethyl carbonate, fluorodimethoxyethane, fluorobenzene, o-difluorobenzene, 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide, end-fluorinated N,N-dimethyltrifluoromethanesulfonamide, ionic liquids.

[0126] In some embodiments, the electrolyte can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0127] [Separator] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous separator having good chemical stability and mechanical stability can be used.

[0128] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0129] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly through a winding process or a stacking process.

[0130] In some embodiments, the secondary battery includes a positive electrode sheet, an electrolyte, a separator, and a negative electrode sheet in some embodiments.

[0131] In some embodiments, the secondary battery includes a sodium-ion battery, a lithium-ion battery, a lithium polymer battery, and optionally, the secondary battery is a lithium-ion battery.

[0132] In some embodiments, the secondary battery can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0133] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, one can cite polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0134] The shape of the secondary battery is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 2 is a square structure as an example of a secondary battery 5.

[0135] In some embodiments, referring to Figure 3 , the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the skilled person can select according to the specific actual needs.

[0136] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by the skilled person according to the application and capacity of the battery module.

[0137] Figure 4 is a battery module 4 as an example. Referring to Figure 4 , in the battery module 4, a plurality of battery monomers 5 can be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Further, the plurality of battery monomers 5 can be fixed by fasteners.

[0138] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery monomers 5 are received in the receiving space.

[0139] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person according to the application and capacity of the battery pack.

[0140] Figure 5 and Figure 6 is a battery pack 1 as an example. Referring to Figure 5 and Figure 6 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be provided on the lower box body 3 to form a closed space for receiving the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0141] In addition, the application also provides a power utilization device comprising at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a tablet computer, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an aerospace vehicle, an energy storage system, etc., but is not limited thereto.

[0142] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof. Figure 7 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the power supply of the power utilization device, the battery pack or the battery module can be used.

[0143] The power utilization device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery monomer can be used as a power supply.

[0144] The beneficial effects of the application are further illustrated in combination with the following examples.

[0145] Examples Hereinafter, examples are described. The examples described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the examples, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0146] I. Preparation method Example 1 (I) Preparation of coated positive electrode active particles 1) Sodium fluoride, ammonium fluoride, calcium nitrite, and gallium nitrate with a total weight of 10 mg were dissolved in 30 mL of deionized water at a molar ratio of 3:11:1:3, and stirred at room temperature for 1 hour to generate a Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F7 coating material solution; 2) 1 g of positive electrode active particles (Na2(Fe 1 / 3 Co 1 / 3 Ni 1 / 3 ) 2+ (Mn 1 / 3 Fe1 / 3 Co 1 / 3 ) 3+ F7, Dv50 particle size of 15 μm) is dispersed in the solution obtained in step 1) in which the positive active particles and Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F7 in a mass ratio of 99:1, stirred for 1 hour, and then placed in a stainless steel autoclave with a polytetrafluoroethylene liner and heated at 160°C for 5 hours in air, and naturally cooled to room temperature to obtain a coated positive active material, at which time the coating layer formed was amorphous; 3) The coated positive active material is washed 3 times with deionized water, dried at 80°C for 6 hours, and the powder obtained is calcined at 500°C for 6 hours in argon to improve the crystallinity of the coating layer and promote material exchange between the coating layer and the positive active particles, and to improve the compactness, and after naturally cooling to room temperature, a dense and uniform nanocrystalline coating layer having a thickness of 5-8 nm (measured by TEM on the cross section of the particles) is obtained, the positive active material including 1% by weight of the fluoride coating material, based on the total weight of the positive active material obtained.

[0147] The solution of the coated material obtained in step 1) above is dried to obtain the fluoride coating material Na 3 / 2Ca 1 / 2 Ga 3 / 2 F7. Figure 1 The X-ray diffraction (XRD) pattern of this fluoride coating material is shown in (a).

[0148] (II) Preparation of the positive electrode sheet The coated positive active particles, conductive carbon (Super P) particles, carbon nanotubes (TUBALL™ BATT), polyvinylidene fluoride (PVDF) binder, and N-methylpyrrolidone (NMP) solvent are mixed to make a slurry (the slurry includes 70% by weight of the coated positive active particles, 19% by weight of Super P, 1% by weight of carbon nanotubes, and 10% by weight of PVDF, based on the dry weight of the slurry); The slurry obtained is spread on a 12 μm thick Al foil with a doctor blade, and dried by heating at 80°C for 12 hours in a vacuum to evaporate the NMP; The dried electrode sheet is roll-pressed and cut to the appropriate size (length 600 mm, width 70 mm).

[0149] (III) Negative electrode sheet A sodium metal negative electrode having a thickness of 30 μm is used.

[0150] (IV) Preparation of the electrolyte: N,N-dimethyltrifluoromethanesulfonamide (PreTFSI) after end group fluorination was used as solvent, sodium bisfluorosulfonylimide (NaFSI) was used as sodium salt; 0.05 mol NaFSI was mixed with 100 mL PreTFSI at 60°C, cooled to 25°C, filtered with a 0.5 μm PTFE filter under argon atmosphere to obtain the electrolyte.

[0151] (V) Preparation of the battery The positive electrode sheet, the separator (polyolefin microporous membrane), and the negative electrode sheet were sequentially stacked to ensure alignment; The tab was welded to the current collector using an ultrasonic spot welding machine; The cell was further dried in a vacuum drying oven; The cell was placed in a formed aluminum-plastic film, and the top surface and side surface of the aluminum-plastic film were heat-sealed; The cell was injected with an appropriate amount of electrolyte, vacuumed and sealed.

[0152] Example 2 The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, NaNi 0.4 Fe 0.2 Mn 0.4 O2 with a Dv50 particle size of 15 μm was used as the positive electrode active particles.

[0153] Example 3 The battery was prepared in the same manner as in Example 1, except that in the preparation of the coated positive electrode active particles, in step 1), sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, magnesium oxalate, gallium nitrate, boron oxide, aluminum nitrate were dissolved in deionized water in a molar ratio of 9:33:1:1:1:5:2:2 to generate a solution of Na 3 / 2 (Ca 1 / 6 Zn 1 / 6 Mg 1 / 6 )(Ga 5 / 6 B 1 / 3Al 1 / 3 )F7 coating material; in step 2), NaNi 0.4 Fe 0.2 Mn 0.4 O2 with a Dv50 particle size of 15 μm was used as the positive electrode active particles. The XRD pattern of the fluoride coating material Na 3 / 2 (Ca 1 / 6 Zn 1 / 6 Mg 1 / 6 )(Ga 5 / 6 B 1 / 3 Al 1 / 3 )F7 prepared in this example is shown inFigure 1 (b) in.

[0154] Example 4: A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in Step 1) sodium fluoride, ammonium fluoride, calcium nitrite, strontium acetate, barium oxalate, gallium nitrate, lanthanum nitrate, yttrium nitrate were dissolved in deionized water in a molar ratio of 9:33:1:1:1:5:2:2 to produce a solution of Na 3 / 2 (Ca 1 / 6 Sr 1 / 6 Ba 1 / 6 )(Ga 5 / 6 La 1 / 3Y 1 / 3 )F7 coating material; in Step 2) NaNi 0.4 Fe 0.2 Mn 0.4 O2 with a Dv50 particle size of 15 pm was used as the positive active particles.

[0155] Example 5: A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in Step 1) sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, indium nitrate, scandium nitrate were dissolved in deionized water in a molar ratio of 10:32:3:1:4:2:2 to produce a solution of Na 5 / 3 (Ca 1 / 2 Zn 1 / 6 )(Ga 2 / 3 In 1 / 3 Sc 1 / 3 )F7 coating material; in Step 2) NaNi 0.4 Fe 0.2 Mn 0.4 O2 with a Dv50 particle size of 15 pm was used as the positive active particles.

[0156] Example 6: A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in Step 1) sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, bismuth acetate, antimony acetate were dissolved in deionized water in a molar ratio of 9:33:1:2:5:2:2 to produce a solution of Na 3 / 2 (Ca 1 / 6 Zn 1 / 3 )(Ga 5 / 6 Bi 1 / 3 Sb 1 / 3 )F7 coating material; in Step 2) NaNi 0.4 Fe0.2 Mn 0.4 O2 as cathode active particles.

[0157] Example 7: A battery was prepared in the same manner as Example 1, except that in the preparation of the coated cathode active particles, in Step 1), sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, cobalt oxalate, gallium nitrate, aluminum nitrate, and ammonium fluorotitanate were dissolved in deionized water in a molar ratio of 9:27:10:7:1:30:23:1 to form a solution of Na 3 / 2 (Ca 5 / 18 Zn 7 / 36 Co 1 / 36 )(Ga 5 / 6Al 23 / 36 Ti 1 / 36 )F7 coating material; in Step 2), NaNi 0.4 Fe 0.2 Mn 0.4 O2 as cathode active particles.

[0158] Example 8: A battery was prepared in the same manner as Example 1, except that in the preparation of the coated cathode active particles, in Step 1), sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, sodium oxide, and sodium chloride were dissolved in deionized water in a molar ratio of 5:33:3:9:1:2 to form a solution of Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 Cl 1 / 3 O 1 / 6 coating material; in Step 2), NaNi 0.4 Fe 0.2 Mn 0.4 O2 as cathode active particles.

[0159] Example 9: A battery was prepared in the same manner as Example 1, except that LiNi 0.8 Co 0.1 Mn 0.1 O2 as cathode active particles, and a lithium metal negative electrode sheet with a thickness of 30 pm was used, and an electrolyte was obtained by mixing 0.05 mol of lithium bisfluorosulfonylimide (LiFSI) with 100 mL of PreTFSI at 60°C, cooling to 25°C, and filtering with a 0.5 m PTFE filter in an argon environment to obtain the electrolyte.

[0160] Example 10 A battery was prepared in the same manner as Example 1, except that, in the preparation of the coated positive active particles, in Step 1) sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, cobalt oxalate, gallium nitrate, aluminum nitrate, manganese acetate were dissolved in deionized water in a molar ratio of 54:198:10:7:1:30:23:1 to produce a solution of Na 3 / 2 (Ca 5 / 18 Zn 7 / 36 Co 1 / 36 )(Ga 5 / 6Al 23 / 36 Mn 1 / 36 )F7coating material; in Step 2) NaNi 0.4 Fe 0.2 Mn 0.4 O2was used as the positive active particles.

[0161] Example 11 A battery was prepared in the same manner as Example 1, except that, in the preparation of the coated positive active particles, in Step 1) sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, copper oxalate, gallium nitrate, aluminum nitrate, manganese acetate were dissolved in deionized water in a molar ratio of 54:198:10:7:1:30:23:1 to produce a solution of Na 3 / 2 (Ca 5 / 18 Zn 7 / 36 Cu 1 / 36 )(Ga 5 / 6Al 23 / 36 Mn 1 / 36 )F7coating material; in Step 2) NaNi 0.4 Fe 0.2 Mn 0.4 O2was used as the positive active particles.

[0162] Example 12 A battery was prepared in the same manner as Example 1, except that, in the preparation of the coated positive active particles, in Step 1) sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, aluminum nitrate, chromium nitrate, titanium chloride were dissolved in deionized water in a molar ratio of 54:192:11:7:30:20:2:2 to produce a solution of Na 3 / 2 (Ca 11 / 36 Zn 7 / 36 )(Ga 5 / 6 Al 5 / 9Cr 1 / 18 Ti 1 / 18 )F 41 / 6 Cl 1 / 6solution of coating material; NaNi 0.4 Fe 0.2 Mn 0.4 O2as positive active particles.

[0163] Example 13 A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in step 1) sodium fluoride, ammonium fluoride, calcium nitrite, zinc oxalate, gallium nitrate, aluminum nitrate, vanadium bromide were dissolved in deionized water in a molar ratio of 54:192:10:8:30:22:2, resulting in a solution of Na 3 / 2 (Ca 5 / 18 Zn 2 / 9 )(Ga 5 / 6 Al 11 / 18 V 1 / 18 )F 41 / 6Br 1 / 6 solution of coating material; NaNi 0.4 Fe 0.2 Mn 0.4 O2as positive active particles.

[0164] Example 14 A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in step 1) sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, sodium sulfide were dissolved in deionized water in a molar ratio of 5:33:3:9:2, resulting in a solution of Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 S 1 / 3 solution of coating material; NaNi 0.4 Fe 0.2 Mn 0.4 O2as positive active particles.

[0165] Example 15 A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in step 1) sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, sodium cyanide were dissolved in deionized water in a ratio of 5:33:3:9:4, resulting in a solution of Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 (CN) 2 / 3 solution of coating material; NaNi0.4 Fe 0.2 Mn 0.4 O2as the positive active particles.

[0166] Example 16 A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in step 1) sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, sodium borohydride were dissolved in deionized water in a molar ratio of 5:33:3:9:4, resulting in a solution of Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 (BF4) 2 / 3 coating material; in step 2) NaNi 0.4 Fe 0.2 Mn 0.4 O2as the positive active particles.

[0167] Example 17 A battery was prepared in the same manner as Example 1, except that in the preparation of the coated positive active particles, in step 1) sodium fluoride, ammonium fluoride, calcium nitrite, gallium nitrate, sodium borohydride were dissolved in deionized water in a molar ratio of 5:33:3:9:4, resulting in a solution of Na 3 / 2 Ca 1 / 2 Ga 3 / 2 F 19 / 3 (BH4) 2 / 3 coating material; in step 2) NaNi 0.4 Fe 0.2 Mn 0.4 O2as the positive active particles.

[0168] Examples 18 to 20 Examples 18, 19 and 20 were prepared in the same manner as Examples 1, 2 and 9, respectively, and the batteries of Examples 18, 19 and 20 were subjected to the corresponding tests at a higher charge cut-off voltage than Examples 1, 2 and 19 (see Test Method 4 Charge-discharge test for the specific tests), the results of which are shown in Table 5 below.

[0169] In the above Examples 2-20, the proportion of coating material in the positive active material was the same as in Example 1.

[0170] Comparative Example 1 A battery was prepared in the same manner as Example 1, except that uncoated Na2(Fe 1 / 3 Co 1 / 3Ni 1 / 3 )2+ (Mn 1 / 3 Fe 1 / 3 Co 1 / 3 ) 3+ F7 positive active particles.

[0171] Comparative Example 2 A battery was prepared in the same way as Example 1, except that uncoated NaNi 0.4 Fe 0.2 Mn 0.4 O2 positive active particles.

[0172] Comparative Example 3 A battery was prepared in the same way as Example 1, except that uncoated LiNi 0.8 Co 0.1 Mn 0.1 O2 positive active particles, and a lithium metal negative electrode tab with a thickness of 30 pm was used, and an electrolyte was used which was obtained by mixing 0.05 mol lithium bisfluorosulfonylimide (LiFSI) with 100 mL PreTFSI at 60 °C, cooling to 25 °C, and filtering with a 0.5 m PTFE filter in an argon atmosphere.

[0173] II. Test Methods 1. Characterization of the coating material structure using XRD: 1) Equipment and instruments X-ray source: Cu-Ka (wavelength 1.54178 ) is usually used.

[0174] Sample stage: different types of sample stages are chosen depending on the sample form (powder, thin film, bulk).

[0175] 2) Sample preparation 2.1) Grinding: the sample is ground into a fine powder (particle size < 10 pm) using a mortar or a ball mill inside a glove box to improve the quality of the diffraction signal.

[0176] 2.2.) Tabletting: the powder is evenly spread on the sample stage, ensuring a flat surface.

[0177] 3) Test parameter settings 3.1) Scan range: 10° - 80°.

[0178] 3.2) Step interval: a step interval of 0.1° - 0.15° is recommended, balancing resolution and test time.

[0179] 3.3) Scan speed: 1° - 5° / min (slower scan speeds can improve signal quality).

[0180] 3.4) Working voltage and current: typically set to 40 kV, 40 mA.

[0181] 4) Test procedure 4.1) Equipment calibration: check if the XRD instrument is working properly and calibrate the peak positions using standard materials (e.g. Si powder).

[0182] 4.2) Sample mounting: fix the sample on the sample holder, ensuring it is stable and does not move.

[0183] 4.3) Test condition setting: input parameters such as scan range, step interval, scan speed, etc.

[0184] 4.4) Start test: initiate the XRD test and collect diffraction data.

[0185] 5) Data analysis Use analysis software (e.g. Jade, HighScore Plus) to process the diffraction data.

[0186] Background subtraction: remove noise and background signals.

[0187] Peak fitting: fit the shape and intensity of the diffraction peaks.

[0188] Peak indexing: match the diffraction peak positions to a known crystal database (e.g. PDF-4+).

[0189] 2. Evaluate the ionic conductivity and ion diffusion coefficient of the coated positive active material during charge-discharge process using Galvanostatic Intermittent Titration Technique (GITT) test: 1) Material preparation Refer to the preparation method of the battery mentioned above.

[0190] 2) Initial charging Charge the battery at a current density of 0.05 C to 5 V to eliminate the influence of side reactions; After the pre-charge is completed, stand for 30 minutes to stabilize the state of the battery.

[0191] 3) GITT test cycle Pulse charging: charge at a current density of 0.05 C for 5 minutes and record the voltage; Relaxation stage: cut off the current and stand for 30 minutes to record the voltage relaxation process; Pulse discharging: discharge at a current density of 0.05 C for 5 minutes and record the voltage; Relaxation stage: cut off the current and stand for 30 minutes to record the voltage relaxation process; Repeat the above charging and discharging cycle until the battery reaches the required charge-discharge depth.

[0192] 4) Data recording Record voltage, current and time data at each pulse and relaxation phase.

[0193] 5) Data analysis 5.1) Voltage relaxation curve analysis: Analyze the battery relaxation curve to determine the trend of voltage change over time; Calculate the chemical diffusion coefficient D of alkali metal ions by linear fitting the voltage relaxation curve.

[0194] 5.2) Calculation of ion diffusion coefficient: Formula: Where L is the thickness of the electrode, t is the relaxation time; Calculate the ion diffusion coefficient under different amounts of intercalated alkali metals by the voltage relaxation curve under different states.

[0195] 5.3) Calculation of ion conductivity: Formula: Where N is the number of diffusing ions (= the number of alkali metal ions contained in each mole of coating material x the molar mass of the coating material), q is the charge carried by the ion (for alkali metal ions, q = 1), V is the total volume of the positive electrode active material, k is the Boltzmann production, T is the temperature.

[0196] 3. Measure the electrochemical window of the coating material using cyclic voltammetry (CV) 1) Instrumentation: Electrochemical workstation (such as Gamry, Solartron, etc.); Three-electrode system: working electrode (such as glassy carbon electrode, platinum electrode, etc.), counter electrode (such as platinum wire), reference electrode (such as saturated calomel electrode or silver / silver chloride electrode); Electrolytic cell (such as three-electrode electrolytic cell); Thermostatic water bath or thermostat (optional, for controlling experimental temperature); Gas purification device (such as argon or nitrogen, for excluding oxygen in the solution).

[0197] 2) Reagents and solutions: Electrolyte solution: 0.5 mol / L NaFSI dissolved in PreTFSI; Material to be tested: Mix the coating material with PVDF binder in a weight ratio of 9:1, use N-methyl pyrrolidone as solvent, adjust the solid content to 15-25%, obtain the slurry, drop the slurry on the center of the working electrode (Pt disc), spread into a uniform film, vacuum dry.

[0198] 3) Experimental steps 3.1) Electrode preparation: Clean the working electrode to ensure the surface is free of impurities. For glassy carbon electrodes, polishing with alumina paste is usually required, followed by cleaning with ultrapure water and ethanol; Prepare the material to be tested into a thin film and attach it to the working electrode.

[0199] 3.2) Solution preparation: Prepare the electrolyte solution, ensuring that the solution is free of impurities and oxygen. The solution can be degassed using argon or nitrogen.

[0200] 3.3) Electrode installation: Install the working electrode, counter electrode, and reference electrode into the electrolysis cell, ensuring good connection of the electrodes to the electrolysis cell.

[0201] 3.4) Parameter setting: Set the parameters for cyclic voltammetry in the electrochemical workstation software: Initial potential: 1 V; Upper limit potential: 7 V; Lower limit potential: 1 V; Scan rate: 10 mV / s; Cycle number: 5 times to ensure data repeatability and reliability.

[0202] 3.5) Start experiment: Start the electrochemical workstation and begin the cyclic voltammetry test. The electrode potential starts from the initial potential and increases linearly to the upper limit potential, then scans back to the lower limit potential to complete one cycle.

[0203] 3.6) Data recording: The electrochemical workstation records the curve of electrode current vs. potential, i.e. the cyclic voltammogram.

[0204] 4) Data analysis In the cyclic voltammogram, the oxidation peak is the peak with positive current, and the reduction peak is the peak with negative current; The oxidation potential is defined as the peak potential of the oxidation peak, and the oxidation potential is recorded; The reduction potential is defined as the peak potential of the reduction peak, and the reduction potential is recorded; The difference between the oxidation potential and the reduction potential is the electrochemical window.

[0205] 4. Charge-discharge test 1) Sample and equipment 1.1) Battery to be tested (see the preparation method of the battery above); 1.2) Battery test system (Arbin or Marccor); 1.3) Oven (for controlling the temperature of the test environment); 1.4) Computer or data logger for recording test data.

[0206] 2) Parameter settings 2.1) Voltage range: 1.5-5 V (vs. ); 2.2) Rate range: C / 20, C / 10, C / 5, C / 2, 1C, 2C, 5C.

[0207] 3) Test procedure 3.1) Charge-discharge test using battery test system in a 25°C oven; 3.2) Constant current charge to cut-off voltage, then constant voltage charge to C / 20 cut-off, and rest for 0.5 hours, then discharge to termination voltage at 1C rate (wherein, in Example 1 and Comparative Example 1 below, the cut-off voltage is 5V; in Examples 2-17 and Comparative Examples 2-3, the cut-off voltage is 4.3V; in Example 18, the cut-off voltage is 5.5V; in Examples 19-20, the cut-off voltage is 4.7V; in Examples 1-20 and Comparative Examples 1-3, the termination voltage is 1.5V); 3.3) Charge-discharge test of the battery at C / 20, C / 10, C / 5, C / 2, 1C, 2C, 5C rates, respectively, with 5 cycles at each rate; 3.4) Record voltage, current and time data.

[0208] 4) Data analysis Specific capacity (mAh / g) = Discharge capacity (mAh) / Active material mass (g), wherein, Discharge capacity (mAh) = Current intensity (mA) x Discharge time (h), for example, 0.1C specific capacity (mAh / g) = [Current intensity (mA) at 0.1C rate x Discharge time (h) at 0.1C rate] / Active material mass (g), 2C specific capacity (mAh / g) = [Current intensity (mA) at 2C rate x Discharge time (h) at 2C rate] / Active material mass (g); First cycle coulombic efficiency = First cycle discharge capacity / Charge capacity x 100% Average working voltage: obtained from the voltage curve (voltage-capacity curve) measured at C / 20 rate, Average working voltage = wherein V is voltage and Q is capacity, is the maximum value of capacity.

[0209] 5. Gas release amount test In an argon-filled glove box, the battery monomer was charged to a cut-off voltage of 5 V at a current density of 0.1 C, and the release amounts of oxygen and carbon dioxide were monitored in real time using a gas detection device.

[0210] III. Analysis of the results of the examples and comparative examples Table 1: Reaction energies (eV / atom) of the coating materials in the examples and common coating materials with electrolyte calculated according to the calculation method described in the “DETAILED DESCRIPTION” section

[0211] It can be seen from the results in Table 1 that the absolute value of the reaction energy of the fluoride coating material of the present application with electrolyte is lower than that of LiNbO3, Li3PO4, and LATP (the more negative the reaction energy, the more violent the reaction), which indicates that the matching of the coating material of the present application with electrolyte is better than that of LiNbO3, Li3PO4, and LATP. In addition, the absolute value of the reaction energy of the fluoride coating material of the present application with some electrolytes is even comparable to that of LiF and Li2ZrF6, which indicates that the fluoride coating material of the present application can replace the commonly used LiF and Li2ZrF6 coating materials to achieve good battery cycle stability without the disadvantages of LiF and Li2ZrF6.

[0212] Table 2: Electrochemical windows of the coating materials in the examples and common coating materials calculated according to the giant potential phase diagram method described in the “DETAILED DESCRIPTION” section

[0213] It can be seen from the results in Table 2 that the coating material of the perfluoroanion framework of the present application has a comparable or even wider electrochemical window than the commonly used coating materials, which can cover the working interval of high-voltage cathodes (working voltage, for example, higher than 5 V) and electrolytes, which indicates that the coating material of the present application has good electrochemical stability and can avoid the electrochemical side reactions between high-voltage cathodes and electrolytes.

[0214] Table 3: Room temperature ionic conductivity and room temperature alkali metal ion diffusion coefficient of the coating materials in the examples and common coating materials obtained by the alternating current impedance method described in the “DETAILED DESCRIPTION” section

[0215] It can be seen from the results in Table 3 that the room temperature ionic conductivity of the coating material of the present application is on the order of 10 -5 S / cm, and the alkali metal ion diffusion ability is significantly stronger than that of LiF and Li2ZrF6, and comparable to that of layered oxide cathodes (10 -5S / cm), which indicates that the coating material of the present application has potential fast-charging capability and does not adversely affect the rate performance of the battery. The structure of the LATP material is loose, which is conducive to the transmission of alkali metal ions, so the ionic conductivity is high, but the stability of the LATP is poor, the electrochemical window is narrow, and the interface side reaction between the high-voltage positive electrode and the electrolyte cannot be inhibited.

[0216] Table 4: Mechanical modulus of the coating material in the examples and commonly used coating materials calculated according to the relevant calculation method described in the “specific embodiments” section

[0217] As can be seen from the results in Table 4, the mechanical modulus of the coating material of the present application is lower than that of LiF, Li2ZrF6, LiNbO3, and Li3PO4, which indicates that the fluoride coating material of the present application is softer and easier to process than commonly used fluorides and oxides, and is not easy to break during rolling and cycling, and will not adversely affect the efficiency and capacity of the positive electrode material.

[0218] Table 5: Test results of various properties of the examples and comparative examples

[0219] As can be seen from the results in the above table, compared with the positive electrode active particles without coating, the positive electrode active particles coated with the coating material of the present application can improve the first cycle coulombic efficiency, rate performance, cycle stability, and safety of the battery. In particular, as can be seen from the O2 and CO2 release amounts, for high-voltage oxide positive electrodes (NaNi 0.4 Fe 0.2 Mn 0.4 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2), the coating material of the present application can effectively improve the thermal runaway of the battery under high charge state and improve the safety of the battery. In addition, as can be seen from the comparison of Examples 18, 19, and 20 with Comparative Examples 1, 2, and 3, after coating the positive electrode active particles with the coating material of the present application, the coated positive electrode active particles can work at a higher voltage and achieve improvement in battery capacity.

[0220] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and achieving the same effects within the scope of the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications that can be thought of by those skilled in the art to the embodiments or by combining part of the constituent elements of the embodiments are also included in the scope of the present application without departing from the spirit of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet comprising a positive electrode active material, characterized by, The positive electrode active material comprises positive electrode active particles and a fluoride coating material coating at least part of surfaces of the positive electrode active particles, the fluoride coating material comprising a compound represented by Formula I: A 7-(2n+3m) M n M' m F 7-x R x / y Formula I wherein 0 < n < 2, 0 < m < 2, 0 < x < 2, y is the absolute value of the valence of R; A comprises Na and / or Li; M comprises at least one of Ca, Zn, Mg, Sr, and Ba; M' comprises at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb; R comprises at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4.

2. The secondary battery according to claim 1, characterized by M further comprises, based on the total moles of M, not more than 10 mol% of a first transition metal element, wherein the first transition metal element comprises at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, and V.

3. The secondary battery according to claim 1 or 2, characterized by M' further comprises, based on the total moles of M', not more than 10 mol% of a second transition metal element, wherein the second transition metal element comprises at least one of Fe, Co, Ni, Mn, V, Ti, and Cr.

4. The secondary battery according to claim 1 or 2, characterized by A further comprises, based on the total moles of A, not more than 20 mol% of K and / or Ag.

5. The secondary battery according to claim 4, characterized by M further comprises, based on the total moles of M, not more than 10 mol% in total of an element of A and an element of M'.

6. The secondary battery according to claim 1 or 2, characterized by M comprises at least one of Ca, Zn, and Mg.

7. The secondary battery according to claim 1 or 2, characterized by M' comprises at least one of Ga and Al.

8. The secondary battery according to claim 1 or 2, characterized by The positive electrode active material comprises 0.01 to 10 wt% of the fluoride coating material, based on the total weight of the positive electrode active material.

9. The secondary battery according to claim 1 or 2, characterized by The fluoride coating material has a coating thickness of 5 to 20 nm.

10. The secondary battery according to claim 1 or 2, characterized by The positive electrode active particles comprise at least one of a layered oxide material, a spinel oxide material, and a fluoride material, wherein: The layered oxide material comprises a compound represented by Formula II: A 1 M a O 2-e / 2 R 1 e / f Formula II In formula II, 0 < e < 0.2, f is the absolute value of the valence state of R 1 , A 1 comprising Li or Na, M a comprising a transition metal element, R 1 comprising at least one of F, Cl; The spinel oxide material comprises a compound represented by Formula III: A 2 M b 2O 4-g / 2 R 2 g / h Formula III In formula III, 0 < g < 0.4, h is the absolute value of the valence state of R 2 , and i is the absolute value of the valence state of R A 2 comprising Li or Na, M b comprising a transition metal element, R 2 comprising at least one of F, Cl; The fluoride material comprises a compound represented by Formula IV: A 3 7-2k-3p M c k M d p F 7-i R 3 (i / j) Formula IV In formula IV, 0 < k < 2, 0 < p < 2, 0 < i < 2, j is the absolute value of the valence of R 3 , A 3 comprising Li or Na, M c comprising a transition metal element having a divalent valence, M d comprising a transition metal element having a trivalent valence, R 3 comprising at least one of F, Cl.

11. The secondary battery according to claim 1 or 2, characterized by The positive electrode active material has one or more of the following characteristics: (1) the Dv50 particle size of the positive electrode active material is in the range of 5 to 30 µm; (2) the BET specific surface area of the positive electrode active material is in the range of 0.1 to 14 m 2 / g. (3) the tap density of the positive electrode active material is 1.1 to 2.3 g / cm 3 ; (4) the hardness of the positive electrode active material is in the range of 6 to 12 GPa.

12. The secondary battery according to claim 1 or 2, characterized by The positive electrode tab comprises a current collector and a positive electrode film layer disposed on at least one surface of the current collector, the positive electrode film layer comprising 70 wt% to 98 wt% of the positive electrode active material, based on the total weight of the positive electrode film layer.

13. The secondary battery according to claim 12, characterized by The positive electrode film layer further comprises, based on the total weight of the positive electrode film layer, 2 wt% to 30 wt% in total of a binder.

14. The secondary battery according to claim 1 or 2, characterized by The compacted density of the positive electrode plate is 2.3 g / cm 3 to 3.7 g / cm 3 .

15. A positive electrode active material comprising positive electrode active particles and a fluoride coating material coating at least part of the surface of the positive electrode active particles, characterized in that, The fluoride coating material comprises a compound represented by Formula I: A 7-(2n+3m) M n M' m F 7-x R x / y Formula I; wherein 0 < n < 2, 0 < m < 2, 0 < x < 2, y is the absolute value of the valence of R; A comprises Na and / or Li; M comprises at least one of Ca, Zn, Mg, Sr, and Ba; M' comprises at least one of Ga, Al, La, Y, B, In, Sc, Bi, and Sb; R comprises at least one of O, S, Se, Te, Cl, Br, I, CN, BF4, and BH4.

16. The positive electrode active material according to claim 15, characterized by M further includes, based on the total moles of M, not more than 10 mol% of a first transition metal element, wherein the first transition metal element includes at least one of Fe, Co, Ni, Mn, Cu, Ti, Cr, and V.

17. The positive electrode active material according to claim 15 or 16, characterized by M' further includes, based on the total moles of M', not more than 10 mol% of a second transition metal element, wherein the second transition metal element includes at least one of Fe, Co, Ni, Mn, V, Ti, and Cr.

18. The positive electrode active material according to claim 15 or 16, characterized by The positive electrode active material includes 0.01 to 10 wt% of a fluoride coating material, based on the total weight of the positive electrode active material.

19. The positive electrode active material according to claim 15 or 16, characterized by The fluoride coating material has a coating thickness of 5 to 20 nm.

20. An electrical device, comprising: A secondary battery including the positive electrode active material according to any one of claims 1 to 14 or the positive electrode active material according to any one of claims 15 to 20.

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