Flame-retardant composite positive electrode material, preparation method thereof, positive plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a flame-retardant composite positive electrode material, a preparation method thereof, a positive plate and a battery. The flame-retardant composite positive electrode material comprises a positive electrode material and a coating layer coating at least part of the surface of the positive electrode material, wherein the coating layer comprises a metal compound containing a first metal, a second metal and a chlorine element, the first metal is selected from aluminum, and the second metal is selected from at least one of alkali metal, alkaline earth metal or transition metal. The positive plate comprises the flame-retardant composite positive electrode material. The battery comprises the positive plate. The flame-retardant composite positive electrode material provided by the invention can play a role in inhibiting the occurrence of thermal runaway, alleviates the problem that the internal temperature of the battery cannot be fundamentally prevented from further rising at present, and is beneficial to improving the safety of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular, to a flame-retardant composite cathode material, a preparation method thereof, a cathode sheet, and a battery. Background Art

[0002] Lithium-ion power batteries have advantages such as high energy density, environmental friendliness, and low energy consumption, and are widely used in many fields such as electric vehicles and energy storage power stations. However, the safety of high specific energy lithium-ion batteries is a bottleneck problem restricting their development. The thermal runaway mechanism of lithium-ion batteries, the thermal runaway propagation characteristics, and the strategies for suppressing thermal runaway propagation are important research fields for improving battery safety. At present, the suppression methods for thermal runaway can be classified into two types according to the location where the safety mechanism reaction occurs, namely outside the battery cell and inside the battery cell.

[0003] In related technologies, some research has been done on suppressing thermal runaway. For example, the patent with the publication number CN220138489U discloses a heat-resistant runaway battery case upper cover, which includes a battery case upper cover main body. The rubber layer is located between the first fiber fabric layer and the second fiber fabric layer. The rubber layer can be made of ceramic silicone rubber material. The rubber layer made of this ceramic silicone rubber material is integrally formed with the above-mentioned first fiber fabric layer and the second fiber fabric layer to obtain the battery case upper cover main body, so as to prevent the flame from overflowing and spraying when the new energy battery has a thermal runaway. Another example is that the patent with the publication number CN114222748A provides a thermal runaway inhibitor. Adding an aryl phosphate compound to the electrolyte is not likely to cause thermal runaway, so as to prevent ignition or rupture caused by internal short circuit. Another example is that the patent with the publication number CN107732035A discloses a thermal runaway prevention battery case, which can effectively wrap the puncture object when the lithium-ion battery is subjected to an external puncture load while isolating the battery cell from the outside air, playing an insulating effect and effectively preventing the occurrence of thermal runaway. However, these above-mentioned methods only suppress the occurrence of thermal runaway by targeting the battery case or adding a flame retardant to the electrolyte. The effect of suppressing thermal runaway is limited, and there is no suppression of thermal runaway from the maximum energy release end of thermal runaway and the main body driven by the entire electrochemical reaction, that is, the active material.

[0004] Therefore, in order to improve the safety of the battery and effectively suppress thermal runaway, it is necessary to further develop more effective cathode active materials with flame retardant properties and their preparation methods. Summary of the Invention

[0005] In view of this, the present invention aims to solve at least one of the technical problems in the related technologies to some extent. For this reason, the present invention provides a flame-retardant composite cathode material, a preparation method thereof, a cathode sheet, and a battery, which are beneficial to improving the thermal stability of the cathode material, enhancing the flame retardancy of the cathode material, and reducing the probability of thermal runaway of the battery.

[0006] To solve the above technical problems, the present application is implemented as follows:

[0007] According to the first aspect of the present application, there is provided a flame-retardant composite cathode material, which includes a cathode material and a coating layer coated on at least a part of the surface of the cathode material;

[0008] Wherein, the coating layer includes a metal compound containing a first metal, a second metal and a chlorine element, the first metal is selected from aluminum, and the second metal is selected from at least one of an alkali metal, an alkaline earth metal or a transition metal.

[0009] In some embodiments, the chemical formula of the metal compound is M x AlCl y , where M includes at least one of an alkali metal, an alkaline earth metal or a transition metal, 1≤x≤3, 4≤y≤8.

[0010] In some embodiments, the M includes at least one of Na, K, Mg, Ti or Mn.

[0011] In some embodiments, the mass ratio of the cathode material to the metal compound is 100:(1-90).

[0012] In some embodiments, the mass ratio of the cathode material to the metal compound is 100:(20-60).

[0013] In some embodiments, the cathode material includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickel manganate, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium cobalt phosphate or a lithium-rich layered oxide.

[0014] In some embodiments, the average particle size of the metal compound is 3nm-200nm.

[0015] In some embodiments, the average particle size of the metal compound is 30nm-50nm.

[0016] In some embodiments, the thickness of the coating layer is 0.1μm-3μm.

[0017] In some embodiments, the thickness of the coating layer is 0.5μm-1μm.

[0018] In some embodiments, the average particle size of the cathode material is 5μm-20μm.

[0019] According to a second aspect of the present application, the present application provides a method for preparing a flame-retardant composite cathode material, the method comprising the following steps:

[0020] Mix the cathode material with a metal compound containing a first metal, a second metal, and chlorine element to obtain a mixed material;

[0021] Sinter the mixed material to obtain the flame-retardant composite cathode material;

[0022] The flame-retardant composite cathode material includes a cathode material and a coating layer coated on at least a part of the surface of the cathode material; the coating layer includes a metal compound containing a first metal, a second metal, and chlorine element, the first metal is selected from aluminum, and the second metal is selected from at least one of alkali metals, alkaline earth metals, or transition metals.

[0023] In some embodiments thereof, the preparation of the metal compound includes: mixing a second metal chloride and aluminum chloride uniformly by a melting method, reacting at 200 °C to 500 °C for 10 h to 24 h, and after washing and filtering, obtaining the metal compound.

[0024] In some embodiments thereof, the chemical formula of the metal compound is M x AlCl y , where M includes at least one of alkali metals, alkaline earth metals, or transition metals, 1 ≤ x ≤ 3, 4 ≤ y ≤ 8.

[0025] In some embodiments thereof, the M includes at least one of Na, K, Mg, Ti, or Mn.

[0026] In some embodiments thereof, the average particle size of the metal compound is 3 nm to 200 nm.

[0027] In some embodiments thereof, the average particle size of the metal compound is 30 nm to 50 nm.

[0028] In some embodiments thereof, the mass ratio of the cathode material to the metal compound is 100:(1 - 90).

[0029] In some embodiments thereof, the mass ratio of the cathode material to the metal compound is 100:(20 - 60).

[0030] In some embodiments thereof, the cathode material includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickel manganate, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium cobalt phosphate, or lithium-rich layered oxide.

[0031] In some of these embodiments, the atmosphere during sintering includes at least one of air or oxygen, and the flow rate of the air or oxygen is 0.5 - 1.5 L / min.

[0032] In some of these embodiments, the sintering temperature is 450°C - 800°C, and the sintering time is 12 h - 24 h.

[0033] In some of these embodiments, after obtaining the mixture, before sintering the mixture, a step of ball-milling the mixture is further included.

[0034] According to the third aspect of the present application, the present application provides a positive electrode sheet, which includes the aforementioned flame-retardant composite positive electrode material or the flame-retardant composite positive electrode material prepared according to the aforementioned preparation method.

[0035] According to the fourth aspect of the present application, the present application provides a battery, which includes the aforementioned flame-retardant composite positive electrode material, or includes the flame-retardant composite positive electrode material prepared according to the aforementioned preparation method, or includes the aforementioned positive electrode sheet.

[0036] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0037] In the embodiments of the present application, the provided flame-retardant composite positive electrode material includes a positive electrode material and a coating layer provided on the surface of the positive electrode material. The coating layer includes a metal compound containing a first metal, a second metal, and a chlorine element. The first metal is selected from aluminum, and the second metal is selected from at least one of alkali metals, alkaline earth metals, or transition metals. Thus, by providing a coating layer containing the above metal compound on the surface of the positive electrode material, the metal compound can react with the oxygen released by the positive electrode material, preventing the oxygen released by the positive electrode material from further reacting with the electrolyte, and reducing the probability of thermal runaway. At the same time, the product obtained by the reaction of the metal compound with oxygen can react with the electrolyte salt (such as lithium salt) in the electrolyte to form a substance that preferentially decomposes on the surfaces of the positive and negative electrodes, forming a dense and stable solid electrolyte interface film (SEI) or cathode electrolyte interface film (CEI); this interface film can prevent the direct contact between the electrolyte and the electrodes (positive and negative electrodes), inhibit the continuous oxidation / reduction decomposition of solvent molecules (such as carbonates), further inhibit the decomposition of the electrolyte, and inhibit the occurrence of thermal runaway, thereby effectively improving the safety of the battery.

[0038] The additional aspects and advantages of the present application will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0039] Figure 1The following is a schematic structural diagram of a flame - retardant composite cathode material provided by some embodiments of the present invention;

[0040] Figure 2 The following is a schematic structural diagram of the flame - retardant composite cathode material provided by Embodiment 1 of the present invention;

[0041] Figure 3 The following is a schematic structural diagram of the flame - retardant composite cathode material provided by Embodiment 2 of the present invention;

[0042] Figure 4 The following is a schematic structural diagram of the flame - retardant composite cathode material provided by Embodiment 3 of the present invention;

[0043] Figure 5 The following is a schematic structural diagram of the flame - retardant composite cathode material provided by Embodiment 4 of the present invention.

[0044] Explanation of reference numerals:

[0045] 10 - cathode material;

[0046] 20 - coating layer. Detailed implementation manners

[0047] The following further elaborates the present application in combination with specific embodiments. It should be understood that these embodiments of the present application are only used to illustrate the present application and not to limit the scope of the present application.

[0048] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0049] If there is no special indication, all implementation manners and optional implementation manners of the present application can be combined with each other to form new technical solutions.

[0050] If there is no special indication, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0051] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0052] Unless otherwise specified, "comprising" and "including" mentioned in this application mean open-ended or may also be closed-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0053] As analyzed in the background art of this application, the safety of current high specific energy lithium-ion batteries is a bottleneck problem restricting their development. In related technologies, most of the methods for suppressing thermal runaway only target the battery housing and adding flame retardants to the electrolyte to suppress the occurrence of thermal runaway, and there is no suppression of thermal runaway from the maximum energy release end of thermal runaway and the main body driven by the entire electrochemical reaction, that is, the active material. Thermal runaway generally goes through several reaction stages, including the decomposition of the negative electrode SEI film, the reaction of the electrolyte with the intercalated lithium in the negative electrode, the decomposition of the positive electrode to release oxygen and the reaction with the electrolyte solvent, the reaction of the oxygen released from the positive electrode with the negative electrode, and the reaction of the positive electrode with the binder. Thermal runaway has three characteristic temperatures, the self-heating start temperature (generally caused by the decomposition of the SEI film), the thermal runaway trigger temperature (caused by the oxygen release of the positive electrode material), and the highest temperature. Among them, controlling the occurrence of the thermal runaway trigger temperature (controlling the oxygen release of the positive electrode material) is the key factor for suppressing the occurrence of battery thermal runaway. However, there is a lack of effective technical means for controlling the thermal runaway trigger temperature in the prior art. In view of the deficiencies in the prior art, the inventors of this application have conducted a large number of research practices and have been able to propose the technical solution of the present invention, providing a flame-retardant composite positive electrode material, its preparation method, a positive electrode sheet, and a battery. The following will further explain the technical solution, its implementation process, and principles, etc.

[0054] [Flame-retardant Composite Positive Electrode Material]

[0055] Please refer to Figure 1 As shown, in some embodiments, this application provides a flame-retardant composite positive electrode material, which includes a positive electrode material 10 and a coating layer 20 coated on at least a part of the surface of the positive electrode material 10;

[0056] Among them, the coating layer 20 includes a metal compound containing a first metal, a second metal, and a chlorine element. The first metal is selected from aluminum, and the second metal is selected from at least one of an alkali metal, an alkaline earth metal, or a transition metal.

[0057] It should be noted that the transition metal in the second metal refers to other transition metals except aluminum, that is, non-aluminum transition metals.

[0058] In this application, the flame-retardant composite cathode material has a core-shell structure, that is, the flame-retardant composite cathode material has a coating layer 20. The flame-retardant composite cathode material with the coating layer 20 has a core-shell structure. The core (inner core) is the cathode material 10, which can be a lithium-ion cathode material, and the shell (outer shell or shell layer) is the coating layer 20. In this application, a coating layer 20 is formed on the surface of the inner-core cathode material 10. The coating layer 20 includes a metal compound containing at least two metal elements and a chlorine (Cl) element, and one of the metal elements is selected from aluminum (Al).

[0059] It should be noted that in this application, the term "coating" is not limited to direct coating, but also includes indirect coating. For example, when the coating layer 20 coats the inner-core cathode material 10, there may be no other structure between the coating layer 20 and the outer surface of the inner-core cathode material 10, or there may be one or more other structures between the coating layer 20 and the outer surface of the inner-core cathode material 10. Preferably, there is no other structure between the coating layer 20 and the outer surface of the inner-core cathode material 10. In this application, if there is one or more other structures between the coating layer 20 and the outer surface of the inner-core cathode material 10, it will affect the coating uniformity of the coating layer 20. Especially when using the solid-phase coating method, if there is an intermediate structure, it will further affect the coating uniformity of the coating layer 20. Therefore, preferably, there is no other structure between the coating layer 20 and the outer surface of the inner-core cathode material 10 in the present invention.

[0060] The above-mentioned coating layer 20 can be formed on at least part of the surface of the inner-core cathode material 10, which can play a role in protecting or improving the inner-core cathode material 10, and can also play a role in improving the overall structural stability of the composite cathode material 10. The coating layer 20 being formed or coating at least part of the surface of the inner-core cathode material 10 means that the coating layer 20 can completely encapsulate the inner-core cathode material 10 within the coating layer 20, or the coating layer 20 can only coat a part of the outer surface of the inner-core cathode material 10; that is, the coating layer 20 can completely coat the inner-core cathode material 10, or can coat a part of the surface of the inner-core cathode material 10, preferably completely coat.

[0061] In this application, the provided flame-retardant composite cathode material can improve the flame-retardant performance of the cathode material, facilitate the control of the thermal runaway trigger temperature (control the oxygen release of the cathode material), and thus, when applied to a battery such as a lithium battery, can play a role in suppressing the occurrence of battery thermal runaway and improving the safety performance of the lithium battery. Specifically:

[0062] The inventors of this application found that by providing a coating layer containing the above metal compound on the surface of the cathode material, the coating layer can absorb oxygen, making the cathode material a cathode material with flame-retardant characteristics, which can effectively solve the problems of flame retardancy and electrochemical performance, significantly improve the flame-retardant performance and electrochemical performance of the cathode material, and enhance the safety and electrochemical performance of the battery.

[0063] On the one hand, in the composite cathode material, the coating layer includes a metal compound containing at least two metal elements and Cl element, and one of the metal elements is selected from Al. This metal compound can be called chloroaluminate, and this chloroaluminate can absorb oxygen. In the early stage of battery thermal runaway, the cathode material decomposes thermally to generate oxygen, and the substance coated on the surface of the cathode material, that is, chloroaluminate, reacts chemically with oxygen to eliminate oxygen. The substances formed by the reaction of this chloroaluminate with oxygen include metal oxides (M x O, M is selected from one or more of alkali metals, alkaline earth metals or non-aluminum transition metals), aluminum oxide (Al2O3) and chlorine gas (Cl2). Thus, through the reaction of chloroaluminate and the oxygen released by the cathode material, the further reaction of oxygen with the electrolyte is prevented, which is conducive to reducing the probability of thermal runaway.

[0064] On the other hand, the Al2O3 formed by the reaction of chloroaluminate and oxygen can react with the electrolyte salt in the electrolyte, and the substances formed can inhibit the further decomposition of the electrolyte and further inhibit the occurrence of thermal runaway. For example, Al2O3 can react with the lithium salt lithium hexafluorophosphate (LiPF6) to form LiPO2F2. Among them, LiPO2F2 can preferentially participate in the oxidation reaction, and the substances formed preferentially decompose on the surfaces of the positive and negative electrodes to form a dense and stable SEI film, or form a stable and dense CEI film on the surface of the cathode material. This interface film can prevent the direct contact of the electrolyte with the electrodes (positive and negative electrodes), inhibit the continuous oxidation / reduction decomposition of solvent molecules (such as carbonates), inhibit the dissolution and phase change of metal ions in the cathode material, and stabilize the crystal structure of the cathode material. Therefore, not only can the structural stability of the composite cathode material be improved, but also the flame-retardant effect can be enhanced.

[0065] On the other hand again, the metal oxide (M x O) formed by the reaction of chloroaluminate and oxygen can further absorb oxygen, react with oxygen to form peroxides, and can also absorb hydrofluoric acid (HF) in the electrolyte to form metal fluorides (MF yIt has a relatively high melting point, which can reach above 800 °C and can improve the stability of the electrolyte in the electrolyte. At the same time, the gaseous substance Cl2 generated by the reaction of the chloroaluminate with oxygen can react with the moisture in the battery, that is, it can remove at least part of the moisture in the battery and inhibit the decomposition of lithium salts such as LiPF6 (the generated HF can damage the SEI film, resulting in poor battery stability); thus, to a certain extent, the structural stability of the SEI film can be improved, and then the stability of the battery can be improved.

[0066] In this application, the reaction equations of the involved reactions are as follows:

[0067] (1) Reaction of chloroaluminate with oxygen:

[0068] M x AlCl y +O2→M x O+Al2O3+Cl2;

[0069] (2) Reaction of Al2O3 with lithium salt lithium hexafluorophosphate (LiPF6):

[0070] Al2O3+LiPF6→LiPO2F2+AlF3;

[0071] (3) Reaction of M x O (such as Na2O) with O2:

[0072] M x O (such as Na2O)+O2→M x O2 (such as Na2O2);

[0073] (4) Reaction of M x O (such as Na2O) with HF:

[0074] M x O (such as Na2O)+HF→MF (such as NaF)+H2O;

[0075] (5) Reaction of Cl2 and H2O:

[0076] Cl2+H2O→HClO+HCl.

[0077] The inventors of the present invention have found through in-depth research that when the flame-retardant composite cathode material of the present application meets the above design conditions, if one or more of the following conditions can also be optionally met, the performance of the flame-retardant composite cathode material can be further improved.

[0078] In some embodiments, the chemical formula of the metal compound is M x AlCl y, wherein M includes at least one of alkali metals, alkaline earth metals or transition metals, 1 ≤ x ≤ 3, and 4 ≤ y ≤ 8. This metal compound can be called chloroaluminate, and M therein is the second metal, and M can be one or more of alkali metals, alkaline earth metals or transition metals. As an example, the alkali metal can be one or more of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), etc.; the alkaline earth metal can be one or more of magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba); the transition metal can be one or more of titanium (Ti), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), vanadium (V), chromium (Cr), yttrium (Y), lanthanum (La), cerium (Ce), etc.

[0079] The above-mentioned M x AlCl y In it, the value range of x is 1 to 3, for example, it can be 1, 2, 3; the value range of y is 4 to 8, for example, it can be 4, 5, 6, 7, 8. Among them, the specific values of x and y can be selected and set according to the different valences of the metal M.

[0080] Preferably, in some embodiments, M includes one or a combination of at least two of Na, K, Mg, Ti or Mn. More preferably, M is selected from one or more of Na, K, Mg.

[0081] In the above-mentioned metal compound, the second metal is preferably one or more of Na, K, Mg, Ti or Mn, and more preferably one or more of Na, K, Mg. Thus, by using chloroaluminate containing the above-mentioned several second metals, not only can it react with oxygen, which is beneficial to inhibiting the decomposition of the electrolyte, improving the stability of the battery, improving the flame retardant effect, but also it has a wide source, low cost, is convenient for processing and preparation, and is beneficial to reducing costs.

[0082] In the present application, the core cathode material in the flame retardant composite cathode material can adopt the conventional cathode materials in the industry.

[0083] In some embodiments, the cathode material 10 includes, but is not limited to, one or a combination of at least two of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickel manganate, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium cobalt phosphate or lithium-rich layered oxide. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0084] As an example, the cathode material 10 can be selected from ternary materials, such as lithium nickel cobalt manganate, lithium nickel cobalt aluminate. Or, the cathode material 10 can be selected from lithium iron phosphate, lithium iron manganese phosphate. Or, the cathode material 10 can be selected from lithium cobaltate, lithium nickel cobaltate, etc.

[0085] Preferably, the positive electrode material 10 is made of a material containing nickel element, such as one or more selected from lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickelate or lithium nickel manganate. By using a positive electrode material containing nickel oxide, oxygen evolution is likely to occur in the battery cell before the valve opens due to the unstable structure at high temperature. In contrast, the P-O structure of phosphoric oxide is relatively stable, and oxygen evolution is not likely to occur in the battery cell before the valve opens.

[0086] In addition, in other embodiments, the above positive electrode material 10 is not limited to the several types listed above. When meeting the basic requirements of the positive electrode active material applicable to lithium batteries, etc., the positive electrode material 10 can also adopt other types, which will not be described in detail one by one here.

[0087] In some embodiments, in the flame-retardant composite positive electrode material, the mass ratio of the positive electrode material 10 to the metal compound is 100:(1 - 90). As an example, the mass ratio of the positive electrode material 10 to the metal compound can be any one of the point values of 100:1, 100:5, 100:10, 100:20, 100:30, 100:40, 100:50, 100:60, 100:80, 100:90 or the range value between any two of them.

[0088] Preferably, in some embodiments, the mass ratio of the positive electrode material 10 to the metal compound is 100:(20 - 60). Further, the mass ratio of the positive electrode material 10 to the metal compound can be 100:(20 - 50).

[0089] By controlling the mass ratio of the positive electrode material 10 to the metal compound within the above suitable range, especially within the range of 100:(20 - 60), the flame-retardant effect and electrochemical performance of the composite positive electrode material can both reach the optimum. For example, when the mass ratio of the positive electrode material to the metal compound is small, such as lower than 100:20, the content of the metal compound is low, and the amount available for reaction with oxygen is small, so the flame-retardant effect cannot be effectively achieved; when the mass ratio of the positive electrode material to the metal compound is large, such as higher than 100:60, the content of the metal compound is high, which will affect the electrochemical performance of the composite positive electrode material and further affect the electrochemical performance of the battery. Therefore, by making the mass ratio of the positive electrode material to the metal compound 100:(20 - 60), the electrochemical performance of the composite positive electrode material is basically not affected, and at the same time, the flame-retardant effect of the composite positive electrode material is not affected.

[0090] In some embodiments, the average particle size of the metal compound is 3nm - 200nm. As an example, the average particle size of the metal compound can be any one of the point values of 3nm, 5nm, 10nm, 20nm, 30nm, 35nm, 40nm, 45nm, 50nm, 60nm, 80nm, 100nm, 150nm, 200nm or the range value between any two of them.

[0091] Preferably, in some embodiments, the average particle size of the metal compound is 30 nm to 50 nm. The average particle size of the metal compound is preferably ≤50 nm.

[0092] In the present application, by using the metal compound within the above-mentioned suitable particle size range, it is beneficial to maximize the improvement effect of the metal compound, improve the flame retardant effect. In particular, when the average particle size of the metal compound is below 50 nm, the achieved flame retardant effect is more excellent, and the structural stability of the composite cathode material can also be improved.

[0093] In some embodiments, the average particle size of the cathode material 10 is 5 μm to 20 μm. Further, the average particle size of the cathode material 10 can be 6 μm to 15 μm. As an example, the average particle size of the cathode material 10 can be any one of the point values of 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or the range value between any two of them.

[0094] By making the particle size of the cathode material 10 within the above-mentioned suitable range, the processing performance of the material can be improved, which is beneficial for processing, can ensure the effective composite of the core cathode material 10 and the metal compound, and can also make the comprehensive electrical performance of the flame retardant composite cathode material better. In addition, using a core cathode material with a smaller particle size is beneficial for improving the initial Coulomb efficiency of the material or the rate performance of the material.

[0095] In the present application, the average particle size can be understood as the equivalent diameter. The present application has no particular limitation on the regulation method of the average particle size of the metal compound, cathode material, etc., as long as the purpose of the present application can be achieved. For example, it can be achieved by directly purchasing a cathode material with an average particle size within the range of the present application, or by means of crushing, grinding or ball milling.

[0096] It should also be noted that in the present application, the average particle size or particle size can be measured by any known method in the art, and there is no limitation on this. For example, the average particle size can be measured by a Malvern high-sensitivity nano particle size analyzer.

[0097] In some embodiments, the thickness of the coating layer 20 is 0.1 μm to 3 μm. As an example, the thickness of the coating layer 20 can be any one of the point values of 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 0.9 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or the range value between any two of them.

[0098] Preferably, in some embodiments, the thickness of the coating layer 20 is 0.5 μm to 1 μm.

[0099] The thickness of the above-mentioned coating layer 20 can be adjusted according to the size of the core cathode material 10. A suitable thickness of the coating layer 20 can not only ensure good processing performance of the composite cathode material, but also avoid the excessive thickness and excessive coating material, which may affect the timely release of active lithium, increase the battery impedance or affect the cycle performance of the battery cell. Or it can also avoid the too thin thickness that is not enough to effectively exert the modification effect of the coating layer 20, that is, it can avoid the too thin thickness that reduces the effect of the coating layer 20 in improving the structural strength of the material.

[0100] Thus, based on the above settings, compared with the prior art, in which flame retardants are usually added to the electrolyte and coatings are applied on the separator to increase the temperature at which battery thermal runaway occurs and delay the time of thermal runaway, there are defects that it cannot fundamentally prevent the further increase in the internal temperature of the battery and prevent the occurrence of thermal runaway. In the present application, by providing a coating layer 20 containing the above-mentioned metal compound, i.e., chloroaluminate, on the surface of the cathode material 10, the chloroaluminate can act as a flame retardant, and the flame retardant performance of the cathode material can be significantly improved. Among them, in the early stage of battery thermal runaway, the cathode material 10 decomposes upon heating to generate oxygen. The substance coated on the surface of the cathode material 10, i.e., chloroaluminate, reacts with oxygen chemically, eliminating the oxygen and preventing the further reaction of oxygen with the electrolyte, preventing the decomposition of the electrolyte, and facilitating the alleviation of the occurrence of thermal runaway. And the Al2O3 generated by the reaction of chloroaluminate and oxygen can react with the electrolyte salt in the electrolyte, and the generated substance can inhibit the further decomposition of the electrolyte, further inhibiting the occurrence of thermal runaway. In some preferred embodiments, by controlling the mass ratio of the cathode material 10 to the metal compound within the range of 100:(20 - 50) and the average particle size of the metal compound within the range of 30 nm - 50 nm, it is helpful to further improve the flame retardant effect and ensure the electrochemical performance of the composite cathode material.

[0101] [Preparation Method of Flame Retardant Composite Cathode Material]

[0102] Correspondingly, in some embodiments, a preparation method of a flame retardant composite cathode material is provided, and the method includes the following steps:

[0103] Mix the cathode material with a metal compound containing a first metal, a second metal and chlorine element to obtain a mixture;

[0104] Sinter the mixture to obtain a flame retardant composite cathode material;

[0105] The flame retardant composite cathode material includes a cathode material and a coating layer coated on at least a part of the surface of the cathode material; the coating layer includes a metal compound containing a first metal, a second metal and chlorine element, the first metal is selected from aluminum, and the second metal is selected from at least one of alkali metals, alkaline earth metals or transition metals.

[0106] In the present invention, the cathode material and the metal compound containing the first metal, the second metal and chlorine element can be prepared separately first, and then the prepared cathode material and the metal compound containing the first metal, the second metal and chlorine element are mixed and sintered, so as to form a coating layer on the surface of the cathode material, and a flame-retardant composite cathode material with a core-shell structure is obtained.

[0107] The preparation method provided by the embodiment of the present invention has simple process, convenient operation, strong feasibility, low energy consumption and is easy to realize industrialization; through this method, a flame-retardant composite cathode material can be prepared, which has good structural stability, better flame-retardant effect and excellent electrochemical performance.

[0108] It should be understood that all the features and advantages described above for the "flame-retardant composite cathode material" also apply to the "preparation method of the flame-retardant composite cathode material", and will not be repeated here one by one.

[0109] In some specific embodiments, the preparation method of the flame-retardant composite cathode material specifically includes the following steps (a) to (c):

[0110] (a) Prepare the cathode material.

[0111] In the present application, the cathode material includes, but is not limited to, at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium nickel manganate, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium cobalt phosphate or lithium-rich layered oxide.

[0112] These cathode materials can be obtained by purchasing from the market, or can be prepared by oneself using known or improved methods in the art. Hereinafter, the preparation of ternary material lithium nickel cobalt manganate (NCM) will be mainly described as an example. However, it should be understood that the preparation of other cathode materials can also be carried out in the same or similar manner, and this is not limited.

[0113] In some embodiments, in step (a), preparing the cathode material includes:

[0114] Mix the ternary precursor (such as the ternary nickel cobalt manganese material precursor) and the lithium salt at room temperature. The molar ratio of each element in the ternary nickel cobalt manganese material precursor is Ni:Co:Mn = (0.5 - 0.9):(0.01 - 0.3):(0.01 - 0.3), for example, Ni:Co:Mn = 0.6:0.2:0.2, and the molar ratio of the lithium source to the ternary nickel cobalt manganese material precursor is Li / (Ni + Co + Mn) = 1.01 - 1.05.

[0115] Subsequently, a lithium source and a nickel-cobalt-manganese ternary material precursor are mixed in a planetary ball mill at a rotation speed of 200 - 500 r / min (preferably 300 r / min) and a revolution speed of 5 - 100 r / min (preferably 10 r / min) for 1 - 3 h to obtain a blended powder.

[0116] Subsequently, the above-mentioned blended powder is sintered. During sintering, the blended powder is heated to 180 - 250 °C at a rate of 1.5 - 5 °C / min and held at a constant temperature for 1 - 3 h, then continues to be heated to 890 - 950 °C at a rate of 1.5 - 5 °C / min and held at a constant temperature for 8 - 15 h, and then is crushed and sieved to obtain the ternary cathode material lithium nickel cobalt manganese oxide, such as NCM622 is prepared.

[0117] Optionally, the average particle size of the cathode material is 5 μm - 20 μm.

[0118] It should be understood that the cathode material of the present application is not limited to the above-mentioned ternary cathode material lithium nickel cobalt manganese oxide. For example, the ternary material can be NCM622, and can also be NCM811, NCM523, NCM111, etc. In addition, other types of cathode materials can be prepared by any known method in the art, which will not be elaborated here.

[0119] (b) Prepare a metal compound.

[0120] In step (b), the preparation of the metal compound includes: mixing a second metal chloride and aluminum chloride uniformly by a melting method, reacting at 200 °C - 500 °C for 10 h - 24 h, and after washing and filtering, a metal compound is obtained.

[0121] In the present application, the metal compound can be prepared by melting a second metal chloride such as MCl y and AlCl3 powder are fully mixed uniformly. Optionally, the molar ratio of MCl y to AlCl3 can be 1:1 - 3:1; then, react in a high-temperature reactor at 200 °C - 500 °C for 10 h - 24 h. For example, the reaction temperature can be any point value among 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 500 °C or the range value between any two of them; the reaction time can be any point value among 10 h, 12 h, 15 h, 16 h, 18 h, 20 h, 24 h or the range value between any two of them. After the reaction, thorough washing and filtering are carried out, and a metal compound can be obtained, such as obtaining a chloroaluminate M x AlCl y .

[0122] In some embodiments, the chemical formula of the metal compound is M x AlCl y, wherein M includes at least one of alkali metals, alkaline earth metals or transition metals, 1≤x≤3, 4≤y≤8. Preferably, in some embodiments, M includes at least one of Na, K, Mg, Ti or Mn.

[0123] In some embodiments, the average particle size of the metal compound is 3 nm to 200 nm. Preferably, the average particle size of the metal compound is 30 nm to 50 nm. By controlling the average particle size of the metal compound within the above preferred range, it is beneficial to make the electrochemical performance and flame retardant performance of the composite cathode material better.

[0124] (c) Prepare a flame-retardant composite cathode material.

[0125] In step (c), the cathode material prepared in the above step (a) and the metal compound prepared in step (b) are mixed and then sintered to obtain a flame-retardant composite cathode material.

[0126] In some embodiments, the mass ratio of the cathode material to the metal compound is 100:(1 - 90). Preferably, the mass ratio of the cathode material to the metal compound is 100:(20 - 60).

[0127] By controlling the mass ratio of the cathode material to the metal compound within the above reasonable range, the coating layer of the obtained composite cathode material can be within a suitable thickness range, which is beneficial to improving the electrochemical performance and flame retardant performance of the material. When the ratio range of the coating material metal compound to the cathode material is not within the preferred range provided by the present invention, the performance of the battery prepared from the obtained composite cathode material will be reduced. This is because if the coating material is too little, the coating layer is too thin to play the coating effect of the coating layer, reducing the flame retardant effect; if the coating material is too much, the coating layer is too thick, which will increase the transmission distance of lithium ions and affect the electrochemical performance of the prepared composite cathode material.

[0128] In some embodiments, the atmosphere during sintering includes at least one of air or oxygen, and the flow rate of air or oxygen is 0.5 - 1.5 L / min. For example, the flow rate of air or oxygen can be 0.5 L / min, 0.6 L / min, 0.8 L / min, 1 L / min, 0.5 L / min, etc.

[0129] Optionally, the sintering atmosphere can be air.

[0130] In some embodiments, the sintering temperature is 450°C to 800°C, and the sintering time is 12h to 24h. As an example, the sintering temperature can be any point value among 450°C, 500°C, 550°C, 600°C, 700°C, 800°C or the range value between any two of them; the sintering time can be any point value among 12h, 16h, 20h, 22h, 24h or the range value between any two of them.

[0131] In some embodiments, after obtaining the mixed material and before sintering the mixed material, it further includes a step of ball-milling the mixed material.

[0132] Optionally, the ball-milling can be wet ball-milling or dry ball-milling, and the present application does not limit this.

[0133] As an example, step (c) may specifically include: mixing the positive electrode material prepared in the above step (a) and the metal compound prepared in step (b), transferring the mixture into a ball mill for ball-milling after mixing; after the ball-milling is completed, sintering is carried out in an air atmosphere, heating with stirring in a roller furnace at 450°C to 800°C, the heating time is 12 - 24h, and the air flow rate is 0.5 - 1.5m / h, and M is completed x AlCl y By uniformly coating the positive electrode material, a flame-retardant composite positive electrode material can be obtained.

[0134] The preparation method of the flame-retardant composite positive electrode material provided by the embodiments of the present application has simple process, strong feasibility, high efficiency and environmental protection, and is easy to realize large-scale production.

[0135] [Positive electrode sheet]

[0136] In some embodiments, the embodiments of the present application provide a positive electrode sheet, which includes a current collector and a positive electrode active material layer provided on the surface of the current collector; the positive electrode active material layer includes the aforementioned flame-retardant composite positive electrode material or the flame-retardant composite positive electrode material prepared by the aforementioned method.

[0137] The positive electrode sheet includes the flame-retardant composite positive electrode material provided by the embodiments of the present application. Therefore, the positive electrode sheet also has the characteristics of excellent electrochemical performance and good flame-retardant effect.

[0138] The present application does not particularly limit the material of the current collector in the positive electrode sheet, as long as the purpose of the present application can be achieved, and it can be selected according to actual needs. For example, in some embodiments, the positive electrode current collector may include aluminum foil, aluminum alloy foil, carbon-coated aluminum foil, etc. Of course, in other embodiments, a composite current collector (such as a composite current collector formed by a metal and a polymer) may also be used.

[0139] In the present application, the positive electrode active material layer can be disposed on one surface in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces in the thickness direction of the positive electrode current collector. Optionally, the positive electrode active material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder in the positive electrode active material layer, as long as the object of the present application can be achieved. The present application does not particularly limit the mass ratio of the flame-retardant composite positive electrode material, the conductive agent, and the binder in the positive electrode active material layer, and those skilled in the art can select according to actual needs, as long as the object of the present application can be achieved. For example, in the positive electrode active material layer, the mass ratio of the flame-retardant composite positive electrode material, the conductive agent, and the binder is (85-95):(1-10):(1-10).

[0140] As an example, in the positive electrode active material layer, the binder may include, but is not limited to, one or more of polyacrylate, polyimide, polyvinyl alcohol, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene copolymer (styrene-butadiene rubber), polytetrafluoroethylene, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or sodium hydroxymethyl cellulose. As an example, in the positive electrode active material layer, the conductive agent may include, but is not limited to, at least one of conductive carbon black (such as acetylene black, Ketjen black), carbon nanotubes (CNTs), carbon fibers, graphene, etc. The above carbon nanotubes may be single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0141] The present application does not particularly limit the preparation method of the positive electrode sheet, and a preparation method well-known in the art can be selected, as long as the object of the present application can be achieved. For example, the preparation method of the positive electrode sheet includes, but is not limited to, the following steps: dispersing the flame-retardant composite positive electrode material, the conductive agent, and the binder in an N-methylpyrrolidone (NMP) solvent and mixing to form a uniform positive electrode slurry, coating the positive electrode slurry on the positive electrode current collector, and obtaining the positive electrode sheet through processes such as drying, cold pressing, and slitting.

[0142] [Battery]

[0143] In some embodiments, the embodiments of the present application provide a battery, which includes the aforementioned positive electrode sheet and a negative electrode sheet.

[0144] This battery includes the above-mentioned flame-retardant composite positive electrode material provided by the embodiments of the present application. Therefore, this battery, such as a lithium ion secondary battery, also has the characteristics of good safety and excellent electrochemical performance.

[0145] This electrochemical cell can be a secondary battery, having high cycle performance and high safety. Specifically, this secondary battery can be specifically a lithium secondary battery.

[0146] The above-mentioned battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the above-mentioned battery can be a lithium-ion secondary battery, a lithium primary battery, etc., but is not limited thereto. The battery structure of the present application includes but is not limited to a soft-pack lithium-ion battery, a square hard-shell battery, a cylindrical hard-shell battery, etc.

[0147] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode material. As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0148] In this embodiment, for the negative electrode sheet, the specific materials, structures, etc. of the negative electrode current collector and the negative electrode active material layer are not limited, and the negative electrode sheet structures and components known to those skilled in the art and applicable to secondary batteries can be selected.

[0149] In some embodiments, the battery further includes an electrolyte and a separator.

[0150] The above-mentioned electrolyte can be an electrolytic solution, and the electrolytic solution applicable to the embodiments of the present application can be an electrolytic solution known in the prior art. The specific type and structure of the electrolytic solution can be the type of electrolytic solution known to those skilled in the art and applicable to secondary batteries. As an example, the electrolytic solution includes a lithium salt and an organic solvent, and may also include optional functional additives.

[0151] In some embodiments, the lithium salt includes, but is not limited to, any one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate borate, and lithium difluorobis(oxalate)phosphate. For the sake of brevity, the combinations within the above range are not listed one by one.

[0152] Preferably, in the present application, the lithium salt includes at least LiPF6, and in addition, may include one or more of other types of lithium salts.

[0153] In some embodiments, in the electrolytic solution, the concentration of the lithium salt is 0.8 mol / L to 1.5 mol / L (M). As an example, the concentration of the lithium salt can be 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc.

[0154] In some embodiments, the organic solvent in the above electrolyte can be an ester solvent, such as a chain carboxylic acid ester compound and / or a cyclic carbonate compound, etc. As an example, the organic solvent includes, but is not limited to, any one or a combination of at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl propionate, ethyl acetate, and methyl acetate. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0155] In addition, in other embodiments, the organic solvent in the above electrolyte is not limited to the several types listed above, and other types can also be used. The organic solvent can adopt the types of organic solvents in conventional electrolytes in batteries, and will not be described in detail one by one here.

[0156] This application has no particular limitation on the type of separator. Any well-known porous separator with good chemical stability and mechanical stability can be selected. As an example, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0157] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents, materials or instruments not specified for the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0158] Example 1

[0159] The preparation of the flame-retardant composite cathode material includes the following steps:

[0160] (a) Mix the nickel-cobalt-manganese ternary material precursor and a lithium salt (lithium carbonate) at room temperature. The molar ratio of each element in the nickel-cobalt-manganese ternary material precursor is Ni:Co:Mn = 0.6:0.2:0.2, and the molar ratio of the lithium source to the nickel-cobalt-manganese ternary material precursor is Li / (Ni + Co + Mn) = 1.02; then, mix the lithium source and the nickel-cobalt-manganese ternary material precursor in a planetary ball mill at a self-rotation speed of 300 r / min and a revolution speed of 10 r / min for 3 h to obtain a blended powder; then, sinter the above blended powder. When sintering, heat the blended powder at a rate of 5 °C / min to 250 °C and keep it at a constant temperature for 3 h, then continue to heat it at a rate of 5 °C / min to 900 °C and keep it at a constant temperature for 10 h, and then crush and screen it to obtain the ternary cathode material lithium nickel cobalt manganate, that is, NCM622. The average particle size of the ternary cathode material lithium nickel cobalt manganate is 20 μm.

[0161] (b) The second metal chloride, sodium chloride (NaCl) powder, is thoroughly mixed with AlCl3 powder by the melting method, and the molar ratio of NaCl to AlCl3 is 3:1. Then, the reaction is carried out in a high-temperature reactor at 200 °C for 20 h. After the reaction, the resulting solution is thoroughly washed and filtered to obtain a metal compound, such as sodium hexachloroaluminate Na3AlCl6 powder. After the obtained solid is crushed, it is sieved, and after sieving, sodium hexachloroaluminate with an average particle size D50 of 30 nm is obtained.

[0162] The reaction in step (b) is: AlCl3 + 3NaCl = Na3AlCl6.

[0163] (c) The ternary cathode material prepared in step (a) above and the metal compound sodium hexachloroaluminate prepared in step (b) are mixed in a mass ratio of 100:20. After mixing, it is transferred to a ball mill for ball milling. After the ball milling is completed, sintering is carried out in an air atmosphere. It is heated with stirring in a roller furnace at 800 °C for 24 h, and the air flow rate is 1.5 m / h to complete the uniform coating of the metal compound on the cathode material, obtaining a flame-retardant composite cathode material.

[0164] The schematic diagram of the flame-retardant composite cathode material prepared in Example 1 is as Figure 2 shown.

[0165] Example 2

[0166] This example is basically the same as Example 1, and the main difference is that:

[0167] In step (b), the average particle size D50 of sodium hexachloroaluminate is 50 nm.

[0168] The rest are the same as in Example 1.

[0169] The schematic diagram of the flame-retardant composite cathode material prepared in Example 2 is as Figure 3 shown.

[0170] Example 3

[0171] This example is basically the same as Example 1, and the main difference is that:

[0172] In step (b), the average particle size D50 of sodium hexachloroaluminate is 55 nm.

[0173] The rest are the same as in Example 1.

[0174] The schematic diagram of the flame-retardant composite cathode material prepared in Example 3 is as Figure 4 shown.

[0175] Example 4

[0176] This example is basically the same as Example 1, and the main differences are as follows:

[0177] In step (b), the average particle size D50 of sodium hexaaluminate is 60 nm.

[0178] The rest are the same as those in Example 1.

[0179] The schematic diagram of the flame-retardant composite cathode material prepared in Example 4 is as Figure 5 shown.

[0180] Example 5

[0181] This example is basically the same as Example 1, and the main differences are as follows:

[0182] In step (b), the average particle size D50 of sodium hexaaluminate is 50 nm.

[0183] In step (c), the mass ratio of the ternary cathode material to sodium hexaaluminate is 100:10.

[0184] The rest are the same as those in Example 1.

[0185] Example 6

[0186] This example is basically the same as Example 1, and the main differences are as follows:

[0187] In step (b), the average particle size D50 of sodium hexaaluminate is 50 nm.

[0188] In step (c), the mass ratio of the ternary cathode material to sodium hexaaluminate is 100:30.

[0189] The rest are the same as those in Example 1.

[0190] Example 7

[0191] This example is basically the same as Example 1, and the main differences are as follows:

[0192] In step (b), the average particle size D50 of sodium hexaaluminate is 50 nm.

[0193] In step (c), the mass ratio of the ternary cathode material to sodium hexaaluminate is 100:50.

[0194] The rest are the same as those in Example 1.

[0195] Example 8

[0196] This example is basically the same as Example 1, and the main differences are as follows:

[0197] In step (b), the average particle size D50 of sodium hexaaluminate is 50 nm.

[0198] In step (c), the mass ratio of the ternary cathode material to sodium hexafluoroaluminate is 100:60.

[0199] The rest are the same as in Example 1.

[0200] Example 9

[0201] This example is basically the same as Example 1, and the main differences are as follows:

[0202] In step (a), the nickel-cobalt-manganese ternary material precursor and the lithium salt (lithium carbonate) are mixed at room temperature. In the nickel-cobalt-manganese ternary material precursor, the molar ratio of each element is Ni:Co:Mn = 0.6:0.2:0.2, and the molar ratio of the lithium source to the nickel-cobalt-manganese ternary material precursor is Li / (Ni + Co + Mn) = 1.02. Then, the lithium source and the nickel-cobalt-manganese ternary material precursor are mixed in a planetary ball mill at a rotation speed of 300 r / min and a revolution speed of 10 r / min for 3 h to obtain a blended powder. Then, the above blended powder is sintered. During sintering, the blended powder is heated to 250 °C at a rate of 5 °C / min and held at a constant temperature for 3 h, then continued to be heated to 500 °C at a rate of 5 °C / min and held at a constant temperature for 5 h, and then crushed to control the primary particle size to be 3 - 8 μm. The crushed powder is sintered at 900 °C and held at a constant temperature for 10 h, and then crushed and sieved to obtain the ternary cathode material lithium nickel cobalt manganate, that is, NCM622. The average particle size of the ternary cathode material lithium nickel cobalt manganate is 10 μm.

[0203] The rest are the same as in Example 1.

[0204] Example 10

[0205] This example is basically the same as Example 1, and the main differences are as follows:

[0206] In step (b), the second metal chloride magnesium chloride (MgCl₂) powder and AlCl₃ powder are fully mixed evenly by the melting method, and the molar ratio of MgCl₂ to AlCl₃ is 1:1. Then, the reaction is carried out in a high-temperature reactor at 200 °C for 20 h. After the reaction, the solution obtained after the reaction is fully washed and filtered to obtain a metal compound, such as obtaining magnesium hexafluoroaluminate MgAlCl₅ powder.

[0207] The rest are the same as in Example 1.

[0208] Comparative Example 1

[0209] The preparation of the cathode material includes the following steps:

[0210] (a)Mix the nickel-cobalt-manganese ternary material precursor and lithium salt (lithium carbonate) at room temperature. The molar ratio of each element in the nickel-cobalt-manganese ternary material precursor is Ni:Co:Mn = 0.6:0.2:0.2, and the molar ratio of lithium source to nickel-cobalt-manganese ternary material precursor is Li / (Ni + Co + Mn) = 1.02. Then, mix the lithium source and the nickel-cobalt-manganese ternary material precursor in a planetary ball mill at a rotation speed of 300 r / min and a revolution speed of 10 r / min for 3 h to obtain a blended powder. Then, sinter the above blended powder. When sintering, heat the blended powder at a rate of 5 °C / min to 250 °C and keep it at a constant temperature for 3 h, then continue to heat it at a rate of 5 °C / min to 900 °C and keep it at a constant temperature for 10 h, and then crush and screen it to obtain the ternary cathode material lithium nickel cobalt manganate, that is, NCM622. The average particle size of the ternary cathode material lithium nickel cobalt manganate is 20 μm.

[0211] In Comparative Example 1, steps (b) and (c) are omitted.

[0212] Performance test

[0213] Prepare the batteries from the flame-retardant composite cathode materials prepared in the above examples and comparative examples respectively, and conduct performance tests on the batteries, specifically including:

[0214] 1. Preparation of the battery

[0215] (1) Preparation of the positive electrode sheet: Mix the above flame-retardant composite cathode material, conductive agent carbon nanotube CNT, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 96.5:1:0.5:2, add the solvent NMP and stir to form a uniformly mixed and stable positive electrode slurry; uniformly coat the positive electrode slurry on the positive electrode current collector aluminum foil, dry it in a forced-air drying oven at 80 °C for 1 h, and then dry it in a vacuum drying oven at 120 °C for 12 h; then cut it into a 100 mm * 200 mm positive electrode sheet with a die cutter.

[0216] (2) Preparation of the negative electrode sheet: Mix the negative electrode active material graphite, conductive agent Super P, thickening agent carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in a mass ratio of 95.5:1.5:1.2:1.8, grind the graphite material, conductive agent Super P, and thickening agent CMC evenly, then add an appropriate amount of water to form a slurry, and then add the SBR solution to obtain a stable negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector copper foil, dry it in a forced-air drying oven at 80 °C for 1 h, and then dry it in a vacuum drying oven at 120 °C for 12 h; then cut it into a 105 mm * 205 mm negative electrode sheet with a die cutter.

[0217] (3) Preparation of electrolyte: Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1 to obtain an organic solvent. Then, the solute LiPF6 was added to the organic solvent and dissolved and mixed evenly to obtain the electrolyte; the concentration of LiPF6 was 1.0 mol / L.

[0218] (4) Selection of separator: The separator uses PP as the base film, and the thickness of the base film is 16 μm. The size of the separator is 110 mm * 210 mm.

[0219] (5) Assembly of the battery: The positive electrode sheet, separator, and negative electrode sheet were arranged in sequence, and the lamination method was selected for assembly. After processes such as baking, liquid injection, formation, aging, and grading, a finished square battery (100 Ah) was finally produced.

[0220] 2. Electrochemical performance tests were carried out on the assembled batteries, including:

[0221] Heating experiment test: A small hole was drilled in the cover plate of the square battery, and one end of the trachea of the gas collector was inserted into the battery, and the small hole was sealed with AB glue. The battery was placed in a hot box at 140 °C, and the temperature of the hot box rose to 140 ± 2 °C at a rate of 5 °C / min until failure or for 6 h. Observe for 10 min, that is, observe the situation of the explosion-proof valve and the situation of the battery catching fire. The collected gas was passed through a gas chromatograph (GC) to calculate the proportion of O2 in it.

[0222] The test results are shown in Table 1.

[0223] Table 1

[0224]

[0225] It can be seen from the data in Table 1 that through the comparison between Examples 1 to 10 and Comparative Example 1, it can be known that the positive electrode material without a coating layer used in Comparative Example 1 is a conventional one in the prior art, and the phenomenon of the battery core catching fire occurred in the heating experiment test, and the proportion of oxygen in the collected gas is relatively high; while for the flame-retardant composite positive electrode materials provided in Examples 1 to 10 of the present invention, due to the setting of this specific coating layer, the phenomenon of the battery core catching fire did not occur in the heating experiment test, effectively suppressing the occurrence of thermal runaway and improving the safety of the battery.

[0226] The parts not detailed in the present invention are well-known technologies to those skilled in the art.

[0227] The basic principles of the present invention have been described above in connection with specific embodiments. However, it should be noted that the advantages, benefits, effects, etc. mentioned in the present invention are merely examples and not limitations, and it cannot be considered that these advantages, benefits, effects, etc. are essential for each embodiment of the present invention. In addition, the specific details disclosed above are only for the purposes of illustration and facilitating understanding, rather than limitations. The above details do not limit the present invention to necessarily adopt the above specific details for implementation.

[0228] It should be noted that the term "and / or" or " / " used herein is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. The singular forms of "a", "the" and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0229] In the specific embodiments and claims, a list of items connected by the terms "at least one of", "at least one", "at least one kind of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0230] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flame retardant composite positive electrode material, characterized in that: The flame-retardant composite positive electrode material comprises a positive electrode material and a coating layer coated on at least a portion of the surface of the positive electrode material; The coating layer comprises a metal compound containing a first metal, a second metal and a chlorine element, the first metal is selected from aluminum, and the second metal is selected from at least one of an alkali metal, an alkaline earth metal or a transition metal.

2. The flame-retardant composite positive electrode material according to claim 1, characterized in that: The chemical formula of the metal compound is M x AlCl y , wherein M comprises at least one of an alkali metal, an alkaline earth metal or a transition metal, 1≤x≤3, 4≤y≤8; Preferably, the M includes at least one of Na, K, Mg, Ti or Mn.

3. The flame-retardant composite positive electrode material according to claim 1, characterized in that: The mass ratio of the positive electrode material to the metal compound is 100:(1-90), preferably, the mass ratio of the positive electrode material to the metal compound is 100:(20-60); and / or, The positive electrode material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium cobalt phosphate or lithium-rich layered oxide.

4. The flame-retardant composite positive electrode material according to claim 1, characterized in that: The average particle size of the metal compound is 3 nm to 200 nm, preferably, the average particle size of the metal compound is 30 nm to 50 nm; and / or, The coating layer has a thickness of 0.1 μm to 3 μm, preferably, the coating layer has a thickness of 0.5 μm to 1 μm; and / or, The average particle size of the positive electrode material is 5 μm to 20 μm.

5. A method for preparing a flame-retardant composite positive electrode material, characterized in that: The following steps are involved: Mixing the positive electrode material with a metal compound containing a first metal, a second metal and a chlorine element to obtain a mixed material; Sintering the mixture to obtain the flame-retardant composite positive electrode material; The flame-retardant composite positive electrode material includes a positive electrode material and a coating layer coated on at least a portion of the surface of the positive electrode material; the coating layer includes a metal compound containing a first metal, a second metal and a chlorine element, the first metal is selected from aluminum, and the second metal is selected from at least one of an alkali metal, an alkaline earth metal or a transition metal.

6. The method for preparing a flame-retardant composite positive electrode material according to claim 5, characterized in that: The preparation of the metal compound comprises: The second metal chloride and aluminum chloride are mixed uniformly by a melting method, reacted at 200° C. to 500° C. for 10 h to 24 h, and washed and filtered to obtain the metal compound; Preferably, the chemical formula of the metal compound is M x AlCl y , wherein M comprises at least one of an alkali metal, an alkaline earth metal or a transition metal, 1≤x≤3, 4≤y≤8; Preferably, the M includes at least one of Na, K, Mg, Ti or Mn; Preferably, the average particle size of the metal compound is 3 nm to 200 nm; Preferably, the average particle size of the metal compound is 30 nm to 50 nm.

7. The method for preparing a flame-retardant composite positive electrode material according to claim 5, characterized in that: The mass ratio of the positive electrode material to the metal compound is 100:(1-90); Preferably, the mass ratio of the positive electrode material to the metal compound is 100:(20-60); Preferably, the positive electrode material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium cobalt phosphate or lithium-rich layered oxide.

8. The method for preparing a flame-retardant composite positive electrode material according to any one of claims 5 to 7, characterized in that: The sintering atmosphere includes at least one of air or oxygen, and the flow rate of the air or oxygen is 0.5 to 1.5 L / min; and / or, The sintering temperature is 450° C. to 800° C., and the sintering time is 12 h to 24 h; and / or, After obtaining the mixed material and before sintering the mixed material, the method further includes a step of ball milling the mixed material.

9. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the flame-retardant composite positive electrode material according to any one of claims 1 to 4 or the flame-retardant composite positive electrode material prepared by the preparation method according to any one of claims 5 to 8.

10. A battery, characterized in that: The battery comprises the flame-retardant composite positive electrode material according to any one of claims 1 to 3, or comprises the flame-retardant composite positive electrode material prepared according to the preparation method according to any one of claims 4 to 8, or comprises the positive electrode sheet according to claim 9.

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