Positive electrode active material and preparation method therefor, battery, and electric device

Abstract

A positive electrode active material and a preparation method therefor, a battery, and an electric device. The positive electrode active material comprises a phosphate particle and a coating layer, wherein the coating layer is disposed on at least part of the surface of the phosphate particle, and the coating layer comprises a carbon skeleton structure and a phosphorus-containing group connected to the carbon skeleton structure. The positive electrode active material can improve the cycle performance of a battery.

Description

Positive electrode active material and preparation method thereof, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application 202311579767.X, filed on November 24, 2023, entitled “Positive electrode active material, preparation method thereof, battery and electrical device,” and the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to a positive electrode active material and a preparation method thereof, a battery and an electrical device. Background Art

[0004] Batteries, with their high capacity and long lifespan, are widely used in electronic devices such as mobile phones, laptops, electric bicycles, electric cars, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy planes, and power tools. Due to the significant progress in the battery field, higher performance requirements are being placed on them. As a key component of batteries, the positive electrode active material has a significant impact on battery performance.

[0005] However, current positive electrode active materials have poor cycle performance when used in batteries.

[0006] Summary of the Invention

[0007] The present application provides a positive electrode active material and a preparation method thereof, a battery and an electrical device, which can improve the cycle performance of the battery.

[0008] In a first aspect, an embodiment of the present application proposes a positive electrode active material, which includes phosphate particles and a coating layer, wherein the coating layer is arranged on at least a portion of the surface of the phosphate particles, and the coating layer includes a carbon skeleton structure and a phosphorus-containing group connected to the carbon skeleton structure.

[0009] Therefore, in the embodiments of the present application, the positive electrode active material includes phosphate particles and a coating layer. The coating layer has a carbon skeleton structure as its main structure, which can provide good coating and protection for the phosphate particles. Since the carbon skeleton structure contains carbon element, it has excellent electronic conductivity, which is beneficial to improving the overall conductivity of the positive electrode active material and helping to maximize the capacity of the phosphate particles. The coating layer also includes phosphorus-containing groups, which can reduce the content of oxygen-containing groups in the carbon skeleton structure, modify the coating layer as a whole, weaken the catalytic activity of the coating layer as a whole, reduce side reactions between the coating layer and the electrolyte, and improve the cycle performance of the battery cell.

[0010] In some embodiments, the coating layer further includes oxygen-containing groups, which are connected to the carbon skeleton structure; based on the total mass of the coating layer, the mass content of oxygen elements in the oxygen-containing groups is ≤3.5%; optionally, the mass content of oxygen elements in the oxygen-containing groups is ≤3.0%.

[0011] Therefore, when the mass content of oxygen-containing groups in the embodiment of the present application meets the above range, the catalytic activity of the coating layer is low, which can alleviate the side reactions between the coating layer and the electrolyte, and is beneficial to further improve the conductivity and specific capacity of the positive electrode active material, and can further improve the expansion rate and cycle performance of the battery cell.

[0012] In some embodiments, the oxygen-containing group includes at least one of a hydroxyl group, a carbonyl group, a carboxyl group, an ester group, and a quinone group; optionally, the oxygen-containing group includes a hydroxyl group.

[0013] In some embodiments, the mass content of phosphorus in the phosphorus-containing groups is 0.5% to 5.5% based on the total mass of the coating layer. When the mass content of the phosphorus-containing groups is within this range, the carbon-continuous six-membered ring structure is substantially not damaged, the overall conductivity of the coating layer is improved, and the specific capacity of the phosphate particles is effectively utilized.

[0014] In some embodiments, the phosphorus-containing group includes at least one of a phosphate group and a pyrophosphate group. When the phosphorus-containing group is the above group, it can effectively reduce the content of oxygen groups.

[0015] In some embodiments, the mass content of the carbon skeleton structure is greater than 0 and less than or equal to 6%, and can be optionally 2% to 5%, based on the total mass of the positive electrode active material. When the mass content of the carbon skeleton structure is within the above range, it can form a good coating effect on the phosphate particles, effectively reducing the risk of side reactions caused by direct contact between the phosphate particles and the electrolyte, reducing the risk of transition metal ion dissolution, and facilitating the improvement of the cycle performance and storage performance of the positive electrode active material. Moreover, when the mass content of the carbon skeleton structure is within the above range, it can effectively improve the overall conductivity of the positive electrode active material, which is conducive to the utilization of the specific capacity of the phosphate particles.

[0016] In some embodiments, the phosphate particles include a molecular formula of Li 1+x Mn 1-y A y P 1-z R z Y wCompound, -0.1≤x≤0.9, 0<y<1, 0≤z≤0.5, 1.8≤w≤4; A includes at least one of Fe, Co, Ni, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; R includes at least one of S, Si, Cl, B, C, and N; Y includes at least one of O and F; optionally, 0<y<0.5. The surface of the phosphate particles is provided with a coating layer, which can effectively modify the phosphate particles to improve their conductivity and specific capacity.

[0017] In some embodiments, the initial gram capacity of the positive electrode active material is 130 mAh / g to 165 mAh / g. The initial gram capacity of the positive electrode active material is relatively high, and the gram capacity utilization is improved.

[0018] In some embodiments, the powder resistivity of the positive electrode active material is ≤500Ω*cm; optionally, ≤390Ω*cm. When the powder resistivity of the positive electrode active material is within the above range, the powder resistivity is relatively low, which helps improve the overall electronic conductivity of the positive electrode active material and facilitates the utilization of the specific capacity of the positive electrode active material.

[0019] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode active material, the method comprising:

[0020] providing an organic carbon source having oxygen-containing groups to the phosphate particles;

[0021] Carbonizing the organic carbon source to form a carbon layer on at least a portion of the surface of the phosphate particles to obtain an intermediate;

[0022] The intermediate and the organic phosphorus source are mixed, and at least part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate phosphorus-containing groups, thereby obtaining a positive electrode active material.

[0023] In some embodiments, the step of mixing the intermediate and the organic phosphorus source, and reacting at least a portion of the oxygen-containing groups in the carbon layer with the organic phosphorus source to form phosphorus-containing groups to obtain the positive electrode active material comprises:

[0024] The intermediate and the organic phosphorus source are mixed, and subjected to heat treatment so that at least part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate phosphorus-containing groups, thereby obtaining a positive electrode active material.

[0025] In some embodiments, the organic phosphorus source includes at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, tetraethyl pyrophosphate, and tetrabenzyl pyrophosphate.

[0026] In some embodiments, the organic carbon source includes at least one of a carbohydrate compound, an olefin polymer, polyvinyl alcohol, polyethylene glycol, citric acid, and toluene; alternatively, the organic carbon source includes at least one of an olefin polymer and toluene.

[0027] In a third aspect, an embodiment of the present application proposes a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one side of the positive electrode collector, and the positive electrode film layer includes a positive electrode active material as in any embodiment of the first aspect of the present application, or a positive electrode active material prepared by the method of any embodiment of the second aspect of the present application.

[0028] In a fourth aspect, the present application further proposes a battery, comprising a positive electrode plate according to any embodiment of the third aspect of the present application.

[0029] In a fifth aspect, the present application further proposes an electrical device, which includes a battery as in any embodiment of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0031] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0032] FIG. 2 is an exploded schematic diagram of an embodiment of the battery cell of FIG. 1 .

[0033] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0034] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0035] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0036] FIG6 is a schematic diagram of an embodiment of an electric device including the battery cell of the present application as a power source.

[0037] The drawings are not necessarily drawn to scale.

[0038] The following are the descriptions of the reference numerals:

[0039] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0040] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0041] 53. Cover plate;

[0042] 6. Electrical equipment. DETAILED DESCRIPTION

[0043] Below, the embodiments of the positive electrode active material and its preparation method, battery and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0044] " Range " disclosed in this application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may 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.

[0048] Phosphates have a high theoretical specific capacity, which is beneficial for improving the energy density of battery cells. However, due to the poor electronic conductivity of phosphates, it is difficult to fully utilize their capacity, which limits their application. In related technologies, in order to improve the capacity of phosphates, phosphates are usually coated and modified, such as using a carbon coating. However, further research has found that phosphates containing carbon coatings and electrolytes may still cause serious side reactions, resulting in the phosphate capacity not being fully utilized, and the battery cells may be at risk of swelling, and the cycle performance of the battery cells may be deteriorated.

[0049] In view of the above problems, the embodiment of the present application proposes a positive electrode active material, which includes phosphate particles and a coating layer. The coating layer has a carbon skeleton structure as the main structure, and the coating layer also includes phosphorus-containing groups. The phosphorus-containing groups can reduce the content of oxygen-containing groups in the carbon skeleton structure, modify the coating layer as a whole, weaken the overall catalytic activity of the coating layer, reduce the side reactions between the coating layer and the electrolyte, and improve the cycle performance of the battery cell.

[0050] Next, the technical solutions of the implementation methods of this application are described in detail.

[0051] positive electrode active material

[0052] In a first aspect, an embodiment of the present application provides a positive electrode active material.

[0053] The positive electrode active material includes phosphate particles and a coating layer, wherein the coating layer is arranged on at least a portion of the surface of the phosphate particles and includes a carbon skeleton structure and a phosphorus-containing group connected to the carbon skeleton structure.

[0054] The carbon skeleton structure, as the main material of the coating layer, can provide good coating and protection for the phosphate particles. Since the carbon skeleton structure contains carbon element, it has excellent electronic conductivity, which is beneficial to improving the overall conductivity of the positive electrode active material and helps to maximize the capacity of the phosphate particles.

[0055] Since the carbon skeleton structure is usually formed by sintering an organic carbon source, which may contain oxygen-containing groups, the oxygen-containing groups may still remain in the carbon skeleton structure during the sintering process of the organic carbon source. The oxygen-containing groups have high reactivity. When the positive electrode active material is applied to the battery cell, the oxygen-containing groups are in contact with the electrolyte and easily catalyze the decomposition of the electrolyte, resulting in gas production, which may cause the battery cell to swell, affecting the reliability of the battery cell. The decomposed electrolyte easily consumes a large amount of active lithium ions, and the SEI (Solid Electrolyte Interphase) film formed on the surface of the negative electrode plate causes the battery cell capacity to decay too quickly. In addition, the decomposed electrolyte may produce hydrofluoric acid HF, which can further dissolve the positive electrode active material, resulting in the dissolution of transition metal ions such as manganese ions, and deteriorate the cycle performance of the battery cell.

[0056] The coating layer also contains phosphorus-containing groups, which are mainly dispersed in the carbon skeleton structure and connected to the carbon atoms of the carbon skeleton structure in the form of chemical bonds. The presence of phosphorus-containing groups can reduce the content of oxygen-containing groups in the carbon skeleton structure, reduce the adverse effects of oxygen-containing groups, reduce the expansion rate of the battery cell, and improve the cycle performance of the battery cell; and the phosphorus-containing groups can play a doping role, which can further enhance the conductivity of the positive electrode active material, which is conducive to further enhancing the capacity of the phosphate particles.

[0057] The carbon skeleton structure mainly exists in the form of a carbon element, for example, in the form of a continuous six-membered ring structure; the oxygen-containing groups can be connected to the carbon atoms in the carbon skeleton structure in the form of chemical bonds. The higher the content of the oxygen-containing groups, the higher the catalytic activity of the coating layer; and the higher the content of the oxygen-containing groups, the more likely it is to destroy the continuous six-membered ring structure of carbon, reduce the conductivity of the carbon coating layer, and the higher the degree of deterioration of the performance of the positive electrode active material; the lower the content of the oxygen-containing groups, the more conducive it is to improving the electrochemical performance of the positive electrode active material in gas production, circulation, storage, etc. in the battery cell. Optionally, based on the total mass of the coating layer, the mass content of the oxygen-containing groups is less than 3%; when the mass content of the oxygen-containing groups meets the above range, the catalytic activity of the coating layer is low, the side reaction of the coating layer and the electrolyte can be alleviated, and it is conducive to further improving the conductivity and specific capacity of the positive electrode active material, and can further improve the expansion rate and cycle performance of the battery cell.

[0058] For example, the coating layer further includes oxygen-containing groups, which are connected to the carbon skeleton structure. Of course, the coating layer can also be free of oxygen-containing groups. In the case where the coating layer includes phosphorus-containing groups, the conductivity of the positive electrode active material can also be improved, which is conducive to further improving the capacity of the phosphate particles.

[0059] Optionally, based on the total mass of the coating layer, the mass content of oxygen in the oxygen-containing groups is ≤3.5%; alternatively, the mass content of oxygen in the oxygen-containing groups is ≤3.0%. For example, the mass content of oxygen in the oxygen-containing groups can be 0%, 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.91%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 2.99%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, or a range consisting of any two of the above values. A mass content of oxygen element in the oxygen-containing groups of 0% means that there are substantially no oxygen-containing groups in the coating layer.

[0060] In some embodiments, the oxygen-containing group may include at least one of a hydroxyl group, a carbonyl group, a carboxyl group, an ester group, and a quinone group; alternatively, the oxygen-containing group may include a hydroxyl group.

[0061] In the embodiment of the present application, the mass content of the oxygen element in the oxygen-containing groups in the coating layer is a meaning well known in the art, and can be detected using equipment and methods well known in the art. For example, 1g of positive electrode active material is taken as a sample, stirred with 1000mL of 0.1mol / L hydrochloric acid to fully react, and the reacted liquid is centrifuged. It is washed with deionized water 20 times, and then washed 5 times with anhydrous ethanol, and finally dried to obtain a coating layer. The coating layer is dispersed in a 0.01mol / L NaOH solution to allow the oxygen-containing groups on the coating layer to fully react with the NaOH solution. It is then titrated with a 0.01mol / L HCl hydrochloric acid solution to obtain the remaining amount of NaOH. The amount of substance of the oxygen element in the oxygen-containing group is calculated based on the consumption of NaOH, and then the mass quality is calculated.

[0062] During the preparation of positive electrode active materials, the organic phosphorus source can release oxygen atoms from oxygen-containing groups. For example, it can release oxygen atoms by capturing hydrogen atoms from oxygen-containing groups. Part of the product can evaporate in the form of gas, and the other part forms phosphorus-containing groups, thereby reducing the mass content of oxygen-containing groups in the carbon skeleton structure.

[0063] The presence of phosphorus-containing groups helps improve the overall conductivity of the coating layer and helps maximize the gram capacity of the phosphate particles. Optionally, the mass content of phosphorus in the phosphorus-containing groups can be 0.5% to 5.5%, or optionally 1% to 5.0%, based on the total mass of the coating layer. Within these ranges, the phosphorus content of the phosphorus-containing groups substantially does not damage the carbon-continuous six-membered ring structure, improving the overall conductivity of the coating layer and facilitating the utilization of the gram capacity of the phosphate particles.

[0064] For example, the mass content of phosphorus in the phosphorus-containing group can be 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.91%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5% or a range consisting of any two of the above values.

[0065] In some embodiments, the phosphorus-containing group includes at least one of a phosphate group and a pyrophosphate group. When the phosphorus-containing group is the above group, it can effectively reduce the content of oxygen groups.

[0066] In the embodiment of the present application, the mass content of the phosphorus-containing group in the coating layer has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, 1g of the positive electrode active material is taken as a sample, stirred with 1000mL of 0.1mol / L hydrochloric acid to fully react, and the liquid after the reaction is centrifuged. The sample is washed with deionized water 20 times, then washed 5 times with anhydrous ethanol, and finally dried to obtain a coating layer. The mass content of phosphorus in the coating layer is tested by inductively coupled plasma emission spectroscopy (ICP) using Agilent ICP-OES730.

[0067] In some embodiments, the mass content of the carbon skeleton structure is greater than 0 and less than or equal to 6%, and can be optionally 2% to 5%, based on the total mass of the positive electrode active material. When the mass content of the carbon skeleton structure is within the above range, it can form a good coating effect on the phosphate particles, effectively reducing the risk of side reactions caused by direct contact between the phosphate particles and the electrolyte, reducing the risk of transition metal ion dissolution, and facilitating the improvement of the cycle performance and storage performance of the positive electrode active material. Moreover, when the mass content of the carbon skeleton structure is within the above range, it can effectively improve the overall conductivity of the positive electrode active material, which is conducive to the utilization of the specific capacity of the phosphate particles.

[0068] For example, the mass content of the carbon skeleton structure can be 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 0.98%, 1%, 1.1% , 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.91, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6% or a range consisting of any two of the above values.

[0069] In the embodiments of the present application, the mass content of the carbon skeleton structure has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, an elemental analyzer (EA) is used to test the mass of the carbon skeleton structure, and the mass of the C element in the test results of the elemental analyzer is used as the mass of the carbon skeleton structure, thereby calculating its mass content.

[0070] In some embodiments, the phosphate particles include a molecular formula of Li 1+x Mn 1-y A y P 1-z R z Y wCompound, -0.1≤x≤0.9, 0<y<1, 0≤z≤0.5, 1.8≤w≤4; A includes at least one of Fe, Co, Ni, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; R includes at least one of S, Si, Cl, B, C, and N; Y includes at least one of O and F. The surface of the phosphate particles is provided with a coating layer, which can effectively modify the phosphate particles and improve their conductivity and specific capacity.

[0071] For example, x can be -0.1, -0.05, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, or a range consisting of any two of the above values.

[0072] For example, y can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90 or a range consisting of any two of the above values. Optionally, 0<y<0.5. The Mn content is relatively high. During the charge and discharge process of the battery cell, the time at high voltage accounts for a high proportion. The catalytic effect of the oxygen-containing groups on the electrolyte is more obvious, which is more likely to cause the deterioration of the battery cell performance. However, in the embodiment of the present application, due to the addition of phosphorus-containing groups, the content of oxygen-containing groups can be effectively reduced, thereby effectively improving the electrochemical properties of the above-mentioned positive electrode active material, thereby improving the cycle performance and storage performance of the battery cell.

[0073] Illustratively, z can be 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, or a range consisting of any two of the above values.

[0074] Illustratively, w can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, or a range consisting of any two of the above values.

[0075] Illustratively, the phosphate particles include Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 、Li 0.994 Mn 0.5 Fe 0.5 Mo 0.001 P 0.999 Si 0.001 O3.999 F 0.001 、Li 0.994 Mn 0.4 Fe 0.6 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 、Li 0.994 Mn 0.60 Fe 0.4 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 、Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 PO 3.999 F 0.001 At least one of .

[0076] During the charge and discharge process, battery cells are accompanied by the deintercalation and deintercalation of active ions, such as Li, and their molar content varies when the battery cells are discharged to different states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the material's initial state, i.e., the state before the materials are added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0077] In the examples of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate.

[0078] In some embodiments, the initial gram capacity of the positive electrode active material is 130 mAh / g to 165 mAh / g. The initial gram capacity of the positive electrode active material is relatively high, and the gram capacity utilization is improved.

[0079] Illustratively, the initial gram capacity of the positive electrode active material can be 130 mAh / g, 132 mAh / g, 135 mAh / g, 138 mAh / g, 140 mAh / g, 142 mAh / g, 145 mAh / g, 148 mAh / g, 150 mAh / g, 152 mAh / g, 155 mAh / g, 158 mAh / g, 160 mAh / g, 162 mAh / g, 165 mAh / g, or a range consisting of any two of the above values.

[0080] In the embodiment of the present application, the initial gram capacity of the positive electrode active material is detected by forming a button battery with a positive electrode sheet containing the positive electrode active material and a lithium metal sheet. Under a constant temperature environment of 25°C, the button battery is charged to 4.3V at 0.1C, then charged at a constant voltage at 4.3V to a current of less than or equal to 0.05mA, allowed to stand for 5 minutes, and then discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial gram capacity, recorded as D0. The electrolyte includes an organic solvent, a lithium salt and an additive. The organic solvent includes ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt includes 1 mol / L LiPF6.

[0081] In some embodiments, the powder resistivity of the positive electrode active material is greater than 0 and less than or equal to 500 Ω*cm; optionally, ≤390 Ω*cm. When the powder resistivity of the positive electrode active material is within the above range, the powder resistivity is relatively low, which helps improve the overall electronic conductivity of the positive electrode active material and facilitates the utilization of the specific capacity of the positive electrode active material.

[0082] Illustratively, the powder resistivity of the positive electrode active material may be 10Ω*cm, 50Ω*cm, 100Ω*cm, 150Ω*cm, 200Ω*cm, 250Ω*cm, 300Ω*cm, 350Ω*cm, 400Ω*cm, 450Ω*cm, 500Ω*cm, or a range consisting of any two of the foregoing values.

[0083] In the embodiments of the present application, the powder resistivity of the positive electrode active material at a pressure of 8 MPa is well known in the art and can be measured using methods known in the art. For example, a PRCD1100 powder resistivity meter can be used for testing, and the national standard GB / T30835-2014 can be used for testing.

[0084] Method for preparing positive electrode active material

[0085] In a second aspect, the present application also provides a method for preparing a positive electrode active material. The positive electrode active material of any embodiment of the first aspect of the present application can be prepared by this method. Of course, the positive electrode active material can also be prepared by commonly used methods in the art.

[0086] Methods include:

[0087] Step S100, providing an organic carbon source having oxygen-containing groups to phosphate particles;

[0088] Step S200, carbonizing the organic carbon source to form a carbon layer on at least a portion of the surface of the phosphate particles to obtain an intermediate;

[0089] In step S300 , the intermediate and the organic phosphorus source are mixed, and at least part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate phosphorus-containing groups, thereby obtaining a positive electrode active material.

[0090] According to the method implemented in the embodiment of the present application, the organic carbon source can form a carbon layer after carbonization treatment and cover the surface of the phosphate particles to form an intermediate; some oxygen-containing groups in the organic carbon source may still remain in the carbon layer, and the intermediate and the organic phosphorus source are further mixed. The organic phosphorus source can chemically react with at least part of the oxygen-containing groups to reduce the content of the oxygen-containing groups and weaken the adverse effects of the oxygen-containing groups; the reaction products may evaporate in a gaseous state, or some non-volatile substances such as phosphorus-containing groups may remain. The phosphorus-containing groups can play a doping role, which can further improve the conductivity of the positive electrode active material, which is beneficial to further improve the capacity of the phosphate particles.

[0091] [Step S100]

[0092] The organic carbon source may be in the form of solid particles, which may be dissolved in a solvent, and then the organic carbon source dissolved in the solvent is mixed with the phosphate particles. The solvent may be deionized water, for example.

[0093] The phosphate particles are polyanionic compounds, which may include manganese phosphate, and further include a molecular formula of Li 1+x Mn 1-y A y P 1-z R z Y w The compound, phosphate particles can be commercially obtained or synthesized according to the following method.

[0094] In some embodiments, a method for preparing phosphate particles comprises:

[0095] Step S110, dissolving the manganese source and the A source in a solvent, and drying the mixture to obtain a metal precursor;

[0096] Step S120, adding a metal precursor, a lithium source, a phosphorus source, and an R source into a solvent, grinding and mixing, and then spray drying to obtain a phosphate precursor;

[0097] Step S130 , sintering the phosphate precursor to form phosphate particles.

[0098] In step S110,

[0099] In some embodiments, the manganese source may be a manganese-containing substance known in the art that can be used to prepare phosphate. For example, the manganese source may include at least one of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0100] In some embodiments, the source of A may include at least one of oxalate, phosphate, acetate, sulfate, citrate, and nitrate.

[0101] In some embodiments, the solvent may include at least one of deionized water and alcohols.

[0102] In step S120,

[0103] In some embodiments, the lithium source may include at least one of lithium carbonate, lithium acetate, lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, lithium oxalate, lithium phosphate, lithium hydrogen phosphate, lithium citrate, lithium silicate, and lithium metaborate.

[0104] In some embodiments, the phosphorus source may include at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0105] In some embodiments, the R source may include at least one of an R-containing acid, an R-containing oxide, and an R-containing organic compound. For example, the silicon source may include at least one of silicic acid, metasilicic acid, silicon tetrachloride, silicon dioxide, and tetraethyl orthosilicate. For example, the boron source may include at least one of boric acid, ammonium borate, and boron oxide.

[0106] In some embodiments, the solvent may include at least one of deionized water and alcohols.

[0107] In some embodiments, the grinding can be performed using a sand mill, for example, grinding and stirring in a sand mill for 8 to 10 hours.

[0108] In some embodiments, the spray drying granulation process can be carried out at 230° C. to 270° C. for 3.5 h to 5 h.

[0109] In step S130,

[0110] The sintering process may be performed in an inert atmosphere, and the inert atmosphere may be at least one of nitrogen and argon.

[0111] The sintering temperature may be 650° C. to 750° C., and the sintering time may be 8 h to 12 h.

[0112] The stoichiometric ratio of each substance in the above steps can be set according to the chemical formula of the desired phosphate particles. The content of each element in the material can be detected by inductively coupled plasma emission spectroscopy (ICP).

[0113] In some embodiments, the organic carbon source may include at least one of a carbohydrate compound, an olefin polymer, polyvinyl alcohol, polyethylene glycol, citric acid, and toluene.

[0114] Illustratively, the carbohydrate compound may include at least one of starch, sucrose, and glucose.

[0115] For example, the olefin polymer may include at least one of polyethylene and polytetrafluoroethylene.

[0116] The above substances can be selected from olefin polymers such as polyethylene, polytetrafluoroethylene, toluene and other organic carbon sources. The hydroxyl content of the above substances is relatively small, or even contains no hydroxyl groups. The amount of residual hydroxyl groups after carbonization is relatively small, which is beneficial to improving the electrochemical performance of the positive electrode active material.

[0117] [Step S200]

[0118] In step S100, during the process of providing the organic carbon source to the phosphate particles, the organic carbon source and the phosphate particles are mixed. Since the organic carbon source is dissolved in the solvent to form a liquid phase, it can flow and coat the surface of the phosphate particles. After the organic carbon source and the phosphate particles are mixed for 4 to 6 hours, the system is carbonized. The carbonization process is as follows: the system can be pre-heat-treated and dried at 120°C to 200°C for 4 to 6 hours to remove the solvent; then sintered at 650°C to 750°C for 8 to 12 hours, and the organic carbon source is carbonized into a carbon layer, which coats at least part of the surface of the phosphate particles.

[0119] [Step S300]

[0120] The organophosphorus source and the intermediate are mixed, and the organophosphorus source and the intermediate can be heat-treated to react with at least a portion of the oxygen-containing groups in the organophosphoric acid and the intermediate.

[0121] When the heat treatment temperature does not exceed the boiling point of the organic phosphorus source, the organic phosphorus source may exist in a liquid phase, and the liquid organic phosphorus source can react with at least part of the oxygen-containing groups in the carbon layer to reduce the content of oxygen-containing groups; the liquid organic phosphorus source has good fluidity, which is conducive to further reducing the content of oxygen-containing groups; after the reaction is completed, the oxygen-containing groups in the carbon layer are reduced, and the phosphorus-containing groups generated by the organic phosphoric acid remain in the carbon layer and are connected to the carbon atoms in the carbon layer. In this case, the carbon layer after the reaction is completed is equivalent to the coating layer mentioned above.

[0122] When the heat treatment temperature exceeds the boiling point of the organic phosphorus source, the organic phosphorus source may exist in the gas phase, and the gas phase organic phosphorus source can react with at least part of the oxygen-containing groups in the carbon layer to reduce the content of oxygen-containing groups; the contact between the gas phase organic phosphorus source and the intermediate is more sufficient, which is more conducive to further reducing the content of oxygen-containing groups; after the reaction is completed, the oxygen-containing groups in the carbon layer are reduced, and the phosphorus-containing groups generated by the organic phosphoric acid remain in the carbon layer and are connected to the carbon atoms in the carbon layer. In this case, the carbon layer after the reaction is completed is equivalent to the coating layer mentioned above.

[0123] In order to increase the reaction rate, the temperature of the system can be increased, for example, to a temperature greater than or equal to the boiling point of the organic phosphorus source, so that the organic phosphorus source is gaseous. The contact area between the gaseous organic phosphorus source and the carbon layer increases, which can effectively increase the reaction rate.

[0124] In some embodiments, the organic phosphorus source may include at least one of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

[0125] In some embodiments, the organic phosphorus source may include at least one of tetraethyl pyrophosphate and tetrabenzyl pyrophosphate.

[0126] Taking trimethyl phosphate as the organic phosphorus source and hydroxyl as the oxygen-containing group as an example, the reaction process is explained:

[0127] -OH+(CH3O)3PO→CH3OH+O(CH3O)2PO,

[0128] -OH+O(CH3O)3PO→CH3OH+O2(CH3O)PO,

[0129] -OH+O2(CH3O)2PO→CH3OH+PO4 3- .

[0130] Trimethyl phosphate can capture hydrogen from hydroxyl groups, and part of the products such as CH3OH evaporate in the form of gas, while the non-volatile phosphorus oxide remains on the surface of the coating layer.

[0131] Positive electrode

[0132] In a third aspect, an embodiment of the present application proposes a positive electrode plate.

[0133] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0134] The positive electrode active material may include the positive electrode active material of any embodiment of the first aspect of the present application, or the positive electrode active material obtained by the method of any embodiment of the second aspect of the present application. Since the positive electrode active material has good conductivity, its capacity utilization is improved, which is beneficial to improving the electrochemical performance of the positive electrode plate; in addition, since the side reaction between the positive electrode active material and the electrolyte is alleviated, when the positive electrode plate is applied to the battery cell, it can reduce the expansion rate of the battery cell and improve the cycle performance of the battery cell.

[0135] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present embodiments do not particularly limit the type of the positive electrode conductive agent. By way of example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent based on the total mass of the positive electrode film layer is ≤5%.

[0136] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and at least one of fluorine-containing acrylic resins. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode binder is ≤5%.

[0137] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0138] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0139] battery cells

[0140] In the fourth aspect, the embodiments of the present application also propose a battery cell, which includes a positive electrode plate as in any embodiment of the third aspect of the present application. Since the positive electrode active material in the positive electrode plate has good conductivity, its capacity is improved and the electrochemical performance of the positive electrode plate is improved; in addition, since the side reaction between the positive electrode active material and the electrolyte is alleviated, when the positive electrode plate is applied to the battery cell, the expansion rate of the battery cell can be reduced and the cycle performance of the battery cell can be improved.

[0141] [Negative electrode]

[0142] In some embodiments, the battery cell further includes a negative electrode plate.

[0143] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0144] The negative electrode active material can be any negative electrode active material known in the art for use in battery cells. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloys.

[0145] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present embodiments do not particularly limit the type of negative electrode conductive agent. For example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent based on the total weight of the negative electrode film layer is ≤5%.

[0146] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application embodiment does not particularly limit the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), a water-soluble unsaturated resin SR-1B, a water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5 wt% based on the total weight of the negative electrode film layer.

[0147] In some embodiments, the negative electrode film layer may optionally include other additives. For example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like. In some embodiments, the weight percentage of the other additives is ≤ 2% based on the total weight of the negative electrode film layer.

[0148] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0149] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0150] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0151] [Electrolyte]

[0152] In some embodiments, the battery cell further includes an electrolyte.

[0153] During the charge and discharge process of a battery cell, active ions are embedded and released back and forth between the positive and negative electrodes, and the electrolyte conducts the active ions between the positive and negative electrodes. The present application embodiment does not specifically limit the type of electrolyte, and the electrolyte can be selected based on actual needs.

[0154] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0155] As an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0156] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0157] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0158] [Isolation film]

[0159] The battery cell also includes a separator.

[0160] In some embodiments, the battery cell further includes a separator. The embodiments of the present application have no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0161] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0162] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0163] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0164] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0165] The present invention has no particular restrictions on the shape of the battery cell, which can be cylindrical, square, or any other shape. FIG1 shows a battery cell 5 with a square structure as an example.

[0166] In some embodiments, as shown in FIG2 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may 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 shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be adjusted according to demand.

[0167] The preparation methods of the battery cells of the embodiments of the present application are well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound and / or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The battery cell is then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell.

[0168] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0169] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in Figure 3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0170] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0171] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0172] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0173] Electrical devices

[0174] A fifth aspect of the embodiments of the present application provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs of the embodiments of the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop 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, a satellite, an energy storage system, etc.

[0175] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0176] FIG6 is a schematic diagram of an exemplary electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device 6, a battery pack or battery module may be used.

[0177] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0178] Example

[0179] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0180] Example 1

[0181] 1. Preparation of positive electrode sheet

[0182] The positive electrode sheet includes a positive electrode current collector aluminum foil and a positive electrode film layer. The positive electrode film layer includes a film layer formed by uniformly coating the positive electrode slurry (the solvent is N-methylpyrrolidone NMP) on the surface of the positive electrode current collector aluminum foil, drying, and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF), and acetylene black in a weight ratio of 90:5:5.

[0183] The positive electrode active material includes phosphate particles and a coating layer, wherein the phosphate particles include a molecular formula of Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 The preparation process of the positive electrode active material is as follows:

[0184] 74.6 g of sucrose was dissolved in 500 ml of deionized water, and then stirred and fully dissolved to obtain a coating solution. The above-mentioned phosphate particles were added to the coating solution, stirred and mixed for 6 hours. After mixing evenly, the mixture was transferred to a 150°C oven and dried for 6 hours, and then sintered at 700°C for 10 hours to obtain an intermediate.

[0185] 100 g of the intermediate was placed in a sealed reaction chamber, trimethyl phosphate gas was introduced under vacuum conditions at 200° C., and the reaction was carried out for 0.5 h to obtain the final positive electrode active material.

[0186] 2. Preparation of negative electrode sheet

[0187] The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode film layer. The negative electrode film layer includes a film layer formed by evenly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode current collector copper foil, drying, and cold pressing. The negative electrode film layer includes a negative electrode active material, a conductive agent acetylene black, a binder styrene-butadiene rubber (SBR), and a thickener sodium carboxymethyl cellulose (CMC-Na) in a weight ratio of 95:2:2:1.

[0188] The negative electrode active material includes artificial graphite and hard carbon (mass ratio is 90:5).

[0189] 3. Isolation film

[0190] The isolation film is a polyethylene film.

[0191] 4. Preparation of electrolyte

[0192] The electrolyte includes an organic solvent, a lithium salt and an additive. The organic solvent includes ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the lithium salt includes 1 mol / L LiPF6.

[0193] 5. Preparation of batteries

[0194] The lithium-ion battery includes an outer packaging shell, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are arranged in the outer packaging shell. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The electrode assembly is a wound electrode assembly, and the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0195] Comparative Example 1

[0196] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the positive electrode was prepared using the following steps:

[0197] The positive electrode sheet includes a positive electrode current collector aluminum foil and a positive electrode film layer. The positive electrode film layer includes a film layer formed by uniformly coating the positive electrode slurry (the solvent is N-methylpyrrolidone NMP) on the surface of the positive electrode current collector aluminum foil, drying, and cold pressing. The positive electrode film layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF), and acetylene black in a weight ratio of 90:5:5.

[0198] The positive electrode active material includes phosphate particles and a coating layer, wherein the phosphate particles include a molecular formula of Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 The preparation process of the positive electrode active material is as follows:

[0199] Dissolve 74.6 g of sucrose in 500 ml of deionized water, then stir and fully dissolve to obtain a coating solution. Add the above-mentioned phosphate particles to the coating solution, stir and mix together for 6 hours. After mixing evenly, transfer to a 150°C oven to dry for 6 hours, and then sinter at 700°C for 10 hours to obtain a positive electrode active material.

[0200] Example 2-1 to Example 2-4

[0201] A lithium ion battery was prepared using a method similar to that of Example 1, except that the content of the organic carbon source was adjusted.

[0202] Example 3-1 and Example 3-2

[0203] A lithium-ion battery was prepared using a method similar to that of Example 1, except that the type of organic carbon source was adjusted.

[0204] Example 4-1 to Example 4-3

[0205] A lithium ion battery was prepared using a method similar to that of Example 1, except that the content of the organic phosphorus source was adjusted.

[0206] Example 5-1 and Example 5-2

[0207] A lithium-ion battery was prepared using a method similar to that of Example 1, except that the type of the organic phosphorus source was adjusted.

[0208] Example 6-1 and Example 6-2

[0209] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the type of material of the positive electrode active material was adjusted.

[0210] Performance Testing

[0211] 1. Preparation of button batteries

[0212] The positive electrode sheet in Example 1 is used as the positive electrode sheet of the button battery;

[0213] A lithium sheet was used as the negative electrode, and the electrolyte included 1 mol / L LiPF6 and an organic solvent, wherein the organic solvent included ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1.

[0214] It is assembled into a button battery in a button box with the negative electrode sheet, positive electrode sheet and electrolyte.

[0215] 2. Measurement method of initial gram capacity of button battery

[0216] At a constant temperature of 25°C, charge the button battery to 4.3V at 0.1C, then charge it at a constant voltage at 4.3V until the current is less than or equal to 0.05mA, let it stand for 5 minutes, and then discharge it to 2.0V at 0.1C. The discharge capacity at this time is the initial gram capacity, recorded as D0.

[0217] 3. Cycling performance test of lithium-ion batteries at 45°C

[0218] At a constant temperature of 45°C, charge the lithium-ion battery at 1C to 4.3V. Then, charge it at a constant voltage at 4.3V until the current is less than or equal to 0.05mA. Let it rest for 5 minutes, then discharge it at 1C to 2.5V. Record the discharge capacity at this point as E0. Repeat the charge and discharge cycle until the discharge capacity drops to 80% of E0. Record the number of cycles the lithium-ion battery has completed.

[0219] 4. Measurement method of Mn (and Mn-doped Fe) dissolution after lithium-ion battery cycling

[0220] At 45° C., the lithium-ion battery, after being cycled until its capacity decayed to 80%, was discharged at a rate of 0.1 C to a cut-off voltage of 2.0 V.

[0221] Then disassemble the lithium-ion battery, take out the negative electrode sheet, and randomly select 30 unit areas (1540.25mm 2 ) discs were measured by inductively coupled plasma emission spectroscopy (ICP) using an Agilent ICP-OES730. The amounts of Fe (if Fe is doped at the Mn site of the cathode active material) and Mn were calculated based on the ICP results, thereby estimating the amount of Mn (and Fe doped at the Mn site) released after cycling. This testing was conducted in accordance with EPA-6010D-2014.

[0222] 5. Lithium-ion battery flatulence test at 60°C

[0223] Lithium-ion batteries with 100% state of charge (SOC) were stored at 60°C as test samples. The open circuit voltage (OCV) and AC internal resistance (IMP) of the lithium-ion batteries were measured before, during and after storage to monitor the SOC, and the volume of the lithium-ion batteries was measured.

[0224] After every 48 hours of storage, remove the lithium-ion battery, let it stand for 1 hour, test the open circuit voltage (OCV) and internal resistance (IMP), and measure the battery volume using the water displacement method after cooling to room temperature. The water displacement method is to first use a balance that automatically converts the dial data to measure the gravity F1 of the battery alone, and then completely place the lithium-ion battery in deionized water (density is known to be 1g / cm 3 ), measure the gravity F2 of the battery at this time, and the buoyancy F 浮 That is F1-F2, and then according to Archimedes principle F 浮 =ρ×g×V, and the battery volume V is calculated to be V=(F1-F2) / (ρ×g).

[0225] From the OCV and IMP test results, the battery of the embodiment always maintained an SOC of more than 99% during the test until the end of storage.

[0226] After storage for 30 days, the battery volume was measured, and the percentage increase in the battery volume after storage relative to the battery volume before storage was calculated.

[0227] Test results

[0228] The test results are shown in Table 1.

[0229] Table 1

[0230] In Table 1, the mass content of the carbon skeleton structure is calculated based on the total mass of the positive electrode active material.

[0231] The mass content of oxygen-containing groups is calculated based on the total mass of the coating layer.

[0232] The mass content of P element is calculated based on the total mass of the coating layer.

[0233] In Examples 1 to 5, the phosphate particles in the positive electrode active material include Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 Compounds;

[0234] In Example 6-1, the phosphate particles in the positive electrode active material include the molecular formula Li 0.994 Mn 0.5 Fe 0.5 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 Compounds;

[0235] In Example 6-2, the phosphate particles in the positive electrode active material include Li 0.994 Mn 0.4 Fe 0.6 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 of compounds.

[0236] In the process of preparing and introducing polytetrafluoroethylene in Example 3-2, oxygen in the air may be carried, so that the coating layer contains some oxygen elements.

[0237] In Comparative Example 1, the positive electrode active material includes phosphate particles. When detecting the P element content, the phosphate particles may interfere with the detection, causing the detected P element mass content to be greater than 0.

[0238] Table 2

[0239] It can be seen from Tables 1 and 2 that oxygen-containing groups may be introduced during the carbon coating of phosphate particles. However, oxygen-containing groups have high reactivity and are prone to side reactions with the electrolyte, thereby deteriorating the performance of the battery.

[0240] The present embodiment further introduces phosphorus-containing groups into the coating layer. The phosphorus-containing groups (phosphoric acid) can reduce the content of oxygen-containing groups in the carbon skeleton structure, modify the coating layer as a whole, weaken the catalytic activity of the coating layer as a whole, reduce the side reactions between the coating layer and the electrolyte, and improve the cycle performance of the battery cell. The present embodiment can also effectively reduce the dissolution of Fe and Mn after cycling, and the dissolution amount is ≤849ppm. The gram capacity of the positive electrode active material in the button cell of the present embodiment is 130mAh / g to 155mAh / g.

[0241] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

[0242] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A positive electrode active material comprising: Phosphate granules; as well as The coating layer is disposed on at least a portion of the surface of the phosphate particles, and the coating layer includes a carbon skeleton structure and a phosphorus-containing group connected to the carbon skeleton structure.

2. The positive electrode active material according to claim 1, wherein The coating layer further comprises an oxygen-containing group, and the oxygen-containing group is connected to the carbon skeleton structure; Based on the total mass of the coating layer, the mass content of oxygen in the oxygen-containing groups is ≤3.5%; optionally, the mass content of oxygen in the oxygen-containing groups is ≤3.0%.

3. The positive electrode active material according to claim 2, wherein The oxygen-containing group includes at least one of a hydroxyl group, a carbonyl group, a carboxyl group, an ester group, and a quinone group.

4. The positive electrode active material according to any one of claims 1 to 3, wherein Based on the total mass of the coating layer, the mass content of phosphorus in the phosphorus-containing group is 0.5% to 5.5%; Optionally, the phosphorus-containing group includes at least one of a phosphate group and a pyrophosphate group.

5. The positive electrode active material according to any one of claims 1 to 4, wherein Based on the total mass of the positive electrode active material, the mass content of the carbon skeleton structure is greater than 0 and less than or equal to 6%, and can be optionally 2% to 5%.

6. The positive electrode active material according to any one of claims 1 to 5, wherein The phosphate particles include a molecular formula of Li 1+x Mn 1-y A y P 1-z R z Y w A compound, -0.1≤x≤0.9, 0<y<1, 0≤z≤0.5, 1.8≤w≤4; A includes at least one of Fe, Co, Ni, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; R includes at least one of S, Si, Cl, B, C, N; Y includes at least one of O and F; Optionally, 0<y<0.

5.

7. The positive electrode active material according to any one of claims 1 to 6, wherein The positive electrode active material satisfies at least one of the following conditions: (1) The initial gram capacity of the positive electrode active material is 130 mAh / g to 165 mAh / g; (2) The powder resistivity of the positive electrode active material is ≤500Ω*cm; optionally ≤390Ω*cm.

8. A method for preparing a positive electrode active material, comprising: providing an organic carbon source having oxygen-containing groups to the phosphate particles; Carbonizing the organic carbon source to form a carbon layer on at least a portion of the surface of the phosphate particles to obtain an intermediate; The intermediate and an organic phosphorus source are mixed, and at least part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate phosphorus-containing groups, thereby obtaining a positive electrode active material.

9. The method according to claim 8, wherein: The step of mixing the intermediate and the organic phosphorus source, and reacting at least part of the oxygen-containing groups in the carbon layer with the organic phosphorus source to generate phosphorus-containing groups to obtain the positive electrode active material comprises: The intermediate and an organic phosphorus source are mixed, and subjected to heat treatment so that at least part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate phosphorus-containing groups, thereby obtaining a positive electrode active material.

10. The method according to claim 8 or 9, wherein: The organic phosphorus source comprises at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, tetraethyl pyrophosphate, and tetrabenzyl pyrophosphate; and / or The organic carbon source includes at least one of sugar compounds, olefin polymers, polyvinyl alcohol, polyethylene glycol, citric acid, and toluene; optionally, the organic carbon source includes at least one of olefin polymers and toluene.

11. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material as described in any one of claims 1 to 7, or the positive electrode active material prepared by the method as described in any one of claims 8 to 10.

12. A battery comprising the positive electrode sheet according to claim 11.

13. An electrical device comprising the battery as claimed in claim 12.

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