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

Abstract

The invention relates to a positive electrode active material and a preparation method thereof, a battery and a power utilization device, the positive electrode active material comprises phosphate particles and a coating layer, the coating layer is arranged on at least part of the surface of the phosphate particles, and the coating layer comprises a carbon skeleton structure body and a phosphorus-containing group connected to the carbon skeleton structure body. The cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present application relates to a positive electrode active material and a preparation method thereof, a battery and an electrical device. Background Art

[0002] Batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, battery cars, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools, etc. Due to the great progress made in the field of batteries, higher requirements are placed on the performance of batteries. As an important component of the battery, the positive electrode active material has a significant impact on the battery performance.

[0003] However, the current positive electrode active materials have poor cycle performance when applied to batteries. Summary of the invention

[0004] 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.

[0005] 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 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.

[0006] Therefore, in the embodiment of the present application, the positive electrode active material includes phosphate particles and a coating layer, and the coating layer is mainly composed of a carbon skeleton structure, which can provide a good coating and protection effect on the phosphate particles; since the carbon skeleton structure contains a single carbon substance, it has excellent electronic conductivity, which is beneficial to improve the overall conductivity of the positive electrode active material and contribute to the capacity of the phosphate particles. The coating layer also includes a phosphorus-containing group, 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 the side reactions between the coating layer and the electrolyte, and improve the cycle performance of the battery cell.

[0007] In some embodiments, the coating layer further comprises oxygen-containing groups 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%.

[0008] 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.

[0009] 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.

[0010] In some embodiments, based on the total mass of the coating layer, the mass content of phosphorus element in the phosphorus-containing group is 0.5% to 5.5%. When the mass content of the phosphorus-containing group is within the above range, it will basically not damage the carbon continuous six-membered ring structure, can improve the overall conductivity of the coating layer, and is beneficial to the discharge capacity of the phosphate particles.

[0011] 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 the oxygen-containing group.

[0012] In some embodiments, 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%. 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, can effectively reduce the risk of side reactions occurring due to direct contact between the phosphate particles and the electrolyte, reduce the risk of transition metal ion dissolution, and is beneficial to the improvement of the cycling 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 beneficial to the discharge capacity of the phosphate particles.

[0013] In some embodiments, the phosphate particles include a compound with the molecular formula Li 1+x Mn 1-y A y P 1-z R z Y w , where -0.1 ≤ x ≤ 0.9, 0 < y < 1, 0 ≤ z ≤ 0.5, and 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, and 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. A coating layer is provided on the surface of the above phosphate particles, and the coating layer can effectively modify the phosphate particles and improve their conductivity and discharge capacity.

[0014] In some embodiments, the initial discharge capacity of the positive electrode active material is 130 mAh / g to 165 mAh / g. The initial discharge capacity of the positive electrode active material is relatively high, and the discharge capacity is improved.

[0015] In some embodiments, the powder resistivity of the positive electrode active material is ≤500 Ω·cm; optionally, it is ≤390 Ω·cm. When the powder resistivity of the positive electrode active material is within the above range, its powder resistivity is relatively low, which is beneficial to improving the overall electronic conductivity of the positive electrode active material and conducive to the exertion of the specific capacity of the positive electrode active material.

[0016] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode active material, the method comprising:

[0017] Providing an organic carbon source having oxygen-containing groups to phosphate particles;

[0018] Carrying out carbonization treatment on the organic carbon source to form a carbon layer on at least a part of the surface of the phosphate particles, obtaining an intermediate;

[0019] Mixing the intermediate and an organic phosphorus source, and reacting at least a part of the oxygen-containing groups in the carbon layer with the organic phosphorus source to generate phosphorus-containing groups, obtaining the positive electrode active material.

[0020] In some embodiments, the step of mixing the intermediate and the organic phosphorus source, and reacting at least a part of the oxygen-containing groups in the carbon layer with the organic phosphorus source to generate phosphorus-containing groups, obtaining the positive electrode active material, includes:

[0021] Mixing the intermediate and the organic phosphorus source, and subjecting them to heat treatment so that at least a part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate phosphorus-containing groups, obtaining the positive electrode active material.

[0022] In some embodiments, the organic phosphorus source includes at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, tetraethyl pyrophosphate, and tetrabenzyl pyrophosphate.

[0023] In some embodiments, the organic carbon source includes at least one of saccharide 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.

[0024] In a third aspect, an embodiment of the present application provides a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material according to any one of the embodiments of the first aspect of the present application, or the positive electrode active material prepared by the method according to any one of the embodiments of the second aspect of the present application.

[0025] In a fourth aspect, the present application further provides a battery, the battery includes the positive electrode plate according to any one of the embodiments of the third aspect of the present application.

[0026] In a fifth aspect, the present application further provides an electrical device, the electrical device includes the battery according to any one of the embodiments of the fourth aspect of the present application. Description of the Drawings

[0027] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the drawings.

[0028] Figure 1 It is a schematic diagram of an embodiment of the battery cell of the present application.

[0029] Figure 2 is Figure 1 An exploded schematic diagram of the embodiment of the battery cell.

[0030] Figure 3 It is a schematic diagram of an embodiment of the battery module of the present application.

[0031] Figure 4 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0032] Figure 5 is Figure 4 An exploded schematic diagram of the embodiment of the battery pack shown.

[0033] Figure 6 It is a schematic diagram of an embodiment of an electrical device including the battery cell of the present application as a power source.

[0034] The drawings are not necessarily drawn to actual scale.

[0035] The description of the reference numerals is as follows:

[0036] 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module;

[0037] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0038] 53. Cover plate;

[0039] 6. Electrical device. Specific embodiments

[0040] Hereinafter, embodiments of the positive electrode active material, its preparation method, battery, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical 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 recited in the claims.

[0041] The "ranges" disclosed in this application are defined in terms of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. 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 are all contemplated: 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 abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0043] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0044] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also 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 can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0045] Phosphates have a high theoretical specific capacity, which is beneficial to 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 for modification, but further research has found that phosphates containing carbon coatings and electrolytes may still have serious side reactions, so that the capacity of the phosphates cannot be fully utilized, and the battery cells may be at risk of swelling, and the cycle performance of the battery cells may be deteriorated.

[0046] 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 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.

[0047] Next, the technical solution of the implementation mode of this application is described in detail.

[0048] Positive electrode active material

[0049] In a first aspect, an embodiment of the present application provides a positive electrode active material.

[0050] The positive electrode active material comprises 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 comprises a carbon skeleton structure and a phosphorus-containing group connected to the carbon skeleton structure.

[0051] The carbon skeleton structure, as the main material of the coating layer, can play a good coating and protective role on the phosphate particles; since the carbon skeleton structure contains carbon element, it has excellent electronic conductivity, which is beneficial to improve the overall conductivity of the positive electrode active material and helps to maximize the capacity of the phosphate particles.

[0052] Since the carbon skeleton structure is usually formed by sintering an organic carbon source, which may contain oxygen-containing groups, during the sintering process of the organic carbon source, the oxygen-containing groups may still remain in the carbon skeleton structure. The reaction activity of the oxygen-containing groups is relatively high. 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 and cause the dissolution of transition metal ions such as manganese ions, thereby deteriorating the cycle performance of the battery cell.

[0053] 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.

[0054] The carbon skeleton structure mainly exists in the form of a single carbon substance, for example, in the form of a continuous six-membered ring structure; the oxygen-containing group can be connected to the carbon atoms in the carbon skeleton structure in the form of a chemical bond, and the higher the content of the oxygen-containing group, the higher the catalytic activity of the coating layer; and the higher the content of the oxygen-containing group, 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 less the content of the oxygen-containing group, the more conducive it is to improve the electrochemical properties of the positive electrode active material in the application of gas production, circulation, storage, etc. in the battery monomer. Optionally, based on the total mass of the coating layer, the mass content of the oxygen-containing group is less than 3%; when the mass content of the oxygen-containing group meets the above range, the catalytic activity of the coating layer is low, the side reactions of the coating layer and the electrolyte can be alleviated, and it is conducive to further improving the conductivity and gram capacity of the positive electrode active material, and can further improve the expansion rate and cycle performance of the battery monomer.

[0055] Exemplarily, the coating layer further includes oxygen-containing groups, which are connected to the carbon skeleton structure. Of course, the coating layer may not have 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.

[0056] Optionally, based on the total mass of the coating layer, the mass content of oxygen in the oxygen-containing group is ≤3.5%; optionally, the mass content of oxygen in the oxygen-containing group is ≤3.0%. For example, the mass content of oxygen in the oxygen-containing group 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. The mass content of oxygen in the oxygen-containing group is 0%, which means that there is basically no oxygen-containing group in the coating layer.

[0057] 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.

[0058] In the embodiment of the present application, the mass content of oxygen element in the oxygen-containing groups in the coating layer is a well-known meaning in the art, and can be detected by 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 liquid after the reaction is centrifuged. And wash with deionized water 20 times, and then wash with anhydrous ethanol 5 times, and finally dry to obtain the 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. Then titrate 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.

[0059] In the process of preparing 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. A 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.

[0060] The presence of the phosphorus-containing group is beneficial to improving the conductivity of the coating layer as a whole, and is helpful to the gram capacity of the phosphate particles; optionally, based on the total mass of the coating layer, the mass content of phosphorus in the phosphorus-containing group can be 0.5% to 5.5%; optionally 1% to 5.0%. When the mass content of phosphorus in the phosphorus-containing group is within the above range, it will basically not damage the carbon continuous six-membered ring structure, can improve the conductivity of the coating layer as a whole, and is beneficial to the gram capacity of the phosphate particles.

[0061] Illustratively, 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.

[0062] 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.

[0063] In the embodiment of the present application, the mass content of the phosphorus-containing group in the coating layer has a meaning known in the art, and can be detected by equipment and methods 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 react fully, and the liquid after the reaction is centrifuged. And washed with deionized water 20 times, and then washed with anhydrous ethanol 5 times, and finally dried to obtain the coating layer, and the mass content of phosphorus in the coating layer is tested by Agilent ICP-OES730 inductively coupled plasma emission spectroscopy (ICP).

[0064] In some embodiments, based on the total mass of the positive electrode active material, the mass content of the carbon framework structure is greater than 0 and less than or equal to 6%, and can be optionally 2% to 5%. When the mass content of the carbon framework structure is within the above range, a good coating effect can be formed on the phosphate particles, the risk of side reactions occurring due to direct contact between the phosphate particles and the electrolyte can be effectively reduced, the risk of transition metal ion dissolution is reduced, which is beneficial to the improvement of the cycling performance and storage performance of the positive electrode active material; moreover, when the mass content of the carbon framework structure is within the above range, the overall conductivity of the positive electrode active material can be effectively improved, which is beneficial to the utilization of the specific capacity of the phosphate particles.

[0065] Exemplarily, the mass content of the carbon framework 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 composed of any two of the above values.

[0066] In the embodiments of the present application, the mass content of the carbon framework structure has the meaning well-known in the art, and can be detected by using the equipment and methods well-known in the art. For example, an elemental analyzer (EA) is used to test the mass of the carbon framework structure, and the mass of the C element in the test result of the elemental analyzer is taken as the mass of the carbon framework structure, and its mass content is calculated therefrom.

[0067] 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 wThe 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. A coating layer is provided on the surface of the above phosphate particles, and the coating layer can effectively modify the phosphate particles, improving their conductivity and specific capacity performance.

[0068] Exemplarily, 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 the range composed of any two of the above values.

[0069] Exemplarily, 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 composed of any two of the above values. Optionally, 0 < y < 0.5. The content of Mn is relatively high. During the charge and discharge process of the battery cell, the time at high voltage accounts for a relatively high proportion, and the catalytic effect of the oxygen-containing groups on the electrolyte is more obvious, which is more likely to cause the deterioration of the performance of the battery cell; while 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 performance of the above-mentioned cathode active material, and thus improving the cycle performance and storage performance of the battery cell.

[0070] Exemplarily, 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 composed of any two of the above values.

[0071] Exemplarily, 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 composed of any two of the above values.

[0072] Exemplarily, 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

[0073] During the charge and discharge process of the battery cell, the insertion and extraction and consumption of active ions such as Li will occur. The molar content of Li is different when the battery cell is discharged to different states. In the listing of the positive electrode active material in the embodiments of the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li may change.

[0074] In the listing of the positive electrode active material in the embodiments of the present application, the molar content of oxygen O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will show fluctuations.

[0075] In some embodiments, the initial specific capacity of the positive electrode active material is 130 mAh / g to 165 mAh / g. The initial specific capacity of the positive electrode active material is relatively high, and the utilization of the specific capacity is improved.

[0076] Exemplarily, the initial specific 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 composed of any two of the above values.

[0077] In the embodiments of the present application, for the detection of the initial specific capacity of the positive electrode active material, specifically, a button cell is formed by using a positive electrode sheet containing the positive electrode active material and a lithium metal sheet. In a constant temperature environment of 25 °C, the button cell is charged at 0.1C to 4.3V, then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05 mA, left standing for 5 minutes, and then discharged at 0.1C to 2.0V. The discharge capacity at this time is the initial specific capacity, denoted as D0. Among them, 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) with a volume ratio of 1:1:1. The lithium salt includes 1 mol / L of LiPF 6 .

[0078] 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; it can be selected as ≤390 Ω·cm. When the powder resistivity of the positive electrode active material is within the above range, its powder resistivity is relatively low, which is beneficial to improving the overall electronic conductivity of the positive electrode active material and beneficial to the exertion of the specific capacity of the positive electrode active material.

[0079] Exemplarily, the powder resistivity of the positive electrode active material can be 10 Ω·cm, 50 Ω·cm, 100 Ω·cm, 150 Ω·cm, 200 Ω·cm, 250 Ω·cm, 300 Ω·cm, 350 Ω·cm, 400 Ω·cm, 450 Ω·cm, 500 Ω·cm or a range composed of any two of the above values.

[0080] In the embodiments of the present application, the powder resistivity of the positive electrode active material under a pressure of 8 MPa has a meaning well-known in the art and can be tested by methods known in the art. For example, it can be tested using a PRCD1100 powder resistivity meter and can be tested with reference to the national standard GB / T30835-2014.

[0081] Method for preparing positive electrode active material

[0082] In a second aspect, the embodiments of the present application also propose a method for preparing a positive electrode active material. The positive electrode active material of any embodiment in 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 means commonly used in the art.

[0083] The method includes:

[0084] Step S100: Provide an organic carbon source with an oxygen-containing group to the phosphate particles;

[0085] Step S200: Carbonize the organic carbon source to form a carbon layer on at least part of the surface of the phosphate particles to obtain an intermediate;

[0086] Step S300: Mix the intermediate and the organic phosphorus source. At least some of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to form phosphorus-containing groups, thereby obtaining the cathode active material.

[0087] According to the method of the embodiment of the present application, after the organic carbon source is carbonized, a carbon layer can be formed on the surface of the phosphate particles to form an intermediate; some of the oxygen-containing groups in the organic carbon source may still remain in the carbon layer. Further mix the intermediate and the organic phosphorus source, and the organic phosphorus source can chemically react with at least some of the oxygen-containing groups to reduce the content of the oxygen-containing groups and weaken the adverse effects brought by the oxygen-containing groups; the reaction products may volatilize in a gaseous state, or some substances that are not easy to volatilize may remain, such as phosphorus-containing groups. The phosphorus-containing groups can play a doping role and can further improve the conductivity of the cathode active material, which is beneficial to further improving the capacity performance of the phosphate particles.

[0088] [Step S100]

[0089] The organic carbon source may be solid particles. The solid organic carbon source can be dissolved in a solvent, and then the organic carbon source dissolved in the solvent and the phosphate particles are mixed. The solvent can be deionized water or the like.

[0090] The phosphate particles are polyanion-type compounds, which may include manganese phosphate salts. Further, it includes a compound with the molecular formula Li 1+x Mn 1-y A y P 1-z R z Y w The phosphate particles can be obtained commercially or synthesized according to the following method.

[0091] In some embodiments, the preparation method of the phosphate particles includes:

[0092] Step S110: Dissolve the manganese source and the A source in a solvent, and obtain a metal precursor through a drying process;

[0093] Step S120: Add the metal precursor, the lithium source, the phosphorus source, and the R source to the solvent, grind and mix them, and then perform spray drying to obtain a phosphate precursor;

[0094] Step S130: Sinter the phosphate precursor to form phosphate particles.

[0095] In step S110,

[0096] In some embodiments, the manganese source can be a manganese-containing substance known in the art that can be used to prepare phosphates. For example, the manganese source may include at least one of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0097] In some embodiments, the A source may include at least one of oxalate, phosphate, acetate, sulfate, citrate, and nitrate.

[0098] In some embodiments, the solvent may include at least one of deionized water and alcohols.

[0099] In step S120,

[0100] 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.

[0101] In some embodiments, the phosphorus source may include at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0102] 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; taking the silicon source as an example, the silicon source may include at least one of silicic acid, metasilicic acid, silicon tetrachloride, silicon dioxide, and tetraethyl orthosilicate. Taking the boron source as an example, the boron source may include at least one of boric acid, ammonium borate, and boron oxide.

[0103] In some embodiments, the solvent may include at least one of deionized water and alcohols.

[0104] In some embodiments, grinding can be carried out using a sand mill, for example, grinding and stirring in a sand mill for 8 h to 10 h.

[0105] In some embodiments, the process of spray drying and granulation can be carried out at 230 °C to 270 °C for 3.5 h to 5 h.

[0106] In step S130,

[0107] The sintering treatment can be carried out in an inert atmosphere, and the inert atmosphere can adopt at least one of nitrogen and argon.

[0108] The sintering temperature can be 650 °C to 750 °C, and the sintering time can be 8 h to 12 h.

[0109] The stoichiometric ratios of the substances in the above steps can be set according to the chemical formula of the required phosphate particles. The contents of the elements in the material can be detected by inductively coupled plasma emission spectrometry (ICP).

[0110] In some embodiments, the organic carbon source may include at least one of saccharide compounds, olefin polymers, polyvinyl alcohol, polyethylene glycol, citric acid, and toluene.

[0111] Exemplarily, the saccharide compound may include at least one of starch, sucrose, and glucose.

[0112] Exemplarily, the olefin polymer may include at least one of polyethylene and polytetrafluoroethylene.

[0113] Each of the above substances may be an olefin polymer such as an organic carbon source like polyethylene, polytetrafluoroethylene, toluene, etc. The above substances have relatively little hydroxyl content, or even no hydroxyl group, and the amount of residual hydroxyl groups after carbonization is relatively small, which is beneficial to improving the electrochemical performance of the cathode active material.

[0114] [Step S200]

[0115] During the process of Step S100 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 h to 6 h, the system is subjected to a carbonization treatment. The carbonization treatment process is as follows: The system can be pre-heat treated and dried at 120°C to 200°C for 4 h to 6 h to remove the solvent; then sintered at 650°C to 750°C for 8 h to 12 h, and the organic carbon source is carbonized into a carbon layer, and the carbon layer coats at least part of the surface of the phosphate particles.

[0116] [Step S300]

[0117] The organic phosphorus source and the intermediate are mixed, and the organic phosphorus source and the intermediate can be heat treated so that at least part of the oxygen-containing groups in the organic phosphoric acid and the intermediate react.

[0118] When the temperature of the heat treatment does not exceed the boiling point of the organic phosphorus source, the organic phosphorus source may exist in a liquid phase. The liquid-phase organic phosphorus source can react with at least part of the oxygen-containing groups in the carbon layer to reduce the content of the oxygen-containing groups; the liquid-phase organic phosphorus source has good fluidity, which is beneficial to further reducing the content of the oxygen-containing groups; after the reaction is completed, the oxygen-containing groups in the carbon layer are reduced, and the organic phosphoric acid generates phosphorus-containing groups and remains in the carbon layer, connecting with the carbon atoms in the carbon layer. In this case, the carbon layer after the reaction is completed is equivalent to the coating layer in the previous text.

[0119] When the temperature of the heat treatment exceeds the boiling point of the organic phosphorus source, the organic phosphorus source may exist in a gas phase. 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 the oxygen-containing groups; the contact between the gas-phase organic phosphorus source and the intermediate is more sufficient, which is more beneficial to further reducing the content of the oxygen-containing groups; after the reaction is completed, the oxygen-containing groups in the carbon layer are reduced, and the organic phosphoric acid generates phosphorus-containing groups and remains in the carbon layer, connecting with the carbon atoms in the carbon layer. In this case, the carbon layer after the reaction is completed is equivalent to the coating layer in the previous text.

[0120] 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.

[0121] In some embodiments, the organic phosphorus source may include at least one of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

[0122] In some embodiments, the organic phosphorus source may include at least one of tetraethyl pyrophosphate and tetrabenzyl pyrophosphate.

[0123] Taking the organic phosphorus source as trimethyl phosphate and the oxygen-containing group as hydroxyl as an example, the reaction process is explained:

[0124] -OH+(CH 3 O) 3 PO→CH 3 OH+O(CH 3 O) 2 PO,

[0125] -OH+O(CH 3 O) 3 PO→CH 3 OH+O 2 (CH 3 O)PO,

[0126] -OH+O 2 (CH 3 O) 2 PO→CH 3 OH+PO 4 3- .

[0127] Trimethyl phosphate can capture hydrogen from hydroxyl groups, and some products such as CH 3 OH evaporates in the form of gas, and the non-volatile phosphorus oxide remains on the surface of the coating.

[0128] Positive electrode sheet

[0129] In a third aspect, an embodiment of the present application proposes a positive electrode plate.

[0130] 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 including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0131] The positive electrode active material may include the positive electrode active material according to any embodiment of the first aspect of the present application, or the positive electrode active material obtained by the method according to 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 enhancing the electrochemical performance of the positive electrode sheet. In addition, since the side reaction between the positive electrode active material and the electrolyte is alleviated, when the positive electrode sheet is applied to a battery cell, the expansion rate of the battery cell can be reduced and the cycle performance of the battery cell can be improved.

[0132] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. There is no particular limitation on the type of the positive electrode conductive agent in the embodiments of the present application. As an example, the positive electrode conductive agent includes 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, based on the total mass of the positive electrode film layer, the mass percentage content of the positive electrode conductive agent is ≤5%.

[0133] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. There is no particular limitation on the type of the positive electrode binder in the embodiments of the present application. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage content of the positive electrode binder is ≤5%.

[0134] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the 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).

[0135] The positive electrode film layer is usually formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optionally the conductive agent, optionally the binder, and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0136] Single battery

[0137] Fourthly, an embodiment of the present application further provides a battery cell, which includes a positive electrode sheet according to any embodiment of the third aspect of the present application. Since the positive electrode active material in the positive electrode sheet has good electrical conductivity, the capacity utilization is improved, and the electrochemical performance of the positive electrode sheet is improved. In addition, since the side reaction between the positive electrode active material and the electrolyte is alleviated, when the positive electrode sheet 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.

[0138] [Negative electrode sheet]

[0139] In some embodiments, the battery cell further includes a negative electrode sheet.

[0140] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0141] The negative electrode active material can be a negative electrode active material known in the art for battery cells. As an example, the negative electrode active material can 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. The silicon-based materials can include at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based materials can include at least one of elemental tin, tin oxides, and tin alloy materials.

[0142] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The embodiment of the present application does not particularly limit the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent can 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, based on the total weight of the negative electrode film layer, the mass percentage content of the negative electrode conductive agent is ≤5%.

[0143] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The embodiment of the present application does not particularly limit the type of the negative electrode binder. As an example, the negative electrode binder can include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, based on the total weight of the negative electrode film layer, the mass percentage content of the negative electrode binder is ≤5wt%.

[0144] In some embodiments, the negative electrode film layer may optionally further include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like. In some embodiments, based on the total weight of the negative electrode film layer, the mass percentage content of the other additives is ≤2%.

[0145] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the 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, copper 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).

[0146] The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is generally formed by dispersing negative electrode active materials, optional conductive agents, optional binders, and other optional additives in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0147] The negative electrode plate does not exclude other additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the embodiments of the present application further includes a conductive bottom layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer. In some other embodiments, the negative electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0148] [Electrolyte solution]

[0149] In some embodiments, the battery cell further includes an electrolyte solution.

[0150] During the charge and discharge process of the battery cell, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte solution plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The type of the electrolyte solution in the embodiments of the present application is not particularly limited and can be selected according to actual needs.

[0151] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.

[0152] As an example, the electrolyte salt may include, but is not limited to, lithium hexafluorophosphate (LiPF 6 )、lithium tetrafluoroborate (LiBF 4)、Lithium perchlorate (LiClO 4 )、Lithium hexafluoroarsenate (LiAsF 6 )、Lithium bis(fluorosulfonyl)imide (LiFSI), Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Lithium trifluoromethanesulfonate (LiTFS), Lithium difluoro(oxalato)borate (LiDFOB), Lithium bis(oxalato)borate (LiBOB), Lithium difluorophosphate (LiPO 2 F 2 ), at least one of lithium difluoro(dioxalato)phosphate (LiDFOP) and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0153] 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).

[0154] In some embodiments, the electrolyte may also optionally include additives. For example, the additives may include anode - forming additives, may also include cathode - forming additives, and may also include additives that can improve certain battery performance, such as additives for improving battery overcharge performance, additives for improving battery high - temperature performance, additives for improving battery low - temperature power performance, etc.

[0155] [Separator membrane]

[0156] The battery cell further includes a separator membrane.

[0157] In some embodiments, the battery cell also includes a separator membrane. The type of the separator membrane is not particularly limited in the embodiments of the present application, and any well - known porous - structure separator membrane with good chemical stability and mechanical stability can be selected.

[0158] In some embodiments, the material of the separator membrane may include at least one of glass fiber, non - woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single - layer film or a multi - layer composite film, without particular limitation. When the separator membrane is a multi - layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0159] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be made into an electrode assembly through a winding process and / or a stacking process.

[0160] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and the electrolyte.

[0161] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0162] The embodiments of the present application do not particularly limit the shape of the battery cell, which can be cylindrical, square, or any other shape. As Figure 1 is a battery cell 5 with a square structure as an example.

[0163] In some embodiments, as Figure 2 shown, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with 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 can form an electrode assembly 52 through a winding process and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, which can be adjusted according to requirements.

[0164] The preparation method of the battery cell according to the embodiments of the present application is well-known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can form an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in the outer package, dried, and then the electrolyte is injected. After processes such as vacuum packaging, standing, formation, and shaping, a battery cell is obtained.

[0165] In some embodiments of the embodiments of the present application, the battery cells according to the embodiments of the present application can be assembled into a battery module. The number of battery cells included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0166] Figure 3 is a schematic diagram of a battery module 4 as an example. As Figure 3As shown, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple battery cells 5 can be fixed by fasteners.

[0167] Optionally, the battery module 4 can further include a housing having an accommodation space, and the multiple battery cells 5 are accommodated in the accommodation space.

[0168] In some embodiments, the above battery modules can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0169] Figure 4 and Figure 5 is a schematic diagram of a battery pack 1 as an example. As Figure 4 and Figure 5 shown, the battery pack 1 can include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in the battery box in any manner.

[0170] Electrical device

[0171] The fifth aspect of the embodiments of the present application provides an electrical device. The electrical device includes at least one of the battery cell, battery module, or battery pack of the embodiments of the present application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or can also be used as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, 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.

[0172] The electrical device can select the battery cell, battery module, or battery pack according to its usage requirements.

[0173] Figure 6 is a schematic diagram of an electrical device 6 as an example. The electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the requirements of the electrical device 6 for high power and high energy density, a battery pack or a battery module can be used.

[0174] Another example of the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This type of electrical device usually requires thin and light design, and a battery cell can be used as the power source.

[0175] Example

[0176] The following examples more specifically describe the content disclosed in the embodiments of the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0177] Example 1

[0178] 1. Preparation of the positive electrode sheet

[0179] The positive electrode sheet includes a positive current collector aluminum foil and a positive electrode film layer. The positive electrode film layer is formed by uniformly coating a positive electrode paste (with N-methylpyrrolidone NMP as the solvent) on the surface of the positive current collector aluminum foil, and then drying and cold pressing. The positive electrode film layer includes a positive active material, a binder polyvinylidene fluoride (PVDF), and acetylene black with a weight ratio of 90:5:5.

[0180] The positive active material includes phosphate particles and a coating layer. The phosphate particles include a compound with the molecular formula 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 active material is as follows:

[0181] Dissolve 74.6 g of sucrose in 500 ml of deionized water, then stir and dissolve thoroughly to obtain a coating solution. Add the above-mentioned phosphate particles to the coating solution, stir and mix for 6 hours. After mixing evenly, transfer it to an oven at 150 °C and dry for 6 hours, and then sinter at 700 °C for 10 hours to obtain an intermediate;

[0182] Place 100 g of the intermediate in a sealed reaction chamber, and introduce trimethyl phosphate gas under a vacuum condition of 200 °C. After reacting for 0.5 h, the final positive active material is obtained.

[0183] 2. Preparation of the negative electrode sheet

[0184] The negative electrode plate includes a negative current collector copper foil and a negative electrode film layer. The negative electrode film layer is formed by uniformly coating a negative electrode paste (with deionized water as the solvent) on the surface of the negative current collector copper foil, followed by drying and cold pressing. The negative electrode film layer includes a negative active material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) with a weight ratio of 95:2:2:1.

[0185] The negative active material includes artificial graphite and hard carbon (with a mass ratio of 90:5).

[0186] 3. Separator

[0187] The separator is a polyethylene film.

[0188] 4. Preparation of electrolyte

[0189] 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) with a volume ratio of 1:1:1. The lithium salt includes 1 mol / L of LiPF 6 。

[0190] 5. Preparation of battery

[0191] The lithium-ion battery includes an outer packaging case, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are disposed inside the outer packaging case. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The electrode assembly is a wound electrode assembly, and the separator is disposed between the positive electrode plate and the negative electrode plate.

[0192] Comparative Example 1

[0193] A lithium-ion battery was prepared using a method similar to that of Example 1. Different from Example 1, the positive electrode plate was prepared using the following steps:

[0194] The positive electrode plate includes a positive current collector aluminum foil and a positive electrode film layer. The positive electrode film layer is formed by uniformly coating a positive electrode paste (with N-methylpyrrolidone NMP as the solvent) on the surface of the positive current collector aluminum foil, followed by drying and cold pressing. The positive electrode film layer includes a positive active material, binder polyvinylidene fluoride (PVDF), and acetylene black with a weight ratio of 90:5:5.

[0195] The positive active material includes phosphate particles and a coating layer. The phosphate particles include a compound with the molecular formula 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 active material is as follows:

[0196] Dissolve 74.6 g of sucrose in 500 ml of deionized water, then stir and dissolve it thoroughly to obtain a coating solution. Add the above-mentioned phosphate particles to the coating solution, stir and mix them together for 6 hours. After mixing evenly, transfer them to an oven at 150 °C and dry for 6 hours, and then sinter at 700 °C for 10 hours to obtain the positive electrode active material.

[0197] Examples 2-1 to 2-4

[0198] Prepare a lithium-ion battery by a method similar to that of Example 1. The difference from Example 1 is that the content of the organic carbon source is adjusted.

[0199] Examples 3-1 and 3-2

[0200] Prepare a lithium-ion battery by a method similar to that of Example 1. The difference from Example 1 is that the type of the organic carbon source is adjusted.

[0201] Examples 4-1 to 4-3

[0202] Prepare a lithium-ion battery by a method similar to that of Example 1. The difference from Example 1 is that the content of the organic phosphorus source is adjusted.

[0203] Examples 5-1 and 5-2

[0204] Prepare a lithium-ion battery by a method similar to that of Example 1. The difference from Example 1 is that the type of the organic phosphorus source is adjusted.

[0205] Examples 6-1 and 6-2

[0206] Prepare a lithium-ion battery by a method similar to that of Example 1. The difference from Example 1 is that the type of the material of the positive electrode active material is adjusted.

[0207] Performance test

[0208] 1. Preparation of button battery

[0209] Use the positive electrode sheet in Example 1 as the positive electrode sheet of the button battery;

[0210] Use a lithium sheet as the negative electrode. The electrolyte includes 1 mol / L of LiPF 6 and an organic solvent. The organic solvent includes ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) with a volume ratio of 1:1:1;

[0211] Assemble into a button battery with the negative electrode sheet, the positive electrode sheet and the electrolyte in a button battery box.

[0212] 2. Measurement method for the initial specific capacity of the button battery

[0213] In a constant temperature environment of 25 °C, the coin cell is charged at 0.1C to 4.3V, then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA, left standing for 5 minutes, and then discharged at 0.1C to 2.0V. The discharge capacity at this time is the initial gram capacity, denoted as D0.

[0214] 3. Cycling performance test of lithium-ion battery at 45 °C

[0215] In a constant temperature environment of 45 °C, the lithium-ion battery is charged at 1C to 4.3V, then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Left standing for 5 minutes, and then discharged at 1C to 2.5V. Record the discharge capacity at this time as E0. Repeat the above charge-discharge cycle until the discharge capacity drops to 80% of E0. Record the number of cycles the lithium-ion battery has gone through at this time.

[0216] 4. Measurement method for the dissolution amount of Mn (and Fe doped at the Mn site) in lithium-ion battery after cycling

[0217] At 45 °C, the lithium-ion battery that has been cycled until the capacity decays to 80% is discharged at a rate of 0.1C to the cut-off voltage of 2.0V.

[0218] Then disassemble the lithium-ion battery, take out the negative electrode plate, and randomly take 30 circular pieces with a unit area of 1540.25mm 2 ). Use Agilent ICP-OES730 to test the inductively coupled plasma emission spectrum (ICP). Calculate the amounts of Fe (if Fe is doped at the Mn site of the positive electrode active material) and Mn according to the ICP results, and thus calculate the dissolution amount of Mn (and Fe doped at the Mn site) after cycling. The test standard is based on EPA-6010D-2014.

[0219] 5. Gas swelling test of lithium-ion battery at 60 °C

[0220] Store the lithium-ion battery with 100% state of charge (SOC) at 60 °C as the test sample, and measure the open circuit voltage (OCV) and AC internal resistance (IMP) of the lithium-ion battery before, during, and after storage to monitor the SOC, and measure the volume of the lithium-ion battery.

[0221] Take out the lithium-ion battery every 48 hours of storage, leave it standing for 1 hour and then test the open circuit voltage (OCV), internal resistance (IMP), and measure the battery volume by the drainage method after cooling to room temperature. The drainage method is to first measure the gravity F1 of the battery alone with a balance that automatically performs unit conversion of the dial data, and then place the lithium-ion battery completely in deionized water (the known density is 1g / cm 3) Measure the gravity F2 of the battery at this time, and the buoyancy F of the battery 浮 is F1 - F2. Then, according to Archimedes' principle F 浮 = ρ×g×V, calculate the battery volume V = (F1 - F2) / (ρ×g).

[0222] Judging from the OCV and IMP test results, during this test process until storage ended, the batteries of the examples always maintained an SOC of over 99%.

[0223] After storing for 30 days, measure the battery volume and calculate the percentage increase in the battery volume after storage relative to the battery volume before storage.

[0224] Test result

[0225] The test results are shown in Table 1.

[0226] Table 1

[0227]

[0228] In Table 1, the mass content of the carbon skeleton structure is calculated based on the total mass of the positive electrode active material.

[0229] The mass content of the oxygen-containing group is calculated based on the total mass of the coating layer.

[0230] The mass content of the P element is calculated based on the total mass of the coating layer.

[0231] In Examples 1 to 5, the phosphate particles in the positive electrode active material include a compound with the molecular formula Li 0.994 Mn 0.65 Fe 0.35 Mo 0.001 P 0.999 Si 0.001 O 3.999 F 0.001 ;

[0232] In Example 6-1, the phosphate particles in the positive electrode active material include a compound with the molecular formula Li 0.994 Mn 0.5 Fe 0.5 Mo 0.00 1 P 0.999 Si 0.001 O 3.999 F 0.001 ;

[0233] In Example 6-2, the phosphate particles in the positive electrode active material include a compound with the molecular formula Li 0.994 Mn 0.4 Fe 0.6 Mo0.00 1 P 0.999 Si 0.001 O 3.999 F 0.001 compounds.

[0234] In Example 3-2, during the preparation and introduction of polytetrafluoroethylene, oxygen in the air may be carried, resulting in the presence of some oxygen elements in the coating layer.

[0235] In Comparative Example 1, the positive electrode active material contains phosphate particles. When detecting the content of P element, the phosphate particles may interfere with the detection, resulting in the detected mass content of P element being greater than 0.

[0236] Table 2

[0237]

[0238] As can be seen from Table 1 and Table 2, during the carbon coating of phosphate particles, oxygen-containing groups may be introduced. The reaction activity of oxygen-containing groups is relatively high, and they are prone to side reactions with the electrolyte, deteriorating the performance of the battery.

[0239] In the examples of the present application, by further introducing 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 overall coating layer, weaken the overall catalytic activity of the coating layer, reduce the side reaction between the coating layer and the electrolyte, and improve the cycle performance of the battery monomer. The examples of the present application can also effectively reduce the dissolution amounts of Fe and Mn after cycling, and the dissolution amounts ≤ 849 ppm. The specific capacity of the positive electrode active material in the coin cell in the examples of the present application is 130 mAh / g to 155 mAh / g.

[0240] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments cannot be construed as limitations on the present application, and the embodiments can be changed, substituted, and modified without departing from the spirit, principle, and scope of the present application.

Claims

1. A positive electrode active material, comprising: phosphate particles; and a coating layer disposed on at least a part of the surface of the phosphate particles, the coating layer comprising a carbon framework structure and a phosphorus-containing group connected to the carbon framework 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 framework structure; based on the total mass of the coating layer, the mass content of oxygen element in the oxygen-containing group ≤ 3.5%; optionally, the mass content of oxygen element in the oxygen-containing group ≤ 3.0%.

3. The positive electrode active material according to claim 2, wherein, the oxygen-containing group comprises at least one of hydroxyl group, carbonyl group, carboxyl group, ester group, 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 element in the phosphorus-containing group is 0.5% to 5.5%; optionally, the phosphorus-containing group comprises at least one of phosphate group, 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 framework structure is greater than 0 and less than or equal to 6%, and can be 2% to 5%.

6. The positive electrode active material according to any one of claims 1 to 5, wherein, The phosphate particles include a compound with the molecular formula Li 1+x Mn 1-y A y P 1-z R z Y w where -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 specific 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 ≤ 500 Ω·cm; optionally, ≤ 390 Ω·cm.

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

9. The method according to claim 8, wherein, the step of mixing the intermediate and the organic phosphorus source, and at least a part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate a phosphorus-containing group to obtain the positive electrode active material, comprises: mixing the intermediate and the organic phosphorus source, and subjecting to heat treatment so that at least a part of the oxygen-containing groups in the carbon layer react with the organic phosphorus source to generate a phosphorus-containing group to obtain the 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, tetrabenzyl pyrophosphate; and / or the organic carbon source comprises at least one of saccharide compounds, olefin polymers, polyvinyl alcohol, polyethylene glycol, citric acid, toluene; optionally, the organic carbon source comprises at least one of olefin polymers, toluene.

11. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material according to any one of claims 1 to 7, or the positive electrode active material prepared by the method according to 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 according to claim 12.

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