Phosphate positive electrode material, preparation method thereof and battery

Abstract

The invention discloses a phosphate positive electrode material, a preparation method thereof and a battery. The phosphate positive electrode material comprises a conductive network skeleton formed by amorphous carbon, wherein active particles are arranged in the conductive network skeleton; each active particle comprises a phosphate core body and a carbon coating layer coating the phosphate core body, and the carbon coating layer is doped with non-metallic elements. According to the phosphate positive electrode material disclosed by the invention, the conductive network skeleton and the carbon coating layer containing the non-metal doped elements of the active particles play a synergistic role in transmission of electrons and lithium ions, so that the electronic conductivity and the ionic conductivity of the phosphate positive electrode material can be effectively improved, and the low-temperature performance of the phosphate positive electrode material is improved. A positive plate in the battery contains a phosphate positive electrode material.

Description

Technical Field

[0001] The present application belongs to the field of electrode materials, and specifically relates to a phosphate positive electrode material, a preparation method thereof, and a battery. Background Art

[0002] Phosphate cathode materials, especially lithium iron phosphate (LiFePO4) cathode materials, have been widely used in the field of energy storage due to their high theoretical specific capacity, stable operating voltage, stable structure, good cyclability, low raw material cost and environmental friendliness.

[0003] However, the electronic conductivity and ionic conductivity of phosphate positive electrode materials such as lithium iron phosphate are low. This is mainly because the intrinsic conductivity and lithium ion diffusion coefficient of phosphate positive electrode materials are very low, which leads to decreased conductivity at low temperatures and a slowdown in the diffusion rate of lithium ions, which in turn causes serious battery capacity decay and increased internal resistance, affecting battery performance. Summary of the invention

[0004] The purpose of the present application is to overcome the above-mentioned deficiencies of the prior art and to provide a phosphate positive electrode material and a preparation method thereof and a battery containing the phosphate positive electrode material, so as to solve the technical problem that the existing phosphate positive electrode material has unsatisfactory low-temperature performance.

[0005] In order to achieve the above application purpose, in the first aspect, the present application provides a phosphate positive electrode material. The phosphate positive electrode material of the present application includes a conductive network skeleton formed by amorphous carbon, and active particles are arranged in the conductive network skeleton; wherein the active particles include a phosphate core and a carbon coating layer coating the phosphate core, and the carbon coating layer is doped with non-metallic elements.

[0006] The phosphate positive electrode material of the present application uses a conductive network skeleton as a loading skeleton for active particles, which is firmly bonded to the active particles, so that the conductive network skeleton and the carbon coating layer doped with non-metallic elements of the active particles can play a synergistic role in the transmission of electrons and lithium ions, which can effectively improve the electronic conductivity and ionic conductivity of the phosphate positive electrode material, and can also control the particle size of the phosphate positive electrode material, thereby improving the low-temperature performance of the phosphate positive electrode material.

[0007] The second aspect of the present application provides a method for preparing the phosphate positive electrode material of the present application. The method for preparing the phosphate positive electrode material of the present application comprises the following steps:

[0008] Preparation of active particle intermediates;

[0009] The active particle intermediate is mixed with the carbon material containing polypyrrole, and then calcined in a protective atmosphere to obtain a phosphate positive electrode material;

[0010] Among them, the carbon source used to form the carbon coating layer contained in the active particles in the phosphate positive electrode material includes a carbon source containing non-metallic elements; the calcination temperature of the calcination treatment includes two relatively set temperature zones, there is a temperature difference between the two temperature zones, and the mixture of the active particle intermediate and the polypyrrole-containing carbon material is set between the two temperature zones.

[0011] The preparation method of the phosphate positive electrode material of the present application comprises the following steps: calcining an active particle intermediate and a carbon material containing polypyrrole, wherein the carbon material containing polypyrrole is carbonized to generate amorphous carbon and constitute a conductive network skeleton; and the active particle intermediate is secondary sintered to generate active particles, so that the active particles are arranged in the conductive network skeleton, thereby achieving a synergistic effect of conducting electrons and ions between the conductive network skeleton and the carbon coating layer containing non-metallic elements in the active particles, thereby improving the electronic conductivity and ionic conductivity of the phosphate positive electrode material, and the prepared phosphate positive electrode material has a high gradation, thereby being able to improve the low-temperature performance of the phosphate positive electrode material.

[0012] In a third aspect of the present application, a battery is provided. The battery of the present application comprises a positive electrode sheet, wherein the positive electrode active material layer of the positive electrode sheet comprises the phosphate positive electrode material of the present application or the phosphate positive electrode material prepared by the preparation method of the present application.

[0013] The positive electrode sheet of the battery of the present application contains the above-mentioned phosphate positive electrode material of the present application. Therefore, the battery of the embodiment of the present application has good low-temperature performance, and further has high energy density and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 A schematic diagram of the structure of a phosphate positive electrode material according to an embodiment of the present application;

[0016] Figure 2 This is another schematic diagram of the structure of the phosphate positive electrode material of the embodiment of the present application;

[0017] Figure 3 These are SEM images of the phosphate positive electrode materials in Examples A1 to A4 of the present application; wherein, Figure a is the SEM image of Example A1, Figure b is the SEM image of Example A2, Figure c is the SEM image of Example A3, and Figure d is the SEM image of Example A4;

[0018] Figure 4 This is a TEM image of the phosphate positive electrode material in Example A4 of the present application; wherein, Figure b is a partial enlarged image of Figure a;

[0019] Figure 5 3C discharge curve diagram of each battery cell in Examples B1 to B4 of the present application at a low temperature of -20°C.

[0020] The reference numerals in the specific implementation manner are as follows:

[0021] 10-conductive network skeleton;

[0022] 20-active particles, 21-phosphate core; 22-carbon coating. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0025] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0026] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0028] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0029] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0030] Phosphate cathode materials have been widely used in electric vehicles and energy storage due to their high theoretical specific capacity, stable operating voltage, stable structure, good cyclability, low raw material cost, non-toxicity, environmental friendliness and good safety performance. For example, in lithium-ion batteries, the products that have been commercialized in cathode materials include lithium manganese oxide, lithium cobalt oxide, ternary materials and lithium iron phosphate (LiFePO4). Among them, lithium iron phosphate materials are very suitable for use in the field of electric vehicles due to their low price, non-toxicity, no environmental pollution, good safety performance and long life, and have huge market opportunities. However, the poor low-temperature performance of phosphate cathode materials such as lithium iron phosphate has always been a bottleneck restricting its application in certain low-temperature environments.

[0031] The reason is that the electronic conductivity and ionic conductivity of phosphate cathode materials such as lithium iron phosphate are low. This is mainly because the intrinsic conductivity of lithium iron phosphate and the diffusion coefficient of lithium ions are very low, which leads to a decrease in its conductivity at low temperatures and a slowdown in the diffusion rate of lithium ions, which in turn causes serious battery capacity decay and increased internal resistance, affecting the performance of the battery. Moreover, as the particles of phosphate cathode materials increase, their electrochemical properties deteriorate sharply, which also leads to a significant decrease in low-temperature performance. For example, at -20°C, the capacity of lithium iron phosphate can only reach 1 / 3 of that at room temperature, and the lithium ion diffusion coefficient is two orders of magnitude lower than that at room temperature; when the temperature drops to -40°C, lithium iron phosphate can only maintain 20% of its capacity at room temperature.

[0032] In order to improve the low-temperature performance of phosphate cathode materials, researchers have mostly used techniques such as morphology and size control, carbon coating, and ion doping to overcome the inherent defects of the material. Among them, metal ion doping is an important method to improve the electrochemical performance of LiFePO4, such as doping titanium ions at the Fe position of LiFePO4. However, although titanium ion doping improves the conductivity of LiFePO4, it is still not ideal and will also affect its compaction density.

[0033] In order to effectively improve the low-temperature performance of phosphate positive electrode materials and further improve their compaction density, the following solution is proposed in the embodiments of the present application.

[0034] [Phosphate cathode material]

[0035] In the first aspect, the embodiments of the present application provide a phosphate positive electrode material. In some embodiments, the phosphate positive electrode material of the embodiments of the present application includes a conductive network skeleton and active particles, and the active particles are arranged in the conductive network skeleton; wherein the conductive network skeleton is formed of amorphous carbon; the active particles are a core-shell structure, which includes a phosphate core and a carbon coating layer coating the phosphate core, and the carbon coating layer is doped with non-metallic elements.

[0036] The amorphous carbon conductive network skeleton contained in the phosphate positive electrode material of the present application embodiment has good electrical conductivity, and the disorder of amorphous carbon increases the specific surface area of ​​the conductive network skeleton, and improves the electronic conductivity and ionic conductivity of the conductive network skeleton. The carbon coating contained in the active particles has good electrical conductivity, and the doping elements contained therein can provide additional electrons and / or holes, and together with the carbon in the carbon coating layer, can significantly improve the charge transport of the carbon coating layer, thereby improving the electrical conductivity of the active particles. Therefore, through the conductive network skeleton and the loaded skeleton of the active particles, the conductive network skeleton is firmly combined with the active particles, and the conductive network skeleton and the carbon coating layer doped with non-metallic elements of the active particles can play a synergistic role in the transmission of electrons and lithium ions, which can effectively improve the electronic conductivity and ionic conductivity of the phosphate positive electrode material, and can also control the particle size of the phosphate positive electrode material, thereby improving the low temperature performance of the phosphate positive electrode material.

[0037] In some embodiments, the active particles contained in the phosphate positive electrode material of the present application embodiment may be embedded in the interior or surface of the conductive network skeleton. Figure 1 As shown, the phosphate positive electrode material includes a conductive network skeleton 10 and active particles 20 , and the active particles 20 are embedded in the interior, surface, etc. of the conductive network skeleton 10 .

[0038] In some embodiments, the conductive network skeleton contained in the phosphate positive electrode material of the present application embodiment can be arranged between two adjacent active particles. Figure 2As shown, the phosphate positive electrode material includes a conductive network skeleton 10 and active particles 20 , and the conductive network skeleton 10 is disposed between two adjacent active particles 20 . At this time, it can be understood that the active particles 20 are partially embedded in the conductive network skeleton 10 .

[0039] No matter how the active particles contained in the phosphate positive electrode material of the embodiment of the present application are arranged on the conductive network skeleton, the conductive network skeleton can be firmly combined with the active particles, so that the conductive network skeleton and the carbon coating layer of the active particles can play a synergistic role in the transmission of electrons and lithium ions, adjust the particle size of the phosphate positive electrode material, and improve the low-temperature performance of the phosphate positive electrode material.

[0040] In some embodiments, the particle size of the phosphate cathode material of the embodiment of the present application is 100-1500nm. In the exemplary embodiment, it can be 100nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1200nm, 1500nm and other typical but non-limiting particle sizes or the range between any two particle sizes. In the embodiment, the phosphate cathode material of the embodiment of the present application includes two types of particles with different particle sizes to form a particle grading, such as a first particle and a second particle, wherein the particle size D1 of the first particle is 100≤D1≤400nm, and the particle size D2 of the second particle is 400≤D2≤1500nm.

[0041] After testing, the phosphate positive electrode material of the embodiment of the present application contains particles with different particle size distributions, and the particle size distribution is within the above-mentioned range, which gives the phosphate positive electrode material of the embodiment of the present application a better grading. On the basis of having good electronic conductivity and ionic conductivity, it has a higher compaction density, thereby improving the capacity density of the electrode sheet.

[0042] Conductive network skeleton:

[0043] In the phosphate cathode material of the embodiment of the present application, the conductive network skeleton and the carbon coating layer contained in the active particles together play a synergistic role in enhancing the electronic conductivity and ionic conductivity of the phosphate cathode material.

[0044] In some embodiments, such as Figure 1 As shown, the conductive network skeleton is distributed in the active particles, so that the active particles are at least embedded in the conductive network skeleton. Figure 1 As shown, the conductive network skeleton can be arranged between two adjacent active particles, that is, the active particles are embedded in the surface of the conductive network skeleton. Regardless of how the conductive network skeleton contacts the active particles, the conductive network skeleton fully exerts the conductive modification effect on the active particles, improves the electronic conductivity and ionic conductivity of the phosphate positive electrode material, and thus can improve the low temperature performance of the phosphate positive electrode material.

[0045] In some embodiments, the conductive network skeleton formed by the amorphous carbon presents a three-dimensional network structure, and at least part of the active particles are embedded in the three-dimensional network structure. The amorphous carbon with a three-dimensional network structure can significantly improve the conductivity and increase the specific surface area of ​​the positive electrode material, thereby significantly improving the ionic conductivity. Therefore, the conductive network skeleton with a three-dimensional network structure can further improve the conductive modification effect on the electrons and ions of the active particles, and further improve the low-temperature performance of the phosphate positive electrode material.

[0046] In some embodiments, the mass percentage of the conductive network skeleton contained in the phosphate positive electrode material of the embodiment of the present application, that is, the mass percentage of the conductive network skeleton in the phosphate positive electrode material of the embodiment of the present application is 0.1wt% to 0.3wt%. In the exemplary embodiment, it can be a typical but non-restrictive content such as 0.1wt%, 0.2wt%, 0.3wt%, or a range between any two content values. The mass content range of both, on the one hand, can give full play to the conductive modification effect of the conductive network skeleton on the ions and electrons of the active particles, further improve the electronic conductivity and ionic conductivity of the phosphate positive electrode material, thereby improving the low temperature performance of the phosphate positive electrode material; on the other hand, it can improve the bonding strength between it and the active particles and improve the structural stability of the phosphate positive electrode material.

[0047] Active particles:

[0048] In the phosphate positive electrode material of the embodiment of the present application, the phosphate core of the active particle naturally contains a lithium phosphate active material. The lithium-containing phosphate active material gives the phosphate positive electrode material of the embodiment of the present application a capacity characteristic, which can be an existing phosphate active material or a phosphate active material improved based on the existing phosphate active material. As in the embodiment, the lithium-containing phosphate active material includes at least one of doped or undoped lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and lithium manganese phosphate. These lithium-containing phosphate active materials have the advantages of high capacity and good safety.

[0049] The carbon coating layer of the active particles can be a complete coating of the phosphate core or a partial coating of the phosphate core. In the embodiment, the thickness of the carbon coating layer is 2 to 5 nm. In the exemplary embodiment, it can be a typical but non-limiting thickness such as 2 nm, 3 nm, 4 nm, 5 nm, or a range between any two thickness values. The carbon coating layer in this thickness range can effectively modify the phosphate core for conductivity. In addition, by adjusting the thickness of the coating layer and the particle size of the phosphate core, the particle size of the active particles can be adjusted, such as adjusting the particle size of the active particles to be controlled within the above particle size range.

[0050] In some embodiments, the graphitization degree of the carbon coating layer of the active particles is higher than the graphitization degree of the conductive network skeleton, thus giving the carbon coating layer high conductivity and mechanical properties, thereby further improving the conductivity and structural stability of the active particles.

[0051] In some embodiments, the non-metallic elements doped in the carbon coating of the active particles include at least one of N and S. These types of non-metallic ions can provide additional electrons and / or holes in the carbon coating, such as N atoms can provide additional electrons, and S atoms can provide additional electron holes, which together with the carbon in the carbon coating can significantly improve the charge transport of the carbon coating, thereby improving the conductivity of the active particles.

[0052] In some embodiments, the content of the non-metallic element doped in the carbon coating layer of the active particles in the phosphate positive electrode material is 500ppm to 1000ppm, and in the exemplary embodiment, it can be 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, etc., which are typical but non-limiting contents, or a range between any two content values. The non-metallic doping elements in this content range can provide an appropriate amount of additional electron holes, and together with the carbon in the carbon coating layer, further improve the charge transport of the carbon coating layer, thereby further improving the conductivity and low temperature performance of the active particles.

[0053] [Preparation method of phosphate positive electrode material]

[0054] In a second aspect, the present application also provides a method for preparing the above phosphate positive electrode material. The method for preparing the phosphate positive electrode material in the present application embodiment comprises the following steps:

[0055] S10: preparing active particle intermediates;

[0056] S20: After mixing the active particle intermediate and the carbon material containing polypyrrole, calcining is performed in a protective atmosphere to obtain a phosphate positive electrode material.

[0057] In the method for preparing the phosphate positive electrode material in the embodiment of the present application, the carbon source used to form the carbon coating layer contained in the active particles in the phosphate positive electrode material includes a carbon source containing non-metallic elements. The calcination temperature of the calcination treatment in step S20 includes two relatively set temperature regions, there is a temperature difference between the two temperature regions, and the mixture of the active particle intermediate and the carbon material containing polypyrrole is set between the two temperature regions.

[0058] The preparation method of the phosphate positive electrode material in the embodiment of the present application comprises the following steps: calcining an active particle intermediate and a carbon material containing polypyrrole, wherein the carbon material containing polypyrrole is carbonized to generate amorphous carbon and constitute a conductive network skeleton; and the active particle intermediate is secondary sintered to generate active particles, so that the active particles are distributed in the conductive network skeleton, thereby achieving a synergistic effect of conducting electrons and ions between the conductive network skeleton and the carbon coating layer containing non-metallic elements in the active particles, thereby improving the electronic conductivity and ionic conductivity of the phosphate positive electrode material, and the prepared phosphate positive electrode material has a high gradation, thereby being able to improve the low-temperature performance of the phosphate positive electrode material.

[0059] In some embodiments, the method for preparing the active particle intermediate comprises the following steps:

[0060] Step S11: mixing the carbon source including non-metallic elements and the raw materials of various source compounds for preparing the phosphate core to form a mixture;

[0061] Step S12: sintering the mixture to obtain an active particle intermediate.

[0062] By preparing the active particle intermediate by this method, a carbon coating layer can be formed on the surface of the phosphate core body, and non-metallic elements can be doped in the carbon coating layer. At the same time, the particle size of the active particle intermediate can be controlled.

[0063] In the embodiment, in step S11, the carbon source containing non-metallic elements and the source compounds for preparing the phosphate core body are mixed according to the ratio of the content of non-metallic elements in the final generated phosphate positive electrode material to 500ppm to 1000ppm. By controlling the addition amount of the carbon source containing non-metallic elements, the content of non-metallic elements in the generated phosphate positive electrode material is 500ppm to 1000ppm as described in the above phosphate positive electrode material.

[0064] In an embodiment, the carbon source containing non-metallic elements in step S11 may include at least one of a carbon source containing nitrogen and sulfur elements, a nitrogen-containing compound, a sulfur-containing compound and a carbon source. In an embodiment, the carbon source containing nitrogen and sulfur elements may include thiourea (CH4N2S). In a further embodiment, the nitrogen-containing compound may include but is not limited to at least one of thiourea (CH4N2S), urea, dicyandiamide, and melamine; the sulfur-containing compound may include but is not limited to at least one of thiourea (CH4N2S), sulfur, and L-cysteine. In this way, thiourea can simultaneously provide doped non-metallic atoms of sulfur and nitrogen, participate in the formation of the carbon coating during the sintering process, and affect the structure of the carbon in the carbon coating, introduce additional electrons or holes, thereby improving the electron transport capacity of the carbon-containing coating and improving the conductivity. In addition, the thiourea can also replace part of the carbon source to save costs. In an embodiment, the carbon source may also include at least one of glucose, sucrose, starch, maltose, or citric acid. These carbon sources can be carbonized during the sintering process to generate a carbon coating doped with non-metallic elements.

[0065] In the embodiment, in step S11, the carbon source containing non-metallic elements is mixed with each source compound in a ratio of 5% to 15% of the total mass of the carbon source containing non-metallic elements to the mass of the phosphate positive electrode material. By controlling the addition amount of the carbon source containing non-metallic elements, the thickness of the carbon coating layer of the active particles in the generated phosphate positive electrode material, such as the phosphate positive electrode material described above, can be 2 to 5 nm.

[0066] The types and mixing ratios of the source compounds used to prepare the phosphate core in step S11 can be selected according to the types of lithium phosphate active materials. For example, when the lithium phosphate active material is lithium iron manganese phosphate, the source compounds include a manganese source, an iron source, a phosphorus source, and a lithium source. And the manganese source, iron source, phosphorus source, and lithium source can be commonly used raw materials for preparing lithium iron manganese phosphate, such as a manganese source can include at least one of manganous sulfate, manganese chloride, manganese nitrate, or manganese acetate.

[0067] The mixing process in step S11 may include but is not limited to stirring, grinding, liquid phase mixing and other mixing methods.

[0068] The sintering treatment in step S12 may be pre-sintering or sintering according to the sintering treatment of the lithium phosphate active material. Through the sintering treatment, each source compound used to prepare the phosphate core body can form an active particle intermediate, and the carbon source containing non-metallic elements is decomposed, carbonized, etc. In the embodiment, the sintering treatment can be performed at a constant temperature of 480-550° C. at a heating rate of 5-20° C. / min under protective gas for 6-10 hours.

[0069] Step S20:

[0070] During the calcination process of the carbon material containing polypyrrole and the active particle intermediate in step S10, the carbon material containing polypyrrole will be carbonized to form amorphous carbon and a conductive network skeleton of the amorphous carbon; and the active particle intermediate is subjected to a secondary sintering treatment to generate active particles, which can be combined with the conductive network skeleton in situ, thereby generating the phosphate positive electrode material of the above-mentioned application embodiment.

[0071] During the calcination process, the active particle intermediate in step S10 is subjected to secondary sintering treatment, which improves the graphitization degree of the carbon coating layer to a certain extent, so that the carbon graphitization degree in the carbon coating layer contained in the generated active particles is higher than that of the conductive network skeleton containing amorphous carbon. The conductivity of the carbon coating layer and the mechanical strength of the coating are improved, and the conductivity and structural stability of the active particles are improved.

[0072] In some embodiments, the carbon material containing polypyrrole is mixed with the active particle intermediate according to the ratio of 5% to 15% of the mass of the carbon material containing polypyrrole to the mass of the phosphate positive electrode material. By controlling the addition amount of the carbon material containing polypyrrole, the mass proportion of the conductive network skeleton in the generated phosphate positive electrode material is 0.1wt% to 0.3wt%, so as to improve the electronic conductivity and ionic conductivity of the generated phosphate positive electrode material, so as to improve the low temperature performance of the phosphate positive electrode material.

[0073] In some embodiments, the carbon material containing polypyrrole may also include polypyrrole, or a combination of polypyrrole and at least one of polyethylene glycol, polystyrene, polyvinyl alcohol, polyethylene and polypropylene. The selected carbon materials of these types can be sintered and carbonized to form amorphous carbon during the calcination process. At the same time, since these carbon materials all have a chain structure, the three-dimensional network structure of the conductive network skeleton is improved, thereby improving the conductivity of the amorphous carbon, and the specific surface area of ​​the conductive network skeleton can be increased, and the electron and ion transport properties of the conductive network skeleton are improved.

[0074] The calcination temperature setting of the calcination treatment in step S20 includes two relatively set temperature zones. Through the two temperature zones with a temperature difference, on the one hand, the calcination temperature range can effectively make the polypyrrole-containing carbon material fully sintered and the active particle intermediate secondary sintered, improve the conductivity of electrons and ions of the generated phosphate positive electrode material, and further improve the structural stability; on the other hand, it can control the particle size distribution of the phosphate positive electrode material, improve the grading of the particles of the phosphate positive electrode material, thereby improving the compaction density and other properties of the phosphate positive electrode material.

[0075] In some embodiments, the two temperature zones of the calcination treatment are set as a first temperature zone and a second temperature zone, the first temperature zone is arranged opposite to the second temperature zone, and there is a temperature difference between the temperatures of the first temperature zone and the second temperature zone. At this time, the mixture of the active particle intermediate and the carbon material containing polypyrrole is arranged between the first temperature zone and the second temperature zone. In an embodiment, the temperature of the calcination treatment can be 650-800°C. In an embodiment, the temperature difference between the first temperature zone and the second temperature zone can be controlled at 30-80°C, and can be optionally 30-50°C. In an exemplary embodiment, the first temperature zone can be arranged above the mixture of the active particle intermediate and the carbon material containing polypyrrole, and the second temperature zone can be arranged below the mixture of the active particle intermediate and the carbon material containing polypyrrole, and the temperature of the first temperature zone is higher than the temperature of the second temperature zone.

[0076] The temperature of the calcination treatment is set to the range of 650-800°C, and the sintering temperature of the calcination treatment is set to two relatively set temperature zones, and there is the above-mentioned temperature difference between the two temperature zones. In this way, the secondary sintering of the active particle intermediates and the formation of the conductive network skeleton can be affected, which ultimately affects the particles of the phosphate positive electrode material, improves the particle grading of the phosphate positive electrode material, and thus improves the generated phosphate positive electrode material particles to have the above-mentioned particle size characteristics and high compaction density.

[0077] In addition, the calcination treatment should be sufficient. For example, in the examples, the calcination treatment time can be 6 to 12 hours at the above calcination treatment temperature.

[0078] In some embodiments, the calcination treatment is performed by heating the temperature to the calcination treatment temperature at a heating rate of 5 to 20° C. / min. The heating rate is used to increase the temperature to the calcination treatment temperature, which can generate a conductive network skeleton and structural stability of the active particles.

[0079] The mixing process in step S20 may include but is not limited to stirring, grinding, liquid phase mixing and other mixing methods.

[0080] [Battery]

[0081] In the third aspect, the embodiment of the present application also provides a battery. The battery of the embodiment of the present application includes necessary components such as a positive electrode sheet, a negative electrode sheet, a diaphragm or a solid electrolyte, and of course other necessary or auxiliary components. Among them, the diaphragm or solid electrolyte is arranged between the positive electrode sheet and the negative electrode sheet. When the battery of the embodiment of the present application is an ion battery, it contains a diaphragm; when the battery of the embodiment of the present application is a solid-state battery, it contains a solid electrolyte.

[0082] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer combined on the surface of the positive electrode current collector. In the embodiment, the positive electrode current collector of the positive electrode can be but not limited to any one of copper foil and aluminum foil.

[0083] The positive electrode active material layer of the positive electrode includes components such as a positive electrode active material binder and a conductive agent, and may further include a lithium supplement material.

[0084] The positive electrode active material in the positive electrode active material layer includes the phosphate positive electrode material of the above-mentioned embodiment of the present application.

[0085] Since the positive electrode sheet of the battery of the embodiment of the present application contains the above-mentioned phosphate positive electrode material of the embodiment of the present application, the battery of the embodiment of the present application has good low temperature performance, such as the discharge capacity of the battery at low temperature 3C can reach 103.91mAh / g. It also has high energy density and cycle performance.

[0086] In the embodiment, the content of the binder in the positive electrode active material layer can be 2wt%-4wt%. In a specific embodiment, the content of the binder can be 2wt%, 3wt%, 4wt% and other typical but non-limiting contents. In a specific embodiment, the binder includes one or more of polyvinylidene fluoride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.

[0087] In the embodiment, the content of the conductive agent in the positive electrode active material layer can be 3wt%-5wt%. In a specific embodiment, the content of the binder can be 3wt%, 4wt%, 5wt% and other typical but non-limiting contents. In a specific embodiment, the conductive agent includes graphite, carbon black, acetylene black, graphene, carbon fiber, C 60 and one or more of carbon nanotubes.

[0088] In the embodiment, the positive electrode preparation process can be: mixing components such as positive electrode active material, conductive agent and binder to obtain positive electrode slurry, coating the positive electrode slurry on the current collector, and preparing the positive electrode through steps such as drying, rolling and die cutting.

[0089] The negative electrode sheet contained in the battery of the embodiment of the present application may be a conventional negative electrode sheet. When the negative electrode sheet is a metal lithium foil, the lithium battery of the embodiment of the present application may be a lithium metal battery.

[0090] The battery of the embodiment of the present application can be assembled according to the existing assembly method of wound cell batteries, cylindrical batteries or laminated cell batteries.

[0091] The following is a description of the phosphate positive electrode material, preparation method, battery, etc. of the present application through a number of specific embodiments.

[0092] 1. Phosphate positive electrode material and preparation method thereof Example:

[0093] Embodiment A1:

[0094] The present embodiment provides a phosphate positive electrode material and a preparation method thereof. The phosphate positive electrode material includes active particles and a conductive network skeleton, wherein the active particles are distributed in the conductive network skeleton of amorphous carbon; wherein the active particles include a lithium iron phosphate core and a carbon coating layer coating the lithium iron phosphate core, wherein the carbon coating layer is doped with S and N elements.

[0095] The method for preparing the phosphate positive electrode material in this embodiment comprises the following steps:

[0096] S1. Preparation of active particle intermediates:

[0097] S11: ferric nitrate, ammonium dihydrogen phosphate and lithium hydroxide are mixed in a ratio of 0.95:1.00:1.04, and 12% by weight of deionized water is added as a dispersant; and 0.5% of manganese acetate is added to obtain a mixed solution A;

[0098] S12: adding 10% by mass of thiourea to the mixed solution A and stirring evenly to obtain a mixed solution B;

[0099] S13: drying solution B to obtain a solid-phase lithium iron phosphate precursor, crushing the precursor and placing it in an atmosphere furnace, sintering it at a constant temperature of 510° C. for 7 h at a heating rate of 5° C. / min under a nitrogen protective atmosphere, keeping the upper and lower temperature zones consistent, and taking out and crushing the material after cooling it to room temperature to obtain an active particle intermediate;

[0100] S2. calcining the mixture of the polypyrrole-containing carbon material and the active particle intermediate:

[0101] The active particle intermediate in step S13 is fully stirred and mixed with 5% polypyrrole, and then the mixture is heated to 700°C in the lower temperature zone at a rate of 10°C / min under a nitrogen atmosphere, and the upper temperature zone is heated to 730°C at the same rate. After the heating is completed, the mixture is kept warm for 10 hours, cooled, and then ground by air jet mill to obtain a phosphate positive electrode material.

[0102] Embodiment A2:

[0103] This embodiment provides a phosphate positive electrode material and a preparation method thereof. Compared with the preparation method of the phosphate positive electrode material in Example A1, the differences are as follows:

[0104] S1. Preparation of active particle intermediates:

[0105] S11: as step S11 in embodiment A1;

[0106] S12: adding 5% by mass of thiourea to the mixed solution A and stirring evenly to obtain a mixed solution B;

[0107] S13: as step S13 in embodiment A1;

[0108] S2. calcining the mixture of the polypyrrole-containing carbon material and the active particle intermediate:

[0109] The active particle intermediate in step S13 is fully stirred and mixed with 10% polypyrrole, and then the mixture is heated to 700°C in the lower temperature zone at a rate of 10°C / min under a nitrogen atmosphere, and the upper temperature zone is heated to 730°C at the same rate. After the heating is completed, the mixture is kept warm for 10 hours, cooled, and then ground by air jet mill to obtain a phosphate positive electrode material.

[0110] Embodiment A3:

[0111] This embodiment provides a phosphate positive electrode material and a preparation method thereof. Compared with the preparation method of the phosphate positive electrode material in Example A1, the differences are as follows:

[0112] S1. Preparation of active particle intermediates:

[0113] S11: as step S11 in embodiment A1;

[0114] S12: as step S12 in embodiment A1;

[0115] S13: as step S13 in embodiment A1;

[0116] S2. calcining the mixture of the polypyrrole-containing carbon material and the active particles:

[0117] The active particle intermediate in step S13 is fully stirred and mixed with 5% polypyrrole, and then the mixture is heated to 700°C in the lower temperature zone at a rate of 10°C / min under a nitrogen atmosphere, and the upper temperature zone is heated to 750°C at the same rate. After the heating is completed, the mixture is kept warm for 10 hours, cooled, and ground by air jet mill to obtain a phosphate positive electrode material.

[0118] Embodiment A4:

[0119] This embodiment provides a phosphate positive electrode material and a preparation method thereof. Compared with the preparation method of the phosphate positive electrode material in Example A1, the differences are as follows.

[0120] The method for preparing the phosphate positive electrode material in this embodiment comprises the following steps:

[0121] S1. Preparation of active particle intermediates:

[0122] S11: as step S11 in embodiment A1;

[0123] S12: adding 5% by mass of thiourea to the mixed solution A and stirring evenly to obtain a mixed solution B;

[0124] S13: as step S13 in embodiment A1;

[0125] S2. calcining the mixture of the polypyrrole-containing carbon material and the active particle intermediate:

[0126] The active particle intermediate in step S13 is fully stirred and mixed with 10% polypyrrole, and then the mixture is heated to 700°C in the lower temperature zone at a rate of 10°C / min under a nitrogen atmosphere, and the upper temperature zone is heated to 750°C at the same rate. After the heating is completed, the mixture is kept warm for 10 hours, cooled, and ground by air jet mill to obtain a phosphate positive electrode material.

[0127] Related performance testing of phosphate positive electrode materials:

[0128] 1. Method for detecting particle size of phosphate cathode material: The phosphate cathode materials in the above-mentioned embodiments are respectively subjected to scanning electron microscope (SEM) analysis, and the particle size of the phosphate cathode material is measured according to the SEM images; wherein the SEM images of Embodiment A1 to Embodiment A3 are as follows: Figure 3 shown.

[0129] 2. Transmission electron microscope (TEM) analysis of phosphate cathode materials: The phosphate cathode materials in the above-mentioned embodiments were subjected to TEM analysis respectively; wherein the TEM image of embodiment A4 is as follows: Figure 4 shown.

[0130] Table 1

[0131]

[0132] From Table 1 and Figure 3 It can be seen from the SEM that the phosphate cathode material has a good gradation, which can improve the compaction density of the phosphate cathode material. For example, the size particle gradation of Example A2 and Example A4 is significantly better than that of Example A1 and Example A3. Therefore, during the calcination process in step S2, expanding the upper and lower temperature zones can better form the gradation and improve the compaction. Therefore, as can be seen from Table 1, the compaction density of the phosphate cathode material in Example A4 can reach 2.60 g / cm 3 .

[0133] Depend on Figure 4 As can be seen from Figure a, the phosphate cathode material in Example A4 contains a conductive network skeleton of amorphous carbon, and the active particles are distributed in the conductive network skeleton of amorphous carbon. Therefore, the conductive network skeleton containing amorphous carbon constructs a three-dimensional conductive network in the phosphate cathode material, which not only improves the conductivity, but also facilitates ion transmission and increases the lithium ion migration rate. Figure 4As can be seen from Figure a, the surface layer of the active particles contains a tightly wrapped graphitized carbon layer with a high degree of graphitization, which is combined with a loosely distributed amorphous carbon conductive network skeleton with a low degree of graphitization.

[0134] 2. Lithium-ion battery example:

[0135] Embodiments B1 to B4 provide a lithium ion battery. Each lithium ion battery is assembled into a lithium ion battery according to the following method:

[0136] 1) Positive electrode:

[0137] The phosphate positive electrode materials provided in Examples A1 to A4 are used as the positive electrode materials of the lithium ion battery Examples B1 to B4 respectively. Under the same conditions, the phosphate positive electrode material: Su-P conductive agent: PVDF binder are mixed in an appropriate amount of NMP in a mass ratio of 98:1:1, and the mixing method is ball milling to prepare a positive electrode slurry; after homogenization-coating-drying-cutting operations, a positive electrode sheet is prepared, and the positive electrode sheet is baked in a vacuum oven at 100°C to remove trace water. Specifically, the positive electrode sheet in the lithium ion battery in Example B1 contains the phosphate positive electrode material in Example A1, the positive electrode sheet in the lithium ion battery in Example B2 contains the phosphate positive electrode material in Example A2, and so on, the positive electrode sheet in the lithium ion battery in Example B4 contains the phosphate positive electrode material in Example A4.

[0138] 2) Negative electrode sheet: The negative electrode active material graphite, conductive agent Super P, thickener carboxymethyl cellulose (CMC), and binder styrene butadiene rubber (SBR) are mixed evenly in deionized water to form a negative electrode slurry, wherein the mass ratio of graphite: Super P: CMC: SBR is 95:2:0.5:2.5. The negative electrode slurry is coated on the current collector copper foil, and after drying-rolling-secondary drying process, the negative electrode sheet is made.

[0139] 3) Diaphragm: 20μm-PP.

[0140] 4) Electrolyte: SW2001A.

[0141] 5) Assembly of secondary batteries:

[0142] The positive electrode sheet, negative electrode sheet, electrolyte and separator are assembled into a lithium-ion soft pack battery according to the lithium-ion battery assembly requirements. The specifications of the soft pack battery are shown in Table 2 below:

[0143] Table 2

[0144]

[0145] Related performance testing of lithium-ion batteries:

[0146] The lithium-ion batteries of each embodiment assembled in Section 5) were subjected to relevant performance tests as shown in Table 3 below, and the measured results are shown in Table 3 below.

[0147] Among them, the relevant performance test methods in Table 3 are as follows:

[0148] The test method of specific capacity of lithium-ion battery cells is as follows: after the capacity of each lithium-ion battery is divided, three battery cells with similar capacity are selected, and at room temperature of 25°C, they are first discharged at 1C constant current with a cut-off voltage of 2V, and then fully charged at 1C constant current and constant voltage with a cut-off voltage of 3.65V; after the room temperature charging is completed, they are left at -20°C for 2h, and finally discharged at 3C constant current with a cut-off voltage of 1.5V. Among them, the 3C discharge curves of each lithium-ion battery in Example B1 to Example B4 at -20°C are as follows: Figure 5 shown.

[0149] Table 3

[0150]

[0151] Combined with Table 1 above, it can be seen from the test results in Table 3 that the battery cell containing the phosphate positive electrode material of the embodiment of the present application still has good discharge performance at -20°C, and the specific capacity under 3C discharge conditions is higher than 93 mAh / g, among which the specific capacity in Example B2 can reach 103.91 mAh / g.

[0152] On this basis, the lithium iron phosphate positive electrode material in the prior art was assembled into a lithium ion battery according to the assembly method in the above lithium ion battery embodiment as a control lithium ion battery, and the lithium ion battery cell specific capacity and discharge capacity were tested under the same conditions. The specific capacity of the control lithium ion battery at -20°C and 3C discharge was significantly lower than the specific capacity of each lithium ion battery in Example B1 to Example B4 in Table 3.

[0153] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A phosphate positive electrode material, characterized in that: It comprises a conductive network skeleton formed of amorphous carbon, in which active particles are arranged; wherein the active particles comprise a phosphate core and a carbon coating layer coating the phosphate core, and the carbon coating layer is doped with non-metallic elements.

2. The phosphate positive electrode material according to claim 1, characterized in that: The conductive network skeleton is at least disposed between two adjacent active particles; and / or At least part of the active particles are embedded in the three-dimensional network structure of the conductive network skeleton.

3. The phosphate positive electrode material according to claim 1, characterized in that: The non-metallic element includes at least one of N and S; and / or The content of the non-metallic element in the phosphate positive electrode material is 500ppm to 1000ppm.

4. The phosphate positive electrode material according to any one of claims 1 to 3, characterized in that: The mass proportion of the conductive network skeleton in the phosphate positive electrode material is 0.1wt% to 0.3wt%.

5. The phosphate positive electrode material according to any one of claims 1 to 3, characterized in that: Including at least one of the following (1) to (3): (1) The thickness of the carbon coating layer is 2 to 5 nm; (2) The phosphate contained in the phosphate core includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and lithium manganese phosphate; (3) The phosphate positive electrode material includes a particle size distribution formed by first particles and second particles, wherein the particle size of the first particles is 100 to 400 nm, and the particle size of the second particles is 400 to 1500 nm.

6. A method for preparing a phosphate positive electrode material, characterized in that: The steps include: Preparation of active particle intermediates; The active particle intermediate is mixed with the carbon material containing polypyrrole, and then calcined in a protective atmosphere to obtain a phosphate positive electrode material; Among them, the carbon source used to form the carbon coating layer contained in the active particles in the phosphate positive electrode material includes a carbon source containing non-metallic elements; the calcination temperature of the calcination treatment includes two relatively set temperature zones, there is a temperature difference between the two temperature zones, and the mixture of the active particle intermediate and the polypyrrole-containing carbon material is set between the two temperature zones.

7. The preparation method according to claim 6, characterized in that: The polypyrrole-containing carbon material and the active particle intermediate are mixed in a ratio of 5% to 15% of the mass of the phosphate positive electrode material; and / or The polypyrrole-containing carbon material includes polypyrrole, or a combination of polypyrrole and at least one of polyethylene glycol, polystyrene, polyvinyl alcohol, polyethylene and polypropylene.

8. The preparation method according to claim 6 or 7, characterized in that: The calcination treatment conditions include at least one of the following (1) to (4): (1) heating the mixture to a calcination temperature at a heating rate of 5 to 20° C. / min; (2) One of the two temperature zones is disposed below the mixture, and the other temperature zone is disposed above the mixture, and the temperature of the temperature zone disposed above the mixture is higher than the temperature of the temperature zone disposed below the mixture; (3) The calcination temperature is 650-800°C; (4) The temperature difference between the two temperature zones is 30 to 80°C; and / or The method for preparing the active particle intermediate comprises the following steps: Mixing raw materials including a carbon source containing non-metallic elements and various source compounds for preparing phosphate core bodies to form a mixed material; The mixed material is sintered to obtain the active particle intermediate.

9. The preparation method according to claim 8, characterized in that: The carbon source containing non-metallic elements includes at least one of a carbon source containing nitrogen and sulfur, a nitrogen-containing compound, a sulfur-containing compound and a carbon source; and / or The carbon source containing non-metallic elements comprises thiourea; and / or The carbon source containing non-metallic elements is mixed with the source compounds according to the ratio of the carbon source containing non-metallic elements to 5% to 15% of the mass of the phosphate positive electrode material.

10. A battery, comprising a positive electrode sheet, characterized in that: The positive electrode active material layer of the positive electrode sheet comprises the phosphate positive electrode material according to any one of claims 1 to 6 or the phosphate positive electrode material prepared by the preparation method according to any one of claims 7 to 9.

Images