Lithium-containing phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, and provides a lithium-containing phosphate positive electrode material and a preparation method and application thereof. The lithium-containing phosphate positive electrode material comprises composite particles and a carbon material, wherein the composite particles comprise a lithium-containing phosphate inner core and a carbon shell layer coating the outer surface of the lithium-containing phosphate inner core; the carbon material forms a three-dimensional conductive network among the composite particles, the particle size of the lithium-containing phosphate positive electrode material is nanoscale, and the lithium-containing phosphate positive electrode material is prepared by adopting a solid-liquid combination method. According to the lithium-containing phosphate positive electrode material provided by the invention, the carbon material forms a continuous three-dimensional conductive network among the composite particles, so that a bridge effect can be formed between the composite particles and the three-dimensional conductive network, and the electron transmission efficiency and the lithium ion migration rate of the positive electrode material are remarkably improved; the solid solution reaction kinetics of the positive electrode material is obviously accelerated, and the positive electrode material shows relatively good rate adaptability and low-temperature performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a lithium-containing phosphate-based positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have been widely applied in various fields of human society. Among them, lithium iron phosphate with an olivine structure has become the preferred positive electrode material of power batteries for new energy electric vehicles and hybrid electric vehicles due to its excellent thermal stability, low cost and environmental safety. The lithium iron phosphate has high lattice stability, but its stable olivine structure also leads to poor electronic conductivity and lithium ion diffusion rate, which makes it perform poorly in the scene of large current charge and discharge. Taking the application of electric vehicles in northern China as an example, the low-temperature environment in autumn and winter makes the activity of lithium iron phosphate battery decrease significantly, the diffusion rate of conductive ions decreases significantly, and the number of lithium ions participating in the charge and discharge reaction decreases sharply, which directly leads to the failure of battery power supply or the significant reduction of capacity retention rate. Such performance degradation not only seriously affects the endurance performance and use experience of electric vehicles, but also forms an application barrier in high-end fields such as aerospace that have strict requirements on battery performance, greatly limiting the popularization range of lithium iron phosphate materials. SUMMARY

[0003] The purpose of the present application is to provide a lithium-containing phosphate-based positive electrode material and a preparation method and application thereof, aiming to solve the problems of poor rate performance and poor low-temperature adaptability of the lithium-containing phosphate-based positive electrode material.

[0004] To achieve the above-mentioned application purposes, the technical solutions adopted by the present application are as follows:

[0005] In a first aspect, the present application provides a lithium-containing phosphate-based positive electrode material, which comprises composite particles and carbon materials, the composite particles comprise a lithium-containing phosphate inner core and a carbon shell layer coated on the outer surface of the lithium-containing phosphate inner core; the carbon materials form a three-dimensional conductive network between the composite particles; and the particle size of the lithium-containing phosphate-based positive electrode material is nanoscale, and the lithium-containing phosphate-based positive electrode material is prepared by a solid-liquid combined method.

[0006] In a second aspect, the present application provides a preparation method of a lithium-containing phosphate-based positive electrode material, comprising the following steps:

[0007] Obtaining raw material components comprising a lithium source, an iron source and a phosphorus source according to the stoichiometric ratio in the lithium-containing phosphate;

[0008] Mixing and treating the raw material components, a reactive carbon source and an inert carbon source in a solution system to obtain a mixture, wherein part of the lithium source reacts with the reactive carbon source to form a water-soluble organic lithium source;

[0009] The mixture is subjected to sand milling to obtain a mixed slurry, and then subjected to spray drying, so that the water-soluble organic lithium source forms a three-dimensional network structure around the phosphorus-containing iron particles, to obtain a precursor;

[0010] The precursor is subjected to sintering treatment to obtain a lithium-containing phosphate-based positive electrode material.

[0011] In a third aspect, the application provides a lithium ion battery, comprising a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises the lithium-containing phosphate-based positive electrode material provided in the first aspect or prepared by the preparation method provided in the second aspect.

[0012] The lithium-containing phosphate-based positive electrode material provided in the first aspect of the application comprises composite particles and carbon material. On the one hand, the composite particles have a core-shell structure of "lithium-containing phosphate core-carbon shell". The carbon shell layer can inhibit particle growth and agglomeration, optimize the particle size of the lithium-containing phosphate core, and help to obtain a lithium-containing phosphate-based positive electrode material with smaller particle size, shorten the diffusion path of lithium ions, and improve the diffusion rate of lithium ions. On the other hand, the carbon material forms a continuous three-dimensional conductive network between the composite particles, which means that the carbon material can extend from the surface of one composite particle to the adjacent particle to form a continuous three-dimensional conductive network through the gap between the composite particles, thereby forming a "bridge effect" between the composite particles and the three-dimensional conductive network, building a cross-particle electron transport channel, and shortening the charge conduction path, thereby further improving the electron transport efficiency of the positive electrode material and the migration rate of lithium ions. In this way, thanks to the synergistic effect of the above-mentioned core-shell structure and three-dimensional conductive network, the nanoscale core shortens the diffusion distance of lithium ions, and the carbon shell layer and the three-dimensional conductive network optimize the interface ion conduction and cross-particle electron conduction, respectively. Therefore, during the charging and discharging of the battery, the solid solution reaction kinetics of the positive electrode material is significantly accelerated, the rate adaptability and low-temperature working stability of the positive electrode material are both significantly improved, and the rapid capacity release under high rate conditions is realized.

[0013] The preparation method of the lithium-containing phosphate-based positive electrode material provided in the second aspect of the present application comprises the following steps: preparing a mixed solution by mixing raw material components including a lithium source, a phosphorus source and an iron source with a reactive carbon source and an inert carbon source, then using the reactive carbon source to dissolve part of the lithium source by a liquid phase method to form a water-soluble organic lithium source, so that lithium ions are uniformly distributed in the mixture, thereby achieving anchoring of the lithium ions and being beneficial to avoiding the generation of lithium-poor phosphate due to uneven distribution of the lithium source. The mixture is subjected to sand milling treatment and spray drying by a solid phase method to perform secondary granulation on the mixture to form agglomerated secondary balls. At this time, the water-soluble organic lithium source is enriched on the surface of the phosphorus-containing iron particles, and then forms in-situ carbon coating with a three-dimensional network structure around the phosphorus-containing iron particles. In the subsequent sintering process, the lithium ions uniformly enter the phosphorus-containing iron particles to react to form a lithium-containing phosphate core, and the inert carbon source and the carbon layer with a three-dimensional network structure are carbonized to form a uniform and dense carbon shell layer on the surface of the lithium-containing phosphate core. The presence of the carbon shell layer can effectively inhibit the melting and growth of the lithium-containing phosphate core in the sintering process, thereby optimizing the particle size of the lithium-containing phosphate core and obtaining a positive electrode material with small particle size, so as to reduce the lithium ion diffusion path and improve the lithium ion diffusion rate. Since the organic part of the water-soluble organic lithium source can be topologically entangled by intermolecular forces, the carbon material after sintering can simultaneously coat the composite particles and fill the gaps between the composite particles to form a three-dimensional conductive network between the composite particles, thereby effectively preparing a positive electrode material with the performance of the lithium-containing phosphate-based positive electrode material as described above. Therefore, the combination of the liquid phase method and the solid phase method is beneficial to obtaining a lithium-containing phosphate-based positive electrode material with high electrical conductivity, uniform lithium ion distribution and small particle size, and the method is simple in process and can be mass-produced in industry.

[0014] The lithium ion battery provided in the third aspect of the present application comprises the lithium-containing phosphate-based positive electrode material, and the lithium-containing phosphate-based positive electrode material has ion conductivity, electronic conductivity and small particle size, so that the lithium ion battery has excellent rate performance and low temperature performance. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0016] Figure 1 is the SEM image of the lithium-containing phosphate-based positive electrode material provided in Example 1 of the present application;

[0017] Figure 2 is the SEM image of the lithium-containing phosphate-based positive electrode material provided in Comparative Example 1 of the present application;

[0018] Figure 3 SEM image of the lithium-containing phosphate cathode material provided by Comparative Example 2 of the present application;

[0019] Figure 4 XRD image of the lithium-containing phosphate cathode material provided by Example 1 of the present application. DETAILED DESCRIPTION

[0020] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects clearer, the present application will be further described in detail below in conjunction with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0021] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent the following cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0022] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0023] It should be understood that in various embodiments of the present application, the size of the sequence number of the above-mentioned processes does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence. The execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0024] 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 the plural forms, unless the context clearly indicates otherwise.

[0025] The weight of the related components mentioned in the embodiment specification 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 each component. Therefore, as long as the content of the related components in the embodiment specification of the present application is proportionally enlarged or reduced, it is within the scope disclosed in the embodiment specification of the present application. Specifically, the mass mentioned in the embodiment specification of the present application can be μg, mg, g, kg, etc. mass units commonly known in the chemical industry.

[0026] The terms "first", "second" are only for descriptive purposes, used to distinguish objects such as substances from each other, and cannot 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 present application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features.

[0027] The first aspect of the present application provides a lithium-containing phosphate-based positive electrode material, which comprises composite particles and carbon material. The composite particles comprise a lithium-containing phosphate inner core and a carbon shell layer coated on the outer surface of the lithium-containing phosphate inner core. The carbon material forms a three-dimensional conductive network between the composite particles, and the particle size of the lithium-containing phosphate-based positive electrode material is nanoscale. The lithium-containing phosphate-based positive electrode material is prepared by a solid-liquid combined method.

[0028] In the technical solution of the present application, the composite particles have a core-shell structure, specifically, the outer surface of the lithium-containing phosphate inner core is coated with a carbon shell layer. The carbon shell layer, on the one hand, can optimize the particle size of the lithium-containing phosphate inner core by inhibiting particle growth and agglomeration, which is beneficial to obtain a lithium-containing phosphate-based positive electrode material with nanoscale particle size, shorten the diffusion path of lithium ions, and improve the diffusion rate of lithium ions; on the other hand, the carbon shell layer can effectively improve the electronic conductivity of the lithium-containing phosphate inner core, reduce the interface resistance, and thus facilitate the extraction and embedding of lithium ions and promote the charge transfer on the material interface.

[0029] The carbon material can form a three-dimensional conductive network between the composite particles, which means that the carbon material can fill the gap between adjacent particles and extend from the surface of one particle to the adjacent particle to form a continuous three-dimensional conductive network by extending across the particles, thereby forming a "bridge effect" between the composite particles and the three-dimensional conductive network of carbon, constructing an inter-particle electron transport channel, and shortening the charge conduction path, thereby further improving the electron transport efficiency of the positive electrode material and the migration rate of lithium ions.

[0030] Based on this, the solid-liquid combined mode is adopted in the present application, the synergistic effect of the core-shell structure and the three-dimensional conductive network is utilized, the refined core is used to shorten the lithium ion diffusion distance, and the carbon shell layer and the three-dimensional conductive network are respectively used to optimize the interface ion conduction and the cross-particle electron conduction. In this way, during the charging and discharging of the battery, the solid solution reaction kinetics of the positive electrode material is significantly accelerated, so that the rate adaptability and the low-temperature working stability of the positive electrode material are both significantly improved, and the rapid capacity release under high rate conditions is realized.

[0031] In some embodiments, the thickness of the carbon shell layer is 1 nm-5 nm.

[0032] For example, the thickness of the carbon shell layer can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, etc. typical but non-limiting values.

[0033] The thickness of the carbon shell layer is within the above range, which not only can effectively coat the lithium-containing phosphate core, realize the optimization of the particle size of the lithium-containing phosphate core, thereby being conducive to obtaining a positive electrode material with smaller particle size, so that the lithium ion has a shorter transmission path, improves the lithium ion diffusion rate, gives the positive electrode material higher ionic conductivity and electronic conductivity, thereby helping to improve the rate performance and low-temperature performance of the battery.

[0034] In some embodiments, in the lithium-containing phosphate-based positive electrode material, the carbon content is 1%-5%.

[0035] For example, in the lithium-containing phosphate-based positive electrode material, the carbon content can be 1%, 2%, 3%, 4%, 5%, etc. typical but non-limiting values.

[0036] In the present application, the carbon content refers to the total mass percentage of carbon elements in the lithium-containing phosphate-based positive electrode material, specifically including the total mass percentage of the carbon shell layer and the carbon material in the composite particles.

[0037] The carbon content is within the above range, which means that there is sufficient carbon source in the lithium-containing phosphate-based positive electrode material, not only can form a carbon shell layer to coat the lithium-containing phosphate core, but also has a certain amount of carbon material to form a continuous conductive network between the composite particles, thereby helping to obtain a positive electrode material with faster lithium ion diffusion rate and higher electron transmission rate.

[0038] In some embodiments, the morphology of the composite particles in the lithium-containing phosphate-based positive electrode material is spherical.

[0039] The spherical particles have high radial symmetry, which makes the diffusion path of lithium ions from the surface to the core approximately equal, thereby helping to shorten the lithium ion diffusion distance, improve the diffusion coefficient of lithium ions, and improve the rate performance of the positive electrode material. Moreover, the spherical surface curvature is uniform, which promotes the uniform occurrence of the solid solution reaction (such as the extraction-embedding of lithium ions) on the particle surface, effectively inhibits the structure distortion caused by local phase change, and prolongs the battery life.

[0040] In some embodiments, the lithium-containing phosphate core includes a molecular formula of LiMn x Fe 1-x-y M y Active material of PO4, 0≤x≤0.5, 0≤y≤0.1, M includes at least one of V, Mg, and Ti.

[0041] As an example, the lithium phosphate core may be at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium iron vanadium phosphate, lithium iron magnesium phosphate, and lithium iron titanium phosphate.

[0042] In some embodiments, the secondary particles of the lithium-phosphate-based positive electrode material have a particle size of 50 nm to 200 nm.

[0043] For example, the secondary particle size of the lithium-containing phosphate-based positive electrode material can be typical but non-limiting values ​​such as 50 nm, 60 nm, 70 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, and 200 nm.

[0044] The secondary particle size of lithium-containing phosphate cathode materials falls within the aforementioned range. On the one hand, the smaller particle size significantly shortens the lithium-ion diffusion path, significantly improving the diffusion kinetics of lithium ions. On the other hand, the nano-sized grains effectively reduce inter-lattice stress, significantly reducing the kinetic resistance of lithium ions in solid solution reactions (such as Li+ intercalation and deintercalation). Therefore, the short diffusion path and low lattice stress together accelerate the solid solution reaction process, significantly increasing the insertion and deintercalation rate of Li+ during charge and discharge, thereby endowing the material with excellent rate adaptability and low-temperature operating stability.

[0045] In some embodiments, the particle size D50 of the lithium phosphate-based positive electrode material is 80 nm to 120 nm.

[0046] For example, the particle size D50 of the lithium-containing phosphate-based positive electrode material may be 80 nm, 90 nm, 100 nm, 120 nm, or other typical but non-limiting values.

[0047] In this article, D50 particle size is the particle size value when the cumulative distribution percentage reaches 50%, also known as median diameter or median particle size.

[0048] In some embodiments, the lithium ion diffusion coefficient of the lithium phosphate-based cathode material is greater than 9×10 -13 cm 2 / S.

[0049] As an example, the lithium ion diffusion coefficient of lithium phosphate-based cathode materials is 9.1×10 -13 cm 2 / S~9.8×10-13 cm 2 / S.

[0050] Lithium ion diffusion coefficient is a physical quantity describing the migration rate of lithium ions in solid, liquid or gas medium, representing the diffusion ability of lithium ions under the driving of concentration gradient, and the unit is cm 2 / S.

[0051] Lithium ion diffusion coefficient can reflect the migration difficulty of lithium ions in the material, and the lithium ion diffusion coefficient in the present application is high, which indicates that the faster the diffusion speed of lithium ions in the medium, the better the electrochemical kinetics performance of the positive electrode material, so that the positive electrode material exhibits high rate performance and good low temperature adaptability.

[0052] In some embodiments, the 5C discharge capacity of the lithium-containing phosphate-based positive electrode material is greater than or equal to 135 mAh / g.

[0053] For example, the 5C discharge capacity of the lithium-containing phosphate-based positive electrode material is 135 mAh / g to 140 mAh / g.

[0054] In some embodiments, the 10C discharge capacity of the lithium-containing phosphate-based positive electrode material is greater than or equal to 124 mAh / g.

[0055] For example, the 10C discharge capacity of the lithium-containing phosphate-based positive electrode material is 124 mAh / g to 130 mAh / g.

[0056] In some embodiments, the 20C discharge capacity of the lithium-containing phosphate-based positive electrode material is greater than or equal to 113 mAh / g.

[0057] For example, the 20C discharge capacity of the lithium-containing phosphate-based positive electrode material is 113 mAh / g to 121 mAh / g.

[0058] The discharge capacity of the lithium-containing phosphate-based positive electrode material at 5C, 10C and 20C is within the above range, which indicates that the lithium-containing phosphate-based positive electrode material has high capacity at high rate.

[0059] This indicates that the embodiments of the present application refine the particle size of the lithium-containing phosphate-based positive electrode material, shorten the diffusion distance of lithium ions, and cooperate with the carbon shell layer and the three-dimensional conductive network, so that the lithium ions have a high diffusion coefficient under high rate conditions, thereby making the positive electrode material exhibit excellent rate performance.

[0060] In some embodiments, the 0.2C discharge capacity of the lithium-containing phosphate-based positive electrode material at -20℃ is greater than or equal to 110 mAh / g.

[0061] For example, the lithium-containing phosphate-based positive electrode material has a 0.2C discharge capacity of 110 mAh / g to 120 mAh / g at -20°C.

[0062] In some embodiments, the lithium-containing phosphate-based positive electrode material has a 1C discharge capacity greater than or equal to 100 mAh / g at -20°C.

[0063] For example, the lithium-containing phosphate-based positive electrode material has a 1C discharge capacity of 100 mAh / g to 110 mAh / g at -20°C.

[0064] In some embodiments, the lithium-containing phosphate-based positive electrode material has a 5C discharge capacity greater than or equal to 90 mAh / g at -20°C.

[0065] For example, the lithium-containing phosphate-based positive electrode material has a 5C discharge capacity of 90 mAh / g to 100 mAh / g at -20°C.

[0066] The lithium-containing phosphate-based positive electrode material has a discharge capacity of 0.2C, 1C and 5C at low temperature (for example, -20°C) within the above range, which indicates that the lithium-containing phosphate-based positive electrode material has a high capacity at low temperature.

[0067] This indicates that the embodiments of the present application can improve the lithium ion diffusion capacity by refining the particle size of the lithium-containing phosphate-based positive electrode material, build a cross-particle electron transport channel by using the carbon material to form a three-dimensional conductive network in the gap between the composite particles, shorten the charge conduction path, further improve the electron transport efficiency of the positive electrode material and the migration rate of lithium ions, and at the same time, the three-dimensional conductive network combined with the carbon shell layer can play a stress buffering role, inhibit the lattice distortion caused by lithium ion deintercalation at low temperature, improve the continuity of the solid solution reaction, so that the positive electrode material exhibits good low temperature adaptability.

[0068] The second aspect of the embodiments of the present application provides a preparation method of a lithium-containing phosphate-based positive electrode material, characterized in that the method comprises the following steps:

[0069] Step S10: obtaining raw material components including a lithium source, an iron source and a phosphorus source according to the stoichiometric ratio in the lithium-containing phosphate;

[0070] Step S20: mixing and processing the raw material components and a reactive carbon source and an inert carbon source in a solution system to obtain a mixture, wherein part of the lithium source reacts with the reactive carbon source to form a water-soluble organic lithium source;

[0071] Step S30: obtaining a mixed slurry after sand milling treatment of the mixture, and then performing spray drying, so that the water-soluble organic lithium source forms a three-dimensional network structure around the phosphorus-iron particles to obtain a precursor;

[0072] S40, sintering the precursor to obtain the lithium-containing phosphate-based positive electrode material.

[0073] The method for preparing the lithium-containing phosphate-based positive electrode material provided in the second aspect of the embodiments of the present application adopts a liquid-solid combined method, which is beneficial to obtaining the lithium-containing phosphate-based positive electrode material with high electrical conductivity, uniform lithium ion distribution and small particle size.

[0074] After the raw material components including a lithium source, a phosphorus source and an iron source are prepared into a mixed solution with a reactive carbon source and an inert carbon source, the lithium source is dissolved by the reactive carbon source using a liquid phase method to form a water-soluble organic lithium source, so that the lithium ions are uniformly distributed in the mixture, which is beneficial to avoiding the generation of lithium-poor phase phosphate due to uneven distribution of the lithium source.

[0075] The mixture is subjected to secondary granulation by sand milling treatment and spray drying using a solid phase method to form agglomerated secondary balls. At this time, the water-soluble organic lithium source is enriched on the surface of the phosphorus-containing iron particles, the anchoring of the lithium ions is realized, and then an in-situ carbon coating with a three-dimensional network structure is formed around the phosphorus-containing iron particles. In this way, in the subsequent sintering process, the lithium ions more uniformly enter the phosphorus-containing iron particles to react to form a lithium-containing phosphate core. The inert carbon source and the carbon layer with a three-dimensional network structure are carbonized to form a uniform and dense carbon shell layer on the surface of the lithium-containing phosphate core. The presence of the carbon shell layer can effectively inhibit the melting and growth of the lithium-containing phosphate core in the sintering process, realize the optimization of the particle size of the lithium-containing phosphate core, and obtain a positive electrode material with small particle size, thereby reducing the lithium ion diffusion path and improving the lithium ion diffusion rate. Since the organic part in the water-soluble organic lithium source can be topologically entangled by intermolecular forces, the carbon material after sintering can simultaneously coat the composite particles and fill the gaps between the composite particles, forming a three-dimensional conductive network between the composite particles, and then effectively preparing a positive electrode material with the performance as described above.

[0076] Therefore, the embodiments of the present application combine the liquid phase method and the solid phase method, which not only can reduce the risk of loss of lithium ions and uneven distribution of lithium ions in the sintering process, but also can inhibit the generation of magnetic impurities such as iron phosphide due to uneven heating of part of the particles under high temperature conditions in the calcination process, and obtain a lithium-containing phosphate-based positive electrode material with good uniformity and excellent electrochemical performance.

[0077] In some embodiments, in step S10, the lithium source includes at least one of lithium carbonate (Li2CO3), lithium dihydrogen phosphate (LiH2PO4), lithium hydroxide (LiOH·H2O), lithium acetate (CH3COOLi), and lithium nitrate (LiNO3).

[0078] The lithium source can react with the water-soluble functional carbon source in the solution system to form a water-soluble organic lithium source, so as to promote the lithium ions to be more uniformly anchored on the surface of the phosphorus-containing iron particles.

[0079] Specifically, the lithium source includes the following typical but non-limiting combinations: lithium carbonate-lithium dihydrogen phosphate, lithium hydroxide-lithium dihydrogen phosphate, lithium carbonate-lithium hydroxide, lithium carbonate-lithium acetate, lithium nitrate-lithium acetate.

[0080] Further, the lithium source includes a lithium carbonate-lithium dihydrogen phosphate combination or a lithium carbonate-lithium hydroxide.

[0081] The lithium source in the above combination can supplement the phosphate in the reaction system or adjust the pH of the mixed system, thereby helping to obtain a lithium phosphate-based positive electrode material with better uniformity, regular morphology, and smaller particle size.

[0082] In some embodiments, in step S10, the iron source includes iron phosphate (FePO4) and at least one iron-containing compound selected from iron nitrate (Fe(NO3)3), iron oxide (Fe2O3), and ferrous sulfate (FeSO4·7H2O).

[0083] Specifically, the iron source includes the following typical but non-limiting combinations: iron phosphate-iron oxide, iron phosphate-iron nitrate, and iron phosphate-ferrous sulfate.

[0084] Iron phosphate is almost insoluble in water, which makes the mixture of raw material components and reactive carbon source and inert carbon source in the solution system a suspension including solid particles. At this time, solid-phase grinding can be used to obtain a slurry with a suitable particle size, so as to form a lithium phosphate-based positive electrode material with a smaller particle size in the sintering process.

[0085] In some embodiments, in step S10, the phosphorus source includes at least one of iron phosphate (FePO4), ammonium phosphate ((NH4)3PO4), ammonium dihydrogen phosphate (NH4H2PO4), lithium dihydrogen phosphate (LiH2PO4), and phosphoric acid (H3PO4).

[0086] Specifically, the phosphorus source includes the following typical but non-limiting combinations: iron phosphate-ammonium phosphate, iron phosphate-ammonium dihydrogen phosphate, and iron phosphate-lithium dihydrogen phosphate.

[0087] In some embodiments, in step S10, the raw material components further include a manganese source.

[0088] For example, the manganese source may include, but is not limited to, at least one of manganese carbonate, manganese fluoride, manganese bromide, manganese chloride, manganese nitride, manganese carbide, manganese phosphide, manganese phosphate, manganese dihydrogen phosphate, manganese nitrate, manganese sulfate, manganese hydrogen phosphate, manganese pyrophosphate, potassium permanganate, potassium manganate, manganese acetate, manganese oxalate, manganese pentacarbonyl, manganese decacarbonyl, manganese acetate, manganese acetylacetonate, and manganese pyrophosphate.

[0089] In some embodiments, in step S10, the raw material components further include a doping metal source, and the doping metal source includes at least one of a manganese source, a vanadium source, a magnesium source, and a titanium source.

[0090] Exemplarily, the doping metal source includes a salt corresponding to the metal element, such as at least one of nitrate, chloride, bromide, fluoride, phosphate, acetate, and sulfate.

[0091] In some embodiments, in step S20, the reactive carbon source includes at least one of citric acid, ethylenediaminetetraacetic acid, tartaric acid, polymaleic acid, polyacrylic acid, polystyrene acid, and polysulfonate polymer.

[0092] Furthermore, the reactive carbon source includes citric acid and at least one selected from the following compounds: ethylenediaminetetraacetic acid, tartaric acid, polymaleic acid, polyacrylic acid, polystyrene acid and polysulfonate polymer.

[0093] The role of these reactive carbon sources is: first, they react with the lithium source by containing carboxyl, sulfonylamino, and sulfonate groups, so that part of the lithium source reacts to form a water-soluble organic lithium source; second, the water-soluble organic lithium source uses intermolecular forces to form topological entanglements, such as intermolecular hydrogen bonds or physical entanglements, so that after spray drying, the water-soluble organic lithium source can form a three-dimensional network structure around the phosphorus-containing iron particles. For example, citric acid can form a three-dimensional network structure through hydroxyl hydrogen bonds and Li+-carboxylate coordination bonds, enhancing stability; polymaleic acid, polyacrylic acid, polystyrene acid, and polysulfonate polymers, etc., contain high molecular weight long chains that are prone to topological entanglement, forming a reversible physical cross-linked network, that is, forming a three-dimensional network structure.

[0094] In some embodiments, in step S20, the inert carbon source includes at least one of polyethylene glycol, glucose, lactose, and sucrose.

[0095] The carbon sources can be sintered to form amorphous carbon, and the amorphous carbon is coated on the surface of the lithium phosphate core to form a carbon shell.

[0096] In some embodiments, in step S20, based on the total mass of the reactive carbon source and the inert carbon source being 100%, the content of the reactive carbon source is 1%-60%.

[0097] Exemplarily, the content of the reactive carbon source can be 1%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, etc., which are typical but non-limiting values.

[0098] Within the above range, the reactive carbon source can fully play a role in dissolving lithium to form a water-soluble organic lithium source; at the same time, the risk of subsequent spray drying caused by excessively high viscosity of the system is reduced.

[0099] In some embodiments, in step S20, the total mass percentage of the reactive carbon source and the inert carbon source in the total mass of the raw material components is 1%-20%.

[0100] Exemplarily, the total mass percentage of the reactive carbon source and the inert carbon source can be 1%, 5%, 10%, 15%, 20%, etc., which are typical but non-limiting values.

[0101] In some embodiments, in step S20, the D50 particle size of the particles in the mixed slurry is 0.2 μm-0.8 μm.

[0102] Exemplarily, the D50 particle size of the particles in the mixed slurry can be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, etc., which are typical but non-limiting values.

[0103] The raw material components are broken by the solid phase grinding process, and the mixed material with the D50 particle size in the above range is obtained, which is beneficial to obtaining the lithium-containing phosphate-based positive electrode material with moderate particle size after sintering treatment.

[0104] In some embodiments, in step S20, the conditions of the sand milling treatment include: the rotation speed is 500 rpm-2000 rpm, and the grinding medium includes at least one of zirconium balls with a diameter of 0.8 μm and zirconium balls with a diameter of 0.3 μm.

[0105] Exemplarily, the rotation speed can be 500 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, etc., which are typical but non-limiting values.

[0106] The raw material components are broken by the sand milling process, and the parameters of the sand milling process are controlled within the above range, so as to perform particle size refinement treatment on the raw material components, thereby obtaining the mixed material with moderate particle size and uniform mixing of each component, avoiding the formation of positive electrode materials with excessively large or small particle size after sintering due to excessively large or small particle size of the mixed material.

[0107] In some embodiments, in step S30, the spray drying conditions include: an inlet air temperature of 150-200°C, an outlet air temperature of 40-60°C, a centrifugal frequency of 300-340Hz, and a feed pump rotation speed of 20-60rpm.

[0108] For example, the inlet air temperature can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc., the outlet air temperature can be 40°C, 45°C, 50°C, 55°C, 60°C, etc., the centrifugal frequency can be 300Hz, 310Hz, 320Hz, 330Hz, 340Hz, etc., and the feed pump rotation speed can be 20rpm, 30rpm, 40rpm, 50rpm, 60rpm, etc.

[0109] The spray drying described above is a centrifugal spray drying, and each parameter is controlled within the above range. The mixture is subjected to secondary granulation by spray drying to form agglomerated secondary balls, and the particle size and morphology regularity of the precursor are effectively controlled to form a precursor with high sphericity and moderate particle size, thereby avoiding uneven heating of some particles during the calcination process, resulting in the formation of magnetic foreign bodies such as iron phosphide under high temperature conditions.

[0110] In some embodiments, in step S40, the sintering process includes first sintering and second sintering performed in sequence; wherein the first sintering includes sintering at 300-450°C for 3-6h at a temperature rising rate of 2-15°C / min, and the second sintering includes sintering at 550-750°C for 4-8h at a temperature rising rate of 2-15°C / min.

[0111] Specifically, the sintering process is performed in a protective atmosphere, for example, the protective atmosphere includes at least one of nitrogen, argon, argon-hydrogen mixed atmosphere, and nitrogen-hydrogen mixed atmosphere.

[0112] For example, the temperature of the first sintering can be 300°C, 350°C, 380°C, 400°C, 450°C, etc., the time can be 3h, 4h, 5h, 6h, etc., and the temperature rising rate can be 2°C / min, 4°C / min, 6°C / min, 8°C / min, 10°C / min, 15°C / min, etc.

[0113] Exemplarily, the temperature of the second sintering treatment can be a typical but non-limiting value of 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, etc., the time can be a typical but non-limiting value of 4h, 5h, 6h, 7h, 8h, etc., and the heating rate can be a typical but non-limiting value of 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, 15℃ / min, etc.

[0114] During the sintering treatment, the inert carbon source is gradually carbonized to form amorphous carbon, which is coated on the surface of the lithium-containing phosphate core to form a carbon shell layer. The carbon shell layer can limit the growth of the lithium-containing phosphate core particles to some extent, reducing the occurrence of oversized core particles.

[0115] Since part of the lithium source reacts with the reactive carbon source to form a water-soluble organic lithium source, and the water-soluble organic lithium source is subjected to spray drying, it can form in-situ carbon coating with a three-dimensional network structure around the phosphorus-containing iron particles, which promotes the organic part of the water-soluble organic lithium source to form carbon materials during the sintering treatment, which can cover the surface of the lithium-containing phosphate core and the gap between adjacent lithium-containing phosphate cores. Specifically, the organic part of the water-soluble organic lithium source carbonizes to form carbon materials, which not only can be coated on the surface of the lithium-containing phosphate core to form a carbon shell layer, but also can be filled in the gap between adjacent composite particles to form a three-dimensional conductive network that penetrates the gap between the composite particles. In this way, not only is a conductive network across the particles constructed, effectively reducing the resistivity of the positive electrode material, but also the growth of the lithium-containing phosphate core particles is limited to some extent.

[0116] It can be understood that the amorphous carbon formed after the carbonization of the inert carbon source can coat the lithium-containing phosphate core; the reactive carbon source and part of the lithium source form a water-soluble organic lithium source, and part of the organic part of the water-soluble organic lithium source carbonizes to form carbon materials, which also coat the surface of the lithium-containing phosphate core.

[0117] It can be understood that the amorphous carbon formed after the carbonization of the inert carbon source can coat the lithium-containing phosphate core; the reactive carbon source and part of the lithium source form a water-soluble organic lithium source, and part of the organic part of the water-soluble organic lithium source carbonizes to form carbon materials, which also coat the surface of the lithium-containing phosphate core.

[0118] In a third aspect, the present application provides a lithium ion battery, comprising a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises the lithium-containing phosphate-based positive electrode material provided in the first aspect or the lithium-containing phosphate-based positive electrode material prepared by the preparation method provided in the second aspect.

[0119] The lithium ion battery provided by the third aspect of the embodiments of the present application comprises the lithium-containing phosphate-based cathode material, and the lithium ion battery has excellent rate performance and low-temperature performance due to the ion conductivity, electron conductivity, small particle size and other characteristics of the lithium-containing phosphate-based cathode material.

[0120] In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active layer comprises the lithium-containing phosphate-based cathode material described in any one of the embodiments. In an embodiment of the present application, the positive electrode current collector comprises, but is not limited to, at least one of an aluminum foil, a carbon-coated aluminum foil, an iron foil, a tin foil, a zinc foil, a nickel foil, a titanium foil and a manganese foil. In an embodiment of the present application, the positive electrode current collector can be an aluminum foil.

[0121] In some embodiments, the preparation of the positive electrode active layer comprises the following steps: mixing the lithium-containing phosphate-based cathode material, the conductive agent and the binder to prepare an electrode slurry, and then coating the electrode slurry on the current collector, and performing drying, rolling, die cutting and other steps to prepare the positive electrode sheet.

[0122] In some embodiments, the mass percentage of the lithium-containing phosphate-based cathode material in the positive electrode active layer is 80% to 95%. Specifically, the mass percentage of the lithium-containing phosphate-based cathode material in the positive electrode active material layer can be 80%, 85%, 88%, 90% or 95%.

[0123] In some embodiments, the content of the binder in the positive electrode active layer is 2wt% to 5wt%. In specific embodiments, the content of the binder can be 2wt%, 3wt%, 4wt% or 5wt%.

[0124] In some embodiments, the binder comprises one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene butadiene rubber, hydroxypropyl methyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.

[0125] In some embodiments, the content of the conductive agent in the positive electrode active material layer is 1wt% to 5wt%. In specific embodiments, the content of the conductive agent can be 3wt%, 4wt% or 5wt%.

[0126] In some embodiments, the conductive agent comprises one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotube.

[0127] The negative electrode sheet, the electrolyte and the separator in the lithium ion battery of the embodiments of the present application are not specifically limited, and can be applied to any battery system.

[0128] In some embodiments, the negative active material of the lithium ion battery includes, but is not limited to, graphite, soft carbon (such as coke and the like), hard carbon and the like carbon materials, or nitrides, tin-based oxides, tin-based oxides, tin alloys, and nano negative materials and the like. The current collector includes, but is not limited to, any one of copper foil, aluminum foil.

[0129] In some embodiments, the step of making the negative electrode sheet includes: mixing the negative active material, the conductive agent such as conductive carbon black, the binder such as carboxymethyl cellulose and butadiene rubber, and the solvent such as water in a mass ratio of (80-99):(1-5):(2-10):100 to form a negative electrode mixed slurry, vacuum degassing, discharging, coating on a coating machine, rolling, slitting, and die cutting to obtain the negative electrode sheet.

[0130] In some embodiments, the separator can block electrons and allow ions to pass. For example, the separator includes, but is not limited to, at least one material including polypropylene fibers, polyacrylonitrile fibers, polyvinyl formal fibers, poly(ethylene terephthalate), polyethylene terephthalate, polyamide fibers, and poly(p-phenylene terephthalamide).

[0131] In some embodiments, the electrolyte includes at least one soluble metal salt. In some specific embodiments, the metal salt includes LiClO4, LiBF4, LiPF6, LiAsF6, LiCF3SO3, LiTDI, Li[(CF3SO2)2N], Li[(FSO2)2N].

[0132] In some embodiments, the lithium ion battery can be a secondary battery, which refers to a lithium ion battery that can be activated by charging after discharging to continue to be used. As an example, the lithium ion battery includes at least one of a battery cell, a battery module, and a battery pack.

[0133] To enable the above-mentioned implementation details and operations of the present application to be clearly understood by those skilled in the art, and the performance of the lithium phosphate-based positive electrode material and the preparation method thereof are significantly embodied, the following examples are provided to illustrate the above technical solutions.

[0134] Example 1

[0135] The present embodiment provides a lithium phosphate-based positive electrode material and a preparation method thereof.

[0136] A lithium phosphate-based positive electrode material includes composite particles and carbon materials. The composite particles include a lithium phosphate-containing core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium phosphate-containing core. The carbon materials form a three-dimensional conductive network between the composite particles.

[0137] A preparation method of a lithium phosphate-based positive electrode material includes the following steps:

[0138] Step 1, 833.3g of lithium carbonate (Li2CO3), 4030g of iron phosphate (FePO4), 450g of reactive carbon source (polymaleic acid) and 400g of inert carbon source (polyethylene glycol) are added to 6000g of deionized water, and mixed uniformly to obtain a mixed slurry.

[0139] Step 2, the mixed slurry is added to a horizontal sand mill with a volume of 2L and grinding medium of zirconium balls with a diameter of 0.3μm, and ground at a speed of 1000rpm until the slurry D50 is 0.2μm, to obtain a mixed material.

[0140] Step 3, the mixed material is pumped by a peristaltic pump at a speed of 40rpm to a centrifugal atomization tower at 340Hz for drying, with an inlet air temperature of 180℃ and an outlet air temperature of 50℃, to obtain a precursor (light yellow powder).

[0141] Step 4, the precursor is subjected to a first sintering process and a second sintering process under a nitrogen atmosphere; the first sintering stage is from room temperature to 300℃ at a heating rate of 5℃ / min, and sintered for 4h; the second sintering process is from 300℃ to 650℃ at a heating rate of 5℃ / min, and sintered for 8h; then cooled from 650℃ to room temperature at a cooling rate of 2℃ / min, to obtain a lithium-containing phosphate-based positive electrode material.

[0142] Example 2

[0143] The present embodiment provides a lithium-containing phosphate-based positive electrode material and a preparation method thereof.

[0144] A lithium-containing phosphate-based positive electrode material, comprising composite particles and a carbon material. The composite particles comprise a lithium-containing phosphate core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium-containing phosphate core; the carbon material forms a three-dimensional conductive network between the composite particles.

[0145] A preparation method of a lithium-containing phosphate-based positive electrode material, comprising the following steps:

[0146] Step 1, 833.3g of lithium carbonate (Li2CO3), 4030g of iron phosphate (FePO4), 100g of reactive carbon source (oxalic acid tetraacetate) and 400g of inert carbon source (polyethylene glycol) are added to 6000g of deionized water, and mixed uniformly to obtain a mixed slurry.

[0147] Step 2, the mixed slurry is added to a horizontal sand mill with a volume of 2L and grinding medium of zirconium balls with a diameter of 0.3μm, and ground at a speed of 1000rpm until the slurry D50 is 0.8μm, to obtain a mixed material.

[0148] Step 3, same as step 3 in Example 1.

[0149] Step 4, under the nitrogen atmosphere, the precursor is subjected to a first sintering treatment and a second sintering treatment; the first sintering stage is to increase the temperature from room temperature to 300℃ at a rate of 5℃ / min, and sinter for 4h; the second sintering treatment is to increase the temperature from 300℃ to 750℃ at a rate of 5℃ / min, and sinter for 6h; then decrease the temperature from 750℃ to room temperature at a rate of 2℃ / min, to obtain the lithium-containing phosphate-based positive electrode material.

[0150] Example 3

[0151] The embodiment provides a lithium-containing phosphate-based positive electrode material and a preparation method thereof.

[0152] The lithium-containing phosphate-based positive electrode material comprises composite particles and a carbon material. The composite particles comprise a lithium-containing phosphate inner core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium-containing phosphate inner core; and the carbon material forms a three-dimensional conductive network between the composite particles.

[0153] The preparation method of the lithium-containing phosphate-based positive electrode material comprises the following steps.

[0154] Step 1, the same as step 1 in the embodiment 1.

[0155] Step 2, the same as step 2 in the embodiment 1.

[0156] Step 3, the mixture is pumped into a 300Hz centrifugal atomization tower by using a peristaltic pump at a rotating speed of 20rpm for drying, the inlet air temperature is 180℃, and the outlet air temperature is 50℃, to obtain the precursor (light yellow powder).

[0157] Step 4, under the nitrogen atmosphere, the precursor is subjected to a first sintering treatment and a second sintering treatment; the first sintering stage is to increase the temperature from room temperature to 300℃ at a rate of 5℃ / min, and sinter for 4h; the second sintering treatment is to increase the temperature from 300℃ to 650℃ at a rate of 5℃ / min, and sinter for 6h; then decrease the temperature from 650℃ to room temperature at a rate of 2℃ / min, to obtain the lithium-containing phosphate-based positive electrode material.

[0158] Example 4

[0159] The embodiment provides a lithium-containing phosphate-based positive electrode material and a preparation method thereof.

[0160] The lithium-containing phosphate-based positive electrode material comprises composite particles and a carbon material. The composite particles comprise a lithium-containing phosphate inner core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium-containing phosphate inner core; and the carbon material forms a three-dimensional conductive network between the composite particles.

[0161] The preparation method of the lithium-containing phosphate-based positive electrode material is different from that in the embodiment 1 in that the reactive carbon source is different, and the specific steps are as follows:

[0162] Step 1, 833.3 g of lithium carbonate (Li2CO3), 4030 g of iron phosphate (FePO4), 450 g of reactive carbon source (citric acid: polymaleic acid = 1:1) and 400 g of inert carbon source (polyethylene glycol) were added to 6000 g of deionized water, and mixed uniformly to obtain a mixed slurry.

[0163] Step 2, same as step 2 in example 1.

[0164] Step 3, same as step 3 in example 1.

[0165] Step 4, same as step 4 in example 1.

[0166] Example 5

[0167] The present embodiment provides a lithium-containing phosphate-based positive electrode material and a preparation method thereof.

[0168] A lithium-containing phosphate-based positive electrode material includes composite particles and a carbon material. The composite particles include a lithium-containing phosphate core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium-containing phosphate core. The carbon material forms a three-dimensional conductive network between the composite particles.

[0169] A preparation method of a lithium-containing phosphate-based positive electrode material, which is different from example 1 in that the reactive carbon source is different, and the specific steps are as follows:

[0170] Step 1, 833.3 g of lithium carbonate (Li2CO3), 4030 g of iron phosphate (FePO4), 450 g of reactive carbon source (citric acid: polymaleic acid = 1:1) and 400 g of inert carbon source (polyethylene glycol) were added to 6000 g of deionized water, and mixed uniformly to obtain a mixed slurry.

[0171] Step 2, same as step 2 in example 1.

[0172] Step 3, same as step 3 in example 1.

[0173] Step 4, same as step 4 in example 1.

[0174] Example 6

[0175] The present embodiment provides a lithium-containing phosphate-based positive electrode material and a preparation method thereof.

[0176] A lithium-containing phosphate-based positive electrode material includes composite particles and a carbon material. The composite particles include a lithium-containing phosphate core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium-containing phosphate core. The carbon material forms a three-dimensional conductive network between the composite particles.

[0177] A preparation method of a lithium-containing phosphate-based positive electrode material, which is different from Example 1 in that the spray drying conditions are different, and the specific steps are as follows:

[0178] Step 1, same as Step 1 in Example 1.

[0179] Step 2, same as Step 2 in Example 1.

[0180] Step 3, the mixture is pumped into a 300Hz centrifugal atomization tower with a peristaltic pump at a rotation speed of 40rpm, the inlet air temperature is 200℃, and the outlet air temperature is 40℃, to obtain a precursor (light yellow powder).

[0181] Step 4, same as Step 4 in Example 1.

[0182] Comparative Example 1

[0183] The present comparative example provides a lithium-containing phosphate-based positive electrode material and a preparation method thereof.

[0184] A lithium-containing phosphate-based positive electrode material, comprising composite particles, the composite particles comprising a lithium-containing phosphate inner core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium-containing phosphate inner core.

[0185] A preparation method of a lithium-containing phosphate-based positive electrode material, comprising the following steps:

[0186] Step 1, 833.3g of lithium carbonate (Li2CO3), 4030g of iron phosphate (FePO4) and 550g of inert carbon source (polyethylene glycol) are added to 6000g of deionized water, and mixed uniformly to obtain a mixed slurry.

[0187] Step 2, same as Step 2 in Example 1.

[0188] Step 3, same as Step 3 in Example 1.

[0189] Step 4, same as Step 4 in Example 1.

[0190] Comparative Example 2

[0191] The present comparative example provides a lithium-containing phosphate-based positive electrode material and a preparation method thereof.

[0192] A lithium-containing phosphate-based positive electrode material, comprising composite particles, the composite particles comprising a lithium-containing phosphate inner core (lithium iron phosphate) and a carbon shell layer coated on the outer surface of the lithium-containing phosphate inner core.

[0193] A preparation method of a lithium-containing phosphate-based positive electrode material, comprising the following steps:

[0194] Step 1, 833.3 g of lithium carbonate (Li2CO3), 2676.6 g of ferric nitrate (Fe(NO3)3), 1241.3 g of phosphorous acid (H3PO3), 1000 g of nitric acid (HNO3) and 400 g of inert carbon source (polyethylene glycol) were added to 6000 g of deionized water, and mixed uniformly to obtain a mixed slurry.

[0195] Step 2, the mixed slurry was added to a horizontal sand mill with a volume of 2 L and grinding media of zirconium balls with a diameter of 0.3 μm, and was ground at a rotation speed of 1000 rpm until the slurry D50 was 0.2 μm to obtain a mixed material.

[0196] Step 3, the mixed material was dried at 60℃ to obtain a precursor.

[0197] Step 4, the precursor was subjected to first sintering treatment and second sintering treatment under a nitrogen atmosphere; the first sintering stage was from room temperature to 300℃ at a heating rate of 5℃ / min, and sintering for 4 h; the second sintering treatment was from 300℃ to 650℃ at a heating rate of 5℃ / min, and sintering for 8 h; then, the temperature was decreased from 650℃ to room temperature at a cooling rate of 2℃ / min to obtain a lithium-containing phosphate-based positive electrode material.

[0198] Lithium ion battery examples:

[0199] The lithium-containing phosphate-based positive electrode material prepared in each of the above examples and the comparative example was applied to a lithium ion battery, and the specific preparation steps were as follows:

[0200] Positive electrode sheet: under the same conditions, (positive electrode active material), SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methyl pyrrolidone) were mixed in a mass ratio of 95:2:3:100, and a closed stirrer was stirred for 2 h to obtain a positive electrode slurry; the prepared positive electrode slurry was coated on an aluminum foil, and a doctor blade was used to evenly scrape it, and then it was dried at 130℃ and rolled to obtain a positive electrode sheet; wherein the positive electrode active material was the phosphate-based positive electrode material provided in the above examples and the phosphate-based positive electrode material provided in the comparative example, respectively.

[0201] Negative electrode sheet: lithium metal sheet.

[0202] Electrolyte: 1.0 mol / L LiPF6 solution was used as electrolyte, and the solvent of the electrolyte was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1.

[0203] Separator: Celgard 2400 microporous membrane.

[0204] Lithium ion battery assembly: the assembly sequence of positive electrode sheet-separator-electrolyte-negative electrode sheet was assembled into a button cell in an inert atmosphere glove box.

[0205] The button cells containing the positive electrode materials provided by Examples 1-6 are respectively denoted as Examples S1-S6, and the button cells containing the positive electrode materials provided by Comparative Examples 1-2 are denoted as Comparative Examples DS1-DS2.

[0206] Related performance test and result analysis

[0207] 1. Related test of lithium-containing phosphate-based positive electrode material

[0208] 1.1 Morphology test

[0209] The lithium-containing phosphate-based positive electrode materials prepared by Examples 1 and Comparative Examples 1-2 are respectively subjected to scanning electron microscope analysis, and the results are shown in Figures 1-3 .

[0210] The SEM image of Example 1 is shown in Figure 1 . It can be seen from the image that the overall particles are regular spherical particles, and the particle size is uniformly distributed in the range of 50-100 nm. The particles are closely adjacent, and the particles are connected and dispersed by the carbon layer, that is, the carbon layer covers the surface of the particles in a continuous network form and bridges adjacent particles. It can be seen from the low-magnification SEM image in Figure 1 that there is still a gap between the nanoscale particles formed by carbonization of the carbon source, which facilitates the full infiltration of the electrolyte into the positive electrode sheet prepared by the lithium-containing phosphate-based positive electrode material, and is beneficial to achieve better high-rate discharge performance.

[0211] The SEM image of Comparative Example 1 is shown in Figure 2 . It can be seen from the image that the particle morphology and particle size are large and different. This shows that the sintering process of the inert carbon source combined with the solid phase method is easy to form large particles, although the compaction density of the positive electrode material is high, but the conductivity is weak.

[0212] The SEM image of Comparative Example 2 is shown in Figure 3 . It can be seen from the image that the morphology of the particles is relatively regular, most of which are spherical, and there is no serious agglomeration phenomenon because the particles are small. This shows that the pure liquid phase method process does not form seeds that can agglomerate into large particles, which makes the particles of the positive electrode material basically small particles.

[0213] 1.2 XRD test

[0214] The lithium-containing phosphate-based positive electrode material prepared by Example 1 is subjected to X-ray diffraction analysis, and the XRD spectrum is obtained, wherein the results of Example 1 and the standard card of LiFePO4 are shown in Figure 4 . It can be seen from Figure 4It can be seen that the characteristic peaks of the XRD pattern of the lithium iron phosphate obtained in Example 1 are consistent with the standard card, no obvious shift occurs, and no impurity phase is generated, which shows that the lithium iron phosphate material is successfully prepared according to the above case.

[0215] 1.3 Physicochemical property test

[0216] The physicochemical properties of the lithium-containing phosphate-based positive electrode materials prepared in the above examples and comparative examples are shown in Table 1 below.

[0217] Table 1

[0218]

[0219] In Table 1:

[0220] D Li refers to the lithium ion diffusion coefficient.

[0221] 2. Related test of lithium ion battery

[0222] The electrochemical properties of each lithium ion battery assembled in the above lithium ion battery examples were tested, and the test results are shown in Table 2 and Table 3 below.

[0223] Table 2

[0224]

[0225] Table 3

[0226]

[0227]

[0228] It can be seen from the data in Tables 1-3 that the compaction density of the lithium-containing phosphate-based positive electrode material provided by Comparative Example 1 is large, but the battery has poor charge-discharge capacity and rate performance due to poor conductivity. Comparative Example 2 is prepared by a liquid phase method, and the lithium ion transmission rate of the prepared lithium-containing phosphate-based positive electrode material is poor, which makes the battery have poor low-temperature adaptability.

[0229] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A lithium-containing phosphate-based positive electrode material, characterized in that: The invention comprises composite particles and carbon materials, wherein the composite particles comprise a lithium-containing phosphate core and a carbon shell coating the outer surface of the lithium-containing phosphate core, and the carbon material forms a three-dimensional conductive network between the composite particles; and the particle size of the lithium-containing phosphate-based positive electrode material is nanometer-scale, and the lithium-containing phosphate-based positive electrode material is prepared by a solid-liquid combination method.

2. The lithium-containing phosphate-based cathode material according to claim 1, wherein: The thickness of the carbon shell layer is 1 nm to 5 nm; and / or, In the lithium-containing phosphate-based positive electrode material, the carbon content is 1%-5%; and / or, The composite particles in the lithium-containing phosphate-based cathode material have a spherical morphology; and / or, The lithium-containing phosphate core includes a molecular formula of LiMn x Fe 1-x-y M y Active material of PO4, 0≤x≤0.5, 0≤y≤0.1, M comprises at least one of V, Mg, and Ti; and / or, The secondary particle size of the lithium-containing phosphate-based positive electrode material is 50nm-200nm.

3. The lithium-containing phosphate-based positive electrode material according to claim 1, wherein: The lithium ion diffusion coefficient of the lithium phosphate-based positive electrode material is greater than 9×10 -13 cm 2 / S; and / or, The 5C discharge capacity of the lithium-phosphate-based positive electrode material is greater than or equal to 135 mAh / g; and / or, The 10C discharge capacity of the lithium-phosphate-based positive electrode material is greater than or equal to 124 mAh / g; and / or, The 20C discharge capacity of the lithium-phosphate-based positive electrode material is greater than or equal to 113 mAh / g; and / or, The 0.2C discharge capacity of the lithium-containing phosphate-based cathode material at -20°C is greater than or equal to 110 mAh / g; and / or, The 1C discharge capacity of the lithium-containing phosphate-based cathode material at -20°C is greater than or equal to 100 mAh / g; and / or, The lithium-containing phosphate-based positive electrode material has a 5C discharge capacity at -20°C greater than or equal to 90 mAh / g.

4. A method for preparing a lithium-containing phosphate-based positive electrode material, characterized in that: The following steps are involved: Obtaining raw material components including a lithium source, an iron source, and a phosphorus source according to the stoichiometric ratio in the lithium-containing phosphate; The raw material components, the reactive carbon source and the inert carbon source are mixed in a solution system to obtain a mixed material, wherein a portion of the lithium source reacts with the reactive carbon source to form a water-soluble organic lithium source; The mixed material is sand-milled to obtain a mixed slurry, and then spray-dried to form a three-dimensional network structure of the water-soluble organic lithium source around the phosphorus-containing iron particles to obtain a precursor; The precursor is sintered to obtain a lithium-containing phosphate-based positive electrode material.

5. The method for preparing a lithium-containing phosphate-based positive electrode material according to claim 4, wherein: The reactive carbon source comprises at least one of citric acid, ethylenediaminetetraacetic acid, tartaric acid, polymaleic acid, polyacrylic acid, polystyrene acid and polysulfonate polymer; and / or, The inert carbon source includes at least one of polyethylene glycol, glucose, lactose, and sucrose; and / or, The lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide, lithium acetate, and lithium nitrate; and / or, The iron source includes ferric phosphate and at least one iron-containing compound selected from ferric nitrate, ferric oxide, and ferrous sulfate; and / or, The phosphorus source includes at least one of ferric phosphate, ammonium phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and phosphoric acid.

6. The method for preparing a lithium-containing phosphate-based cathode material according to claim 4, wherein: Based on the total mass of the reactive carbon source and the inert carbon source as 100%, the content of the reactive carbon source is 1%-60%; and / or, Based on the total mass of the raw material components being 100%, the total mass of the reactive carbon source and the inert carbon source accounts for 1%-20%.

7. The method for preparing a lithium-containing phosphate-based positive electrode material according to claim 4, wherein: The D50 particle size of the particles in the mixed slurry is 0.2 μm-0.8 μm; and / or, The sand grinding conditions include: a rotation speed of 500 rpm to 2000 rpm, and a grinding medium including at least one of a zirconium ball with a diameter of 0.8 μm and a zirconium ball with a diameter of 0.3 μm.

8. The method for preparing a lithium-containing phosphate-based cathode material according to claim 4, wherein: The spray drying conditions include: air inlet temperature of 150° C.-200° C., air outlet temperature of 40° C.-60° C., centrifugal frequency of 300 Hz-340 Hz, and feed pump speed of 20 rpm-60 rpm.

9. The method for preparing a lithium-containing phosphate-based cathode material according to any one of claims 4 to 8, wherein: The sintering treatment includes a first sintering treatment and a second sintering treatment performed sequentially; wherein the first sintering treatment includes sintering at 300°C-450°C for 3h-6h at a heating rate of 2°C / min-15°C / min, and the second sintering treatment includes sintering at 550°C-750°C for 4h-8h at a heating rate of 2°C / min-15°C / min.

10. A lithium-ion battery comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The positive electrode plate includes the lithium-phosphate-based positive electrode material according to any one of claims 1 to 3 or the lithium-phosphate-based positive electrode material prepared by the preparation method according to any one of claims 4 to 9.

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