A positive electrode material, a preparation method thereof, a positive electrode sheet, and a battery

Abstract

The application provides a positive electrode material, a preparation method thereof, a positive electrode sheet and a battery. The positive electrode material comprises a lithium iron manganese phosphate core, a first coating layer and a second coating layer. The first coating layer is coated on at least part of the surface of the lithium iron manganese phosphate core, and the second coating layer is coated on at least part of the surface of the first coating layer. The first coating layer comprises a metal oxide material, and the second coating layer comprises a carbon material. The positive electrode material has high structural stability and can improve the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and more particularly to a cathode material and its preparation method, a cathode sheet, and a battery. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) X Fe 1-X Lithium manganese iron phosphate (LMFP) cathode materials are suitable for diverse applications as core active components in lithium-ion battery cathodes due to their low cost, high specific capacity, and environmental friendliness. For example, in the field of energy storage systems, LMFP cathode materials can be used to produce cathodes for lithium-ion batteries specifically designed for grid energy storage and home energy storage, leveraging their high specific capacity to improve the energy density of lithium-ion batteries. However, the structural stability of existing LMFP cathode materials remains relatively poor, leading to insufficient cycle performance in lithium-ion batteries.

[0003] Therefore, it is urgent to improve the structural stability of lithium manganese iron phosphate cathode materials in order to enhance the cycle performance of batteries. Summary of the Invention

[0004] This invention provides a cathode material, its preparation method, a cathode sheet, and a battery. The cathode material provided by this invention exhibits high structural stability and can improve the cycle performance of the battery.

[0005] In a first aspect, embodiments of the present invention provide a cathode material, comprising: a lithium manganese iron phosphate core, a first coating layer, and a second coating layer;

[0006] The first coating layer covers at least a portion of the surface of the lithium manganese iron phosphate core, and the second coating layer covers at least a portion of the surface of the first coating layer;

[0007] The first coating layer comprises a metal oxide material; the second coating layer comprises a carbon material.

[0008] In some embodiments of the present invention, the porosity of the positive electrode material is 4% to 20%;

[0009] And / or, the specific surface area of ​​the positive electrode material is 16 m². 2 / g~25m 2 / g;

[0010] And / or, the metal oxide material includes at least one of aluminum oxide, titanium oxide, zirconium oxide, and magnesium oxide;

[0011] And / or, the carbon material includes at least one of amorphous carbon or graphite.

[0012] In some embodiments of the present invention, the thickness of the first coating layer is 5 nm to 30 nm;

[0013] And / or, the thickness of the second coating layer is 5nm~30nm.

[0014] In some embodiments of the present invention, the lithium manganese iron phosphate core includes LiMn X Fe 1-X PO4, where 0.1 ≤ x ≤ 0.9.

[0015] Secondly, embodiments of the present invention provide a method for preparing the cathode material according to any of the first aspects, comprising the following steps:

[0016] The first raw material system, including lithium source, manganese source, iron source and phosphorus source, is subjected to a first mixing treatment to obtain lithium manganese iron phosphate core precursor;

[0017] The second raw material system, including the lithium manganese iron phosphate core precursor and the metal salt, is subjected to a second mixing process to obtain a second mixed system.

[0018] The third raw material system, including the second mixed system and the carbon source, is subjected to a third mixing process to obtain a cathode material precursor.

[0019] The cathode material precursor is sintered to obtain the cathode material.

[0020] In some embodiments of the present invention, the first raw material system further includes a reducing agent;

[0021] And / or, the second raw material system further includes a first pore-forming agent;

[0022] And / or, the third raw material system further includes a second pore-forming agent;

[0023] The first pore-forming agent and the second pore-forming agent each independently include at least one of urea and melamine.

[0024] In some embodiments of the present invention, the mass of the metal salt is 3wt% to 7wt% of the lithium manganese iron phosphate core precursor;

[0025] And / or, the mass of the carbon source is 3wt% to 20wt% of the lithium manganese iron phosphate core precursor;

[0026] And / or, the mass of the first pore-forming agent is 2wt% to 7wt% of the lithium manganese iron phosphate core precursor;

[0027] And / or, the mass of the second pore-forming agent is 1wt% to 5wt% of the lithium manganese iron phosphate core precursor.

[0028] In some embodiments of the present invention, the sintering treatment temperature is 600℃~800℃ and the treatment time is 4h~20h.

[0029] Thirdly, embodiments of the present invention provide a positive electrode sheet, comprising any of the positive electrode materials described in the first aspect or a positive electrode material prepared by any of the preparation methods described in the second aspect.

[0030] Fourthly, embodiments of the present invention provide a battery comprising any of the positive electrode materials described in the first aspect, or a positive electrode material prepared by any of the preparation methods described in the second aspect, or a positive electrode sheet described in the third aspect.

[0031] This invention provides a cathode material and its preparation method, a cathode sheet, and a battery. The cathode material comprises a lithium manganese iron phosphate core, a first coating layer, and a second coating layer. The first coating layer covers at least a portion of the surface of the lithium manganese iron phosphate core, and the second coating layer covers at least a portion of the surface of the first coating layer. The first coating layer comprises a metal oxide material, and the second coating layer comprises a carbon material. By sequentially coating at least a portion of the surface of the lithium manganese iron phosphate core with the first coating layer and the second coating layer, the lattice of the lithium manganese iron phosphate core can be stabilized to improve the structural stability of the lithium manganese iron phosphate cathode material, thereby improving the cycle performance of the battery. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The structural stability of lithium manganese iron phosphate cathode materials in existing technologies is still relatively poor, which will result in insufficient battery cycle performance.

[0034] The inventors attempted to coat the surface of LMFPs with metal oxide layers (such as aluminum oxide and magnesium oxide) to improve the structural stability of LMFPs by inhibiting manganese dissolution and reducing lattice distortion. However, while the above techniques improve the structural stability of LMFPs, they also reduce the conductivity of LMFPs and deteriorate the rate performance of the battery.

[0035] Therefore, the inventors aimed to improve the structural stability and conductivity of lithium manganese iron phosphate cathode material, attempting to improve the battery's cycle performance while maintaining good rate performance.

[0036] Based on the above research, in a first aspect, embodiments of the present invention provide a cathode material, comprising: a lithium manganese iron phosphate core, a first coating layer, and a second coating layer; the first coating layer coats at least a portion of the surface of the lithium manganese iron phosphate core, and the second coating layer coats at least a portion of the surface of the first coating layer; the first coating layer comprises a metal oxide material; and the second coating layer comprises a carbon material.

[0037] The cathode material of this invention has good structural stability and high conductivity, which can improve battery cycle performance while maintaining good rate performance.

[0038] The inventors analyzed that the positive electrode material of the present invention has good structural stability and high conductivity because: the positive electrode material of the present invention includes a lithium manganese iron phosphate core, which is beneficial to improving the first-cycle discharge capacity of the battery; at the same time, when the first coating layer on at least part of the surface of the lithium manganese iron phosphate core includes a metal oxide material, the metal oxide coating layer can form a physical barrier on the surface of the lithium manganese iron phosphate core, inhibiting manganese ions from being extracted from the crystal lattice and dissolved into the electrolyte of the battery, while anchoring the atoms on the crystal lattice surface and relieving the crystal lattice stress, thereby reducing the crystal lattice distortion of the lithium manganese iron phosphate core, thereby improving the crystal lattice stability of the lithium manganese iron phosphate core and thus improving the structural stability of the positive electrode material, thereby improving the cycle performance of the battery; the second coating layer, since it includes carbon material, can enhance the electronic conductivity of the lithium manganese iron phosphate core, thereby enabling the positive electrode material to maintain high conductivity, and thus enabling the battery to maintain good rate performance. With the synergistic effect of the first and second coating layers, the core structure of lithium manganese iron phosphate is first stabilized by metal oxide materials, and then the conductivity of the cathode material can be improved by carbon materials on the basis of improving the lattice stability of the lithium manganese iron phosphate core, so as to achieve a balance between improving the battery cycle performance and rate performance.

[0039] The present invention does not limit whether the first coating layer can completely cover the surface of the lithium manganese iron phosphate core; it can be a partial coating or a complete coating. The present invention also does not limit whether the second coating layer can completely cover the first coating layer; it can be a partial coating or a complete coating.

[0040] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the above-described structure and composition of the cathode material, such as EDS and TEM. In specific implementation, the battery can be completely discharged and disassembled to separate the cathode sheet. Then, the cross-section of the cathode sheet can be obtained using FIB for EDS and TEM testing to obtain the structure and composition of the cathode material.

[0041] In some embodiments of the present invention, a porosity of 4% to 20% in the cathode material is more conducive to improving the conductivity of the cathode material and thus more conducive to improving the rate performance of the battery. Specifically, pores can be formed in the coating layer. The pores existing in the first coating layer and the second coating layer increase the electrolyte transport channels, further accelerate the lithium ion transport efficiency, and thus improve the conductivity of the cathode material to improve the rate performance of the battery.

[0042] The porosity of the cathode material can be tested using conventional testing methods and instruments in the art, as described in this embodiment of the invention. In one specific embodiment, a specific surface area analyzer can be used to perform the test using the nitrogen adsorption-desorption method.

[0043] The embodiments of the present invention can employ conventional testing methods and instruments in the art to observe the pore structure of the positive electrode material. In one specific embodiment, the battery can be completely discharged and disassembled to separate the positive electrode sheet. Then, a cross-section of the positive electrode sheet can be obtained using FIB (Film Injection Biometry), and the microstructure of the positive electrode material can be observed using TEM (Microscopic Transformation) to determine the pore structure of the first and second coating layers.

[0044] In some embodiments of the present invention, the specific surface area of ​​the positive electrode material is 16 m². 2 / g~25m 2 / g. Among them, when the cathode material has a specific surface area within the above range, it can have better structural stability and higher conductivity, which can further improve the battery cycle performance while maintaining good rate performance.

[0045] The specific surface area of ​​the cathode material can be tested using conventional testing methods and instruments in the art, as described in this embodiment of the invention. In one specific embodiment, a specific surface area analyzer can be used to perform the test using the nitrogen adsorption-desorption method.

[0046] In some embodiments of the present invention, the metal oxide material includes at least one selected from aluminum oxide, titanium oxide, zirconium oxide, and magnesium oxide. When the cathode material of the embodiments of the present invention has the above composition, it is more beneficial to improve the lattice stability of the lithium manganese iron phosphate core, thereby better enhancing the structural stability of the cathode material and thus better improving the cycle performance of the battery.

[0047] In some embodiments of the present invention, the carbon material includes at least one of amorphous carbon or graphite. When the cathode material of the embodiments of the present invention has the above-described composition, the conductivity of the cathode material can be better maintained, thereby better maintaining the rate performance of the battery.

[0048] In some embodiments of the present invention, the thickness of the first coating layer is 5 nm to 30 nm. In the above embodiments, when the thickness of the first coating layer is within this range, it can better enhance the structural stability of the lithium manganese iron phosphate core, thereby better improving the structural stability of the cathode material and thus improving the cycle performance of the battery. The effect is even better when the thickness of the first coating layer is 15 mm to 25 mm.

[0049] In some embodiments of the present invention, the thickness of the second coating layer is 5 nm to 30 nm. In the above embodiments, when the thickness of the second coating layer is within this range, the positive electrode material can maintain higher conductivity, thereby enabling the battery to maintain better rate performance. The effect is even better when the thickness of the second coating layer is 15 mm to 25 mm.

[0050] For example, the thickness of the first coating layer is, for example, a range of 5 nm, 10 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, or any combination thereof.

[0051] For example, the thickness of the second coating layer is, for example, a range of 5 nm, 10 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, or any two of these.

[0052] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the thickness of the first and second coating layers of the positive electrode material. For example, TEM can be used for testing. In specific implementation, the battery can be completely discharged and disassembled to separate the positive electrode sheet. Then, FIB is used to obtain the cross-section of the positive electrode sheet, and TEM is used to observe the thickness of the two coating layers. When the thickness of the first and second coating layers is not uniform, the average thickness from multiple fields of view is taken as the thickness of the first and second coating layers.

[0053] In some embodiments of the present invention, the lithium manganese iron phosphate core includes LiMn X Fe 1-X PO4, where 0.1 ≤ x ≤ 0.9. When the value of x is within the above range, the structural stability and conductivity of the cathode material can be further improved, thereby further enhancing the cycle performance and rate performance of the battery.

[0054] For example, the value of x is, for example, a range of 0.1, 0.11, 0.12, 0.13, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or any combination thereof.

[0055] In a second aspect, embodiments of the present invention provide a method for preparing any of the cathode materials described in the first aspect, comprising the following steps: performing a first mixing treatment on raw materials including a lithium source, a manganese source, an iron source, and a phosphorus source to obtain a lithium manganese iron phosphate core precursor; performing a second mixing treatment on raw materials including the lithium manganese iron phosphate core precursor and a metal salt to obtain a second mixed system; performing a third mixing treatment on raw materials including the second mixed system and a carbon source to obtain a cathode material precursor; and performing a sintering treatment on the cathode material precursor to obtain a cathode material.

[0056] The present invention provides an embodiment of the cathode material prepared by the above-described method. The cathode material comprises: a lithium manganese iron phosphate core, a first coating layer, and a second coating layer; the first coating layer coats at least a portion of the surface of the lithium manganese iron phosphate core, and the second coating layer coats at least a portion of the surface of the first coating layer; the first coating layer comprises a metal oxide material; and the second coating layer comprises a carbon material. The present invention provides an embodiment of the cathode material with good structural stability and high conductivity, which can improve battery cycle performance while maintaining good rate performance.

[0057] Specifically, in the above preparation process, the present invention first obtains a lithium manganese iron phosphate core precursor through a first mixing treatment to facilitate the subsequent preparation of the lithium manganese iron phosphate core; through a second mixing treatment, the metal salt can be uniformly coated on at least a portion of the surface of the lithium manganese iron phosphate core precursor, which is beneficial to forming a uniform first coating layer; through a third mixing treatment, the carbon source can be uniformly coated on at least a portion of the surface of the product of the second mixing treatment, which is beneficial to forming a uniform second coating layer; after sintering treatment, the cathode material provided in the embodiments of the present invention can finally be obtained. The cathode material has good structural stability and high conductivity, and can improve the battery cycle performance while maintaining good rate performance.

[0058] The embodiments of the present invention do not impose special limitations on the raw materials of lithium source, manganese source, iron source and phosphorus source, which can be commercial products or raw materials synthesized by conventional synthesis methods in the art.

[0059] Exemplary examples, in some embodiments of the present invention, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; exemplary examples, in some embodiments of the present invention, the manganese source includes at least one of manganese tetroxide, manganese phosphate, and ferric manganese carbonate; exemplary examples, in some embodiments of the present invention, the iron source includes at least one of iron tetroxide, ferric manganese carbonate, ferric oxalate, and ferric phosphate; exemplary examples, in some embodiments of the present invention, the phosphorus source includes at least one of manganese phosphate, ferric phosphate, phosphoric acid, and lithium dihydrogen phosphate. Lithium dihydrogen phosphate can be used as both a lithium source and a phosphorus source; manganese phosphate can be used as both a manganese source and a phosphorus source; ferric phosphate can be used as both an iron source and a phosphorus source; and ferric manganese carbonate can be used as both a manganese source and an iron source. The selection of the above-mentioned lithium source, manganese source, iron source, and phosphorus source is beneficial to further improve the preparation efficiency of the cathode material, and can further enable the prepared cathode material to have better structural stability and higher conductivity, thereby improving battery cycle performance while maintaining good rate performance.

[0060] The embodiments of the present invention do not impose special limitations on the raw materials for metal salts, which can be commercially available products or raw materials synthesized by conventional synthesis methods in the art.

[0061] In some embodiments of the present invention, the metal salt includes at least one selected from aluminum nitrate, aluminum chloride, aluminum sulfate, titanium nitrate, titanium chloride, and titanium oxide. The selection of the aforementioned metal salt can further improve the lattice stability of the lithium manganese iron phosphate core, thereby giving the prepared cathode material better structural stability and improving the cycle performance of the battery.

[0062] The embodiments of this invention do not impose special limitations on the raw materials for the carbon source, which can be commercially available products or raw materials synthesized by conventional synthesis methods in the art. Exemplarily, in some embodiments of this invention, the carbon source may include one or more of ascorbic acid, glucose, citric acid, sucrose, polyethylene glycol, polyvinylpyrrolidone, and acetylene black, which is beneficial for further improving the preparation efficiency of the cathode material.

[0063] In some embodiments of the present invention, the first raw material system further includes a reducing agent, which may include glucose. In the above embodiments, by adding glucose as a reducing agent to the first raw material system, the trivalent manganese and iron elements in the manganese source can be reduced to divalent manganese and iron elements during calcination. Simultaneously, the reducing agent will not remain in the lithium manganese iron phosphate core after calcination. That is, the reducing agent can further enhance the stability of the resulting lithium manganese iron phosphate core lattice, further improving the structural stability of the resulting cathode material and thus improving the cycle performance of the battery.

[0064] The present invention does not impose a special limitation on the amount of reducing agent added, and can be selected according to the actual situation. In a specific embodiment, the mass of the reducing agent can account for 5 wt% of the total mass of the first raw material system.

[0065] In some embodiments of the present invention, the second raw material system further includes a first pore-forming agent. In the above embodiments, by adding a first pore-forming agent to the second raw material system, the resulting first coating layer can have higher porosity, which is more conducive to maintaining higher conductivity in the resulting cathode material, thereby better enabling the battery to maintain higher rate performance.

[0066] In some embodiments of the present invention, the third raw material system further includes a second pore-forming agent. In the above embodiments, by adding a second pore-forming agent to the third raw material system, the resulting second coating layer can have higher porosity, which is more conducive to improving the conductivity of the resulting cathode material, thereby better improving the rate performance of the battery. Furthermore, the second pore-forming agent can dope nitrogen atoms into the lattice of the carbon material, increasing the number of active sites in the second coating layer, thereby further improving the conductivity of the second coating layer, and thus improving the conductivity of the cathode material to improve the rate performance of the battery.

[0067] The embodiments of the present invention do not specifically limit the types of the first pore-forming agent and the second pore-forming agent, and they can be commercially available products or pore-forming agents used by conventional synthesis methods in the art. Exemplarily, in some embodiments of the present invention, the first pore-forming agent and the second pore-forming agent each independently include at least one of urea and melamine. The aforementioned pore-forming agents are more conducive to improving the porosity of the first coating layer and the second coating layer, and are more conducive to maintaining higher electrical conductivity in the obtained cathode material, thereby better enabling the battery to maintain higher rate performance.

[0068] In some embodiments of the present invention, before the first mixing treatment, in the raw materials including lithium source, manganese source, iron source, and phosphorus source, the molar ratio of lithium to phosphorus is (1~1.05):1; the molar ratio of iron to phosphorus is (0.1~0.9):1; and the molar ratio of manganese to phosphorus is (0.1~0.9):1. Specifically, the embodiments of the present invention do not impose special limitations on the mass ratio of lithium source, manganese source, iron source, and phosphorus source among themselves, but by further controlling the molar ratio of the elements, it is more beneficial to obtain the positive electrode material with better structural stability and higher conductivity provided by the embodiments of the present invention, and more beneficial to improve the battery cycle performance while maintaining good rate performance.

[0069] For example, the molar ratio of lithium to phosphorus is 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, or any range thereof; for example, the molar ratio of iron to phosphorus is 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7... The molar ratio of manganese to phosphorus is, for example, a range consisting of 1, 0.8:1, 0.85:1, 0.9:1, or any two thereof; for example, the molar ratio of manganese to phosphorus is, for example, a range consisting of 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.85:1, 0.9:1, or any two thereof.

[0070] In some embodiments of the present invention, the mass of the metal salt is 3wt% to 7wt% of the lithium manganese iron phosphate core precursor. In the above embodiments, by controlling the amount of metal salt added, the thickness of the first coating layer in the obtained cathode material can be further controlled, which is more conducive to improving the lattice stability of the lithium manganese iron phosphate core, and further makes the obtained cathode material have better structural stability, which can better improve the cycle performance of the battery.

[0071] For example, the metal salt is a precursor of lithium manganese iron phosphate core in a range of 3 wt%, 3.1 wt%, 3.2 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 7 wt%, or any two of these.

[0072] In some embodiments of the present invention, the mass of the carbon source is 3wt% to 20wt% of the lithium manganese iron phosphate core precursor. In the above embodiments, by controlling the amount of carbon source added, the thickness of the second coating layer in the obtained cathode material can be further controlled, which is more conducive to maintaining a higher conductivity in the obtained cathode material, and thus better enabling the battery to maintain a higher rate performance.

[0073] For example, the carbon source is a lithium manganese iron phosphate core precursor with a mass of, for example, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 18.5 wt%, 19 wt%, 19.5 wt%, 20 wt%, or any combination thereof.

[0074] In some embodiments of the present invention, the mass of the first pore-forming agent is 2wt% to 7wt% of the lithium manganese iron phosphate core precursor. In the above embodiments, by controlling the amount of the first pore-forming agent added, the porosity of the first coating layer in the obtained cathode material can be further controlled, which is more conducive to maintaining a higher conductivity in the obtained cathode material, and thus better enabling the battery to maintain a higher rate performance.

[0075] For example, the first pore-forming agent is a lithium manganese iron phosphate core precursor in a range of, for example, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, or any two of these.

[0076] In some embodiments of the present invention, the mass of the second pore-forming agent is 1wt% to 5wt% of the lithium manganese iron phosphate core precursor. In the above embodiments, by controlling the amount of the second pore-forming agent added, the porosity of the second coating layer in the obtained cathode material can be further controlled, which is more conducive to making the obtained cathode material have higher electrical conductivity, and thus better enabling the battery to maintain higher rate performance.

[0077] For example, the second pore-forming agent is a range consisting of, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or any two thereof, of the lithium manganese iron phosphate core precursor.

[0078] The embodiments of the present invention do not impose special limitations on the mixing methods of the first mixing treatment, the second mixing treatment, and the third mixing treatment, and can use mixing methods commonly used in the art. In one specific embodiment, the first mixing treatment is ball milling; in another specific embodiment, the second mixing treatment is stirring and blending; and in yet another specific embodiment, the second mixing treatment is stirring and blending. These mixing methods allow for more uniform mixing of the raw materials, which is more conducive to obtaining the positive electrode material with better structural stability and higher conductivity provided by the embodiments of the present invention, and is also more conducive to improving battery cycle performance while maintaining good rate performance.

[0079] In some embodiments of the present invention, after the first mixing treatment, the second mixing treatment, and the third mixing treatment, the treated mixed system is subjected to a first drying treatment, a second drying treatment, and a third drying treatment, respectively. The embodiments of the present invention do not impose special limitations on the processing methods of the first drying treatment, the second drying treatment, and the third drying treatment; they can be common drying treatment methods in the art. In a specific embodiment, the first drying treatment, the second drying treatment, and the third drying treatment are all spray drying treatments. These drying treatments are more conducive to implementing the preparation method of the positive electrode material provided in the embodiments of the present invention, more conducive to obtaining the positive electrode material with better structural stability and higher conductivity provided in the embodiments of the present invention, and more conducive to improving battery cycle performance while maintaining good rate performance.

[0080] In some embodiments of the present invention, the sintering temperature is 600℃~800℃, and the processing time is 4h~20h. In these embodiments, by controlling the temperature and time of the calcination treatment, the reaction efficiency in the preparation method of the cathode material of the present invention is more easily improved, which is more conducive to obtaining the cathode material with better structural stability and higher conductivity provided by the present invention, and more conducive to improving battery cycle performance while maintaining good rate performance.

[0081] For example, the sintering temperature is a range of 600°C, 605°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or any combination thereof.

[0082] For example, the sintering process time is, for example, a range of 4h, 4.5h, 5h, 5.5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or any combination thereof.

[0083] In some embodiments of the present invention, the sintering process is performed under a protective atmosphere. The embodiments of the present invention do not specifically limit the type of protective atmosphere and can use any protective atmosphere commonly found in the art. In a specific embodiment, the sintering process is performed under a nitrogen atmosphere. In the above embodiments, performing the sintering process under a nitrogen atmosphere is more conducive to improving the purity of the lithium manganese iron phosphate core, the first coating layer, and the second coating layer, and is more conducive to obtaining the cathode material with better structural stability and higher conductivity provided by the embodiments of the present invention. It is also more conducive to improving battery cycle performance while maintaining good rate performance.

[0084] Thirdly, embodiments of the present invention provide a positive electrode sheet, comprising any of the positive electrode materials described in the first aspect or a positive electrode material prepared by any of the preparation methods described in the second aspect. The positive electrode sheet includes a positive electrode material layer, and the positive electrode layer includes the aforementioned positive electrode material. The aforementioned positive electrode sheet has advantages corresponding to the aforementioned positive electrode materials, which will not be elaborated upon here.

[0085] Fourthly, embodiments of the present invention also provide a battery, including the positive electrode sheet of the third aspect. The battery provided by the present invention has advantages corresponding to the above-described positive electrode materials, which will not be elaborated here.

[0086] The battery in this embodiment of the invention can be a lithium-ion battery (such as a lithium-ion power battery).

[0087] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0088] Specifically, the positive electrode includes a positive current collector and a positive electrode material layer located on at least one side surface of the positive current collector. Specifically, the positive electrode material layer can be provided on one side surface in the thickness direction of the positive current collector, or positive electrode material layers can be provided on both opposite sides surface in the thickness direction of the positive current collector.

[0089] Specifically, when the battery in this embodiment of the invention is a lithium-ion battery, the positive electrode material layer may include a positive electrode material, a conductive agent, and a binder. In the positive electrode material layer, the mass percentage of the positive electrode material may be 70% to 99%, for example, a range consisting of 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any two of these. The mass fraction of the conductive agent may be 0.5% to 15%, for example, a range consisting of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any two of these. The mass fraction of the binder may be 0.5% to 15%, for example, a range consisting of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or any two of these.

[0090] In some embodiments of the present invention, the conductive agent in the positive electrode material layer can be a conventional conductive material in the art. For example, the conductive agent in the positive electrode material layer may include at least one of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fiber, graphene, acetylene black, and Ketjen black.

[0091] In some embodiments of the present invention, the binder in the positive electrode material layer can be a conventional adhesive material in the art. For example, the binder in the positive electrode material layer may include at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0092] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0093] In some embodiments of the present invention, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode material, conductive agent, binder, and other components used to form the positive electrode material layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations in preparing positive electrode sheets using the coating method, and the equipment used can be conventional equipment in the art, without any particular limitation.

[0094] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer located on at least one side surface of the negative electrode current collector. Specifically, the negative electrode material layer can be provided on one side surface of the negative electrode current collector, or negative electrode material layers can be provided on both opposite sides of the negative electrode current collector in the thickness direction.

[0095] Specifically, the negative electrode material layer may include a negative electrode material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the negative electrode material may include at least one of natural graphite, artificial graphite, petroleum coke, and silicon carbide materials; the conductive agent may include at least one of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; and the binder may include at least one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0096] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0097] In some embodiments of the present invention, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode material layer, such as the negative electrode material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations in preparing negative electrode sheets using the coating method, and the equipment used can be conventional equipment in the art, without any particular limitation.

[0098] The electrolyte in this embodiment of the invention can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate, but are not limited thereto.

[0099] In some embodiments of the present invention, a separator is used to separate the positive and negative electrode plates, preventing short circuits caused by contact between the positive and negative electrode plates. The embodiments of the present invention can use conventional separators in the art, and there are no particular limitations. For example, the separator material can be a separator made of at least one of the following: high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0100] In some embodiments of the present invention, conventional housing materials in the art may be used to encapsulate the battery cells. This is an example and not a limitation. The housing may include flexible packaging materials such as aluminum-plastic film.

[0101] The embodiments of the present invention can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection (i.e., injection of electrolyte) and encapsulation, the battery is obtained.

[0102] Fifthly, embodiments of the present invention provide a battery pack including the above-described battery, which has advantages corresponding to the above-described positive electrode material, and will not be elaborated further.

[0103] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0104] Sixthly, embodiments of the present invention provide an electrical device including the above-described battery or battery pack. This electrical device has advantages corresponding to the above-described positive electrode material, which will not be elaborated further.

[0105] The electrical equipment used in the embodiments of the present invention can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on this.

[0106] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0107] Unless otherwise specified, the testing methods involved in this invention are all conventional methods used in the art; the reagents involved in the embodiments of this invention are all commercially available products and can be purchased through commercial channels.

[0108] Example

[0109] Example 1

[0110] The cathode material in this embodiment is prepared by the following method:

[0111] 1) The first raw material system, including lithium source (lithium carbonate), manganese source (manganese tetroxide), iron source (iron phosphate), phosphorus source (lithium dihydrogen phosphate), and reducing agent (glucose), is mixed with water and then ball-milled (600 r / min). After spray drying, a lithium manganese iron phosphate core precursor is obtained, wherein the mass of glucose accounts for 5 wt% of the first raw material system, and the molar ratio of each element in the lithium manganese iron phosphate core precursor is: Li / P = 1, Fe / P = 0.4, and Mn / P = 0.6.

[0112] 2) The above-mentioned lithium manganese iron phosphate core precursor, metal salt (aluminum nitrate, with a mass of 5 wt% of the lithium manganese iron phosphate core precursor), and first pore-forming agent (urea, with a mass of 5 wt% of the lithium manganese iron phosphate core precursor) are stirred and mixed, and then spray-dried to obtain a second mixed system.

[0113] 3) The above second mixing system, carbon source (glucose, with a mass of 10wt% of the lithium manganese iron phosphate core precursor), and second pore-forming agent (urea, with a mass of 3wt% of the lithium manganese iron phosphate core precursor) are stirred and mixed, and spray dried to obtain the cathode material precursor.

[0114] 4) The above-mentioned cathode material precursor was sintered under nitrogen protection (gas flow rate 60 sccm) at a temperature of 760℃ for 6 hours to obtain the cathode material.

[0115] Example 2

[0116] This embodiment is basically the same as embodiment 1, except that the mass of the first pore-forming agent added in this embodiment is different, and its mass is 2 wt% of the lithium manganese iron phosphate core precursor.

[0117] Example 3

[0118] This embodiment is basically the same as embodiment 1, except that the mass of the first pore-forming agent added in this embodiment is different, and its mass is 7 wt% of the lithium manganese iron phosphate core precursor.

[0119] Example 4

[0120] This embodiment is basically the same as Embodiment 1, except that the mass of the second pore-forming agent added in this embodiment is 1 wt% of the lithium manganese iron phosphate core precursor.

[0121] Example 5

[0122] This embodiment is basically the same as Embodiment 1, except that the mass of the second pore-forming agent added in this embodiment is 5 wt% of the lithium manganese iron phosphate core precursor.

[0123] Example 6

[0124] This embodiment is basically the same as Embodiment 1, except that the metal salt in this embodiment is titanium oxide, and the added mass is 5 wt% of the lithium manganese iron phosphate core precursor.

[0125] Example 7

[0126] This embodiment is basically the same as Embodiment 1, except that the carbon source in this embodiment is polyethylene glycol, and the added mass is 10 wt% of the lithium manganese iron phosphate core precursor.

[0127] Example 8

[0128] This embodiment is basically the same as Embodiment 1, except that the mass of metal salt added in this embodiment is 3 wt% of the lithium manganese iron phosphate core precursor, and the mass of carbon source added is 3 wt% of the lithium manganese iron phosphate core precursor.

[0129] Example 9

[0130] This embodiment is basically the same as Embodiment 1, except that the added mass of metal salt in this embodiment is 7 wt% of the lithium manganese iron phosphate core precursor, and the added mass of carbon source is 20 wt% of the lithium manganese iron phosphate core precursor.

[0131] Example 10

[0132] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the elemental molar ratio of the lithium manganese iron phosphate core precursor is 0.1 for Fe / P and 0.9 for Mn / P.

[0133] Example 11

[0134] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the elemental molar ratio of the lithium manganese iron phosphate core precursor is 0.9 for Fe and 0.1 for Mn.

[0135] Example 12

[0136] This embodiment is basically the same as embodiment 1, except that the mass of the first pore-forming agent added in this embodiment is different, and its mass is 1 wt% of the lithium manganese iron phosphate core precursor.

[0137] Example 13

[0138] This embodiment is basically the same as embodiment 1, except that the mass of the first pore-forming agent added in this embodiment is different, and its mass is 10 wt% of the lithium manganese iron phosphate core precursor.

[0139] Example 14

[0140] This embodiment is basically the same as Embodiment 1, except that the mass of the second pore-forming agent added in this embodiment is 0.5 wt% of the lithium manganese iron phosphate core precursor.

[0141] Example 15

[0142] This embodiment is basically the same as Embodiment 1, except that the mass of the second pore-forming agent added in this embodiment is 10 wt% of the lithium manganese iron phosphate core precursor.

[0143] Example 16

[0144] This embodiment is basically the same as Embodiment 1, except that the sintering temperature in this embodiment is 800℃ and the time is 20h.

[0145] Example 17

[0146] This embodiment is basically the same as Embodiment 1, except that the sintering temperature in this embodiment is 600℃ and the time is 4h.

[0147] Comparative Example

[0148] Comparative Example 1

[0149] The difference between this comparative example and Example 1 is that this comparative example directly proceeds to step 3) after step 1), without performing step 2).

[0150] Comparative Example 2

[0151] The difference between this comparative example and Example 1 is that this comparative example directly proceeds to step 4 after step 2), without performing step 3.

[0152] Comparative Example 3

[0153] The difference between this comparative example and Example 1 is that this comparative example directly proceeds to step 4) after step 1), without performing steps 2) and 3).

[0154] Test case

[0155] Test Example 1

[0156] The porosity, coating thickness, and specific surface area of ​​the cathode materials obtained in the examples and comparative examples were tested. The testing process is as follows:

[0157] 1) Porosity test of cathode material: The porosity was tested using a specific surface area analyzer and the nitrogen adsorption-desorption method. The test results are shown in Table 1.

[0158] 2) Coating thickness test: The thickness of the two coating layers was observed using TEM. The test results are shown in Table 1.

[0159] 3) Specific surface area test of cathode material: The specific surface area of ​​the cathode material was tested using a Jin'ai Spectrometer (model F-Sorb 2400CE) according to the static nitrogen adsorption method of national standard GB / T 19587-2004. The test results are shown in Table 1.

[0160] Table 1:

[0161]

[0162] Test Example 2

[0163] Battery Assembly: After fabricating the positive electrode material obtained in the examples and comparative examples into a positive electrode sheet, it is assembled with a negative electrode sheet, electrolyte, and separator according to the following method to obtain a lithium-ion battery. The method includes:

[0164] 1) The positive electrode materials from the examples and comparative examples were mixed with conductive carbon black and PVDF at a mass ratio of 96%:2%:2%, respectively, and dispersed to obtain a positive electrode slurry. This slurry was then coated onto an aluminum foil positive electrode current collector, with a positive electrode areal density of 4.12 g / cm³. 3 The positive electrode sheet is prepared by rolling.

[0165] 2) Artificial graphite, styrene-diene rubber (SBR), sodium carboxymethyl cellulose, and conductive carbon black are mixed in a mass ratio of 94%:3%:2%:1%. The mixture is dispersed in water and then mixed using a double planetary mixer to obtain a negative electrode slurry. This slurry is coated onto a copper current collector negative electrode fluid, followed by rolling and drying to obtain a negative electrode sheet.

[0166] 3) Assemble the positive electrode, negative electrode, and separator into a lithium-ion battery and inject a non-aqueous electrolyte. The electrolyte is prepared by mixing ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC) in a mass ratio of 2:5:3. Then, add 5% fluoroethylene carbonate (FEC) and 13% lithium hexafluorophosphate (LiPF6) by mass, along with the additive vinylene carbonate, with the additive content accounting for 2% of the total electrolyte content.

[0167] The above-mentioned batteries were subjected to performance tests, and the test content and methods are as follows:

[0168] First-cycle 0.2C discharge specific capacity: The lithium-ion battery prepared above was left to stand at 25℃ for 4 hours and then charged at 0.2C to 4.3V (constant voltage 4.3V, cutoff current 0.05C). After standing for 3 minutes, it was discharged at 0.2C to 3.0V, and the first discharge specific capacity (mAh / g) was recorded. The test results are shown in Table 2.

[0169] 5C discharge specific capacity: The lithium-ion battery prepared above was left to stand at 25℃ for 4 hours and then fully charged at 0.2C (4.3V, constant voltage to 0.02C). After standing for 5 minutes, it was discharged at 5C to 3.0V. The 5C discharge specific capacity (mAh / g) was recorded. The test was performed in three parallel tests and the average value was taken. The test results are shown in Table 2.

[0170] Capacity retention after 300 cycles: The lithium-ion battery prepared above was left to stand at 25°C for 4 hours, then charged and discharged at 1C (4.3V~3.0V, constant voltage charging to 0.05C). The discharge capacity Q1 of the first cycle and Q1 of the 300th cycle were recorded. 300 Press (Q) 300 The capacity retention rate is calculated by multiplying the result by 100% ( / Q1). The results are taken as the average of three parallel tests. The test results are shown in Table 2.

[0171] Table 2:

[0172]

[0173] As shown in Table 2, compared with the comparative example, the embodiment of the present invention can effectively improve the cycle performance of the battery by sequentially coating the surface of the lithium manganese iron phosphate core with a first coating layer and a second coating layer from the inside out, and at the same time, it can also make the battery have better rate performance.

[0174] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that, include: Lithium manganese iron phosphate core, first coating layer and second coating layer; The first coating layer covers at least a portion of the surface of the lithium manganese iron phosphate core, and the second coating layer covers at least a portion of the surface of the first coating layer; The first coating layer comprises a metal oxide material; the second coating layer comprises a carbon material.

2. The cathode material according to claim 1, characterized in that, The porosity of the positive electrode material is 4%~20%; And / or, the specific surface area of ​​the positive electrode material is 16 m². 2 / g~25m 2 / g; And / or, the metal oxide material includes at least one of aluminum oxide, titanium oxide, zirconium oxide, and magnesium oxide; And / or, the carbon material includes at least one of amorphous carbon or graphite.

3. The cathode material according to claim 1, characterized in that, The thickness of the first coating layer is 5nm~30nm; And / or, the thickness of the second coating layer is 5nm~30nm.

4. The cathode material according to claim 1, characterized in that, The lithium manganese iron phosphate core includes LiMn. X Fe 1- X PO4, where 0.1 ≤ x ≤ 0.

9.

5. A method for preparing the positive electrode material according to any one of claims 1-4, characterized in that, Includes the following steps: The first raw material system, including lithium source, manganese source, iron source and phosphorus source, is subjected to a first mixing treatment to obtain lithium manganese iron phosphate core precursor; The second raw material system, including the lithium manganese iron phosphate core precursor and the metal salt, is subjected to a second mixing process to obtain a second mixed system. The third raw material system, including the second mixed system and the carbon source, is subjected to a third mixing process to obtain a cathode material precursor. The cathode material precursor is sintered to obtain the cathode material.

6. The method for preparing the cathode material according to claim 5, characterized in that, The first raw material system also includes a reducing agent; And / or, the second raw material system further includes a first pore-forming agent; And / or, the third raw material system further includes a second pore-forming agent; The first pore-forming agent and the second pore-forming agent each independently include at least one of urea and melamine.

7. The method for preparing the cathode material according to claim 6, characterized in that, The mass of the metal salt is 3wt%~7wt% of the lithium manganese iron phosphate core precursor; And / or, the mass of the carbon source is 3wt% to 20wt% of the lithium manganese iron phosphate core precursor; And / or, the mass of the first pore-forming agent is 2wt% to 7wt% of the lithium manganese iron phosphate core precursor; And / or, the mass of the second pore-forming agent is 1wt% to 5wt% of the lithium manganese iron phosphate core precursor.

8. The method for preparing the cathode material according to claim 5, characterized in that, The sintering process is carried out at a temperature of 600℃ to 800℃ for a duration of 4 hours to 20 hours.

9. A positive electrode plate, characterized in that, It includes the cathode material described in any one of claims 1-4 or the cathode material prepared by any one of the preparation methods described in claims 5-8.

10. A battery, characterized in that, It includes the positive electrode material according to any one of claims 1-4, or the positive electrode material prepared by any one of the preparation methods according to claims 5-8, or the positive electrode sheet according to claim 9.

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