Positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention discloses a positive electrode material, a preparation method thereof and a lithium ion battery and belongs to the technical field of batteries. The positive electrode material comprises a substrate, a carbon coating layer and a second coating layer. The carbon coating layer coats at least part of the surface of the matrix, and the second coating layer coats at least part of the surface of the carbon coating layer. The matrix is a lithium-containing phosphate positive electrode active material, and the second coating layer contains boron-silicon-lithium oxide. The positive electrode material has good electronic conductivity, lithium ion diffusion coefficient and electrolyte corrosion resistance, and when the positive electrode material is applied to the lithium ion battery, the rate capability and cycle stability of the lithium ion battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] In recent years, with the continuous development of lithium ion battery technology, lithium ion batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] At present, according to the classification of positive electrode materials, lithium ion secondary batteries mainly include lithium iron phosphate batteries, lithium manganese batteries, lithium cobalt batteries, and ternary batteries containing nickel, cobalt and manganese elements. Among them, lithium iron phosphate batteries have the advantages of high safety, low cost and high cycle stability, and are increasingly widely used.

[0004] However, the capacity of the current lithium iron phosphate battery decays seriously at high rate. Therefore, it is necessary to provide a lithium iron phosphate positive electrode material capable of improving the rate performance of the battery. SUMMARY

[0005] Based on the above-mentioned deficiencies, the present application provides a positive electrode material, a preparation method thereof and a lithium ion battery to improve the rate performance and cycle stability of the lithium ion battery.

[0006] The present application is implemented as follows: In a first aspect, examples of the present application provide a positive electrode material, comprising a substrate, a carbon coating layer coated on at least part of the surface of the substrate, and a second coating layer coated on at least part of the surface of the carbon coating layer. The substrate is a lithium-containing phosphate positive electrode active material, and the second coating layer contains boron-silicon-lithium oxide.

[0007] In the above implementation process, the carbon coating layer and the second coating layer are sequentially coated on the surface of the lithium-containing phosphate positive electrode active material substrate. The carbon coating layer has good electronic conductivity, and the second coating layer contains boron-silicon-lithium oxide. The [BO3] triangular units and [BO4] tetrahedrons formed by B2O3 can be connected to the [SiO4] tetrahedrons formed by SiO2 through bridge oxygen to form a three-dimensional network structure. The interstitial sites in the three-dimensional network structure can provide lithium ion migration channels, reduce the migration energy barrier of lithium ions, and Li2O can react with B-O-B or Si-O-Si to form B-O - Li + or Si-O - Li +, generates movable lithium ions, replenishes the lithium loss of the electrode. And, the surface of the lithium-containing phosphate positive electrode active material substrate is coated with a carbon coating layer and a second coating layer in turn, and the double-layer coating structure can improve the electrolyte corrosion resistance of the positive electrode material. When the above-mentioned positive electrode material is applied to a lithium ion battery, the rate performance and cycle stability of the lithium ion battery can be improved.

[0008] In combination with the first aspect, in an optional implementation of the present application, the lithium-containing phosphate positive electrode active material is LiFe 1- x A x PO4, 0≤x≤0.02, A includes at least one of Mn, Ti, Nb, V, Mg, Al, Zn, Zr, Co or Ni.

[0009] Optionally, 0.005≤x≤0.02.

[0010] In the above implementation process, LiFe 1-x A x PO4 is used as the substrate, and the carbon coating layer and the second coating layer are coated on the surface of the substrate in turn, which can make the positive electrode material have the advantages of high safety, long cycle life and high rate performance. And, doping the above-mentioned doping elements in the substrate material can further improve the electronic conductivity of the positive electrode material, while causing lattice distortion, expanding the lithium ion transmission channel, and further improving the lithium ion diffusion coefficient. When the above-mentioned positive electrode material is applied to a lithium ion battery, the rate performance of the lithium ion battery can be further improved.

[0011] In combination with the first aspect, in an optional implementation of the present application, the carbon coating layer is doped with nitrogen elements, and the nitrogen elements form Fe-N bonds with the substrate.

[0012] Optionally, the proportion of nitrogen elements in the total mass of the positive electrode material is 0.1%~0.4%.

[0013] In the above implementation process, a proper amount of nitrogen elements is doped in the carbon coating layer, and the nitrogen elements can form Fe-N bonds with Fe in LiFe 1-x A x PO4, which enhances the interface stability of the substrate and the carbon coating layer, inhibits the first coating layer from falling off, and thus improves the cycle stability of the lithium ion battery. And, the Fe-N bond can also act as an "electron bridge" to reduce the contact resistance between the first coating layer and the substrate, thereby further improving the electronic conductivity of the positive electrode material, and thus further improving the rate performance of the lithium ion battery.

[0014] In combination with the first aspect, in an optional implementation of the present application, in the boron-silicon-lithium oxide, the molar ratio of B:Si:Li is 1:(0.8~1.2):(1.8~2.2).

[0015] Optionally, the molar ratio of B:Si:Li in the lithium borosilicate oxide is 1:(0.9-1.1):(1.8-2.2).

[0016] In the above implementation process, the molar ratio of B:Si:Li in the lithium borosilicate oxide is controlled to be 1:(0.8-1.2):(1.8-2.2), the appropriate boron-silicon ratio can form a stable three-dimensional network structure, and the appropriate lithium content can improve the ionic conductivity and avoid the generation of by-products due to excessive lithium content.

[0017] In combination with the first aspect, in an optional implementation of the present application, the lithium borosilicate oxide is further doped with a metal oxide other than lithium oxide, and the ionic radius of the metal ion in the metal oxide is 0.05-0.12 nm.

[0018] In the above implementation process, the above metal oxide is doped in the lithium borosilicate oxide, and the ionic radius of the metal ion in the metal oxide is 0.05-0.12 nm, which can locally expand the gap space of the three-dimensional network structure, further widen the lithium ion migration channel, and is conducive to further reducing the migration energy barrier of lithium ions, thereby promoting the rapid migration of lithium ions and further improving the lithium ion diffusion coefficient of the positive electrode material.

[0019] In combination with the first aspect, in an optional implementation of the present application, the metal oxide includes at least one of copper oxide, nickel oxide, cobalt oxide, or manganese oxide.

[0020] In the above implementation process, the above metal oxide is doped in the lithium borosilicate oxide, and the metal ion in the metal oxide not only has an appropriate ionic radius, can locally expand the gap space of the network structure, further widen the lithium ion migration channel, reduce the migration energy barrier of lithium ions, thereby promote the rapid migration of lithium ions, but also has good electronic conductivity, which can further improve the lithium ion diffusion coefficient and electronic conductivity of the positive electrode material.

[0021] In combination with the first aspect, in an optional implementation of the present application, in the second coating layer, the metal element M in the metal oxide satisfies the molar ratio of B:Si:Li:M is 1:(0.8-1.2):(1.8-2.2):(0.02-0.1).

[0022] In the above implementation process, in the second coating layer, the molar ratio of B:Si:Li:M is controlled to be 1:(0.8~1.2):(1.8~2.2):(0.02~0.1), which can form a stable three-dimensional network structure. The three-dimensional network structure has suitable stiffness and toughness, and can embed metal ions with high ionic radii, widening the lithium ion migration channels. This enables the cathode material to have good electronic conductivity and lithium ion diffusion coefficient, which can improve the rate performance of lithium ion batteries when applied to lithium ion batteries.

[0023] In conjunction with the first aspect, in optional embodiments of this application, the thickness of the carbon coating layer is 2-6 nm. And / or, the thickness of the second coating layer is 1-3 nm.

[0024] In the above process, a carbon coating layer of 2-6 nm thickness and a second coating layer of 1-3 nm thickness are sequentially coated on the surface of the lithium phosphate positive electrode active material matrix. This can ensure that the positive electrode material has good electronic conductivity, lithium ion diffusion coefficient and electrolyte corrosion resistance, while also enabling the positive electrode material to have a high proportion of active material. When applied to lithium-ion batteries, this can improve the overall electrical performance of lithium-ion batteries.

[0025] In a second aspect, an example of this application provides a method for preparing a cathode material, comprising: A first coating is obtained, the first coating comprising a matrix and a carbon coating layer covering at least a portion of the surface of the matrix, the matrix being a lithium phosphate positive electrode active material.

[0026] A mixture is obtained by mixing a first lithium source, a boron source, a silicon source, and a first coating body. The mixture is then sintered to form a second coating layer containing borosilicate lithium oxide on at least the surface of the first coating body.

[0027] In the above process, during the preparation of the cathode material, a lithium phosphate material coated with a carbon coating is uniformly mixed with a first lithium source, a boron source, and a silicon source to form a mixture. This mixture is then sintered, allowing the first lithium source, boron source, and silicon source to react in situ on the surface of the first coating to form borosilicate lithium oxide. In the borosilicate lithium oxide, the [BO3] triangular units and [BO4] tetrahedra formed by B2O3 can connect with the [SiO4] tetrahedra formed by SiO2 through bridging oxygen to form a three-dimensional network structure. The interstitial sites in this three-dimensional network structure provide lithium-ion migration channels, reducing the lithium-ion migration energy barrier and giving the cathode material good ionic conductivity. Li2O can react with BOB or Si-O-Si to generate BO3. - Li + or Si-O - Li +This process generates mobile lithium ions, replenishing the lithium losses in the electrode. Furthermore, the borosilicate lithium oxide coating on the surface of the first coating also serves as a coating layer, improving the electrolyte corrosion resistance of the cathode material. Since the surface of the lithium phosphate cathode active material matrix is ​​coated with a carbon coating layer, which possesses good electronic conductivity, the resulting cathode material, when applied to lithium-ion batteries, can improve the rate performance and cycle stability of the lithium-ion battery.

[0028] In conjunction with the second aspect, in an optional embodiment of this application, the mixture further contains a first metal element source. The metal element in the first metal element source does not include lithium. The ionic radius of the metal ions in the first metal element source is 0.05-0.12 nm.

[0029] Optionally, the first metal element source includes at least one of a copper source, a nickel source, a cobalt source, or a manganese source.

[0030] Optionally, the first lithium source includes at least one of lithium acetate, lithium hydroxide, lithium nitrate, and lithium carbonate. And / or, the boron source includes at least one of boric acid, trimethyl borate, and boron oxide. And / or, the silicon source includes at least one of tetraethyl orthosilicate, silica sol, lithium silicate, and methyltriethoxysilane. And / or, the first metal element source includes at least one of copper acetate, copper acetylacetonate, copper nanoparticles, copper nitrate, and copper formate.

[0031] Optionally, the sintering temperature is 400~500℃.

[0032] In the above-described process, when preparing the second coating layer, the aforementioned first metal element source is added to the mixture. During sintering, the first lithium source, boron source, silicon source, and first metal element source in the mixture can react in situ on the surface of the first coating body to form a borosilicate lithium oxide coating layer doped with metal oxides, which can be denoted as bB₂O₃·cSiO₂·dLi₂O·aMO, where M represents the metal element. Doping the borosilicate lithium oxide with the aforementioned metal oxide not only allows the metal ions in the metal oxide to have suitable ionic radii, enabling them to locally expand the interstitial space of the three-dimensional network structure, further widening the lithium ion migration channels, and reducing the lithium ion migration energy barrier, thereby promoting rapid lithium ion migration, but also provides good electronic conductivity, which further improves the lithium ion diffusion coefficient and electronic conductivity of the cathode material.

[0033] In conjunction with the second aspect, in an optional embodiment of this application, the method for obtaining the first coating includes: The raw materials used to form lithium phosphate positive electrode active materials are mixed with a carbon source to form a precursor powder; the precursor powder is sintered to obtain a first coating having a carbon coating layer on at least a portion of the surface of the matrix.

[0034] Optionally, the lithium phosphate cathode active material is LiFe. 1-x A x PO4, 0≤x≤0.02, A includes at least one of Mn, Ti, Nb, V, Mg, Al, Zn, Zr, Co or Ni. A nitrogen source is also added to the mixture.

[0035] Optionally, the ratio of the total mass of raw materials to the mass of carbon source to nitrogen source is 1:(0.05~0.15):(0~0.03).

[0036] Optionally, the nitrogen source includes at least one of polydopamine, 1,10-phenanthroline, melamine, polyaniline, and pyridine.

[0037] Optionally, the carbon source includes at least one of glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, and polyethylene glycol.

[0038] Optionally, the raw materials include a second lithium source, a phosphorus source, and a second metal element source.

[0039] In the above-mentioned process, when preparing the first coating, the raw materials used to form the lithium phosphate positive electrode active material, such as the second lithium source, phosphorus source and the second metal element source, are mixed with the organic carbon source to form a precursor powder. When the precursor powder is sintered, the second lithium source, phosphorus source and the second metal element source can react to form a lithium phosphate positive electrode active material matrix. The carbon source is carbonized in situ on the surface of the matrix to form a carbon coating layer, so that the carbon coating layer can be more uniformly and tightly coated on the surface of the matrix, thereby improving the electronic conductivity and stability of the first coating.

[0040] Furthermore, by adding the aforementioned nitrogen source to the precursor powder during the preparation of the first coating, nitrogen doping of the carbon coating layer can be achieved. This allows nitrogen to form Fe-N bonds with Fe in the matrix, enhancing the interfacial stability between the matrix and the carbon coating layer, inhibiting the shedding of the first coating layer, and thus improving the stability of the cathode material. Additionally, the Fe-N bonds can also act as "electron bridges," reducing the contact resistance between the first coating layer and the matrix, thereby further improving the electronic conductivity of the cathode material.

[0041] In a third aspect, an example of this application provides a lithium-ion battery, including the cathode material provided in the first aspect, or the cathode material prepared according to the preparation method provided in the second aspect.

[0042] In the above-described process, the aforementioned positive electrode material is added to the lithium-ion battery. This positive electrode material's active material is a lithium phosphate-containing positive electrode active material, which possesses advantages such as high safety, low cost, and high cycle stability. Furthermore, a carbon coating layer and a second coating layer are sequentially coated onto the surface of the lithium phosphate-containing positive electrode active material matrix, enabling the positive electrode material to simultaneously possess good electronic conductivity, lithium-ion diffusion coefficient, and resistance to electrolyte corrosion. This, in turn, allows the lithium-ion battery to exhibit excellent rate performance and cycle stability. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0044] Figure 1 A schematic diagram of the cathode material provided as an example in this application; Figure 2 HRTEM image of the cathode material provided in Embodiment 1 of this application; Figure 3 XPS spectrum of the cathode material provided in Example 1 of this application; Figure 4 XPS spectrum of N1s of the cathode material provided in Example 1 of this application.

[0045] Icons: 100 - Cathode material; 101 - Substrate; 102 - Carbon coating layer; 103 - Second coating layer. Detailed Implementation

[0046] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0047] Lithium iron phosphate (LiFePO4) is widely used in power batteries and energy storage due to its advantages such as high safety, long cycle life, and low cost. However, current lithium iron phosphate batteries often suffer from severe capacity decay at high rates, resulting in poor rate performance and failing to meet the requirements of high-rate charge and discharge scenarios.

[0048] Analysis revealed that the intrinsic electronic conductivity of lithium iron phosphate materials is (~10) -9 S / cm) and lithium-ion diffusion coefficient (~10) -14 cm 2 Its low ( / s) limits its high-rate performance.

[0049] To improve the rate performance of lithium iron phosphate (LFP) batteries, an attempt was made to coat the surface of LFP materials with a carbon layer to increase the electronic conductivity of the cathode material, hoping to improve the rate performance of lithium-ion batteries. However, the lithium-ion diffusion rate of carbon-coated LFP materials could not be effectively improved, and lithium ions were difficult to quickly insert into or extract from the material during high-rate charge and discharge processes, thus failing to effectively improve the rate performance of lithium-ion batteries.

[0050] The inventors believe that if a layer of ion conductor material with high lithium-ion diffusion performance is coated on the surface of carbon-coated lithium iron phosphate material, the lithium-ion diffusion coefficient of the cathode material can be improved, which may improve the rate performance of lithium iron phosphate lithium-ion batteries.

[0051] Currently, ion conductor materials with good lithium-ion diffusion coefficients mainly include other types of positive electrode active materials or solid electrolyte materials, such as lithium cobalt oxide. However, if another layer of lithium cobalt oxide or other positive electrode active materials is coated on the surface of carbon-coated lithium iron phosphate, side reactions can easily occur upon contact with the electrolyte. This not only fails to effectively improve the rate performance of the battery but also affects the cycle performance of the lithium-ion battery. Therefore, the choice of which ion conductor material to coat the surface of lithium iron phosphate material often directly affects the overall electrical performance of the lithium-ion battery.

[0052] To achieve the above objectives, after repeated research, the inventors discovered that if a layer containing borosilicate lithium oxide is coated onto the surface of lithium iron phosphate, the structure of this borosilicate lithium oxide, in which B2O3 forms [BO3] triangular units and [BO4] tetrahedra, can connect with the [SiO4] tetrahedra formed by SiO2 through bridging oxygen to form a three-dimensional network. The interstitial sites in this three-dimensional network can provide lithium-ion migration channels, lowering the lithium-ion migration energy barrier and promoting rapid lithium-ion migration during charging and discharging. Furthermore, the lithium oxide in the borosilicate lithium oxide can directly react with B2O3 and SiO2 at relatively low temperatures to generate BO3. - Li + or Si-O - Li + This process generates mobile lithium ions, compensating for irreversible lithium loss caused by side reactions between the electrode and the electrolyte. Furthermore, borosilicate lithium oxide can prevent electrolyte decomposition products such as HF and PF5 from corroding the positive electrode active material, thereby reducing the formation of side reactions and byproducts and giving lithium-ion batteries excellent cycle stability.

[0053] Furthermore, the inventors discovered that, in addition to lithium iron phosphate, sequentially coating the surface of other lithium phosphate positive electrode active materials with a carbon coating layer and the aforementioned coating layer containing borosilicate lithium oxide can also improve their electronic conductivity and lithium-ion diffusion efficiency. When applied to lithium-ion batteries, this enables the lithium-ion batteries to simultaneously possess good rate performance and cycle stability.

[0054] The cathode material of this application will now be described in further detail.

[0055] The cathode material provided in this application includes a substrate, a carbon coating layer, and a second coating layer. The carbon coating layer covers at least a portion of the surface of the substrate, and the second coating layer covers at least a portion of the surface of the carbon coating layer. The substrate is a lithium phosphate-containing cathode active material, and the second coating layer contains borosilicate lithium oxide.

[0056] Please refer to the schematic diagram showing the positional relationship between the matrix, carbon coating, and second coating. Figure 1 .like Figure 1 As shown, in the cathode material 100, a carbon coating layer 102 covers at least a portion of the surface of the substrate 101, and a second coating layer 103 covers at least a portion of the surface of the carbon coating layer 102. It is understood that... Figure 1 The positional relationships and coating shapes shown are for illustrative purposes only and do not represent the actual morphology of the cathode material.

[0057] In this application, "the carbon coating layer covering at least a portion of the substrate surface" means that the carbon coating layer can cover the entire surface of the substrate for full coverage, or it can cover a portion of the substrate surface for partial coverage. The structure formed by covering at least a portion of the substrate surface with the carbon coating layer can be referred to as the first coating body.

[0058] Similarly, the second coating layer can fully or partially cover the first coating. It is understandable that when the carbon coating layer partially covers the substrate, a portion of the second coating layer can also directly contact the substrate not covered by the carbon coating layer.

[0059] The double-coating structure of the cathode material can be seen from the HRTEM image of the cathode material, which shows that two coating layers are formed outside the matrix.

[0060] The cathode material provided in this application uses conventional lithium phosphate-containing cathode active materials from the lithium-ion battery field as the matrix. Examples of lithium phosphate-containing cathode active materials may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, also known as LFP) and its doped materials, lithium manganese phosphate (such as LiMnPO4) and its doped materials, or lithium manganese iron phosphate and its doped materials.

[0061] In some embodiments, the lithium phosphate-containing positive electrode active material can be LiFe 1-x A x PO4, 0 ≤ x ≤ 0.02, A includes at least one of Mn, Ti, Nb, V, Mg, Al, Zn, Zr, Co, or Ni. LiFe 1-x A xUsing PO4 as a matrix, and sequentially coating the surface of the matrix with a carbon coating layer and a second coating layer, enables the cathode material to have advantages such as high safety, long cycle life and high rate performance.

[0062] This application does not limit the specific value of x, and it can be selected as needed within the above range. As an example, x can be one of 0, 0.001, 0.005, 0.01, 0.015, or 0.02, or a range between any two.

[0063] Furthermore, in some embodiments, 0.005 ≤ x ≤ 0.02. Doping lithium iron phosphate materials with appropriate amounts of the aforementioned doping elements can further improve the electronic conductivity of the cathode material, while simultaneously causing lattice distortion, expanding the lithium-ion transport channels, and further improving the lithium-ion diffusion coefficient.

[0064] In this application, the carbon coating layer refers to a coating layer formed from carbon materials. The carbon coating layer exhibits good electronic conductivity. In some embodiments, the carbon material may be an organic material containing C, H, and O elements, formed by carbonization. It is understood that this application does not limit the carbon coating layer to be formed by carbonization of organic materials. In some embodiments, the carbon coating layer may also be formed by mechanically ball-milling a conventional conductive carbon material with a matrix. Conventional conductive carbon materials include, but are not limited to, artificial graphite, natural graphite, soft carbon, hard carbon, superconducting carbon, acetylene black, carbon black, or Ketjen black.

[0065] In some embodiments, the carbon coating layer is also doped with nitrogen. As an example, the nitrogen doped in the carbon coating layer may be pyrrole nitrogen, pyridine nitrogen, or graphitic nitrogen.

[0066] Furthermore, in some embodiments, the nitrogen content in the total mass of the cathode material is 0.1% to 0.4%. As an example, the nitrogen content in the total mass of the cathode material is one or any two of 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, or 0.4%.

[0067] When the matrix material includes LiFe 1-x A x In the presence of PO4, the nitrogen element in the carbon coating layer can form Fe-N bonds with the Fe element in the matrix, enhancing the interfacial stability between the matrix and the carbon coating layer, inhibiting the shedding of the first coating layer, and thus improving the cycle stability of the cathode material. Furthermore, the Fe-N bond can also act as an "electron bridge," reducing the contact resistance between the first coating layer and the matrix, thereby further improving the electronic conductivity of the cathode material.

[0068] Nitrogen doping elements and Fe-N bonds in cathode materials can be detected using XPS technology. To determine the mass content of nitrogen in cathode materials, an elemental analyzer can be used. The initial mass of the cathode material is recorded, and the sample is completely combusted under high temperature and high oxygen conditions. The nitrogen is converted into nitrogen oxides, which are then converted into nitrogen gas (N2) in a reduction furnace. The amount of nitrogen gas is measured using a thermal conductivity detector (TCD), thereby calculating the nitrogen content in the cathode sample. The nitrogen content is calculated as (nitrogen mass / initial mass of cathode material) × 100%.

[0069] In some embodiments, the thickness of the carbon coating layer can be 2-6 nm. Coating the substrate surface with a carbon coating layer of appropriate thickness can improve the electronic conductivity of the cathode material, reduce the content of inactive substances in the cathode material, and increase the energy density of the cathode material.

[0070] As an example, the thickness of the carbon coating can be one of 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm or 6nm or any combination thereof.

[0071] When measuring the thickness of the carbon coating layer in the cathode material, a high-resolution transmission electron microscope (HRTEM) can be used to image the cross-section of the cathode material particles, and the thickness of the carbon coating layer can be measured from the HRTEM image.

[0072] The second coating layer contains borosilicate lithium oxide, with [BO3] triangular units and [BO4] tetrahedra formed by B2O3, which can connect with [SiO4] tetrahedra formed by SiO2 through bridging oxides to form a three-dimensional network. The interstitial positions in the three-dimensional network structure provide lithium-ion migration channels, lowering the lithium-ion migration energy barrier and promoting rapid lithium-ion migration during charging and discharging. Li2O has a theoretical lithium content as high as 46.4%, good thermal stability, and can directly react with B2O3 and SiO2 at relatively low temperatures to form BO3. - Li + or Si-O - Li + This generates mobile lithium ions, compensating for irreversible lithium loss caused by side reactions between the electrode and the electrolyte.

[0073] The borosilicate lithium oxide in this application is an amorphous material. When detecting the second coating layer, XPS analysis can be performed on the cathode material to determine the presence of Si, B, Li, and O elements.

[0074] In some embodiments, the molar ratio of B:Si:Li in the borosilicate lithium oxide is 1:(0.8~1.2):(1.8~2.2). Controlling the molar ratio of B:Si:Li to 1:(0.8~1.2):(1.8~2.2) allows for the formation of a stable three-dimensional network structure, while a suitable lithium content improves ionic conductivity and avoids the generation of byproducts due to excessive lithium content.

[0075] This application does not limit the specific proportions of each element in borosilicate lithium oxide. As an example, the molar ratio of B to Si can be one of 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1.0, 1:1.05, 1:1.1, 1:1.15, or 1:2, or any range between two of these. As an example, the molar ratio of B to Li can be one of 1:1.8, 1:1.9, 1:2.0, 1:2.1, or 2.2, or any range between two of these.

[0076] Furthermore, in some embodiments, the molar ratio of B:Si:Li is 1:(0.9~1.1):(1.8~2.2).

[0077] In some embodiments, the thickness of the second coating layer is 1-3 nm. Coating the substrate surface with a second coating layer of appropriate thickness can improve the lithium-ion diffusion coefficient of the cathode material, reduce the content of inactive substances in the cathode material, and increase the energy density of the cathode material.

[0078] As an example, the thickness of the second coating layer can be one of 1 nm, 1.5 nm, 2 nm, 2.5 nm or 3 nm or any combination thereof.

[0079] The thickness of the second coating layer in the cathode material can be measured by referring to the method described above for measuring the carbon coating layer, and will not be repeated here.

[0080] Furthermore, in some embodiments, the borosilicate lithium oxide is also doped with a metal oxide other than lithium oxide, wherein the ionic radius of the metal ions in the metal oxide is 0.05~0.12 nm. The metal oxide described in this application does not contain lithium oxide. Doping the borosilicate lithium oxide with the aforementioned metal oxide, wherein the ionic radius of the metal ions in the metal oxide is 0.05~0.12 nm, can locally expand the interstitial space of the network structure, further widening the lithium ion migration channels, which is beneficial for reducing the lithium ion migration energy barrier, thereby promoting rapid lithium ion migration and further improving the lithium ion diffusion coefficient of the cathode material.

[0081] The detection of metal oxides in the second coating layer can be performed by referring to the method described above for detecting the elemental types of borosilicate lithium oxides. The ionic radius can be obtained by consulting relevant literature based on the detected metal element type.

[0082] This application does not limit the specific ionic radius of the metal ion in the metal oxide, and the appropriate selection can be made within the above range as needed. As an example, the ionic radius of the metal ion can be one of 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11 or 0.12 or any combination thereof.

[0083] Furthermore, in some embodiments, the electronic conductivity of the elemental metal corresponding to the metal ion in the metal oxide is not less than 1.7 × 10⁻⁶. 4 The S / cm ratio can further improve the electronic conductivity of the cathode material.

[0084] In metal oxides, the metallic element corresponding to the metal ion refers to, for example, copper oxide, where the corresponding metallic element is elemental copper, and the electronic conductivity of elemental copper is not less than 1.7 × 10⁻⁶. 4 S / cm. The detection of metal oxides in the second coating layer can be performed by referring to the method described above for measuring the elemental types of borosilicate lithium oxides. Based on the detected metal element type, the electronic conductivity of the metal element can be obtained by consulting relevant literature.

[0085] In some embodiments, the metal oxide doped in the borosilicate lithium oxide may be at least one of copper oxide, nickel oxide, cobalt oxide, or manganese oxide.

[0086] As an example, the second coating layer can be borosilicate lithium copper oxide. As an example, the second coating layer can be borosilicate lithium copper oxide. As an example, the second coating layer can be borosilicate lithium copper oxide. As an example, the second coating layer can be borosilicate lithium copper oxide.

[0087] Furthermore, in some embodiments, in the second coating layer, the metal element M in the metal oxide satisfies a molar ratio of B:Si:Li:M of 1:(0.8~1.2):(1.8~2.2):(0.02~0.1). Doping borosilicate lithium oxide with an appropriate amount of metal oxide can reduce the probability of lithium-ion diffusion channels being blocked due to excessive metal ions, and reduce the impact of insufficient metal ions on the electronic conductivity and lithium-ion diffusion coefficient of the second coating layer, thereby improving the lithium-ion diffusion coefficient and electronic conductivity of the cathode material.

[0088] Similarly, detecting the amount of metal oxide doping in the second coating layer allows for XPS elemental analysis of the cathode material, determining the content of Si, B, Li, and other metal elements, and calculating the molar ratio.

[0089] Furthermore, embodiments of this application also provide a method for preparing the above-mentioned cathode material, comprising: S1. Obtain the first coating. The first coating includes a matrix and a carbon coating layer covering at least a portion of the surface of the matrix, wherein the matrix is ​​a lithium phosphate positive electrode active material.

[0090] S2. A mixture is obtained by mixing a first lithium source, a boron source, a silicon source, and a first coating body. The mixture is then sintered to form a second coating layer containing borosilicate lithium oxide on at least the surface of the first coating body.

[0091] In step S1, this application does not limit how the first coating is obtained; commercially available carbon-coated lithium iron phosphate cathode materials can be purchased.

[0092] Alternatively, this application embodiment also provides a method for preparing the first coating: S11. The raw materials used to form lithium phosphate cathode active materials are mixed with a carbon source to form a precursor powder. The precursor powder is sintered to obtain a first coating having a carbon coating layer on at least a portion of the surface of the substrate.

[0093] Lithium phosphate cathode active materials are conventional lithium phosphate series cathode materials in the field of lithium-ion batteries.

[0094] It is understood that the raw materials used to form lithium phosphate cathode active materials include a second lithium source, a phosphorus source, and a second metal element source. As an example, the second lithium source can be at least one of lithium hydroxide, lithium carbonate, lithium acetate, or lithium nitrate. As an example, the phosphorus source can be at least one of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, iron phosphate, lithium phosphate, or lithium dihydrogen phosphate. When the lithium phosphate cathode active material is lithium iron phosphate, the second metal element source is an iron source. When the lithium phosphate cathode active material is LiFe... 1-x A x When PO4 and A include at least one of Mn, Ti, Nb, V, Mg, Al, Zn, Zr, Co, or Ni, the second metal element source includes an iron source and an A source. The A source includes at least one of Mn source, Ti source, Nb source, V source, Mg source, Al source, Zn source, Zr source, Co source, or Ni source.

[0095] As an example, the carbon source includes at least one of glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, or polyethylene glycol.

[0096] In some embodiments, the ratio of the total mass of the raw materials to the mass of the carbon source can be 1:(0.05~0.15). As an example, the ratio of the total mass of the raw materials to the mass of the carbon source can be one of 1:0.05, 1:0.10, or 1:0.15, or a range between any two.

[0097] As an example, in step S11, the method for preparing the precursor powder includes: According to the stoichiometric ratio of the lithium phosphate cathode active material, a second lithium source, a second metal source, a phosphorus source, and an optional A source were weighed out, and a carbon source was added. The mixture was stirred in pure water until homogeneous, and then milled to obtain a milled slurry. The milled slurry was then spray-dried to obtain a precursor powder.

[0098] Furthermore, in some embodiments, the precursor powder also contains a nitrogen source.

[0099] As an example, the nitrogen source includes at least one of polydopamine, 1,10-phenanthroline, melamine, polyaniline, and pyridine.

[0100] In some embodiments, the ratio of the total mass of the raw materials to the mass of the nitrogen source can be 1:(0~0.03). As an example, the ratio of the total mass of the raw materials to the mass of the nitrogen source can be one of 1:0.01, 1:0.02, or 1:0.03, or a range between any two.

[0101] As an example, in step S11, according to the stoichiometric ratio of the lithium phosphate cathode active material, a second lithium source, a second metal source, a phosphorus source, and an optional A source are weighed, and a carbon source is added. The mixture is stirred in pure water until homogeneous, and then milled to obtain a milled slurry. The D50 of the milled slurry is 100~450nm, and the solid content is 30%~50%. The milled slurry is then spray-dried at an inlet air temperature of 170~220℃ and an outlet air temperature of 90~120℃ to obtain precursor powder. The precursor powder is then subjected to a first-stage sintering and a second-stage sintering: the first-stage sintering temperature is 350~550℃, the holding time is 2~6h, and the heating rate is 1~3℃ / min. After the first-stage sintering, a second-stage sintering is performed at a holding temperature of 760~830℃, the holding time is 8~15h, and the heating rate is 2~6℃ / min.

[0102] Understandably, in step S11, during sintering, the carbon source can carbonize to form a carbon coating layer, so the sintering atmosphere should be inert to prevent the carbon source from oxidizing and releasing carbon dioxide. Similarly, in step S2, to prevent the carbon coating layer from oxidizing during sintering, the sintering of the mixture can also be carried out under an inert atmosphere. As an example, the inert atmosphere can be a nitrogen atmosphere or an argon atmosphere.

[0103] In step S2, the first lithium source includes at least one of lithium acetate, lithium hydroxide, lithium nitrate, or lithium carbonate. The boron source includes at least one of boric acid, trimethyl borate, or boron oxide. The silicon source includes at least one of tetraethyl orthosilicate, silica sol, lithium silicate, or methyltriethoxysilane.

[0104] In some embodiments, in step S2, a first metal element source is further added to the mixture. The metal element in the first metal element source does not include lithium. The ionic radius of the metal ions in the first metal element source is 0.05~0.12 nm. Adding the first metal element source to the mixture allows for the doping of metal oxides into borosilicate lithium oxide.

[0105] As an example, the first metal element source includes at least one of a copper source, a nickel source, a cobalt source, or a manganese source.

[0106] As an example, when the metal element in the first metal element source is copper, the copper source includes at least one of copper acetate, copper acetylacetonate, nano copper powder, copper nitrate, and copper formate. As an example, the nickel source, cobalt source, or manganese source can be selected from corresponding metal salts or elemental metal powders, etc.

[0107] As an example, in step S2, according to the molar ratio of B:Si:Li:Cu of 1:(0.8~1.2):(1.8~2.2):(0.02~0.1), the corresponding boron source, silicon source, first lithium source, and copper source are weighed, added to a solvent, and heated and stirred to form a sol. In the sol, the total mass of the first lithium source, boron source, silicon source, and copper source to the volume ratio of the solvent is 1g:(10~20)mL, and the solvent is a mixed solvent of ethanol:water = 1~(5:1) (volume ratio). Then, according to the mass ratio of the first coating body to the volume of the sol of 1g:(10~20)mL, the first coating body is dispersed in the above sol, ultrasonically treated for 20~40min, dried at a drying temperature of 70~100℃, and sintered under an argon atmosphere at a sintering temperature of 400~500℃ to obtain the final cathode material.

[0108] The cathode material provided in this application embodiment has a content of not less than 1.12 × 10⁻⁶. -3 Electronic conductivity of S / cm and not less than 1.13×10 -11 cm 2 The lithium-ion diffusion coefficient is 1 / s.

[0109] As an example, the cathode material provided in this application embodiment has an electronic conductivity of 1.12 × 10⁻⁶. -3 ~1.74×10 -3 S / cm, lithium-ion diffusion coefficient is 1.13×10 -11 ~2.94×10 -11 cm 2 / s.

[0110] Furthermore, embodiments of this application also provide a lithium-ion battery, including the above-mentioned positive electrode material.

[0111] Understandably, in lithium-ion batteries, the aforementioned positive electrode material is used to form the positive electrode sheet. Of course, in addition to the positive electrode sheet, a lithium-ion battery also includes a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode sheets. The electrolyte acts as a conductor of ions between the positive and negative electrode sheets. The separator, placed between the positive and negative electrode sheets, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0112] This application does not limit the specific types of the negative electrode, electrolyte, and separator mentioned above; appropriate selections can be made based on conventional lithium-ion batteries in the field.

[0113] The cathode material of this application will be further described in detail below with reference to the embodiments.

[0114] Example 1 This embodiment provides a cathode material, and the preparation method is as follows: (1) Weigh Li2CO3 (second lithium source), FeC2O4·2H2O (iron source), NH4H2PO4 (phosphorus source), and TiO2 (doped element titanium, A source) according to the molar ratio Li:Fe:Ti:P=1:0.995:0.005:1. Then weigh glucose (carbon source) and polydopamine (nitrogen source) according to the ratio of total mass of second lithium source, iron source, phosphorus source and titanium source (i.e., total mass of raw materials): mass of carbon source: mass of nitrogen source=1:0.08:0.012. Add the above substances to pure water and control the solid content to 30%. Stir until uniformly mixed, then perform sand milling and control the D50 of the sand milling slurry to 380nm.

[0115] (2) The sand-milled slurry was then spray-dried at an inlet air temperature of 180°C and an outlet air temperature of 100°C to obtain precursor powder. The precursor powder was then subjected to a first-stage and second-stage sintering process under an argon atmosphere: the precursor powder was heated to 450°C at a heating rate of 2°C / min for a first-stage sintering, with a holding time of 4 hours. Then, it was heated to 810°C at a heating rate of 3°C / min for a second-stage sintering, with a holding time of 10 hours. Natural cooling was then performed to obtain the first coating body. The matrix of the first coating body was LiFe. 0.995 Ti 0.005 PO4 (hereinafter referred to as LFTP).

[0116] (3) Weigh out H3BO3 (boron source), tetraethyl orthosilicate (TEOS, silicon source), LiNO3 (first lithium source), and copper nitrate (first metal element source, copper ion radius is about 0.0736 nm, and the electronic conductivity of metallic copper is about 5.8 × 10⁻⁵) according to the molar ratio B:Si:Li:Cu=1:1:2:0.05.7 (S / m), and then these substances were dissolved in an ethanol-water mixed solvent with a volume ratio of 3:1, according to the total mass of the first lithium source, boron source, silicon source and copper source: solvent volume of 1g:15mL, and stirred at 60℃ to form a sol. Next, the first coating body was dispersed in the sol at a ratio of 1g:15mL, ultrasonicated for 30min, and dried at 80℃ to obtain a mixture. Then, under an argon atmosphere, the mixture was heated to 450℃ and sintered for 2h at a heating rate of 2℃ / min to obtain the cathode material.

[0117] Example 2 This embodiment provides a cathode material that differs from Embodiment 1 in that the total mass of the second lithium source, iron source, phosphorus source, and titanium source (i.e., the total mass of the raw materials) in step (1) is: the mass of the carbon source is: the mass of the nitrogen source is = 1:0.08:0. That is, no nitrogen source is added to the precursor powder, and no nitrogen element is doped in the carbon coating layer.

[0118] Example 3 This embodiment provides a cathode material, which differs from Embodiment 1 in that the total mass of the second lithium source, iron source, phosphorus source and titanium source in step (1) (i.e. the total mass of the raw materials) is: the mass of the carbon source is: the mass of the nitrogen source = 1:0.08:0.03.

[0119] Example 4 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu=1:1:2:0.02.

[0120] Example 5 This embodiment provides a positive electrode material, which differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu=1:1:2:0.1.

[0121] Example 6 This embodiment provides a cathode material that differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu = 1:1:2:0. That is, the borosilicate lithium oxide in the second coating layer is not doped with metal oxides such as copper oxide.

[0122] Example 7 This embodiment provides a positive electrode material, which differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu=1:1.3:2:0.05.

[0123] Example 8 This embodiment provides a positive electrode material, which differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu=1:0.7:2:0.05.

[0124] Example 9 This embodiment provides a positive electrode material, which differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu=1:1:2.3:0.05.

[0125] Example 10 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu=1:1:1.7:0.05.

[0126] Example 11 This embodiment provides a positive electrode material, which differs from Embodiment 1 in that, in step (3), B:Si:Li:Cu=1:1:2:0.2.

[0127] Example 12 This embodiment provides a cathode material that differs from Embodiment 1 in that, in step (3), the metal oxide is nickel oxide, with a B:Si:Li:Ni ratio of 1:1:2:0.05. That is, the borosilicate lithium oxide in the second coating layer is doped with nickel oxide (nickel ion radius is approximately 0.069 nm, and the electronic conductivity of metallic nickel is approximately 1.43 × 10⁻⁶). 5 S / cm).

[0128] Example 13 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (3), the metal oxide is beryllium oxide, with B:Si:Li:Be=1:1:2:0.05. That is, the borosilicate lithium oxide in the second coating layer is doped with beryllium oxide (the radius of beryllium ions is about 0.045 nm).

[0129] Example 14 This embodiment provides a cathode material, which differs from Embodiment 1 in that a titanium source is not added in step (1). That is, the matrix material is lithium iron phosphate (hereinafter referred to as LFP).

[0130] Example 15 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (1), Li2CO3 (second lithium source), manganese nitrate (manganese source), and NH4H2PO4 (phosphorus source) are weighed according to a molar ratio of Li:Mn:P=1:1:1. That is, the matrix material is lithium manganese phosphate (hereinafter referred to as LMP).

[0131] Example 16 This embodiment provides a cathode material, which differs from Embodiment 1 in that the total mass of the second lithium source, iron source, phosphorus source and titanium source (i.e., the total mass of raw materials) in step (1) is: the mass of the carbon source is: the mass of the nitrogen source is = 1:0.16:0.05. In step (2), the first coating body is dispersed in the sol according to the ratio of first coating body:sol = 1g:30mL, ultrasonically treated for 30min, and dried at 80℃ to obtain a mixture.

[0132] Comparative Example 1 This comparative example provides a cathode material that differs from Example 1 in that no carbon source or nitrogen source is added in step (1). That is, the cathode material does not contain a carbon coating layer.

[0133] Comparative Example 2 This comparative example provides a cathode material that differs from Example 1 in that step (3) is omitted. That is, the cathode material does not contain a second coating layer.

[0134] Comparative Example 3 This comparative example provides a cathode material that differs from Example 1 in that, in step (3), the molar ratio of Li:B:Mg is 2:1:0.05, and LiNO3 (first lithium source), H3BO3 (boron source), and magnesium oxide (first metal element source, magnesium source) are weighed.

[0135] Comparative Example 4 This comparative example provides a cathode material that differs from Example 1 in that, in step (1), Li2CO3 (second lithium source), FeC2O4·2H2O (iron source), NH4H2PO4 (phosphorus source), and TiO2 (doped element titanium, source A) are weighed according to a molar ratio of Li:Fe:Ti:P=1:0.995:0.005:1. H3BO3 (boron source), tetraethyl orthosilicate (TEOS, silicon source), LiNO3 (first lithium source), and copper nitrate (first metal element source, with a copper ion radius of approximately 0.0736 nm and an electronic conductivity of approximately 5.8 × 10⁻⁶) are weighed according to a molar ratio of B:Si:Li:Cu=1:1:2:0.05. 7 Then, these substances were dissolved in an ethanol-water mixture with a volume ratio of 3:1, according to the total mass of the first lithium source, boron source, silicon source, and copper source: solvent volume of 1g:15mL, and stirred at 60°C to form a sol. Next, the above raw materials were dispersed in the sol according to the total mass of the second lithium source, iron source, phosphorus source, and titanium source (i.e., the total mass of raw materials): sol = 1g:15mL, ultrasonicated for 30min, and dried at 80°C to obtain a mixture.

[0136] (2) Under an argon atmosphere, the mixture was heated to 450°C and sintered for 2 hours at a heating rate of 2°C / min to obtain the first coating. The first coating is a borosilicate lithium oxide coating layer coated on the surface of the substrate.

[0137] (3) According to the ratio of the mass of the first coating body: the mass of the carbon source: the mass of the nitrogen source = 1:0.08:0.012, glucose (carbon source) and polydopamine (nitrogen source) were weighed, and the above substances were added to pure water and the solid content was controlled at 30%, and then dried. Then, a first-stage sintering and a second-stage sintering treatment were carried out under an argon atmosphere: the precursor powder was heated to 450℃ at a heating rate of 2℃ / min for a first-stage sintering and the holding time was 4h. Then, the temperature was raised to 810℃ at a heating rate of 3℃ / min for a second-stage sintering and the holding time was 10h. Then, natural cooling was carried out to obtain the cathode material. That is, in the cathode material, the surface of the substrate is successively coated with a borosilicate lithium oxide coating layer and a carbon coating layer. Hereinafter, the borosilicate lithium oxide coating layer in Comparative Example 4 is referred to as the inner coating layer, and the carbon coating layer in Comparative Example 4 is referred to as the outer coating layer.

[0138] Test Example 1 The cross-sectional morphology of the cathode materials provided in the above embodiments and comparative examples was analyzed, and the thicknesses of the carbon coating layer and the second coating layer were measured based on HRTEM images. The HRTEM image for Example 1 is shown below. Figure 2 The measurement data are shown in Table 1. Since the thickness of the carbon coating layer is not absolutely consistent at different locations, the thickness values ​​in Table 1 are range values.

[0139] XPS tests were performed on the cathode material provided in Example 1 and the first coating obtained in step (2). See the XPS spectra below. Figure 3 The XPS spectrum of the N1s of the first coating is shown in [reference needed]. Figure 4 .

[0140] Results analysis: From Figure 2 As can be seen, the cathode material provided in this application embodiment includes a substrate (the black substance in the upper half of the figure), and the surface of the substrate is sequentially covered with two coating layers. From Figure 2 It can be seen that in Example 1, the thickness of the carbon coating layer is approximately 2-3 nm, and the thickness of the second coating layer is approximately 1-2 nm. From... Figure 3 It can be seen that the cathode material provided in this application embodiment contains oxygen, lithium, boron, copper, and silicon, indicating that the second coating layer is a borosilicate lithium oxide doped with copper oxide. From Figure 4 It can be seen that the carbon coating layer provided in Example 1 of this application is doped with nitrogen and contains Fe-N bonds.

[0141] Test Example 2 The elemental content of the cathode materials provided in the above embodiments and comparative examples was tested using the following methods: XPS and XRD tests were performed on the cathode material samples to determine the phase and elemental content (wherein, the total Li content includes the Li content in the matrix and the Li content in the second coating layer; the Li content in the matrix is ​​equal to the P content. Therefore, the Li content in the second coating layer can be obtained by subtracting the P content from the total Li content), and the proportion of each element was calculated.

[0142] The nitrogen content in the cathode material can be determined using an elemental analyzer: The initial mass of the cathode material sample is recorded. The sample is then completely combusted under high temperature and high oxygen conditions, converting the nitrogen into nitrogen oxides, which are then converted back into nitrogen gas (N2) in a reduction furnace. The amount of nitrogen gas is measured using a thermal conductivity detector (TCD), thus calculating the nitrogen content in the cathode sample. The nitrogen content is calculated as (nitrogen mass / initial mass of the cathode material sample) × 100%.

[0143] The test results are shown in Tables 1 and 2.

[0144] Table 1

[0145] Table 2

[0146] In Comparative Example 4, the cross-section of the cathode material can be tested by EDS elemental distribution. The B, Si, and Cu elements are located between the matrix and the carbon coating layer, which indicates that the borosilicate lithium coating layer is coated first and then the carbon coating layer is coated.

[0147] Test Example 2 The electronic conductivity and lithium-ion diffusion coefficient of the cathode materials provided in the above embodiments and comparative examples were tested. The test method was as follows: the electronic conductivity of the cathode materials was tested using the four-probe method. The lithium-ion diffusion coefficient was obtained by intermittent titration with constant current (GITT). The test results are shown in Table 3.

[0148] Test Example 3 The above-mentioned cathode material is used to fabricate a lithium-ion battery. The preparation method is as follows: Preparation of the positive electrode sheet: The positive electrode material, conductive agent (conductive carbon black, SP), and PVDF provided in the above examples and comparative examples were uniformly dispersed in the solvent N-methylpyrrolidone (NMP) at a ratio of 90:5:5, and a positive electrode slurry was obtained by mechanical stirring. The uniformly mixed positive electrode slurry was uniformly coated onto an aluminum foil current collector and placed in a vacuum oven for vacuum baking at 100°C for 10 hours to obtain the positive electrode sheet.

[0149] Battery assembly: The positive electrode and lithium sheet (as the negative electrode) obtained in step (1) are assembled into a coin cell. The separator is a polyethylene membrane. The electrolyte is prepared by mixing ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, and dissolving LiPF6 in the mixed solvent to obtain the electrolyte. The concentration of LiPF6 in the electrolyte is 1 mol / L.

[0150] The following battery performance tests were performed on the aforementioned lithium-ion batteries: Rate performance testing: The capacitor was charged to 3.75V at a constant current of 0.1C at room temperature, and then discharged to 2.0V at different discharge rates (0.1C, 1C, 5C, 10C), and the discharge specific capacity was recorded. Specifically, the charge / discharge voltage range of Example 15 was 2.5~4.4V. The test results are shown in Table 3.

[0151] Cyclic performance test: The lithium-ion battery was charged to 3.75V at a constant current of 10C at 25℃, and then discharged to 2.0V at a constant current of 10C at 25℃. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is recorded as C1. The lithium-ion battery was then subjected to the same charge-discharge test, and the discharge capacity of the 500th cycle was recorded as C2. The capacity retention rate (%) of the lithium-ion battery after 500 cycles = (C2 / C1) × 100%. A higher capacity retention rate indicates better cycle stability of the lithium-ion battery. The test results are shown in Table 3.

[0152] Table 3

[0153] Results analysis: As can be seen from Table 3, the cathode material with a double-layer coating structure provided in this embodiment has high electronic conductivity, lithium-ion diffusion coefficient and electrolyte corrosion resistance, thereby enabling the lithium-ion battery to have excellent rate performance and cycle stability.

[0154] Comparing Example 1 with Comparative Examples 1, 2, 3, and 4, it can be seen that in Comparative Example 1, without a carbon coating layer, the electronic conductivity of the cathode material is significantly reduced, indicating that the carbon coating layer can significantly improve the electronic conductivity of the cathode material. In Comparative Example 2, without a second coating layer, the lithium-ion diffusion coefficient of the cathode material is significantly reduced, indicating that the second coating layer can significantly improve the lithium-ion diffusion coefficient of the cathode material, which is beneficial for reducing polarization and thus improving the rate performance and cycle performance of the material. In Comparative Example 3, a boron-lithium-magnesium oxide coating layer is applied outside the carbon coating layer, which cannot effectively improve the lithium-ion diffusion coefficient of the cathode material, resulting in poor rate performance and cycle performance of the lithium-ion battery. Analysis suggests that the possible reason is that, compared with Example 1, Comparative Example 3 does not contain silicon oxide, which cannot form a three-dimensional structure with boron oxide, and therefore cannot provide lithium-ion diffusion channels, leading to lower ionic conductivity. Compared to Comparative Example 2, which lacks a second coating layer, Comparative Example 3, while lacking silicon oxide to form a three-dimensional structure, incorporates magnesium oxide and lithium oxide in its second coating layer. Therefore, Comparative Example 3 exhibits slightly higher electronic conductivity and lithium-ion diffusion compared to Comparative Example 2. Comparative Example 4, which first coats the cathode material with a borosilicate lithium oxide coating layer followed by a carbon coating layer, fails to effectively improve the electronic conductivity and lithium-ion diffusion coefficient, resulting in poor rate performance and cycle performance of the lithium-ion battery. Analysis suggests the following possible reasons: the intrinsic electronic conductivity of the substrate is poor. In Example 1, the direct contact between the carbon coating layer and the substrate significantly improves the electronic conductivity of the cathode material compared to Comparative Example 4, where a borosilicate lithium oxide coating layer separates the substrate and the carbon coating layer. Furthermore, in Comparative Example 4, the carbon coating layer is located on the outer layer, making it susceptible to corrosion and damage from electrolytes and other contaminants.

[0155] Compared to Example 1, in Example 2, the carbon coating layer was not doped with nitrogen (N), and both the electronic conductivity of the cathode material and the capacity retention of the lithium-ion battery were lower than in Example 1. This indicates that doping the carbon coating layer with nitrogen can improve the electronic conductivity of the cathode material, thereby improving the rate performance and cycle stability of the lithium-ion battery. In Example 3, the carbon coating layer was doped with more nitrogen (N), and both the electronic conductivity and capacity retention of the cathode material were lower than in Example 1. This indicates that doping the carbon coating layer with an appropriate amount of nitrogen (N) can improve the rate performance and cycle stability of the lithium-ion battery.

[0156] Comparing Examples 1, 4, and 5, it can be seen that as the copper content in the borosilicate lithium oxide coating layer increases, the electronic conductivity of the cathode material gradually increases, but the lithium-ion diffusion coefficient gradually decreases. This may be because excessive copper will block the lithium-ion diffusion channels, thereby affecting the diffusion of lithium ions.

[0157] Comparing Examples 1, 7, and 8, it can be seen that Example 1, by controlling the B:Si ratio in the second coating layer to be 1:(0.8~1.2), with an appropriate boron-silicon ratio, can further improve the lithium-ion diffusion coefficient of the cathode material, which helps to improve the rate performance and cycle performance of the lithium-ion battery. Comparing Examples 1, 9, and 10, Example 1, by controlling the B:Si:Li ratio in the second coating layer to be 1:(0.8~1.2):(1.8~2.2), with an appropriate lithium content, can further improve the lithium-ion diffusion coefficient of the cathode material, which helps to improve the rate performance and cycle performance of the lithium-ion battery. Comparing Examples 1, 11, 12, and 13, Example 1, by doping the boron-silicon lithium oxide coating layer with an appropriate amount of copper oxide, can further improve the electronic conductivity and lithium-ion diffusion coefficient of the cathode material, which helps to improve the rate performance and cycle performance of the lithium-ion battery. Comparing Examples 1 and 14, it can be seen that doping the matrix with titanium can simultaneously improve the electronic conductivity and lithium-ion diffusion coefficient of the cathode material, thereby improving the rate performance and cycle stability of the lithium-ion battery. This is because titanium doping can introduce additional electrons, broaden the lithium-ion diffusion channel, and promote lithium-ion migration.

[0158] As can be seen from Example 15, the preparation method provided in this application is also applicable to lithium phosphate positive electrode active materials such as lithium manganese phosphate.

[0159] Comparing Examples 1 and 16, compared to Example 16 where the carbon coating thickness was 8-9 nm, the second coating thickness was 5-6 nm, and the nitrogen content was 0.473%, the carbon coating thickness in Example 1 was 2-3 nm, the second coating thickness was 1-2 nm, and the nitrogen content was 0.129%. The electronic conductivity and lithium-ion diffusion coefficient of the cathode material provided in Example 1 were superior to those in Example 16. This indicates that suitable carbon coating thickness, suitable second coating thickness, and suitable nitrogen content can shorten the electron and ion transport path, reduce transport resistance, and further improve the electronic conductivity and lithium-ion diffusion coefficient of the cathode material, which is beneficial for improving the rate performance and cycle performance of lithium-ion batteries.

[0160] In summary, the cathode material provided in this application, by sequentially coating the surface of a lithium phosphate cathode active material matrix with a carbon coating layer and a borosilicate lithium oxide coating layer, can effectively improve the electronic conductivity and lithium-ion diffusion coefficient of the cathode material, which is beneficial to improving the rate performance and cycle performance of lithium-ion batteries.

[0161] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The material includes a substrate, a carbon coating layer covering at least a portion of the surface of the substrate, and a second coating layer covering at least a portion of the surface of the carbon coating layer; the substrate is a lithium phosphate positive electrode active material, and the second coating layer contains borosilicate lithium oxide.

2. The cathode material according to claim 1, characterized in that, The lithium phosphate-containing positive electrode active material is LiFe. 1-x A x PO4, 0≤x≤0.02, A includes at least one of Mn, Ti, Nb, V, Mg, Al, Zn, Zr, Co or Ni; Alternatively, 0.005 ≤ x ≤ 0.

02.

3. The cathode material according to claim 2, characterized in that, The carbon coating layer is doped with nitrogen, and the nitrogen forms Fe-N bonds with the matrix. Optionally, the nitrogen element accounts for 0.1% to 0.4% of the total mass of the cathode material.

4. The cathode material according to claim 1, characterized in that, In the borosilicate lithium oxide, the molar ratio of B:Si:Li is 1:(0.8~1.2):(1.8~2.2); Optionally, in the borosilicate lithium oxide, the molar ratio of B:Si:Li is 1:(0.9~1.1):(1.8~2.2).

5. The positive electrode material according to claim 1, characterized in that, The borosilicate lithium oxide is also doped with metal oxides other than lithium oxide, and the ionic radius of the metal ions of the metal oxides is 0.05~0.12 nm.

6. The cathode material according to claim 5, characterized in that, The metal oxide includes at least one of copper oxide, nickel oxide, cobalt oxide, or manganese oxide.

7. The cathode material according to claim 5, characterized in that, In the second coating layer, the metal element M in the metal oxide satisfies the molar ratio of B:Si:Li:M as 1:(0.8~1.2):(1.8~2.2):(0.02~0.1).

8. The positive electrode material according to claim 1, characterized in that, The thickness of the carbon coating layer is 2~6 nm; And / or, the thickness of the second coating layer is 1~3nm.

9. A method for preparing a positive electrode material, characterized in that, include: A first coating is obtained, the first coating comprising a matrix and a carbon coating layer covering at least a portion of the surface of the matrix; The substrate is a lithium phosphate positive electrode active material; A mixture is obtained by mixing a first lithium source, a boron source, a silicon source and the first coating body; the mixture is then sintered to form a second coating layer containing boron silicon lithium oxide on at least the surface of the first coating body.

10. The preparation method according to claim 9, characterized in that, The mixture also contains a first metal element source; the metal element in the first metal element source does not include lithium; the ionic radius of the metal ions in the first metal element source is 0.05~0.12nm; Optionally, the first metal element source includes at least one of a copper source, a nickel source, a cobalt source, or a manganese source; Optionally, the first lithium source includes at least one of lithium acetate, lithium hydroxide, lithium nitrate, and lithium carbonate; and / or, the boron source includes at least one of boric acid, trimethyl borate, and boron oxide; and / or, the silicon source includes at least one of tetraethyl orthosilicate, silica sol, lithium silicate, and methyltriethoxysilane; and / or, the first metal element source includes at least one of copper acetate, copper acetylacetonate, copper nanoparticles, copper nitrate, and copper formate. Optionally, the sintering temperature is 400~500℃.

11. The preparation method according to claim 9, characterized in that, The method for obtaining the first coating body includes: The raw materials used to form the lithium phosphate positive electrode active material are mixed with a carbon source to form a precursor powder; the precursor powder is sintered to obtain a first coating having the carbon coating layer coated on at least a portion of the surface of the substrate; Optionally, the lithium phosphate-containing positive electrode active material is LiFe. 1-x A x PO4, 0≤x≤0.02, A includes at least one of Mn, Ti, Nb, V, Mg, Al, Zn, Zr, Co or Ni; the mixture also contains a nitrogen source; Optionally, the ratio of the total mass of the raw materials to the mass of the carbon source to the mass of the nitrogen source is 1:(0.05~0.15):(0~0.03); Optionally, the nitrogen source includes at least one of polydopamine, 1,10-phenanthroline, melamine, polyaniline, or pyridine; Optionally, the carbon source includes at least one of glucose, fructose, sucrose, citric acid, tartaric acid, ascorbic acid, or polyethylene glycol; Optionally, the raw materials include a second lithium source, a phosphorus source, and a second metal element source.

12. A lithium-ion battery, characterized in that, It includes the cathode material according to any one of claims 1 to 8, or the cathode material prepared by the preparation method according to any one of claims 9 to 11.

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