Phosphate positive electrode material and use thereof

Abstract

Provided in the present disclosure are a phosphate positive electrode material and the use thereof. The phosphate positive electrode material comprises an inner core and a plurality of linear structures connected to the surface of the inner core, wherein the linear structures are made of lithium manganese iron phosphate. The phosphate positive electrode material can reduce the interfacial diffusion impedance, improve the solid-phase diffusion coefficient of ions, increase the energy density of a positive electrode sheet, and improve the electrochemical performance of a battery.

Description

Phosphate cathode materials and their applications

[0001] This disclosure claims priority to Chinese Patent Application No. 202410704005.6, filed on May 31, 2024, entitled "Phosphate Cathode Material and Its Application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of battery materials, specifically to phosphate cathode materials and their applications. Background Technology

[0003] Currently, phosphate cathode materials have become the mainstream choice for power batteries due to their low cost and high safety. However, in practical applications, phosphate cathode materials have low ion solid-phase diffusion coefficients and high interfacial diffusion resistance, resulting in low energy density and poor overall electrochemical performance of the cathode sheets. Therefore, it is necessary to develop a phosphate cathode material that combines high ion solid-phase diffusion coefficients and low interfacial diffusion resistance to improve the energy density of the cathode sheets. Summary of the Invention

[0004] In view of this, the present disclosure provides a phosphate cathode material and its application. The phosphate cathode material has a special structure that improves the ion solid-phase diffusion coefficient, reduces the interfacial diffusion resistance, and increases the energy density of the cathode sheet, which is beneficial to the application of phosphate cathode materials.

[0005] In a first aspect, this disclosure provides a phosphate cathode material, the phosphate cathode material comprising a core and a plurality of linear structures connected to the surface of the core.

[0006] Optionally, the linear structure includes a first outer branch and a second outer branch, wherein the molar ratio of manganese to the sum of iron and manganese in the first outer branch is greater than the molar ratio of manganese to the sum of iron and manganese in the second outer branch.

[0007] Optionally, the molar ratio of manganese to the sum of iron and manganese in the first outer branch is greater than or equal to 0.55, and the molar ratio of manganese to the sum of iron and manganese in the second outer branch is less than 0.55.

[0008] Optionally, the particle size D50 of the phosphate cathode material is 1.1 μm-2.5 μm, and the particle size D50 of the core is 0.5 μm-1.5 μm.

[0009] Optionally, the molar ratio of manganese to iron and the sum of manganese in the phosphate cathode material is 0.5-0.7.

[0010] Optionally, the kernel includes Li a Mn bFe c M 1-b-c PO4, 0.98≤a≤1.02, 0<b+c≤1, b≥0, c≥0, wherein M includes one or more of Al, Mg, Co, V, Ga, Ti, Cr, Cu, Zn and Mo.

[0011] Optionally, the linear structure includes a linear body and at least one linear branch, the linear body being connected to the kernel and the linear branch being connected to the linear body.

[0012] Optionally, the specific surface area of ​​the phosphate cathode material is greater than or equal to 20 m². 2 / g.

[0013] Optionally, the ion solid-phase diffusion coefficient of the phosphate cathode material is greater than or equal to 10. - 11 cm / s.

[0014] The phosphate cathode material disclosed herein has a core and multiple linear structures connected to the surface of the core, which increases the number of ion diffusion paths, shortens the length of the ion solid-phase diffusion path, and improves the energy density of the cathode sheet.

[0015] In a second aspect, this disclosure provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on the surface of the positive current collector, the positive active material layer comprising the phosphate positive electrode material described in the first aspect.

[0016] The positive electrode provided in this disclosure has high ionic conductivity and electronic conductivity, high energy density, excellent electrochemical performance, and high safety performance.

[0017] Thirdly, this disclosure provides a battery, the battery comprising a negative electrode and the positive electrode described in the second aspect.

[0018] The battery disclosed herein has high energy density, excellent charge and discharge performance, and superior overall performance.

[0019] Fourthly, this disclosure provides an electrical device, which includes the battery described in the third aspect.

[0020] The electrical equipment products disclosed herein are highly competitive and conducive to their widespread use. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The specific embodiments described herein are merely illustrative of this disclosure and are not intended to limit this disclosure.

[0022] Figure 1 is a cross-sectional schematic diagram of a phosphate cathode material provided in one embodiment of the present disclosure;

[0023] Figure 2 is an enlarged schematic diagram of the dashed area in Figure 1;

[0024] Figure 3 is a schematic diagram of the radial thickness of a linear structure provided in one embodiment of this disclosure;

[0025] Figure 4 is a scanning electron microscope image of the phosphate cathode material prepared in Example 1 of this disclosure. Detailed Implementation

[0026] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0027] In related technologies, in order to improve the overall performance of phosphate cathode materials, element doping modification is performed on them. The commonly used dopant is metallic manganese, and the content of metallic manganese is controlled. However, if the content of metallic manganese is too low, the energy density of the phosphate cathode material will decrease. If the content of metallic manganese is too high, the interfacial diffusion resistance will increase and the ion solid-phase diffusion rate will decrease, thereby causing a decline in the overall performance of the phosphate cathode material.

[0028] To address the aforementioned technical problems, this disclosure provides a phosphate cathode material. Referring to Figure 1, which is a cross-sectional schematic diagram of a phosphate cathode material provided in one embodiment of this disclosure, the phosphate cathode material 100 includes a core 10 and multiple linear structures 20 connected to the surface of the core 10. The phosphate cathode material provided in this disclosure includes a core and multiple linear structures connected to the surface of the core. The linear structures do not generate high ion migration barriers due to grain boundaries, enabling faster ion solid-phase diffusion paths, reducing the path length of ion solid-phase diffusion, increasing the ion solid-phase diffusion coefficient, and increasing the energy density of the cathode sheet. Simultaneously, the core structure improves the compactness of the phosphate cathode material, ensuring that the prepared cathode sheet has a high compaction density. Therefore, the phosphate cathode material with a core and linear structures connected to the core surface can improve the ion solid-phase diffusion coefficient, reduce interfacial diffusion resistance, obtain excellent ionic and electronic conductivity, and also increase the energy density of the cathode sheet.

[0029] In this disclosure, the core provides connection sites for a linear structure. The core can be a solid structure to improve the high density of the phosphate cathode material, increase the compaction density of the cathode sheet, and thus improve the energy density of the cathode sheet. In one embodiment of this disclosure, the core of the phosphate cathode material includes Li a Mn b Fe c M 1-b-c PO4, 0.98≤a≤1.02, 0<b+c≤1, b≥0, c≥0, M can be, but is not limited to, at least one of Al, Mg, Co, V, Ga, Ti, Cr, Cu, Zn, and Mo. The elements are uniformly distributed in the core, and the doped metal element M can improve the electronic conductivity of the phosphate-based cathode material. For example, a can be, but is not limited to, 0.98, 0.99, 1, 1.01, or 1.02, b can be, but is not limited to, 0, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, or 1, and c can be, but is not limited to, 0, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, or 1; b and c cannot both be 0. Specifically, the core can be, but is not limited to, LiMn. 0.4 Fe 0.6 PO4, Li 0.98 Mn 0.5 Fe 0.3 Al 0.2 PO4, Li 1.01 Mn 0.7 Fe 0.2 Zn 0.1 PO4, Li 0.99 Mn 0.5 Al 0.5 PO4, LiMnPO4, or LiFePO4, etc. In one embodiment of this disclosure, the core of the phosphate cathode material includes Li... a Mn b Fe c M 1-b-c PO4, 0.98≤a≤1.02, 0<b+c≤1, b>0, c>0. In another embodiment of this disclosure, the core of the phosphate cathode material includes Li. a Mn b M 1-b PO4, 0.98≤a≤1.02, 0<b≤1. In yet another embodiment of this disclosure, the core of the phosphate cathode material includes Li a Fe c M 1-c PO4, 0.98≤a≤1.02, 0<c≤1.

[0030] In one embodiment of this disclosure, the core particle size D50 is 0.5 μm-1.5 μm, which can improve the compaction performance of the phosphate cathode material, increase the compaction density of the cathode sheet, and improve the energy density of the cathode sheet. Specifically, the core particle size D50 can be, but is not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm. In one embodiment of this disclosure, the core particle size D50 can be 0.9 μm-1.5 μm. In another embodiment of this disclosure, the core particle size D50 can be 0.5 μm-1 μm.

[0031] Referring to Figure 1, the linear structure 20 includes a first outer branch 21 and a second outer branch 22. The molar ratio of manganese to iron and the sum of manganese in the first outer branch 21 is greater than that in the second outer branch 22. The first outer branch 21, with its higher molar ratio of manganese to iron and the sum of manganese, increases the overall manganese content of the phosphate cathode material, thereby increasing the energy density of the cathode. The second outer branch 22, with its lower molar ratio of manganese to iron and the sum of manganese, reduces the interfacial diffusion resistance of the phosphate cathode material and increases the ion solid-phase diffusion coefficient.

[0032] In one embodiment of this disclosure, the first outer branch includes Li e Mn f Fe g N 1-f-g PO4, 0.98≤e≤1.02, 0<f+g≤1, f>0, g>0, N can include, but is not limited to, at least one of Al, Mg, Co, V, Ga, Ti, Cr, Cu, Zn, and Mo. The first outer branch ensures the presence of manganese and iron elements in the linear structure, providing conditions for subsequent control of the linear structure by manganese and iron elements. The doped metal element N can further improve the electronic conductivity of the linear structure. For example, e can be, but is not limited to, 0.98, 0.99, 1, 1.01, or 1.02, f can be, but is not limited to, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, or 1, and g can be, but is not limited to, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, or 0.95. Specifically, the linear structure can be, but is not limited to, LiMn. 0.4 Fe 0.6 PO4, Li 0.98 Mn 0.5 Fe 0.3 Al 0.2 PO4, Li 1.01 Mn 0.7 Fe 0.2 Zn 0.1 PO4, Li 1.01 Mn0.65 Fe 0.2 Ti 0.15 PO4, LiMn 0.7 Fe 0.3 PO4 or Li 1.02 Mn 0.5 Fe 0.5 PO4, etc.

[0033] In one embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the first outer branch is greater than or equal to 0.55, that is, in Li e Mn f Fe g N 1-f-g In PO4, f / (g+f) ≥ 0.55, which increases the manganese content of the phosphate cathode material, thereby helping to improve the energy density of the phosphate cathode material. Specifically, the molar ratio of manganese to the sum of iron and manganese in the first outer branch can be, but is not limited to, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or 0.9. In one embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the first outer branch is 0.55-1. In another embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the first outer branch can be 0.7-0.9. In yet another embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the first outer branch can be 0.65-1.

[0034] In one embodiment of this disclosure, the second outer branch includes Li h Mn m Fe n R 1-m-n PO4, 0.98≤h≤1.02, 0<n+m≤1, m≥0, n>0, R can include, but is not limited to, at least one of Al, Mg, Co, V, Ga, Ti, Cr, Cu, Zn, and Mo. The second outer branch ensures the presence of manganese and iron elements in the linear structure, providing conditions for subsequent control of the linear structure by manganese and iron elements. The doped metal element R can further improve the electronic conductivity of the linear structure. For example, h can be, but is not limited to, 0.98, 0.99, 1, 1.01, or 1.02, m can be, but is not limited to, 0, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, or 0.95, and n can be, but is not limited to, 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, 0.9, or 1. Specifically, the linear structure can be, but is not limited to, LiMn. 0.4 Fe 0.6 PO4, Li 0.98 Mn 0.5 Fe 0.3 Al 0.2PO4, Li 1.01 Mn 0.7 Fe 0.2 Zn 0.1 PO4, Li 1.01 Mn 0.65 Fe 0.2 Ti 0.15 PO4, LiMn 0.7 Fe 0.3 PO4 or Li 1.02 Mn 0.5 Fe 0.5 PO4, etc.

[0035] In one embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the second outer branch is less than 0.55, that is, in Li h Mn m Fe n N 1-m-n In PO4, m / (m+n) ≤ 0.55 can reduce the manganese content in the phosphate cathode material, enhance the ion solid-phase diffusion coefficient of the phosphate cathode material, and reduce the interfacial diffusion resistance. Specifically, the molar ratio of manganese to the sum of iron and manganese in the second outer branch can be, but is not limited to, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.53, or 0.54. In one embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the second outer branch can be 0-0.55. In one embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the first outer branch can be 0.2-0.5. In another embodiment of this disclosure, the molar ratio of manganese to the sum of iron and manganese in the first outer branch can be 0.3-0.47.

[0036] In one embodiment of this disclosure, multiple linear structures are connected to the core surface. The linear structures include a first outer branch and a second outer branch. The molar ratio of manganese to iron and manganese in the first outer branch is greater than or equal to 0.55, and the molar ratio of manganese to iron and manganese in the second outer branch is less than 0.55. That is, multiple first outer branches and multiple second outer branches are respectively connected to the core surface. The high manganese content in the first outer branch ensures the manganese content in the phosphate cathode material, which is beneficial to improving the energy density of the phosphate cathode material. The low manganese content in the second outer branch avoids the problem of low ion solid-phase diffusion rate caused by excessive manganese. Thus, the phosphate cathode material has both excellent energy density and excellent ionic conductivity and electronic conductivity, with excellent overall performance, which is beneficial to improving the electrochemical performance of the cathode sheet and the battery.

[0037] In one embodiment of this disclosure, the linear structure and the core may simultaneously include iron and manganese elements, which can further improve the electronic conductivity and ionic conductivity of the phosphate cathode material and enhance the overall electrochemical performance of the battery.

[0038] In one embodiment of this disclosure, the first outer branch and the second outer branch are evenly distributed on the surface of the core, which avoids the problem of some elements having extremely high or low content in a certain part of the linear structure. This is beneficial to further increase the energy density of the positive electrode and reduce the ionic and electronic conductivity of the phosphate positive electrode material.

[0039] In one embodiment of this disclosure, the linear structure includes a linear body and at least one linear branch. The linear body is connected to the core, and the linear branch is connected to the linear body. That is, the linear structure is dendritic. Referring to Figure 2, which is an enlarged schematic diagram of the dashed area in Figure 1, the linear structure 20 includes a linear body 201 and a linear branch 202 connected to the linear body 201. The linear structure 20 is connected to the core 10, which can further increase the number of ion solid-phase diffusion paths and improve the ion solid-phase diffusion coefficient. In some embodiments of this disclosure, the linear structure is a linear body. The linear body can extend in a straight line or in a curve.

[0040] In one embodiment of this disclosure, the radial thickness of the linear structure is 0.3 μm-0.5 μm. Referring to Figure 3, which is a schematic diagram of the radial thickness of the linear structure provided in one embodiment of this disclosure, point A is the endpoint on the linear structure with the largest distance from the core surface 101, and the vertical distance between point A and the core surface 101 is the radial thickness of the linear structure. That is, the linear structure connected to the core surface has a certain length, which not only increases the number of ion solid-phase diffusion paths but also shortens the length of the ion solid-phase diffusion paths, thereby improving the ion solid-phase diffusion coefficient in the phosphate cathode material and reducing the interfacial diffusion resistance. Specifically, the radial thickness of the linear structure can be, but is not limited to, 0.3 μm, 0.32 μm, 0.35 μm, 0.38 μm, 0.4 μm, 0.45 μm, or 0.5 μm. In one embodiment of this disclosure, the radial thickness of the linear structure can be 0.3 μm-0.4 μm. In another embodiment of this disclosure, the radial thickness of the linear structure can be 0.4 μm-0.5 μm.

[0041] In one embodiment of this disclosure, the molar ratio of manganese to iron and the sum of manganese in the phosphate cathode material is 0.5-0.7. This improves the energy density of the phosphate cathode material and enhances the ion solid-phase diffusion coefficient, resulting in a phosphate cathode material with excellent overall performance. Specifically, the molar ratio of manganese to iron and the sum of manganese in the phosphate cathode material can be, but is not limited to, 0.5, 0.55, 0.6, 0.62, 0.65, 0.68, or 0.7. In one embodiment of this disclosure, the molar ratio of manganese to iron and the sum of manganese in the phosphate cathode material can be 0.5. In another embodiment of this disclosure, the molar ratio of manganese to iron and the sum of manganese in the phosphate cathode material can be 0.7.

[0042] In this disclosure, the phosphate cathode material can be spherical, near-spherical, or irregularly shaped. In one embodiment of this disclosure, the particle size D50 of the phosphate cathode material is 1.1 μm-2.5 μm. Maintaining the particle size D50 at the micrometer level allows the phosphate cathode material with a smaller D50 to increase the compaction density of the cathode sheet and enhance its energy density. Specifically, the particle size D50 of the phosphate cathode material can be, but is not limited to, 1.1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 1.9 μm, 2 μm, 2.3 μm, 2.4 μm, or 2.5 μm. In one embodiment of this disclosure, the particle size D50 of the phosphate cathode material can be 1.1 μm-2 μm. In another embodiment of this disclosure, the particle size D50 of the phosphate cathode material can be 1.5 μm-2.5 μm. In yet another embodiment of this disclosure, the particle size D50 of the phosphate cathode material can be 1.1 μm-1.6 μm.

[0043] In one embodiment of this disclosure, the specific surface area of ​​the phosphate cathode material is greater than or equal to 20 m². 2 / g. A larger specific surface area indicates a larger contact area between phosphate cathode materials and between the phosphate cathode material and the electrolyte, resulting in higher mass transfer efficiency and improved ionic and electronic conductivity. Specifically, the specific surface area of ​​the phosphate cathode material can be, but is not limited to, 20m². 2 / g、21m 2 / g、22m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g or 40m 2 / g etc. In one embodiment of this disclosure, the specific surface area of ​​the phosphate cathode material can be greater than or equal to 22.5m². 2 / g. In another embodiment of this disclosure, the specific surface area of ​​the phosphate cathode material can be greater than or equal to 24.3m². 2 / g.

[0044] In one embodiment of this disclosure, the ion solid-phase diffusion coefficient of the phosphate cathode material is greater than or equal to 10. -11 The higher the ion solid-state diffusion coefficient (cm / s), the faster the lithium-ion diffusion rate of the phosphate cathode material, and the stronger its ion conductivity. Specifically, the ion solid-state diffusion coefficient of the phosphate cathode material can be, but is not limited to, greater than or equal to 10 cm / s. -11 cm / s, greater than or equal to 2×10 -10 cm / s, greater than or equal to 5×10 - 10 cm / s, greater than or equal to 8×10 -10 cm / s, greater than or equal to 5×10 -9 cm / s or greater than or equal to 7 × 10 - 9 cm / s, etc.

[0045] In one embodiment of this disclosure, the preparation method of the phosphate cathode material can be as follows: a certain amount of MnSO4, FeSO4, (NH)2HPO4, metal-doped sulfate, and LiOH are dissolved in deionized water in proportion, and stirred to form a mixture. The mixture is placed in a hydrothermal reactor, and after hydrothermal reaction, an appropriate amount of inositol manganese hexaphosphate chelate, isopropanol, and polyvinyl alcohol are added. After sealing, the mixture is placed in an oven and allowed to stand. Then, stirring is started to form a linear structure with a certain radial thickness. After natural cooling, the mixture is vacuum dried to obtain the phosphate cathode material. This disclosure forms a linear structure of the phosphate cathode material through the dual effects of chemical chelation and physical stirring. In particular, the inositol manganese hexaphosphate chelate preferentially binds at the Mn sites in the crystal, and stirring can prevent the inositol manganese hexaphosphate chelate from being too concentrated at specific Mn binding sites, which would result in unsatisfactory performance improvement of the phosphate cathode material; at the same time, stirring can also promote the growth of linear structure and linear branches. Preferably, the particle size of the phosphate cathode material and the Mn / Fe distribution in the linear structure can be further controlled by adjusting the concentration of each sulfate, the amount of inositol manganese hexaphosphate, the standing time, the stirring rate, and the reaction time.

[0046] This disclosure provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on the surface of the positive current collector, wherein the positive active material layer includes the phosphate positive electrode material in any of the above embodiments.

[0047] In some embodiments of this disclosure, the positive current collector includes aluminum foil.

[0048] In some embodiments of this disclosure, the positive electrode active material layer further includes at least one of a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent can improve the conductive contact of the phosphate positive electrode material and increase electronic conductivity. Specifically, the positive electrode conductive agent may include, but is not limited to, one or more of carbon black, conductive graphite, carbon fiber, carbon nanotubes, and graphene. In one embodiment of this disclosure, the mass ratio of the positive electrode conductive agent to the positive electrode active material is 0.5%-5%. Specifically, the mass ratio of the positive electrode conductive agent to the positive electrode active material may be, but is not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. In one embodiment of this disclosure, the mass ratio of the positive electrode conductive agent to the positive electrode active material may be 0.5%-2%. In another embodiment of this disclosure, the mass ratio of the positive electrode conductive agent to the positive electrode active material is 3%-4.5%. In yet another embodiment of this disclosure, the mass ratio of the positive electrode conductive agent to the positive electrode active material is 1.5%-5%. The positive electrode binder can enhance the bonding strength of the positive electrode sheet and improve its mechanical properties. Specifically, the positive electrode binder may include, but is not limited to, one or more of polyvinyl alcohol, polytetrafluoroethylene, polyolefins, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylonitrile, polyimide, polyacrylic acid, polyacrylate, epoxy resin, carboxymethyl cellulose, and sodium alginate. In one embodiment of this disclosure, the mass ratio of the positive electrode binder to the positive electrode active material is 0.1%-10%. Specifically, the mass ratio of the positive electrode binder to the positive electrode active material may be, but is not limited to, 0.1%, 1%, 1.5%, 2%, 3%, 4%, 5%, 8%, 7%, or 9%. In one embodiment of this disclosure, the mass ratio of the positive electrode binder to the positive electrode active material may be 0.1%-4%. In another embodiment of this disclosure, the mass ratio of the positive electrode binder to the positive electrode active material is 3%-7.5%. In yet another embodiment of this disclosure, the mass ratio of the positive electrode binder to the positive electrode active material is 1%-9%.

[0049] In one embodiment of this disclosure, the volumetric energy density of the positive electrode is greater than or equal to 1350 mWh / cm³. 3 Volumetric energy density = (discharge capacity × discharge plateau voltage) / volume. Discharge capacity and discharge plateau voltage are tested at a discharge rate of 0.1C. Volume is calculated based on the compaction density of the positive electrode sheet. Volumetric energy density represents the electrical energy released per unit volume. Higher compaction density of the phosphate positive electrode material results in a smaller positive electrode sheet volume and a higher volumetric energy density, indicating more electrical energy stored per unit volume and better battery energy storage. Specifically, the volumetric energy density of the positive electrode sheet can be, but is not limited to, greater than or equal to 1350 mWh / cm³. 3 ≥1360mWh / cm 3 ≥1370mWh / cm 3 ≥1380mWh / cm3 or greater than or equal to 1390 mWh / cm 3 Etc. In one embodiment of this disclosure, the volumetric energy density of the positive electrode is greater than or equal to 1360 mWh / cm³. 3 .

[0050] In one embodiment of this disclosure, the gravimetric energy density of the positive electrode is greater than or equal to 535 mWh / g. Gravimetric energy density = (discharge capacity × discharge plateau voltage) / weight, and the discharge capacity and discharge plateau voltage are tested at a discharge rate of 0.1C. Gravimetric energy density represents the electrical energy released per unit mass on average; the higher the gravimetric energy density, the more electrical energy is stored per unit mass, and the higher the battery's energy storage capacity. Specifically, the gravimetric energy density of the positive electrode can be, but is not limited to, greater than or equal to 535 mWh / g, greater than or equal to 540 mWh / g, greater than or equal to 545 mWh / g, greater than or equal to 550 mWh / g, greater than or equal to 570 mWh / g, or greater than or equal to 580 mWh / g, etc. In one embodiment of this disclosure, the gravimetric energy density of the positive electrode is greater than or equal to 555 mWh / g.

[0051] This disclosure provides a battery comprising a negative electrode and a positive electrode as described in any of the above embodiments. The positive electrode has high energy density, excellent ion solid-phase diffusion coefficient, and high electronic and ionic conductivity, resulting in good electrochemical performance of the battery and facilitating its widespread application.

[0052] In one embodiment of this disclosure, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector. Specifically, the negative current collector includes aluminum foil or copper foil, and the negative active material layer includes a negative active material. The negative active material can be, but is not limited to, at least one of silicon-based materials, carbon-based materials, lithium-based materials, and tin-based materials. In some embodiments of this disclosure, the negative active material layer further includes at least one of a negative conductive agent and a negative binder. The negative conductive agent can improve the conductive contact of the negative active material, accelerate the movement speed of electrons in the negative electrode, improve electronic conductivity, and reduce the internal resistance of the battery. Specifically, the negative conductive agent can be, but is not limited to, at least one of carbon black, conductive graphite, carbon fiber, carbon nanotubes, graphene, nickel powder, and copper powder. In one embodiment of this disclosure, the mass ratio of the negative conductive agent to the negative active material is 0.1%-10%. Specifically, the mass ratio of the negative electrode conductive agent to the negative electrode active material can be, but is not limited to, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. In one embodiment of this disclosure, the mass ratio of the negative electrode conductive agent to the negative electrode active material can be 0.5%-2%. In another embodiment of this disclosure, the mass ratio of the negative electrode conductive agent to the negative electrode active material is 3%-7%. In yet another embodiment of this disclosure, the mass ratio of the negative electrode conductive agent to the negative electrode active material is 0.1%-5%. The negative electrode binder can enhance the bonding strength of the negative electrode sheet. Specifically, the negative electrode binder can include, but is not limited to, at least one of polyvinyl alcohol, polytetrafluoroethylene, polyolefins, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylonitrile, polyimide, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, and sodium alginate. In one embodiment of this disclosure, the mass ratio of the negative electrode binder to the negative electrode active material is 0.1%-10%. Specifically, the mass ratio of the negative electrode binder to the negative electrode active material can be, but is not limited to, 0.1%, 1%, 1.5%, 2%, 3%, 4%, 5%, 8%, 7%, or 9%. In one embodiment of this disclosure, the mass ratio of the negative electrode binder to the negative electrode active material can be 0.1%-0.8%. In another embodiment of this disclosure, the mass ratio of the negative electrode binder to the negative electrode active material is 1%-3%. In yet another embodiment of this disclosure, the mass ratio of the negative electrode binder to the negative electrode active material is 5.5%-9%.

[0053] In one embodiment of this disclosure, the battery further includes a separator disposed between the positive electrode and the negative electrode. Specifically, the separator can be, but is not limited to, a woven membrane, nonwoven fabric, microporous membrane, composite membrane, rolled membrane, or separator paper. In one embodiment of this disclosure, the battery further includes an electrolyte. At least a portion of the positive electrode and at least a portion of the negative electrode are immersed in the electrolyte. The electrolyte disclosed herein is not particularly limited and can be, but is not limited to, any substance in the art that can be used as a battery electrolyte.

[0054] This disclosure provides an electrical device, including the battery in any of the above embodiments. The electrical device provided by this disclosure has excellent performance and strong product competitiveness. The electrical device disclosed in this disclosure can refer to vehicles, electronic devices, energy storage systems, etc., and the aforementioned electrochemical device can be installed in the electrical device in the form of a single cell, battery module, battery pack, capacitor, etc.

[0055] The effects of this disclosed technical solution will be further illustrated below with specific examples.

[0056] Example 1

[0057] MnSO4, FeSO4 4、 (NH)₂HPO₄ and LiOH are dissolved in deionized water and mixed for 2 hours to form a mixed solution, in which MnSO₄ is present. 4、 The molar ratio of FeSO4 to (NH)2HPO4 was 6:4:10:10. The mixture was placed in a hydrothermal reactor and reacted at 200°C for 6 hours. Then, 1% wt of dispersant (manganese inositol hexaphosphate chelate, isopropanol, and polyvinyl alcohol) was added, and the mixture was sealed and placed in a 200°C oven for 5 hours, followed by stirring (200 rpm) for 10 hours. After natural cooling, the mixture was vacuum dried to obtain phosphate cathode material powder.

[0058] Figure 4 is a scanning electron microscope image of the phosphate cathode material prepared in Example 1 of this disclosure. It can be seen that the phosphate cathode material includes a core and a linear structure connected to the surface of the core.

[0059] Example 2

[0060] The difference from Example 1 is that the molar ratio of MnSO4 to FeSO4 is 5:5.

[0061] Example 3

[0062] The difference from Example 1 is that the molar ratio of MnSO4 to FeSO4 is 7:3.

[0063] Example 4

[0064] The difference from Example 1 is that the molar ratio of MnSO4 to FeSO4 is 4:6.

[0065] Example 5

[0066] The difference from Example 1 is that after sealing, it is placed in a 200°C oven and left to stand for 5 hours, and then stirred (at a speed of 150 r / min) for 5 hours.

[0067] Example 6

[0068] The difference from Example 1 is that after sealing, it is placed in a 200°C oven and left to stand for 3.5 hours, and then stirred (at a speed of 200 r / min) for 7.5 hours.

[0069] Example 7

[0070] The difference from Example 1 is that after sealing, it is placed in a 200°C oven and left to stand for 2 hours, and then stirred (at a speed of 250 r / min) for 5 hours.

[0071] Example 8

[0072] The difference from Example 1 is that MnSO4 was not added. The mixture was stirred for 2 hours to form a solution, sealed, and placed in a 200°C oven for 6 hours to form a LiFePO4 core. The solution was then replaced with a 5:5 molar ratio of MnSO4 to FeSO4, and 1% wt of dispersant (manganese inositol hexaphosphate chelate, isopropanol, and polyvinyl alcohol) was added. The mixture was then sealed and placed in a 200°C oven for 5 hours, with stirring (200 rpm) for 10 hours. After natural cooling, the mixture was vacuum dried to obtain phosphate cathode material powder.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that no dispersant (manganese inositol hexaphosphate chelate, isopropanol and polyvinyl alcohol) was added.

[0075] Comparative Example 2

[0076] The difference from Example 1 is that the standing time is 7 hours, no subsequent stirring is performed, and the phosphate cathode material is solid LiMn. 0.6 Fe 0.4 PO4.

[0077] Comparative Example 3

[0078] The difference from Example 1 is that MnSO4 is not added, and the inositol manganese hexaphosphate chelate is replaced with the same mass percentage of inositol iron hexaphosphate chelate. The core and linear structure of the resulting phosphate cathode material are made of LiFePO4.

[0079] Comparative Example 4

[0080] The difference from Example 1 is that MnSO4 was not added, and the mixture was stirred for 2 hours to form a solution. The solution was then placed in a hydrothermal reactor and reacted at 200°C for 6 hours to form a LiFePO4 core. Subsequently, the solution was replaced with a solution containing MnSO4 and FeSO4. 4、 The solution of (NH)2HPO4 was left to stand for 7 hours without the addition of dispersants (manganese inositol hexaphosphate chelate, isopropanol and polyvinyl alcohol), and then placed in a 200℃ oven for 5 hours without stirring.

[0081] Performance testing

[0082] The phosphate cathode materials prepared in Examples 1-8 and Comparative Examples 1-4 were tested for particle size D50 using a laser particle size analyzer. The results are shown in Table 1.

[0083] The phosphate cathode materials prepared in Examples 1-8 and Comparative Examples 1-4 were obtained by plasma cutting using scanning electron microscopy. The cross-section of the phosphate cathode material was obtained by scanning electron microscopy, the diameter of the core cross-section was measured, and the average value was calculated to obtain the core particle size D50. The results are shown in Table 1.

[0084] The phosphate cathode materials prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to elemental content and ratio tests using scanning electron microscopy. The test process was as follows: SEM-EDS was used for measurement. More than 100 points were selected in the entire particle range using EDS spot scanning mode. The average value of all points was statistically analyzed to calculate the Mn / (Fe+Mn) ratio of the phosphate cathode material. The results are shown in Table 1.

[0085] The phosphate cathode materials obtained in Examples 1-8 and Comparative Examples 1-4 were combined with PVDF (5%) binder and CNT (5%) conductive agent to form a cathode slurry, which was then coated onto a cathode current collector. After drying and rolling, a cathode electrode sheet was formed. The cathode electrode sheet, a negative electrode sheet (the negative electrode active material was artificial graphite), an electrolyte (EC / EMC = 1:1, 1M LiPF6), and a separator (PP) were used to form a coin cell.

[0086] The batteries prepared in Examples 1-8 and Comparative Examples 1-4 were tested for their ion solid-phase diffusion coefficients using a constant current intermittent titration method. The volumetric energy density and gravimetric energy density of the batteries were measured at a discharge rate of 0.1C. The energy density W = capacity Q × average voltage V was obtained by charging and discharging the batteries at 2V-4.35V and 0.1C. The mass m of the active material in the electrode (excluding binder and conductive agent) was weighed, and the electrode volume v was measured. The gravimetric energy density Wm = W / m and the volumetric energy density Wv = W / v were then calculated and tested. The results are shown in Table 2.

[0087] Table 1 Performance test results of cathode materials

[0088] Table 2 Battery performance test results

[0089] As can be seen from the data in the embodiments and comparative examples, the phosphate cathode material provided in this disclosure includes a core and multiple linear structures connected to the surface of the core, which improves the ion solid-phase diffusion coefficient and energy density of the phosphate cathode material. According to Examples 1 and 3-8, suitable molar ratios of manganese to iron and the sum of manganese in the phosphate cathode material, the particle size D50 of the phosphate cathode material, the particle size D50 of the core, the molar ratios of manganese to iron and the sum of manganese in the core, the molar ratios of manganese to iron and the sum of manganese in the first outer branch, and the molar ratios of manganese to iron and the sum of manganese in the second outer branch can yield a phosphate cathode material with both high ion solid-phase diffusion coefficient and high energy density. As can be seen from Examples 1 and Comparative Examples 1-4, the phosphate cathode material has a linear structure, and the first and second outer branches within the linear structure have different molar ratios of manganese to iron and the sum of manganese, which can improve the ion solid-phase diffusion coefficient and energy density of the phosphate cathode material, thus improving the electrochemical performance of the battery.

[0090] The above description represents preferred embodiments of this disclosure, but should not be construed as limiting the scope of this disclosure. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this disclosure, and these improvements and modifications are also considered to be within the scope of protection of this disclosure.

Claims

1. A phosphate cathode material (100), characterized in that, The phosphate cathode material (100) includes a core (10) and a plurality of linear structures (20) connected to the surface (101) of the core, wherein the linear structures (20) are made of lithium manganese iron phosphate.

2. The phosphate cathode material (100) as described in claim 1, characterized in that, The linear structure (20) includes a first outer branch (21) and a second outer branch (22), wherein the molar ratio of manganese to iron and manganese in the first outer branch (21) is greater than the molar ratio of manganese to iron and manganese in the second outer branch (22).

3. The phosphate cathode material (100) as described in claim 2, characterized in that, The molar ratio of manganese to iron and manganese in the first outer branch (21) is greater than or equal to 0.55, and the molar ratio of manganese to iron and manganese in the second outer branch (22) is less than 0.

55.

4. The phosphate cathode material (100) as described in claim 1, characterized in that, The particle size D50 of the phosphate cathode material (100) is 1.1μm-2.5μm, and the particle size D50 of the core (10) is 0.5μm-1.5μm.

5. The phosphate cathode material (100) as described in claim 1, characterized in that, The molar ratio of manganese to iron and the sum of manganese in the phosphate cathode material (100) is 0.5-0.

7.

6. The phosphate cathode material (100) as described in claim 1, characterized in that, The kernel (10) includes Li a Mn b Fe c M 1-b-c PO4, 0.98≤a≤1.02, 0<b+c≤1, b≥0, c≥0, wherein M includes one or more of Al, Mg, Co, V, Ga, Ti, Cr, Cu, Zn and Mo.

7. The phosphate cathode material (100) as described in claim 1, characterized in that, The linear structure (20) includes a linear body (201) and at least one linear branch (202), the linear body (201) being connected to the kernel (10), and the linear branch (202) being connected to the linear body (201).

8. The phosphate cathode material (100) as described in claim 1, characterized in that, The specific surface area of ​​the phosphate cathode material (100) is greater than or equal to 20 m². 2 / g.

9. The phosphate cathode material (100) as described in claim 1, characterized in that, The ion solid-phase diffusion coefficient of the phosphate cathode material (100) is greater than or equal to 10. -11 cm / s.

10. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector, wherein the positive active material layer includes the phosphate positive electrode material (100) according to any one of claims 1-9.

11. A battery, characterized in that, The battery includes a negative electrode and a positive electrode as described in claim 10.

12. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 11.

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