Lithium-rich manganese-based positive electrode material, preparation method thereof, positive electrode sheet and battery

Abstract

This application provides a lithium-rich manganese-based cathode material, its preparation method, cathode sheet, and battery. The chemical formula of the lithium-rich manganese-based cathode material includes Li[Li] a Ni x Co y Mn z M d N e ]O 2‑f D f M is a metallic element, and the ionic radius of element M is greater than that of Mn. 4+ The oxidation state of element M is not less than +5; N includes at least one of Ce, Zr, Sn, La, Mg, Ti, Si, Sr, Se, Fe, Cr, V, Ca, Hf, Al, K, and Na; D includes at least one oxyacid anion of P and one oxyacid anion of S; the cathode material is a polycrystalline material, with at least a portion of the oxyacid anions of P and at least a portion of the oxyacid anions of S distributed at the grain boundaries of the primary particles of the cathode material, and at least a portion of M distributed within the lattice of the primary particles of the cathode material. The lithium-rich manganese-based cathode material of this application possesses both high ionic conductivity and low irreversible lattice oxygen loss under high voltage.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a lithium-rich manganese-based cathode material, its preparation method, cathode sheet, and battery. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, society is placing increasingly higher demands on the energy density, safety, and cycle life of secondary batteries. Currently, lithium batteries based on liquid electrolytes are the most widely used electrochemical energy storage system.

[0003] However, traditional liquid lithium batteries face a dual bottleneck in technological evolution: (1) Safety bottleneck: The liquid organic electrolyte used in current commercial batteries is flammable, prone to leakage, and has poor chemical stability. When the battery is subjected to mechanical abuse, overcharging, or internal short circuit, the electrolyte is prone to decomposition, vaporization, or even combustion, causing serious safety accidents; (2) Energy density bottleneck: Liquid battery systems are gradually approaching their theoretical limits in terms of material selection.

[0004] To address these issues, solid-state batteries were developed. The core feature of solid-state batteries is the complete replacement of the liquid electrolyte and separator in traditional batteries with a solid-state electrolyte (SSE).

[0005] Lithium-rich manganese-based cathode materials are one of the two major branches of high-energy-density solid-state battery cathode materials, with superior safety and energy density compared to high-nickel ternary materials. However, their development faces two major bottlenecks: first, limited ion transport at the solid-solid interface leads to high interface impedance and poor rate performance; second, irreversible loss of lattice oxygen under high voltage causes structural degradation and voltage decay.

[0006] Therefore, improving the ionic conductivity of lithium-rich manganese-based cathode materials and suppressing irreversible loss of lattice oxygen under high voltage are urgent technical challenges that need to be addressed. Summary of the Invention

[0007] This application provides a lithium-rich manganese-based cathode material and its preparation method, cathode sheet and battery, which can improve the ionic conductivity of the lithium-rich manganese-based cathode material and suppress irreversible loss of lattice oxygen under high voltage.

[0008] Firstly, this application provides a lithium-rich manganese-based cathode material, wherein the chemical formula of the lithium-rich manganese-based cathode material includes Li[Li a Ni x Co y Mn z M d N e O 2-f D fWhere a + x + y + z + d + e = 1, 0 ≤ a ≤ 0.25, 0.12 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.15, 0.5 ≤ z ≤ 0.75, 0 <d≤0.05,0≤e≤0.1,0<f≤0.1;

[0009] M is a metallic element, and the ionic radius of element M is greater than that of Mn. 4+ Furthermore, the oxidation state of element M is not lower than +5;

[0010] N includes at least one of the elements Ce, Zr, Sn, La, Mg, Ti, Si, Sr, Se, Fe, Cr, V, Ca, Hf, Al, K, and Na;

[0011] D includes at least the oxyacid radicals of P and the oxyacid radicals of S;

[0012] The lithium-rich manganese-based cathode material is a polycrystalline material, with at least a portion of the P oxyacid anions and at least a portion of the S oxyacid anions distributed at the grain boundaries of the primary particles of the lithium-rich manganese-based cathode material, and at least a portion of the M anions distributed within the lattice of the primary particles of the lithium-rich manganese-based cathode material.

[0013] In one possible implementation, the grain boundaries of the primary particles include at least Li3PO4 and Li2SO4.

[0014] In one possible implementation, M includes at least one element selected from Mo, W, Ta, Nb, Sb, and Te.

[0015] In one possible implementation, the aspect ratio of the primary particles of the lithium-rich manganese-based cathode material is 1.2-2.0.

[0016] In one possible implementation, D further includes dopant ions, said dopant ions including F. - Cl - and I - At least one of the ions.

[0017] In one possible implementation, the molar ratio of the oxyacid radicals of P to the oxyacid radicals of S in the lithium-rich manganese-based cathode material is 1:(1-4).

[0018] Secondly, this application provides a method for preparing the above-mentioned lithium-rich manganese-based cathode material, the method comprising:

[0019] S1: Mix the precursor, lithium source, and M source containing element M to obtain mixture A; the chemical formula of the precursor includes Ni. x Co y Mn z (OH)2 or Ni x Co y Mnz CO3, 0.12≤x≤0.4, 0≤y≤0.18, 0.5≤z≤0.75, x+y+z=1;

[0020] S2: Disperse the oxyacid sources of phosphorus and sulfur in a solvent to form a mixed solution B;

[0021] S3: Add mixed solution B dropwise to mixture A to obtain mixture C; freeze-dry mixture C to obtain a dry powder;

[0022] S4: The dry powder is subjected to a first sintering and a second sintering in an oxygen-containing atmosphere, and the lithium-rich manganese-based cathode material is obtained by cooling after the second sintering.

[0023] The first sintering temperature is 300-600℃; the second sintering temperature is 800-930℃.

[0024] In one possible implementation, the cooling includes at least a first cooling stage; the cooling rate of the first cooling stage is 1°C / min-3°C / min, and the first cooling stage includes cooling from the second sintering temperature to 300-400°C;

[0025] And / or; step S1 includes mixing the precursor, lithium source, N source containing N element and M source containing M element.

[0026] Thirdly, this application provides a positive electrode sheet comprising the aforementioned lithium-rich manganese-based positive electrode material.

[0027] Fourthly, this application provides a battery including the aforementioned positive electrode.

[0028] This application provides a lithium-rich manganese-based cathode material and its preparation method, cathode sheet and solid-state battery. The lithium-rich manganese-based cathode material is a polycrystalline material. At least some of the oxyacid radicals of P and at least some of the oxyacid radicals of S are distributed at the grain boundaries of the primary particles of the lithium-rich manganese-based cathode material, and at least some of the M are distributed in the lattice of the primary particles of the lithium-rich manganese-based cathode material. Thus, the lithium-rich manganese-based cathode material of this application has at least the following advantages: (1) The M element is a high-valence element with a large radius. When doped in the lattice, it can achieve multiple functions such as widening the lithium ion channel, suppressing cation mixing, "pinning" effect on oxygen and "charge compensation ordering" under high pressure, fundamentally suppressing structural oxygen loss and transition metal migration, thereby suppressing voltage decay; (2) (2) The oxyacid radicals of P act as grain boundary functional modifiers, causing them to segregate at the interface of primary particles, forming a continuous high ionic conductivity network (such as Li3PO4), which significantly improves the bulk ion transport rate; (3) The oxyacid radicals of S act as cosolvents to optimize grain growth kinetics, promoting dense bonding between primary particles during sintering, making the primary particles more uniform, improving the mechanical stability of lithium-rich manganese-based cathode materials, ensuring the smooth transport of lithium ions between multiple primary particles, and further guaranteeing the continuous three-dimensional fast ion transport "highway"; (4) The M element promotes the segregation of the oxyacid radicals of P at the grain boundary: The high-valence M element has a very strong oxygen affinity. After entering the lattice, lattice strain and charge imbalance will be generated around it. During the cooling process after sintering, in order to relax this strain, the system tends to "expel" the size / charge mismatched phosphate ions from the lattice, driving them to accumulate at the grain boundary. That is, high-valence doping actively promotes the segregation of P at the grain boundaries, making its distribution more continuous and uniform; (5) the oxyacid anions of S promote the more uniform distribution of the oxyacid anions of P at the grain boundaries. As a co-solvent, the oxyacid anions of S can form a eutectic liquid phase with other components (such as Li2CO3 and transition metal oxides) in the lithium-rich manganese-based cathode material. This liquid phase can promote the diffusion of the oxyacid anions of P, which can make the oxyacid anions of P more uniformly distributed at the grain boundaries. Attached Figure Description

[0029] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0030] Figure 1 EPMA diagram of the lithium-rich manganese-based cathode material of Example 1 provided in this application;

[0031] Figure 2 Provided for this application Figure 1 The element distribution diagram of the corresponding P element;

[0032] Figure 3 Provided for this application Figure 1 The corresponding element distribution diagram of element S;

[0033] Figure 4 EPMA diagram of the lithium-rich manganese-based cathode material provided in Comparative Example 3 for this application;

[0034] Figure 5 Provided for this application Figure 4 The element distribution diagram of the corresponding P element;

[0035] Figure 6 This is a schematic diagram illustrating the measurement of the length and width of primary particles of lithium-rich manganese-based cathode material using SEM, as provided in this application.

[0036] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present invention, this application will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the invention and are not intended to limit its scope. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0038] Firstly, this application provides a lithium-rich manganese-based cathode material, the chemical formula of which includes Li[Li] a Ni x Co y Mn z M d N e O 2-f D f Where a + x + y + z + d + e = 1, 0 ≤ a ≤ 0.25, 0.12 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.15, 0.5 ≤ z ≤ 0.75, 0 <d≤0.05,0≤e≤0.1,0<f≤0.1;

[0039] M is a metallic element, and the ionic radius of element M is greater than that of Mn. 4+ Furthermore, the oxidation state of element M is not lower than +5;

[0040] N includes at least one of the elements Ce, Zr, Sn, La, Mg, Ti, Si, Sr, Se, Fe, Cr, V, Ca, Hf, Al, K, and Na;

[0041] D includes at least the oxyacid radicals of P and the oxyacid radicals of S;

[0042] The lithium-rich manganese-based cathode material is a polycrystalline material, with at least some of the oxyacid radicals of P and at least some of the oxyacid radicals of S distributed at the grain boundaries of the primary particles of the lithium-rich manganese-based cathode material, and at least some of the M distributed within the lattice of the primary particles of the lithium-rich manganese-based cathode material.

[0043] The lithium-rich manganese-based cathode material provided in this application is a polycrystalline material. At least a portion of the oxyacid radicals of P and at least a portion of the oxyacid radicals of S are distributed at the grain boundaries of the primary particles of the lithium-rich manganese-based cathode material, and at least a portion of the M radicals are distributed within the crystal lattice of the primary particles of the lithium-rich manganese-based cathode material. This gives the lithium-rich manganese-based cathode material of this application at least the following advantages:

[0044] (1) M element is a high-valence element with a large radius. When doped in the crystal lattice, it can achieve multiple functions such as widening lithium ion channels, suppressing cation mixing, "pinning" oxygen and "charge compensation ordering" under high pressure. It can fundamentally suppress structural oxygen loss and transition metal migration, thereby suppressing voltage decay.

[0045] (2) The oxyacid radicals of P act as grain boundary functional modifiers, causing them to segregate at the primary particle interface and form a continuous high ionic conductivity network (such as Li3PO4), which significantly improves the bulk ion transport rate.

[0046] (3) The oxygen-containing acid radical of S acts as a co-solvent to optimize the grain growth kinetics, promote the dense bonding between primary particles during sintering, make the primary particles more uniform, improve the mechanical stability of lithium-rich manganese-based cathode materials, ensure the smooth transport of lithium ions between multiple primary particles, and further guarantee the through-through three-dimensional fast ion transport "highway".

[0047] (4) M element promotes the segregation of oxyacid anions of P at grain boundaries: High-valence M element has a very strong oxygen affinity. After entering the crystal lattice, lattice strain and charge imbalance will be generated around it. During the cooling process after sintering, in order to relax this strain, the system tends to "expel" the size / charge mismatched phosphate ions from the crystal lattice, driving them to accumulate at the grain boundaries. That is, high-valence doping actively promotes the segregation of P at grain boundaries, making its distribution more continuous and uniform;

[0048] (5) The oxyacid anions of S promote the more uniform distribution of the oxyacid anions of P at the grain boundaries. As a co-solvent, the oxyacid anions of S can form a eutectic liquid phase with other components (such as Li2CO3 and transition metal oxides) in lithium-rich manganese-based cathode materials. This liquid phase can promote the diffusion of the oxyacid anions of P, which can make the oxyacid anions of P more uniformly distributed at the grain boundaries.

[0049] In one possible implementation, the grain boundaries of the primary particles include at least Li3PO4 and Li2SO4. That is, the oxyacid anions of P and S in this application exist at the grain boundaries in the form of Li3PO4 and Li2SO4, respectively. Li3PO4 and Li2SO4 are relatively stable, which facilitates the sulfate and phosphate anions to exert their respective functions more stably.

[0050] In one possible implementation, M includes at least one element selected from Mo, W, Ta, Nb, Sb, and Te.

[0051] In one possible implementation, the aspect ratio of the primary particles in the lithium-rich manganese-based cathode material is 1.2-2.0. The aspect ratio of the primary particles in the lithium-rich manganese-based cathode material of this application is within the above range, which allows for a more compact bonding between the primary particles and a more consistent ion transport path length, thus improving the lithium-ion transport rate.

[0052] In one possible implementation, D further includes dopant ions, the dopant ions including F. - Cl - and I - At least one of the elements. The cathode material of this application is doped with the above-mentioned anions, which can improve capacity, stabilize cations, and inhibit the migration of transition metals.

[0053] In one possible implementation, within the lithium-rich manganese-based cathode material, the molar ratio of P oxyacid radicals to S oxyacid radicals is 1:(1-4). This molar ratio of P oxyacid radicals to S oxyacid radicals within the aforementioned range enhances the promoting effect of S oxyacid radicals on achieving a more uniform distribution of P oxyacid radicals at grain boundaries.

[0054] It is understandable that the molar ratio of the oxyacid anions of P to the oxyacid anions of S is 1:(1-4), such as 1:1, 1:2, 1:3, 1:4 or any range of two of the above values.

[0055] Secondly, this application provides a method for preparing the above-mentioned lithium-rich manganese-based cathode material, comprising:

[0056] S1: Mix the precursor, lithium source, and M source containing element M to obtain mixture A; the chemical formula of the precursor includes Ni. x Co y Mn z (OH)2 or Ni x Co y Mn z CO3, 0.12≤x≤0.5, 0≤y≤0.18, 0.5≤z≤0.75, x+y+z=1;

[0057] S2: Disperse the oxyacid sources of phosphorus and sulfur in a solvent to form a mixed solution B;

[0058] S3: Add mixed solution B dropwise to mixture A to obtain mixture C; freeze-dry mixture C to obtain a dry powder;

[0059] S4: In an oxygen-containing atmosphere, the dry powder is subjected to a first sintering and a second sintering. After the second sintering, the powder is cooled to obtain a lithium-rich manganese-based cathode material.

[0060] The temperature for the first sintering is 300-600℃; the temperature for the second sintering is 800-930℃.

[0061] The liquid-phase mixing in step S2 and the freeze-drying in step S3 of this application are intended to allow the PS source to penetrate the pores of the precursor as much as possible, which is beneficial for entering the grain boundaries during the subsequent sintering process.

[0062] The first sintering process uses a low temperature to decompose the lithium source and react initially with the precursor to form initial crystal nuclei, and to allow high-valence elements to diffuse initially. The second sintering process uses a high temperature to fully form a liquid phase of phosphorus oxyacid anions, allowing them to diffuse sufficiently to the grain boundaries. Furthermore, during the second sintering process, sulfur oxyacid anions can form a eutectic liquid phase with other components in the lithium-rich manganese-based cathode material (such as Li₂CO₃ and transition metal oxides). This liquid phase can promote the segregation of P oxyacid anions at the grain boundaries, resulting in a more uniform distribution of P oxyacid anions at the grain boundaries, thus facilitating the formation of a continuous ion conduction network.

[0063] It is understandable that the temperature of the first sintering is 300-600℃, such as 300℃, 400℃, 500℃, 600℃ or any combination of two of the above values.

[0064] It is understandable that the second sintering temperature is 800-930℃, such as 800℃, 850℃, 900℃, 930℃ or any combination of two of the above values.

[0065] In one possible implementation, the lithium source includes at least one of lithium nitrate, lithium nitrite, lithium chloride, lithium hydroxide, lithium bromide, lithium iodide, lithium sulfide, lithium fluoride, lithium carbonate, lithium sulfate, lithium sulfite, lithium perchlorate, lithium manganese oxide, lithium peroxide, and lithium superoxide.

[0066] In one possible implementation, the oxyacid source of phosphorus includes at least one of ammonium phosphate, lithium phosphate, sodium phosphate, potassium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium pyrophosphate, ammonium pyrophosphate, sodium metaphosphate, sodium hexametaphosphate, sodium phosphite, ammonium phosphite, sodium hypophosphite, and ammonium hypophosphite.

[0067] In one possible implementation, the oxyacid source of sulfur includes at least one of lithium sulfate, sulfur powder, sodium sulfate, sodium persulfate, sodium sulfite, ammonium sulfate, ammonium persulfate, sodium thiosulfate, thiourea, manganese sulfide, nickel sulfide, and cobalt sulfide.

[0068] In one possible implementation, the solvent includes deionized water and anhydrous ethanol.

[0069] In one possible implementation, the precursor, lithium source, and M source containing element M are ball-milled to obtain mixture A.

[0070] In one possible implementation, mixed solution B is added dropwise to mixture A while stirring is performed during the dropwise addition.

[0071] In one possible implementation, the freeze-drying temperature is -60 to -80°C, and the time is 10 to 24 hours.

[0072] In one possible implementation, the first sintering time is 3h-6h, and the heating rate of the first sintering is 1℃ / min-10℃ / min; the second sintering time is 7h-16h, and the heating rate of the second sintering is 1℃ / min-10℃ / min.

[0073] It is understandable that the first sintering time is 3h-6h, for example, 3h, 4h, 5h, 6h or any two of the above values.

[0074] It is understandable that the heating rate of the first sintering is 1℃ / min-10℃ / min, such as 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min or any range of two of the above values.

[0075] It is understandable that the second sintering time is 7h-16h, such as 7h, 10h, 12h, 14h, 16h or any range of two of the above values.

[0076] It is understood that the heating rate of the second sintering is 1℃ / min-10℃ / min, for example, 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min or any range of two of the above values.

[0077] In one possible implementation, the cooling includes at least a first cooling stage; the cooling rate of the first cooling stage is 1°C / min-3°C / min, and the first cooling stage includes cooling from the temperature of the second sintering to 300-400°C.

[0078] Understandably, during cooling, the first cooling stage uses a relatively slow cooling rate to gradually lower the temperature. This is a crucial stage for the crystallization and bonding of lithium phosphate at the grain boundaries. Slow cooling allows it to form a stable phase that is well-crystallized and firmly bonded to the matrix.

[0079] It is understandable that the cooling rate of the first cooling stage is 1℃ / min-3℃ / min, such as 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min or any range of two of the above values.

[0080] In one possible implementation, the cooling also includes a second cooling after the first cooling phase has ended, which is natural cooling to room temperature.

[0081] In one possible implementation, step S1 includes mixing the precursor, the lithium source, the N source containing the N element, and the M source containing the M element.

[0082] In one possible implementation, step S1 includes mixing the precursor, lithium source, M source containing element M, and compound containing doped ions to obtain mixture A.

[0083] In one possible implementation, the dopant ions include F - Cl - and I - At least one of the ions.

[0084] Thirdly, this application provides a positive electrode sheet comprising the aforementioned lithium-rich manganese-based positive electrode material.

[0085] Fourthly, this application provides a battery including the aforementioned positive electrode.

[0086] In one possible implementation, the battery includes a solid-state battery.

[0087] It is conceivable that, in addition to the aforementioned positive electrode, the solid-state battery of this application also includes a negative electrode and a solid electrolyte.

[0088] This application does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0089] This application does not strictly limit the type of solid electrolyte, which may be an oxide solid electrolyte, a sulfide solid electrolyte, a polymer solid electrolyte, a halide solid electrolyte, a composite solid electrolyte, etc.

[0090] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0091] Example 1

[0092] The preparation method of the lithium-rich manganese-based cathode material in this embodiment is as follows:

[0093] S1: Ni hydroxide precursor 0.167 Co 0.167 Mn 0.666 (OH)₂ was ball-milled at low speed (150 rpm) with lithium carbonate, tantalum oxide, magnesium oxide, and lithium chloride for 10 hours to obtain mixture A. The molar ratios of the hydroxide precursor to lithium carbonate were 1:0.75, to tantalum oxide, magnesium oxide, and lithium chloride, respectively.

[0094] S2: Lithium phosphate and lithium sulfate are mixed at a P:S molar ratio of 1:2, and then dissolved in a solvent to form a mixed solution B. The solvent is a mixture of deionized water and anhydrous ethanol, with an anhydrous ethanol volume concentration of 60%.

[0095] S3: Slowly add mixed solution B dropwise to mixture A while stirring to ensure the liquid wets all the powder, to obtain mixture C; freeze-dry mixture C to obtain a dry powder. In mixture C, the molar ratio of hydroxide precursor to lithium phosphate is controlled at 1:0.0188; the freeze-drying parameters are -70℃ for 16 hours.

[0096] S4: In an oxygen-containing atmosphere in a box furnace, the dry powder is subjected to a first sintering and a second sintering. The temperature of the first sintering is 450℃, the time of the first sintering is 4.5h, and the heating rate of the first sintering is 5℃ / min. The temperature of the second sintering is 900℃, the time of the second sintering is 12h, and the heating rate of the second sintering is 5℃ / min.

[0097] S5: After the second sintering, the first cooling stage and the second cooling stage are carried out. The first liquid cooling stage uses a rate of 2℃ / min to liquid cool to 300℃, and the second cooling stage uses natural cooling with the furnace to room temperature to obtain the lithium-rich manganese-based cathode material of this embodiment.

[0098] Figure 1 The image shows the EPMA diagram of the lithium-rich manganese-based cathode material obtained in Example 1. Figure 2 Provided for this application Figure 1 The corresponding element distribution diagram of element P. Figure 3 Provided for this application Figure 1 The corresponding element distribution diagram of element S, based on Figure 2-3 This indicates that phosphate and sulfate ions are evenly distributed at the grain boundaries inside the particles.

[0099] Example 2

[0100] The preparation method of the lithium-rich manganese-based cathode material in this embodiment is as follows:

[0101] S1: Ni hydroxide precursor 0.35 Mn 0.65 (OH)₂ was ball-milled at low speed (150 rpm) for 10 hours with lithium carbonate, tungsten oxide, magnesium oxide, and lithium fluoride to obtain mixture A. The molar ratios of the hydroxide precursor to lithium carbonate were 1:0.65, 1:0.0012, 1:0.0575, and 1:0.0345, respectively.

[0102] S2: Lithium phosphate and lithium sulfate are mixed at a P:S molar ratio of 1:1, and then dissolved in a solvent to form a mixed solution B. The solvent is a mixture of deionized water and anhydrous ethanol, with an anhydrous ethanol volume concentration of 60%.

[0103] S3: Slowly add mixed solution B dropwise to mixture A while stirring to ensure the liquid wets all the powder, obtaining mixture C; freeze-dry mixture C to obtain a dry powder. In mixture C, the molar ratio of hydroxide precursor to lithium phosphate is controlled at 1:0.023; the freeze-drying parameters are -60℃ for 24 hours.

[0104] S4: In an oxygen-containing atmosphere in a box furnace, the dried powder undergoes a first sintering and a second sintering. The temperature of the first sintering is 300℃, the time is 6 hours, and the heating rate is 5℃ / min. The temperature of the second sintering is 800℃, the time is 16 hours, and the heating rate is 5℃ / min.

[0105] S5: After the second sintering, the first cooling stage and the second cooling stage are carried out. The first liquid cooling stage uses a rate of 1℃ / min to liquid cool to 300℃, and the second cooling stage uses natural cooling with the furnace to room temperature to obtain the lithium-rich manganese-based cathode material of this embodiment.

[0106] Example 3

[0107] The preparation method of the lithium-rich manganese-based cathode material in this embodiment is as follows:

[0108] S1: Ni hydroxide precursor 0.5 Mn 0.5 (OH)₂ was ball-milled with lithium carbonate and molybdenum oxide at a low speed of 150 rpm for 10 hours to obtain mixture A. The molar ratio of the hydroxide precursor to lithium carbonate was 1:0.75, and the molar ratio of the hydroxide precursor to molybdenum oxide was 1:0.004.

[0109] S2: Lithium phosphate and lithium sulfate are mixed at a P:S molar ratio of 1:4, and then dissolved in a solvent to form a mixed solution B. The solvent is a mixture of deionized water and anhydrous ethanol, with an anhydrous ethanol volume concentration of 60%.

[0110] S3: Slowly add mixed solution B dropwise to mixture A while stirring to ensure the liquid wets all the powder, obtaining mixture C; freeze-dry mixture C to obtain a dry powder. In mixture C, the molar ratio of hydroxide precursor to lithium phosphate is controlled at 1:0.02; the freeze-drying parameters are -80℃ for 10 hours.

[0111] S4: In an oxygen-containing atmosphere in a box furnace, the dried powder undergoes a first sintering and a second sintering. The temperature of the first sintering is 600℃, the time is 3 hours, and the heating rate is 5℃ / min. The temperature of the second sintering is 930℃, the time is 7 hours, and the heating rate is 5℃ / min.

[0112] S5: After the second sintering, the first cooling stage and the second cooling stage are carried out. The first liquid cooling stage uses a rate of 3℃ / min to liquid cool to 400℃, and the second cooling stage uses natural cooling with the furnace to room temperature to obtain the lithium-rich manganese-based cathode material of this embodiment.

[0113] Example 4

[0114] The difference from Example 1 is that the N source is Ce. It is added during the preparation of mixture A in step S1, with a mass ratio of hydroxide precursor to cerium oxide of 1:0.00125.

[0115] Example 5

[0116] The difference from Example 1 is that lithium phosphate and lithium sulfate are mixed at a P:S molar ratio of 1:0.5.

[0117] Example 6

[0118] The difference from Example 1 is that lithium phosphate and lithium sulfate are mixed at a P:S molar ratio of 1:5.

[0119] Example 7

[0120] The difference from Example 1 is that the first cooling stage is not performed.

[0121] Comparative Example 1

[0122] The difference from Example 1 is that lithium phosphate was not added.

[0123] Comparative Example 2

[0124] The difference from Example 1 is that tantalum oxide was not added.

[0125] Comparative Example 3

[0126] The difference from Example 1 is that lithium sulfate was not added.

[0127] Figure 4 EPMA diagram of the lithium-rich manganese-based cathode material provided in Comparative Example 3 for this application; Figure 5 Provided for this application Figure 4 The corresponding element distribution diagram of element P. And... Figure 4 and Figure 5 It can be clearly seen that phosphate ions are enriched in the pores inside the particles and do not diffuse well and distribute at the grain boundaries.

[0128] Comparative Example 4

[0129] The preparation method of the lithium-rich manganese-based cathode material in this comparative example is as follows:

[0130] Ni hydroxide precursor 0.167 Co 0.167 Mn 0.666 (OH)₂ is ball-milled with lithium carbonate, tantalum oxide, lithium phosphate, and lithium sulfate, and then directly subjected to steps S4 and S5 of Example 1. The hydroxide precursor Ni... 0.167 Co 0.167 Mn 0.666 The amounts of (OH)2, lithium carbonate, tantalum oxide, lithium phosphate, and lithium sulfate added were the same as in Example 1, and the ball milling parameters were also the same as in Example 1.

[0131] Comparative Example 5

[0132] The difference from Example 1 is that the mixture C was directly sintered without freeze-drying.

[0133] Application example:

[0134] All lithium-rich manganese-based cathode materials obtained from the examples and comparative examples were assembled into solid-state batteries, as detailed below:

[0135] Preparation of the positive electrode sheet: The positive electrode sheet includes a positive electrode active layer and a current collector. Lithium-rich manganese-based positive electrode material, solid electrolyte (LPSC), and conductive agent (VGCF) are weighed into a mortar at a mass ratio of 85:15:1 and manually mixed for at least 30 minutes to obtain a mixture. Then, 1% (by mass) of polytetrafluoroethylene (PTFE) particles are added. The mixture is heated at 150°C for 5 minutes on a heating stage and then manually ground to form a film, pre-fiberizing the PTFE. The resulting film is then heated and rolled on a calender at 150°C. The film thickness is adjusted by controlling the gap width between the two hot rollers. Repeated rolling is performed to obtain a composite positive electrode material film with a thickness of 50 μm. This composite positive electrode material film is then calendered onto the surface of a 15 μm thick Al foil current collector to obtain the positive electrode sheet.

[0136] The above positive electrode sheet is die-cut into a circular sheet with a diameter of 8mm. Then, in a glove box filled with Ar atmosphere, it is stacked with Li6PS5Cl sulfide solid electrolyte membrane and LiIn, and cold-pressed to obtain an all-solid-state battery.

[0137] Test case

[0138] ICP testing was performed on the lithium-rich manganese-based cathode materials obtained in the above embodiments and comparative examples. The testing method was as follows:

[0139] After complete digestion of lithium-rich manganese-based cathode material with acid solution, the solution was cooled and diluted to a specific volume with deionized water. The resulting solution was then atomized and introduced into an inductively coupled plasma atomic emission spectrometer (ICP-AES). Characteristic emission spectra were generated in the high-temperature plasma, and the content of each element in the sample was calculated based on the intensity of its characteristic spectral lines. The aspect ratio of the primary particles of the lithium-rich manganese-based cathode material was tested.

[0140] The morphology of the lithium-rich manganese-based cathode material was captured by SEM. 10K images were selected, and using Nano Measurer software, 100 primary particles were randomly selected, and their length and width were measured individually. (See attached image.) Figure 6 For illustration. Take the average of 100 data points to obtain the average length / width value.

[0141] The molar ratio of oxyacid anions of P to oxyacid anions of S: The mass fractions of P and S are obtained by ICP testing. The molar ratio of oxyacid anions of P to oxyacid anions of S is obtained by dividing the mass fractions of P and S by the relative molecular masses of P and S, respectively.

[0142] Distribution of P and S in cathode material: EPMA test shows that P and S elements are uniformly distributed inside the particles, and the oxyacid anions of P and S are large in size and difficult to enter the crystal lattice, indicating that phosphate and sulfate are uniformly distributed at the grain boundaries inside the particles.

[0143] In addition, analysis using a soft X-ray emission spectrometer (SXES) mounted on an FE-SEM can confirm that no obvious P / S peaks are observed in the center of the primary particles, but P / S peaks are observed at the grain boundaries of the secondary particles (the surface of the primary particles), confirming the presence of P and S. At the same time, the elemental distribution map shows that P / S is relatively uniformly present at the grain boundaries.

[0144] XPS testing: The sample to be tested is fixed on the sample stage, and monochromatic Al Kα rays are used as the excitation source under ultra-high vacuum conditions to scan the sample surface and obtain full-spectrum scanning and high-resolution photoelectron energy spectrum; the spectrum is then fitted and calibrated using a standard binding energy database to determine the valence states of S, P, Mo, W, Ta, Nb, Sb and Te elements.

[0145] Electrical performance testing:

[0146] The all-solid-state battery was charged at 25°C with a constant current rate of 0.1C to a voltage of 4.2V (vs. Li+ / LiIn). The specific capacity at this time was recorded as the 0.1C charging specific capacity. After being left to stand for 5 minutes, it was discharged at a constant current rate of 0.1C to a voltage of 1.4V (vs. Li+ / LiIn). The specific capacity at this time was recorded as the battery's 0.1C discharge specific capacity.

[0147] Then, it is charged at a constant current rate of 0.33C until the voltage is 4.2V (vs. Li+ / LiIn). The specific capacity at this time is recorded as the 0.33C charging specific capacity. After resting for 5 minutes, it is discharged at a constant current rate of 0.33C until the voltage is 1.4V (vs. Li+ / LiIn). The specific capacity at this time is recorded as the battery's 0.33C discharge specific capacity. Therefore, the rate performance = 0.33C discharge specific capacity / 0.1C charging specific capacity.

[0148] Cycle at 0.33C for 50 cycles, and record the discharge specific capacity on the 1st and 50th cycles. Then, the capacity retention rate = discharge specific capacity on the 50th cycle / discharge specific capacity on the 1st cycle × 100%.

[0149] The results of all the above tests are shown in Table 1.

[0150] Table 1

[0151]

[0152] Compared with Examples 1 and 5, since the molar ratio of P:S is relatively small, the effect of the oxyacid anions of S on promoting the uniform distribution of the oxyacid anions of P at the grain boundaries is relatively limited. P is more distributed on the outer surface of the secondary particles, resulting in a slight decrease in capacity and rate of return in Example 5.

[0153] Compared with Examples 1 and 6, due to the larger P:S molar ratio, the primary particle growth in Example 6 was larger, and the ion transport path inside the particle was longer, resulting in a slight decrease in the capacity and rate of increase of Example 6.

[0154] Compared with Examples 1 and 7, the capacity and rate of Example 7 were slightly reduced because the first cooling stage was not performed, which was not conducive to the growth of oxyacid radicals of P at the grain boundaries.

[0155] Compared with Example 1 and Comparative Examples 1-3, the absence of lithium phosphate, high-valence elements, and lithium sulfate all resulted in a decrease in capacity and rate of return.

[0156] Compared with Example 1 and Comparative Example 4, solid-state sintering is not conducive to the distribution of oxyanions of P at grain boundaries. Therefore, it will cause a decrease in capacity and rate capability.

[0157] In Examples 1 and 5, the absence of freeze-drying is detrimental to the distribution of P-containing oxyacid radicals at grain boundaries, which tend to agglomerate in internal pores, thus causing a decrease in capacity and rate of return.

[0158] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, The chemical formula of the lithium-rich manganese-based cathode material includes Li[Li] a Ni x Co y Mn z M d N e O 2-f D f Where a + x + y + z + d + e = 1, 0 ≤ a ≤ 0.25, 0.12 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.15, 0.5 ≤ z ≤ 0.75, 0 <d≤0.05,0≤e≤0.1,0<f≤0.1; M is a metallic element, and the ionic radius of element M is greater than that of Mn. 4+ Furthermore, the oxidation state of element M is not lower than +5; N includes at least one of the elements Ce, Zr, Sn, La, Mg, Ti, Si, Sr, Se, Fe, Cr, V, Ca, Hf, Al, K, and Na; D includes at least the oxyacid radicals of P and the oxyacid radicals of S; The lithium-rich manganese-based cathode material is a polycrystalline material, with at least a portion of the P oxyacid anions and at least a portion of the S oxyacid anions distributed at the grain boundaries of the primary particles of the lithium-rich manganese-based cathode material, and at least a portion of the M anions distributed within the lattice of the primary particles of the lithium-rich manganese-based cathode material.

2. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The grain boundaries of the primary particles include at least Li3PO4 and Li2SO4.

3. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, M includes at least one element selected from Mo, W, Ta, Nb, Sb, and Te.

4. The lithium-rich manganese-based cathode material according to claim 3, characterized in that, The aspect ratio of the primary particles of the lithium-rich manganese-based cathode material is 1.2-2.

0.

5. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, D also includes doped ions, said doped ions including F. - Cl - and I - At least one of the ions.

6. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, In the lithium-rich manganese-based cathode material, the molar ratio of the oxyacid anions of P to the oxyacid anions of S is 1:(1-4).

7. A method for preparing a lithium-rich manganese-based cathode material according to any one of claims 1-6, characterized in that, The method includes: S1: Mix the precursor, lithium source, and M source containing element M to obtain mixture A; the chemical formula of the precursor includes Ni. x Co y Mn z (OH)2 or Ni x Co y Mn z CO3, 0.12≤x≤0.5, 0≤y≤0.18, 0.5≤z≤0.75, x+y+z=1; S2: Disperse the oxyacid sources of phosphorus and sulfur in a solvent to form a mixed solution B; S3: Add mixed solution B dropwise to mixture A to obtain mixture C; freeze-dry mixture C to obtain a dry powder; S4: The dry powder is subjected to a first sintering and a second sintering in an oxygen-containing atmosphere, and the lithium-rich manganese-based cathode material is obtained by cooling after the second sintering. The first sintering temperature is 300-600℃; the second sintering temperature is 800-930℃.

8. The preparation method according to claim 7, characterized in that, The cooling process includes at least a first cooling stage; the cooling rate of the first cooling stage is 1℃ / min-3℃ / min, and the first cooling stage includes cooling from the second sintering temperature to 300-400℃; And / or; step S1 includes mixing the precursor, lithium source, N source containing N element and M source containing M element.

9. A positive electrode plate, characterized in that, Including the lithium-rich manganese-based cathode material according to any one of claims 1-6.

10. A battery, characterized in that, Includes the positive electrode sheet according to claim 9.

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