A lithium-rich manganese-based positive electrode material for a sulfide solid-state battery and a preparation method thereof

Abstract

This invention relates to the field of new energy materials technology, and in particular to a lithium-rich manganese-based cathode material for sulfide solid-state batteries and its preparation method. The material has the general chemical formula [chemical formula not specified], and its core lies in the introduction of elements with different diffusion depths to construct a multi-scale layered rock-salt symbiotic structure within the particles, extending from the bulk phase to the surface: diffusing deep into the bulk phase to form a stable framework, and accumulating on the surface to form a protective layer. The preparation method employs a co-precipitation method combined with high-temperature solid-state sintering. The resulting cathode material exhibits excellent cycle stability in all-solid-state batteries, with a capacity retention of >99% after 200 cycles and extremely low voltage decay, solving a key bottleneck in the application of lithium-rich materials in high-energy-density solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and in particular to a lithium-rich manganese-based cathode material for sulfide solid-state batteries and its preparation method. Background Technology

[0002] All-solid-state lithium batteries, using non-flammable solid electrolytes, fundamentally eliminate the safety hazards of liquid organic electrolytes and are considered a core technology for next-generation high-safety, high-energy-density batteries. Among many solid electrolyte systems, sulfide solid electrolytes (such as...) , ) with its exceeding With a room-temperature lithium-ion conductivity of S / cm, it is comparable to that of liquid electrolytes, making it the electrolyte choice with the greatest industrialization potential.

[0003] However, for sulfide electrolytes to truly be applied, they must be matched with high-voltage, high-specific-capacity cathode materials to fully realize their energy density advantages. Li-rich Mn-based oxide (LMR) cathode materials are widely recognized as ideal cathode candidates for sulfide all-solid-state batteries due to their outstanding advantages, including a high specific capacity exceeding 250 mAh / g, high operating voltage, and low cost. However, when the two are directly matched, a "triple crisis" caused by the intrinsic properties of the materials will be encountered: The first crisis stems from the "bulk structure collapse" of LMR materials themselves. In a deeply delithiated state, oxygen ions in the LMR lattice undergo irreversible oxidation, while transition metal ions continuously migrate from the transition metal layer to the lithium layer. This process drives the layered structure to continuously transform into the spinel phase and even the electrochemically inert rock salt phase, resulting in a continuous decay of the battery's operating voltage and a continuous loss of usable capacity. This is a fatal flaw that LMR materials have already exposed in liquid battery systems.

[0004] The second crisis is the "uncontrolled surface reactive oxygen species" in LMR materials. Under high operating voltages, lattice oxygen in the near-surface region of LMR particles readily reacts with highly reactive singlet oxygen or... It is released outwards in the form of reactive oxygen species. This reactive oxygen species has extremely strong oxidizing properties and is the root cause of all subsequent side reactions.

[0005] The third crisis, and the most critical one, is the interfacial compatibility challenge—the intrinsic chemical fragility of sulfide solid electrolytes. Sulfide electrolytes are rich in easily oxidized... The ions have an extremely narrow electrochemical stability window. When the highly reactive oxygen species deposited on the LMR surface come into contact with sulfide particles, they will be rapidly oxidized at the solid-solid interface. In situ, a heterogeneous interface layer composed of sulfates, sulfites, and polysulfides is formed. This interface layer not only has extremely low ionic conductivity, severely blocking lithium-ion cross-interface transport, but also accumulates and thickens continuously during cycling, leading to a surge in battery internal resistance and a sharp decline in capacity. Even more seriously, trace amounts of alkaline lithium salts remaining on the LMR surface (… , It will react chemically with sulfides, releasing... Gas directly causes the failure of physical contact at the interface.

[0006] The three crises are not isolated but deeply coupled and mutually causal: the phase transition of the bulk structure drives stronger surface oxygen release; uncontrolled surface oxygen directly attacks the sulfide electrolyte; and the accumulation of interfacial products, in turn, alters the chemical environment of the LMR surface, accelerating the structural degradation of the bulk phase. This vicious cycle makes achieving long cycle life in LMR-sulfide all-solid-state batteries an almost unsolvable technical challenge.

[0007] Existing technological solutions may focus on bulk elemental doping (such as...) , To suppress layered phase transitions, or to focus on surface coatings (such as...) , To isolate reactive oxygen species diffusion, these single-dimensional strategies have fundamental limitations: bulk doping is unlikely to affect the chemical activity of the particle surface and cannot prevent oxygen evolution; moreover, there is often lattice mismatch and interfacial stress between the mechanical coating layer and the matrix material, which is prone to cracking and detachment under charge-discharge volume expansion and contraction, and the additional coating layer itself is an additional barrier to lithium-ion migration. In short, existing "doping" or "coating" strategies have failed to establish a multi-scale synergistic protection mechanism from the bulk phase to the surface and then to the electrolyte interface, and therefore cannot simultaneously curb the three interlocking problems of bulk structure degradation, surface oxygen escape, and interfacial side reactions.

[0008] In summary, the only way to achieve stable application of lithium-rich manganese-based cathode materials in sulfide all-solid-state batteries lies in designing a novel material structure—one that must be able to stabilize the lattice deep within the bulk phase, passivate active oxygen on the particle surface, and construct a chemically inert and lithium-conducting buffer layer at the sulfide interface, thereby achieving integrated protection across the entire chain from the atomic scale to the particle scale. This is precisely the core technical problem that this invention aims to solve. Summary of the Invention

[0009] In order to overcome the above-mentioned defects of the prior art, the present invention provides a lithium-rich manganese-based cathode material for sulfide solid-state batteries and a method for preparing the same, so as to solve the problems existing in the background art.

[0010] This invention provides the following technical solution: a lithium-rich manganese-based cathode material for sulfide solid-state batteries, with the general chemical formula: , where x+y+z+w=1, and 0.1≤x≤0.25, 0≤y≤0.2, 0≤z≤0.2, 0.55≤w≤0.8; The cathode material particles have a multi-scale layered-rock salt symbiotic structure induced by the first and second doping elements. The first doping element is Its molar doping amount accounts for 0.1%-1.0% of the total molar amount of transition metal, and it is mainly distributed in the bulk phase region above 20 nm from the particle surface; The second doping element is Its molar doping amount accounts for 0.1%-1.0% of the total molar amount of transition metal, and it is mainly enriched in the surface and near-surface regions 5-20 nm away from the particle surface.

[0011] Furthermore, the secondary particles of the cathode material are spherical with a D50 particle size of 5-15 μm and a surface residual alkali content of less than 500 ppm.

[0012] Furthermore, after 200 cycles at a 0.2C rate, its capacity retention is greater than 99%.

[0013] A method for preparing a cathode material as described above, comprising the following steps: a) Using a co-precipitation method, a mixed solution of nickel, cobalt, and manganese salts was reacted with a sodium carbonate and ammonia complexing agent solution under an inert atmosphere, with the pH controlled at 8±0.5 and the temperature at 55±5℃, to prepare spherical [substances / forms]. Precursor; b) The precursor is uniformly mixed with a lithium source, a compound containing a first doping element, and a compound containing a second doping element in stoichiometric proportions. c) The mixture obtained in step b) is pre-sintered at 450±50℃ for 3-6 hours in an air or oxygen atmosphere, then calcined at 900±50℃ for 10-15 hours, and the target product is obtained after natural cooling.

[0014] Furthermore, the lithium source mentioned in step b) is or The compound containing the first dopant element is tetrabutyl titanate or... The compound containing the second dopant element is .

[0015] Furthermore, step c) includes washing and drying the product to control the surface residual alkali content to below 500 ppm.

[0016] An all-solid-state lithium battery comprising the positive electrode material, sulfide solid electrolyte, and negative electrode as described above.

[0017] Furthermore, the sulfide solid electrolyte is selected from... At least one of them.

[0018] Furthermore, the mass ratio of the positive electrode material to the sulfide solid electrolyte is (6-8):(1-3).

[0019] Use of the cathode material as described in any one of the above description in the preparation of lithium-ion batteries with high energy density and long cycle life.

[0020] The technical effects and advantages of this invention are as follows: Through the first doping element Diffusion into the bulk phase and second doping elements Enriched towards the surface and near-surface regions, it spontaneously constructs a multi-scale layered-rock salt symbiotic structure from the bulk phase to the surface within the grains; wherein, the bulk phase region consists of The induced layered and rock-salt phase nanoscale intergrowth structure effectively stabilized the lattice oxygen framework, suppressed transition metal ion migration, and prevented the irreversible transformation from long-range layered to spinel phase; the surface region was transformed from... The dense rock salt symbiotic layer formed by enrichment has high chemical inertness, which can suppress the evolution of active oxygen under high voltage and act as a physical barrier to isolate the active material from direct contact with the sulfide solid electrolyte, thereby reducing the degree of interfacial side reactions and reducing the formation rate of high impedance interfacial layer. Under the synergistic effect of the above-mentioned bulk phase and surface dual stabilization mechanism, the cathode material exhibits improved cycle capacity retention and voltage stability in all-solid-state batteries matched with sulfide solid electrolyte. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view of the multi-scale layered-rock salt symbiotic structure inside the cathode material particles of the present invention.

[0022] Figure 2 This is a scanning electron microscope (SEM) image of the secondary particles of the cathode material prepared in Example 1 of the present invention.

[0023] Figure 3 This is an energy dispersive X-ray spectroscopy (EDS) elemental distribution diagram of a single particle cross-section of the cathode material prepared in Example 1 of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0025] Example 1 Step 1: Precursor Preparation Spherical carbonate precursors were prepared using a co-precipitation method. The specific procedures are as follows: Weigh out 49.28g of nickel sulfate hexahydrate ( 0.1875 mol), 56.23 g cobalt sulfate heptahydrate ( 0.2 mol) and 105.63 g manganese sulfate monohydrate ( Dissolve 0.625 mol of metal salt in 500 mL of deionized water and stir thoroughly until completely dissolved to obtain a mixed metal salt solution A.

[0026] Weigh out 106g of anhydrous sodium carbonate ( Dissolve it in 500 mL of deionized water to prepare a precipitant solution B with a concentration of 2 mol / L.

[0027] Measure 6.8 mL of 25% ammonia solution (by mass). Dilute the solution to 500 mL to prepare a complexing agent solution C with a concentration of 0.2 mol / L.

[0028] 1L of deionized water was added to a 5L continuous stirred tank reactor as a base liquid. High-purity nitrogen was introduced for protection, stirring was started, the speed was set to 1000rpm, and the temperature inside the reactor was raised to 55℃.

[0029] Three feed solutions, A, B, and C, are simultaneously pumped into the reactor in a parallel flow. The flow rate of solution A is maintained at 100 mL / min using a flow control system, while the flow rates of solutions B and C are automatically adjusted based on feedback from an online pH meter to stabilize the pH of the reaction system at 8.0 ± 0.3 and the temperature at 55 ± 2℃. The feeding process lasts approximately 2 hours.

[0030] After the addition of materials is complete, stirring is stopped, and the resulting suspension is allowed to stand and age for 12 hours at the reaction temperature. After aging, the precipitate is repeatedly washed and filtered with deionized water until the pH of the filtrate is close to 7. The filter cake is dried in a vacuum drying oven at 120°C for 12 hours to obtain spherical carbonate precursors. .

[0031] Step 2: Mixing Weigh 1.000g of the precursor obtained in step one above, and 0.470g of lithium carbonate ( 0.0043g niobium pentoxide (analytical grade) (analytical grade) and 0.0073g tetrabutyl titanate ( The precursor (analytical grade) was ball-milled in a planetary ball mill at 300 rpm for 4 hours using anhydrous ethanol as the milling medium. The milled slurry was then dried at 80°C to obtain a uniformly mixed solid precursor powder.

[0032] The amount of lithium carbonate used is determined according to the molar ratio of lithium to the total amount of transition metals in the chemical formula. In this embodiment, the lithium ratio is lithium:(nickel+cobalt+manganese)=1.19:1 (molar ratio). The amount of niobium pentoxide used makes the molar doping amount of niobium account for 0.25% of the total molar amount of transition metals, and the amount of tetrabutyl titanate used makes the molar doping amount of titanium account for 0.25% of the total molar amount of transition metals.

[0033] Step 3: High-temperature solid-state calcination The mixed powder obtained in step two was placed in an alumina crucible and then placed in a box-type high-temperature furnace. Under a flowing air atmosphere (air flow rate of 200 mL / min), the temperature was increased from room temperature to 450°C at a rate of 5°C / min, and pre-sintered at this temperature for 5 hours. Subsequently, the temperature was increased to 900°C at the same rate, and high-temperature calcination was carried out at this temperature for 12 hours. After calcination, the furnace was allowed to cool naturally to room temperature, and the sample was removed.

[0034] Step 4: Post-processing The calcined product obtained in step three was rapidly washed with deionized water (washing time was 30 seconds) to remove the small amount of residual lithium compounds on the particle surface. The washed product was separated by vacuum filtration, dried in a vacuum drying oven at 150°C for 5 hours, and passed through a 300-mesh sieve to obtain the final cathode material product, designated MLR-1.

[0035] The obtained material was analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine its chemical formula as follows: Scanning electron microscopy (SEM) revealed that the secondary particles of the material were spherical, and the D50 particle size was determined to be 10.2 μm by laser particle size analyzer. Coulometric analysis showed that the surface residual alkali content was 320 ppm.

[0036] Analysis of the cross-section of a single particle using transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) clearly revealed the following: In the deep bulk region above 20 nm from the particle surface, a layered structure (R-3m space group) and a rock salt structure (Fm-3m space group) exhibited a nanoscale symbiotic relationship. EDS energy dispersive spectroscopy in this region showed a uniform distribution of Ti. Similarly, a dense layered-rock salt symbiotic structure was observed in the near-surface region of the outermost layer (approximately 5-20 nm), and EDS energy dispersive spectroscopy showed significant Nb enrichment in this region.

[0037] Example 2 Repeat all the steps of Example 1, except that the amount of dopant is adjusted in step two: the amount of niobium pentoxide added is increased from 0.0043 g to 0.0086 g (niobium doping amount accounts for 0.50% of the total molar amount of transition metal), and the amount of tetrabutyl titanate added is increased from 0.0073 g to 0.0146 g (titanium doping amount accounts for 0.50% of the total molar amount of transition metal). The amounts of lithium carbonate and precursor remain unchanged.

[0038] The target product obtained was designated MLR-2, and its chemical formula is: The secondary particles of the material are spherical with a D50 particle size of 9.8 μm and a surface residual alkali content of 280 ppm. TEM cross-sectional analysis also confirmed the multi-scale layered-rock salt symbiotic structure characterized by uniform distribution of Ti in the bulk phase and enrichment of Nb on the surface.

[0039] Example 3 The steps of Example 1 were repeated, except that in step three, the high-temperature calcination temperature was adjusted from 900℃ to 880℃, and the holding time was extended from 12 hours to 15 hours. The resulting product was designated MLR-3, with a D50 particle size of 8.5μm and a surface residual alkali content of 260ppm, and also possessed the aforementioned multi-scale layered-rock salt symbiotic structure characteristics.

[0040] Comparative Example 1 (Undoped blank sample) The steps of Example 1 were repeated, except that in step two, niobium pentoxide and tetrabutyl titanate were completely omitted; only 1.000 g of the precursor and 0.470 g of lithium carbonate were used as a mixture. The calcination process was exactly the same as in Example 1. The resulting product was designated PLR, and its chemical formula was [chemical formula missing]. Characterization revealed that the material possesses only a conventional layered structure and lacks the characteristics of a layered-rock salt symbiotic structure.

[0041] Comparative Example 2 (Single Ti Doping) The steps of Example 1 were repeated, except that in step two, only 0.0073 g of tetrabutyl titanate (titanium doping content 0.25%) was added, and niobium pentoxide was not added. The resulting product was designated Ti-LMR. Characterization showed that Ti was distributed throughout the entire particle area, and there was no Nb enrichment layer on the surface.

[0042] Comparative Example 3 (Single Nb Doping) The steps of Example 1 were repeated, except that in step two, only 0.0043 g of niobium pentoxide (0.25% niobium doping) was added, and tetrabutyl titanate was not added. The resulting product was designated Nb-LMR. Characterization showed that Nb was mainly enriched on the surface, and there was no Ti doping in the bulk phase.

[0043] Application example: Assembly and performance testing of all-solid-state lithium batteries The cathode materials prepared in the above embodiments and comparative examples were respectively mixed with sulfide solid electrolytes. Mix the powders at a mass ratio of 7:3 and grind them manually in a mortar and pestle for 30 minutes to obtain composite cathode powder. Weigh 80 mg of the above composite cathode powder and place it in a 10 mm diameter polyetheretherketone (PEEK) mold. Spread it evenly, and then add 100 mg of pure [material name missing] on top. Electrolyte powder was used as a solid electrolyte separator, and both were densified by applying a pressure of 150 MPa. Subsequently, a lithium metal foil was attached to the other side of the electrolyte layer as a negative electrode, and then pressed together by applying a pressure of 100 MPa. Finally, the mixture was sealed using a mold, and electrochemical performance tests were conducted under a constant external pressure of 4 MPa and a constant temperature of 25 °C.

[0044] Constant current and constant voltage charge-discharge cycle tests were conducted at a voltage window of 2.0-4.8V and a rate of 0.2C. The results are shown in the table below: The test results above show that MLR-1, MLR-2, and MLR-3 in the embodiments of this invention all exhibit excellent cycle stability in all-solid-state batteries, with capacity retention exceeding 98.5% after 200 cycles and average voltage decay below 15mV. In contrast, although the undoped PLR comparative example has a higher initial capacity, its capacity and voltage decay are severe; while the single-doped Ti-LMR and Nb-LMR show improved cycle performance, they are still far inferior to the dual-doping synergistic scheme of this invention.

[0045] This indicates that the present invention is achieved through Diffusion of stable lattice framework into the bulk phase The multi-scale layered-rock-salt symbiotic structure design, which enriches the surface to form a chemically inert protective layer, achieves dual ultrastability in both the bulk and surface phases. This effectively suppresses interfacial side reactions with the sulfide solid electrolyte and significantly improves the cycle stability and voltage retention capability of lithium-rich manganese-based cathode materials in all-solid-state batteries. The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A lithium-rich manganese-based cathode material for sulfide solid-state batteries, characterized in that, Its general chemical formula is , where x+y+z+w=1, and 0.1≤x≤0.25, 0≤y≤0.2, 0≤z≤0.2, 0.55≤w≤0.8; The cathode material particles have a multi-scale layered-rock salt symbiotic structure induced by the first and second doping elements. The first doping element is Its molar doping amount accounts for 0.1%-1.0% of the total molar amount of transition metal, and it is mainly distributed in the bulk phase region above 20 nm from the particle surface; The second doping element is Its molar doping amount accounts for 0.1%-1.0% of the total molar amount of transition metal, and it is mainly enriched in the surface and near-surface regions 5-20 nm away from the particle surface.

2. The cathode material according to claim 1, characterized in that, The secondary particles of the cathode material are spherical with a D50 particle size of 5-15 μm and a surface residual alkali content of less than 500 ppm.

3. The cathode material according to claim 1, characterized in that, After 200 cycles at a 0.2C rate, its capacity retention is greater than 99%.

4. A method for preparing the cathode material according to any one of claims 1-3, characterized in that, Includes the following steps: a) Using a co-precipitation method, a mixed solution of nickel, cobalt, and manganese salts was reacted with a sodium carbonate and ammonia complexing agent solution under an inert atmosphere, with the pH controlled at 8±0.5 and the temperature at 55±5℃, to prepare spherical [substances / forms]. Precursor; b) The precursor is uniformly mixed with a lithium source, a compound containing a first doping element, and a compound containing a second doping element in stoichiometric proportions. c) The mixture obtained in step b) is pre-sintered at 450±50℃ for 3-6 hours in an air or oxygen atmosphere, then calcined at 900±50℃ for 10-15 hours, and the target product is obtained after natural cooling.

5. The preparation method according to claim 4, characterized in that, The lithium source mentioned in step b) is or The compound containing the first dopant element is tetrabutyl titanate or... The compound containing the second dopant element is .

6. The preparation method according to claim 4, characterized in that, Step c) is followed by washing and drying the product to control the surface residual alkali content to below 500 ppm.

7. An all-solid-state lithium battery, characterized in that, It comprises the positive electrode material, sulfide solid electrolyte, and negative electrode as described in any one of claims 1-3.

8. The all-solid-state lithium battery according to claim 7, characterized in that, The sulfide solid electrolyte is selected from At least one of them.

9. The all-solid-state lithium battery according to claim 7, characterized in that, The mass ratio of the positive electrode material to the sulfide solid electrolyte is (6-8):(1-3).

10. The use of the cathode material as described in any one of claims 1-3 in the preparation of lithium-ion batteries with high energy density and long cycle life.

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