Patent Application
20230382763
The invention belongs to the technical field of lithium ion battery materials, and specifically relates to a lithium-transition metal oxide material coated with a fast ionic conductor and a preparation method thereof.
Layered cathode materials for Lithium-ion batteries have higher capacity, discharge plateau and compaction density, and are currently one of the most fully researched and most widely used cathode materials for commercial lithium-ion batteries. Lithium-ion cathode materials are in direct contact with an electrolyte and are easily corroded by the electrolyte, followed by dissolution of Co, Mn, Ni and other transition metals. Then the materials' original layered structure is destroyed, and the electrolyte is oxidized and decomposed, which produces gas, and finally resulting in a rapid decay of battery capacity and safety problems such as battery bulging, or even burning and explosion.
Coating other materials on the surface of lithium-containing transition metal oxide cathode materials can effectively reduce the contact area between the cathode material and an electrolyte, reduce the dissolution amount of the transition metals such as Co, Mn, and Ni, and improve structural stability and cycle performance. Commonly used coating materials are metal oxides, such as ZnO, Al2O3, La2O3, TiO2, ZrO2, etc. This type of material has a stable structure and does not react with an electrolyte so as to protect a cathode material. But most of the oxides are electronically insulated. Coating with the oxides will increase the electronic conductivity of a cathode material and reduce the capacity. Besides coating materials can be metal phosphates, such as AlPO4, Li3PO4, LiPO3, Li3Al (PO4)2, LiMgPO4, etc. The structures of this kind of materials can promote the capacity retention rate, improve the lithium ion diffusion coefficient and thermal stability in a charged state. However, phosphate coatings cannot avoid the corrosion of the electrolyte on the surface of a cathode material under high voltage, and the protection ability under high voltage is limited.
Yong Jeong Kim et al. used a sputtering method to coat a layer of Al2O3 with a thickness of about 30 nm on the surface of a lithium cobalt oxide cathode material. The results show that the Al2O3 coated lithium cobalt oxide has better structural stability and capacity retention rate during a half-cell cycle at 2.75˜4.4V. But in the first 80 cycles, the lithium ion diffusion coefficient of the Al2O3 coated lithium cobalt oxide cathode material is lower than that of the uncoated lithium cobalt oxide cathode material, indicating the oxide coating affected the capacity performance to a certain extent and the overall performance is reduced (see Chem. Mater. 2003, 15, 1505-1511).
The related art discloses a preparation method of alumina-coated nickel-cobalt-manganese ternary cathode material. The method comprises forming a of Al2O3 coating layer on the surface of a ternary cathode material to inhibit side reactions between the material and an electrolyte, and at the same time improve safety performance and cycle performance of the battery. However, the coating layer Al2O3 is not an excellent conductor for lithium ion transportation. While improving the cycle performance of the battery, it also increases the internal resistance of the battery and sacrifices the specific discharge capacity of the battery. Coated ternary cathode material is prone to the problem of delamination between the coating layer and the material surface, as well as the problems in the coating amount and coating uniformity.
Jaephil Cho et al. used a precipitation coating method to prepare AlPO4-coated lithium cobalt oxide. Compared with uncoated lithium cobalt oxide and Al2O3-coated lithium cobalt oxide, during a half-cell cycle at 3.0˜4.5V, the AlPO4-coated lithium cobalt oxide batteries have better structural stability and capacity retention rate, and the lithium ion diffusion coefficient and thermal stability in the charged state are the highest. But there are problems such as the matching of the cathode material and the coating material, and under high voltage the cathode material is corroded by the electrolyte (see Journal of Power Sources, 2005, 146, 58-64).
The related art discloses a lithium cobalt oxide composite material coated with a lithium super-ion conductor. A lithium super-ion conductor is coated on the surface of a layered lithium cobalt oxide material by a solid-phase mixing method or a precipitation coating method. Layered coating of small particles of the lithium super-ion conductor is uniformly formed on the surface of the lithium cobalt oxide material particles and the preparation method is disclosed. The phosphate ions in the lithium super-ion conductor combines with the lithium in the lithium cobalt oxide material to form Li3PO4. The above method is only tested to have capacity retention rate under C is 90% after 50 cycles under 4.6V at 0.7 C, which does not reflect the cycle performance under higher voltage. Meanwhile, because the lithium super-ion conductor was directly coated on the cathode material, it is prone to mismatch and fall off during the cycles.
Due to the structural differences between the layered electrode material and the coating material, directed coating of a fast ionic conductor has the shortage of poor interface contact and the coating is likely to fall off during the cycles in use, resulting in problems such as diving during cycles.
The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, a first objective of the present invention is to provide a fast ionic conductor coated lithium-transition metal oxide material; the second object of the present invention is to provide a method for preparing such a fast ionic conductor coated lithium-transition metal oxide material. The third objective of the present invention is to provide the application of the lithium-transition metal oxide material coated with the fast ionic conductor. The lithium-transition metal oxide material prepared by the present invention has lower impedance, excellent cycle performance and safety performance at high voltage, especially when the charging voltage is greater than 4.62V or even 4.65V.
In order to achieve the aforementioned objectives, the following technical solution is adopted in the invention.
A fast ionic conductor coated lithium-transition metal oxide material, having a chemical formula of (1−x)Li1+a(Ni(1−m−n)ConMnm)1−bMbO2·xLicAldTieM′fM″g(PO4)3; wherein M is at least one selected from the group consisting of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, S, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb and Ca; said M′ is an oxide of one or two elements selected form the group consisting of La, Al, Sc, Ti, Y, V or Zr; said M″ is an oxide of one element selected from the group consisting of Ni, Se, Fe, Mn and Co; wherein 0<x≤0.1, 0≤a≤0.1, 0<b≤0.1, 0≤m≤1, 0≤n≤1, 0≤c≤1, 0<d≤1, 0<e≤2, 0≤f≤2, 0≤g≤2, 1×c+3×d+4×e=9.
Preferably, the structure of the fast ionic conductor coated lithium-transition metal oxide material comprises an inner layer, a surface layer, and a transition layer formed during a reaction.
Preferably, the lithium-transition metal oxide material has a layered structure, and has a chemical formula of (1−x)Li1+a(Ni(1−m−n)ConMnm)1−bMbO2, and M is at least one selected from the group consisting of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, S, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb and Ca, wherein 0≤a≤0.1, 0<b≤0.1, 0≤m≤1, 0≤n≤1.
Preferably, the chemical formula of the fast ionic conductor is LicAldTieM′fM″g(PO4)3, and M′ is an oxide of one or two elements selected from the group consisting of La, Al, Sc, Ti, Y, V, and Zr; said M″ is an oxide of one element selected from the group consisting of Ni, Se, Fe, Mn, Co, wherein 0≤c≤1, 0<d≤1, 0<e≤2, 0≤f≤2, 0≤g≤2, wherein 1×c+3×d+4×e=9.
Preferably, the coated lithium-transition metal oxide material is prepared by a solid-phase method, and has a particle size of 2-27 μm.
Preferably, the preparation method of the fast ionic conductor comprises a solid-phase calcinating method or a liquid-phase precipitation-calcinating method.
Preferably, the preparation method of the fast ionic conductor coated lithium-transition metal oxide material comprises a solid-phase mixing method or a precipitation coating method.
The present invention also provides a method for preparing the fast ionic conductor coated lithium-transition metal oxide material, comprising the following steps:
Preferably, in step 1), the lithium source is one or two selected from the group consisting of lithium carbonate and lithium hydroxide.
Preferably, in step 1), the transition metal compound is at least one selected from the group consisting of a cobalt source, a nickel source and a manganese source; the transition metal compound is at least on selected from the group consisting of cobalt tetraoxide, cobalt oxyhydroxide, cobalt hydroxide, nickel-cobalt-manganese oxide, nickel-cobalt-manganese hydroxide, manganese hydroxide, nickel hydroxide, nickel oxide and manganese oxide.
Preferably, in step 1), the calcination is carried out at 750-1100° C., more preferably at 800-1090° C.
Preferably, in step 1), the calcination is carried out for 3-15 hours, more preferably 5-14 hours.
Preferably, in step 1), the lithium-transition metal oxide primary powder has a particle size of 1 to 23 μm.
Preferably, in step 2), M′ is an oxide of one or two elements selected from the group consisting of La, Al, Ti, V and Zr.
Preferably, in step 2), M″ is an oxide of one element selected from the group consisting of Ni, Se, Mn and Co.
Preferably, in step 2), the calcination is carried out at 700-1020° C., more preferably at 800-1010° C.
Preferably, in step 2), the calcination is carried out for 3-12 hours, and more preferably, for 5-10 hours.
Preferably, in step 2), the lithium-transition metal oxide material powder has a particle size of 1.5-26 μm.
Preferably, in step 3), the ethanol and water are in a weight-to-volume ratio (g/mL) of 100 (mL):1 (g)-98 (mL):1 (g).
Preferably, in step 3), the alcohol is one selected from the group consisting of methanol, ethanol and propanol, and further preferably, the alcohol is ethanol.
Preferably, in step 3), the crosslinking agent is tetrabutyl titanate.
Further preferably, the tetrabutyl titanate and the ethanol are in a weight-to-volume ratio (g/mL) of 1 (g):5 (mL)-1 (g):100 (mL), more preferably 1 (g):5 (mL)-1 (g):80 (mL).
Preferably, in step 3), the lithium salt is at least one selected from the group consisting of lithium carbonate and lithium acetate.
Preferably, in step 3), the aluminum salt is at least one selected from the group consisting of aluminum nitrate and aluminum acetate.
Preferably, in step 3), the phosphorus source is at least one selected from the group consisting of ammonium dihydrogen phosphate, lithium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, lithium phosphate and a phosphate ester.
More preferably, the phosphate ester is at least one selected from the group consisting of phosphate monoester and phosphate diester.
Preferably, in step 3), the concentration of the lithium salt, aluminum salt, and phosphorus source in the solution B is 0.02-2.5 mol/L respectively, more preferably, the concentration of the lithium salt, aluminum salt and phosphorus source in the solution B is 0.03-2.0 mol/L, respectively.
Preferably, in step 4), the stirring is carried out for 0.2-2.0 hours, and more preferably, for 0.5-1.5 hours.
Preferably, in step 4), the heating comprises the steps of heating the mixture to 40-100° C., stirring and evaporating to dryness, and more preferably, the heating comprises the steps of heating the mixture to 50-80° C., stirring and evaporating to dryness.
Preferably, in step 4), the drying is carried out in an oven for 10-15 hours, and more preferably in an oven for 8-12 hours.
Preferably, in step 4), the calcinating is carried out at 300-900° C., and more preferably, the at 400-700° C.
Preferably, in step 4), the calcination is carried out for 1-10 hours, more preferably 2-8 hours.
Preferably, in step 5), after the fast ionic intermediate product and the lithium-transition metal oxide material powder are mixed, the calcination is carried out at 300-900° C.; further preferably, at 400-800° C.
Preferably, in step 5), the calcination is carried out for 1-10 hours, more preferably 2-8 hours.
Preferably, in step 5), the fast ionic conductor intermediate product and the lithium-transition metal oxide material powder are in a mass ratio of (0.01-0.05):(0.95-0.99).
Preferably, in step 5), the weight of the fast ionic conductor does not exceed 5% of the total weight of the fast ionic conductor coated lithium-transition metal oxide material; further preferably, does not exceed 3% of the total weight of the fast ionic conductor coated lithium-transition metal oxide material.
Preferably, in steps 4 and 5), the slightly disaggregating is carried out by methods of performing screening on a vibrating sieve, mechanical milling, or jet milling.
The present invention also provides another method for preparing a fast ionic conductor coated lithium-transition metal oxide material, comprising the following steps:
Preferably, in step 1), the lithium source is at least one selected from the group consisting of lithium carbonate and lithium hydroxide.
Preferably, in step 1), the transition metal compound is at least one selected from the group consisting of a cobalt source, a nickel source and a manganese source; the transition metal compound is at least one selected from the group consisting of cobalt tetraoxide, cobalt oxyhydroxide, cobalt hydroxide, nickel-cobalt-manganese oxide, nickel-cobalt-manganese manganese hydroxide, manganese hydroxide, nickel hydroxide, nickel oxide and manganese oxide.
Preferably, in step 1), the calcination is carried out at 750-1100° C., more preferably the at 800-1090° C.
Preferably, in step 1), the calcination is carried out for 3-15 hours, more preferably for 5-14 hours.
Preferably, in step 1), the lithium-transition metal oxide primary powder has a particle size of 1 to 23 μm.
Preferably, in steps 2) to 4), the alcohol is one selected from the group consisting of methanol, ethanol and propanol, and further preferably, the alcohol is ethanol.
Preferably, in step 2), the crosslinking agent is tetrabutyl titanate.
Further preferably, the tetrabutyl titanate and the ethanol are in a weight-to-volume ratio (g/mL) of 1 (g):5 (mL)-1 (g):100 (mL), more preferably 1 (g):5 (mL)-1 (g):80 (mL).
Preferably, in step 2), the lithium salt is at least one selected from the group consisting of lithium carbonate and lithium acetate, and the aluminum salt is at least one selected from the group consisting of aluminum nitrate and aluminum acetate.
Preferably, in step 2), the lithium salt, aluminum salt and phosphorus source are dissolved in ethanol to reach a concentration of 0.01-2 mol/L respectively, and more preferably, to reach a concentration of 0.02-1.5 mol/L.
Preferably, in step 2), the phosphorus source is at least one selected from the group consisting of ammonium dihydrogen phosphate, lithium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, lithium phosphate, or a phosphate ester.
More preferably, the phosphate ester is at least one selected from the group consisting of phosphate monoester, phosphate diester and phosphate triester.
Preferably, in step 3), the mixed solution b is an acidic ethanol solution containing M′ and M″, and the major elements in M′ and M″ are in the form of ions with a concentration of 0.02-1.5 mol/L respectively.
Preferably, in step 5), the stirring is carried out for 0.5-5 hours, and further for 1-3 hours;
Preferably, in step 5), the steps of heating, stirring and evaporating to dryness are carried at 50-90° C., and further preferably, at 60 to 80° C.
Preferably, in step 5), the drying is carried out at 70-120° C., more preferably at 80-110° C.
Preferably, in step 5), the drying is carried out for 5-20 hours, more preferably for 8-16 hours.
Preferably, in step 5), the slightly disaggregating comprises subjecting a dried material to vibrating screening, mechanical milling, or jet milling; and more preferably, subjecting to vibrating screening.
Preferably, in step 6), the calcination is carried out at a temperature of 300-900° C., more preferably at a temperature of 400-800° C.; followed by holding the temperature for 3-12 hours, more preferably for 5-10 hours.
Preferably, in step 6), the weight of the fast ionic conductor does not exceed 5% of the total weight of the fast ionic conductor coated lithium-transition metal oxide material; further preferably, it does not exceed 3% of the total weight of the fast ionic conductor coated lithium-transition metal oxide material.
According to some embodiments of the present invention, the fast ionic conductor LicAldTieM′fM″g(PO4)3 is produced by a reaction of the fast ionic conductor intermediate product LicAldTie (PO4)3 with the oxides M′ and M″, and the reaction is carried out by methods including but not limited to spraying, drying, wet mixing, magnetron sputtering, multiple co-precipitation method, etc.
According to some embodiments of the present invention, the use of other types of fast ionic conductor intermediate products to react with the oxides M′ and M″ in surface layer to produce fast ionic conductor products containing M′ and M″ are all within the scope of the present invention.
The mechanism of the present invention is as follows: the movement of ions in a crystal depends on the crystal structure and chemical bonds. When a large number of defects are generated in a cathode material through doping and surface modification, there are occupied vacancies near the migrating ions, and the number of the vacancies is far more than the number of ions. Under this condition, the movement of ions is accelerated to form a fast ionic conductor. A continuous ion transmission channel is then formed in a fast ionic conductor, which further accelerates ion conduction. Under a high voltage, in order to suppress the phase change and improve the cycle performance, it is usually to dope with more elements on the electrode material. And with more elements doped, the lithium ion conductivity decreases while the interface reaction intensifies under high voltage. In order to reduce the side reaction of the interface reaction, the lithium-transition oxide is often coated with more inert oxides. This coating increases the impedance, which is not conducive to the capacity performance improvement. When the fast ionic conductor is coated on the surface of the material, the fast ionic conductor on the surface will decompose to form an open ion transmission channel, which can improve the lithium ion transmission capacity. However, the lithium-transition metal oxide material and the fast ionic conductor have different types of structures. There is a compatibility problem on the surface.
Compared with the conventional fast ionic conductor coating material, the cathode material provided by the present invention can form a transitional layer structure on the shallow surface layer during the cycle, and form an open ion transmission channel, so at to significantly increase the diffusion path of lithium ions and improve the lithium ion conductivity of the cathode material. Besides, the structure of the surface layer composed of lithium phosphorus oxide, lithium titanium oxide and lithium aluminum oxide has a very stable framework and can provide more active sites for electrochemical reactions, effectively increasing the active specific surface area for lithium ion deintercalation reaction. The surface structure is high voltage resistant, thereby improving the cycle performance under a high voltage.
Compared with the prior art, the beneficial effects of the present invention are as follows:
The fast ionic conductor coated lithium-transition metal oxide of the present invention has lower impedance, excellent cycle performance and safety performance under a high voltage, especially a charging voltage greater than 4.62V, 4.65V or higher. The Lithium-transition metal oxide can be obtained by a primary calcination, and a final product of the lithium-transition metal oxide material coated with fast ionic conductor can be obtained by a secondary calcination.
Hereinafter, the concept of the present invention and the technical effects produced by it will be described clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the applications of the present invention, rather than all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work belong to the scope of protection of the present invention.
In the present invention, LicAldTieM′fM″g(PO4)3 is abbreviated as LAT M′M″P or LATPM′M″; LicAldTie(PO4)3 is abbreviated as LATP.
The preparation method of the fast ionic conductor coated lithium cobalt oxide material of this embodiment comprises the following specific steps:
Since the fast ionic conductor intermediate product will react with M′·M″ on the surface of the modified lithium cobalt oxide powder, a stable shallow fast ionic conductive layer is formed by chemical interactions among the lithium-transition metal material, M′·M″ and fast ionic conductor intermediate product on the surface. During a cycling, the cathode material and its coating layer will not fall apart easily.
Weighing and adding lithium carbonate, nickel-cobalt-manganese hydroxide (Ni:Co:Mn=8:1:1), magnesium oxide, aluminum oxide, and lanthanum oxide in a molar ratio according to the chemical formula of Li1.04(Ni0.8Co0.1Mn0.1)0.955Mg0.01Al0.03Zr0.005O2 in a three-dimensional mixer; adding balls in a mass ratio of 1.5:1 and mixing for 3 hours to obtain a mixed powder; subjecting the mixed powder to calcination at a temperature of 800° C., and holding the temperature for 10 hours, followed by natural cooling and crushing to obtain a modified ternary NiCoMn-811 primary powder.
The preparation method of the fast ionic conductor coated lithium cobalt oxide material of this embodiment comprises the following specific steps:
The method is roughly the same as in Example 1, except that the lithium-transition metal oxide used is a ternary layered material 622 series, the primary calcination is carried out at a temperature of 700° C., and the additives used for doping are zirconia oxide, alumina oxide and boron oxide with a doping amount of 0.02%, 0.02%, 0.02% respectively. After natural cooling, 5% fast ionic conductor coated modified ternary 622 material product is obtained.
The method is roughly the same as in Example 1, except that the lithium-transition metal oxide used is a ternary layered material 523 series, the primary calcination is carried out at a temperature of 900° C., and the additives used for doping are zirconia oxide, alumina oxide and magnesia oxide with a doping amount of 0.03%, 0.02%, 0.02% respectively. M′ and M″ are titanium oxide and cobalt oxide respectively, and a 4% fast ionic conductor coated modified ternary 523 material product is obtained.
The method is roughly the same as in Example 3. The difference is that the lithium-transition metal oxide used is a ternary layered material 622 series, the primary calcination temperature is 720° C., and the additives used for doping are zirconium oxide and strontium oxide, with a doping amount of 0.03%, 0.02% respectively. After natural cooling, 5% fast ionic conductor coated modified ternary 622 material product is obtained.
The method is roughly the same as in Example 3. The difference is that the lithium-transition metal oxide used is a ternary layered material 523 series, the primary calcination is carried out at a temperature of 920° C., and the doping additives are zirconia oxide and alumina oxide with a doping amount of 0.03%, 0.04% respectively. M′ and M″ are titanium oxide and cobalt oxide, respectively, and a 3% fast ionic conductor coated modified ternary 523 material product is obtained.
The preparation method of the modified lithium cobalt oxide material of this comparative example comprises the following specific steps:
The preparation method of the fast ionic conductor coated lithium cobalt oxide material of this embodiment comprises the following specific steps:
The preparation method of the fast ionic conductor coated lithium cobalt oxide material of this comparative example comprises the following specific steps:
The preparation method of the nickel-cobalt-manganese material of this comparative example comprises the following specific steps:
The preparation method of the fast ionic conductor coated nickel-cobalt-manganese material of this comparative example comprises the following specific steps:
Results Comparison:
The specific preparation methods of the lithium batteries using the compounds of Examples 1-7 and Comparative Examples 1-5 are as follows:
The test method is as follows:
Capacity test: Take 7 repetitions of the batteries prepared from the compounds of Comparative Examples 1-2, 4-5 and Example 1-3, and charge them to the voltage of V1 at a constant current rate of 0.1 C at a room temperature of 25° C. Furtherly, under a constant voltage of V1, charge them until the current is lower than 0.05 C to reach a fully charged state. Then discharge the battery at a constant current to V2 at a rate of 0.1 C and obtain the discharge capacity. The discharge gram capacity at a rate of 0.1 C can be calculated by the following formula: discharge gram capacity=discharge capacity/mass of the cathode material.
Cycle performance test: At room temperature 25° C., charging-discharging and storing are performed alternatively, that is, storing after a charge-discharge process, and then performing a charge-discharge test to proceed a cyclic test. Cycle capacity retention rate=(discharge capacity at the 50th cycle/discharge capacity at the first cycle)×100%.
Different lithium-transition metal oxides have different requirements for charging and discharging voltage in capacity test and cycle test, which are specified as follows:
When the fast ionic conductor coated lithium-transition metal oxide in the positive pole pieces of Example 2 and Comparative Examples 4-5 comprises a ternary 811 material, the discharge capacity per gram is tested at 0.1 C to 3.0-4.25 V and the cycle performance is tested at 0.1 C to a charge-discharge voltage of 3.0-4.25 V. The results are shown in Table 1.
When the fast ionic conductor-coated lithium-transition metal oxide in the positive pole pieces of Comparative Example 1-2 and Examples 1 and 3 comprises the high-voltage lithium-cobalt oxide, the discharge capacity per gram is tested at 0.1 C to 3.0-4.55 V. The cycle performance is tested at 0.5 C to a charge-discharge voltage of 3.0-4.62 V/4.65 V, and the results are shown in Table 2.
The method for characterizing the electrical properties of the fast ionic conductor coated lithium-transition metal oxide materials in the present invention is as follows:
In Comparative Example 1 it is coated with oxide, and the capacity decreases significantly; Comparative Example 2 is the fast ionic intermediate product, the capacity change is small but the cycle attenuation is obvious. The single-coated fast ionic conductor has the problem of matching between the substrate and the surface layer, which makes the cycle attenuation proceed fast.
The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above-mentioned embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various modifications can be made without departing from the purpose of the present invention. Variety. In addition, in the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202110345374.7 | Mar 2021 | CN | national |
The present application is a continuation application of PCT application No. PCT/CN2021/142288 filed on Dec. 29, 2021, which claims the benefit of Chinese Patent Application No. 202110345374.7 filed on Mar. 31, 2021. The contents of all of the aforementioned applications are incorporated by reference herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2021/142288 | Dec 2021 | US |
| Child | 18230198 | US |
