High-entropy compound positive electrode lithium supplement agent and preparation method thereof, positive electrode plate and lithium ion battery

Abstract

The invention relates to the technical field of battery materials, in particular to a high-entropy compound positive pole lithium supplement agent and a preparation method thereof, a positive pole piece and a lithium ion battery, the chemical formula of the high-entropy compound positive pole lithium supplement agent is LixM1aM2b... MyeAZ, 1 < x < = 4, 5 < = y < = 13, a + b +... + e = 1, M1, M2... My respectively represent metal elements, and the sum of the metal elements is 1 < x < = 4. The metal elements comprise at least five of iron, manganese, aluminum, magnesium, vanadium, titanium, nickel, cobalt, potassium, calcium, copper, zinc and cadmium, A represents a non-metal element, and the non-metal element comprises oxygen. After the positive electrode lithium supplement agent provided by the invention is applied to the lithium ion battery, the gas production rate is relatively low, and meanwhile, the lithium ion battery can have excellent cycling stability.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a high-entropy compound positive electrode lithium replenisher and a preparation method thereof, a positive electrode plate and a lithium ion battery. Background Art

[0002] In modern society, with the widespread use of mobile electronic devices and electric vehicles, lithium-ion batteries are widely used due to their high energy density and long life. However, during activation and use, active lithium is continuously consumed, resulting in a decrease in battery capacity and a shortened cycle life. To address this issue, researchers have proposed lithium replenishment technology, which replenishes lithium ions into the battery during the manufacturing process to maintain battery capacity and life.

[0003] The use of lithium salt replenishers for positive electrode replenishment only requires adding a certain amount of lithium salt replenisher when preparing the positive electrode slurry, without changing the lithium-ion battery production process. This is compatible with the current lithium-ion battery manufacturing process. Li2NiO2 (lithium nickel-rich lithium) is a lithium salt replenisher that is currently widely used. The biggest problem is that it produces a lot of gas after being applied to lithium-ion batteries, such as CO2, CO, etc., which not only reduces the battery capacity and cycle life, but also increases the safety risk of the battery. At the same time, lithium-ion batteries using Li2NiO2 as a replenisher have poor cycle stability. Therefore, how to provide a positive electrode replenisher that produces less gas after being applied to lithium-ion batteries and can make lithium-ion batteries have excellent cycle stability is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a high-entropy compound positive electrode lithium replenisher and its preparation method, a positive electrode plate and a lithium ion battery. The positive electrode lithium replenisher provided by the present invention produces less gas after being applied to a lithium ion battery, and can also make the lithium ion battery have excellent cycle stability.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a high entropy compound positive electrode lithium replenisher, the chemical formula of the high entropy compound positive electrode lithium replenisher is Li x M1 a M2 b …My e A Z, wherein 1<x≤4, 5≤y≤13, a+b+…+e=1, M1, M2…My respectively represent metal elements, and the metal elements include at least 5 of iron, manganese, aluminum, magnesium, vanadium, titanium, nickel, cobalt, potassium, calcium, copper, zinc, and cadmium; A represents a non-metallic element, and the non-metallic element includes oxygen.

[0007] The positive electrode lithium supplement provided by the present invention produces less gas after being applied to a lithium ion battery, and can also enable the lithium ion battery to have excellent cycle stability.

[0008] Furthermore, the non-metallic element also includes at least one of carbon, nitrogen, boron, silicon, sulfur, and phosphorus;

[0009] and / or, when the non-metallic element further includes at least one of carbon, nitrogen, boron, silicon, sulfur, and phosphorus, the molar percentage of oxygen ions to total anions is 90%-97%;

[0010] and / or, the stoichiometric coefficients of each of the metal elements are equal;

[0011] and / or, the difference in atomic radius of each metal element is controlled within 15%;

[0012] And / or, the high entropy compound positive electrode lithium replenisher is at least partially coated with an oxide or nitride with high stability and high conductivity, and the oxide or nitride with high stability and high conductivity includes an oxide of titanium, aluminum, or zirconium, or a nitride of titanium, aluminum, or zirconium.

[0013] In a second aspect, the present invention provides a method for preparing the high entropy compound positive electrode lithium replenisher as described in the first aspect, the preparation method comprising the following steps:

[0014] S1. Weigh the chemical formula Li x M1 a M2 b …My e A Z The stoichiometric ratios of M1 source, M2 source, My source and lithium source are shown in FIG;

[0015] S2. Mixing the M1 source, M2 source...My source and the lithium source, and then calcining the mixture to obtain the high entropy compound positive electrode lithium supplement.

[0016] Furthermore, the preparation method also includes: in step S1, weighing a non-metallic element source; in step S2, mixing the M1 source, M2 source...My source, the lithium source and the non-metallic element source, wherein the non-metallic element source includes at least one of a carbon source, a nitrogen source, a boron source, a silicon source, a sulfur source, and a phosphorus source.

[0017] Furthermore, the carbon source includes at least one of glucose, citric acid, polyacrylonitrile, and starch; the nitrogen source includes at least one of urea, ammonia water, dicyandiamide, pyrrole, and aniline; the boron source includes at least one of boron oxide, sodium borohydride, and boron nitride; the silicon source includes at least one of tetraethyl orthosilicate, silica sol, sodium silicate, and a silane coupling agent; the sulfur source includes at least one of thiourea, sodium thiosulfate, sulfur powder, and L-cysteine; and the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, red phosphorus, and phytic acid.

[0018] Furthermore, the M1 source, M2 source...My source include at least one of corresponding metal powder, corresponding metal oxide, and corresponding metal salt;

[0019] And / or, the lithium source comprises at least one of lithium powder, LiOH, and Li2CO3;

[0020] And / or, in step S2, the calcination temperature is 600-900° C., the calcination time is 6-20 hours, and the calcination atmosphere is oxygen atmosphere, air atmosphere or inert gas atmosphere;

[0021] And / or, after the calcination in step S2 is completed, the preparation method further comprises the following steps:

[0022] S3, annealing: annealing the product of step S2 under a protective gas atmosphere, and then naturally cooling it to room temperature, wherein the annealing temperature is lower than the calcining temperature;

[0023] And / or, after step S2, the preparation method further comprises the following steps:

[0024] S4. An oxide or nitride coating having high stability and high conductivity is provided on the surface of the product in step S2 or the product in step S3.

[0025] Furthermore, in step S3, the protective gas includes argon, the annealing temperature is 200-500° C., and the annealing time is 1-3 hours;

[0026] And / or, in step S4, an oxide or nitride coating with high stability and high conductivity is provided on the surface of the product in step S2 or the product in step S3 by an atomic layer deposition method.

[0027] In a third aspect, the present invention provides a positive electrode plate, comprising a positive electrode collector and a positive electrode active layer covering at least one surface of the positive electrode collector; the positive electrode active layer comprises the high-entropy compound positive electrode lithium replenisher described in the first aspect, or the high-entropy compound positive electrode lithium replenisher prepared by the preparation method described in the second aspect.

[0028] Furthermore, the positive electrode active layer further includes a positive electrode active material, and the mass ratio of the positive electrode active material to the high entropy compound positive electrode lithium replenisher is 1:(0.01-0.15).

[0029] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0030] Compared with the prior art, the present invention has at least one of the following advantages:

[0031] (1) The positive electrode lithium supplement provided by the present invention produces less gas after being applied to a lithium ion battery, and can also make the lithium ion battery have excellent cycle stability.

[0032] (2) The positive electrode lithium supplement provided by the present invention improves the cycle stability and capacity of lithium-ion batteries.

[0033] (3) The present invention synthesizes high-entropy materials with excellent performance as positive-electrode lithium replenishers, effectively improving the stability and capacity of the lithium replenisher. High-entropy materials have unique multi-principal element, multi-coordination, and multi-phase structural characteristics, which can effectively inhibit the decomposition of lithium salts and reduce gas generation, thereby improving the capacity and life of the battery.

[0034] (4) Simplified operation process: The positive electrode lithium supplement prepared by the present invention is added during the positive electrode homogenization process, which is the same as the conventional battery manufacturing process, is easy to implement, avoids production line modification and reduces costs.

[0035] (5) Improved lithium replenishment efficiency: The high-entropy material of the present invention, as a positive electrode lithium replenisher, can effectively improve lithium replenishment efficiency. Because the high-entropy material has excellent electrical conductivity, it can promote the migration of lithium ions, thereby improving lithium replenishment efficiency and shortening the replenishment time.

[0036] (6) Environmental friendliness: The high-entropy material of the present invention is environmentally friendly as a positive electrode lithium supplement. During production and use, the high-entropy material does not produce harmful pollutants and is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 This is a SEM image of the high entropy compound positive electrode lithium replenisher provided in Example 1 of the present invention at a magnification of 30,000 times;

[0039] Figure 2 This is a SEM image of the high entropy compound positive electrode lithium replenisher provided in Example 1 of the present invention at a magnification of 50,000 times. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0041] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0042] In the first aspect, the present invention provides a high entropy compound positive electrode lithium replenisher, the chemical formula of the high entropy compound positive electrode lithium replenisher is Li x M1 a M2 b …My e A Z , wherein 1<x≤4 (for example, it can be 1.5, 2, 3 or 4), 5≤y≤13 (for example, it can be 5, 7, 9, 11 or 13), a+b+…+e=1, M1, M2…My respectively represent metal elements, and the metal elements include at least 5 of iron, manganese, aluminum, magnesium, vanadium, titanium, nickel, cobalt, potassium, calcium, copper, zinc, and cadmium, and A represents a non-metallic element, and the non-metallic element includes oxygen.

[0043] Here, a, b, ..., e are the stoichiometric coefficients of each M element, and a+b+...+e=1, indicating that the sum of the stoichiometric coefficients of all M elements is 1.

[0044] Z represents the stoichiometric coefficient of A.

[0045] The positive electrode lithium supplement provided by the present invention produces less gas after being applied to a lithium ion battery, and can also enable the lithium ion battery to have excellent cycle stability.

[0046] The high entropy material of the present invention is used as a positive electrode lithium supplement, and the lithium removal reaction formula is: Li xM1 a M2 b …My e A Z -xe - =M1 a M2 b …My e A Z +xLi + , the lithium supplement agent does not produce gas when delithium is removed, which can reduce the gas production problem of conventional lithium supplement agents. In addition, since high entropy materials have excellent thermal stability and chemical stability, they can effectively inhibit the reaction between lithium salts and electrolytes, reduce the generation of by-products, and thus reduce the safety risk of batteries. In the above-mentioned high entropy compound positive electrode lithium supplement agent, as an optional embodiment, the non-metallic element also includes at least one of carbon, nitrogen, boron, silicon, sulfur, and phosphorus. By doping with non-metallic elements, the gas production can be further reduced, and the cycle stability and capacity of lithium-ion batteries can also be improved.

[0047] In the above-mentioned high entropy compound positive electrode lithium replenisher, as an optional embodiment, when the non-metallic element also includes at least one of carbon, nitrogen, boron, silicon, sulfur, and phosphorus, the molar percentage of oxygen ions to total anions (i.e., the proportion of oxygen to total anion sites) is 90%-97%, for example, it can be 90%, 93%, 95% or 97%.

[0048] In the above-mentioned high entropy compound positive electrode lithium replenisher, as an optional embodiment, each component in the chemical formula satisfies the conservation of charge.

[0049] In the aforementioned high-entropy compound cathode lithium replenisher, as an optional embodiment, the stoichiometric coefficients of each metal element (M) are equal. Having similar molar ratios of the metal elements maximizes mixing entropy, promotes single-phase formation, and thus improves structural stability and lithium replenishment efficiency.

[0050] In the aforementioned high-entropy compound positive electrode lithium replenisher, as an optional embodiment, the atomic radius of each metal element is controlled to be within 15%, preferably nickel, iron, manganese, magnesium, and aluminum. Having similar atomic radii of each metal element can further reduce gas production while also improving the cycle stability and capacity of the lithium-ion battery.

[0051] The present invention optimizes the structure of the high entropy material by limiting the stoichiometric coefficients of each metal element (M) to be equal and controlling the difference in atomic radius of each metal element to be within 15%, thereby making it have a more stable crystal structure and a higher coordination number, thereby further improving the stability and capacity of the lithium supplement. A high coordination number has the following advantages: (1) Enhanced structural stability: A higher coordination number means that the bonds between atoms are tighter and the lattice structure is more stable; the multi-principal element characteristics of the high entropy material lead to lattice distortion, and a high coordination number can alleviate this distortion and reduce internal stress, thereby improving the structural stability of the material. Under extreme conditions such as high temperature, high pressure or electrochemical cycling, a high coordination number helps maintain the integrity of the material and reduce phase change or decomposition; (2) Improved electrochemical performance: A high coordination number can provide a more stable crystal structure, reduce volume expansion and contraction during charge and discharge, thereby improving cycle stability; a high coordination number also helps the rapid diffusion of lithium ions, because more coordinated atoms can provide more diffusion paths, thereby improving the ionic conductivity of the material.

[0052] In the aforementioned high-entropy compound positive electrode lithium replenisher, as an optional embodiment, the high-entropy compound positive electrode lithium replenisher is at least partially coated with an oxide or nitride having high stability and high conductivity. In other words, the oxide or nitride having high stability and high conductivity is at least partially coated on the outer surface of the high-entropy oxide positive electrode lithium replenisher.

[0053] In the above-mentioned high entropy compound positive electrode lithium replenisher, as an optional embodiment, the oxide or nitride with high stability and high conductivity includes an oxide of titanium, aluminum, or zirconium, or a nitride of titanium, aluminum, or zirconium.

[0054] In a second aspect, the present invention provides a method for preparing the high entropy compound positive electrode lithium replenisher as described in the first aspect, the preparation method comprising the following steps:

[0055] S1. Weigh the chemical formula Li x M1 a M2 b …My e A Z The stoichiometric ratios of M1 source, M2 source, My source and lithium source are shown in FIG;

[0056] S2. Mixing the M1 source, M2 source...My source and the lithium source, and then calcining the mixture to obtain the high entropy compound positive electrode lithium supplement.

[0057] In the above-mentioned preparation method of the high-entropy compound positive electrode lithium replenisher, as an optional embodiment, the preparation method further includes: in step S1, weighing a non-metallic element source; in step S2, mixing the M1 source, M2 source...My source, the lithium source and the non-metallic element source, wherein the non-metallic element source includes at least one of a carbon source, a nitrogen source, a boron source, a silicon source, a sulfur source, and a phosphorus source.

[0058] In the preparation method of the above-mentioned high-entropy compound positive electrode lithium replenisher, as an optional embodiment, the carbon source includes at least one of glucose, citric acid, polyacrylonitrile (PAN), and starch, the nitrogen source includes at least one of urea, ammonia water, dicyandiamide, pyrrole, and aniline, the boron source includes at least one of boron oxide, sodium borohydride, and boron nitride (BN), the silicon source includes at least one of tetraethyl orthosilicate, silica sol (nano-SiO2 dispersion), sodium silicate (Na2SiO3), and a silane coupling agent, the sulfur source includes at least one of thiourea, sodium thiosulfate, sulfur powder, and L-cysteine; the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, red phosphorus, and phytic acid.

[0059] In the above-mentioned method for preparing the high-entropy compound positive electrode lithium replenisher, as an optional embodiment, the M1 source, M2 source...My source include at least one of the corresponding metal powder, the corresponding metal oxide, and the corresponding metal salt.

[0060] In the above-mentioned method for preparing the high-entropy compound positive electrode lithium replenisher, as an optional embodiment, the lithium source includes at least one of lithium powder, LiOH, and Li2CO3.

[0061] In the preparation method of the above-mentioned high entropy compound positive electrode lithium replenisher, as an optional embodiment, in step S2, the calcination temperature is 600-900°C (for example, it can be 600°C, 700°C, 800°C or 900°C), the calcination time is 6-20 hours (for example, it can be 6 hours, 10 hours, 15 hours or 20 hours), and the calcination atmosphere is an oxygen atmosphere, an air atmosphere or an inert gas atmosphere.

[0062] In the above-mentioned preparation method of the high entropy compound positive electrode lithium replenisher, as an optional embodiment, after the calcination in step S2 is completed, the preparation method further includes the following steps:

[0063] S3. Annealing: annealing the product in step S2 under a protective gas atmosphere, and then naturally cooling it to room temperature, wherein the annealing temperature is lower than the calcining temperature.

[0064] After annealing, the high-entropy compound positive electrode lithium replenisher has a more stable crystal structure and the coordination number can be further improved, thereby further reducing the gas production and also improving the cycle stability and capacity of the lithium-ion battery.

[0065] In the above-mentioned method for preparing a high-entropy compound positive lithium supplement, as an optional embodiment, in step S3, the protective gas includes argon, the annealing temperature is 200-500°C (for example, 200°C, 300°C, 400°C, or 500°C), and the annealing time is 1-3 hours. Limiting the annealing temperature has the following beneficial effects: controlling grain growth: A lower annealing temperature can avoid excessive grain growth, maintain the material's fine or nanocrystalline structure, and thus optimize mechanical and functional properties.

[0066] In the above-mentioned method for preparing the high entropy compound positive electrode lithium replenisher, as an optional embodiment, after step S2, the preparation method further includes the following steps:

[0067] S4. An oxide or nitride coating having high stability and high conductivity is provided on the surface of the product in step S2 or the product in step S3.

[0068] In the above-mentioned method for preparing a high-entropy compound positive electrode lithium replenisher, as an optional embodiment, in step S4, an oxide or nitride coating with high stability and high conductivity is provided on the surface of the product in step S2 or the product in step S3 by an atomic layer deposition (ALD) method.

[0069] In the above-mentioned method for preparing a high-entropy compound positive electrode lithium replenisher, as an optional embodiment, in step S4, the thickness of the oxide or nitride coating with high stability and high conductivity is 5-15 nanometers, for example, it can be 5 nanometers, 7 nanometers, 9 nanometers, 11 nanometers, 13 nanometers or 15 nanometers.

[0070] In a third aspect, the present invention provides a positive electrode plate, comprising a positive electrode collector and a positive electrode active layer covering at least one surface of the positive electrode collector; the positive electrode active layer comprises the high-entropy compound positive electrode lithium replenisher described in the first aspect, or the high-entropy compound positive electrode lithium replenisher prepared by the preparation method described in the second aspect.

[0071] In the above-mentioned positive electrode sheet, as an optional embodiment, the positive electrode active layer further includes a positive electrode active material, and the mass ratio of the positive electrode active material to the high entropy compound positive electrode lithium replenisher is 1:(0.01-0.15), for example, it can be 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.11, 1:0.13 or 1:0.15.

[0072] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0073] In the above-mentioned lithium-ion battery, as an optional embodiment, the formation method of the lithium-ion battery includes: charging at a constant current of 0.05C at 45°C and a negative pressure of -70kPa to the decomposition voltage of the high-entropy compound positive lithium replenisher (e.g., 4.3V). During the lithium-ion battery formation process, fully charging to the decomposition voltage of the high-entropy compound positive lithium replenisher in one step can allow all lithium ions in the lithium replenisher to be released.

[0074] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0075] Example 1

[0076] This embodiment provides a high entropy compound positive electrode lithium replenisher, the chemical formula of the high entropy compound positive electrode lithium replenisher is Li 2.2 (Fe 0.2 K 0.2 Ca 0.2 Mn 0.2 Mg 0.2 )O2.

[0077] The preparation method of the high entropy compound positive electrode lithium replenisher provided in this embodiment includes the following steps:

[0078] S1, according to the chemical formula Li 2.2 (Fe 0.2 K 0.2 Ca 0.2 Mn 0.2 Mg 0.2 )O2 (the molar ratio of lithium, iron, potassium, calcium, manganese and magnesium elements is 11:1:1:1:1:1);

[0079] S2. Li2CO3, ferrous sulfate, K2CO3, calcium carbonate, manganese carbonate and MgO are mixed, and the mixture is placed in a muffle furnace, calcined at 700°C in an argon atmosphere for 12 hours, and then cooled to room temperature to obtain the high entropy compound positive electrode lithium supplement powder.

[0080] The structure of the high entropy compound positive electrode lithium replenisher prepared in this example was analyzed by X-ray diffraction (XRD), and it was found that its crystal structure was a body-centered cubic structure with a coordination number of 8.

[0081] The high entropy compound positive electrode lithium replenisher prepared in this example was analyzed by scanning electron microscopy (SEM). Figure 1 and Figure 2 As shown by Figure 1 and Figure 2 It can be seen that the high entropy compound positive electrode lithium replenisher particles prepared in this example are evenly distributed without obvious large agglomerations.

[0082] Example 2

[0083] The preparation method of the high entropy compound positive electrode lithium replenisher provided in this embodiment is basically the same as that in Example 1, except that after calcination at 700° C. for 12 hours in step S2, the preparation method further includes the following steps:

[0084] S3. Annealing: Cool down to 500°C at a rate of 5°C / min, keep the high entropy material at 500°C for 2 hours under argon atmosphere, and then cool naturally to room temperature.

[0085] The structure of the high entropy compound positive electrode lithium replenisher prepared in this example was analyzed by X-ray diffraction (XRD), and it was found that its crystal structure was a disordered rock salt structure (Fm-3m space group) with a coordination number of 12.

[0086] Example 3

[0087] The preparation method of the high entropy compound positive electrode lithium replenisher provided in this embodiment is basically the same as that in Example 2, except that, after step S3, the preparation method further includes the following steps:

[0088] S4. After cooling in step S3, an aluminum oxide coating is provided on the surface of the product: a stable aluminum oxide coating is applied on the surface of the high entropy material by atomic layer deposition (ALD) method, and the coating thickness is 10 nanometers, wherein the specific method of atomic layer deposition (ALD) is as follows: (1) Pretreatment: Surface cleaning: Place the high entropy material sample in an ultrasonic cleaning machine, and use acetone, ethanol and deionized water to clean it in turn to remove surface pollutants; Drying: Place the sample in a vacuum drying oven and dry it at 80°C for 1 hour to ensure that there is no moisture residue on the surface; (2) ALD deposition process: Step 1: TMA (trimethylaluminum) pulse: reverse TMA gas is introduced into the reaction chamber with a pulse time of 0.5 seconds to allow TMA molecules to adsorb on the surface of the high entropy material; Step 2: N2 purge: high-purity N2 is introduced for 20 seconds to remove unreacted TMA and by-products; Step 3: H2O pulse: H2O gas is introduced with a pulse time of 0.5 seconds to react with the adsorbed TMA to generate Al2O3; Step 4: N2 purge: N2 is introduced again for 30 seconds to remove unreacted H2O and by-products; Step 5: cycle step: repeat steps 1-4 until the target coating thickness is reached; (3) post-treatment: after deposition is completed, the sample is cooled to room temperature under N2 atmosphere.

[0089] Example 4

[0090] This embodiment provides a high entropy compound positive electrode lithium replenisher, the chemical formula of the high entropy compound positive electrode lithium replenisher is Li1.6(Fe0.2Ni0.2Mn0.2Mg0.2Al0.2)O2.

[0091] The preparation method of the high-entropy compound positive electrode lithium replenisher provided in this embodiment is basically the same as that in Example 1, except that Li2CO3, ferrous sulfate, nickel oxide, manganese carbonate MnCO3, MgO and Al2O3 are weighed according to the stoichiometric ratio shown in the chemical formula Li1.6(Fe0.2Ni0.2Mn0.2Mg0.2Al0.2)O2 (the molar ratio of lithium, iron, nickel, manganese, magnesium and aluminum elements is 8:1:1:1:1:1:1); Li2CO3, ferrous sulfate, nickel oxide, manganese carbonate MnCO3, MgO and Al2O3 are mixed.

[0092] The structure of the high entropy compound positive electrode lithium replenisher prepared in this example was analyzed by X-ray diffraction (XRD), and it was found that its crystal structure was a disordered rock salt structure (Fm-3m space group) with a coordination number of 12.

[0093] Example 5

[0094] This embodiment provides a high entropy compound positive electrode lithium replenisher, the chemical formula of the high entropy compound positive electrode lithium replenisher is Li 2.2 (Fe 0.2 K 0.2 Ca 0.2 Mn 0.2 Mg 0.2 )O 1.9 S 0.1 .

[0095] The preparation method of the high entropy oxide positive electrode lithium supplement provided in this embodiment is basically the same as that in Example 1, except that according to the chemical formula Li 2.2 (Fe 0.2 K 0.2 Ca 0.2 Mn 0.2 Mg 0.2 )O 1.9 S 0.1 Li2CO3, ferrous sulfate, K2CO3, calcium carbonate CaCO3, manganese carbonate MnCO3, MgO and thiourea were weighed in the stoichiometric ratio shown (the molar ratio of lithium, iron, potassium, calcium, manganese, magnesium and sulfur elements was 11:1:1:1:1:1:0.5); Li2CO3, ferrous sulfate, K2CO3, calcium carbonate, manganese carbonate, MgO and thiourea were mixed.

[0096] The structure of the high entropy compound positive electrode lithium replenisher prepared in this example was analyzed by X-ray diffraction (XRD), and it was found that its crystal structure was a disordered rock salt structure (Fm-3m space group) with a coordination number of 12.

[0097] Example 6

[0098] This embodiment provides a high entropy compound positive electrode lithium replenisher, the chemical formula of the high entropy compound positive electrode lithium replenisher is Li4(Fe 0.2 Ni 0.2 Mn 0.2 Mg 0.2 Ti 0.2 )O 3.3 .

[0099] The preparation method of the high entropy oxide positive electrode lithium supplement provided in this embodiment is basically the same as that in Example 1, except that the preparation method is as follows: 0.2 Ni 0.2 Mn 0.2 Mg 0.2 Ti 0.2 )O 3.3 Li2CO3, ferrous sulfate, nickel oxide, manganese carbonate MnCO3, MgO and TiO2 were weighed in the stoichiometric ratio shown (the molar ratio of lithium, iron, nickel, manganese, magnesium and titanium elements is 20:1:1:1:1:1); Li2CO3, ferrous sulfate, nickel oxide, manganese carbonate MnCO3, MgO and TiO2 were mixed.

[0100] The structure of the high entropy compound positive electrode lithium replenisher prepared in this example was analyzed by X-ray diffraction (XRD), and it was found that its crystal structure was a disordered rock salt structure (Fm-3m space group) with a coordination number of 10.

[0101] Example 7

[0102] The preparation method of the high entropy compound positive electrode lithium replenisher provided in this embodiment is basically the same as that in Example 1, except that after calcination at 700° C. for 12 hours in step S2, the preparation method further includes the following steps:

[0103] S3. Annealing: Cool down to 300°C at a rate of 5°C / min, keep the high entropy material at 300°C for 2 hours under argon atmosphere, and then cool naturally to room temperature.

[0104] The structure of the high entropy compound positive electrode lithium replenisher prepared in this example was analyzed by X-ray diffraction (XRD), and it was found that its crystal structure was a disordered rock salt structure (Fm-3m space group) with a coordination number of 12.

[0105] Comparative Example 1

[0106] The lithium supplement is Li2NiO2.

[0107] Performance Testing

[0108] 1. The positive electrode lithium supplement provided in each embodiment and comparative example is assembled into a button battery. The specific production method is as follows:

[0109] 1. Mix the positive electrode lithium supplement powder, conductive agent Super P and binder PVDF in a mass ratio of 92:5:3, add solvent (N-methylpyrrolidone NMP) and grind until a uniform slurry is obtained;

[0110] 2. Coat the slurry on the aluminum foil current collector with a coating density of 150g / m 2 ), followed by vacuum drying at 105°C for 12 hours;

[0111] 3. The dried electrode is compacted by a roller press to increase the electrode density, and then punched into discs with a diameter of about 12 mm to obtain the positive electrode;

[0112] 4. Battery assembly: In a glove box (H2O / O2 < 0.1ppm), stack the batteries in the following order: negative electrode shell → lithium sheet → electrolyte → diaphragm → electrolyte → positive electrode sheet → spring sheet → positive electrode shell, and finally seal with a sealing machine. After assembly, the battery needs to be left to stand for 12 hours to allow the electrolyte to soak in before conducting a gram capacity test.

[0113] Gram capacity test: Charge at 0.5C constant current and constant voltage, with a cutoff voltage of 4.3V (high entropy compound) or 4.2V (Li2NiO2), and a cutoff current of 0.05C. Then discharge at 0.5C constant current, with a cutoff voltage of 2.7V (high entropy compound) or 2.5V (Li2NiO2). Record the discharge capacity of the lithium supplement. Discharge gram capacity = discharge capacity / mass of the lithium supplement.

[0114] 2. The positive electrode lithium supplement provided in each embodiment and comparative example is made into a positive electrode sheet, which is then assembled into a lithium-ion battery. The specific production method is as follows:

[0115] 1. Preparation of positive electrode:

[0116] (a) The binder PVDF-5130 powder and the solvent NMP were stirred and mixed to obtain a glue solution with a solid content of 5±1%;

[0117] (b) Adding a conductive agent SP (the mass ratio of the conductive agent SP to the binder PVDF-5130 is 1:1.8) to the glue solution and stirring at 1600 RPM for 2 h to obtain a conductive slurry;

[0118] (c) The active material lithium iron phosphate and the positive electrode lithium replenisher were added to the conductive slurry at a mass ratio of active material: SP: PVDF: lithium replenisher = 94.7:1:1.8:2.5, and stirred at 1600 RPM for 3 h to obtain a positive electrode slurry with a solid content of 50±2%. The positive electrode slurry contained the active material lithium iron phosphate, the conductive agent SP, the binder PVDF-5130, the positive electrode lithium replenisher, and the solvent NMP;

[0119] (d) The positive electrode slurry was evenly coated on a carbon-coated aluminum foil with a thickness of 13 μm using a transfer coater to obtain a positive electrode sheet;

[0120] 2. Preparation of negative electrode sheet:

[0121] (a) Dissolve CMC-2200 powder in deionized water and stir to obtain a glue solution with a solid content of 1.5 ± 0.5%;

[0122] (b) Dry mixing the negative electrode main material graphite and SP at 1300 RPM for 1 h to obtain a mixture;

[0123] (c) Adding an appropriate amount of deionized water and a certain amount of SBR and CMC glue (wherein the negative electrode main material: SP:SBR:CMC = 96:1:1.5:1.5, by mass ratio) to the above mixture, and stirring at a high speed of 2000 RPM to finally obtain a negative electrode slurry with a solid content of 50±2%;

[0124] (d) The slurry was evenly coated on a copper foil with a thickness of 6 μm using a transfer coater to obtain a negative electrode sheet;

[0125] 3. Preparation of lithium-ion batteries:

[0126] The positive electrode sheets and the negative electrode sheets are rolled, die-cut, and slit, and then stacked with the separator to form a core package, assembled into a battery cell, and then baked, injected, left to stand at high temperature, formed, and divided into volumes to obtain a lithium-ion battery, wherein the electrolyte is selected to contain a mixed solvent of highly stable ethylene carbonate (EC) and dimethyl carbonate (DMC), and the solvent mass ratio is 1:1. Lithium hexafluorophosphate (LiPF6) with a mass fraction of 1wt% is added to the electrolyte as an electrolyte, and fluoroethylene carbonate (FEC) with a mass fraction of 0.1wt% is added to the electrolyte as an additive.

[0127] The lithium-ion batteries made from the positive lithium supplement agents of the above examples and comparative examples were subjected to cycle performance tests and gas production tests.

[0128] Cycling performance test: The initial test temperature was 45°C. The lithium-ion batteries in each group were subjected to constant current charge and discharge cycles at a rate of 1C at 2.5-3.65V. The discharge capacity retention rate was recorded after 200 cycles.

[0129] Gas production test: The battery was initially fully charged to 100% SOC, placed in a sealed container, and stored at 55°C for 7 days. The gas composition and content inside the lithium-ion battery were analyzed by gas chromatography, and the volume (ml) of gas corresponding to each gram of active material (lithium iron phosphate) was recorded.

[0130] The specific test results are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] From Table 1, we can see at least the following points:

[0135] (1) By comparing Examples 1-7 with Comparative Example 1, it can be seen that the positive electrode lithium supplement provided by the present invention produces less gas after being applied to a lithium ion battery, and at the same time, it can also make the lithium ion battery have excellent cycle stability and increase the capacity of the lithium ion battery.

[0136] (2) By comparing Example 1 with Example 2, it can be seen that the crystal structure of the high entropy compound positive electrode lithium replenisher after annealing is more stable and the coordination number can be further improved, so that the positive electrode lithium replenisher produces less gas after being applied to the lithium ion battery, and also improves the cycle stability and capacity of the lithium ion battery.

[0137] (3) Comparing Example 1 with Example 4, it can be seen that the close atomic radius of each metal element can further reduce the gas production, while also improving the cycle stability and capacity of the lithium-ion battery. The applicant speculates that the reason may be that the close atomic radius of each metal element can reduce lattice distortion, thereby improving structural stability and increasing lithium replenishment efficiency.

[0138] (4) Comparing Example 1 with Example 5, it can be seen that by doping the non-metallic element S, the gas production can be further reduced, and the cycle stability and capacity of the lithium-ion battery can also be improved. The applicant speculates that the reason may be that the addition of S can adjust the crystal structure, electronic structure and chemical bond characteristics of the high-entropy compound, thereby improving its mechanical properties, electrochemical properties, thermal stability and functional properties. By optimizing the structure of the high-entropy compound, it has a more stable crystal structure and a higher coordination number, thereby further improving the stability and capacity of the lithium supplement.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high entropy compound positive electrode lithium replenisher, characterized in that: The chemical formula of the high entropy compound positive electrode lithium replenisher is Li x M1 a M2 b …My e A Z , wherein 1<x≤4, 5≤y≤13, a+b+…+e=1, M1, M2…My respectively represent metal elements, and the metal elements include at least 5 of iron, manganese, aluminum, magnesium, vanadium, titanium, nickel, cobalt, potassium, calcium, copper, zinc, and cadmium; A represents a non-metallic element, and the non-metallic element includes oxygen.

2. The high entropy compound positive electrode lithium replenisher according to claim 1, characterized in that The non-metallic element further includes at least one of carbon, nitrogen, boron, silicon, sulfur, and phosphorus; and / or, when the non-metallic element further includes at least one of carbon, nitrogen, boron, silicon, sulfur, and phosphorus, the molar percentage of oxygen ions to total anions is 90%-97%; and / or, the stoichiometric coefficients of each of the metal elements are equal; and / or, the difference in atomic radius of each metal element is controlled within 15%; And / or, the high entropy compound positive electrode lithium replenisher is at least partially coated with an oxide or nitride with high stability and high conductivity, and the oxide or nitride with high stability and high conductivity includes an oxide of titanium, aluminum, or zirconium, or a nitride of titanium, aluminum, or zirconium.

3. A method for preparing a high entropy compound positive electrode lithium replenisher according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: S1. Weigh the chemical formula Li x M1 a M2 b …My e A Z The stoichiometric ratios of M1 source, M2 source, My source and lithium source are shown in FIG; S2. Mixing the M1 source, M2 source...My source and the lithium source, and then calcining the mixture to obtain the high entropy compound positive electrode lithium supplement.

4. The method for preparing the high entropy compound positive electrode lithium supplement according to claim 3, wherein: The preparation method also includes: in step S1, weighing a non-metallic element source; in step S2, mixing the M1 source, M2 source...My source, the lithium source and the non-metallic element source, wherein the non-metallic element source includes at least one of a carbon source, a nitrogen source, a boron source, a silicon source, a sulfur source, and a phosphorus source.

5. The method for preparing the high entropy compound positive electrode lithium supplement according to claim 4, characterized in that: The carbon source includes at least one of glucose, citric acid, polyacrylonitrile, and starch; the nitrogen source includes at least one of urea, ammonia water, dicyandiamide, pyrrole, and aniline; the boron source includes at least one of boron oxide, sodium borohydride, and boron nitride; the silicon source includes at least one of tetraethyl orthosilicate, silica sol, sodium silicate, and a silane coupling agent; the sulfur source includes at least one of thiourea, sodium thiosulfate, sulfur powder, and L-cysteine; and the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, red phosphorus, and phytic acid.

6. The method for preparing the high entropy compound positive electrode lithium supplement according to claim 3, characterized in that: The M1 source, M2 source...My source include at least one of corresponding metal powder, corresponding metal oxide, and corresponding metal salt; And / or, the lithium source comprises at least one of lithium powder, LiOH, and Li2CO3; And / or, in step S2, the calcination temperature is 600-900° C., the calcination time is 6-20 hours, and the calcination atmosphere is oxygen atmosphere, air atmosphere or inert gas atmosphere; And / or, after the calcination in step S2 is completed, the preparation method further comprises the following steps: S3, annealing: annealing the product of step S2 under a protective gas atmosphere, and then naturally cooling it to room temperature, wherein the annealing temperature is lower than the calcining temperature; And / or, after step S2, the preparation method further comprises the following steps: S4. An oxide or nitride coating having high stability and high conductivity is provided on the surface of the product in step S2 or the product in step S3.

7. The method for preparing the high entropy compound positive electrode lithium supplement according to claim 6, characterized in that: In step S3, the protective gas includes argon, the annealing temperature is 200-500° C., and the annealing time is 1-3 hours; And / or, in step S4, an oxide or nitride coating with high stability and high conductivity is provided on the surface of the product in step S2 or the product in step S3 by an atomic layer deposition method.

8. A positive electrode plate, characterized in that: The positive electrode plate includes a positive electrode current collector and a positive electrode active layer covering at least one surface of the positive electrode current collector; the positive electrode active layer includes the high entropy compound positive electrode lithium replenisher according to claim 1 or 2, or the high entropy compound positive electrode lithium replenisher prepared by the preparation method according to any one of claims 3-7.

9. The positive electrode sheet according to claim 8, characterized in that: The positive electrode active layer further includes a positive electrode active material, and the mass ratio of the positive electrode active material to the high entropy compound positive electrode lithium replenisher is 1:(0.01-0.15).

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 8 or 9.

Images