Composite lithium supplement agent and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention relates to a composite lithium supplement agent and a preparation method thereof, a positive plate and a lithium ion battery. The composite lithium supplement agent comprises an inner core, and a middle layer and a shell layer which are formed in situ along a direction far away from the center of the inner core, the material of the inner core comprises lithium-rich lithium nickelate; the material of the middle layer comprises lithium-rich lithium ferrite; and the material of the shell layer comprises lithium-rich lithium nickelate. According to the invention, the lithium-rich lithium ferrite intermediate layer is arranged between the lithium-rich lithium nickelate core and the shell, and the concentration gradient of lithium ions is matched with a specific electric field structure formed by a double-heterogeneous interface, so that the improvement of the electronic conductivity and the ionic conductivity in the lithium-rich lithium ferrite is driven; and meanwhile, the lithium-rich lithium nickelate shell improves the air stability of the composite lithium supplementing agent, so that the composite lithium supplementing agent has high lithium supplementing capacity and also has good rate capability and air stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to positive electrode lithium replenishing agents, and more particularly to a composite lithium replenishing agent and its preparation method, a positive electrode sheet, and a lithium-ion battery. Background Technology

[0002] Solid electrolyte interphase (SEI) membrane is a passivation film formed during the first charge of a lithium-ion battery, resulting from the electrochemical reduction reaction of the electrolyte on the negative electrode surface. The formation of the SEI membrane consumes active lithium, leading to a decrease in the battery's initial efficiency. Furthermore, during subsequent charge and discharge cycles, the SEI continuously breaks down and regenerates, further consuming active lithium and impacting the cycle life of the lithium-ion battery.

[0003] To compensate for the loss of active lithium during the initial charging process and ensure the full utilization of the cathode material's capacity, lithium replenishment agents are typically used. These agents usually possess high irreversible capacity, allowing lithium to irreversibly escape during the initial charging process, thus replenishing the active lithium consumed in the formation of the SEI film. Existing cathode lithium replenishment agents that have been extensively studied include lithium-rich nickel oxide (Li₂NiO₂) and lithium-rich lithium iron oxide (Li₅FeO₄).

[0004] Lithium-rich nickel oxide has advantages such as good air stability, good electronic and ionic conductivity, and good rate performance. It can be fully delithiated without extremely small current and high electrode, but the irreversible capacity it can provide is only about 300 mAh / g. While lithium-rich iron oxide can provide an irreversible capacity of nearly 700 mAh / g, significantly reducing the amount of lithium replenishing agent, it has problems such as poor air stability, low conductivity, and poor rate performance. It requires extremely small current and high voltage to be fully delithiated, and the storage environment and lithium replenishment conditions are more stringent than those of lithium-rich nickel oxide.

[0005] CN117727937A discloses a composite lithium-rich nickel oxide material, its preparation method, and its applications. It includes a lithium-rich nickel oxide material doped with metal M and a polythiophene derivative coated on its surface; the molecular formula of the composite lithium-rich nickel oxide material is Li. x Ni y M zO2@PTi, 1.95≤x≤2.05, 0.9≤y≤1, 0≤z≤0.1, where M is one or more of Mg, Ti, V, Mn, Fe, Co, Cu, Zn, Zr, Nb, Mo, W, Al, Sn, La, and Ce; and PTi represents a polythiophene derivative. NiO is obtained through a precipitation reaction of a nickel source, a precipitant, and a metal dopant. This NiO is then mixed with a lithium source and sintered to obtain a lithium-rich lithium nickelate material. Further coating with a polythiophene derivative solution via solvent precipitation results in a composite lithium-rich lithium nickelate material, which improves the first-cycle charge specific capacity of the lithium-rich lithium nickelate material.

[0006] CN114050258A discloses a positive electrode lithium replenishing agent, a positive electrode sheet, and a method for preparing the positive electrode lithium replenishing agent, wherein the molecular formula of the positive electrode lithium replenishing agent is Li5Fe. a M b O4, where 0.1≤a≤0.9, 0.1≤b≤0.9, a+b=1, and element M is one or more of Ni, Co, Mn, and Cu; the center of the positive electrode lithium supplement is Fe element, and there is a concentration gradient distribution of element M from the center to the material surface. This invention improves Li5Fe by fusing transition metal elements onto the surface of a large-particle-size Fe source. During sintering, the dopant elements migrate and diffuse towards the particle core to form a concentration gradient distribution. Due to the enrichment of dopant elements on the surface, the Li5Fe content is increased. a M b The stability of the O4 surface, its low surface alkalinity, and its high lithium replenishment capacity can effectively improve the energy density of lithium-ion batteries.

[0007] CN118026272A discloses a method for preparing lithium ferrite cathode lithium supplement, including the following steps: preparation of composite lithium salt; mixing of composite lithium salt and iron source; mixing the mixture of composite lithium salt and iron source with carbon source; sintering and crushing. Carbon coating of lithium ferrite can prevent lithium ferrite from contacting water and carbon dioxide, thereby improving the stability of carbon-coated lithium ferrite material. Using lithium ferrite material to prepare lithium batteries can improve the specific capacity and efficiency of the first charge and discharge of lithium batteries. The preparation process is simple, easy to realize industrial production, and has economic and scalability.

[0008] Therefore, it is of great significance to provide a lithium supplement with high irreversible capacity, good lithium replenishment effect, good air stability, and excellent rate performance. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a composite lithium replenishing agent, its preparation method, a positive electrode sheet, and a lithium-ion battery. The composite lithium replenishing agent provided by the present invention has a three-layer structure resembling an eggshell, with a lithium-rich lithium iron phosphate intermediate layer positioned between a lithium-rich lithium nickel phosphate core and an outer shell. Utilizing the lithium-ion concentration gradient combined with a specific electric field structure formed by the dual heterogeneous interface, the electronic and ionic conductivity of the lithium-rich lithium iron phosphate is increased. Simultaneously, the lithium-rich lithium nickel phosphate shell improves the air stability of the composite lithium replenishing agent, resulting in a composite lithium replenishing agent with high lithium replenishment capacity, good rate performance, and excellent air stability.

[0010] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a composite lithium supplement, the composite lithium supplement comprising a core, and an intermediate layer and an outer shell layer formed in situ in a direction away from the center of the core; the core is made of lithium-rich nickel oxide; the intermediate layer is made of lithium-rich lithium ferrite; and the outer shell layer is made of lithium-rich nickel oxide.

[0011] This invention provides a composite lithium replenisher with a three-layer structure resembling an eggshell. The middle layer of the composite lithium replenisher is set as lithium-rich lithium iron phosphate to improve the lithium replenishment capacity. The core and outer shell are set as lithium-rich lithium nickel phosphate. Since lithium-rich lithium nickel phosphate has good ionic and electronic conductivity, during the first charge, the outer shell of lithium-rich lithium nickel phosphate delithirate first, forming a lithium ion concentration gradient with the core and middle layer, driving the diffusion of lithium ions from the core to the outer shell. The electronic and ionic conductivity of the lithium-rich lithium iron phosphate middle layer is improved, thereby enhancing the rate performance of the composite lithium replenisher. The migration of lithium ions in the composite lithium replenisher is smoother, promoting the delithiation of lithium during the first charge and improving the lithium replenishment capacity of the composite lithium replenisher.

[0012] Meanwhile, the lithium-rich nickel oxide core and the lithium-rich iron oxide intermediate layer can form a first heterogeneous interface, and the lithium-rich iron oxide intermediate layer and the lithium-rich nickel oxide shell can form a second heterogeneous interface. The two heterogeneous interfaces reconstruct the electric field of the material, further improving the overall ionic conductivity and electronic conductivity of the material, and further improving the rate performance and capacity of the composite lithium supplement.

[0013] In addition, the outermost lithium-rich nickel oxide layer can provide a protective layer for the composite lithium supplement, optimize the interfacial energy, and thus improve the air stability of the material.

[0014] In summary, the composite lithium replenishing agent provided by this invention has high lithium replenishing capacity, good rate performance, and air stability.

[0015] Preferably, in the composite lithium supplement, the molar ratio of lithium-rich nickel oxide in the core, lithium-rich ferrite in the middle layer, and lithium-rich nickel oxide in the outer shell is (1~2):(7~8):(1~2).

[0016] Preferably, the D50 particle size of the composite lithium supplement is 5μm~10μm.

[0017] In a second aspect, the present invention provides a method for preparing the composite lithium supplement as described in the first aspect, the method comprising: (1) Mix nickel salt solution and precipitant solution, and precipitate to obtain nickel-based precursor core suspension; (2) Mix the nickel-based precursor core suspension, iron salt solution and precipitant solution, and perform a precipitation reaction to obtain an iron-nickel composite precursor core suspension. (3) Mix the core suspension of the iron-nickel composite precursor, the nickel salt solution and the precipitant solution, and perform a precipitation reaction to obtain the composite lithium supplement precursor; (4) The composite lithium supplement precursor and the lithium source are mixed and sintered to obtain the composite lithium supplement.

[0018] This invention prepares a composite lithium supplement precursor by precipitation, sequentially forming an iron base layer and a nickel base layer on the surface of a nickel-based core. The prepared composite lithium supplement precursor is then sintered with a lithium source in one step to obtain the composite lithium supplement. This effectively eliminates the interfacial influence between the lithium-rich nickel oxide core and the lithium-rich ferrite layer, as well as between the lithium-rich ferrite layer and the lithium-rich nickel oxide layer, allowing the performance of the composite lithium supplement to be fully utilized.

[0019] Preferably, the temperature of the precipitation reaction in steps (1) to (3) is 1℃~100℃.

[0020] Preferably, the pH of the precipitation reaction in steps (1) to (3) is 9 to 12.

[0021] Preferably, the precipitant in the precipitant solution in steps (1) to (3) includes any one or a combination of at least two of ammonia, sodium hydroxide, potassium hydroxide or lithium hydroxide.

[0022] Preferably, the concentration of the precipitant solution in steps (1) and (2) is 0.1 mol / L to 1 mol / L.

[0023] Preferably, the nickel salt in the nickel salt solution in steps (1) and (3) includes any one or a combination of at least two of nickel oxalate, nickel sulfate, nickel chloride, nickel nitrate, or nickel dicerocene.

[0024] Preferably, the iron salt in the iron salt solution in step (2) includes any one or a combination of at least two of ferric oxalate, ferric sulfate, ferric chloride, or ferric nitrate.

[0025] Preferably, the concentrations of the nickel salt solution in step (1) and step (3) and the iron salt solution in step (2) are each independently 0.1 mol / L to 3 mol / L.

[0026] Preferably, in step (4), the molar amount of Ni in the composite lithium replenisher is denoted as a, the molar amount of Fe is denoted as b, and the molar amount of lithium in the lithium source is denoted as c. a, b and c satisfy: c / (2a+5b)=1~1.3.

[0027] Preferably, the sintering temperature is 700℃~900℃.

[0028] Preferably, the sintering time is 20h to 30h.

[0029] Preferably, the sintering atmosphere includes nitrogen and / or an inert gas.

[0030] Thirdly, the present invention provides a positive electrode sheet comprising the composite lithium supplement agent as described in the first aspect.

[0031] Fourthly, the present invention provides a lithium-ion battery comprising a composite lithium replenishing agent as described in the first aspect, or a positive electrode as described in the third aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) The composite lithium supplement provided by the present invention has a three-layer structure of eggshell and yolk shell. The lithium iron phosphate intermediate layer is set between the lithium nickel phosphate core and the shell. The concentration gradient of lithium ions combined with the specific electric field structure formed by the double heterostructure drives the improvement of electronic conductivity and ionic conductivity in lithium iron phosphate. At the same time, the lithium nickel phosphate shell improves the air stability of the composite lithium supplement. This makes the composite lithium supplement have high lithium supplement capacity, good rate performance and air stability.

[0033] (2) The composite lithium supplement agent with a three-layer yolk shell structure provided by the present invention not only possesses the high irreversible capacity of lithium-rich lithium iron ferrite, improving lithium supplementation efficiency and reducing costs, but also overcomes the inherent problems of poor rate performance and poor air stability of lithium-rich lithium iron ferrite. Furthermore, compared with the prior art technology that uses carbon sources to modify the conductivity of lithium-rich lithium iron ferrite, the composite lithium supplement agent provided by the present invention can effectively prevent the carbon coating layer formed by the carbon source from absorbing the Fe in lithium-rich lithium iron ferrite. 3+ Reduced to Fe 2+ This improves the performance of the composite lithium supplement.

[0034] (3) The present invention prepares a composite lithium supplement precursor by precipitation method, and forms an iron base layer and a nickel base layer in situ on the surface of a nickel-based core. Then, the prepared composite lithium supplement precursor is sintered with a lithium source in one step to obtain a composite lithium supplement. This effectively eliminates the interface influence between the core and the intermediate layer, as well as between the intermediate layer and the outer shell layer, so that the performance of the composite lithium supplement can be fully utilized. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the composite lithium supplement provided in Embodiment 1 of the present invention.

[0036] Figure 2 This is a SEM image of the composite lithium supplement provided in Example 1 of the present invention.

[0037] Figure 3 This is the XRD pattern of the composite lithium supplement provided in Example 1 of the present invention.

[0038] Figure 4 This is a charge-discharge curve diagram of Embodiment 1 of the present invention.

[0039] Figure 5 This is a SEM image of the composite lithium supplement provided in Example 9 of the present invention.

[0040] Figure 6 This is the XRD pattern of the composite lithium supplement provided in Example 9 of the present invention.

[0041] Figure 7 This is a SEM image of the composite lithium supplement provided in Comparative Example 1 of this invention.

[0042] Figure 8 This is the XRD pattern of the composite lithium supplement provided in Comparative Example 1 of the present invention.

[0043] Among them, 1-kernel; 2-intermediate layer; 3-outer shell layer. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0045] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0046] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0048] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0049] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0050] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0051] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0052] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0053] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0054] In one specific embodiment, the present invention provides a composite lithium supplement agent, the composite lithium supplement agent comprising a core, and an intermediate layer and an outer shell layer formed in situ in a direction away from the center of the core; the core is made of lithium-rich nickel oxide; the intermediate layer is made of lithium-rich lithium ferrite; and the outer shell layer is made of lithium-rich nickel oxide.

[0055] This invention provides a composite lithium replenisher with a three-layer structure resembling an eggshell. The middle layer of the composite lithium replenisher is set as lithium-rich lithium iron phosphate to improve the lithium replenishment capacity. The core and outer shell are set as lithium-rich lithium nickel phosphate. Since lithium-rich lithium nickel phosphate has good ionic and electronic conductivity, during the first charge, the outer shell of lithium-rich lithium nickel phosphate delithirate first, forming a lithium ion concentration gradient with the core and middle layer, driving the diffusion of lithium ions from the core to the outer shell. The electronic and ionic conductivity of the lithium-rich lithium iron phosphate middle layer is improved, thereby enhancing the rate performance of the composite lithium replenisher. The migration of lithium ions in the composite lithium replenisher is smoother, promoting the delithiation of lithium during the first charge and improving the lithium replenishment capacity of the composite lithium replenisher.

[0056] Meanwhile, the lithium-rich nickel oxide core and the lithium-rich iron oxide intermediate layer can form a first heterogeneous interface, and the lithium-rich iron oxide intermediate layer and the lithium-rich nickel oxide shell can form a second heterogeneous interface. The two heterogeneous interfaces reconstruct the electric field of the material, further improving the overall ionic conductivity and electronic conductivity of the material, and further improving the rate performance and capacity of the composite lithium supplement.

[0057] In addition, the outermost lithium-rich nickel oxide layer can provide a protective layer for the composite lithium supplement, optimize the interfacial energy, and thus improve the air stability of the material.

[0058] In summary, the composite lithium replenishing agent provided by this invention has high lithium replenishing capacity, good rate performance, and air stability.

[0059] Compared to existing technologies that use carbon sources to modify the conductivity of lithium-rich lithium iron ferrite, the composite lithium supplement agent provided by this invention can effectively prevent the carbon coating layer formed by the carbon source from affecting the Fe in lithium-rich lithium iron ferrite. 3+ Reduced to Fe 2+ This improves the performance of the composite lithium supplement.

[0060] In this invention, the molar ratio of lithium-rich nickel oxide in the core, lithium-rich lithium ferrite in the intermediate layer, and lithium-rich nickel oxide in the outer shell affects the overall performance of the composite lithium supplement. If the molar ratio of lithium-rich nickel oxide in the core is too high and the molar ratio of lithium-rich lithium ferrite in the intermediate layer is too low, it is not conducive to improving the specific capacity. Therefore, the total molar ratio of lithium-rich nickel oxide in the core and shell should not exceed 30% of the composite lithium supplement. Conversely, if the molar ratio of lithium-rich nickel oxide in the core is too low and the molar ratio of lithium-rich lithium ferrite in the intermediate layer is too high, the lithium ion concentration gradient formed between the core and shell will be insufficient to drive the diffusion of lithium ions in the lithium-rich lithium ferrite intermediate layer. This will prevent the effective improvement of the electronic conductivity and ionic conductivity of the composite lithium supplement, and thus prevent the effective improvement of the rate performance of the composite lithium supplement.

[0061] In some embodiments, the molar ratio of lithium-rich nickel oxide in the core, lithium-rich ferrite in the middle layer, and lithium-rich nickel oxide in the outer shell of the composite lithium supplement is (1~2):(7~8):(1~2), for example, it can be 1:7.5:1.5, 1:7:2, 1.5:7:1.5, 2:7:1, 1.5:7.5:1 or 1:8:1.

[0062] In some embodiments, the D50 particle size of the composite lithium supplement is 5μm to 10μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0063] In another specific embodiment, the present invention provides a method for preparing the composite lithium supplement as described in the foregoing specific embodiment, the preparation method comprising: (1) Mix nickel salt solution and precipitant solution, and precipitate to obtain nickel-based precursor core suspension; (2) Mix the nickel-based precursor core suspension, iron salt solution and precipitant solution, and perform a precipitation reaction to obtain an iron-nickel composite precursor core suspension. (3) Mix the core suspension of the iron-nickel composite precursor, the nickel salt solution and the precipitant solution, and perform a precipitation reaction to obtain the composite lithium supplement precursor; (4) The composite lithium supplement precursor and the lithium source are mixed and sintered to obtain the composite lithium supplement.

[0064] This invention prepares a composite lithium supplement precursor by precipitation, sequentially forming an iron base layer and a nickel base layer on the surface of a nickel-based core. The prepared composite lithium supplement precursor is then sintered with a lithium source in one step to obtain the composite lithium supplement. This effectively eliminates the interfacial influence between the lithium-rich nickel oxide core and the lithium-rich ferrite layer, as well as between the lithium-rich ferrite layer and the lithium-rich nickel oxide layer, allowing the performance of the composite lithium supplement to be fully utilized.

[0065] In some embodiments, the temperature of the precipitation reaction in steps (1) to (3) is 1°C to 100°C, for example, it can be 1°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0066] In some embodiments, the pH of the precipitation reaction in steps (1) to (3) is 9 to 12, for example, it can be 9, 9.5, 10, 10.5, 11, 11.5 or 12.

[0067] In some embodiments, the precipitant in the precipitant solution in steps (1) to (3) includes any one or a combination of at least two of ammonia, sodium hydroxide, potassium hydroxide, or lithium hydroxide.

[0068] In some embodiments, the concentration of the precipitant solution in steps (1) and (2) is 0.1 mol / L to 1 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L.

[0069] In some embodiments, the nickel salt in the nickel salt solution described in steps (1) and (3) includes any one or a combination of at least two of nickel oxalate, nickel sulfate, nickel chloride, nickel nitrate, or nickel dicerocene.

[0070] In some embodiments, the iron salt in the iron salt solution in step (2) includes any one or a combination of at least two of ferric oxalate, ferric sulfate, ferric chloride, or ferric nitrate.

[0071] In some embodiments, the concentrations of the nickel salt solution in step (1) and step (3) and the iron salt solution in step (2) are each independently 0.1 mol / L to 3 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0072] In some embodiments, in step (4), the molar amount of Ni in the composite lithium replenisher is denoted as a, the molar amount of Fe is denoted as b, and the molar amount of lithium in the lithium source is denoted as c. a, b, and c satisfy: c / (2a+5b)=1~1.3, for example, it can be 1, 1.05, 1.1, 1.15, 1.2, 1.25, or 1.3.

[0073] In this invention, the sintering temperature affects the material's charging capacity, as well as its physicochemical properties such as particle size, residual alkali, and phase purity.

[0074] In some embodiments, the sintering temperature is 700℃~900℃, for example, 700℃, 750℃, 800℃, 850℃ or 900℃. In some embodiments, the sintering time is 20h~30h, for example, 20h, 22h, 25h, 28h or 30h.

[0075] In some embodiments, the sintering atmosphere includes nitrogen and / or an inert gas, including argon.

[0076] In yet another embodiment, the present invention provides a positive electrode sheet comprising a composite lithium supplement agent as described in the preceding embodiment.

[0077] In another specific embodiment, the present invention provides a lithium-ion battery comprising a composite lithium replenishing agent as described in one of the preceding specific embodiments, or comprising a positive electrode sheet as described in yet another specific embodiment.

[0078] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0079] Example 1 This embodiment provides a composite lithium supplement, such as Figure 1 As shown, the composite lithium supplement includes a core 1; along the direction away from the center of the core 1, an in-situ formed intermediate layer 2 and an outer shell layer 3 are sequentially disposed on the surface of the core 1; the core 1 is made of lithium-rich nickel oxide; the intermediate layer 2 is made of lithium-rich lithium ferrite; the outer shell layer 3 is made of lithium-rich nickel oxide; the molar ratio of lithium-rich nickel oxide in the core 1, lithium-rich lithium ferrite in the intermediate layer 2 and lithium-rich nickel oxide in the outer shell layer 3 is 1.5:7.5:1; the D50 particle size of the composite lithium supplement is 7 μm.

[0080] The preparation method of the composite lithium supplement includes: (1) Add 0.3 mol / L sodium hydroxide solution to 0.5 mol / L nickel nitrate solution, adjust the pH to 11, and precipitate at 40℃ to obtain nickel-based precursor core suspension; (2) The nickel-based precursor core suspension, 0.6 mol / L ferric nitrate solution and 0.5 mol / L ammonia solution are mixed, the pH is adjusted to 11.2, and a precipitation reaction is carried out at 40°C to obtain the iron-nickel composite precursor core suspension, wherein the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 1.5:7.5; (3) Mix the core suspension of the iron-nickel composite precursor, a nickel nitrate solution with a concentration of 1 mol / L and an ammonia solution with a concentration of 0.5 mol / L, adjust the pH to 10.9, and carry out a precipitation reaction to obtain the composite lithium supplement precursor. The molar ratio of Ni and Fe in the core suspension of the iron-nickel composite precursor to Ni in the nickel nitrate solution is 1.5:7.5:1. (4) Let a be the molar amount of Ni in the composite lithium supplement, b be the molar amount of Fe, and c be the molar amount of lithium in the lithium source. a, b, and c satisfy: c / (2a+5b)=1.15. Mix the composite lithium supplement precursor with the lithium source and sinter at 800℃ for 25h to obtain the composite lithium supplement. Its SEM image is shown below. Figure 2 As shown, the XRD pattern is as follows Figure 3 As shown in the figure, the composite lithium supplement prepared in this embodiment includes lithium-rich nickel oxide and lithium-rich iron oxide, and has high purity, with almost no NiO impurity peaks observed.

[0081] Example 2 This embodiment provides a composite lithium replenishing agent, which includes a core; along the direction away from the center of the core, an in-situ formed intermediate layer and an outer shell layer are sequentially disposed on the surface of the core; the core is made of lithium-rich nickel oxide; the intermediate layer is made of lithium-rich lithium ferrite; the outer shell layer is made of lithium-rich nickel oxide; the molar ratio of lithium-rich nickel oxide in the core, lithium-rich lithium ferrite in the intermediate layer and lithium-rich nickel oxide in the outer shell layer is 1:8:1; the D50 particle size of the composite lithium replenishing agent is 7.5 μm.

[0082] The preparation method of the composite lithium supplement includes: (1) Add 0.3 mol / L sodium hydroxide solution to 0.5 mol / L nickel nitrate solution, adjust the pH to 9, and precipitate at 20℃ to obtain nickel-based precursor core suspension; (2) Mix the nickel-based precursor core suspension, 0.1 mol / L ferric nitrate solution and 0.4 mol / L ammonia solution, adjust the pH to 9, and carry out a precipitation reaction at 20°C to obtain the iron-nickel composite precursor core suspension, wherein the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 1:8. (3) Mix the core suspension of the iron-nickel composite precursor, a nickel nitrate solution with a concentration of 1 mol / L and an ammonia solution with a concentration of 0.4 mol / L, adjust the pH to 9, and carry out a precipitation reaction to obtain the composite lithium supplement precursor. The molar ratio of Ni and Fe in the core suspension of the iron-nickel composite precursor to Ni in the nickel nitrate solution is 1:8:1. (4) Let a be the molar amount of Ni in the composite lithium supplement, b be the molar amount of Fe, and c be the molar amount of lithium in the lithium source. a, b and c satisfy: c / (2a+5b)=1. Mix the composite lithium supplement precursor and the lithium source, and sinter at 700℃ for 30h to obtain the composite lithium supplement.

[0083] Example 3 This embodiment provides a composite lithium supplement agent, which includes a core; along the direction away from the center of the core, an in-situ formed intermediate layer and an outer shell layer are sequentially disposed on the surface of the core; the core is made of lithium-rich nickel oxide; the intermediate layer is made of lithium-rich lithium ferrite; the outer shell layer is made of lithium-rich nickel oxide; the molar ratio of lithium-rich nickel oxide in the core, lithium-rich lithium ferrite in the intermediate layer and lithium-rich nickel oxide in the outer shell layer is 2:7:1; the D50 particle size of the composite lithium supplement agent is 6.8 μm.

[0084] The preparation method of the composite lithium supplement includes: (1) Add 1 mol / L sodium hydroxide solution to a 3 mol / L nickel nitrate solution, adjust the pH to 12, and precipitate at 100℃ to obtain a nickel-based precursor core suspension. (2) Mix the nickel-based precursor core suspension, ferric nitrate solution with a concentration of 2.5 mol / L and ammonia solution with a concentration of 0.8 mol / L, adjust the pH to 12, and carry out a precipitation reaction at 90°C to obtain the iron-nickel composite precursor core suspension, wherein the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 2:7. (3) Mix the core suspension of the iron-nickel composite precursor, a nickel nitrate solution with a concentration of 2 mol / L and an ammonia solution with a concentration of 0.8 mol / L, adjust the pH to 11.5, and carry out a precipitation reaction to obtain the composite lithium supplement precursor. The molar ratio of Ni and Fe in the core suspension of the iron-nickel composite precursor to Ni in the nickel nitrate solution is 2:7:1. (4) Let a be the molar amount of Ni in the composite lithium supplement, b be the molar amount of Fe, and c be the molar amount of lithium in the lithium source. a, b and c satisfy: c / (2a+5b)=1.3. Mix the composite lithium supplement precursor and the lithium source, and sinter at 900℃ for 20h to obtain the composite lithium supplement.

[0085] Example 4 This embodiment provides a composite lithium supplement agent. Except that the molar ratio of lithium-rich nickel oxide in the core, lithium-rich ferrite in the middle layer, and lithium-rich nickel oxide in the outer shell is 1:7:2, all other aspects are the same as in Example 1.

[0086] The preparation method of the composite lithium supplement is the same as in Example 1, except that in step (2) the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 1:7, and in step (3) the molar ratio of Ni and Fe in the iron-nickel composite precursor core suspension to Ni in the nickel nitrate solution is 1:7:2.

[0087] Example 5 This embodiment provides a composite lithium supplement agent. Except that the molar ratio of lithium-rich nickel oxide in the core, lithium-rich ferrite in the middle layer, and lithium-rich nickel oxide in the outer shell is 0.5:7.5:2, all other aspects are the same as in Example 1.

[0088] The preparation method of the composite lithium supplement is the same as in Example 1, except that in step (2) the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 0.5:7, and in step (3) the molar ratio of Ni and Fe in the iron-nickel composite precursor core suspension to Ni in the nickel nitrate solution is 0.5:7.5:2.

[0089] Example 6 This embodiment provides a composite lithium supplement agent. Except that the molar ratio of lithium-rich nickel oxide in the core, lithium-rich ferrite in the middle layer, and lithium-rich nickel oxide in the outer shell is 2:7.5:0.5, all other aspects are the same as in Example 1.

[0090] The preparation method of the composite lithium supplement is the same as in Example 1, except that in step (2) the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 2:7.5, and in step (3) the molar ratio of Ni and Fe in the iron-nickel composite precursor core suspension to Ni in the nickel nitrate solution is 2:7.5:0.5.

[0091] Example 7 This embodiment provides a composite lithium supplement agent. Except that the molar ratio of lithium-rich nickel oxide in the core, lithium-rich ferrite in the middle layer, and lithium-rich nickel oxide in the outer shell is 2:6.5:1.5, all other aspects are the same as in Example 1.

[0092] The preparation method of the composite lithium supplement is the same as in Example 1, except that in step (2) the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 2:6.5, and in step (3) the molar ratio of Ni and Fe in the iron-nickel composite precursor core suspension to Ni in the nickel nitrate solution is 2:6.5:1.5.

[0093] Example 8 This embodiment provides a composite lithium supplement, which is the same as that in Example 1 except that the sintering temperature is 600°C during the preparation process.

[0094] Example 9 This embodiment provides a composite lithium supplement. Except for the sintering temperature of 1000℃ during preparation, everything else is the same as in Example 1. Its SEM image is shown below. Figure 5 As shown, the XRD pattern is as follows Figure 6 As shown in the figure, a strong NiO impurity peak can be clearly observed, indicating a significant decrease in the purity of the composite lithium supplement.

[0095] Comparative Example 1 This comparative example provides a composite lithium supplement, which is a physical mixture of lithium-rich lithium iron ferrite with a D50 particle size of 7.5 μm and lithium-rich lithium nickel ferrite in a molar ratio of 7.5:2.5. It does not possess the yolk-shell structure of Example 1, and its SEM image is shown below. Figure 7 As shown, the XRD pattern is as follows Figure 8 As shown.

[0096] Comparative Example 2 This comparative example provides a composite lithium supplement, which is the same as in Example 1 except that it only includes a lithium iron phosphate core and a lithium nickel phosphate shell with a molar ratio of 7.5:2.5, and does not include the lithium nickel phosphate core.

[0097] The preparation method of the composite lithium supplement includes: (1) Add 0.4 mol / L ammonia solution to 0.1 mol / L ferric nitrate solution, adjust the pH to 9, and carry out precipitation reaction at 40℃ to obtain iron-based precursor core suspension; (2) The iron-based precursor core suspension, a nickel nitrate solution with a concentration of 1 mol / L and an ammonia solution with a concentration of 0.4 mol / L were mixed, the pH was adjusted to 9, and a precipitation reaction was carried out at 40°C to obtain the composite lithium supplement precursor. The molar ratio of Fe in the iron-based precursor core suspension to Ni in the nickel nitrate solution was 7.5:2.5. (3) Let a be the molar amount of Ni in the composite lithium supplement, b be the molar amount of Fe, and c be the molar amount of lithium in the lithium source. a, b and c satisfy: c / (2a+5b)=1.15. Mix the composite lithium supplement precursor and the lithium source, and sinter at 800℃ for 25h to obtain the composite lithium supplement.

[0098] Comparative Example 3 This comparative example provides a composite lithium supplement, which is the same as in Example 1 except that it only includes a lithium-rich nickel oxide core and a lithium-rich iron oxide shell with a molar ratio of 2.5:7.5, and does not include the lithium-rich nickel oxide shell.

[0099] The preparation method of the composite lithium supplement includes: (1) Add 0.3 mol / L sodium hydroxide solution to 0.5 mol / L nickel nitrate solution, adjust the pH to 11, and precipitate at 40℃ to obtain nickel-based precursor core suspension; (2) The nickel-based precursor core suspension, 0.6 mol / L ferric nitrate solution and 0.5 mol / L ammonia solution are mixed, the pH is adjusted to 11.2, and a precipitation reaction is carried out at 40°C to obtain the iron-nickel composite precursor core suspension, wherein the molar ratio of Ni in the nickel-based precursor core suspension to Fe in the ferric nitrate solution is 7.5:2.5; (3) Let a be the molar amount of Ni in the composite lithium supplement, b be the molar amount of Fe, and c be the molar amount of lithium in the lithium source. a, b and c satisfy: c / (2a+5b)=1.15. Mix the composite lithium supplement precursor and the lithium source, and sinter at 800℃ for 25h to obtain the composite lithium supplement.

[0100] Performance testing: Test 1: The composite lithium supplement provided in all the above examples and comparative examples was dispersed in NMP with PVDF and SP at a mass ratio of 94:3:3 to prepare a positive electrode slurry. The prepared positive electrode slurry was coated onto the surface of carbon-coated aluminum foil to prepare a positive electrode sheet. The prepared positive electrode sheet was matched with lithium metal, and a 1 mol / L lithium hexafluorophosphate EC / DEC (volume ratio 1:1) solution was used as the electrolyte. A polypropylene separator was used to assemble a coin cell lithium-ion battery, and the battery's electrical performance was tested. The initial charge specific capacity was tested at 25℃ and a voltage range of 2.5V to 4.4V at rates of 0.1C, 0.5C, and 1C. The test results are shown in Table 1. The initial charge-discharge curves of the composite lithium replenishing agent provided in Example 1 are shown in Table 1. Figure 4 .

[0101] Test 2: After placing the composite lithium replenishing agent provided in all the above examples and comparative examples in an air environment of 25°C and 30% humidity for 24 hours, coin-type lithium-ion batteries were assembled in the manner of Test 1. The 0.1C charging specific capacity was tested at 25°C and within a voltage range of 2.5V~4.4V. The test results are shown in Table 1.

[0102] Table 1 Based on the test results of Examples 1 to 4 in Table 1, the composite lithium supplement with a yolk-shell three-layer structure provided by the present invention, by setting the lithium-rich lithium iron phosphate intermediate layer between the lithium-rich nickel phosphate core and the outer shell, utilizes the lithium ion concentration gradient and the specific electric field structure formed by the dual heterogeneous interface to drive the improvement of electronic conductivity and ionic conductivity in lithium-rich lithium iron phosphate. At the same time, the lithium-rich nickel phosphate shell improves the air stability of the composite lithium supplement, thus achieving a simultaneous improvement in the specific capacity, rate performance and air stability of the composite lithium supplement.

[0103] Based on the test results of Examples 1, 5, and 6, when the molar ratio of the lithium-rich nickel oxide core decreases to 0.5, a sufficient lithium-ion concentration gradient and electric field structure cannot be formed between it and the lithium-rich nickel oxide shell. Consequently, the electronic and ionic conductivity of the lithium-rich iron oxide interlayer cannot be improved, resulting in a decrease in the rate performance and poor capacity of the composite lithium supplementer. Furthermore, when the molar ratio of the lithium-rich nickel oxide shell decreases to 0.5, while the rate performance and capacity decrease compared to Example 1, the air stability of the composite lithium supplementer also deteriorates significantly.

[0104] Based on the test results of Examples 1 and 7, when the molar ratio of lithium iron phosphate intermediate layer is reduced to 6.5, the 0.1C charging capacity of composite lithium replenisher is reduced by 50 mAh / g compared to Example 1, while the rate performance and air stability are not significantly improved. This indicates that the decrease in the molar ratio of lithium iron phosphate intermediate layer does not necessarily lead to an improvement in the rate performance and air stability of composite lithium replenisher, and there is a synergistic effect among the three.

[0105] Based on the test results of Examples 1, 8, and 9, excessively high or low sintering temperatures affect the charging capacity, particle size, residual alkali, phase purity, and other physicochemical properties of the material, leading to a decrease in its electrochemical performance. In Example 8, the sintering temperature was too low, resulting in a strong NiO impurity phase peak, poor material crystallinity, and a significant decrease in specific capacity, rate performance, and air stability. Compared to Example 1, the material provided in Example 8 showed a 52 mAh / g decrease in 0.1C discharge specific capacity, and a significant decrease in air stability; after being placed in an air environment at 25°C and 30% humidity for 24 hours, the capacity retention rate decreased by 5% compared to Example 1. In Example 9, the sintering temperature was too high, leading to agglomeration and adhesion between particles, and an increase in particle size. Figure 5 As shown, and as Figure 6 The XRD pattern shown indicates that the peak intensity of the NiO impurity phase is relatively strong. The 0.1C specific capacity of the material is 59 mAh / g lower than that of Example 1, and the rate performance is also reduced. Moreover, from the perspective of energy consumption and energy saving, the economic efficiency is significantly reduced.

[0106] According to the test results of Example 1 and Comparative Example 1, if lithium-rich nickel oxide and lithium-rich iron oxide are simply physically mixed without constructing the specific yolk shell structure provided by this invention, it is impossible to form a lithium ion concentration gradient between the lithium-rich nickel oxide core and the lithium-rich nickel oxide shell, and it is impossible to construct a double-layer heterogeneous interface. Consequently, it is impossible to effectively drive the improvement of electronic conductivity and ionic conductivity of the lithium-rich iron oxide intermediate layer, and therefore it is impossible to achieve simultaneous improvement in capacity, rate performance and air stability.

[0107] According to the test results of Example 1, Comparative Examples 2 and 3, it is not possible to achieve simultaneous improvement in capacity, rate performance and air stability if only a portion of the eggshell structure provided by the present invention is present.

[0108] In summary, this invention achieves simultaneous improvement in the specific capacity, rate performance, and air stability of the composite lithium supplement by placing a lithium-rich lithium iron oxide intermediate layer between the lithium-rich lithium nickel oxide core and the outer shell, and utilizing the lithium ion concentration gradient combined with the specific electric field structure formed by the dual heterogeneous interface.

[0109] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite lithium supplement, characterized in that, The composite lithium replenishing agent includes a core, and an intermediate layer and an outer shell layer formed in situ in a direction away from the center of the core; The core material includes lithium nickel oxide rich in lithium; The intermediate layer is made of lithium iron ferrite rich in lithium; The outer shell layer is made of lithium-rich nickel oxide.

2. As described in claim 1, characterized in that, In the composite lithium supplement, the molar ratio of lithium-rich nickel oxide in the core, lithium-rich ferrite in the middle layer, and lithium-rich nickel oxide in the outer shell is (1~2):(7~8):(1~2). And / or, the D50 particle size of the composite lithium supplement is 5μm~10μm.

3. A method for preparing the composite lithium supplement as described in claim 1 or 2, characterized in that, The preparation method includes: (1) Mix nickel salt solution and precipitant solution, and precipitate to obtain nickel-based precursor core suspension; (2) Mix the nickel-based precursor core suspension, iron salt solution and precipitant solution, and perform a precipitation reaction to obtain an iron-nickel composite precursor core suspension. (3) Mix the core suspension of the iron-nickel composite precursor, the nickel salt solution and the precipitant solution, and perform a precipitation reaction to obtain the composite lithium supplement precursor; (4) The composite lithium supplement precursor and the lithium source are mixed and sintered to obtain the composite lithium supplement.

4. The preparation method according to claim 3, characterized in that, The temperature of the precipitation reaction in steps (1) to (3) is 1℃~100℃; And / or, the pH of the precipitation reaction described in steps (1) to (3) is 9 to 12.

5. The preparation method according to claim 3, characterized in that, The precipitant in the precipitant solution described in steps (1) to (3) includes any one or a combination of at least two of ammonia, sodium hydroxide, potassium hydroxide, or lithium hydroxide; And / or, the concentration of the precipitant solution in steps (1) and (2) is 0.1 mol / L to 1 mol / L.

6. The preparation method according to claim 3, characterized in that, The nickel salt in the nickel salt solution mentioned in steps (1) and (3) includes any one or a combination of at least two of nickel oxalate, nickel sulfate, nickel chloride, nickel nitrate, or nickel dicerocene; And / or, the iron salt in the iron salt solution in step (2) includes any one or a combination of at least two of ferric oxalate, ferric sulfate, ferric chloride or ferric nitrate; And / or, the concentrations of the nickel salt solution in step (1) and step (3) and the iron salt solution in step (2) are each independently 0.1 mol / L to 3 mol / L.

7. The preparation method according to claim 3, characterized in that, In step (4), the molar amount of Ni in the composite lithium replenisher is denoted as a, the molar amount of Fe is denoted as b, and the molar amount of lithium in the lithium source is denoted as c. a, b and c satisfy: c / (2a+5b)=1~1.

3.

8. The preparation method according to claim 3, characterized in that, The sintering temperature is 700℃~900℃; And / or, the sintering time is 20h~30h; And / or, the sintering atmosphere includes nitrogen and / or an inert gas.

9. A positive electrode plate, characterized in that, The positive electrode includes the composite lithium supplement agent as described in claim 1 or 2.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the composite lithium replenishing agent as described in claim 1 or 2, or includes the positive electrode sheet as described in claim 9.

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