CN116936803A

CN116936803A - Positive electrode lithium supplementing material and preparation method and application thereof

Info

Publication number: CN116936803A
Application number: CN202310604873.2A
Authority: CN
Inventors: 谭旗清; 万远鑫; 孔令涌; 裴现一男; 戴浩文; 骆文森; 赖日鑫
Original assignee: Foshan Defang Chuangjie New Energy Technology Co ltd; Qujing Defang Chuangjie New Energy Technology Co ltd; Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
Current assignee: Foshan Defang Chuangjie New Energy Technology Co ltd; Qujing Defang Chuangjie New Energy Technology Co ltd; Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
Priority date: 2023-05-25
Filing date: 2023-05-25
Publication date: 2023-10-24

Abstract

The application belongs to the technical field of batteries, and particularly relates to a positive electrode lithium supplementing material, and a preparation method and application thereof. The positive electrode lithium supplementing material comprises lithium metal oxide, wherein metal ions in the lithium metal oxide comprise lithium ions, doped cations and M ions, M is at least one metal element selected from IB to VIIIB, IVA and VA, and the element electronegativity of the doped cations is smaller than that of the M ions. The positive electrode lithium supplementing material can inhibit gas generation and improve the problem of high gas generation of the positive electrode lithium supplementing material.

Description

Positive electrode lithium supplementing material and preparation method and application thereof

Technical Field

The application belongs to the technical field of batteries, and particularly relates to a positive electrode lithium supplementing material, and a preparation method and application thereof.

Background

In the first charge and discharge process of the lithium ion battery, a large amount of solid electrolyte interface films are generated on the surface of the negative electrode of the battery, limited lithium ions and electrolyte in the battery are consumed, irreversible capacity loss is caused, the energy density of the lithium ion secondary battery is reduced, the charge and discharge efficiency of electrode materials is reduced, and the application of the lithium ion battery is limited. In the prior art, the first irreversible capacity loss of the lithium battery can be effectively compensated by adding the lithium supplementing material into the positive electrode material. However, the existing lithium supplementing material is unstable in structure, gas is easy to generate in the first charging process, residual alkali substances (such as carbonate) existing on the surface can react with electrolyte at high temperature to generate gaseous substances such as carbon dioxide and the like, so that the gas generation of a battery is increased or the impedance of the battery is increased, and finally the performance of the battery is reduced.

Disclosure of Invention

The application aims to provide a positive electrode lithium supplementing material, a preparation method and application thereof, and aims to solve the problem of high gas production of the positive electrode lithium supplementing material.

In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows:

in a first aspect, the present application provides a positive electrode lithium-supplementing material, the positive electrode lithium-supplementing material comprising a lithium metal oxide, wherein metal ions in the lithium metal oxide comprise lithium ions, doped cations and M ions, M is at least one metal element selected from groups IB to VIIIB, IVA and VA, and the element electronegativity of the doped cations is less than the element electronegativity of the M ions.

In the embodiment of the application, the anode lithium supplementing material contains doped cations, the doped cations have lower electronegativity than other metals (other metals except lithium), have stronger binding capacity with oxygen and are difficult to dissociate, so that the doped cations can be tightly combined with the oxygen, and the dissociation of the oxygen is inhibited, and the generation of gas is inhibited.

In a second aspect, the present application provides a method for preparing a positive electrode lithium supplementing material, including: mixing a lithium source and a non-lithium metal source in proportion, and sintering in an inert atmosphere; wherein the non-lithium metal source comprises a source of M selected from at least one metal element of groups IB to VIIIB, IVA and VA and a source of a doping cation having an elemental electronegativity that is less than the elemental electronegativity of M.

The positive electrode lithium supplementing material provided by the embodiment of the application comprises lithium metal oxide, and can be obtained only through simple sintering treatment, and the preparation method is simple.

In a third aspect, the present application provides a positive electrode comprising the positive electrode lithium-supplementing material described above or the positive electrode lithium-supplementing material prepared by the method described above.

The positive electrode lithium supplementing material provided by the embodiment of the application can inhibit gas production, so that the positive electrode containing the positive electrode lithium supplementing material has the effect of low gas production, and the safety performance and the electrochemical performance of a lithium battery can be improved.

In a fourth aspect, the present application provides a secondary battery comprising the above-described positive electrode.

The positive electrode contains the positive electrode lithium supplementing material provided by the application and has the effect of low gas production, so that the secondary battery containing the positive electrode has good safety performance and electrochemical performance.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.

In the present application, the term "and/or" describes an association relationship of an association object, which means that three relationships may exist, for example, a and/or B may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.

In the present application, "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c" may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

It should be understood that, in various embodiments of the present application, the sequence number of each process described above does not mean that the execution sequence of some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weights of the relevant components mentioned in the description of the embodiments of the present application may refer not only to the specific contents of the components, but also to the proportional relationship between the weights of the components, so long as the contents of the relevant components in the description of the embodiments of the present application are scaled up or down within the scope of the disclosure of the embodiments of the present application. Specifically, the mass described in the specification of the embodiment of the application can be mass units known in the chemical industry field such as mu g, mg, g, kg.

The terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated for distinguishing between objects such as substances from each other. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.

According to a first aspect of the embodiment of the application, a positive electrode lithium supplementing material is provided, the positive electrode lithium supplementing material comprises lithium metal oxide, metal ions in the lithium metal oxide comprise lithium ions, doped cations and M ions, M is at least one metal element selected from IB to VIIIB, IVA and VA, and the electronegativity of the doped cations is smaller than that of the M ions.

"electronegativity" means the ability of an atom of an element to attract electrons in a compound, the greater the electronegativity of an element, the greater the ability of its atom to attract electrons in a compound; the smaller the electronegativity of an element, the weaker the ability of its atoms to attract electrons in the compound, while giving electrons a greater tendency. The electronegativity of the oxygen element is 3.5, and the electronegativity of the metal element is smaller than that of the oxygen element. That is, the metal element generally has weaker electron-attracting ability than the oxygen element. The metal element with smaller electronegativity has larger tendency to give out electrons, and the oxygen element has strong electron withdrawing capability; then, in the case where it is in the same compound as the oxygen element, the oxygen element exhibits a strong electron withdrawing ability, and the metal element exhibits a strong electron donating ability, so that it has a stronger binding action with the oxygen element. That is, the smaller the electronegativity of the metal element, the stronger the binding action with the oxygen element.

Group IB to VIIIB refer to elements from columns 3 to 12 of the periodic table, including group IIIB, IVB, VB, VIB, VIIB, VIII and IB, IIB, which are primarily transition metal elements. Group IVA and group VA refer to the elements of columns 13 and 14 of the periodic Table of the elements.

In the embodiment of the application, the anode lithium supplementing material contains doped cations, and the doped cations have lower electronegativity than other metals (other metals except lithium), have stronger binding capacity with oxygen and are difficult to dissociate, so that the anode lithium supplementing material can be tightly combined with the oxygen, thereby inhibiting dissociation of the oxygen and further inhibiting gas generation. Therefore, the safety performance and the electrochemical performance of the lithium battery can be improved by carrying out specific design on the positive electrode lithium supplementing material.

In some embodiments, the lithium metal oxide has a core-shell structure comprising an inner core and a coating layer coated on the surface of the inner core; the core comprises a first lithium metal oxide and the cladding comprises a second lithium metal oxide; the metal ions in the second lithium metal oxide include lithium ions, doped cations, and M ions. The inner core and the coating layer both contain lithium metal oxide, so that the effect of lithium supplementing can be realized; meanwhile, the second lithium metal oxide in the coating layer can inhibit dissociation of oxygen in the whole structure of the positive electrode lithium-supplementing material by utilizing doped cations, so that the generation of gas is reduced.

In some embodiments, the number of lithium atoms in the second lithium metal compound is less than or equal to the number of lithium atoms in the first lithium metal compound. In the case where the second lithium metal oxide has the same number of lithium atoms as the first lithium metal oxide, both the second lithium metal oxide and the first lithium metal oxide can effectively realize the effect of lithium supplementation. Under the condition that the second lithium metal oxide has a lithium content lower than that of the first lithium metal oxide, namely the second lithium metal oxide has a lithium content lower than that of the first lithium metal oxide, as the lithium content is related to the residual alkali content (generally, the residual alkalinity is high when the lithium content is high), namely the second lithium metal oxide has a lower residual alkalinity than that of the first lithium metal oxide of the inner core, the surface residual alkalinity of the lithium-supplementing material of the positive electrode can be reduced, the surface interface stability of the inner core is improved, the lithium-supplementing material of the positive electrode is prevented from reacting with electrolyte under the condition of high temperature, and gas substances such as carbon dioxide and the like are generated, so that the safety performance of the battery is further improved.

In some embodiments, the first lithium metal oxide comprises Li _a A _b O _c Wherein a is more than 3 and less than or equal to 8, b is more than 0 and less than or equal to 5, c is more than 0 and less than 13, and A is selected from at least one metal element in IB to VIIIB, IIIA, IVA and VA. Li (Li) _a A _b O _c Has high lithium content and can effectively realize the effect of lithium supplement.

In some embodiments, the second lithium metal oxide comprises Li _2+x M _1-y2 D _y2 O _z The method comprises the steps of carrying out a first treatment on the surface of the Wherein x is more than or equal to-0.5 and less than or equal to 0.2, y2 is more than 0 and less than 1, and z is more than 0 and less than 3; d is a doping cation. Li (Li) _2+x M _1-y2 D _y2 O _z The doped cation D has lower electronegativity, has stronger binding capacity with oxygen and is difficult to dissociate, so that the doped cation D can be tightly combined with oxygen in the coating layer, and thus the dissociation of the oxygen in the inner core and the coating layer is inhibited, and the generation of gas is further inhibited; and Li is _2+x M _1-y D _y O _z The lithium content is low, which is beneficial to reducing the residual alkali content of the whole cathode lithium supplementing material.

In the first lithium metal oxide and the second lithium metal oxide, A is at least one metal element selected from IB to VIIIB, IIIA, IVA and VA, M is at least one metal element selected from IB to VIIIB, IVA and VA, overlapping parts exist between A and M optional metal elements, and A and M can be the same or different.

In some embodiments, 0 < y2 < 0.6; alternatively, 0.01.ltoreq.y2.ltoreq.0.2. Under the proper doping amount of D element, the battery adopting the anode lithium supplementing material has low gas yield, high first-circle charge capacity and high capacity retention rate after long-term circulation.

In some embodiments, the first lithium metal oxide comprises Li _2+x M _y1 O _z The second lithium metal oxide includes Li _2+x M _1-y2 D _y2 O _z Wherein x is more than or equal to 0.5 and less than or equal to 0.8, y1 is more than 0 and less than or equal to 1, y2 is more than 0 and less than 1, and z is more than 0 and less than 3; d is a doping cation. In this case, the second lithium metal oxide has the same number of lithium atoms as the first lithium metal oxide, and the second lithium metal oxide is the same as the first lithiumThe metal oxide can effectively realize the effect of lithium supplementing.

In some embodiments, the difference in the electronegativity of the cation-doped element and the electronegativity of the oxygen element is greater than 0.5 in absolute value, and more preferably, the difference in electronegativity of the two is greater than or equal to 2.0 in absolute value. The larger the difference between the electronegativity of the element doped with cations and the electronegativity of the oxygen element, i.e. the smaller the electronegativity of the element doped with cations, the larger the binding capacity of the element doped with cations with oxygen element, which is more beneficial to inhibiting dissociation of oxygen in the inner core and the coating layer, thereby inhibiting gas generation.

In some embodiments, the cation-doped elemental electronegativity is less than or equal to 1.5; in other embodiments, the cation-doped element has an electronegativity of 0.5 to 1.5. The smaller the electronegativity of the element doped with cations is, the larger the binding capacity of the element doped with cations with oxygen is, which is more beneficial to inhibiting dissociation of oxygen in the inner core and the coating layer, thereby inhibiting gas generation.

In some embodiments, the doping cations are selected from one or more of Be, mg, ca, sr, ba, K, na, cs, rb, al, sc, Y. The metal elements have lower electronegativity, and the electronegativity of each element is as follows: be 1.5, mg 1.2, ca 1.0, sr 1.0, ba 0.9, K0.8, na 0.9, cs 0.7, rb 0.98, al 1.5, sc 1.3, Y1.2.

In some embodiments, the doping cations have an atomic number doping content of 0.1% to 20% in the coating; in other embodiments, the doping cations are present in the coating in a mass percent of 0.1% to 10%, or 1% to 10%. The atomic number doping content of the doping cation in the coating layer means the total atomic number of all metal elements except Li in the coating layer. For example, assume that the cladding layer contains Li ₂ Mn _0.99 Ca _0.01 O ₂ Wherein the doping content of the doping element Ca in the coating layer is [ 0.01/(0.99+0.01) ×100%]=1%. Under the condition of proper content of doped cations, the coating layer can effectively inhibit the gas production of the anode lithium supplementing material, and meanwhile, the crystallinity of the coating layer is not reduced.

In some embodiments, the mass of the cladding is 0.1% to 50% of the core; in some embodiments, the mass of the cladding is 0.5% to 10%, or 1% to 5% of the core. In the anode lithium supplementing material provided by the embodiment of the application, the coating layer has proper mass ratio, has stronger coating acting force on the core, and does not influence the capacity exertion of the core.

In some embodiments, the coating has an average thickness of 1nm to 5 μm; in other embodiments, the coating has an average thickness of 3nm to 4 μm. Under proper thickness, the coating layer has a strong coating effect on the inner core, and the transmission rate of lithium ions of the inner core material is not influenced.

In some embodiments, the purity of the positive electrode lithium-compensating material is greater than or equal to 70%; in some embodiments, the purity of the positive electrode lithium-compensating material may reach 90% and above. Under high purity, the positive electrode lithium supplementing material can effectively exert the lithium supplementing effect, and meanwhile, the second lithium metal oxide in the material can be utilized to realize the effect of inhibiting gas production, so that the safety performance and the electrochemical performance of the battery are improved.

In some embodiments, the median particle diameter D50 of the first lithium metal oxide satisfies: d50 is more than or equal to 0.5 μm and less than or equal to 35 μm; in other embodiments, 1 μm.ltoreq.D50.ltoreq.10μm. In the positive electrode lithium supplementing material provided by the embodiment of the application, the first lithium metal oxide has a particle size with proper size, is not easy to agglomerate, has good dispersibility and is easy to coat.

In some embodiments, the median particle diameter D50 of the second lithium metal oxide satisfies: d50 is more than or equal to 50nm and less than or equal to 10 mu m; in other embodiments, 100 nm.ltoreq.D50.ltoreq.5 μm. The second lithium metal oxide has a particle size of a proper size, is not easy to agglomerate, can well form a coating layer, and is uniformly coated; meanwhile, the second lithium metal oxide with the particle size has little influence on the transmission rate of lithium ions in the core.

In some embodiments, the median particle diameter D50 of the positive electrode lithium-compensating material satisfies: d50 is less than or equal to 1 mu m and less than or equal to 50 mu m; in other embodiments, 5 μm.ltoreq.D50.ltoreq.30 μm. Under the proper particle size, the positive electrode lithium supplementing material particles can be well dispersed in the positive electrode slurry, so that the positive electrode sheet containing the positive electrode lithium supplementing material has good electronic conduction and ion conduction performance, and the electrical performance of the lithium ion secondary battery is improved.

In some embodiments, the positive electrode lithium supplementing material has a BET specific surface area of 0.5-100 m ² /g; in other embodiments, the BET specific surface area of the positive electrode lithium-supplementing material is 10 to 50m ² And/g. Under the BET specific surface area with proper size, the positive electrode lithium supplementing material has higher pores, is favorable for improving the transmission rate of lithium ions, and does not reduce the structural stability due to overhigh pores.

In some embodiments, the coating layer further comprises an inert substance comprising one or more of a carbon material, an oxide, a carbide, and a phosphate; the inert material is mixed with the second lithium metal oxide and/or the inert material coats the surface of the second lithium metal oxide.

Here, the inert substances refer to materials having very stable chemical properties, and are not easily chemically reacted with other substances, and in the embodiment of the present application, the inert substances do not react with the second lithium metal oxide of the inner core, do not react with the second lithium metal oxide in the coating layer, and do not react with the electrolyte in the battery.

Exemplary carbon materials may include one or more of graphite, carbon black, hard carbon, and the like. The oxide may be an oxygen vacancy oxide, or an oxide free of oxygen vacancy defects, or a metal oxide, or a non-metal oxide, such as a metal (or non-metal) oxide free of oxygen vacancy defects: one or more of silica, molybdenum dioxide, boron dioxide, alumina, and the like, and oxygen-vacancy metal (or non-metal) oxides: mnO (MnO) _0.97 、TiO _1.68 、SiO _1.87 And the like. For carbide, one or more of boron carbide, silicon carbide may be included. The phosphate comprises one or more of nickel phosphate, zinc phosphate and zirconium phosphate.

By adding the inert substances in the coating layer, the inert substances have very low residual alkalinity and even do not contain alkaline substances, the residual alkalinity of the coating layer can be diluted, the residual alkalinity of the surface of the positive electrode lithium-supplementing material is further reduced, the positive electrode lithium-supplementing material is prevented from reacting with electrolyte at high temperature to generate gaseous substances such as carbon dioxide, and the safety performance and the electrochemical performance of the lithium battery are improved.

In some embodiments, the inert material is present in the coating in an amount of 0 to 20% by mass; in other embodiments, the inert material is present in the coating in an amount of 0.5 to 10% by mass. The content of the inert substances in the coating layer is low, so that the exertion of the effect of inhibiting the gas production of the second lithium metal oxide is not influenced.

In some embodiments, the residual alkaline mass content of the positive electrode lithium-compensating material is less than or equal to 8%; in other embodiments, the residual alkaline mass content of the positive electrode lithium-compensating material is less than or equal to 5%. The residual alkali mass content, also referred to as residual alkalinity, refers herein to the mass percent of residual alkali in the positive electrode lithium-supplementing material. The anode lithium supplementing material provided by the embodiment of the application has proper combination of the inner core and the coating layer, so that the anode lithium supplementing material has lower residual alkalinity, the anode lithium supplementing material can be prevented from reacting with electrolyte under the high temperature condition to generate carbon dioxide and other gas substances, and the safety performance and the electrochemical performance of the lithium battery are improved.

In some embodiments, the first-turn gas yield of the positive electrode lithium-replenishing material is less than or equal to 10mL/g; in other embodiments, the positive electrode lithium-supplementing material has a first-turn gas yield of 0.1 to 5mL/g. The first circle gas production amount of the positive electrode lithium supplementing material refers to the total gas production amount of the battery after the first charge and discharge is finished after the positive electrode lithium supplementing material is applied to the positive electrode of the battery. The first-turn gas yield of the traditional lithium supplementing material under the same conditions is usually above 10mL/g, even up to 20mL/g. The positive electrode lithium supplementing material provided by the embodiment of the application has very low first-circle gas production rate, and compared with the traditional lithium supplementing material, the first-circle gas production rate is obviously reduced. Therefore, the positive electrode lithium supplementing material can effectively inhibit gas production and improve the safety of the battery. In some embodiments, the group IB to VIIIB metal element is selected from at least one of Fe, ni, mn, cu, zn, co, cr, zr, ti, V, mo; the group IIIA metal element includes Al; the group IVA metal element includes Sn; the group VA metal element includes Sb.

The second aspect of the embodiment of the application provides a preparation method of a positive electrode lithium supplementing material, which comprises the following steps: mixing a lithium source and a non-lithium metal source in proportion, and sintering in an inert atmosphere; wherein the non-lithium metal source comprises a source of M and a source of doped cations, M is selected from at least one metal element from groups IB to VIIIB, IVA and VA, and the elemental electronegativity of the doped cations is less than the elemental electronegativity of M.

Non-lithium metal source refers to a metal source other than lithium that is capable of forming a lithium metal oxide with lithium. The non-lithium metal source in the embodiment of the application can only comprise an M source and a doped cation source, and can also comprise an M source and other metal sources except the doped cation source. The positive electrode lithium supplementing material provided by the embodiment of the application comprises lithium metal oxide, and can be obtained only through simple sintering treatment, and the preparation method is simple.

In some embodiments, a method of preparing a positive electrode lithium-compensating material includes:

s1, mixing a lithium source and a non-lithium metal source in proportion, and sintering in an inert atmosphere to obtain a first lithium metal oxide;

s2, mixing the lithium source, the M source and the doped cation source in proportion, and sintering in an inert atmosphere to obtain a second lithium metal oxide; m is selected from at least one metal element in IB-VIIIB, IVA and VA, and the electronegativity of the element doped with cations is smaller than that of the M ions;

s3, carrying out blending sintering treatment on the first lithium metal oxide and the second lithium metal oxide in an inert atmosphere to obtain the positive electrode lithium supplementing material.

The first lithium metal oxide and the second lithium metal oxide are respectively prepared, and then the second lithium metal oxide is coated on the surface of the first lithium metal oxide through simple blending sintering treatment, so that the positive electrode lithium supplementing material with a core-shell structure is formed, and the preparation method is simple.

In some embodiments, in step S1, the first lithium metal oxide comprises Li _a A _b O _c Wherein a is more than 3 and less than or equal to 8, b is more than 0 and less than or equal to 5, and c is more than 0 and less than or equal to 513, A is selected from at least one metal element of groups IB to VIIIB, IIIA, IVA and VA; the preparation method of the first lithium metal oxide comprises the following steps: mixing the lithium source and the A source according to a certain proportion, and sintering in an inert atmosphere.

In some embodiments, in step S1, the sintering treatment is performed at a temperature of 500-900 ℃ for 1-20 hours; in other embodiments, the sintering process is performed at a temperature of 700 to 900 ℃ and maintained for 5 to 10 hours.

In some embodiments, in step S2, the second lithium metal oxide comprises Li _2+x M _1-y2 D _y O _z Wherein x is more than or equal to 0.5 and less than or equal to 0.2, y2 is more than 0 and less than 1, and z is more than 0 and less than 3; d is doping cation; the preparation method of the second lithium metal oxide comprises the following steps: mixing the lithium source, the M source and the D source according to a certain proportion, and sintering in an inert atmosphere.

In some embodiments, in step S2, the sintering treatment is performed at a temperature of 400-800 ℃ for 1-24 hours; in other embodiments, the sintering process is performed at a temperature of 700 to 800 ℃ and maintained for 5 to 10 hours.

In some embodiments, the first lithium metal oxide comprises Li _2+x M _y1 O _z The second lithium metal oxide includes Li _2+x M _1-y2 D _y2 O _z Wherein x is more than or equal to 0.5 and less than or equal to 0.8, y1 is more than 0 and less than or equal to 1, y2 is more than 0 and less than 1, and z is more than 0 and less than 3; d is a doping cation. Step S1 specifically includes: mixing a lithium source and an M source according to a proportion, and sintering in an inert atmosphere; the step S2 specifically comprises the following steps: mixing the lithium source, the M source and the D source according to a certain proportion, and sintering in an inert atmosphere.

In some embodiments, in step S3, the temperature of the blending sintering treatment of the first lithium metal oxide and the second lithium metal oxide is 400-900 ℃, and the temperature is kept for 1-15 hours; in other embodiments, the temperature at which the first lithium metal oxide and the second lithium metal oxide are co-sintered is 500 to 800 ℃ and maintained for 1 to 5 hours.

In some embodiments, in steps S1 and S2, the lithium source employed each independently comprises one or more of lithium hydroxide, lithium oxide, lithium carbonate, lithium sulfate, lithium oxalate.

In some embodiments, the non-lithium metal source comprises one or more of an oxide of a non-lithium metal, a hydroxide of a non-lithium metal, a carbonate of a non-lithium metal, a nitrate of a non-lithium metal, a sulfate of a non-lithium metal, an acetate of a non-lithium metal.

In some embodiments, the source of dopant cations comprises one or more of a cation-doped oxide, a cation-doped hydroxide, a cation-doped carbonate, a cation-doped nitrate, a cation-doped sulfate, a cation-doped acetate.

In some embodiments, the source of a comprises one or more of an oxide of a, a hydroxide of a, a carbonate of a, a nitrate of a, a sulfate of a, an acetate of a.

In some embodiments, the M source comprises one or more of an oxide of M, a hydroxide of M, a carbonate of M, a nitrate of M, a sulfate of M, an acetate of M.

In some embodiments, the D source comprises one or more of an oxide of D, a hydroxide of D, a carbonate of D, a nitrate of D, a sulfate of D, an acetate of D.

In some embodiments, the inert atmosphere in any of the above steps independently comprises at least one of nitrogen, argon, helium, neon, respectively.

In some embodiments, steps S1 and S2, the sintering treatment step is followed by a crushing step, respectively and independently. Through crushing, the inner core and the coating layer have proper particle sizes, which is beneficial to the subsequent blending sintering treatment of the inner core and the coating layer.

In some embodiments, a method of preparing a positive electrode lithium-compensating material includes: mixing a second lithium metal oxide with an inert substance to obtain a coating material; and carrying out blending sintering treatment on the first lithium metal oxide and the coating layer material.

Alternatively, the preparation method of the positive electrode lithium supplementing material comprises the following steps: carrying out blending sintering treatment on the second lithium metal oxide and inert substances to obtain a coating layer material; and carrying out blending sintering treatment on the first lithium metal oxide and the coating layer material.

By adding the inert substances, the inert substances have very low residual alkalinity and even do not contain alkaline substances, the residual alkalinity of the coating layer can be diluted, the residual alkalinity of the surface of the positive electrode lithium-supplementing material is further reduced, the positive electrode lithium-supplementing material is prevented from reacting with electrolyte under the condition of high temperature, gas substances such as carbon dioxide and the like are generated, and the safety performance and the electrochemical performance of the lithium battery are improved.

The third aspect of the embodiment of the application provides a positive electrode, which comprises the positive electrode lithium supplementing material or the positive electrode lithium supplementing material prepared by the method.

In some embodiments, the positive electrode includes a current collector and a positive electrode active layer, the positive electrode active layer being coupled to the current collector, the positive electrode active layer including the above-described lithium-supplementing material or the positive electrode lithium-supplementing material prepared as described above.

In some embodiments, the positive electrode active layer further comprises a positive electrode material, and the positive electrode material and the positive electrode lithium supplementing material together form a positive electrode active layer, and are combined with the current collector. The anode lithium supplementing material can be independently used as an anode material to manufacture an anode, and can be used together with common anode materials to jointly form an anode active layer to be combined with a current collector. When the lithium supplementing material and the positive electrode material are used together, the positive electrode material and the positive electrode lithium supplementing material are generally mixed together, meanwhile, the positive electrode material and the necessary conductive agent, binder and the like are mixed to form positive electrode slurry, the positive electrode slurry is coated on the surface of a current collector, and a positive electrode active layer is obtained through drying treatment. The mass ratio of the positive electrode material to the positive electrode lithium supplementing material can be determined according to actual requirements and general technology in the field, and the mass of the exemplary positive electrode lithium supplementing material is 1% -10% of that of the positive electrode material. The positive electrode material can be at least one of common positive electrode materials of lithium ion batteries, such as lithium cobaltate, lithium manganate, lithium nickelate, nickel cobalt manganese ternary materials, lithium borate, lithium iron phosphate and lithium manganese iron phosphate.

A fourth aspect of the embodiment of the present application provides a secondary battery including the above-described positive electrode.

The positive electrode contains the positive electrode lithium supplementing material provided by the embodiment of the application and has the effect of low gas production, so that the secondary battery containing the positive electrode has good safety performance and electrochemical performance.

In some embodiments, the secondary battery further includes a negative electrode, and the positive electrode and the negative electrode form a circuit during charge and discharge of the secondary battery.

In some embodiments, the secondary battery further includes an electrolyte and a separator stacked between the positive electrode and the negative electrode.

In some embodiments, the secondary battery comprises a lithium ion battery.

The following description is made with reference to specific embodiments.

Example 1

The embodiment provides a positive electrode lithium supplementing material, which has a core-shell structure and comprises a core and a coating layer coated on the surface of the core. Wherein the inner core is Li ₅ FeO ₄ The coating layer is Li ₂ Mn _0.99 Ca _0.01 O ₂ . The coating layer accounts for 1% of the core by mass. The coating layer of this example was a Ca cation-doped lithium metal oxide in which O differs from Ca by 2.5 in electronegativity, the atom number doping content of Ca cations in the coating layer was 1%, and the thickness of the coating layer was 3.5nm.

The preparation method of the positive electrode lithium supplementing material in the embodiment comprises the following steps:

step 1: iron hydroxide and lithium hydroxide are mixed according to a mole ratio of 1:5, after being uniformly mixed, sintering for 8 hours at 800 ℃ under nitrogen inert atmosphere, taking materials and crushing after the tube furnace is cooled down, thus obtaining Li with D50 of 3.5 mu m ₅ FeO ₄ 。

Step 2: manganese oxide, calcium chloride and lithium hydroxide were mixed in a molar ratio=0.99: 0.01:2, after mixing evenly, sintering for 8 hours at 750 ℃ under nitrogen inert atmosphere, taking and crushing after the tube furnace is cooled down, and obtaining Li with D50 of 3.5 mu m ₂ Mn _0.99 Ca _0.01 O ₂ 。

Step 3: taking 3g of Li obtained in the step 1 ₅ FeO ₄ 1wt% Li is added ₂ Mn _0.99 Ca _0.01 O ₂ And (3) after uniformly mixing, sintering for 2 hours at 650 ℃ in nitrogen inert atmosphere, and crushing to obtain the positive electrode lithium supplementing material with the D50 of 3.8 mu m.

The BET specific surface area of the positive electrode lithium supplementing material is 10.5m ² The purity per gram is 95%, and the mass content of residual alkali is 1.5%.

Example 2

This example provides a positive electrode lithium supplementing material, which differs from example 1 in that: the coating layer was 5% by mass of the core, and the thickness of the coating layer was 14.6nm, otherwise the same as in example 1.

step 1: as in step 1 of example 1.

Step 2: step 2 in example 1.

Step 3: the difference from step 3 in example 1 is that the coating layer accounts for 5% of the mass of the core.

The BET specific surface area of the positive electrode lithium supplementing material is 9.4m ² The purity per gram is 91 percent, and the residual alkali mass content is 1.0 percent.

Example 3

This example provides a positive electrode lithium supplementing material, which differs from example 1 in that: the coating layer was 50% by mass of the core, and the thickness of the coating layer was 3.7. Mu.m, in the same manner as in example 1.

step 1: as in step 1 of example 1.

Step 2: step 2 in example 1.

Step 3: the difference from step 3 in example 1 is that the coating layer accounts for 50% of the mass of the core.

The BET specific surface area of the positive electrode lithium supplementing material is 13.8m ² Per gram, the purity is 96%,the residual alkali mass content is 1.7%.

Example 4

This example provides a positive electrode lithium supplementing material, which differs from example 1 in that: the doping content of Ca atoms in the coating layer is 20 percent, and the chemical formula of the coating layer is Li ₂ Mn _0.80 Ca _0.20 O ₂ . Otherwise, the same as in example 1 was used.

step 1: as in step 1 of example 1.

Step 2: the difference from step 2 in example 1 is that the molar ratio of manganese oxide, calcium chloride and lithium hydroxide is 0.8:0.2:2.

step 3: as in step 3 of example 1.

The BET specific surface area of the positive electrode lithium supplementing material is 12.9m ² The purity per gram is 86%, and the residual alkali mass content is 4.8%.

Example 5

The embodiment provides a positive electrode lithium supplementing material, which has a core-shell structure and comprises a core and a coating layer coated on the surface of the core. Wherein the inner core is Li ₆ MnO ₄ The coating layer is Li ₂ Ni _0.97 Al _0.03 O ₂ . The coating layer accounts for 5% of the mass of the core. The coating layer of this example was an Al cation doped lithium metal oxide in which the difference in electronegativity between O and Al was 2.0, the atomic number doping content of Al cations was 3%, and the coating layer thickness was 13.5nm.

step 1: manganese oxide and lithium hydroxide are mixed according to a mole ratio of 1:6, after uniformly mixing, sintering for 8 hours at 860 ℃ under nitrogen inert atmosphere, taking and crushing after the tube furnace is cooled down, and obtaining Li with D50 of 3.5 mu m ₆ MnO ₄ 。

Step 2: nickel oxide, aluminum oxide and lithium hydroxide were mixed in a molar ratio=0.97: 0.03:2, after uniformly mixing, sintering for 8 hours at 750 ℃ under nitrogen inert atmosphere, taking materials and crushing after the tube furnace is cooled down to obtain D50Li of 3.5 μm ₂ Ni _0.97 Al _0.03 O ₂ 。

Step 3: taking 3g of Li obtained in the step 1 ₆ MnO ₄ 5wt% Li is added ₂ Ni _0.97 Al _0.03 O ₂ And (3) after uniformly mixing, sintering for 4 hours at 600 ℃ in an inert nitrogen atmosphere, and crushing to obtain the positive electrode lithium supplementing material with the D50 of 3.8 mu m.

The BET specific surface area of the positive electrode lithium supplementing material is 16.1m ² The purity per gram is 92%, and the mass content of residual alkali is 2.3%.

Example 6

The embodiment provides a positive electrode lithium supplementing material, which has a core-shell structure and comprises a core and a coating layer coated on the surface of the core. Wherein the inner core is Li ₂ NiO ₂ The coating layer is Li ₂ Ni _0.98 Y _0.02 O ₂ . The coating layer accounts for 5% of the mass of the core. The coating layer of this example was lithium metal oxide doped with Y cations, wherein the difference in electronegativity between O and Y was 2.3, the doping content of the number of atoms of Y cations was 2%, and the coating layer thickness was 15.5nm.

step 1: nickel oxide and lithium hydroxide are mixed according to a mole ratio of 1:2, after being evenly mixed, sintering for 8 hours at 760 ℃ under nitrogen inert atmosphere, taking and crushing after the tube furnace is cooled down, and obtaining Li with D50 of 3.5 mu m ₂ NiO ₂ 。

Step 2: nickel oxide, yttrium oxide and lithium hydroxide in a molar ratio=0.98: 0.02:2, after mixing evenly, sintering for 8 hours at 750 ℃ under nitrogen inert atmosphere, taking and crushing after the tube furnace is cooled down, and obtaining Li with D50 of 3.5 mu m ₂ Ni _0.98 Y _0.02 O ₂ 。

Step 3: taking 3g of Li obtained in the step 1 ₂ NiO ₂ 5wt% Li is added ₂ Ni _0.98 Y _0.02 O ₂ And (3) after uniformly mixing, sintering for 4 hours at 600 ℃ in an inert nitrogen atmosphere, and crushing to obtain the positive electrode lithium supplementing material with the D50 of 3.8 mu m.

Through testing, the positive electrode supplements lithiumBET specific surface area of the material was 18.2m ² The purity per gram is 96%, and the mass content of residual alkali is 0.3%.

Example 7

This example provides a positive electrode lithium supplementing material, which differs from example 1 in that: does not contain an inner core material Li ₅ FeO ₄ . That is, the positive electrode lithium supplementing material of the embodiment is Li ₂ Mn _0.99 Ca _0.01 O ₂ 。

step 1: step 2 in example 1.

The BET specific surface area of the positive electrode lithium supplementing material is 10.6m ² And/g, wherein the residual alkali mass content is 1.8%.

Comparative example 1

This comparative example provides a positive electrode lithium supplementing material, which differs from example 1 in that: there is no coating. Namely, the positive electrode lithium supplementing material of the comparative example is Li ₅ FeO ₄ 。

The BET specific surface area of the positive electrode lithium supplementing material is 10.6m ² And/g, the residual alkali mass content is 9.5%.

Comparative example 2

This comparative example provides a positive electrode lithium supplementing material, which differs from example 1 in that: the coating layer is not doped with Ca, i.e. the coating layer is Li ₂ MnO ₂ . Otherwise, the same as in example 1 was used.

The BET specific surface area of the positive electrode lithium supplementing material is 10.6m ² And/g, the residual alkali mass content is 14.2%.

The relevant parameters for the cores, coating layers, and positive electrode lithium-compensating materials of the examples and comparative examples are summarized in table 1:

TABLE 1 parameters related to core and cladding

Analysis shows that the lithium supplementing materials in examples 1-7 have very low residual alkali mass content under the combined action of the inner core and the coating layer with specific compositions; the lithium supplementing materials in comparative examples 1 to 2 have no core-shell structure or D element is not doped in the coating layer, and the residual alkali mass content is obviously increased compared with examples 1 to 7.

Electrochemical performance test:

the positive electrode lithium supplementing materials prepared in each example and comparative example are applied to a lithium ion battery, and the preparation steps of the lithium ion battery specifically comprise:

(1) preparation of a positive plate: the positive electrode lithium supplementing materials prepared in each example and comparative example and lithium iron manganese phosphate are mixed according to a mass ratio of 5:95, and mixing the mixture with SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) according to a mass ratio of 93.5:2.5:4:100, stirring for 2 hours by using a ball mill stirrer, and uniformly mixing to obtain anode slurry; and (3) adding the prepared positive electrode slurry on an aluminum foil, uniformly scraping the positive electrode slurry by a scraper, drying the positive electrode slurry at 130 ℃, and rolling the positive electrode slurry to obtain the positive electrode plate.

(2) And (3) assembling a lithium ion battery: pasting the positive plate prepared in the step (1) on a positive metal shell by using a conductive adhesive, using a metal lithium plate as a negative electrode, using a Celgard 2400 microporous membrane as a diaphragm, and using a LiPF6 solution with the volume ratio of 1.0mol/L as an electrolyte, wherein the solvent of the electrolyte is as follows: 1:1, ethylene Carbonate (EC), diethyl carbonate (DEC) and ethylmethyl carbonate (EMC) were combined in a glove box to form a button lithium ion battery.

And (3) carrying out electrochemical performance test on each lithium ion battery assembled in the step (2) and containing the positive electrode lithium supplementing material of the embodiment or the comparative example, wherein the test conditions are as follows:

and (3) gas production test: when the battery is charged and discharged for the first time, a battery gas production testing device is adopted to detect the gas production after the battery is charged and discharged for the first time.

First charge-discharge capacity: constant-current and constant-voltage charging is carried out to 4.2V at the rate of 0.055C, and the cut-off current is 0.02C; standing for 10min, and discharging at 0.055C constant current to 2.0V;

capacity retention test: when the first charge and discharge of the battery are finished, the charge and discharge voltage window is controlled at 2.0-3.70V at the normal temperature of 25 ℃, the battery is charged at 1C (cut-off current is 0.025C), the 1C is discharged, and the cycle is 200 circles. Capacity retention after 200 cycles formula = discharge capacity/charge capacity 100%.

The test results are as follows.

TABLE 2 electrochemical test results

	Gas production rate mL/g	First-turn charge capacity mAh/g	Capacity retention%
				Example 1	2.58	171.32	89.68
Example 2	2.30	166.41	91.67
				Example 3	1.41	165.30	95.32
Example 4	2.92	168.26	84.61
				Example 5	2.10	167.19	93.60
Example 6	1.82	166.48	90.89
				Example 7	1.02	164.40	94.6
Comparative example 1	16.21	161.20	75.24
				Comparative example 2	14.67	160.31	75.89

From the above data, it can be seen that the lithium iron manganese phosphate active materials in examples 1 to 7 inhibit the gas production phenomenon of the battery and improve the electrochemical performance and safety performance of the battery due to the addition of the lithium supplementing material with specific composition. The method has the advantages that the doping of the lithium supplementing material by adopting the element with specific electronegativity can enhance the binding force between the doping element and oxygen, improve the structural stability of the lithium supplementing material, and prevent the lithium supplementing material from generating gas which influences the electrochemical performance and the safety performance of the battery due to the reaction of the released lattice oxygen in the lithium supplementing material and the electrolyte caused by the release of lithium ions in the lithiation process.

From examples 1 to 3, it can be seen that as the mass ratio of the coating layer in the lithium supplementing material increases, the gas yield of the battery gradually decreases, and the corresponding first-turn charging capacity is in opposite trend, which indicates that the mass ratio of the coating layer of the lithium supplementing agent affects the gas yield and the gas yield of the battery at the same time, and the performance of the battery in all aspects can be comprehensively improved within a proper mass ratio range.

From examples 1 and 4, it is understood that the ratio of the amount of doping element in the coating layer of the lithium supplementing material has an effect on the gas yield, capacity and capacity retention rate (mainly related to the structural stability of the coating layer) of the battery. Under the proper proportion of doping elements, the battery has low gas yield and high first-turn charge capacity, and meanwhile, the coating layer has good structural stability and capacity retention rate.

In comparative examples 1 to 2, however, the lithium-supplementing material added to the lithium iron manganese phosphate active material had an unsuitable structure, so that the electrochemical properties and safety properties were lower than those of examples 1 to 7. Specifically, in the lithium supplementing materials of comparative examples 1 and 2, the coating layer is not provided or the coating layer is not doped with the D element, so that the gas yield is significantly increased and the capacity retention rate is reduced.

The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the application.

Claims

1. The positive electrode lithium supplementing material is characterized by comprising lithium metal oxide, wherein metal ions in the lithium metal oxide comprise lithium ions, doped cations and M ions, M is at least one metal element selected from IB to VIIIB, IVA and VA, and the electronegativity of the doped cations is smaller than that of the M ions.

2. The positive electrode lithium supplementing material according to claim 1, wherein the lithium metal oxide has a core-shell structure, and comprises a core and a coating layer coated on the surface of the core; the inner core comprises a first lithium metal oxide and the cladding layer comprises a second lithium metal oxide; the metal ions in the second lithium metal oxide include lithium ions, doped cations, and M ions.

3. The positive electrode lithium-supplementing material according to claim 2, wherein the number of lithium atoms in the second lithium metal oxide is smaller than or equal to the number of lithium atoms in the first lithium metal oxide;

and/or the first lithium metal oxide comprises Li _a A _b O _c Wherein a is more than 3 and less than or equal to 8, b is more than 0 and less than or equal to 5, c is more than 0 and less than 13, and A is at least one metal element selected from IB to VIIIB, IIIA, IVA and VA;

and/or the second lithium metal oxide comprises Li _2+x M _1-y2 D _y2 O _z The method comprises the steps of carrying out a first treatment on the surface of the Wherein x is more than or equal to-0.5 and less than or equal to 0.2, y2 is more than 0 and less than 1, and z is more than 0 and less than 3; and D is doping cations.

4. The positive electrode lithium supplementing material according to claim 2 or 3, wherein the first lithium metal oxide comprises Li _2+x M _y1 O _z The second lithium metal oxide includes Li _2+x M _1-y2 D _y2 O _z Wherein x is more than or equal to 0.5 and less than or equal to 0.2, y1 is more than 0 and less than or equal to 1, y2 is more than 0 and less than 1, and z is more than 0 and less than 3; and D is doping cations.

5. The positive electrode lithium-supplementing material according to claim 1 or 2, wherein an absolute value of a difference between an electronegativity of the cation-doped element and an electronegativity of an oxygen element is greater than 0.5;

and/or the element electronegativity of the doped cations is less than or equal to 1.5;

and/or the doping cations are selected from one or more of Be, mg, ca, sr, ba, K, na, cs, rb, al, sc, Y.

6. The positive electrode lithium supplementing material according to claim 2, wherein the doping content of the doping cations in the coating layer is 0.1% -20% of the number of atoms;

and/or the mass of the coating layer is 0.1% -50% of that of the inner core;

and/or the average thickness of the coating layer is 1 nm-5 mu m;

and/or the purity of the positive electrode lithium supplementing material is more than or equal to 70%;

and/or the coating layer further comprises an inert substance comprising one or more of a carbon material, an oxide, a carbide, and a phosphate; the inert substance and the second lithium metal oxide are mixed with each other, and/or the inert substance is coated on the surface of the second lithium metal oxide;

and/or, the residual alkali mass content of the positive electrode lithium supplementing material is less than or equal to 8%;

and/or the first-circle gas yield of the positive electrode lithium supplementing material is less than or equal to 10mL/g.

7. The preparation method of the positive electrode lithium supplementing material is characterized by comprising the following steps of: mixing a lithium source and a non-lithium metal source in proportion, and sintering in an inert atmosphere; wherein the non-lithium metal source comprises a source of M selected from at least one metal element of groups IB to VIIIB, IVA and VA and a source of a doping cation having an elemental electronegativity that is less than the elemental electronegativity of M.

8. The method of manufacturing according to claim 7, wherein the method of manufacturing the positive electrode lithium-supplementing material comprises:

mixing a lithium source and a non-lithium metal source in proportion, and sintering in an inert atmosphere to obtain a first lithium metal oxide;

mixing a lithium source, an M source and a doped cation source in proportion, and sintering in an inert atmosphere to obtain a second lithium metal oxide;

and carrying out blending sintering treatment on the first lithium metal oxide and the second lithium metal oxide in an inert atmosphere to obtain the positive electrode lithium supplementing material.

9. A positive electrode comprising the positive electrode lithium-supplementing material according to any one of claims 1 to 6 or the positive electrode lithium-supplementing material produced by the method according to claim 7 or 8.

10. A secondary battery comprising the positive electrode of claim 9.