A positive electrode material and preparation method thereof, positive electrode and battery

Abstract

The present invention relates to the field of lithium-ion batteries, and more specifically, to a positive electrode material, a preparation method thereof, a positive electrode, and a battery. The present invention provides a positive electrode material comprising a lithium-rich core and a conductive layer coated on the surface of the lithium-rich core; at least one of the core and the conductive layer is doped with at least one of the elements P and B. The positive electrode material provided by the present invention, having a conductive layer doped with at least one of the elements P and B, can stabilize the material structure and improve the material's rate capability and cycling stability.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, in particular to a positive electrode material and a preparation method thereof, a positive electrode and a battery. Background Art

[0002] Lithium-ion battery cathode materials are one of the key raw materials for lithium-ion batteries, and their performance directly affects the performance of lithium-ion batteries. Currently, the main cathode materials on the market include lithium cobalt oxide, spinel lithium manganese oxide, nickel cobalt lithium manganese oxide, nickel cobalt oxide, and lithium ferrous phosphate. Among them, lithium cobalt oxide is the most mature, but its resource reserves are limited and its cost is high. Spinel lithium manganese oxide is inexpensive and safe, but has low specific capacity and poor cycle performance. Compared with lithium cobalt oxide, lithium nickel cobalt manganese oxide offers lower cost, higher specific capacity, better safety, and environmental friendliness, but has a lower platform voltage and lower compaction density. While lithium ferrous phosphate has excellent electrochemical properties, it is expensive and has poor safety.

[0003] At present, lithium-rich manganese-based cathode materials have become a research hotspot because of their advantages such as high discharge capacity, high discharge voltage, high energy density, low cost, high safety, and long cycle life. Moreover, lithium-rich manganese-based cathode materials not only have the same lithium replenishing effect as other lithium replenishing materials, but can also be used as cathode materials themselves. Lithium replenishing materials can make up for the irreversible capacity loss caused by the formation of SEI film during the first charging process of lithium-ion batteries. Therefore, the future market potential is large. However, during the cycle, the structural transformation of the material (from layered to spinel) causes a voltage drop; Mn in the spinel structure 3+ The Jahn-Teller effect will also gradually destroy the spinel structure and cause the capacity to decay; at the same time, Mn 3+ The disproportionation reaction with the trace amount of HF in the electrolyte causes Mn to dissolve into the electrolyte, resulting in poor cycle stability. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a positive electrode material having a conductive layer doped with at least one of the elements P and B, with a stable material structure, high rate performance and cycle stability.

[0005] The present invention provides a positive electrode material, comprising a lithium-rich material core and a conductive layer coated on the surface of the lithium-rich material core; at least one of the core and the conductive layer is doped with at least one of the elements P and B.

[0006] The positive electrode material of the present invention comprises a lithium-rich material core. In certain embodiments of the present invention, the lithium-rich material is a material having a molecular formula of Li 1+x R y Mn z O sA lithium-rich manganese-based material; wherein R is selected from a metal element, 0 < x ≤ 1, 0 ≤ y < 1, 0 < z ≤ 1, and 1 ≤ s ≤ 4. In certain embodiments of the present invention, R is selected from at least one of transition metal elements such as Ni, Fe, Co, V, Cu, Mo, Al, Ti, Mg, Cr, Zr, Sn, and Zn.

[0007] If the D50 of the lithium-rich material core of the present invention is too small, the particles will easily agglomerate, thereby increasing the electronic conductivity and the internal resistance of the prepared lithium-ion battery, and deteriorating the performance; if the D50 is too large, the Li + The diffusion path of Li + The diffusion kinetics are relatively slow, which greatly reduces the reversible capacity of the material. In certain embodiments of the present invention, the D50 of the lithium-rich material core is 0.3μm to 50μm. Within this range, the particles are less likely to agglomerate and the diffusion path is moderate, which is conducive to the material's charge and discharge performance.

[0008] The positive electrode material of the present invention includes a conductive layer coated on the surface of the lithium-rich material core. The conductive layer of the present invention is a conductive encapsulation layer coated on the surface of the lithium-rich material core, which is uniformly coated on the outer surface of the core. The conductive layer includes at least one of a carbon layer, a conductive polymer layer, or a conductive oxide layer. In certain embodiments of the present invention, the carbon includes at least one of amorphous carbon, carbon nanotubes, graphite, carbon black, graphene, etc.; the conductive oxide may include at least one of In2O3, ZnO, SnO2; the conductive polymer includes [C6H7O6Na] n Organic polymers with the structure [C6H7O2(OH)2OCH2COONa] n Organic polymers with the structure [C3H4O2] n Organic polymers with the structure [C3H3O2M a ] n Organic polymers with the structure [C3H3N] n An organic polymer with the structure -[CH2-CF2] n - At least one of an organic polymer with a structure, etc.

[0009] If the mass fraction of the conductive layer in the positive electrode material of the present invention is too low, the conductive layer coating will be discontinuous, resulting in side reactions between the material and the electrolyte; if the mass fraction of the conductive layer in the positive electrode material is too high, it will hinder the diffusion of lithium during the deintercalation process and increase the resistance of the electrode / electrolyte interface, hindering the movement of electrons, thereby causing capacity decay; while within the preferred range, a uniform and thin coating layer will be formed, maintaining the normal transmission of lithium ions and electrons, thereby improving the performance of the material. In certain embodiments of the present invention, the mass fraction of the conductive layer in the positive electrode material is preferably 0.05wt% to 10wt%; the thickness of the conductive layer is preferably 1nm to 50nm.

[0010] At least one of the core and the conductive layer of the present invention is doped with at least one of the elements P and B. Element P can inhibit the structural transformation of the positive electrode material from layered to spinel, and doping with element B can also effectively inhibit the structural transformation of the positive electrode material, suppress the activity of side reactions on the surface of the positive electrode material, and improve the cycling performance of the positive electrode material. In certain embodiments of the present invention, only the conductive layer may be doped with at least one of the elements P and B, only the core may be doped with at least one of the elements P and B, or both the core and the conductive layer may be doped with at least one of the elements P and B.

[0011] In certain embodiments of the present invention, the conductive layer is a carbon layer, and only the carbon layer is doped with element P. The carbon layer of the present invention improves the conductivity of the positive electrode material, while element P inhibits the structural transformation of the positive electrode material from layered to spinel.

[0012] In certain embodiments of the present invention, the conductive layer is a carbon layer, and only the carbon layer is doped with element B. The carbon layer of the present invention improves the conductivity of the positive electrode material, while element B inhibits the structural transformation of the positive electrode material from layered to spinel, and also inhibits the activity of side reactions on the surface of the positive electrode material, thereby improving the cycle performance of the positive electrode material.

[0013] In some embodiments of the present invention, the conductive layer is a carbon layer, and only the carbon layer is doped with elements P and B. The elements P and B may be uniformly distributed in the carbon layer, or may be distributed in a gradient from the outside to the inside.

[0014] In some embodiments, the conductive layer is a carbon layer, and only the carbon layer is doped with the elements P and B, and the doping amounts of the elements P and B in the carbon layer increase gradually from the outside to the inside. The gradient distribution of the elements P and B can form a gradient distribution of the concentration of the doping elements in the carbon layer, with a higher concentration near the surface of the lithium-rich material core, which can effectively inhibit side reactions and metal dissolution, and prevent material structural transformation. The lower concentration away from the surface of the lithium-rich material core means that the pure carbon layer can further improve the conductivity of the material, thereby improving the cycle stability of the positive electrode material.

[0015] In certain embodiments of the present invention, the conductive layer is doped with elements P and B, and the mass fraction of the elements P and B in the positive electrode material is 0.01wt% to 5wt%. It should be noted that if the doping amount of elements P and B is too low, the side reactions and metal dissolution cannot be effectively suppressed, thereby leading to a transformation of the material structure; if the doping amount of elements P and B is too high, the proportion of active material in the positive electrode material will be reduced, thereby causing a decrease in the specific capacity of the positive electrode material. Therefore, the use of an appropriate amount of element doping in the present invention is beneficial to suppressing the side reactions between the electrode surface and the electrolyte during the cycle, thereby improving the cycle stability of the positive electrode material.

[0016] In certain embodiments of the present invention, the conductive layer is doped with P and B, with the molar ratio of P to B being 1:1 to 2.5. It is understood that compared to P doping, B doping can not only effectively suppress the structural transformation of the positive electrode material but also inhibit the activity of side reactions on the surface of the positive electrode material. Therefore, appropriately increasing the B doping level can further improve the cycling performance of the positive electrode material. In some embodiments, the molar ratio of P to B can be 1:1, 1:1.5, or 1:2, etc.

[0017] The positive electrode material provided by the present invention has a lithium-rich material as a core, the surface of the core is coated with a conductive layer, and at least one of the core and the conductive layer is doped with at least one of the elements P and B, which can inhibit the side reaction of the active material with the electrolyte, thereby stabilizing the material structure; at the same time, a conductive dense layer is provided, which improves the conductivity and enhances the rate performance and cycle stability of the material.

[0018] The present invention provides a method for preparing the above-mentioned positive electrode material, comprising: mixing and sintering at least one of a phosphorus source and a boron source, a conductive material and a lithium-rich material. In certain embodiments of the present invention, the lithium-rich material is a material having a molecular formula of Li 1+ x R y Mn z O sA lithium-rich manganese-based material; wherein R is selected from a metal element, 0 < x ≤ 1, 0 ≤ y < 1, 0 < z ≤ 1, and 1 ≤ s ≤ 4. In certain embodiments of the present invention, R is selected from at least one of transition metal elements such as Ni, Fe, Co, V, Cu, Mo, Al, Ti, Mg, Cr, Zr, Sn, and Zn.

[0019] In certain embodiments of the present invention, the phosphorus source is selected from at least one of an organic phosphorus source or an inorganic phosphorus source; the organic phosphorus source is selected from at least one of tetraphenylphosphonium bromide, tetraphenylphosphonium iodide, and tetraphenylphosphonium chloride; the inorganic phosphorus source is selected from at least one of sodium pyrophosphate, potassium pyrophosphate, sodium acid pyrophosphate, and potassium acid pyrophosphate.

[0020] In certain embodiments of the present invention, the boron source is selected from at least one of an organic boron source or an inorganic boron source; the organic boron source is selected from at least one of sodium tetraphenylborate, tetraphenylboron bromide, and potassium tetraphenylborate; and the inorganic boron source is selected from at least one of sodium borohydride, boric acid, B2O3, and B2H6.

[0021] In some embodiments of the present invention, the conductive material is selected from at least one of a carbon material, a conductive polymer, or a conductive oxide. In some embodiments of the present invention, the carbon material includes at least one of amorphous carbon, carbon nanotubes, graphite, carbon black, graphene, sucrose, glucose, citric acid, fructose, stearic acid, lauric acid, etc.; the conductive oxide may include at least one of In2O3, ZnO, and SnO2; the conductive polymer includes [C6H7O6Na] n Organic polymers with the structure [C6H7O2(OH)2OCH2COONa] n Organic polymers with the structure [C3H4O2] n Organic polymers with the structure [C3H3O2M a ] n Organic polymers with the structure [C3H3N] n An organic polymer with the structure -[CH2-CF2] n -structured organic polymers, etc. In certain embodiments of the present invention, the sintering temperature is 300° C. to 500° C., and the sintering time is 2 hours to 6 hours.

[0022] The preparation method provided by the present invention can prepare three positive electrode materials with different structures. For example, the prepared positive electrode material has the lithium-rich material as the core, and the surface of the core is coated with a conductive layer doped with at least one of the elements P and B; or, the lithium-rich material is used as the core, the surface of the core is coated with a conductive layer, and at least one of the elements P and B is doped in the core; or, the prepared positive electrode material has the lithium-rich material as the core, the surface of the core is coated with a conductive layer, and the core and the conductive layer are independently doped with at least one of the elements P and B.

[0023] The present invention can first mix at least one of the phosphorus source and the boron source with a conductive material to react to obtain a conductive material doped with at least one of the elements P and B, and then mix the conductive material with a lithium-rich material and sinter them. The obtained positive electrode material has the lithium-rich material as the core, and the surface of the core is covered with a conductive layer doped with at least one of the elements P and B.

[0024] In certain embodiments of the present invention, the phosphorus source, boron source, and conductive material are mixed and reacted in a solution to obtain a conductive material doped with the elements P and B; the conductive material doped with the elements P and B is mixed and sintered with the lithium-rich material to obtain the above-mentioned positive electrode material. In certain embodiments of the present invention, the phosphorus source, boron source, and conductive material are dissolved in anhydrous ethanol, mixed and reacted, and dried to obtain a conductive material doped with the elements P and B; the conductive material doped with the elements P and B is mixed with the lithium-rich material, stirred in anhydrous ethanol, dried, and sintered under a protective gas atmosphere to obtain the above-mentioned positive electrode material.

[0025] The protective gas of the present invention is selected from at least one of nitrogen, helium or argon; the phosphorus source, boron source, conductive material and lithium-rich material are the same as those described above and will not be described in detail. In certain embodiments of the present invention, the mass ratio of the phosphorus source to the boron source is 1:0.5 to 8; the mass fraction of the carbon material doped with elements P and B in the total amount after mixing with the lithium-rich material is 0.05wt% to 20wt%. In some embodiments, the reaction temperature is 150°C to 180°C, and the reaction time is 5h to 12h. The sintering temperature of the present invention is the same as that described above and will not be described in detail.

[0026] The phosphorus source and boron source of the present invention are preferably selected from organic phosphorus sources and organic boron sources. By using organic matter as the phosphorus source and boron source, a conductive layer can be formed without adding additional conductive materials, which makes the operation simpler and the cost lower. The organic phosphorus source and the organic boron source are mixed and reacted to obtain a carbon material doped with elements P and B. The carbon material is then mixed and sintered with a lithium-rich material to obtain a positive electrode material with the lithium-rich material as the core and a carbon layer doped with elements P and B on the surface of the core. Specifically, the organic phosphorus source and the organic boron source are mixed and reacted in a solution to obtain a carbon material doped with elements P and B; the carbon material doped with elements P and B and the lithium-rich material are mixed and sintered to obtain the above-mentioned positive electrode material. In certain embodiments of the present invention, the organic phosphorus source and the organic boron source are dissolved in anhydrous ethanol, mixed and reacted, and dried to obtain a carbon material doped with elements P and B; the carbon material doped with elements P and B and the lithium-rich material are mixed, stirred in anhydrous ethanol, dried, and sintered under a protective gas atmosphere to obtain the above-mentioned positive electrode material. The protective gas, organic phosphorus source, organic boron source, lithium-rich material, the temperature and time of the reaction, the temperature and time of the sintering, the mass ratio of the phosphorus source and the boron source, and the mass fraction of the carbon material doped with elements P and B in the total amount after mixing with the lithium-rich manganese-based material are the same as those described above and will not be repeated here.

[0027] When preparing the positive electrode material of the above structure, the present invention can use the method of spraying to make the elements P and B be gradiently doped in the conductive layer from the outside to the inside. The present invention sprays a solution containing a phosphorus source, a boron source and a conductive material on the surface of the heated lithium-rich material, and presses it; then repeats the steps of spraying and pressing on the lithium-rich material after spraying and pressing, that is, pressing once for each spraying. Such an operation can make the inner layer more pressed the more times, and the doping amount of elements B and P is also greater. Specifically, it includes: A) spraying a solution containing a phosphorus source, a boron source and a conductive material on the surface of the heated lithium-rich material, and pressing; B) after repeating step A), calcining the obtained product, and the obtained positive electrode material has the lithium-rich material as the core, and the surface of the core is coated with a conductive layer doped with elements P and B, and the elements P and B are gradiently doped in the conductive layer from the outside to the inside. In certain embodiments of the present invention, the process comprises: A) spraying a mixed solution of a phosphorus source, a boron source, and a conductive material onto the surface of a lithium-rich material at a temperature of 200°C to 300°C, and then pressing the resulting product into a cake; B) repeating step A), and then calcining the resulting product under an inert gas atmosphere to obtain the aforementioned positive electrode material. In some embodiments, the number of repetitions is 10 to 50. In some embodiments, the concentration of the mixed solution is 1 mol / L to 3 mol / L, preferably 2 mol / L; the mass ratio of the phosphorus source, boron source, and carbon source in the mixed solution is 0.5 to 1.5:0.5 to 4:10 to 15, preferably 1:3.5:12. In some embodiments, the calcination temperature is 300°C to 500°C, preferably 400°C, and the calcination time is 5 to 10 hours. In some embodiments, the inert gas is selected from at least one of helium and argon. The phosphorus source, boron source, conductive material, and lithium-rich material described herein are the same as those described above and are not further described.

[0028] In the present invention, at least one of the phosphorus source and the boron source can be mixed with a lithium-rich material and sintered to obtain a lithium-rich material doped with at least one of the elements P and B. The lithium-rich material doped with at least one of the elements P and B can then be mixed with a conductive material and sintered to obtain a positive electrode material having the lithium-rich material as a core, the surface of the core being coated with a conductive layer, and the at least one of the elements P and B being doped in the core. The phosphorus source, boron source, conductive material, lithium-rich material, sintering temperature and time, and mass ratio of the phosphorus source to the boron source described in the present invention are the same as those described above and are not further described.

[0029] The present invention can also directly mix and sinter at least one of the phosphorus source and the boron source, a conductive material, and a lithium-rich material together to obtain a positive electrode material having the lithium-rich material as a core, the surface of the core being coated with a conductive layer, and the core and the conductive layer being independently doped with at least one of the elements P and B. The phosphorus source, boron source, conductive material, and lithium-rich material, as well as the sintering temperature and time, and the mass ratio of the phosphorus source to the boron source are the same as those described above and are not further described.

[0030] In certain embodiments of the present invention, the lithium-rich material is selected from the above-mentioned molecular formula Li 1+x R y Mn z O s The lithium-rich manganese-based material, the preparation method of which includes the following steps: mixing a manganese source, an R source, a precipitant and a complexing agent, reacting in a solution to obtain a precursor; mixing the precursor with a lithium source, calcining, to obtain a lithium-rich manganese-based material. In some embodiments, under a nitrogen or argon atmosphere, a solution containing a manganese source and an R source is mixed with a solution containing a precipitant and a complexing agent and the mixing conditions are controlled to perform co-precipitation to obtain a precursor; the precursor is mixed with a lithium source and calcined at a high temperature to obtain a lithium-rich manganese-based material. In some embodiments, under a nitrogen or argon atmosphere, a solution containing a manganese source and a N source is mixed with a solution containing a precipitant and a complexing agent at a temperature of 50°C to 60°C, and stirred at a speed of 600rpm to 800rpm, the pH value is adjusted to 9.5 to 10.5, and co-precipitation is performed for 20h to 30h to obtain a precursor; the precursor is mixed with a lithium source, calcined at a high temperature, and naturally cooled to obtain a lithium-rich manganese-based material. The calcination described in the present invention is a three-stage calcination, that is, the temperature is increased to 300°C to 500°C at a heating rate of 2°C / min to 5°C / min and kept warm for 2h to 6h, then the temperature is increased to 750°C to 900°C at a heating rate of 2°C / min to 5°C / min and kept warm for 8h to 15h, and the temperature is reduced to 500°C to 700°C at a rate of 2°C / min to 5°C / min and kept warm for 10h to 15h.

[0031] The manganese source of the present invention is selected from at least one of MnSO4, Mn(NO3)2, or MnCO3; the R source is selected from a salt of Ni, Fe, Co, V, Cu, Mo, Al, Ti, Mg, Cr, Zr, Sn, or Zn, wherein the salt is at least one of sulfate, nitrate, or carbonate; the precipitant is selected from at least one of hydroxide, carbonate, or oxalate; the complexing agent is selected from at least one of ammonia, citric acid, or ethylenediamine; and the lithium source is selected from at least one of LiOH·H2O, LiNO3, Li2CO3, LiF, or Li2O. In certain embodiments of the present invention, the molar ratio of the lithium source to the precursor is 1 to 1.5:1.

[0032] The present invention provides a positive electrode comprising the positive electrode material or the positive electrode material obtained by the above preparation method. In certain embodiments of the present invention, the positive electrode is a lithium ion battery positive electrode.

[0033] The present invention also provides a battery comprising the aforementioned positive electrode, negative electrode, and a separator disposed between the positive and negative electrodes. The negative electrode and separator described herein are independently any of the common negative electrodes and separators known to those skilled in the art. In certain embodiments of the present invention, the battery is a lithium-ion battery comprising the aforementioned positive electrode, negative electrode, and separator disposed between the positive and negative electrodes.

[0034] The present invention provides a positive electrode material comprising a lithium-rich material core and a conductive layer coated on the surface of the lithium-rich material core; at least one of the core and the conductive layer is doped with at least one of the elements P and B. The element P can inhibit the structural transformation of the positive electrode material from layered to spinel, and the doping with the element B can also effectively inhibit the structural transformation of the positive electrode material and suppress the activity of side reactions on the surface of the positive electrode material, thereby improving the cycling performance of the positive electrode material. The positive electrode material provided by the present invention, having a conductive layer doped with at least one of the elements P and B, has a stable material structure, high rate performance, and high cycling stability. DETAILED DESCRIPTION

[0035] The present invention discloses a positive electrode material and a method for preparing the same, a positive electrode, and a battery. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0036] The present invention will be further described below with reference to the embodiments:

[0037] Example 1

[0038] This embodiment provides a B, P co-doped carbon-coated manganese-rich positive electrode material (B, P@C@Li 1.3 Ni 0.35 Mn 0.65 O2), which is Li 1.3 Ni 0.35 Mn 0.65O2 is the core, and the surface of the core is covered with a conductive layer, which is a carbon layer co-doped with B and P, wherein the mass fraction of the carbon layer in the positive electrode material is 0.05wt%, the thickness of the carbon layer is 1nm, the molar ratio of the elements P and B is 1:1, and the mass fraction of the elements P and B in the positive electrode material is 0.01wt%.

[0039] The preparation of element co-doped carbon-coated lithium-rich manganese-based cathode materials is carried out according to the following steps:

[0040] Step 1: In a nitrogen atmosphere, a 1.6 mol / L aqueous solution of nickel sulfate and manganese sulfate (Ni / Mn=0.35:0.65) is pumped into a continuously stirred reactor. At the same time, a 1.6 mol / L NaOH solution and a certain concentration of NH4OH are pumped into the reactor as a precipitant and a complexing agent, respectively. The reaction is carried out at 55°C, pH=10.5, a stirring speed of 800 rpm, and a reaction time of 20 h to obtain a precursor. The molecular formula of the precursor is Ni 0.35 Mn 0.65 (OH)2.

[0041] Step 2: Ni 0.35 Mn 0.65 (OH)2 and LiOH·H2O were uniformly mixed and placed in a tube furnace in an air atmosphere. The mixture was first heated from room temperature to 500℃ at a heating rate of 5℃ / min and kept at that temperature for 5h. Then, the mixture was heated to 850℃ at the same heating rate and calcined for 12h. The mixture was then cooled to 600℃ at the same cooling rate and kept at that temperature for 10h. Finally, the lithium-rich manganese-based material Li 1.3 Ni 0.35 Mn 0.65 O2.

[0042] Step 3: Tetraphenylphosphonium bromide and sodium tetraphenylborate in a mass ratio of 1:0.82 are dissolved in anhydrous ethanol, placed in a water bath at 180° C. for 5 h, and then dried to obtain B and P co-doped carbon (B,P@C).

[0043] Step 4: 1w% B, P@C, Li 1.3 Ni 0.35 Mn 0.65 O2 and anhydrous ethanol were mixed and stirred for 4 hours, dried and then heat-treated at 400℃ for 2 hours under nitrogen atmosphere to obtain a B, P co-doped carbon-coated manganese-rich cathode material (B,P@C@Li 1.3 Ni 0.35 Mn 0.65 O2).

[0044] Example 2

[0045] This embodiment provides a B, P co-doped carbon-coated manganese-rich positive electrode material (B, P@C@Li 1.3 Ni 0.35 Mn 0.65 O2), which is Li 1.3 Ni 0.35 Mn 0.65 O2 is the core, and the surface of the core is covered with a conductive layer, which is a carbon layer co-doped with B and P, wherein the mass fraction of the carbon layer in the positive electrode material is 1.5wt%, the thickness of the carbon layer is 2nm, the molar ratio of the elements P and B is 1:1.22, and the mass fraction of the elements P and B in the positive electrode material is 0.05wt%.

[0046] The preparation method of the product of this embodiment is different from that of Example 1 in that the 1w% B, P@C in step 4 is changed to 3w% B, P@C, and the other steps remain the same.

[0047] Example 3

[0048] This embodiment provides a B, P co-doped carbon-coated manganese-rich positive electrode material (B, P@C@Li 1.3 Ni 0.35 Mn 0.65 O2), which is Li 1.3 Ni 0.35 Mn 0.65 O2 is the core, and the surface of the core is covered with a conductive layer, which is a carbon layer co-doped with B and P, wherein the mass fraction of the carbon layer in the positive electrode material is 10wt%, the thickness of the carbon layer is 50nm, the molar ratio of the elements P and B is 1:2.5, and the mass fraction of the elements P and B in the positive electrode material is 5wt%.

[0049] The preparation method of the product of this embodiment is different from that of Example 1 in that the 1w% B, P@C in step 4 is changed to 20w% B, P@C, and the other steps remain the same.

[0050] Example 4

[0051] This embodiment provides a B, P co-doped carbon-coated manganese-rich positive electrode material (B, P@C@Li 1.2 Fe 0.2 Mn 0.6 O2), which is Li 1.2 Fe 0.2 Mn 0.6 O2 is the core, and the surface of the core is covered with a conductive layer, which is a carbon layer co-doped with B and P, wherein the mass fraction of the carbon layer in the positive electrode material is 2.1wt%, the thickness of the carbon layer is 2.8nm, the molar ratio of the elements P and B is 1:1.24, and the mass fraction of the elements P and B in the positive electrode material is 0.08wt%.

[0052] The preparation of element co-doped carbon-coated lithium-rich manganese-based cathode materials is carried out according to the following steps:

[0053] Step 1: In a nitrogen atmosphere, a 1.6 mol / L aqueous solution of nickel sulfate and manganese sulfate (Fe / Mn=0.2:0.6) was pumped into a continuously stirred reactor. At the same time, a 1.6 mol / L NaOH solution and a certain concentration of NH4OH were pumped into the reactor as a precipitant and a complexing agent, respectively. The reaction was carried out at 50°C, pH=10.2, a stirring speed of 600 rpm, and a reaction time of 15 h to obtain a precursor. The molecular formula of the precursor is Fe 0.2 Mn 0.6 (OH)2.

[0054] Step 2: Fe 0.2 Mn 0.6 (OH)2 and LiOH·H2O were uniformly mixed and placed in a tube furnace in an air atmosphere. The temperature was first raised from room temperature to 450℃ at a heating rate of 3℃ / min and kept at that temperature for 4h. Then the temperature was raised to 800℃ at the same heating rate and calcined for 12h. Then the temperature was lowered to 650℃ at the same cooling rate and kept at that temperature for 12h. Finally, the lithium-rich manganese-based positive electrode material Li 1.2 Fe 0.2 Mn 0.6 O2.

[0055] Step 3: Tetraphenylphosphonium bromide and sodium tetraphenylborate at a mass ratio of 1:1.01 are dissolved in anhydrous ethanol, placed in a water bath at 160° C. for 8 h, and then dried to obtain B and P co-doped carbon (B,P@C).

[0056] Step 4: 4w% B, P@C, Li 1.2 Fe 0.2 Mn 0.6 O2 and anhydrous ethanol were mixed and stirred for 5 h, dried and then heat treated at 450 ° C for 4 h in a nitrogen atmosphere to obtain a B, P co-doped carbon-coated manganese-rich cathode material (B, P@C@Li 1.2 Fe 0.2 Mn 0.6 O2).

[0057] Example 5

[0058] This embodiment provides a positive electrode material, which is Li 1.3 Ni 0.35 Mn 0.65O2 is the core, which is a core co-doped with B and P. The surface of the core is covered with a carbon layer, wherein the mass fraction of the carbon layer in the positive electrode material is 1.8wt%, the thickness of the carbon layer is 2.4nm, the molar ratio of the elements P and B is 1:1.23, and the mass fraction of the elements P and B in the positive electrode material is 0.065wt%.

[0059] The preparation of lithium-rich manganese-based cathode materials with element co-doping only in the core is carried out according to the following steps:

[0060] Step 1: In a nitrogen atmosphere, a 1.6 mol / L aqueous solution of nickel sulfate and manganese sulfate (Ni / Mn=0.35:0.65) is pumped into a continuously stirred reactor. At the same time, a 1.6 mol / L NaOH solution and a certain concentration of NH4OH are pumped into the reactor as a precipitant and a complexing agent, respectively. The reaction is carried out at 55°C, pH=10.5, a stirring speed of 800 rpm, and a reaction time of 20 h to obtain a precursor. The molecular formula of the precursor is Ni 0.35 Mn 0.65 (OH)2.

[0061] Step 2: Ni 0.35 Mn 0.65 (OH)2, LiOH·H2O, B2O3 and Na4P2O7 were uniformly mixed and placed in a tube furnace in an air atmosphere. The mixture was first heated from room temperature to 500℃ at a heating rate of 5℃ / min and kept at that temperature for 5h. Then, the mixture was heated to 800℃ at the same heating rate and calcined for 15h. The mixture was then cooled to 550℃ at the same cooling rate and kept at that temperature for 15h. Finally, the B, P co-doped manganese-rich cathode material B,P@Li was obtained. 1.3 Ni 0.35 Mn 0.65 O2.

[0062] Step 3, B,P@Li 1.3 Ni 0.35 Mn 0.65 O2 and 3wt% C8H 11 NO2, after ball milling at 25 Hz for 60 min, was placed in a tube furnace in an argon atmosphere and heated from room temperature to 550 °C at a heating rate of 2 °C / min for 3 h. Finally, a B, P co-doped manganese-rich cathode material was obtained and carbon-coated (B,P@Li 1.3 Ni 0.35 Mn 0.65 O2@C).

[0063] Example 6

[0064] This embodiment provides a positive electrode material, which is Li 1.3 Ni0.35 Mn 0.65 O2 is the core, the core is a core co-doped with B and P, the surface of the core is covered with a carbon layer co-doped with B and P, wherein the mass fraction of the carbon layer in the positive electrode material is 2.3wt%, the thickness of the carbon layer is 2.9nm, the molar ratio of the elements P and B is 1:1.27, and the mass fraction of the elements P and B in the positive electrode material is 0.11wt%.

[0065] The preparation of lithium-rich manganese-based cathode materials with element co-doping in both the core and the carbon layer is carried out according to the following steps:

[0066] Step 1: In a nitrogen atmosphere, a 1.6 mol / L aqueous solution of nickel sulfate and manganese sulfate (Ni / Mn=0.35:0.65) is pumped into a continuously stirred reactor. At the same time, a 1.6 mol / L NaOH solution and a certain concentration of NH4OH are pumped into the reactor as a precipitant and a complexing agent, respectively. The reaction is carried out at 55°C, pH=10.5, a stirring speed of 800 rpm, and a reaction time of 20 h to obtain a precursor. The molecular formula of the precursor is Ni 0.35 Mn 0.65 (OH)2.

[0067] Step 2: Ni 0.35 Mn 0.65 (OH)2, LiOH·H2O, B2O3, Na4P2O7 and C6H 12 O6 was evenly mixed by ball milling and placed in an air atmosphere of a tube furnace. The temperature was first raised from room temperature to 450°C at a heating rate of 3°C / min and kept at that temperature for 5 h. Then, the temperature was raised to 780°C at the same heating rate and calcined for 10 h. Then, the temperature was lowered to 650°C at the same cooling rate and kept at that temperature for 12 h. Finally, B and P co-doped carbon-coated manganese-rich positive electrode material B,P-Li 1.3 Ni 0.35 Mn 0.65 O2@C.

[0068] Example 7

[0069] This embodiment provides a B-doped carbon-coated manganese-rich positive electrode material (B@C@Li 1.3 Ni 0.35 Mn 0.65 O2), which is Li 1.3 Ni 0.35 Mn 0.65O2 is the core, and the surface of the core is covered with a conductive layer, which is a B-doped carbon layer. The mass fraction of the carbon layer in the positive electrode material is 1.83wt%, the thickness of the carbon layer is 2.4nm, and the mass fraction of element B in the positive electrode material is 0.062wt%.

[0070] The preparation of B-doped carbon-coated lithium-rich manganese-based cathode material was carried out according to the following steps:

[0071] Step 1: In a nitrogen atmosphere, a 1.6 mol / L aqueous solution of nickel sulfate and manganese sulfate (Ni / Mn=0.35:0.65) is pumped into a continuously stirred reactor. At the same time, a 1.6 mol / L NaOH solution and a certain concentration of NH4OH are pumped into the reactor as a precipitant and a complexing agent, respectively. The reaction is carried out at 55°C, pH=10.5, a stirring speed of 800 rpm, and a reaction time of 20 h to obtain a precursor. The molecular formula of the precursor is Ni 0.35 Mn 0.65 (OH)2.

[0072] Step 2: Ni 0.35 Mn 0.65 (OH)2 and LiOH·H2O were uniformly mixed and placed in a tube furnace in an air atmosphere. The mixture was first heated from room temperature to 500℃ at a heating rate of 5℃ / min and kept at that temperature for 5h. Then, the mixture was heated to 850℃ at the same heating rate and calcined for 12h. The mixture was then cooled to 600℃ at the same cooling rate and kept at that temperature for 10h. Finally, the lithium-rich manganese-based material Li 1.3 Ni 0.35 Mn 0.65 O2.

[0073] Step 3: Sodium tetraphenylborate was dissolved in anhydrous ethanol at a mass percentage of 9.2 wt %, and the mixture was placed in a water bath at 170° C. for 5 h and then dried to obtain B-doped carbon (B@C).

[0074] Step 4: 1.2w% B@C, Li 1.3 Ni 0.35 Mn 0.65 O2 and anhydrous ethanol were mixed and stirred for 4 hours, dried and then heat-treated at 500℃ for 2 hours under nitrogen atmosphere to obtain a B-doped carbon-coated manganese-rich cathode material (B@C@Li 1.3 Ni 0.35 Mn 0.65 O2).

[0075] Example 8

[0076] This embodiment provides a P-doped carbon-coated manganese-rich positive electrode material (P@C@Li 1.3 Ni 0.35 Mn0.65 O2), which is Li 1.3 Ni 0.35 Mn 0.65 O2 is the core, and the surface of the core is covered with a conductive layer, which is a P-doped carbon layer. The mass fraction of the carbon layer in the positive electrode material is 1.58wt%, the thickness of the carbon layer is 2.1nm, and the mass fraction of element P in the positive electrode material is 0.054wt%.

[0077] The preparation of P-doped carbon-coated lithium-rich manganese-based cathode material was carried out according to the following steps:

[0078] Step 1: In a nitrogen atmosphere, a 1.6 mol / L aqueous solution of nickel sulfate and manganese sulfate (Ni / Mn=0.35:0.65) is pumped into a continuously stirred reactor. At the same time, a 1.6 mol / L NaOH solution and a certain concentration of NH4OH are pumped into the reactor as a precipitant and a complexing agent, respectively. The reaction is carried out at 55°C, pH=10.5, a stirring speed of 800 rpm, and a reaction time of 20 h to obtain a precursor. The molecular formula of the precursor is Ni 0.35 Mn 0.65 (OH)2.

[0079] Step 2: Ni 0.35 Mn 0.65 (OH)2 and LiOH·H2O were uniformly mixed and placed in a tube furnace in an air atmosphere. The mixture was first heated from room temperature to 500℃ at a heating rate of 5℃ / min and kept at that temperature for 5h. Then, the mixture was heated to 850℃ at the same heating rate and calcined for 12h. The mixture was then cooled to 600℃ at the same cooling rate and kept at that temperature for 10h. Finally, the lithium-rich manganese-based material Li 1.3 Ni 0.35 Mn 0.65 O2.

[0080] Step 3: Tetraphenylphosphonium bromide was dissolved in anhydrous ethanol at a mass percentage of 7.9 wt %, and the mixture was placed in a water bath at 150° C. for 10 h and then dried to obtain P-doped carbon (P@C).

[0081] Step 4: 1.05w% P@C, Li 1.3 Ni 0.35 Mn 0.65 O2 and anhydrous ethanol were mixed and stirred for 4 hours, dried and then heat-treated at 300℃ for 6 hours under nitrogen atmosphere to obtain a P-doped carbon-coated manganese-rich cathode material (P@C@Li 1.3 Ni 0.35 Mn 0.65 O2).

[0082] Example 9

[0083] This embodiment provides a B, P co-doped carbon-coated manganese-rich positive electrode material (B, P-gradient@C@Li 1.3 Ni 0.35 Mn 0.65 O2), which is Li 1.3 Ni 0.35 Mn 0.65 O2 is the inner core, and the surface of the inner core is covered with a conductive layer, wherein the conductive layer is a carbon layer co-doped with B and P, wherein the doping amounts of B and P increase gradually from the outside to the inside of the carbon layer; the mass fraction of the carbon layer in the positive electrode material is 1.68wt%, the thickness of the carbon layer is 2.2nm, the molar ratio of the elements P and B is 1:1.23, and the mass fraction of the elements P and B in the positive electrode material is 0.058wt%.

[0084] The preparation of element gradient co-doped carbon-coated lithium-rich manganese-based cathode materials was carried out according to the following steps:

[0085] Step 1: In a nitrogen atmosphere, a 1.6 mol / L aqueous solution of nickel sulfate and manganese sulfate (Ni / Mn=0.35:0.65) is pumped into a continuously stirred reactor. At the same time, a 1.6 mol / L NaOH solution and a certain concentration of NH4OH are pumped into the reactor as a precipitant and a complexing agent, respectively. The reaction is carried out at 55°C, pH=10.5, a stirring speed of 800 rpm, and a reaction time of 20 h to obtain a precursor. The molecular formula of the precursor is Ni 0.35 Mn 0.65 (OH)2.

[0086] Step 2: Ni 0.35 Mn 0.65 (OH)2 and LiOH·H2O were uniformly mixed and placed in a tube furnace in an air atmosphere. The mixture was first heated from room temperature to 500℃ at a heating rate of 5℃ / min and kept at that temperature for 5h. Then, the mixture was heated to 850℃ at the same heating rate and calcined for 12h. The mixture was then cooled to 600℃ at the same cooling rate and kept at that temperature for 10h. Finally, the lithium-rich manganese-based material Li 1.3 Ni 0.35 Mn 0.65 O2.

[0087] Step 3, Li 1.3 Ni 0.35 Mn 0.65 O2 was heated to 200℃, and B2O3, Na4P2O7 and C8H 11 The mixed solution of NO2 is sprayed onto the Li 1.3 Ni 0.35 Mn 0.65O2 surface, and pressed into a cake-shaped product with a diameter of 2 cm and a thickness of 0.5 cm by external pressure, and the steps of spraying the pressed product with the mixed solution and then pressing were repeated 22 times; the product obtained after repeated spraying and pressing was heated to 400 ° C for 8 h under an argon atmosphere at a heating rate of 2 ° C / min, and finally a B, P gradient co-doped carbon-coated manganese-rich positive electrode material (B, P-gradient@C@Li 1.3 Ni 0.35 Mn 0.65 O2).

[0088] Comparative Example 1

[0089] This embodiment provides a carbon-coated manganese-rich positive electrode material (Li 1.3 Ni 0.35 Mn 0.65 O2@C), which is Li 1.3 Ni 0.35 Mn 0.65 O2 is the core, the surface of the core is covered with a conductive layer, and the conductive layer is a carbon layer, wherein the mass fraction of the carbon layer in the positive electrode material is 1.57wt%, and the thickness of the carbon layer is 2nm.

[0090] Performance Testing

[0091] Furthermore, in order to verify the progress of the embodiments of the present application, the following performance tests were performed on the lithium-rich materials of Examples 1 to 9 and Comparative Example 1:

[0092] 1. Withholding power assessment method:

[0093] A) Battery Assembly:

[0094] ① Positive electrode sheet: The positive electrode materials of Examples 1 to 9 and Comparative Example 1 were respectively used as active materials, and the active materials were mixed with polyvinylidene fluoride and SP-Li in a mass ratio of 95:3:2 by ball milling to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil and dried at 120°C for 30 minutes to obtain positive electrode sheets;

[0095] ②Negative electrode: lithium metal sheet;

[0096] ③ Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 with a concentration of 1 mol / L was added to form an electrolyte;

[0097] ④Separator: polypropylene microporous separator;

[0098] ⑤ Lithium-ion battery assembly: Lithium-ion batteries were assembled in an inert atmosphere glove box in the order of negative electrode - diaphragm - electrolyte - positive electrode plate; wherein, the lithium-ion batteries corresponding to the positive electrode materials of Examples 1 to 9 were batteries A1 to A9, respectively, and the lithium-ion battery corresponding to the positive electrode material of Comparative Example 1 was battery B1, respectively.

[0099] B) Performance testing:

[0100] The electrochemical performance of batteries A1 to A9 and battery B1 was tested. The test conditions were as follows: the assembled batteries were placed at room temperature for 6 hours and then charged and discharged. The charge and discharge voltage was 2.0 to 4.6 V and the rate was 0.1C.

[0101] The test results are shown in Table 2 below:

[0102] Table 2

[0103]

[0104]

[0105] The test results for Battery B1 in Table 2 show that simple carbon coating is far from sufficient to stabilize the material structure and improve performance. The charge-discharge capacity, coulombic efficiency, and capacity retention after 50 cycles at 0.1C are all inferior to those of Batteries A1-A9. However, the test results for Batteries A1-A3 show that assembling a battery with a positive electrode material containing a P- and B-co-doped carbon layer, when the carbon layer is 2 nm thick, can achieve a thin and uniform coating on the surface of the lithium-rich material, resulting in optimal material performance.

[0106] Among batteries A1 to A6, compared with batteries A1 and A3, battery A5 (elements are doped in the core and then coated with a carbon layer on the surface of the core), battery A6 (elements are doped in both the core and the carbon layer), battery A2 and battery A4 (using a liquid phase one-step synthesis method to form a P and B co-doped carbon layer) are more conducive to suppressing the side reactions between the active material and the electrolyte, thereby stabilizing the material structure; at the same time, a conductive dense layer is provided, which improves the conductivity and improves the cycle stability of the material; it also has a better charge and discharge specific capacity and coulomb efficiency. In addition, the core material changes, the theoretical capacity is different, Li 1.3 Ni 0.35 Mn 0.65 The theoretical capacity of O2 is 358mAh / g, Li 1.2 Fe 0.2 Mn 0.6 The theoretical capacity of O2 is 381mAh / g, so the performance of battery A4 will be slightly higher than other batteries.

[0107] As shown in Table 2, the performance of batteries A7 and A8 is slightly inferior to that of batteries A2, A4, A5, and A6. This indicates that the effect of doping with element B or element P alone is slightly inferior to that of co-doping with elements P and B. However, the performance of batteries A7 and A8 is still much higher than that of battery B1. The performance of battery A9 is slightly better than that of batteries A2, A4, A5, and A6, indicating that gradient doping of the doping elements can better suppress side reactions between the active material and the electrolyte and stabilize the material structure.

[0108] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that It comprises a lithium-rich material core and a conductive layer coated on the surface of the lithium-rich material core; At least one of the core and the conductive layer is doped with at least one of elements P and B; The conductive layer is a carbon layer, and the carbon layer is doped with elements P and B; in the carbon layer, the doping amounts of the elements P and B increase gradually from the outside to the inside; The molar ratio of the elements P and B is 1:1-2.5; The mass fraction of the elements P and B in the positive electrode material is 0.01 wt% to 5 wt%.

2. The positive electrode material according to claim 1, characterized in that The lithium-rich material has a molecular formula of Li 1+x R y Mn z O s Lithium-rich manganese-based materials; Wherein, the R is selected from at least one metal element, 0<x≤1, 0≤y<1, 0<z≤1, 1≤s≤4.

3. The positive electrode material according to claim 1, characterized in that The mass fraction of the conductive layer to the positive electrode material is 0.05 wt% to 10 wt%; The thickness of the conductive layer is 1 nm to 50 nm.

4. The positive electrode material according to claim 1, characterized in that The D50 of the lithium-rich material core is 0.3 μm~50 μm.

5. A method for preparing the positive electrode material according to any one of claims 1 to 4, characterized in that: include: A) spraying a solution containing a phosphorus source, a boron source, and a carbon source onto the surface of a heated lithium-rich material and pressing; B) Repeating step A), the obtained product is calcined to obtain a positive electrode material.

6. A positive electrode, characterized in that The invention comprises the positive electrode material according to any one of claims 1 to 4 or the positive electrode material obtained by the preparation method according to claim 5.

7. A battery comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, characterized in that: The positive electrode is the positive electrode according to claim 6.

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