CN111732126A - Layered lithium-rich manganese oxide cathode material, preparation method and application thereof - Google Patents

Abstract

The invention relates to the field of lithium ion batteries, and discloses a layered lithium-rich manganese oxide positive electrode material capable of effectively inhibiting voltage decay during cycling, a preparation method and application thereof. The preparation method of the layered lithium-rich manganese oxide positive electrode material includes the following steps: in the preparation process of the layered lithium-rich manganese oxide positive electrode material precursor of the lithium ion battery, adding the raw material precursor of the modified material, and then heat treatment at high temperature to obtain Layered lithium-rich manganese oxide composite cathode material. In the present invention, Ni element can effectively inhibit the migration of transition metal elements during the cycle process of the layered lithium-rich manganese positive electrode material, and inhibit the formation of a spinel phase, thereby effectively inhibiting the capacity/voltage decay during the cycle process. The positive electrode and lithium ion battery using the material belong to the technical field of energy materials and energy conversion. The material has the advantages of high energy density, good cycle stability and good rate performance as a cathode material for lithium-ion batteries.

Description

Layered lithium-rich manganese oxide cathode material, preparation method and application thereof

technical field

The invention relates to the field of positive electrode materials for lithium ion batteries, in particular to a layered lithium-rich manganese oxide positive electrode material capable of effectively suppressing voltage decay during cycling, and a preparation method and application thereof.

Background technique

Lithium-ion batteries have been widely used in portable electronic products, electric vehicles and energy storage power stations due to their high energy density and other characteristics. The new generation of electronic products puts forward higher requirements for the performance of lithium-ion batteries, that is, lithium-ion batteries need to have the characteristics of high power and long cycle life while improving high energy density. The cathode material of Li-ion batteries is one of the key factors to achieve their high energy density. The mature applied cathode materials on the market are lithium cobalt oxide (LiCoO2), nickel cobalt lithium manganate ternary material (LiMO2, M=Ni, Co, Mn/Al), spinel lithium manganate (LiMn2O4) and lithium iron phosphate (LiFePO4) and so on. However, the specific capacity obtained by layered cathode materials is always limited to within 150 mAh/g. The theoretical specific capacity of the spinel-structured LiMn2O4 cathode material and the polyanionic LiFePO4 cathode material is only 148 mAh/g and 170 mAh/g respectively, and the actual capacity is lower, which is far from satisfying the high specific energy density of lithium ions. Battery performance requirements for cathode materials. Therefore, the cathode material becomes the bottleneck for further improvement of the performance of Li-ion batteries. Li-rich manganese-based cathode materials have attracted the attention of scientists and engineers all over the world due to their ultra-high specific capacity (>250mAh·g ^-1 ), low cost and high safety.

However, due to the poor cycle stability and rate performance of the layered Li-rich manganese oxide cathode material, and the low first Coulomb efficiency, its practical application is seriously restricted. The migration and structural rearrangement of transition metal (TM) ions in the layered Li-rich manganese oxide cathode material during cycling lead to the formation of spinel structure, which is the fundamental cause of its capacity/voltage fading. Studies have reported that ion doping/substitution methods can usually be used to improve the structural stability of layered Li-rich manganese oxide cathode materials and suppress their phase transitions during charge and discharge, thereby suppressing their capacity/voltage fading. At present, the commonly used method is to use inactive elements such as Mg, Al, Fe and other inactive elements to dope and modify the layered lithium-rich manganese oxide cathode material. However, the doping modification of these inactive elements will reduce the electrochemical capacity of the electrode material. , and its modification effect is not very obvious.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide a method for preparing a layered lithium-rich manganese oxide positive electrode material. This modification method can effectively improve the energy density and cycle life of the layered lithium-rich manganese positive electrode material, and further promote the Industrialization of layered lithium-rich manganese cathode materials. The second object of the present invention is to provide a lithium ion battery positive electrode using the positive electrode material. A third object of the present invention is to provide a lithium ion battery using the positive electrode.

In order to realize the above-mentioned first purpose, the present invention adopts the following technical scheme:

A method for preparing a layered lithium-rich manganese oxide positive electrode material, comprising the following steps: in the process of preparing a layered lithium-rich manganese oxide positive electrode material precursor for a lithium ion battery, adding a raw material precursor of metallic nickel, and then heat treatment at a high temperature to obtain Layered lithium-rich manganese oxide composite cathode material.

The invention also discloses a layered lithium-rich manganese oxide cathode material prepared by the above preparation method.

In order to realize the above-mentioned second purpose, the present invention adopts following technical scheme:

A positive electrode of a lithium ion battery, using the above-mentioned layered lithium-rich manganese oxide positive electrode material as a positive electrode material, and mixing with a conductive agent and then performing ball milling to obtain a mixture, and then mixing the mixture and a binder to form a slurry, and the slurry is The material is smeared on the aluminum foil, and after drying, the positive electrode of the lithium ion battery is obtained.

In order to realize the above-mentioned third purpose, the present invention adopts following technical scheme:

A lithium ion battery includes a positive electrode, a negative electrode capable of deintercalating lithium ions, and an electrolyte between the negative electrode and the positive electrode, wherein the positive electrode is the above-mentioned positive electrode of the lithium ion battery.

Compared with the prior art, the present invention has the following beneficial effects:

(1) the modification method of the present invention has the advantages of being simple, effective, fast, low in cost, strong in controllability and wide in scope of application;

(2) In the present invention, excess Ni element is added to the layered lithium-rich manganese, and the ion exchange characteristics between Ni and Li are used to realize the doping of Ni at the Li site, thereby effectively suppressing the cycle process of the layered lithium-rich manganese oxide cathode material The migration of the mid-transition metal ions to the lithium layer inhibits the formation of the spinel phase, which can effectively suppress the capacity/voltage fading during cycling without reducing the energy density of the original material.

Description of drawings

Fig. 1 is the XRD pattern comparison of the product of Example 1 of the present invention;

Fig. 2 is (a) cycle performance curve of the product of Example 1 of the present invention, (b) midpoint voltage decay curve;

Fig. 3 is (a) rate performance curve of the product of Example 1 of the present invention, (b) rate capacity retention rate curve;

Fig. 4 is (a) cycle performance curve of the product of Example 2 of the present invention, (b) midpoint voltage decay curve;

Fig. 5 is the XRD pattern comparison of the product of Example 3 of the present invention;

Fig. 6 is (a) cycle performance curve of the product of Example 3 of the present invention, (b) midpoint voltage decay curve;

Fig. 7 is the cycle performance curve of the product of Example 4 of the present invention;

Fig. 8 is the midpoint voltage decay curve of the product of Example 4 of the present invention;

Fig. 9 is the midpoint voltage decay curve comparison of the product of Example 5 of the present invention;

Fig. 10 is the midpoint voltage decay curve comparison of the product of Example 6 of the present invention;

Figure 11 is a comparison of the midpoint voltage decay curves of the product of Example 7 of the present invention;

12 is a comparison of the midpoint voltage decay curves of the product of Example 8 of the present invention;

Figure 13 is the cycle performance curve of the product of Example 9 of the present invention;

FIG. 14 is the cycle performance curve of the mid-site discharge voltage of the product of Example 9 of the present invention.

Detailed ways

The endpoints of ranges and any values disclosed herein are not limited to the precise ranges or values, which are to be understood to encompass values proximate to those ranges or values. For ranges of values, the endpoints of each range, the endpoints of each range and the individual point values, and the individual point values can be combined with each other to yield one or more new ranges of values that Ranges should be considered as specifically disclosed herein.

A first aspect of the present invention provides a method for preparing a layered lithium-rich manganese oxide positive electrode material, comprising the following steps: in the process of preparing a layered lithium-rich manganese oxide positive electrode material precursor for a lithium ion battery, adding raw materials of the modified material The precursor is then heat treated at high temperature to obtain a layered lithium-rich manganese oxide composite cathode material.

In the present invention, during the preparation process of the layered lithium-rich manganese oxide positive electrode material for lithium ion batteries, excess Ni element precursor is added to regulate the structure of the layered lithium-rich manganese oxide positive electrode material, because the Ni element can effectively inhibit the layered lithium-rich manganese oxide positive electrode material. The migration of transition metal elements during cycling of manganese cathode materials inhibits the formation of spinel phases, thereby effectively suppressing capacity/voltage decay during cycling. The positive electrode and lithium ion battery using the material belong to the technical field of energy materials and energy conversion. The material has the advantages of high energy density, good cycle stability and good rate performance as a cathode material for lithium-ion batteries. The composite material has a simple preparation method and is suitable for large-scale production.

According to the present invention, the layered lithium-rich manganese oxide cathode material is xLi ₂ MnO ₃ -(1-x)LiMO ₂ , wherein M is selected from at least one of Ni, Co, Mn, Cr and Fe; 0 ≤x≤1, preferably, 0.1≤x≤0.8.

Preferably, in the layered lithium-rich manganese oxide cathode material, 0.1≤x≤0.8, and if x is too small or too large, the comprehensive electrochemical performance of the lithium-rich material will decrease. Therefore, x should be selected in a reasonable range.

Preferably, the modification material is Ni element.

Preferably, the raw material precursor of the modified material is added in an amount such that the molar ratio of the doping amount of metallic Ni relative to the layered lithium-rich manganese oxide cathode material is 0.01-0.1, preferably 0.01-0.06. If the doping amount is too small, the modification effect will not be achieved; if the doping amount is too large, the structure of the original material will be affected, thereby affecting its electrochemical performance.

Preferably, the preparation method of the precursor is selected from at least one of spray method, co-precipitation method, sol-gel method, combustion method, solid phase method and molten salt method. The phase structure, composition distribution, morphology, particle size, etc. of the materials obtained by different preparation methods are different, which have an important influence on the various properties of the electrode materials.

Preferably, the raw materials used in the layered lithium-rich manganese oxide cathode material precursor and the raw material precursor of the modified material are independently selected from acetate, nitrate, sulfate, carbonate, grass at least one of acid salts and metal oxides. Different raw materials have different solubility and melting point, which will have an important influence on the composition distribution and phase composition of synthetic materials.

Preferably, the temperature of the heat treatment is 600-1000°C; the atmosphere of the high-temperature heat treatment is at least one of oxygen, air and vacuum; and the heat treatment time is 5-48 hours. The phase structure, composition distribution, morphology, particle size, etc. of the materials obtained by different heat treatment temperatures, atmospheres and times have an important impact on the various properties of electrode materials.

The invention also discloses a layered lithium-rich manganese oxide positive electrode material prepared by adopting any one of the above technical solutions.

A second aspect of the present invention provides a positive electrode for a lithium ion battery. The above-mentioned layered lithium-rich manganese oxide positive electrode material is used as the positive electrode material for the lithium ion battery, and is mixed with a conductive agent and then ball-milled to obtain a mixed material, and then the mixed material and the adhesive are mixed. The binder is mixed to form a slurry, the slurry is smeared on the aluminum foil, and after drying, the positive electrode of the lithium ion battery is obtained.

Preferably, the conductive agent is selected from at least one of graphite, acetylene black, Super P, carbon nanotubes, graphene and scientific black.

Preferably, based on the total weight of the slurry, the content of the conductive agent is 2wt% to 30wt%.

Preferably, during the ball milling, the mass ratio of the balls is 5:1 to 300:1; the ball milling speed is 100 rpm to 800 rpm; the ball milling time is 0.5 hours to 48 hours; the ball milling atmosphere is selected from air, At least one of oxygen, nitrogen, hydrogen, argon, carbon dioxide and helium.

Preferably, the binder is an aqueous binder or a non-aqueous binder known to those skilled in the art, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTEE), styrene-butadiene rubber (SBR) ), at least one of sodium carboxymethyl cellulose (CMC) and sodium alginate (SA); based on the total weight of the slurry, the amount of the binder is 1wt% to 30wt%.

A third aspect of the present invention provides a lithium ion battery, the lithium ion battery includes a positive electrode, a negative electrode that can deintercalate lithium ions, and an electrolyte between the negative electrode and the positive electrode, wherein the positive electrode is the above-mentioned lithium ion battery positive electrode.

In the lithium ion battery of the present invention, the negative electrode material can use various conventional negative electrode active materials known to those skilled in the art, such as graphite, silicon and various silicon alloys, iron oxides, tin oxides and various tin alloys, titanium Anode materials such as oxides. The electrolyte can be a conventional non-aqueous electrolyte known to those skilled in the art, wherein the lithium salt in the electrolyte can be lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), fluorohydroxysulfonic acid One or more of lithium oxide (LiC(SO2CF3)3). The non-aqueous solvent can be dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC) one or more of them.

The present invention will be described in detail below by means of examples. In the following examples, examples and comparative examples are all commercially available products.

Example 1

Excess Ni-doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material prepared by spray pyrolysis method:

Add Li, Ni, Co, Mn acetates into a certain amount of deionized water according to the stoichiometric ratio, and use mechanical stirring to obtain a uniform reaction solution; %) nickel acetate is added to the reaction solution; the reaction solution is subjected to spray pyrolysis to obtain a precursor. The obtained precursors were heat-treated at 900 °C for 10 hours to obtain excess Ni-doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ positive electrode materials, marked as Ni-0, Ni-2, Ni- 4. Ni-6.

The LNCMO-Ni positive electrode material and the binder were mixed in a certain proportion, and a uniform slurry was obtained by magnetic stirring for 4 hours, and then the slurry was uniformly coated on the aluminum foil to obtain the electrode material. The battery was characterized by a 2025 button cell, the assembly process was completed in a glove box filled with Ar, and the water and oxygen contents were both less than 0.1 ppm. The positive electrode is the prepared electrode sheet; the reference electrode and the counter electrode are metal Li sheets; the separator is Celgard-2400; the electrolyte is LiPF6 (1mol/L)/EC+DEC+EMC (1:1:1), the assembled battery is placed for testing.

Figure 1 shows the XRD patterns of Ni-0, Ni-2, Ni-4, and Ni-6 electrode materials. As shown in Fig. 1, all diffraction peaks can be correlated with the hexagonal LiMO ₂ (M=Ni, Co, Mn, etc.) (R-3m) (PDF#85-1966) and the monoclinic Li ₂ MO ₃ (M=Ni, Co, Mn, etc.) (C/2m) (PDF#84-1634) corresponds well. The diffraction peaks between 20 and 25° (2θ) are characteristic peaks of the Li ₂ MO ₃ phase, which are caused by the ordered superstructure of LiTM ₂ in the transition metal (TM) layer in its structure. "R" and "M" under the diffraction index in the figure represent LiMO ₂ with hexagonal structure and Li ₂ MO ₃ with monoclinic structure, respectively. The research results in Chapter 5 have confirmed that the LNCMO cathode materials are hexagonal LiMO ₂ (M=Ni, Co, Mn, etc.) (R-3m) (PDF#85-1966) and monoclinic Li ₂ MO ₃ (M=Ni, Co, Mn, etc.) (C/2m) composites dominated by nanoscale interactions. In addition, it can be seen from the XRD patterns that with the increase of Ni content, the structure of the LNCMO cathode material does not change significantly.

Figure 2(a) shows the cycle performance curves of Ni-0, Ni-2, Ni-4, and Ni-6 electrode materials. As shown in the figure, increasing the content of Ni element can effectively improve the cycling performance of LNCMO cathode materials. The results show that the first discharge specific capacities of Ni-0, Ni-2, Ni-4, Ni-6 electrodes are: 226, 218, 206, 192mAh g ^{-1 at the current density of 200mA g -1 ;} after 150 cycles The discharge specific capacities are: 190, 188, 183, 181mAh g ^-1 ; the discharge capacity retention rates are: 84, 86, 89, 94%, respectively. The results show that the specific discharge capacity of LNCMO cathode material at a current density of 200 mA g ^-1 decreases with the increase of Ni content, but its capacity retention rate increases with the increase of Ni content. It can be seen that increasing the Ni content can effectively improve the cycle stability although the electrochemical capacity of the LNCMO cathode material will be reduced. Figure 2(b) shows that increasing the Ni content can improve the discharge midpoint voltage of the LNCMO cathode material and suppress the voltage decay during cycling of the LNCMO cathode material.

Figure 3(a) shows the rate performance curves of Ni-0, Ni-2, Ni-4, and Ni-6 electrode materials, and the rate capacity retention ratios at different rates are shown in Figure 3(b). The results show that the Ni-0 electrode material shows higher rate capacity at a rate below 1C, while the Ni electrode material shows relatively higher rate capacity when the charge-discharge rate is >1C. At a high rate of 10C, the discharge rate capacity of Ni-4 electrode material is 158mAh g ^-1 , while the discharge rate capacity of Ni-0 electrode material is only 130mAh g ^-1 . The results show that increasing the Ni content can improve the high-rate performance of LNCMO cathode materials.

Example 2

Excess Ni-doped 0.7Li ₂ MnO ₃ -0.3LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO-1) cathode material was prepared by spray pyrolysis.

Li, Ni, Co, Mn acetates were added to a certain amount of deionized water according to the stoichiometric ratio, and a uniform reaction solution was obtained by mechanical stirring; Adding nickel acetate into the reaction solution; spraying and pyrolyzing the reaction solution to obtain a precursor. The obtained precursors were heat-treated at 900 degrees Celsius for 10 hours to obtain excess Ni-doped LNCMO-1 cathode materials, which were labeled as Ni-1-0, Ni-1-2, Ni-1-4, Ni-1- 6.

Electrode material preparation and battery assembly were the same as in Example 1.

Figure 4(a) shows the cycle performance curves of Ni-1-0, Ni-1-2, Ni-1-4, and Ni-1-6 electrode materials. As shown in the figure, increasing the content of Ni element can effectively improve the cycling performance of LNCMO-1 cathode material. Under the current density of 200mA g ^-1 , the first discharge specific capacities of Ni-1-0, Ni-1-2, Ni-1-4, Ni-1-6 electrodes are: 203, 211, 224, 226mAh g ^-1 ; The discharge specific capacities after 150 cycles are: 135, 148, 169, 190mAh g ^-1 ; the discharge capacity retention rates are: 66.5, 70.1, 75.4, 84.1%, respectively. The results show that the specific discharge capacity of LNCMO cathode material at a current density of 200 mA g ^-1 increases with the increase of Ni content, and its capacity retention rate increases with the increase of Ni content.

Figure 4(b) shows that increasing the Ni content can improve the discharge midpoint voltage of the LNCMO-1 cathode material and suppress the voltage decay during cycling of the LNCMO-1 cathode material.

Example 3

Preparation of Excess Ni Doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) Cathode Material-Nitrate by Spray Pyrolysis

Li, Ni, Co, Mn nitrates were added to a certain amount of deionized water according to the stoichiometric ratio, and a uniform reaction solution was obtained by mechanical stirring; The nickel nitrate is added to the reaction solution; the reaction solution is subjected to spray pyrolysis to obtain a precursor. The obtained precursors were heat-treated at 900 degrees Celsius for 10 hours to obtain excess Ni-doped LNCMO cathode materials, which were labeled as Ni-1-0, Ni-1-2, Ni-1-4, and Ni-1-6 electrodes, respectively. The preparation and battery assembly were the same as in Example 1.

As shown in Figure 5, all the diffraction peaks can be correlated with the hexagonal LiMO ₂ (M=Ni, Co, Mn, etc.) (R-3m) (PDF#85-1966) and the monoclinic Li ₂ MO ₃ (M=Ni, Co, Mn, etc.) (C/2m) (PDF#84-1634) corresponds well. The diffraction peaks between 20 and 25° (2θ) are characteristic peaks of the Li ₂ MO ₃ phase, which are caused by the ordered superstructure of LiTM ₂ in the transition metal (TM) layer in its structure. "R" and "M" under the diffraction index in the figure represent LiMO ₂ with hexagonal structure and Li ₂ MO ₃ with monoclinic structure, respectively. The research results in Chapter 5 have confirmed that the LNCMO cathode materials are hexagonal LiMO ₂ (M=Ni, Co, Mn, etc.) (R-3m) (PDF#85-1966) and monoclinic Li ₂ MO ₃ (M=Ni, Co, Mn, etc.) (C/2m) composites dominated by nanoscale interactions. In addition, it can be seen from the XRD patterns that with the increase of Ni content, the structure of the LNCMO cathode material does not change significantly.

Figure 6(a) shows the cycle performance curves of Ni-1-0, Ni-1-2, Ni-1-4, and Ni-1-6 electrode materials. Figure 6(b) shows that increasing the Ni content can improve the discharge midpoint voltage of the LNCMO cathode material and suppress the voltage decay during cycling of the LNCMO cathode material.

Example 4

Excessive Ni-doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode materials were prepared by spray pyrolysis - different heat treatment temperatures.

Li, Ni, Co, Mn nitrates were added to a certain amount of deionized water according to the stoichiometric ratio, and a uniform reaction solution was obtained by mechanical stirring; In the reaction solution; the reaction solution is subjected to spray pyrolysis to obtain the precursor. The obtained precursors were heat-treated at 400, 500, 600, 700, 800, 900, 1000, and 1100 degrees Celsius for 10 hours to obtain excess Ni-doped LNCMO cathode materials.

Electrode preparation and battery assembly were the same as in Example 1.

Figure 7 shows the cycle performance curves of the LNCMO cathode material at different heat treatment temperatures. The results show that the heat treatment temperature has a great influence on the cycle stability and cycle capacity of the LNCMO cathode material. At a current density of 20 mA/g, after 40 cycles, the discharge specific capacities of LNCMO cathode materials at different heat treatment temperatures were 69.8, 145.9, 182.2, 212.9, 215.3, 277.4, 214.8, 175.4 mA/g; capacity retention ratio 36.8, 66.9, 77.1, 83.4, 90.6, 96.2, 80.4, 83.3%, respectively. The results show that the LNCMO cathode material obtained by heat treatment at 900 degrees Celsius has the highest cycle capacity.

Figure 8 shows the midpoint voltage decay curves during cycling of LNCMO cathode materials at different heat treatment temperatures at a current density of 20 mA/g. It can be seen from the curves that the midpoint voltage gradually shifts to lower potentials as the cycle progresses. The midpoint voltages of the first discharge of LNCMO cathode materials at different heat treatment temperatures are: 3.20, 3.41, 3.57, 3.58, 3.62, 3.66, 3.64, and 3.49 volts; after 40 cycles, the midpoint voltage retention rates are: 76.8, 76.9, 74.7, 77.6, 80.2, 78.6, 78.0, 90.8%. It can be seen from the data results that from 400 degrees Celsius to 900 degrees Celsius, the midpoint potential of the LNCMO cathode material increases with the increase of temperature as a whole; at 1000 degrees Celsius and 1100 degrees Celsius, the decrease in the midpoint potential is due to the LiM in the LNCMO cathode material. ₂ O ₄ spinel phase is formed.

Example 5

Excess Ni doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material was prepared by spray pyrolysis.

Li, Ni, Co, Mn acetates were added to a certain amount of deionized water according to the stoichiometric ratio, and a uniform reaction solution was obtained by mechanical stirring; adding to the reaction solution; spray pyrolysis of the reaction solution to obtain a precursor. The obtained precursor was heat-treated in an oxygen atmosphere at 900 degrees Celsius for 10 hours to obtain an excess Ni-doped LNCMO cathode material.

Electrode preparation and battery assembly were the same as in Example 1.

Figure 9 shows that increasing the Ni content can improve the discharge midpoint voltage of the LNCMO cathode material, and can suppress the voltage decay during cycling of the LNCMO cathode material.

Example 6

Excess Ni doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material was prepared by spray pyrolysis.

Li, Ni, Co, Mn acetates were added to a certain amount of deionized water according to the stoichiometric ratio, and a uniform reaction solution was obtained by mechanical stirring; adding to the reaction solution; spray pyrolysis of the reaction solution to obtain a precursor. The obtained precursor was heat-treated in an air atmosphere at 900 degrees Celsius for 48 hours to obtain an LNCMO cathode material doped with excess Ni element.

Electrode preparation and battery assembly were the same as in Example 1.

Figure 10 shows that increasing the Ni content can improve the discharge midpoint voltage of the LNCMO cathode material, and can suppress the voltage decay during cycling of the LNCMO cathode material.

Example 7

Ni element doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material was prepared by sol-gel method.

Li, Ni, Co, Mn acetates were added to a certain amount of ethanol solution according to the stoichiometric ratio, and then the nickel acetate was added to the reaction solution according to the molar percentage (6mol%) of Ni element added to the reaction solution. , magnetic stirring until a sol is formed, and then drying at 120 degrees Celsius for 12 hours to obtain a gel precursor. The obtained precursor was heat-treated at 900 degrees Celsius for 10 hours to obtain the LNCMO cathode material doped with excess Ni element.

The preparation of electrodes and the assembly of batteries were the same as in Example 1.

Figure 11 shows the mid-point voltage decay curve during cycling of LNCMO prepared by sol-gel method and 6% Ni doped cathode material at a current density of 20 mA/g. It can be seen from the results that excess Ni doping can effectively suppress the voltage decay during cycling of the LNMCO cathode material.

Example 8

Excess Ni doped 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material was prepared by co-precipitation method.

Li, Ni, Co, Mn acetates were added to a certain amount of deionized aqueous solution according to the stoichiometric ratio, and then the lithium acetate and nickel acetate were added to the reaction according to the molar percentage (6mol%) of Ni element respectively. The solution was added to the reaction solution, the pH value was adjusted to 10 with ammonia water, mechanically stirred for 10 hours until the reactant was precipitated, then the reaction solution was removed by suction filtration, and the product was dried at 120 degrees Celsius for 12 hours to obtain the precursor. The obtained precursors were heat-treated at 900 degrees Celsius for 10 hours to obtain LNCMO cathode materials doped with different Ni elements.

The preparation of electrodes and the assembly of batteries were the same as in Example 1.

Figure 12 shows the mid-point voltage decay curve during cycling of LNCMO prepared by co-precipitation method and 6% Ni-doped cathode material at a current density of 20 mA/g. It can be seen from the results that excess Ni doping can effectively suppress the voltage decay during cycling of the LNMCO cathode material.

Example 9

According to the preparation method in Example 1, a 6% Ni-doped LNCMO positive electrode material was prepared.

The LNCMO@Er2O3 cathode material and the binder were mixed in a certain proportion, and a uniform slurry was obtained by magnetic stirring for 4 hours, and then the slurry was uniformly coated on the aluminum foil to obtain the electrode material. The characterization battery adopts the 18650 battery, and the assembly process is completed in a glove box filled with Ar, and the water and oxygen contents are both less than 0.1 ppm. The positive electrode is the prepared electrode sheet; the reference electrode and the counter electrode are graphite sheets; the diaphragm is Celgard-2400; the electrolyte is LiPF6 (1mol/L)/EC+DEC+EMC (1:1:1), the assembled The battery is placed to be tested.

As shown in Fig. 13, the full battery with 6% Ni-doped LNCMO cathode material and graphite as the anode has a first discharge capacity of 2295 mAh, and the capacity retention rate after 300 cycles is 92.9%. The full battery with unmodified LNCMO as the positive electrode and graphite as the negative electrode has a first discharge capacity of 2543 mAh, and the capacity retention rate after 300 cycles is only 76.6%. The more significant results are the 6% Ni-doped LNCMO cathode material, the full cell with graphite as the anode has a midpoint potential of 3.63 volts for the first discharge and 3.46 volts after 300 cycles, with a midpoint potential retention rate of 95.3%. . However, the unmodified full cell had a midpoint potential of only 3.50 volts for the first discharge and 2.98 volts after 300 cycles, and the midpoint potential retention was only 85.1%.

The above results fully demonstrate that the doping modification of LNCMO cathode material with excess Ni element can effectively suppress the capacity/voltage decay during cycling, that is, effectively improve the energy density of the battery.

The preferred embodiments of the present invention have been described above in detail, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, a variety of simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed in the present invention. All belong to the protection scope of the present invention.

Claims (10)

1. a preparation method of layered lithium-rich manganese oxide positive electrode material, is characterized in that, the method comprises the following steps: in lithium ion battery layered lithium-rich manganese oxide positive electrode material precursor preparation process, adding modified material The raw material precursor is then heat treated at high temperature to obtain a layered lithium-rich manganese oxide cathode material. 2 . The preparation method according to claim 1 , wherein the layered lithium-rich manganese oxide cathode material is xLi ₂ MnO ₃ -(1-x)LiMO ₂ , wherein M is selected from Ni, Co, At least one of Mn, Cr and Fe; 0≤x≤1, preferably, 0.1≤x≤0.8. 3. The preparation method according to claim 1, wherein the modified material of the layered lithium-rich manganese oxide positive electrode material is metal Ni; Preferably, the raw material precursor of the modified material is added in an amount such that the molar ratio of the doping amount of metallic nickel to the layered lithium-rich manganese oxide cathode material is 0.01-0.1, preferably 0.01-0.06. 4. preparation method according to claim 1, is characterized in that, the preparation method of described precursor is selected from spraying method, co-precipitation method, sol-gel method, combustion method, solid phase method and molten salt method. at least one; Preferably, the atmosphere of the high temperature heat treatment is at least one of oxygen, air and vacuum; the temperature of the heat treatment is 400-1400°C; and the time of the heat treatment is 0.5-72 hours. 5. The preparation method according to claim 1, wherein the raw materials used in the layered lithium-rich manganese oxide positive electrode material precursor and the raw material precursor of the modified material are independently selected from acetic acid At least one of salts, nitrates, sulfates, carbonates, oxalates, and metal oxides. 6 . The layered lithium-rich manganese oxide cathode material prepared by the method of any one of claims 1 to 5 . 7. a lithium ion battery positive electrode, is characterized in that: adopt the described positive electrode material of claim 6 as positive electrode material, and carry out ball milling after mixing with conductive agent, obtain mixture, then mixture and binder are mixed to form slurry material, smear the slurry on the aluminum foil, and dry to obtain the positive electrode of the lithium ion battery. 8. The lithium ion battery positive electrode according to claim 7, wherein the conductive agent is selected from at least one of graphite, acetylene black, Super P, carbon nanotubes, graphene and Kexing black; Based on the total weight of the slurry, the content of the conductive agent is 2wt% to 30wt%; Preferably, the binder is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, styrene-butadiene rubber, sodium carboxymethyl cellulose and sodium alginate; Based on the total weight of the slurry, the amount of the binder is 1wt% to 30wt%. 9 . The lithium ion battery positive electrode according to claim 7 , wherein, during the ball milling, the mass ratio of the ball material is 5:1 to 300:1; the ball milling speed is 100 rpm to 800 rpm; 9 . The ball milling time is 0.5 hour to 48 hours; the ball milling atmosphere is selected from at least one of air, oxygen, nitrogen, hydrogen, argon, carbon dioxide and helium. 10. A lithium ion battery, characterized in that: the lithium ion battery comprises a positive electrode, a negative electrode that can deintercalate lithium ions, and an electrolyte between the negative electrode and the positive electrode, wherein the positive electrode is the one according to claim 7- The lithium ion battery positive electrode of any one of 9.

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