CN107293707A - Rich lithium manganese anode material of a kind of stratiform and its preparation method and application - Google Patents

Abstract

The invention relates to the field of positive electrode materials for lithium ion batteries, in particular to a layered lithium-rich manganese positive electrode material and a preparation method and application thereof. A layered lithium-rich manganese positive electrode material, the structural formula of the lithium-rich manganese positive electrode material is as follows: xLi ₂ MnO ₃ ‑(1‑x)LiMO ₂ M=one or more of Ni, Co, Mn, Cr, Fe , 0≤x≤1; it uses Mg ²⁺ ions to replace part of Li ⁺ in the lithium layer of the lithium-rich manganese cathode material. In the present invention, the method of replacing part of Li ⁺ with Mg ²⁺ ions can effectively improve the energy density and cycle life of the layered lithium-rich manganese cathode material, and further promote the industrialization of the layered lithium-rich manganese cathode material.

Description

A kind of layered lithium-rich manganese cathode material and its preparation method and application

technical field

The invention relates to the field of positive electrode materials for lithium ion batteries, in particular to a layered lithium-rich manganese positive electrode material and a preparation method and application thereof.

Background technique

With the increasing demand for energy and the deepening understanding of the importance of sustainable social and economic development, lithium-ion batteries characterized by high energy efficiency and environmental protection have attracted more and more attention. Applications such as new energy storage, electric vehicles, and smart grids have put forward higher requirements on the energy density, cycle life, power density, safety, cost, and environmental friendliness of lithium-ion batteries. At present, the specific capacity of layered oxide cathode materials such as LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , etc., is always limited within 150 mAh/g. The theoretical specific capacity of the spinel structure LiMn ₂ O ₄ cathode material and the polyanionic LiFePO ₄ cathode material are only 148 mAh/g and 170 mAh/g respectively, and the actual capacity is even lower, which is far from meeting the requirements of high specific capacity. Energy density lithium-ion battery performance requirements for cathode materials. Therefore, the positive electrode material has become the bottleneck for the further improvement of the performance of lithium-ion batteries. The layered lithium-rich manganese oxide cathode material has attracted the attention of scientists due to its unique advantages:

(a) High discharge capacity: the first discharge specific capacity at room temperature is greater than 280 mAh/g, far greater than 140 mAh/g of LiCoO ₂ and 150 mAh/g of LiFePO ₄ ;

(b) The average voltage is moderate: the average discharge voltage is 3.6 volts, and the voltage is within the safe voltage range of the current organic electrolyte (electrolyte safe voltage window is 0~5 volts);

(c) High mass-to-energy density: its energy density is greater than 1000 Wh/kg;

(d) Low cost: The Mn element in the layered lithium-rich manganese oxide has replaced a large number of expensive metal elements such as Co and Ni in the ternary material, which greatly reduces the cost of the material.

(e) The synthesis and electrode preparation process is simple: the layered lithium-rich manganese oxide cathode material can be synthesized by simple solid-phase ball milling method, liquid-phase co-precipitation method, spray pyrolysis method and other methods suitable for large-scale production, and Its heat treatment process is simple, it only needs heat treatment at 800-900 degrees Celsius in the air, and it does not need atmosphere protection like LiFePO ₄ . There is no need to consider the oxidation of the active material during the preparation of the pole piece, so that the unpredictability factor in the preparation process of the pole piece is greatly reduced.

However, the practical applications of layered lithium-rich manganese oxide cathode materials are severely restricted due to poor cycle stability, poor rate performance, and low initial Coulombic efficiency. The migration and structural rearrangement of transition metal (TM) ions during the cycling of layered lithium-rich manganese oxide cathode materials lead to the formation of spinel structures, which is the root cause of their capacity/voltage decay. It has been reported that ion doping/substitution methods can generally be used to improve the structural stability of layered lithium-rich manganese oxide cathode materials, suppress their phase transition during charge and discharge, and thus suppress their capacity/voltage decay. At present, the commonly used method is to use Mg ²⁺ , Al ³⁺ , Fe ³⁺ plasma to replace the layered lithium-rich manganese oxide cathode material xLi ₂ MnO ₃ -(1-x)LiMO ₂ (M=Ni, Co,Mn, Cr, Fe) transition metal elements. However, the replacement of transition metal elements by these inactive ions will reduce the electrochemically active components in electrode materials, thereby reducing their electrochemical capacity. In addition, since these ions replace the transition metal elements in the transition metal layer of layered Li-rich manganese, they cannot effectively inhibit the migration of transition metal elements to the Li layer during cycling. The approach of transition metal elements in oxides has very limited effect on suppressing their capacity/voltage fading during cycling.

Contents of the invention

An object of the present invention is to provide a layered lithium-rich manganese cathode material, which uses Mg ²⁺ ions to replace part of Li ⁺ , which can effectively improve the energy density and cycle life of the layered lithium-rich manganese cathode material. 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 achieve the above-mentioned first purpose, the present invention adopts the following technical solutions:

A layered lithium-rich manganese positive electrode material, the structural formula of the lithium-rich manganese positive electrode material is as follows:

xLi ₂ MnO ₃ -(1-x)LiMO ₂

M=one or more of Ni, Co, Mn, Cr, Fe, 0≤x≤1;

It is characterized in that part of Li ⁺ in the lithium layer of the lithium-rich manganese cathode material is replaced by Mg ²⁺ ions.

If x is too small or too large, the comprehensive electrochemical performance of the lithium-rich material will be reduced. Preferably, 0.1≤x≤0.8. Therefore, it is more reasonable to select 0.1≤x≤0.8 for x.

If the amount of substitution is too small, the modification effect will not be achieved; if the amount of substitution is too large, the structure of the original material will be affected, thereby affecting its electrochemical performance. Preferably, the molar percentage of Mg ²⁺ replacing Li ⁺ is 0.1%~30%; as more preferably, the molar percentage of Mg ²⁺ replacing Li ⁺ is the molar percentage of Mg ²⁺ replacing Li ⁺ The percentage is 0.5% to 20%; as a further preference, the molar percentage of ^{Mg 2+ replacing} Li ⁺ is ¹ % to 10%.

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

A method for preparing the layered lithium-rich manganese positive electrode material. In the preparation process of the precursor of the layered lithium-rich manganese oxide positive electrode material, a raw material precursor containing Mg element is added, and then the layered lithium-rich manganese is obtained by high-temperature heat treatment Oxide cathode material.

Preferably, the precursor preparation method used is spray method, co-precipitation method, sol-gel method, combustion method, solid phase method or molten salt method. The phase structure, composition distribution, morphology, and particle size of the materials obtained by different synthesis methods are different, which have an important impact on various properties of electrode materials.

As preferably, the raw material that precursor adopts is acetate, nitrate, sulfate, carbonate, oxalate or metal oxide; As more preferably, the precursor of preparation is carried out heat treatment; As more preferably, heat treatment atmosphere Oxygen, air, vacuum; the heat treatment temperature used is 400-1400 degrees Celsius; the heat treatment time is 0.5-7 hours. The phase structure, composition distribution, morphology, and particle size of the materials obtained by different heat treatment temperatures, atmospheres, and times are different, which have an important impact on various properties of electrode materials.

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

A lithium-ion battery positive electrode, using the layered lithium-rich manganese positive electrode material as the positive electrode material and conductive agent ball milling mixture, and then mixed with a binder to form a slurry, the slurry is applied on the aluminum foil, after drying, Obtain the positive electrode of the lithium ion battery.

As preferably, the conductive agent includes graphite, acetylene black, Super P, carbon nanotubes, graphene, Cotton black, and one or more mixed conductive agents of various carbon materials, and the content of the conductive agent is The mass percentage is 2%~30%; as a preference, the binder includes one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, styrene-butadiene rubber, sodium carboxymethyl cellulose and sodium alginate One or more mixed binders, the mass percentage of the binder is 1%~30%.

Preferably, the ball-to-material ratio is a mass ratio of 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: air, oxygen, nitrogen, One or a mixture of two or more of hydrogen, argon, carbon dioxide, and helium.

In order to achieve the above-mentioned fourth purpose, the present invention adopts the following technical solutions:

A lithium ion battery is composed of the positive electrode, the negative electrode capable of deintercalating lithium ions, and the electrolyte between the negative electrode and the positive electrode.

In the lithium ion battery of the present invention, the negative electrode material can adopt 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, Negative electrode materials such as titanium oxide. 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 (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), One or several kinds of lithium fluorohydroxysulfonate (LiC(SO ₂ CF ₃ ) ₃ ). Non-aqueous solvents 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.

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

1) The main innovation point of the present invention is to use Mg ²⁺ ions to replace the layered lithium-rich manganese positive electrode material xLi ₂ by utilizing the characteristics that Mg ²⁺ ions have similar ionic radii to Li ⁺ ions, and Mg ²⁺ ions can occupy the position of Li ⁺ ions Part of Li ⁺ in MnO ₃ -(1-x)LiMO ₂ (M=Ni, Co, Mn, Cr, Fe) lithium layer. For the traditional method of replacing transition metal elements with metal ions such as Mg ²⁺ , Al ³⁺ , Fe ³⁺ , since the ion substitution position is the position of the transition metal element in the transition metal layer, it cannot effectively suppress the transition metal element during the cycle. The migration of elements to the lithium layer, so its role in inhibiting the capacity/voltage decay of layered lithium-rich manganese cathode materials during cycling is limited. In comparison, in the present invention, since Mg ²⁺ ions occupy part of Li ⁺ in the lithium layer, Mg ²⁺ ions can effectively inhibit the transfer of transition metal ions to the lithium layer during the cycle of the layered lithium-rich manganese oxide cathode material. Migration, inhibiting the formation of spinel phase, thereby effectively inhibiting its capacity/voltage decay during cycling;

2) Part of Li ⁺ replaced by Mg ²⁺ ions can also increase the Li ₂ MO ₃ phase content in the layered lithium-rich manganese cathode material, thereby improving its electrochemical capacity;

3) The modification method of the present invention has the advantages of simplicity, effectiveness, quickness, low cost, strong controllability, and wide application range.

Description of drawings

Fig. 1 is the XRD and TEM pattern contrast of the product of embodiment 1 of the present invention;

Fig. 2 is (a) first charge and discharge curve, (b) cycle performance curve, (c) midpoint voltage decay curve, (d) capacity retention rate and midpoint voltage retention curve of the product of Example 1 of the present invention;

Fig. 3 is the rate performance curve of the product of Example 1 of the present invention;

Fig. 4 is (a) first charge and discharge curve, (b) cycle performance curve, (c) midpoint voltage decay curve, (d) capacity retention rate and midpoint voltage retention curve of the product of Example 2 of the present invention;

Fig. 5 is the XRD pattern contrast of the product of embodiment 3 of the present invention;

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

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;

Figure 9 is the (a) cycle performance curve and (b) midpoint voltage decay curve of the product of Example 5 of the present invention;

Figure 10 is the (a) cycle performance curve and (b) midpoint voltage decay curve of the product of Example 6 of the present invention;

Figure 11 is the (a) cycle performance curve and (b) midpoint voltage decay curve of the product of Example 7 of the present invention;

Figure 12 is the (a) cycle performance curve and (b) midpoint voltage decay curve of the product of Example 8 of the present invention;

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

Fig. 14 is the midpoint voltage decay curve of the product of Example 9 of the present invention.

detailed description

The following examples can better understand the present invention, but the invention is not limited to the following examples.

Example 1

Preparation of Mg ²⁺ Substitute 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) Cathode Material by Spray Pyrolysis

Add Li, Ni, Co, Mn acetate into a certain amount of deionized water according to the ^{stoichiometric} ratio, and use mechanical stirring to obtain a uniform reaction solution; , 8 mol %) magnesium acetate was added to the reaction solution; the reaction solution was subjected to spray pyrolysis to obtain the precursor. The resulting precursor was heat-treated at 900°C for 10 hours to obtain 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ cathode materials substituted by Mg ²⁺ , which were marked as Mg0, Mg2, Mg4, and Mg8, respectively.

Mix Mg0, Mg2, Mg4, Mg8 positive electrode materials and binders in a certain proportion, and use magnetic stirring for 4 hours to obtain a uniform slurry, and then evenly coat the slurry on aluminum foil to obtain electrode materials. The characterization battery uses a 2025 button battery, and the assembly process is completed in a glove box filled with Ar, and the water and oxygen content are 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 LiPF ₆ (1mol/L)/EC+DEC+EMC (1:1:1), assembled The completed battery is placed for testing.

Figure 1(a) shows the XRD patterns of Mg0, Mg2, Mg4, Mg8 electrode materials. As shown in Figure 1, all the diffraction peaks can be compared 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) correspond well. Among them, the diffraction peak between 20 and 25º (2θ) is the characteristic peak of Li ₂ MO ₃ phase, which is 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. In addition, it can be seen from Figure 1(b) that as the amount of Mg ²⁺ substitution increases, the (002) _M characteristic peak of the C/2m phase in the XRD of LNCMO cathode materials gradually increases, which indicates that Mg ²⁺ substitution can increase Li ₂ MO ₃ (M=Ni, Co, Mn, etc.) (C/2m) content. Figure 1(c,e) are HRTEM of Mg0 and Mg4 samples. It can be seen that both Mg0 and Mg4 samples are composite structures dominated by nanoscale interactions between LiMO ₂ (R-3m) phase and Li ₂ MO ₃ (C2/m) phase. The Fourier transform of HRTEM (Fig. 1(d, f)) shows that there are two sets of diffraction spots corresponding to LiMO ₂ (R-3m) phase and Li ₂ MO ₃ (C2/ m) phase, further confirming that the Mg0 and Mg4 samples are both LiMO ₂ (R-3m) phase and Li ₂ MO ₃ (C2/m) phase nanoscale interaction dominated composite structure.

Figure 2(a) shows the initial charge-discharge curves of Mg0, Mg2, Mg4 and Mg8 electrodes at a current density of 20 mA/g. The results showed that the first discharge specific capacities of Mg0, Mg2, Mg4 and Mg8 electrodes were 293, 297, 315, 310 mAh/g, respectively. The results show that the replacement of Mg ²⁺ ions can effectively improve the discharge specific capacity of LNCMO cathode materials, among which, ⁴ % Mg ²⁺ ion replacement has the highest discharge specific capacity. Mg ²⁺ ion substitution improves the discharge specific capacity of LNCMO cathode materials, mainly because Mg ²⁺ substitution increases the content of Li ₂ MO ₃ phase.

Figure 2(b) shows the cycle performance curves of Mg0, Mg2, Mg4 and Mg8 electrodes at a current density of 200 mA/g. It can be seen from the figure that the cycle capacity of the sample replaced by Mg ²⁺ ions is higher than that of the original sample, and the sample replaced by 4% Mg ²⁺ has the highest cycle capacity. At the same time, the cycle curve also shows that as the cycle progresses, the cycle capacity of the LNCMO cathode material gradually decays. The main reason for its decay may be due to the voltage decay during cycling. Figure 2(c) shows that the discharge midpoint voltages of Mg0, Mg2, Mg4 and Mg8 electrodes gradually decay as the cycle progresses. However, it is also obvious from the figure that the substitution of Mg ²⁺ ions can effectively suppress the electrode material voltage. The attenuation of , and its inhibitory effect increases with the replacement of Mg ²⁺ ions. As shown in Figure 2(d), after 500 cycles, the capacity retention ratios of Mg0, Mg2, Mg4 and Mg8 electrodes are: 81.7, 86.8, 91.2, 86.5%, respectively; the discharge midpoint voltage retention ratios are: 77.5, 80.2%, respectively. , 85.3, 89.1%. It can be seen that the substitution of Mg ²⁺ ions can effectively suppress the capacity/voltage decay of LNCMO cathode materials during cycling, thereby improving their cycle stability.

Figure 3 is the rate performance curves of Mg0, Mg2, Mg4, and Mg8. As shown in the figure, the LNCMO (Mg4) electrode material replaced by 4% Mg ²⁺ ions has the highest rate capacity. Under the high rate condition of 10 C, the discharge specific capacity of the Mg4 electrode is 172 mAh/g; Under the same conditions, the discharge specific capacity of the unsubstituted modified electrode Mg0 is 131 mAh/g. The results indicate that Mg ²⁺ ion substitution can improve the high-rate performance of LNCMO cathode materials.

Example 2

Mg ²⁺ Substitution of 0.7Li ₂ MnO ₃ -0.3LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO-1) Cathode Material Prepared by Spray Pyrolysis

Add Li, Ni, Co, Mn acetate into a certain amount of deionized water according to the ^{stoichiometric} ratio, and use mechanical stirring to obtain a uniform reaction solution; , 8 mol %) magnesium acetate was added to the reaction solution; the reaction solution was subjected to spray pyrolysis to obtain the precursor. The resulting precursors were heat-treated at 900°C for 10 hours to obtain 0.7Li ₂ MnO ₃ -0.3LiNi _0.33 Co _0.33 Mn _0.33 O ₂ cathode materials substituted by Mg ²⁺ , respectively marked as Mg0-1, Mg2-1, Mg4- 1, Mg8-1.

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

Figure 4(a) shows the first charge and discharge curves of Mg0-1, Mg2-1, Mg4-1 and Mg8-1 electrodes at a current density of 200 mA/g. It can be seen from the figure that the cycle capacity of the sample replaced by Mg ²⁺ ions is higher than that of the original sample, among which, the sample replaced by 4% Mg ²⁺ has the highest cycle capacity. The cycle curve in Figure 4(b) also shows that the cycle capacity of the LNCMO cathode material gradually decays as the cycle progresses. The main reason for its decay may be due to the voltage decay during cycling. As shown in Figure 4(c), as the cycle progresses, the discharge midpoint voltages of Mg0-1, Mg2-1, Mg4-1 and ^Mg8-1 electrodes gradually decay. Ion substitution can effectively suppress the voltage decay of electrode materials, and its suppression effect increases with the increase of the substitution amount of Mg ²⁺ ions. As shown in Figure 4(d), after 400 cycles, the capacity retention rates of Mg0-1, Mg2-1, Mg4-1 and Mg8-1 electrodes are: 78, 80, 87, 83%, respectively; the discharge midpoint voltage Retention rates are: 79, 80, 84, 86%. It can be seen that the substitution of Mg ²⁺ ions can effectively suppress the voltage decay of the LNCMO cathode material during cycling, thereby inhibiting its capacity decay and improving its cycle stability.

Example 3

Spray pyrolysis method to prepare Mg ²⁺ instead of 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material-nitrate

Add Li, Ni, Co, Mn nitrate into a certain amount of deionized water according to the ^{stoichiometric} ratio, and use mechanical stirring to obtain a uniform reaction solution; 8 mol %) magnesium nitrate was added to the reaction solution; the reaction solution was subjected to spray pyrolysis to obtain the precursor. The resulting precursor was heat-treated at 900°C for 10 hours to obtain 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ cathode materials substituted by Mg ²⁺ , which were marked as Mg0-2, Mg2-3, Mg4- 2, Mg8-2.

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

Figure 5 shows the XRD patterns of Mg0-2, Mg2-2, Mg4-2, Mg8-2 electrode materials. As shown in the figure, all the diffraction peaks can be compared 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) correspond well. Among them, the diffraction peak between 20 and 25º (2θ) is the characteristic peak of Li ₂ MO ₃ phase, which is 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. In addition, it can be seen from the figure that with the increase of Mg ²⁺ substitution, the (002) _M characteristic peak of the C/2m phase in the XRD of the LNCMO cathode material gradually increases, which indicates that Mg ²⁺ substitution can improve Li ₂ MO ₃ (M=Ni, Co, Mn, etc.) (C/2m) content.

Figure 6(a) shows the cycle performance curves of Mg0-2, Mg2-2, Mg4-2, and Mg8-2 electrode materials. Increasing the amount of Mg ²⁺ substitution can improve the cycle performance of LNCMO cathode materials. Figure 6(b) shows that increasing the amount of Mg ²⁺ substitution can suppress the voltage decay during cycling of LNCMO cathode materials.

Example 4

Mg ²⁺ substituted 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode materials prepared by spray pyrolysis-different heat treatment temperatures

By stoichiometric ratio, Li, Ni, Co, Mn acetate are added to a certain amount of ^deionized water, and mechanical stirring is used to obtain a uniform reaction solution; added into the reaction solution; the reaction solution is sprayed and pyrolyzed 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 Mg ²⁺ substituted LNCMO cathode materials.

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

Figure 7 shows the cycle performance curves of LNCMO cathode materials replaced by Mg ²⁺ 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 LNCMO cathode materials. At a current density of 20 mA/g, after 40 cycles, the discharge specific capacities of LNCMO cathode materials replaced by Mg ²⁺ at different heat treatment temperatures were 70.8, 142.9, 183.2, 213.1, 215.3, 278.4, 218.1, 172.7 mAh/ grams; after 40 cycles, the capacity retention rates were 35.9, 67.8, 79.9, 83.4, 90.0, 92.1, 81.4, 83.8%. The results show that the Mg ²⁺ substituted LNCMO cathode material obtained by heat treatment at 900 °C has the highest cycle capacity.

Fig. 8 is the midpoint voltage decay curve during the cycling process of the LNCMO cathode material replaced by Mg ²⁺ at different heat treatment temperatures at a current density of 20 mA/g. It can be seen from the curve that as the cycle progresses, the midpoint voltage gradually shifts to a low potential. The first discharge midpoint voltages of LNCMO cathode materials replaced by Mg ²⁺ at different heat treatment temperatures are: 3.21, 3.43, 3.52, 3.56, 3.64, 3.65, 3.66, 3.47 volts; after 40 cycles, the midpoint voltage retention rates are : 76.2, 76.7, 73.7, 77.6, 81.2, 79.0, 78.0, 91.1%. From the data results, it can be seen that from 400 degrees Celsius to 900 degrees Celsius, the midpoint potential of the LNCMO cathode material replaced by Mg ²⁺ increases with the increase of temperature as a whole; at 1000 degrees Celsius and 1100 degrees Celsius, the midpoint potential decreases because It is caused by the formation of LiM ₂ O ₄ spinel phase in the LNCMO cathode material.

Example 5

Preparation of Mg ²⁺ Substitute 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) Cathode Material by Spray Pyrolysis

Add Li, Ni, Co, Mn acetate into a certain amount of deionized water according to the ^{stoichiometric} ratio, and use mechanical stirring to obtain a uniform reaction solution; adding magnesium acetate into the reaction solution; performing spray pyrolysis on the reaction solution to obtain a precursor. The obtained precursors were heat-treated in an oxygen atmosphere at 900 degrees Celsius for 10 hours to obtain Mg ²⁺ substituted LNCMO cathode materials, which were marked as Mg0-3 and Mg4-3, respectively.

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

Figure 9 (a, b) is the cycle performance curve and midpoint voltage decay curve of Mg0-3 and Mg4-3 cathode materials at a current density of 20 mA/g, respectively. It can be seen from the results that Mg ²⁺ substitution can not only improve the electrochemical capacity of layered lithium-rich manganese cathode materials, but also effectively inhibit the capacity/voltage decay of LNMCO cathode materials during cycling.

Example 6

Preparation of Mg ²⁺ Substitute 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) Cathode Material by Spray Pyrolysis

Add Li, Ni, Co, Mn acetate into a certain amount of deionized water according to the ^{stoichiometric} ratio, and use mechanical stirring to obtain a uniform reaction solution; ) adding magnesium acetate to the reaction solution; performing spray pyrolysis on the reaction solution to obtain a precursor. The obtained precursors were heat-treated in an air atmosphere at 900 degrees Celsius for 48 hours to obtain Mg ²⁺ substituted LNCMO cathode materials, which were marked as Mg0-4 and Mg4-4, respectively.

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

Figure 10 (a, b) are the cycle performance curves and midpoint voltage decay curves of Mg0-4 and Mg4-4 cathode materials at a current density of 20 mA/g, respectively. It can be seen from the results that Mg ²⁺ substitution can not only improve the electrochemical capacity of layered lithium-rich manganese cathode materials, but also effectively inhibit the capacity/voltage decay of LNMCO cathode materials during cycling.

Example 7

Preparation of Mg ²⁺ substituted 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material by sol-gel method

Add Li, Ni, Co, Mn acetate to a certain amount of ethanol solution according to the stoichiometric ratio, and then add magnesium acetate to the reaction solution according to the molar percentage of Mg ²⁺ substitution (0, 4 mol %); Stir magnetically until a sol is formed, and then dry at 120°C for 12 hours to obtain a gel precursor. The resulting precursors were heat-treated at 900 °C for 10 hours to obtain LNCMO cathode materials with different Mg ²⁺ substitutions, which were labeled as Mg0-5 and Mg4-5, respectively.

The preparation of the electrode and the assembly of the battery are the same as in Example 1.

Figure 11(a, b) are the cycle performance curves and midpoint voltage decay curves of Mg0-5 and Mg4-5 cathode materials prepared by the sol-gel method at a current density of 20 mA/g, respectively. It can be seen from the results that Mg ²⁺ substitution can not only improve the electrochemical capacity of layered lithium-rich manganese cathode materials, but also effectively inhibit the capacity/voltage decay of LNMCO cathode materials during cycling.

Example 8

Co-precipitation method to prepare Mg ²⁺ instead of 0.5Li ₂ MnO ₃ -0.5LiNi _0.33 Co _0.33 Mn _0.33 O ₂ (LNCMO) cathode material

Add Li, Ni, Co, Mn acetate to a certain amount of deionized aqueous solution according to the stoichiometric ratio, and then add magnesium acetate to the reaction solution according to the molar percentage of Mg ²⁺ substitution (0, 4 mol %) Middle: adjust the pH value to 10 with ammonia water, stir mechanically for 10 hours until the reactant precipitates, then remove the reaction solution by suction filtration, and dry the product at 120 degrees Celsius for 12 hours to obtain a precursor. The resulting precursors were heat-treated at 900°C for 10 hours to obtain LNCMO cathode materials with different Mg ²⁺ substitutions, which were labeled as Mg0-6 and Mg4-6, respectively.

The preparation of the electrode and the assembly of the battery are the same as in Example 1.

Figure 12 (a, b) are the cycle performance curves and midpoint voltage decay curves of the Mg0-6 and Mg4-6 cathode materials prepared by the co-precipitation method at a current density of 20 mA/g. It can be seen from the results that Mg ²⁺ substitution can not only improve the electrochemical capacity of layered lithium-rich manganese cathode materials, but also effectively inhibit the capacity/voltage decay of LNMCO cathode materials during cycling.

Example 9 full battery

Mg0 and Mg4 prepared by the preparation method in Example 1 are positive electrode materials.

The Mg0 and Mg4 positive electrode materials were mixed with the binder in a certain proportion, and magnetically stirred for 4 hours to obtain a uniform slurry, and then the slurry was uniformly coated on an aluminum foil to obtain an electrode material. The characterization battery uses a 18650 battery. The assembly process is completed in a glove box filled with Ar, and the water and oxygen contents are 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 LiPF ₆ (1mol/L)/EC+DEC+EMC (1:1:1), assembled The battery is placed for testing.

As shown in Figure 13, the first discharge capacity of the full battery with Mg4 as the positive electrode material and graphite as the negative electrode is as high as 2440 mAh, and the capacity retention rate after 300 cycles is 87%. The full battery with Mg0 as the positive electrode and graphite as the negative electrode has a discharge capacity of only 2210 mAh for the first time, and the capacity retention rate after 300 cycles is only 82%. As shown in Figure 14, the more remarkable result is that the full battery with Mg4 as the positive electrode material and graphite as the negative electrode has a midpoint potential of 3.49 volts for the first discharge, and 2.94 volts after 300 cycles, and the midpoint potential retention rate is 84. %. However, the midpoint potential of the unmodified full battery was only 3.42 V at the first discharge and 2.62 V after 300 cycles, and the midpoint potential retention rate was only 76%. The above results fully demonstrate that the replacement modification of LNCMO cathode materials by Mg ²⁺ can effectively improve its cycle capacity, and can also inhibit the capacity/voltage decay during the cycle process, that is, effectively improve the energy density of the battery.

Claims (10)

1. a kind of rich lithium manganese anode material of stratiform, the structural formula of the rich lithium manganese anode material is as follows：

xLi₂MnO₃-(1-x)LiMO₂

One or more in M=Ni, Co, Mn, Cr, Fe, 0≤x≤1；

It is characterized in that：Using Mg²⁺Part Li in ion substitution richness lithium manganese anode material lithium layer⁺。

2. the rich lithium manganese anode material of a kind of stratiform according to claim 1, it is characterised in that：0.1≤x≤0.8.

3. the rich lithium manganese anode material of a kind of stratiform according to claim 1 or 2, it is characterised in that：Its described Mg²⁺Substitute Li⁺Molar percentage is 0.1% ~ 30%；Preferably, its described Mg²⁺Substitute Li⁺Molar percentage is its described Mg²⁺Replace For Li⁺Molar percentage is 0.5% ~ 20%；As further preferably, its described Mg²⁺Substitute Li⁺Molar percentage is its described Mg^{2 +}Substitute Li⁺Molar percentage is 1% ~ 10%.

4. the method that one kind prepares the rich lithium manganese anode material of stratiform described in claim 1 ~ 3 any one claim, it is special Levy and be：In forerunner's production procedure of stratiform richness lithium manganese oxide anode material, the former material material precursor of the element containing Mg is added, Then high-temperature heat treatment obtains the rich lithium manganese oxide anode material of stratiform.

5. method according to claim 4, its feature exists：The forerunner's preparation used is spray-on process, co-precipitation Method, sol-gel process, combustion method, solid phase method or molte-salt synthesis.

6. method according to claim 4, its feature exists：The raw material that presoma is used is acetate, nitrate, sulphur Hydrochlorate, carbonate, oxalates or metal oxide；Preferably, being heat-treated to the presoma of preparation；As further preferably, Heat-treating atmosphere is oxygen, air, vacuum；The heat treatment temperature used is 400 ~ 1400 degree Celsius；Heat treatment time is 0.5 ~ 7 hours.

7. a kind of lithium ion cell positive, it is characterised in that：Using the stratiform described in claim 1 ~ 3 any one claim Then rich lithium manganese anode material is mixed to form slurry with binding agent, slurry is applied as positive electrode and conductive agent ball mill mixing It is put on aluminium foil, after drying, obtains lithium ion cell positive.

8. a kind of lithium ion cell positive according to claim 7, it is characterised in that：Conductive agent include graphite, acetylene black, Super P, CNT, graphene, section's property is black, and mixing conductive agent more than one or both of various carbon materials, Conductive agent content is mass percent 2% ~ 30%；Binding agent includes polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polyacrylonitrile, butylbenzene One or both of rubber, sodium carboxymethylcellulose and sodium alginate binding agent mixed above, the mass percent of binding agent For 1% ~ 30%.

9. a kind of lithium ion cell positive according to claim 7, it is characterised in that described ball grinding method is：Ratio of grinding media to material It is 5 for mass ratio:1~300:1；Rotational speed of ball-mill is 100 revs/min to 800 revs/min；Ball-milling Time is 0.5 hour small to 48 When；Milling atmosphere is：Mixing more than one or both of air, oxygen, nitrogen, hydrogen, argon gas, carbon dioxide, helium Gas.

10. a kind of lithium ion battery, it is characterised in that：Use positive pole described in claim 7, can deintercalate lithium ions negative pole with And the electrolyte composition between the negative pole and positive pole.