A lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure, its preparation method and application

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and discloses a lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure, a preparation method thereof, and an application thereof. The chemical formula of the cathode material is x(Mn3Ni)O7·(1-x)Li 1.2 Mn 0.6 Ni 0.2 O2, where x = 0.0001 to 0.05; it is prepared by uniformly mixing a carbonate precursor of a transition metal and a weak base salt, performing a hydrothermal reaction at 150 to 180 °C, washing and drying, mixing the treated precursor, a lithium compound, and a molten salt, performing a heat treatment at 700 to 1000 °C, cooling with the furnace after the reaction ends, washing with water and drying. The initial Coulombic efficiency of the cathode material is 85.2%, and the discharge specific capacity is as high as 310.7 mAhg ‑1 ; when the current density is 200 mA / g, the capacity retention rate of the cathode material after 200 cycles is higher than 93%, and it can be applied in lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and more specifically, relates to a lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure, a preparation method thereof, and an application thereof. Background Art

[0002] The universality of consumer electronics and the rapid development of electric vehicles require the next generation of lithium-ion batteries to have higher energy density and longer lifespan, both of which are mainly limited by the cathode material. Among typical cathode materials, lithium-rich layered oxides (LLO) have attracted extensive attention due to their extremely high reversible capacity (>250 mAh / g). A large number of studies have shown that the extraordinary capacity of LLO is attributed to the cumulative contribution of the reversible redox processes of cations and anions at high working voltages (>4.6 V). However, in a high-voltage environment, LLO materials are prone to surface interface side reactions with the electrolyte, resulting in irreversible O2 release and surface corrosion. Eventually, this will lead to an irreversible phase transformation from the layered phase to the spinel phase. The structural deterioration starts from the outermost layer of the material and gradually spreads to the interior, eventually causing the structure to collapse. In summary, the above problems will seriously hinder the commercialization process of LLO. Summary of the Invention

[0003] In order to solve the above-mentioned deficiencies and drawbacks in the prior art, the primary object of the present invention is to provide a lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure. The surface of this cathode material has a rock salt phase structure, with high capacity. After 200 cycles, the capacity retention rate of the samples treated with different weak base salts is greater than 93%, showing very excellent voltage and capacity stability, and overcoming the shortcomings of the rapid attenuation of capacity and voltage of the lithium-rich manganese-based layered oxide material.

[0004] Another object of the present invention is to provide a preparation method of the above-mentioned lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure. This method uses a weak base salt for the carbonate precursor of the lithium-rich manganese-based layered oxide material to induce element segregation and promote particle growth, thereby in-situ constructing a rock salt structure on the surface of the sample particles; this rock salt structure has excellent lattice arrangement with the internal structure of the lithium-rich manganese-based oxide cathode material, which helps to improve the surface structure stability, inhibit the interfacial reaction, and continuously improve the electrochemical performance. This method has the advantages of simple process, easy control, and good repeatability.

[0005] Another object of the present invention is to provide an application of the above-mentioned lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] The chemical formula of a lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure is x(Mn3Ni)O7·(1 - x)Li1.2 Mn 0.6 Ni 0.2 O2, where x = 0.0001 - 0.05.

[0008] The preparation method of the lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure includes the following steps:

[0009] S1. Mix the carbonate precursor of the transition metal with the weak base salt, carry out a hydrothermal reaction at 150 - 180 °C, wash and dry after the reaction ends to obtain the precursor treated with the weak base salt;

[0010] S2. Mix the precursor treated with the weak base salt, the lithium compound and the molten salt evenly, carry out a heat treatment at 700 - 1000 °C, cool with the furnace after the reaction ends, wash with water carbonate and dry to obtain the lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure.

[0011] Preferably, in step S1, the weak base salt is 5 - 30 wt% of the carbonate precursor of the transition metal; the carbonate of the transition metal is Mn 0.75 Ni 0.25 CO3; the weak base salt is NH4HCO3, (NH4)2CO3 or (NH4)2SO4.

[0012] Preferably, in step S2, the lithium compound is one or more of lithium carbonate, lithium hydroxide, lithium nitrate or lithium chloride.

[0013] Preferably, in step S2, the molten salt is sodium chloride or potassium chloride; the molar ratio of the carbonate precursor of the transition metal to the lithium compound is 1:(1 - 1.1); the total molar ratio of the carbonate precursor of the transition metal and the lithium compound to the molten salt is 1:(4 - 4.5).

[0014] Preferably, the time of the hydrothermal reaction in step S1 is 8 - 12 h.

[0015] Preferably, the time of the heat treatment in step S2 is 8 - 16 h.

[0016] The application of the lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure in the field of lithium-ion batteries.

[0017] The present invention modifies and improves the cobalt-free lithium-rich oxide cathode material, making the material structure more stable and maintaining the stability of the battery during long cycling. Through the solid-phase method, a weak base salt is used to inhibit the surface interface reaction of the growth of secondary particles on the carbonate precursor of the lithium-rich oxide cathode material, induce element segregation, and promote particle growth, thereby in-situ constructing a rock salt structure on the surface of the cathode material particles. This rock salt structure has an excellent lattice arrangement with the internal structure of the LLO cathode, which helps to improve the surface structure stability, inhibit the interface reaction, and continuously improve the electrochemical performance.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure of the present invention is used as the cathode of a lithium-ion battery. When the voltage window is 2.0 - 4.8V and the current density is 20 mA / g, the initial Coulombic efficiency of this cathode material is 85.2%, and the discharge specific capacity is as high as 310.7 mAh / g. -1 ; When the current density is 200 mA / g, the capacity retention rate of this cathode material after 200 cycles is higher than 93%, overcoming the disadvantages of rapid capacity decay and intense surface interface reaction.

[0020] 2. The lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure of the present invention treats the carbonate precursor with a weak base salt, and constructs a rock salt structure layer on the surface of the particles of a typical cobalt-free lithium-rich layered cathode (Li 1.2 Mn 0.6 Ni 0.2 O2). SEM and TEM results prove that the element segregation in the treated precursor is the main factor for the formation of the surface rock salt layer. This is a rock salt structure layer formed by epitaxial growth, which has good lattice compatibility with the bulk layered phase. It avoids separation during long cycling, thereby inhibiting the electrolyte-cathode interface reaction, reducing the structural evolution, and enabling the lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure to have a rock salt structure surface layer. After 200 cycles, the capacity retention rate of the cathode material is greater than 93%, showing excellent voltage and capacity stability.

[0021] 3. The method of using a weak base salt to modify the interface of the carbonate precursor of transition metals in the lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure of the present invention induces the construction of a rock salt structure layer on the surface of the material particles, which not only improves the structural stability, but also has the advantages of high capacity, simple synthesis process, easy control, good repeatability, etc., and has great commercial prospects. Description of the Drawings

[0022] Figure 1 For the surface-modified cobalt-free lithium-rich oxide powder modified in Examples 1 - 3 and Li of Comparative Example 1 1.2 Mn0.6 Ni 0.2 Cycling performance diagram of NiO2 powder

[0023] Figure 2 For 0.1(Mn3Ni)O7·0.9Li in Examples 1 - 3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and LiMnO2 powder of Comparative Example 1 1.2 Mn 0.6 Ni 0.2 X - ray diffraction pattern of NiO2 powder

[0024] Figure 3 For 0.1(Mn3Ni)O7·0.9Li in Examples 1 - 3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and LiMnO2 powder of Comparative Example 1 1.2 Mn 0.6 Ni 0.2 SEM images of NiO2 powder

[0025] Figure 4 For 0.1(Mn3Ni)O7·0.9Li in Examples 1 - 3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and LiMnO2 powder of Comparative Example 1 1.2 Mn 0.6 Ni 0.2 TEM images of NiO2 powder

[0026] Figure 5For 0.1(Mn3Ni)O7·0.9Li of Examples 1-3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powders and Li 1.2 Mn 0.6 Ni 0.2 O2 powders as the positive electrode, the first charge-discharge curves at 20 mA / g at room temperature -1 when.

[0027] Figure 6 For 0.1(Mn3Ni)O7·0.9Li of Examples 1-3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powders and Li 1.2 Mn 0.6 Ni 0.2 O2 powders as the positive electrode, the voltage stability curves at 200 mA / g at room temperature -1 when. Detailed implementation mode

[0028] The content of the present invention will be further described below in conjunction with specific embodiments, but it should not be construed as a limitation of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0029] Example 1

[0030] 1. Take 0.01 mol of transition metal salt precursor (Mn 0.75 Ni 0.25 CO3) and NH4HCO3, mix them, and perform hydrothermal reaction at 180°C for 12 h. After rinsing, filtering, and drying, a modified transition metal precursor is obtained.

[0031] 2. 1.1588 g of the modified transition metal precursor, 0.5878 g of lithium salt (Li2CO3), 4.6303 g of potassium salt (KCl), and 2.4198 g of sodium salt (NaCl) were thoroughly ground and then heat-treated in a muffle furnace at 850 °C for 12 h. After washing with water, filtering, and drying, 0.1(Mn3Ni)O7·0.9Li was obtained. 1.2 Mn 0.6 Ni 0.2 O2 powder.

[0032] Example 2

[0033] 1. Weigh 1.1588 g of the transition metal carbonate precursor (Mn 0.75 Ni 0.25 CO3) and 0.1170 g of (NH4)2CO3, mix them thoroughly, and then carry out a hydrothermal reaction at 180 °C for 12 h. Cool with the furnace, wash with water, and dry to obtain the modified transition metal precursor powder.

[0034] 2. Put 1.1588 g of the modified transition metal precursor powder, 0.5878 g of lithium salt (Li2CO3), 4.6303 g of potassium salt (KCl), and 2.4198 g of sodium salt (NaCl) into a crucible after thorough grinding. Heat-treat at 850 °C for 12 h and cool with the furnace. After washing with water, filtering, and drying, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2 powder.

[0035] Example 3

[0036] 1. Weigh 1.1588 g of the transition metal carbonate precursor (Mn 0.75 Ni 0.25 CO3) and 0.4717 g of (NH4)2SO4, mix them thoroughly, and then carry out a hydrothermal reaction at 180 °C for 12 h. Cool with the furnace, wash with water, and dry to obtain the modified transition metal precursor powder.

[0037] 2. Put 1.1588 g of the modified transition metal precursor powder, 0.5878 g of lithium salt (Li2CO3), 4.6303 g of potassium salt (KCl), and 2.4198 g of sodium salt (NaCl) into a crucible after thorough grinding. React at 850 °C for 12 h and cool with the furnace. After washing with water, filtering, and drying, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder.

[0038] Comparative Example 1

[0039] Take 1.1588 g of transition metal precursor, 0.5878 g of lithium salt (Li2CO3), 4.6303 g of potassium salt (KCl) and 2.4198 g of sodium salt (NaCl). After thorough grinding, heat-treat in a muffle furnace at 850 °C for 12 h. After washing with water, filtering and drying, obtain Li 1.2 Mn 0.6 Ni 0.2 O2 powder.

[0040] Figure 1 It is the cyclic performance diagram of the modified surface-modified cobalt-free lithium-rich oxide powder of Examples 1-3 and the cobalt-rich lithium-oxide powder of Comparative Example 1. From Figure 1 It can be seen that the lithium-rich manganese-based layered cathode material powders with in-situ surface integrated structures in Examples 1-3 can all significantly improve the initial Coulomb efficiency. At the same time, observing the cyclic performance of the lithium-rich manganese-based layered cathode material powders with different in-situ surface integrated structures, the lithium-rich manganese-based layered cathode material of Example 1 has the best performance.

[0041] Figure 2 For 0.1(Mn3Ni)O7·0.9Li in Examples 1-3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and the X-ray diffraction pattern of the Li 1.2 Mn 0.6 Ni 0.2 O2 powder of Comparative Example 1. From Figure 2 It can be seen that the synthesized powder is an O3-type lithium-rich oxide, which is a mixed phase of Li2MnO3 and ternary layered material. Figure 3 For 0.1(Mn3Ni)O7·0.9Li in Examples 1-3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and the SEM photos of the Li 1.2 Mn 0.6 Ni 0.2 O2 powder of Comparative Example 1. From Figure 3It can be seen that the synthesized cathode material powder is assembled into microspheres. Figure 4 For 0.1(Mn3Ni)O7·0.9Li in Examples 1-3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and the Li 1.2 Mn 0.6 Ni 0.2 O2 powder in Comparative Example 1. From Figure 4 It can be seen that the surface and internal lattice fringes of the TEM image of the synthesized powder are clear and the boundaries are distinct. The measured interplanar spacing is 0.474 nm, and this spacing corresponds to the (003) crystal plane of the R-3m hexagonal layered structure or the (001) crystal plane of the C2 / m monoclinic structure. The sample exhibits a good layered structure (R-3m and C2 / M).

[0042] Taking 0.1(Mn3Ni)O7·0.9Li 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2 powder, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder, conductive carbon black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 as the electrode, a lithium metal sheet as the counter electrode, 1 mol·L -1 LiPF6 / EC+DMC+EMC (volume ratio of EC:DMC:EMC is 1:1:1) as the electrolyte, a polypropylene material as the separator, a Neware battery test system, and a charge-discharge voltage window of 2.0-4.8 V. The charge-discharge current densities are respectively selected as 20 mA g -1 and 200 mA g -1 . Figure 5 Using 0.1(Mn3Ni)O7·0.9Li 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and Li of Comparative Example 1 1.2 Mn 0.6 Ni 0.2 The first charge-discharge curves of O2 powder and Li of Comparative Example 1 as the positive electrode at 20 mA g at room temperature -1 when. From Figure 5 It can be seen that at a charge-discharge current density of 20 mA g -1 the first discharge specific capacities are 310.7 and 274.1 mAh g respectively -1 . Figure 6 For 0.1(Mn3Ni)O7·0.9Li of Examples 1-3 1.2 Mn 0.6 Ni 0.2 O2, 0.2(Mn3Ni)O7·0.8Li 1.2 Mn 0.6 Ni 0.2 O2, 0.5(Mn3Ni)O7·0.5Li 1.2 Mn 0.6 Ni 0.2 O2 powder and Li of Comparative Example 1 1.2 Mn 0.6 Ni 0.2 The voltage stability curves when O2 powder is used as the positive electrode at 200 mA g at room temperature -1 when. From Figure 6 It can be seen that at a charge-discharge current density of 200 mA g -1 the voltage decay rates after 200 cycles are 1.24 and 1.30 mV / cycle, and the capacity retention rates after 200 cycles are 94.6 and 93.9%, indicating that the material exhibits good electrochemical performance when used as the positive electrode of a lithium-ion battery.

[0043] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure, characterized in that, The chemical formula of the lithium-rich manganese-based layered cathode material of the in-situ surface integration structure is x(Mn3Ni)O7·(1-x)Li 1.2 Mn 0.6 Ni 0.2 O2, where x = 0.0001 - 0.05; the surface of the cathode material has a rock salt phase structure; when the voltage window is 2.0 - 4.8V and the current density is 20mA / g, the initial Coulombic efficiency of the cathode material is 85.2%, and the discharge specific capacity is as high as 310.7mAhg -1 ; when the current density is 200mA / g, the capacity retention rate of the cathode material after 200 cycles is higher than 93%.

2. The preparation method of the lithium-rich manganese-based layered cathode material of the in-situ surface integrated structure according to claim 1, characterized in that, It includes the following steps: S1. Mix a carbonate precursor of a transition metal with a weak base salt, carry out a hydrothermal reaction at 150-180 °C, wash and dry after the reaction ends to obtain a precursor treated with the weak base salt; S2. Mix the precursor treated with the weak base salt, a lithium compound and a molten salt, carry out a heat treatment at 700-1000 °C, cool with the furnace after the reaction ends, wash with water, filter and dry to obtain a lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure.

3. The preparation method of the lithium-rich manganese-based layered cathode material of the in-situ surface integrated structure according to claim 2, characterized in that, The weak base salt described in step S1 is 5-30 wt% of the carbonate precursor of the transition metal; the carbonate of the transition metal is Mn 0.75 Ni 0.25 CO3; the weak base salt is NH4HCO3, (NH4)2CO3 or (NH4)2SO4.

4. The preparation method of the lithium-rich manganese-based layered cathode material of the in-situ surface integrated structure according to claim 2, characterized in that, The lithium compound described in step S2 is one or more of lithium carbonate, lithium hydroxide, lithium nitrate or lithium chloride.

5. The preparation method of the lithium-rich manganese-based layered cathode material of the in-situ surface integrated structure according to claim 2, characterized in that, The molten salt described in step S2 is sodium chloride or / and potassium chloride; the molar ratio of the carbonate precursor of the transition metal to the lithium compound is 1:(1-1.1); the total molar ratio of the carbonate precursor of the transition metal and the lithium compound to the molten salt is 1:(4-4.5).

6. The preparation method of the lithium-rich manganese-based layered cathode material of the in-situ surface integrated structure according to claim 2, characterized in that, The time of the hydrothermal reaction described in step S1 is 8-12 h.

7. The preparation method of the lithium-rich manganese-based layered cathode material of the in-situ surface integrated structure according to claim 2, characterized in that, The time of the heat treatment described in step S2 is 8-16 h.

8. Application of the lithium-rich manganese-based layered cathode material with an in-situ surface integrated structure according to claim 1 in the field of lithium-ion batteries.

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