Surface and grain boundary double-coated sodium ion battery layered oxide positive electrode material

Abstract

The chemical formula of the surface and grain boundary double-coated sodium ion battery layered oxide positive electrode material is NaaLabNicFedMneTMfO2, 0.85 < = a < = 0.99, 0.01 < = b < = 0.15, 0.25 < = c < = 0.4, 0.25 < = d < = 0.4, 0.3 < = e < = 0.5, 0.01 < = f < = 0.15, a + b = 1, c + d + e + f = 1, and TM is one or more of Ca, Ba, Pr, Nd, Gd, Zr, Sr, Ti, V, Cr and Co. According to the positive electrode material disclosed by the invention, a uniform, full-covering and high-ionic-conductivity coating layer is constructed on the surface and the grain boundary of the material, and the coating layer performs dual protection on the positive electrode material, so that the side reaction of an electrolyte and the positive electrode material is relieved, and the ionic conductivity and the mechanical strength of the positive electrode material are improved. Therefore, the positive electrode material provided by the invention has the characteristics of good cycle stability, high rate capability, high compaction density and good air stability.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of positive electrode materials for sodium ion batteries, and in particular to a sodium ion battery layered oxide positive electrode material with double coating on the surface and grain boundary. Background Art

[0002] Sodium-ion batteries, with their widely distributed, easily accessible and affordable sodium resource base and many similarities in electrochemical properties with lithium-ion batteries, have shown unique competitive potential in large-scale energy storage technology and power applications. The positive electrode material of sodium-ion batteries is the key to determining its performance. Layered oxide positive electrode materials have become a research hotspot due to their outstanding energy density and compaction density.

[0003] During the cycle, layered oxide positive electrode materials are prone to side reactions with the electrolyte, consuming the electrolyte while producing a large amount of gas, resulting in poor cycle stability and rate performance. Researchers have adopted the strategy of constructing a coating layer on the surface of the positive electrode material to inhibit the side reactions between the electrolyte and the positive electrode material. Due to the simple preparation process and low cost, element doping is a widely used coating strategy. However, the coating layer of the positive electrode material prepared by this process is prone to form an island structure, which is unevenly distributed on the surface of the material. In addition, once the coating layer on the surface of the positive electrode material is damaged, the electrolyte will further destroy the grain boundaries inside the positive electrode material and cause the material to degrade. Moreover, during the cycle, the coating layer with low ion conductivity will hinder the Na + Insertion and extraction, thereby reducing the overall performance of the positive electrode material. Summary of the invention

[0004] In order to solve the above problems, the present invention aims to provide a sodium ion battery layered oxide positive electrode material with double coating on the surface and grain boundary. Specifically, the positive electrode material is doped with La element and TM element (the TM element can form an ABO 3 The perovskite layered phase of the structure is one or more of Ca, Ba, Pr, Nd, Gd, Zr, Sr, Ti, V, Cr, and Co. The two can form a uniform perovskite layered phase on the surface and grain boundary of the positive electrode material. The layered phase can provide dual protection for the positive electrode material to avoid side reactions between the electrolyte and the positive electrode material, and can also improve the air stability of the positive electrode material. At the same time, the formed perovskite layered phase has excellent Na + transport properties, thus improving the Na + Transfer rate.

[0005] The present invention is achieved through the following technical solutions:

[0006] A sodium ion battery layered oxide positive electrode material with double coating on the surface and grain boundary, the chemical formula is Na a La b Ni c Fe d Mn e TM f O 2 , 0.85≤a≤0.99, 0.01≤b≤0.15, 0.25≤c≤0.4, 0.25≤d≤0.4, 0.3≤e≤0.5, 0.01≤f≤0.15, a+b=1, c+d+e+f=1, the TM element can form ABO with La element 3 The perovskite layered phase has a structure, wherein the perovskite layered phase uniformly covers the surface and grain boundaries of the positive electrode material, and TM is one or more of Ca, Ba, Pr, Nd, Gd, Zr, Sr, Ti, V, Cr, and Co.

[0007] 0.85≤a≤0.99,0.01≤b≤0.15, 0.25≤c≤0.3266, 0.25≤d≤0.3266, 0.3≤e≤0.425, 0.01≤f≤0.15.

[0008] The preparation method of the above-mentioned positive electrode material is prepared by solid phase synthesis, comprising the following steps: step 11, fully mixing the precursor with the sodium source compound and the lanthanum source compound according to a molar ratio to obtain a uniform mixture powder, wherein the precursor is a sodium ion precursor containing TM; step 12, calcining the mixture powder in two steps.

[0009] The precursor is obtained by coprecipitation; the sodium source compound is one or more of sodium carbonate, sodium oxide, sodium acetate, sodium chloride, sodium nitrate and sodium citrate; the lanthanum source compound is one or more of lanthanum oxide, lanthanum sulfate, lanthanum nitrate and lanthanum chloride;

[0010] The molar ratio of the precursor to the sodium source compound is 1-1.06; the mixing method is one or more of grinding mixing, ball milling mixing, high mixer mixing, solvent mixing, and spray pyrolysis mixing.

[0011] The two-step calcination described in step 12 is carried out in an air atmosphere, which is divided into a first step of pre-calcination and a second step of high-temperature calcination; the heating temperature of the first step of pre-calcination is 400-600°C, the heating rate is 2-10°C / min, and the insulation is 4-10h; the heating temperature of the second step of high-temperature calcination is 750-950°C, the heating rate is 2-10°C / min, and the insulation is 10-24h, and the temperature is lowered to room temperature after the insulation is completed.

[0012] In the high temperature stage of the sintering process, affected by solubility, the La element and TM element (one or more of Ca, Ba, Pr, Nd, Gd, Zr, Sr, Ti, V, Cr, Co) dissolved in the precursor precipitates from the precursor and forms ABO on the surface of the precursor and at the grain boundary. 3 The uniform perovskite layered phase of the structure can not only fill the gaps inside the particles and make the particles solid, but also avoid the side reaction between the electrolyte and the positive electrode material, and improve the air stability of the positive electrode material. + The layered perovskite phase with high transport properties can significantly improve the overall Na + Transfer rate.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0014] The positive electrode material of the present invention constructs a uniform, fully covered, high ion conductivity coating layer on the material surface and grain boundaries, and the coating layer provides dual protection for the positive electrode material, alleviates the side reaction between the electrolyte and the positive electrode material, and improves the ion conductivity and mechanical strength of the positive electrode material. Therefore, the positive electrode material provided by the present invention has the characteristics of good cycle stability, high rate performance, high compaction density, and good air stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0016] Figure 1 This is a SEM image of the positive electrode material prepared in Example 1 of the present invention.

[0017] Figure 1-1 This is the XRD diagram of the positive electrode material prepared in Example 1 of the present invention.

[0018] Figure 1-2 This is the first charge and discharge curve of the positive electrode material prepared in Example 1 of the present invention.

[0019] Figure 2 This is a SEM image of the positive electrode material prepared in Example 2 of the present invention.

[0020] Figure 3 This is a SEM image of the positive electrode material prepared in Example 3 of the present invention.

[0021] Figure 4 This is a SEM image of the positive electrode material prepared in Example 4 of the present invention.

[0022] Figure 5 This is a SEM image of the positive electrode material prepared in Comparative Example 1 of the present invention.

[0023] Figure 6 This is a SEM image of the positive electrode material prepared in Comparative Example 2 of the present invention.

[0024] Figure 7 This is a SEM image of the positive electrode material prepared in Comparative Example 3 of the present invention.

[0025] Figure 8 This is the in-situ heating XRD test diagram of Example 2 of the present invention.

[0026] Fig. 9 This is the element distribution diagram of Example 2. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0028] Example 1

[0029] This embodiment provides a method for preparing a sodium ion battery layered oxide positive electrode material with dual coating on the surface and grain boundary, the preparation method comprising the following steps:

[0030] The sodium source compound, the precursor and the lanthanum source compound are mixed according to the stoichiometric ratio, sintered in two stages in an air atmosphere, and crushed and screened to obtain the sodium ion battery layered oxide positive electrode material Na 0.85 La 0.15 Ni 0.2125 Fe 0.212 5 Mn 0.425 Cr 0.15 O 2 .

[0031] The sodium source is sodium carbonate;

[0032] The chemical formula of the precursor is Ni 0.2125 Fe 0.2125 Mn 0.425 Cr 0.15 (OH) 2 ;

[0033] The lanthanum source is lanthanum oxide;

[0034] The molar ratio of the sodium source to the precursor is 1.04:1;

[0035] The heating rate of the first sintering stage is 3°C / min, the calcining temperature is 500°C, and the holding time is 4h; the heating rate of the second sintering stage is 3°C / min, the calcining temperature is 900°C, and the holding time is 14h;

[0036] The SEM image of the layered oxide positive electrode material for sodium ion batteries obtained in this example (see Figure 1 As shown in the figure, it can be seen that the uniformly precipitated ABO 3 The phase makes the positive electrode material have a dense internal structure; XRD diagram (such as Figure 1-1 As shown in the figure, the layered oxide positive electrode material for sodium ion batteries obtained in this embodiment is mainly a layered phase with an O3 structure (space group is R-3m, accounting for 91.5%), and the secondary phase is a layered phase with an ABO structure. 3 The perovskite layered phase of the structure (space group is R-3c, accounting for 8.5%).

[0037] The prepared material is used as the positive electrode, sodium metal as the negative electrode, and glass fiber as the separator. 6 The diethylene glycol dimethyl ether solution was used as the electrolyte to assemble button cells. The charge and discharge test was carried out in the voltage window of 2-4.0V and the current density of 12mA / g. The charge and discharge curves are shown in Figure 1-2 The initial discharge specific capacity is 138.0 mAh / g, the discharge medium voltage is 3.01 V, and the capacity retention rate after 200 cycles is 93%.

[0038] Example 2

[0039] This embodiment provides a method for preparing a sodium ion battery layered oxide positive electrode material with dual coating on the surface and grain boundary, the preparation method comprising the following steps:

[0040] The sodium source compound, the precursor and the lanthanum source compound are mixed according to the stoichiometric ratio, sintered in two stages in an air atmosphere, and crushed and screened to obtain the sodium ion battery layered oxide positive electrode material Na 0.99 La 0.01 Ni 0.3266 Fe 0.326 6 Mn 0.3266 Ti 0.02 O 2

[0041] The sodium source is sodium carbonate;

[0042] The chemical formula of the precursor is Ni 0.3266 Fe 0.32663 Mn .03266 Ti 0.02 (OH) 2 ;

[0043] The lanthanum source is lanthanum oxide;

[0044] The molar ratio of the sodium source to the precursor is 1.04:1;

[0045] The heating rate of the first sintering stage is 5°C / min, the calcining temperature is 500°C, and the holding time is 4h; the heating rate of the second sintering stage is 5°C / min, the calcining temperature is 900°C, and the holding time is 14h;

[0046] The SEM image of the layered oxide positive electrode material for sodium ion batteries obtained in this example (see Figure 2 As shown in the figure, it can be seen that the uniformly precipitated ABO 3 The phase gives the positive electrode material a dense internal structure. Figure 8 As shown, in order to explore ABO 3 In-situ heating XRD test (XRK) was carried out to investigate the phase formation process. 2 The diffraction peak of La disappeared, proving that the Ti element diffused into the cathode material. As the temperature increased, at 650 °C, 2 O 3 The diffraction peak disappears, proving that La element diffuses into the cathode material. In the range of 650-775℃, there is no La 2 O 3 and TiO 2 The relevant diffraction peaks appear, proving that La and Ti elements exist in the positive electrode particles at the same time. As the temperature continues to rise, La and Ti elements precipitate from the positive electrode material due to solubility, forming a uniform ABO on the particle surface and grain boundary of the positive electrode material. 3 phase. And we have in the element distribution diagram (such as Fig. 9 A rare uneven precipitation was found in the sample (shown in Figure 2), and it can be seen that La and Ti elements have the same distribution position, proving that the precipitated ABO 3 The phase is mainly composed of La and Ti elements.

[0047] The main phase of the sodium ion battery layered oxide positive electrode material obtained in this embodiment is a layered phase with an O3 structure (space group is R-3m, accounting for 97.5%), and the secondary phase is a layered phase with an ABO structure. 3 The perovskite layered phase of the structure (space group is R-3c, accounting for 2.5%).

[0048] The prepared material is the positive electrode, sodium metal is the negative electrode, glass fiber is the separator, and NaPF 6 The button cell was assembled with diethylene glycol dimethyl ether solution as the electrolyte. The charge and discharge test was carried out in the voltage window of 2-4.0V and the current density of 12mA / g. The initial discharge capacity was 142mAh / g, the discharge medium voltage was 3.0V, and the capacity retention rate after 200 cycles was 90%.

[0049] Example 3

[0050] This embodiment provides a method for preparing a sodium ion battery layered oxide positive electrode material with dual coating on the surface and grain boundary. In addition to changing the type of TM element (one or more of Ca, Ba, Pr, Nd, Gd, Zr, Sr, Ti, V, Cr, and Co) in the precursor, the chemical formula of the obtained sodium ion battery layered oxide positive electrode material is Na 0.99 La 0.01 Ni 0.33 Fe 0.33 Mn 0.33 Sr 0.0 1 O 2 , the rest are the same as in Example 2.

[0051] The SEM image of the layered oxide positive electrode material for sodium ion batteries obtained in this example (see Figure 3 As shown in the figure, it can be seen that the uniformly precipitated ABO 3 The main phase of the sodium ion battery layered oxide positive electrode material obtained in this embodiment is a layered phase with an O3 structure (space group is R-3m, accounting for 97.9%), and the secondary phase is a layered phase with an ABO structure. 3 The perovskite layered phase of the structure (space group is R-3c, accounting for 2.1%).

[0052] The prepared material is used as the positive electrode, sodium metal as the negative electrode, and glass fiber as the separator. 6 The button cell was assembled with diethylene glycol dimethyl ether solution as the electrolyte. The charge and discharge test was carried out in the voltage window of 2-4.0V and the current density of 12mA / g. The initial discharge capacity was 139.6mAh / g, the discharge medium voltage was 2.98V, and the capacity retention rate after 200 cycles was 91.5%.

[0053] Example 4

[0054] This embodiment provides a method for preparing a sodium ion battery layered oxide positive electrode material with dual coating on the surface and grain boundary. In addition to changing the type of TM element (one or more of Ca, Ba, Pr, Nd, Gd, Zr, Sr, Ti, V, Cr, and Co) in the precursor, the chemical formula of the obtained sodium ion battery layered oxide positive electrode material is Na 0.99 La 0.01 Ni 0.33 Fe 0.33 Mn 0.33 Zr 0.0 1 O 2 , the rest are the same as in Example 2.

[0055] The SEM image of the layered oxide positive electrode material for sodium ion batteries obtained in this example (see Figure 4As shown in the figure, it can be seen that the uniformly precipitated ABO 3 The main phase of the sodium ion battery layered oxide positive electrode material obtained in this embodiment is a layered phase with an O3 structure (space group is R-3m, accounting for 97.1%), and the secondary phase is a layered phase with an ABO structure. 3 The perovskite layered phase of the structure (space group is R-3c, accounting for 2.9%).

[0056] The prepared material is used as the positive electrode, sodium metal as the negative electrode, and glass fiber as the separator. 6 The button cell was assembled with diethylene glycol dimethyl ether solution as the electrolyte. The charge and discharge test was carried out in the voltage window of 2-4.0V and the current density of 12mA / g. The initial discharge capacity was 141mAh / g, the discharge medium voltage was 2.99V, and the capacity retention rate after 200 cycles was 90%.

[0057] Comparative Example 1

[0058] Similar to Example 1, the difference is that the positive electrode material does not contain La element, and its chemical formula is NaNi 0.2125 Fe 0.2125 Mn 0.425 Cr 0.15 O 2 .

[0059] SEM image of the layered oxide positive electrode material for sodium ion battery obtained in the example (as shown in Figure 5 As shown in the figure, it can be seen that the lack of ABO 3 The positive electrode material is filled with a phase, and there are gaps inside the positive electrode material; XRD test shows that the layered oxide positive electrode material for sodium ion batteries obtained in this embodiment is a layered phase with an O3 structure.

[0060] The prepared material is used as the positive electrode, sodium metal as the negative electrode, and glass fiber as the separator. 6 The button cell was assembled using diethylene glycol dimethyl ether solution as the electrolyte. The charge and discharge test was carried out at a voltage window of 2-4.0V and a current density of 12mA / g. The initial discharge capacity was 142mAh / g, the discharge medium voltage was 3.01V, and the capacity retention rate after 200 cycles was 75%.

[0061] Comparative Example 2

[0062] Similar to Example 1, the difference is that the positive electrode material does not contain Cr element, and its chemical formula is Na 0.85 La 0.15 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 .

[0063] SEM image of the layered oxide positive electrode material for sodium ion battery obtained in the example (as shown in Figure 6 As shown in the figure, it can be seen that the lack of ABO 3 The positive electrode material is filled with a gap; XRD test shows that the main phase of the layered oxide positive electrode material for sodium ion batteries obtained in this embodiment is a layered phase with an O3 structure (space group is R-3m, accounting for 93%), and the impurity phase is LaMnO 3 (Space group is R-3c, accounting for 7%).

[0064] The prepared material is used as the positive electrode, sodium metal as the negative electrode, and glass fiber as the separator. 6 The button cell was assembled with diethylene glycol dimethyl ether solution as the electrolyte. The charge and discharge test was carried out at a voltage window of 2-4.0V and a current density of 12mA / g. The initial discharge capacity was 132mAh / g, the discharge medium voltage was 3.01V, and the capacity retention rate after 200 cycles was 78%.

[0065] Comparative Example 3

[0066] Similar to Example 1, the difference is that the positive electrode material is doped with other metal elements, and the chemical formula is Na 0.85 Mg 0.15 Ni 0.2125 Fe 0.2125 Mn 0.425 Cu 0.15 O 2 .

[0067] SEM image of the layered oxide positive electrode material for sodium ion battery obtained in the example (as shown in Figure 7 As shown in the figure, it can be seen that the lack of ABO 3 The positive electrode material is filled with a phase, and there are gaps inside the positive electrode material; XRD test shows that the layered oxide positive electrode material for sodium ion batteries obtained in this embodiment is a layered phase with an O3 structure (space group is R-3m).

[0068] The prepared material is used as the positive electrode, sodium metal as the negative electrode, and glass fiber as the separator. 6 The button cell was assembled with diethylene glycol dimethyl ether solution as the electrolyte. The charge and discharge test was carried out at a voltage window of 2-4.0V and a current density of 12mA / g. The initial discharge capacity was 135mAh / g, the discharge medium voltage was 3.01V, and the capacity retention rate after 200 cycles was 80%.

[0069] It can be seen from the SEM images of the embodiments and comparative examples that the layered oxide positive electrode material for sodium ion batteries of the present invention has good internal uniformity and almost no voids inside the positive electrode material. This may be due to the formation of uniform ABO 3The phase fills the gaps inside the positive electrode material particles. However, there are more gaps in the comparative example, indicating that it is not possible to obtain a uniform layered structure coated on the surface of the positive electrode material particles, and it is also impossible to fill more gaps.

[0070] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sodium ion battery layered oxide positive electrode material with double coating on the surface and grain boundary, characterized in that: The chemical formula is <h2 style=";text-align:left;direction:ltr">Na<h2 style=";text-align:left;direction:ltr"> a <h2 style=";text-align:left;direction:ltr"> No<h2 style=";text-align:left;direction:ltr"> b <h2 style=";text-align:left;direction:ltr"> Ni<h2 style=";text-align:left;direction:ltr"> c <h2 style=";text-align:left;direction:ltr"> Fe<h2 style=";text-align:left;direction:ltr"> d <h2 style=";text-align:left;direction:ltr"> Mn<h2 style=";text-align:left;direction:ltr"> e <h2 style=";text-align:left;direction:ltr"> TM<h2 style=";text-align:left;direction:ltr"> f <h2 style=";text-align:left;direction:ltr"> O2,0.85≤a≤0.99,0.01≤b≤0.15,0.25≤c≤0.4,0.25≤d≤0.4,0.3≤e≤0.5, 0.01≤f≤0.15, a+b=1, c+d+e+f=1, the TM element can form a perovskite layered phase with the La element having an ABO3 structure, and the perovskite layered phase uniformly covers the surface and grain boundaries of the positive electrode material, and the TM element is one or more of Ca, Ba, Pr, Nd, Gd, Zr, Sr, Ti, V, Cr, and Co.

2. The positive electrode material according to claim 1, characterized in that 0.85≤a≤0.99,0.01≤b≤0.15,0.25≤c≤0.3266,0.25≤d≤0.3266,0.3≤e≤0.425,0.01≤f≤0.

15.

3. The method for preparing the positive electrode material according to claim 1 or 2, characterized in that: The preparation is obtained by solid phase synthesis, which includes the following steps: step 11, fully mixing the precursor with the sodium source compound and the lanthanum source compound according to the molar ratio to obtain a uniform mixture powder, wherein the precursor is a sodium ion precursor containing TM; step 12, calcining the mixture powder in two steps.

4. The method for preparing the positive electrode material according to claim 3, characterized in that: The precursor is obtained by coprecipitation; the sodium source compound is one or more of sodium carbonate, sodium oxide, sodium acetate, sodium chloride, sodium nitrate and sodium citrate; the lanthanum source compound is one or more of lanthanum oxide, lanthanum sulfate, lanthanum nitrate and lanthanum chloride.

5. The method for preparing the positive electrode material according to claim 3, characterized in that: The molar ratio of the precursor to the sodium source compound is 1-1.

06.

6. The method for preparing the positive electrode material according to claim 3, characterized in that: The mixing method is one or more of grinding mixing, ball milling mixing, high-mixer mixing, solvent mixing, and spray pyrolysis mixing.

7. The method for preparing the positive electrode material according to claim 3, characterized in that: The two-step calcination described in step 12 is carried out in an air atmosphere, which is divided into a first step of pre-calcination and a second step of high-temperature calcination; the heating temperature of the first step of pre-calcination is 400-600°C, the heating rate is 2-10°C / min, and the insulation is 4-10h; the heating temperature of the second step of high-temperature calcination is 750-950°C, the heating rate is 2-10°C / min, and the insulation is 10-24h, and the temperature is lowered to room temperature after the insulation is completed.

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