A lithium cobalt oxide cathode material with stable active crystal face

Abstract

The application discloses a lithium cobaltate positive electrode material with stable active crystal face and belongs to the technical field of lithium ion battery positive electrode materials. a M b CoO2, wherein M at least contains one of Mg, Al and Ti, 0.7<=a<=1 and 0.001<=b<=0.005.The exposed active crystal face of the material is mainly (1 0 0) crystal face, and the active crystal face is stabilized due to surface coating and the penetration of metal ions M, and no obvious layer cracking phenomenon occurs.The battery assembled with the positive electrode material has the advantages of long service life and good rate performance compared with the existing similar positive electrode materials.In addition, the positive electrode material is prepared by an ion exchange method, the preparation method is simple and easy to implement, no additional processing steps are added, and the cost and quality control in industrial production are facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery materials and electrochemistry, in particular to a lithium ion battery cathode material with stable active crystal faces and a preparation method and battery thereof. BACKGROUND

[0002] Lithium ion battery is a widely used secondary battery, which has the characteristics of high working voltage, high specific capacity and high energy density. The positive active material of the battery is of great concern because it accounts for a large proportion of the overall cost of the battery and largely determines the theoretical energy density of the battery. The main positive electrode materials at present are olivine lithium iron phosphate LiFePO4, layered lithium cobalt oxide LiCoO2, high-nickel positive electrode LiNi x Co y Mn 1-x-y O2, lithium-rich manganese-based positive electrode Li[Li x Mn y Co z Ni 1-x-y-z ]O2, etc.

[0003] Ion exchange method is a method for preparing lithium battery cathode material by replacing sodium ions or potassium ions in the precursor with lithium ions. This method has attracted attention because it can prepare materials with thermodynamic metastable structure that cannot be prepared by general solid phase method. However, the cathode material obtained by ion exchange retains special active crystal faces from the precursor. Active crystal face refers to the outer surface through which lithium ions are deintercalated during the operation of the cathode material. Such crystal faces are not stable during battery charge and discharge cycles, and the material prepared by this method is prone to cracking along the layer, which is not conducive to the service life of the cathode material. SUMMARY

[0004] Based on the above problems, the present application provides a lithium cobalt oxide cathode material with stable active crystal faces, a preparation method thereof and a corresponding battery.

[0005] The present application adopts the following technical solutions:

[0006] A lithium cobalt oxide cathode material with stable active crystal faces is a layered O3-type lithium cobalt oxide, and its chemical general formula is Li a M bCoO2, wherein M at least contains one of Mg, Al, Ti, 0.7≤a≤1, 0.001≤b≤0.005. It is prepared by ion exchange method, and the doping and coating of M is realized by adding a molten salt reaction additive containing M in the ion exchange reaction. According to electron microscope observation, the exposed active crystal surface is mainly (1 0 0) crystal surface, there is M ion gradient doping and coating layer effect at the exposed active crystal surface, and the doped metal ion M mainly occupies the Li layer, and the penetration depth is about 3 nm. X-ray diffraction (XRD) results show that there is a (3 1 1) peak of Fd-3m space group, indicating that the coating layer is a spinel structure. In addition, the positive electrode material has no obvious layer cracking phenomenon.

[0007] The preparation method of the lithium cobaltate positive electrode material with stable active crystal surface of the application comprises the following steps:

[0008] S1, mix sodium source and cobalt source according to a predetermined ratio, and calcine to obtain a precursor;

[0009] S2, mix the precursor, lithium molten salt and molten salt reaction additive according to a predetermined molar ratio, calcine to above the melting temperature, and then heat preservation, ion exchange reaction, at the same time, the molten salt reaction additive is dissociated and participates in the reaction in the molten state. After the reaction is completed, cool to room temperature, wash, filter and dry the product to obtain a lithium ion battery positive electrode material.

[0010] Specifically, in step S1, the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium oxide and sodium peroxide; the cobalt source is selected from one or more of tricobalt tetroxide, dicobalt trioxide, cobalt suboxide and cobalt carbonate. Mix the sodium source and the cobalt source according to the proportion, heat to 800-1000 degrees Celsius for calcination, and heat preservation for 2-10 hours, to obtain a precursor P2 type Na a CoO2, 0.7≤a≤1. The morphology of the primary particles is a particle exposing (1 0 0) crystal surface.

[0011] In step S2, the molten salt reaction additive is a compound containing magnesium, aluminum and / or titanium, including but not limited to one or more of magnesium nitrate, magnesium chloride, magnesium oxide, magnesium sulfate, magnesium hydroxide, magnesium acetate, aluminum nitrate, aluminum chloride, aluminum oxide, aluminum sulfate, aluminum hydroxide, aluminum acetate, titanium dioxide, titanyl sulfate, titanium sulfate, titanium chloride, lithium titanium phosphate, lithium aluminum titanium phosphate.

[0012] Preferably, the molten salt reaction additive is one or more of magnesium nitrate, magnesium chloride, aluminum nitrate, lithium titanium phosphate, lithium aluminum titanium phosphate.

[0013] In step S2, the lithium molten salt is selected from one or more of lithium nitrate, lithium chloride, lithium carbonate, lithium hydroxide, and the amount is 2-10 times the molar amount of the precursor.

[0014] In step S2, the amount of the molten salt reaction additive is 0.1%-5% of the molar amount of the total amount of magnesium, aluminum and titanium in the precursor.

[0015] In step S2, the temperature of the molten salt is 300-650 DEG C, and the holding time is 1-6 hours, and then cooling.

[0016] The lithium cobalt oxide positive electrode material with stable active crystal faces can be used to prepare a positive electrode sheet, which, together with a negative electrode sheet, a separator, an electrolyte and the like, forms a lithium ion battery.

[0017] The present application has the following advantages:

[0018] The present application provides a lithium cobalt oxide positive electrode material with stable active crystal faces and a preparation method thereof. Different from the general ion exchange method, an additive is added in the molten salt reaction system, so that the ion exchange reaction and the stabilization reaction of the active crystal face are simultaneously performed for the first time, and the cracking along the layer is inhibited. The method can significantly improve the cycle life and rate performance of the positive electrode material prepared by the ion exchange method, and does not increase the additional processing steps, which is beneficial to the cost and quality control in industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 SEM images of the precursor used for preparing the positive electrode material of examples 1-2 and comparative examples 1-2 of the present application.

[0020] Figure 2 SEM image of the positive electrode material prepared in example 1 of the present application.

[0021] Figure 3 TEM image (left) and electron diffraction image (right) of the positive electrode material prepared in example 1 of the present application.

[0022] Figure 4 STEM image (left) and intensity signal energy spectrum signal integral image (right) of the positive electrode material prepared in example 1 of the present application.

[0023] Figure 5 SEM image of the positive electrode material prepared in example 2 of the present application.

[0024] Figure 6 SEM image of the positive electrode material prepared in comparative example 1 of the present application.

[0025] Figure 7 Partial XRD image of the positive electrode material prepared in example 1 and comparative example 1 of the present application.

[0026] Figure 8 SEM image of the positive electrode material prepared in comparative example 2 of the present application.

[0027] Figure 9 SEM image of the positive electrode material prepared for Invention Comparative Example 3. DETAILED DESCRIPTION

[0028] The application will be further described in conjunction with the accompanying drawings and examples, but the scope of the application is not limited to this. Any modification or equivalent replacement of the technical solutions of the application without departing from the spirit and scope of the application shall be covered in the protection scope of the application.

[0029] Example 1. Magnesium-coated O3-type lithium cobaltate positive electrode material

[0030] The preparation method is as follows: 0.4 g of NaCoO2(seen in Example 1), 0.01 g of magnesium nitrate, and 2 g of lithium nitrate are mixed uniformly in a mortar under a dry atmosphere. The mixture is heated to 550°C at a rate of 5°C / min in a tube furnace, and after being kept at this temperature for 4 hours, it is cooled to room temperature. Then, it is washed with deionized water three times, suction filtered, and dried in a blast drying oven at 100°C. Figure 1

[0031] The electrode tab preparation and battery assembly method is as follows: the magnesium-coated O3-type lithium cobaltate positive electrode material prepared by the above method is mixed with Super P and PVDF (polyvinylidene fluoride) at a mass ratio of 8:1:1, and grinded uniformly with N-methyl pyrrolidone as the solvent. Then, it is coated on an aluminum foil and placed in a blast drying oven at 100°C for 24 hours. After being taken out, it is rolled several times on a rolling machine and cut into electrode discs. This is used as the positive electrode tab, lithium sheet is used as the negative electrode tab, battery separator model is Celgard 2400, electrolyte is M-M Chemicals LB-726 type electrolyte, and CR2032 button batteries are assembled in an O2, H2O <0.1 ppm atmosphere glove box. The test is performed on a Xunwei battery test system, and the test temperature is 30°C.

[0032] The prepared lithium cobaltate positive electrode material has no significant interlayer cracking phenomenon, and the exposed active crystal surface is mainly the (1 00) crystal surface, which can be confirmed by the 120° geometric relationship and electron diffraction of the exposed crystal surface, seen in Figure 2 and Figure 3 The spherical aberration electron microscope results show that magnesium forms a coating layer and an infiltration layer at the active crystal surface, the infiltration layer has a thickness of about 3 nm, and the magnesium ion mainly occupies the Li layer, seen in Figure 4 .

[0033] Example 2. Aluminum and titanium-coated O3-type lithium cobaltate positive electrode material

[0034] ​The preparation method is as follows: 0.4 g of NaCoO2, 0.03 g of titanium aluminum lithium phosphate, and 2 g of lithium chloride are uniformly mixed in a mortar under a dry atmosphere, the mixture is heated to 650°C at a rate of 5°C / min in a tube furnace, and then cooled to room temperature after being kept at 650°C for 4 hours. Then, the mixture is washed with deionized water three times, filtered, and dried in a blast drying oven at 100°C. The prepared lithium cobaltate positive electrode material has no significant interlayer cracking phenomenon, and there is a granular coating on the surface, as shown in Figure 5 .

[0035] The electrode sheet preparation and battery assembly method are the same as those in Example 1.

[0036] Comparative Example 1. Lithium cobaltate No. 1 of O3 type

[0037] The preparation method is the same as that in Example 1 except that magnesium nitrate is not added. The prepared lithium cobaltate material has a significant interlayer cracking phenomenon, which is not conducive to the cycle life of the positive electrode material, as shown in Figure 6 Compared with Comparative Example 1, the XRD of the magnesium-coated O3-type lithium cobaltate positive electrode material prepared in Example 1 has an Fd-3m space group (3 1 1) peak, which corresponds to a spinel phase caused by the gradient penetration of the coating layer and metal ions on the surface, as shown in Figure 7 .

[0038] The electrode sheet preparation and battery assembly method are the same as those in Example 1.

[0039] Comparative Example 2. Lithium cobaltate No. 2 of O3 type

[0040] The preparation method is the same as that in Example 2 except that titanium aluminum lithium phosphate is not added. The prepared lithium cobaltate material has a significant interlayer cracking phenomenon, which is not conducive to the cycle life of the positive electrode material, as shown in Figure 8 .

[0041] The electrode sheet preparation and battery assembly method are the same as those in Example 2.

[0042] The long cycle and rate performance of the lithium cobaltate materials prepared in Example 2 and Comparative Example 2 are shown in Table 1. As can be seen, Example 2 with a stable active crystal face has more excellent rate performance and cycle stability.

[0043] Table 1

[0044]

[0045] Comparative Example 3. Lithium cobaltate No. 3 of O3 type

[0046] The preparation method is as follows: Li2CO3 and Co3O4 are mixed in a Li / Co molar ratio of 1.05:1, the mixture is heated to 650°C at a rate of 5°C / min in a tube furnace, and then cooled to room temperature after being kept at 650°C for 6 hours. The product is ground with a mortar. The lithium cobaltate material prepared in Comparative Example 3 has a relatively round shape, and less edges, and the exposed active crystal face is not the (1 0 0) face, as shown in Figure 9 .

[0047] The electrode plate preparation and battery assembly method are the same as those in Example 1.

[0048] Comparative Example 4. Solid-phase sintering coated O3-type lithium cobaltate

[0049] The preparation method is as follows: Comparative Example 3 is mixed with an alcohol solution containing 1% molar ratio of magnesium acetate, stirred uniformly, and evaporated at 80°C. The precipitate is heated to 650°C and kept for 4 hours, and then cooled to room temperature. The product is ground with a mortar.

[0050] The electrode plate preparation and battery assembly method are the same as those in Example 1.

[0051] At a charge-discharge rate of 1C=200mA / g and a voltage range of 3-4.6V, after experiencing 1 cycle of activation, the long cycle performance and rate performance of the lithium cobaltate materials prepared in Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 4 are shown in Table 2. It can be seen that the lithium cobaltate materials in Example 1 and Comparative Example 1, which expose the active crystal face (1 0 0), have more excellent rate performance than Comparative Example 4 and Comparative Example 3, respectively, and the lithium cobaltate material in Example 1, which has a stabilized active crystal face, has more excellent cycle stability than Comparative Example 4.

[0052] Table 2

[0053]

[0054] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application. These improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A lithium ion battery cathode material, which is a layered O3-type lithium cobaltate material with stable active crystal faces prepared by ion exchange method, M-doped and coated by adding a molten salt reaction additive containing M in the ion exchange reaction, and its general chemical formula is Li a M b CoO2, wherein, M at least contains one of Mg, Al, Ti, 0.7≤a≤1, 0.001≤b≤0.005; the exposed active crystal surface of the material is (1 0 0) crystal surface, the exposed active crystal surface simultaneously exists M ion gradient doping and a coating layer, and the doped metal ion M mainly occupies the Li layer, and the coating layer is a spinel structure.

2. The lithium-ion battery cathode material of claim 1, wherein, The positive electrode material has no obvious layer cracking phenomenon.

3. The preparation method of the lithium ion battery positive electrode material according to claim 1 or 2, comprising the following steps: S1, calcining the mixture of sodium source and cobalt source in a preset ratio to obtain a precursor P2 type Na a CoO2; S2, mixing the precursor P2 type Na a CoO2, lithium molten salt, molten salt reaction additive are mixed uniformly, calcined to more than melting temperature and kept, ion exchange reaction is carried out, wherein the molten salt reaction additive is a compound containing magnesium, aluminum and / or titanium;After the reaction is completed, it is cooled to room temperature, and the product is washed, filtered and dried to obtain a layered O3 type lithium cobaltate material with stable active crystal surface.

4. The production method according to claim 3, wherein In step S1, the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium oxide and sodium peroxide; and the cobalt source is selected from one or more of tricobalt tetroxide, dicobalt trioxide, cobalt suboxide and cobalt carbonate.

5. The production method according to claim 3, wherein In step S1, after mixing the sodium source and the cobalt source, the temperature is raised to 800-1000 DEG C for calcination.

6. The production method according to claim 3, wherein The morphology characteristics of the primary particles of the precursor obtained in step S1 are particles exposing (1 0 0) crystal surface.

7. The production method according to claim 3, wherein In step S2, the molten salt reaction additive is selected from one or more of magnesium nitrate, magnesium chloride, magnesium oxide, magnesium sulfate, magnesium hydroxide, magnesium acetate, aluminum nitrate, aluminum chloride, aluminum oxide, aluminum sulfate, aluminum hydroxide, aluminum acetate, titanium dioxide, titanyl sulfate, titanium sulfate, titanium chloride, lithium titanium phosphate, lithium aluminum titanium phosphate.

8. The production method according to claim 3, wherein The lithium molten salt described in step S2 is selected from one or more of lithium nitrate, lithium chloride, lithium carbonate, lithium hydroxide, in an amount of 2-10 times the molar amount of CoO2. a CoO2.

9. The production method according to claim 3, wherein In step S2, the melting and holding temperature is 300-650 DEG C.

10. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, characterized by, The positive electrode tab comprises the lithium ion battery positive electrode material according to claim 1 or 2.

Images