WO2024012605A1

WO2024012605A1 - Lithium nickelate positive electrode material and preparation method therefor, and application

Info

Publication number: WO2024012605A1
Application number: PCT/CN2023/116925
Authority: WO
Inventors: 李林森
Original assignee: 宁波致良新能源有限公司
Priority date: 2022-07-12
Filing date: 2023-09-05
Publication date: 2024-01-18
Also published as: CN115101745A

Abstract

A lithium nickelate positive electrode material and a preparation method therefor, and an application. The chemical formula of the positive electrode material is Li_1+xNi_1-xO₂, wherein 0.02≤x≤0.08, the crystal structure is an α-NaFeO₂ type hexagonal layered structure, and the space group is the R-3m type. The surplus Li relative to the Ni stoichiometric ratio occupies the octahedral voids in the Ni layers and is randomly distributed in the octahedral voids. The preparation method comprises the following steps: (1) causing a nickel source and a lithium source to react with oxygen in the presence of a molten salt additive, to obtain a lithium nickelate-containing product; and (2) purifying the lithium nickelate-containing product, to obtain a lithium nickelate-containing powder, and placing the powder in an oxygen environment, to obtain the lithium nickelate positive electrode material. When the positive electrode material is used for a lithium ion battery, high energy density, and excellent cycling stability and thermal stability can be achieved.

Description

A kind of lithium nickelate cathode material and its preparation method and application

Technical field

The invention belongs to the technical field of lithium ion batteries, and specifically relates to a lithium nickelate cathode material and its preparation method and application.

Background technique

Ternary materials represented by lithium nickel cobalt manganate and lithium nickel cobalt aluminate can provide better energy density and power density and have been widely used in manufacturing power batteries. Increasing the nickel content can increase the energy density of the ternary cathode material, but will reduce the cycle stability and thermal stability of the material. Lithium nickelate (LiNiO ₂ ) has a high energy density (>900Wh/kg material level). However, it is difficult to obtain a phase that meets the theoretical stoichiometric ratio during the synthesis of this type of material. It is usually lithium deficient (Li and Ni substances The ratio of the amount is less than 1). During the electrochemical cycle, the material is prone to structural transformation from the lamellar phase to the rock salt phase, and is also prone to losing lattice oxygen. Therefore, the cycle stability is poor, and the structural transformation also leads to poor rate performance. In order to improve energy density, the existing technology proposes a variety of lithium-rich cathode materials (usually the ratio of Li and transition metal substances is greater than 1.1:0.9), but traditional lithium-rich cathode materials are composed of two structural units, namely R -3m (layered structure LiMO ₂ , M=Ni, Co, Mn and other transition metals) and c/2m (monoclinic structure Li ₂ MO ₃ , M=Mn, Co, or Ni) structural units, but contain c/2m Due to its thermodynamic properties, the material of the unit (Li ₂ MO ₃ unit, M=Mn, Co or Ni) needs to be charged to a high voltage (>4.5V vs Li ⁺ /Li) in order to deintercalate more lithium ions and achieve high energy density. Such high voltage exceeds the stability window of the electrolyte, resulting in poor material interface stability and affecting its cycle life. That is, it is difficult for cathode materials in the existing technology to achieve high energy density, excellent cycle stability and thermal stability.

Contents of the invention

In view of the shortcomings and deficiencies of the existing technology, the present invention provides a lithium nickelate cathode material. When used in a lithium-ion battery, the lithium-ion battery has high energy density and excellent cycle stability and thermal stability.

In order to solve the above technical problems, a technical solution adopted by the present invention is as follows:

A lithium nickelate cathode material. The chemical formula of the lithium nickelate cathode material is Li _1+x Ni _1-x O ₂ , where 0.02≤x≤0.08; the crystal structure of the lithium nickelate cathode material is α- NaFeO ₂ type hexagonal layered structure, the space group of the crystal structure of the lithium nickelate cathode material is R-3m type; in the crystal structure of the lithium nickelate cathode material, Li occupies a layer that is surplus in the Ni stoichiometric ratio The octahedral voids in the Ni layer in the structure are randomly distributed in the octahedral voids.

The molar ratio of Li to Ni in the above-mentioned lithium nickelate cathode material is slightly greater than 1:1, and the cathode material is in a slightly lithium-rich state.

In some embodiments, 0.03≤x≤0.06.

In some embodiments, 0.04≤x≤0.05.

In some embodiments, using neutron diffraction detection, no Li ₂ NiO ₃ unit containing space group c/2m in the crystal structure is detected.

The invention also provides a lithium nickelate cathode material. The chemical formula of the lithium nickelate cathode material is Li _1+x Ni _1-x O ₂ , where 0.02≤x≤0.08; the crystal of the lithium nickelate cathode material The structure is an α-NaFeO ₂ -type hexagonal layered structure, and the space group of the crystal structure is R-3m type.

In some embodiments, 0.03≤x≤0.06.

In some embodiments, 0.04≤x≤0.05.

In some embodiments, in the crystal structure of the lithium nickelate cathode material, Li which is abundant relative to the Ni stoichiometric ratio occupies the octahedral voids in the Ni layer in the layered structure and is randomly distributed in the octahedral voids. .

In the present invention, during neutron diffraction test characterization, no peaks of the superstructure can be observed, that is, no Li ₂ NiO ₃ unit with space group c/2m can be detected. Therefore, it can be determined that the crystal structure of the lithium nickelate cathode material does not contain Li ₂ NiO ₃ unit with space group c/2m.

The invention also provides a lithium nickelate cathode material. The chemical formula of the lithium nickelate cathode material is Li _1+x Ni _1-x O ₂ , where 0.02≤x≤0.08. The lithium nickelate cathode material includes It is prepared by the preparation method of the following steps: (1) reacting a nickel source and a lithium source with oxygen in the presence of a molten salt additive to obtain a product containing lithium nickelate; (2) conducting the reaction on the product containing lithium nickelate Purify to obtain a powder containing lithium nickelate, and place the powder in an oxygen environment to obtain the lithium nickelate cathode material.

In the present invention, the molten salt additive refers to an additive that can form a eutectic mixture with a lower eutectic point with the lithium source in the reaction raw materials. The molten salt additive can be a lithium-containing molten salt or a lithium-free molten salt. Salt.

The present invention also provides a method for preparing the aforementioned lithium nickelate cathode material, which can stably prepare slightly lithium-rich lithium nickelate cathode material. The preparation method includes the following steps:

(1) react the nickel source and the lithium source with oxygen in the presence of a molten salt additive to obtain a product containing lithium nickelate;

(2) Purify the product containing lithium nickelate to obtain a powder containing lithium nickelate, and place the powder in an oxygen environment to obtain the lithium nickelate cathode material.

The product containing lithium nickelate obtained in the aforementioned step (1) usually contains an excess of lithium source and molten salt additives in addition to lithium nickelate.

The purification step in the aforementioned step (2) can remove excess lithium source and molten salt additives, but this process may cause damage to the surface structure of lithium nickelate. In step (2), placing the powder in an oxygen environment can The surface structure of lithium nickelate is repaired, so that the crystal structure of the final lithium nickelate cathode material has a perfect layered structure with a space group of only R-3m.

In some embodiments, the nickel source is selected from one or more of NiO, Ni(OH) ₂ or _NiCO3 .

In some embodiments, the lithium source is selected from LiOH or LiOH·H ₂ O.

The molten salt additive is selected from one or more of Li ₂ SO ₄ , Na ₂ SO ₄ and K ₂ SO ₄ .

In some embodiments, the molten salt additive is Li ₂ SO ₄ .

In some embodiments, the material amount ratio of the lithium source to the nickel source is 1.1-1.7:1.

In some embodiments, the material amount ratio of the lithium source to the nickel source is 1.3-1.5:1.

In some embodiments, the ratio of the molten salt additive to the amount of the nickel source is 0.1-0.5:1.

In some embodiments, the ratio of the molten salt additive to the amount of the nickel source is 0.27-0.5:1.

In some embodiments, in step (1), the reaction temperature is 550-650°C.

In some embodiments, in step (1), the reaction time is 10-20 hours.

In some embodiments, in step (2), the temperature of the oxygen environment is 450-550°C.

In some embodiments, in step (2), the time of being placed in an oxygen environment is 2-5 hours.

In some embodiments, in step (2), the purification includes water washing and filtration.

In some embodiments, the method further includes the step of pulverizing the lithium nickelate-containing product prior to the purification.

In some embodiments, the method includes the following steps:

(1) Mix the nickel source, lithium source and molten salt additive evenly to obtain a mixture, place the mixture in a reactor, pass oxygen into the reactor, and heat up to react to obtain a product containing lithium nickelate ;

(2) The product containing lithium nickelate is pulverized, washed with water, and filtered to obtain a powder containing lithium nickelate. The powder is placed in a reactor, oxygen is introduced into the reactor, and the temperature is raised to obtain The lithium nickelate cathode material. The aforementioned water washing can remove excess lithium source and molten salt additives.

In some embodiments, in step (1), the flow rate of oxygen is 0.1-0.5L/min.

In some embodiments, in step (1), the heating rate is 2-10°C/min.

In some embodiments, in step (1), the reaction is followed by cooling. Preferably, the temperature cooling rate is 2-10°C/min.

In some embodiments, in step (2), the flow rate of oxygen is 0.1-0.5L/min.

In some embodiments, in step (2), the heating rate is 2-10°C/min.

In some embodiments, in step (2), the temperature is lowered after the temperature increase. Preferably, the temperature decrease rate is 2-10°C/min.

In some embodiments, the reactor is a tube furnace.

The present invention also provides the application of the aforementioned lithium nickelate cathode material in lithium ion batteries.

The present invention also provides a lithium ion battery, including a positive electrode, and the positive electrode includes the aforementioned lithium nickelate positive electrode material. In some embodiments, the first discharge energy density of the lithium-ion battery is greater than or equal to 904Wh/kg at a rate of 0.1C.

In some embodiments, the discharge specific capacity retention rate of the lithium-ion battery is greater than or equal to 92.3% after 100 cycles of charge and discharge cycles in a voltage range of 4.3-2.8V at a rate of 1C.

In some embodiments, the thermal runaway temperature T2 of the lithium-ion battery (the temperature at which the self-heating temperature rise is greater than 1°C/min) is greater than or equal to 253.2°C.

Compared with the existing technology, the present invention has the following technical advantages:

The lithium nickelate cathode material of the present invention has a thermodynamically stable α-NaFeO _2- type hexagonal layered structure. The space group of its crystal structure is R-3m type and does not contain Li ₂ NiO ₃ units with a space group of c/2m. It overcomes the problem of In order to overcome the shortcoming of traditional cathode materials that cannot simultaneously satisfy excellent cycle stability and high rate performance, the lithium nickelate cathode material of the present invention has high cycle stability, high rate performance and high thermal stability at the same time.

The present invention introduces a slightly excessive stoichiometric ratio of lithium ions into the nickel layer in the layered structure of lithium nickel oxide through the method of molten salt chemistry, thereby obtaining a slightly lithium-rich lithium nickelate positive electrode without changing the layered crystal structure. Material, when applied to the cathode of a lithium-ion battery, the lithium-ion battery can achieve an energy density of >900Wh/kg when charged to 4.3V (vs Li ⁺ /Li), and has excellent cycle stability and rate performance.

Description of drawings

Figure 1. Neutron diffraction test results of cathode material 1 in Example 1;

Figure 2. Scanning transmission electron microscope photo of cathode material 1 in Example 1;

Figure 3. Electrochemical charge and discharge test results of cathode material 1 in Example 1 and comparative cathode material 1 in Comparative Example 1;

Figure 4. Rate test results of positive electrode material 1 in Example 1 and comparative positive electrode material 1 in Comparative Example 1;

Figure 5. The first charge-discharge curve of cathode material 1 in Example 1;

Figure 6. Thermal safety test results of the positive electrode material 1 in Example 1 and the comparative positive electrode material 1 in Comparative Example 1 in the charged state;

Figure 7. Oxygen release test results of positive electrode material 1 in Example 1 and conventional lithium-deficient lithium nickelate in the prior art;

Figure 8. Scanning transmission electron microscopy imaging results of cathode material 1 in Example 1;

Figure 9. Neutron diffraction pattern of the cathode material in Comparative Example 6.

Detailed ways

Lithium nickelate (LiNiO ₂ ) has a high energy density (>900Wh/kg). However, it is not easy to obtain a phase that meets the theoretical stoichiometric ratio during the synthesis of this type of material. It is usually lithium deficient (the amount of Li and Ni substances The ratio is less than 1). During the electrochemical cycle, the material is prone to structural transformation from the lamellar phase to the rock salt phase, and is also prone to losing lattice oxygen. Therefore, the cycle stability is poor, and the structural transformation also leads to poor rate performance.

Traditional lithium nickelate is usually prepared through solid-state reaction, resulting in lithium-deficient lithium nickelate, whose chemical formula is Li _1-y Ni _1+y O ₂ . In order to improve the performance of the lithium nickelate, it is usually doped through lattice Or surface coating to modify the structure.

The slightly lithium-rich lithium nickelate cathode material with the chemical formula Li _1+x Ni _1-x O ₂ cannot be prepared by traditional solid-state reaction preparation methods. It turns out that although the phase of this material is predicted to be a possible phase based on the Li-Ni-O phase diagram, it cannot be actually prepared through experiments.

Although there are other types of lithium-rich cathode materials in the prior art, the ratio of Li to transition metals in such materials is usually greater than 1.1:0.9. However, in the crystal structure of such materials, except for the layered structure of R- In addition to the 3m structural unit, there are also c/2m (monoclinic structure Li ₂ NiO ₃ ) structural units. As a result, although this type of material can achieve high energy density under high pressure, its cycle stability is poor.

The present invention creatively adopts the method of molten salt chemistry and adds molten salt additives when synthesizing lithium nickelate to prepare a slightly lithium-rich lithium nickelate cathode material with a layered structure containing only R-3m structural units. Its chemical formula is: Li _1+x Ni _1-x O ₂ . When the cathode material is used in lithium-ion batteries, the lithium-ion battery has high energy density, excellent cycle stability and thermal stability.

Example 1

Mix Ni(OH) ₂ with LiOH and Li ₂ SO ₄ evenly (the ratio of the amounts of materials between the three is 1:1.3:0.27), then add the mixed powder to the corundum porcelain boat and put it into the tube furnace , pure oxygen is introduced at a flow rate of 0.2 liters/minute, and the temperature is raised to 600 degrees at a heating rate of 5 degrees/minute. After being kept at 600 degrees for 15 hours, it is lowered to room temperature at a cooling rate of 5 degrees/minute.

Then take out the cooled powder, mechanically crush it and add deionized water to dissolve excess LiOH and Li ₂ SO ₄ . After filtering, take the solid part and air-dry it at 60 degrees. The dried powder is added to the corundum porcelain boat again, placed in a tube furnace, pure oxygen is introduced at a flow rate of 0.2 liters/minute, raised to 500 degrees at a heating rate of 5 degrees/minute, and kept at 500 degrees for 5 hours. , lowered to room temperature at a cooling rate of 5 degrees/min, and obtained cathode material 1.

The crystal structure of the cathode material 1 was characterized by neutron diffraction (Figure 1), and it was confirmed that it has a layered structure, the space group is R-3m, and it does not contain c/2m Li ₂ NiO _{3 units because no c/2m Li 2 NiO 3} units were observed. The peak of the superstructure, where the superstructure refers to the in-plane superstructure caused by the orderly arrangement of Li and Ni forming Li@Ni6 in the Ni layer. This superstructure corresponds to the Li ₂ NiO ₃ unit of c/2m symmetry. . Scanning transmission electron microscopy imaging was further used to confirm that excess Li ions were randomly distributed in the Ni layer. The results of scanning transmission electron microscopy imaging are shown in Figure 8. Since Li is lighter than Ni, the contrast is darker. From Figure 8 It can be seen that the darker points correspond to the presence of Li atoms replacing Ni in the Ni layer, and are randomly distributed (as pointed by the arrows in Figure 8). Scanning transmission electron microscopy imaging also confirmed that the material has a layered structure (Figure 2). The elemental composition of the material was analyzed using ICP, and it was confirmed that the material ratio of Li and Ni was 1.04:0.96 (i.e., x=0.04 in the chemical formula Li _1+x Ni _1-x O ₂ ). The results are shown in Table 1.

Example 2

Mix Ni(OH) ₂ with LiOH and Li ₂ SO ₄ evenly (the ratio of the amounts of materials between the three is 1:1.1:0.27), then add the mixed powder to the corundum porcelain boat and put it into the tube furnace , pure oxygen is introduced at a flow rate of 0.5 liters/minute, and the temperature is raised to 650 degrees at a heating rate of 2 degrees/minute. After being kept at 650 degrees for 15 hours, it is lowered to room temperature at a cooling rate of 2 degrees/minute.

Then take out the cooled powder, mechanically crush it, add deionized water to dissolve excess LiOH and Li ₂ SO ₄ , and filter Then take the solid part and dry it with air at 60 degrees. The dried powder is added to the corundum porcelain boat again, placed in a tube furnace, pure oxygen is introduced at a flow rate of 0.5 liters/minute, raised to 450 degrees at a heating rate of 2 degrees/minute, and kept at 450 degrees for 2 hours. , to room temperature at a cooling rate of 2 degrees/minute, to obtain cathode material 2. The elemental composition of the material was analyzed using ICP, and the results are shown in Table 1.

Example 3

Mix Ni(OH) ₂ with LiOH and Li ₂ SO ₄ evenly (the ratio of the amounts of materials between the three is 1:1.7:0.27), then add the mixed powder to the corundum porcelain boat and put it into the tube furnace , pure oxygen is introduced at a flow rate of 0.1 liters/minute, and the temperature is raised to 550 degrees at a heating rate of 10 degrees/minute. After being kept at 550 degrees for 15 hours, it is lowered to room temperature at a cooling rate of 10 degrees/minute.

Then take out the cooled powder, mechanically crush it and add deionized water to dissolve excess LiOH and Li ₂ SO ₄ . After filtering, take the solid part and air-dry it at 60 degrees. The dried powder is added to the corundum porcelain boat again, placed in a tube furnace, pure oxygen is introduced at a flow rate of 0.1 liters/minute, raised to 550 degrees at a heating rate of 10 degrees/minute, and kept at 550 degrees for 4 hours. , lowered to room temperature at a cooling rate of 10 degrees/min, and obtained cathode material 3. The elemental composition of the material was analyzed using ICP, and the results are shown in Table 1.

Example 4

Mix Ni(OH) ₂ with LiOH and Li ₂ SO ₄ evenly (the ratio of the amounts of materials between the three is 1:1.5:0.1), then add the mixed powder to the corundum porcelain boat and put it into the tube furnace , pure oxygen is introduced at a flow rate of 0.2 liters/minute, and the temperature is raised to 600 degrees at a heating rate of 5 degrees/minute. After being kept at 600 degrees for 15 hours, it is lowered to room temperature at a cooling rate of 5 degrees/minute.

Then take out the cooled powder, mechanically crush it and add deionized water to dissolve excess LiOH and Li ₂ SO ₄ . After filtering, take the solid part and air-dry it at 60 degrees. The dried powder is added to the corundum porcelain boat again, placed in a tube furnace, pure oxygen is introduced at a flow rate of 0.2 liters/minute, raised to 500 degrees at a heating rate of 5 degrees/minute, and kept at 500 degrees for 5 hours. , lowered to room temperature at a cooling rate of 5 degrees/min, and obtained cathode material 4. The elemental composition of the material was analyzed using ICP, and the results are shown in Table 1.

Example 5

Mix Ni(OH) ₂ with LiOH and Li ₂ SO ₄ evenly (the ratio of the amounts of materials between the three is 1:1.5:0.5), then add the mixed powder to the corundum porcelain boat and put it into the tube furnace , pure oxygen is introduced at a flow rate of 0.2 liters/minute, and the temperature is raised to 600 degrees at a heating rate of 5 degrees/minute. After being kept at 600 degrees for 15 hours, it is lowered to room temperature at a cooling rate of 5 degrees/minute.

Then take out the cooled powder, mechanically crush it and add deionized water to dissolve excess LiOH and Li ₂ SO ₄ . After filtering, take the solid part and air-dry it at 60 degrees. The dried powder is added to the corundum porcelain boat again, placed in a tube furnace, pure oxygen is introduced at a flow rate of 0.2 liters/minute, raised to 500 degrees at a heating rate of 5 degrees/minute, and kept at 500 degrees for 5 hours. , lowered to room temperature at a cooling rate of 5 degrees/min, and obtained cathode material 5. The elemental composition of the material was analyzed using ICP, and the results are shown in Table 1.

Example 6

Mix NiO, LiOH·H ₂ O and Li ₂ SO ₄ evenly (the ratio of the three substances is 1:1.3:0.27), then add the mixed powder to the corundum porcelain boat and put it into the tube furnace , pure oxygen is introduced at a flow rate of 0.2 liters/minute, and the temperature is raised to 600 degrees at a heating rate of 5 degrees/minute. After being kept at 600 degrees for 15 hours, it is lowered to room temperature at a cooling rate of 5 degrees/minute.

Then take out the cooled powder, mechanically crush it and add deionized water to dissolve the excess LiOH·H ₂ O and Li ₂ SO _4. After filtering, take the solid part and dry it with air at 60 degrees. The dried powder is added to the corundum porcelain boat again, placed in a tube furnace, pure oxygen is introduced at a flow rate of 0.2 liters/minute, raised to 500 degrees at a heating rate of 5 degrees/minute, and kept at 500 degrees for 5 hours. , lowered to room temperature at a cooling rate of 5 degrees/min, and obtained cathode material 6. The elemental composition of the material was analyzed using ICP, and the results are shown in Table 1.

Example 7

Mix NiCO ₃ with LiOH and Li ₂ SO ₄ evenly (the ratio of the amounts of materials between the three is 1:1.3:0.27), then add the mixed powder to the corundum porcelain boat and put it into the tube furnace. Pure oxygen was introduced at a flow rate of 0.2 liters/minute, and the temperature was raised to 600 degrees at a heating rate of 5 degrees/minute. After being kept at 600 degrees for 15 hours, it was lowered to room temperature at a cooling rate of 5 degrees/minute.

Then take out the cooled powder, mechanically crush it and add deionized water to dissolve excess LiOH and Li ₂ SO ₄ . After filtering, take the solid part and air-dry it at 60 degrees. The dried powder is added to the corundum porcelain boat again, placed in a tube furnace, pure oxygen is introduced at a flow rate of 0.2 liters/minute, raised to 500 degrees at a heating rate of 5 degrees/minute, and kept at 500 degrees for 5 hours. , lowered to room temperature at a cooling rate of 5 degrees/min, and obtained cathode material 7. The elemental composition of the material was analyzed using ICP, and the results are shown in Table 1.

Comparative example 1

Mix Ni(OH) ₂ and LiOH evenly (the ratio of the two substances is 1:1.02), then add the mixed powder to the corundum porcelain boat, put it into a tube furnace, and heat it at 0.2 liters/minute. Pour in pure oxygen at a flow rate, raise it to 485 degrees at a heating rate of 5 degrees/minute, keep it warm for 3 hours, then continue to raise the temperature to 700 degrees and keep it warm for 20 hours, then drop to room temperature at a cooling rate of 5 degrees/minute. Comparative positive electrode material 1 was obtained. The elemental composition of the material was analyzed using ICP, and the results are shown in Table 1.

Performance Testing:

Electrochemical cycle stability: The positive electrode material 1 of Example 1 was mixed with a lithium sheet, a separator, and an electrolyte (lithium hexafluorophosphate dissolved in dimethyl carbonate and fluoroethylene carbonate with a volume ratio of 1:1, a solution of lithium hexafluorophosphate The concentration is 1mol/L) and assembled into a button cell in an argon-protected glove box, and charged and discharged at a voltage range of 4.3-2.8V at a rate of 1C. The same operation was performed on the cathode material 1 of Example 1, and the electrochemical cycle stability results tested are shown in Figure 3.

Rate performance: The same button battery as mentioned above was used to evaluate the rate performance of the two materials. After charging to 4.3V at a rate of 0.2C, it was discharged at a rate of 0.5 to 10C. The test results are shown in Figure 4. Among them, the first discharge energy density of the battery corresponding to the cathode material 1 of Example 1 is obtained by integrating the charge and discharge curves, and is 904 Wh/kg (Figure 5).

Example 8 (thermal safety test)

The cathode material 1 of Example 1 was used to assemble a pouch battery for thermal safety evaluation. The assembly method is as follows: (1) Positive electrode sheet production: combine active material (positive electrode material 1 in Example 1), conductive agent (carbon black) and binder (5wt% polyvinylidene fluoride/N-methylpyrrolidone solution) Mix it at a mass ratio of 94:3:3, add N-methylpyrrolidone (NMP) to adjust the solid content to 65%, coat it on 13μm aluminum foil, dry it and use a punching machine to punch it into 55mm*35mm (H*W ) pole piece, after rolling, vacuum bake at 120°C for 12 hours; (2) Negative pole piece production: combine active material (graphite), conductive agent (carbon black) and binder (5wt% polyvinylidene fluoride/N- Methyl pyrrolidone solution) was mixed at a mass ratio of 94:3:3, and NMP was added to adjust the solid content to 45%. Coat it on a 10 μm copper foil. After drying, use a punching machine to punch it into 57mm*37mm (H*W). The pole pieces are rolled and vacuum dried at 80°C for 12 hours. (3) Soft-packed battery core production: 16μm PE separator and positive and negative electrodes are stacked to form a battery core, ensuring that each positive electrode has a corresponding negative electrode, and the outermost layer is wrapped with a separator and then polyimide The tape sticks. Use an ultrasonic welding machine to weld the aluminum and nickel tabs to the positive and negative exposed tabs respectively. The welds are taped with polyimide tape. The outer layer of the battery core is wrapped with aluminum plastic film and an opening is left for injecting electrolyte. The finished battery cells are vacuum baked at 60°C for 6 hours. The battery capacity is set to 30mAh. (4) Battery production: Use a straw to add 0.5g of electrolyte (the electrolyte composition is a 1.2M lithium hexafluorophosphate solution, the solvent is a mixed solvent of ethylene carbonate EC and ethyl methyl carbonate EMC with a weight ratio of 3:7, and the solvent is Inject vinylene carbonate (VC) containing 2% mass percentage into the battery core, and use a sealing machine to seal the injection port. Test after placing it flat for 10 hours. (5) Battery formation and testing: Clamp the battery with a clamp and test it on a charge and discharge tester. Charge it to 4.25V with a constant current of 0.1C (22mA/g, based on the mass of the positive active material, the same below). Press to 0.05C. Use 0.1C to discharge to 2.75V, cycle the above steps three times, and the battery formation is completed.

The thermal safety evaluation method is as follows: charge the two soft-pack batteries at a constant current of 0.1C to 4.25V, and then use a constant voltage of 0.05C for later use. Open the acceleration calorimeter cavity, stick the front end of the thermocouple to the center of one battery with aluminum tape, then overlap the other battery, use aluminum tape to join the two batteries together and fix them on a special test rack in the cavity. Close the upper cover of the acceleration calorimeter and start the acceleration calorimeter program for testing. The specific test procedure is: start the test at 25°C, first enter the heating mode to heat the cavity, heat 5°C (10 minutes) each time and monitor the battery temperature. Then, let it stand for 30 minutes and enter the search mode. During this period, if the temperature rise rate is lower than 0.02℃/min, heating will continue after the rest. If the temperature rise rate is higher than 0.02℃/min, it will enter the heat release mode. , the cavity is no longer heated, and only the temperature changes are recorded. After the temperature exceeds 300°C, it enters cooling mode and the test is completed. The test results are shown in Figure 6. The battery equipped with the cathode material 1 of Example 1 has a relatively high T2 temperature (thermal runaway temperature, a temperature where the self-heating temperature rise is greater than 1 degree/min), which is 253.2 degrees.

Comparative Example 2 (Thermal Safety Test)

The assembly method and thermal safety evaluation method of the soft-pack battery are the same as in Example 8, except that the positive electrode material 1 of Example 1 is replaced by the comparative positive electrode material 1 of Comparative Example 1. The test results are shown in Figure 6. The T2 temperature (thermal runaway temperature, self-heating temperature rise is greater than 1 degree/min temperature) is 179.0 degrees. Therefore, Comparative Example 2 is more prone to thermal runaway than Example 8.

In-situ differential electrochemical mass spectrometry DEMS was used to conduct oxygen and carbon dioxide release tests on the lithium nickelate cathode material of Example 1 and the conventional lithium-deficient lithium nickelate cathode material in the prior art. The test conditions were the first charge, The magnification is 0.1C, and the results are shown in Figure 7, where A is conventional lithium nickelate (LNO), and B is the lithium nickelate of Example 1 (slightly lithium-rich LR-LNO). It can be seen that in conventional lithium nickelate, the removal When lithium is used, 4.2 μmol/g of O ₂ and 86.5 μmol/g of CO ₂ are produced, while the lithium nickelate of Example 1 does not release oxygen at all.

Example 9

It is basically the same as Example 1, except that Li ₂ SO ₄ is replaced by Na ₂ SO ₄ .

Example 10

It is basically the same as Example 1, except that Li ₂ SO ₄ is replaced by K ₂ SO ₄ .

Comparative example 3

Basically the same as Example 1, the only difference is that Li ₂ SO ₄ is not added.

Comparative example 4

Basically the same as Example 1, the only difference is that the ratio of the amounts of Ni(OH) ₂ , LiOH and Li ₂ SO ₄ is 1:1.05:0.27.

Comparative example 5

Basically the same as Example 1, the only difference is that the ratio of the amounts of Ni(OH) ₂ , LiOH and Li ₂ SO ₄ is 1:2:0.27.

Comparative example 6

The solution of the embodiment in JP2015082345A is as follows:

Lithium peroxide (Li ₂ O ₂ ) and nanoscale nickel oxide are used as starting materials. These raw materials are pulverized and mixed to a molar ratio of Li/Ni=1.9. The mixture is filled into a platinum tank. By using a cubic anvil type high pressure The device is used to sinter the raw material mixture at 700°C for 1 hour under a pressure of 4 GPa to obtain lithium-rich lithium nickelate. The average particle size is about 50 to 100nm. The amount of each element was analyzed by ICP emission spectrum analysis, and it was confirmed that its composition is Li _1.30 Ni _0.70 O ₂ . Figure 2 (neutron diffraction pattern) of the patent is shown in Figure 9. It can be seen that the cathode material has a layered structure. In addition to R-3m, the space group also contains c/2m Li ₂ NiO ₃ units, because Figure There is a very obvious superstructure peak in 9 (2θ is in the range of 20-25 degrees, corresponding to the dotted box), corresponding to the c/2m Li ₂ NiO ₃ (here M = Ni) unit, that is, the Li@Ni6 The sequence is arranged in the Ni layer.

The elemental composition of the materials of Examples 9-10 and Comparative Examples 3-5 was analyzed by ICP, and the results are shown in Table 1.

Table 1. Elemental analysis results of Examples and Comparative Examples

Claims

A lithium nickelate cathode material, characterized in that the chemical formula of the lithium nickelate cathode material is Li 1+x Ni 1-x O 2 , where 0.02≤x≤0.08; the crystal of the lithium nickelate cathode material The structure is an α-NaFeO 2- type hexagonal layered structure, and the space group of the crystal structure of the lithium nickelate cathode material is R-3m type; in the crystal structure of the lithium nickelate cathode material, there is a surplus relative to the Ni stoichiometric ratio Li occupies the octahedral voids in the Ni layer in the layered structure and is randomly distributed in the octahedral voids.
The lithium nickelate cathode material according to claim 1, characterized in that, 0.03≤x≤0.06.
The lithium nickelate cathode material according to claim 1, characterized in that, 0.04≤x≤0.05.
A lithium nickelate cathode material, characterized in that the chemical formula of the lithium nickelate cathode material is Li 1+x Ni 1-x O 2 , where 0.02≤x≤0.08; the crystal of the lithium nickelate cathode material The structure is an α-NaFeO 2 -type hexagonal layered structure, and the space group of the crystal structure is R-3m type.
The lithium nickelate cathode material according to claim 4, characterized in that, in the crystal structure of the lithium nickelate cathode material, Li which is excess relative to the Ni stoichiometric ratio occupies the octahedral voids in the Ni layer in the layered structure. , and randomly distributed in the octahedral voids.
The lithium nickelate cathode material according to claim 1 or 4, characterized in that, using neutron diffraction detection, no Li 2 NiO 3 unit with a space group of c/2m is detected in the crystal structure.
A lithium nickelate cathode material, characterized in that the chemical formula of the lithium nickelate cathode material is Li 1+x Ni 1-x O 2 , where 0.02≤x≤0.08, and the lithium nickelate cathode material includes It is prepared by the preparation method of the following steps: (1) reacting a nickel source and a lithium source with oxygen in the presence of a molten salt additive to obtain a product containing lithium nickelate; (2) conducting the reaction on the product containing lithium nickelate Purify to obtain a powder containing lithium nickelate, and place the powder in an oxygen environment to obtain the lithium nickelate cathode material.
A method for preparing the lithium nickelate cathode material according to any one of claims 1 to 6, characterized in that the method includes the following steps:

(1) react the nickel source and the lithium source with oxygen in the presence of a molten salt additive to obtain a product containing lithium nickelate;

(2) Purify the product containing lithium nickelate to obtain a powder containing lithium nickelate, and place the powder in an oxygen environment to obtain the lithium nickelate cathode material.
The method of claim 8, wherein the nickel source is selected from one or more of NiO, Ni(OH) 2 or NiCO3 .
The method of claim 8, wherein the lithium source is selected from LiOH or LiOH·H 2 O.
The method according to claim 8, characterized in that the molten salt additive is selected from one or more of Li 2 SO 4 , Na 2 SO 4 and K 2 SO 4 .
The method of claim 8, wherein the molten salt additive is Li 2 SO 4 .
The method according to claim 8, characterized in that the ratio of the material amounts of the lithium source and the nickel source is 1.1-1.7:1; and/or, the ratio of the material amounts of the molten salt additive to the nickel source The ratio is 0.1-0.5:1.
The method according to claim 8, characterized in that the ratio of the material amounts of the lithium source and the nickel source is 1.3-1.5:1; and/or, the ratio of the material amounts of the molten salt additive to the nickel source The ratio is 0.27-0.5:1.
The method according to claim 8, characterized in that, in step (1), the reaction temperature is 550-650°C; and/or, in step (1), the reaction time is 10-20 hours ; And/or, in step (2), the temperature of the oxygen environment is 450-550°C; and/or, in step (2), the time of being placed in the oxygen environment is 2-5 hours.
The method according to claim 8, characterized in that in step (2), the purification includes water washing and filtration; and/or the method further includes, before the purification, treating the lithium nickelate-containing The product undergoes a crushing step.
The method according to claim 8, characterized in that the method includes the following steps:

(1) Mix the nickel source, lithium source and molten salt additive evenly to obtain a mixture, place the mixture in a reactor, pass oxygen into the reactor, and heat up to react to obtain a product containing lithium nickelate ;

(2) The product containing lithium nickelate is pulverized, washed with water, and filtered to obtain a powder containing lithium nickelate. The powder is placed in a reactor, oxygen is introduced into the reactor, and the temperature is raised to obtain The lithium nickelate cathode material.
The method according to claim 17, characterized in that, in step (1), the flow rate of oxygen introduced is 0.1-0.5L/min; and/or, in step (1), the rate of temperature increase is 2-10℃/min.
The method according to claim 17, characterized in that, in step (2), the flow rate of oxygen introduced is 0.1-0.5L/min; and/or, in step (2), the rate of temperature increase is 2-10℃/min.
Application of the lithium nickelate cathode material according to any one of claims 1 to 7 in lithium ion batteries.
A lithium ion battery includes a positive electrode, characterized in that the positive electrode includes the lithium nickelate positive electrode material according to any one of claims 1 to 7.
The lithium-ion battery according to claim 21, wherein the first discharge energy density of the lithium-ion battery is greater than or equal to 904Wh/kg at a rate of 0.1C; and/or the lithium-ion battery has an energy density of 4.3 at a rate of 1C. After 100 cycles of charge and discharge cycles in the -2.8V voltage range, the discharge specific capacity retention rate is greater than or equal to 92.3%.