Lithium nickelate cathode material, method for manufacturing the same, and use

Abstract

A lithium nickel oxide positive electrode material and its manufacturing method and use, wherein the positive electrode material has the chemical formula L i1+x Ni 1-x O2, where 0.02≦x≦0.08, and its crystal structure is an α-NaFeO2-type hexagonal layered structure and the space group is R-3m. Li, which is in stoichiometric excess over Ni, occupies the octahedral voids in the Ni layers and is randomly distributed in the octahedral voids. The preparation method includes: (1) reacting a nickel source and a lithium source with oxygen in the presence of a molten salt additive to obtain a lithium nickel oxide-containing product; and (2) purifying the lithium nickel oxide-containing product to obtain a lithium nickel oxide-containing powder, which is then placed in an oxygen environment to obtain a lithium nickel oxide positive electrode material. When used in lithium-ion batteries, this positive electrode material can achieve high energy density and exhibit excellent cycling and thermal stability.

Description

[Technical Field]

[0001] This invention belongs to the field of lithium-ion technology, and more specifically, relates to lithium nickelate cathode materials, methods for producing the same, and their use. [Background technology]

[0002] Ternary materials, such as lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, can provide good energy density and power density and are widely used in the manufacture of power batteries. Increasing the nickel content can increase the energy density of ternary cathode materials, but it can decrease the cycle stability and thermal stability of the material. Lithium nickelate (LiNiO2) has a high energy density (>900 Wh / kg material level), but this type of material is difficult to synthesize into a phase that conforms to the theoretical stoichiometric ratio and is usually lithium-deficient (the ratio of the amount of Li to Ni is less than 1). In the electrochemical cycle process, this material is prone to structural transformation from a layered phase to a rock salt phase and is prone to losing lattice oxygen, resulting in low cycle stability and reduced magnification performance due to structural transformation. To improve energy density, conventional technologies have proposed various lithium-rich cathode materials (typically those with a ratio of Li to transition metal greater than 1.1:0.9). However, conventional lithium-rich cathode materials are composed of two structural units: R-3m (layered structure LiMO2, M=Ni, Co, Mn, or other transition metals) and c / 2m (monoclinic structure Li2MO3, M=Mn, Co, or Ni). Materials containing the c / 2m unit (Li2MO3 unit, M=Mn, Co, or Ni) can extract more lithium ions due to their thermodynamic properties, and to achieve high energy density, high voltage (>4.5V vs Li) is required. + It is necessary to charge up to 1 / Li. Such high voltages exceed the electrolyte's stability window, reducing the stability of the material interface and affecting its cycle life. In other words, it is difficult to achieve high energy density, excellent cycle stability, and excellent thermal stability with conventional cathode materials. [Overview of the project] [Problems that the invention aims to solve]

[0003] In order to address the shortcomings and deficiencies of the prior art, the present invention provides a lithium nickelate cathode material that, when used in lithium-ion batteries, simultaneously provides lithium-ion batteries with high energy density, excellent cycling stability and thermal stability. [Means for solving the problem]

[0004] To solve the above technical problems, the technical solutions adopted in the present invention are as follows.

[0005] A lithium nickelate cathode material, wherein the lithium nickelate cathode material has the chemical formula Li 1+x Ni 1-x The ratio is O2, where 0.02 ≤ x ≤ 0.08. The lithium nickelate cathode material has a hexagonal layered crystalline structure of the α-NaFeO2 type. The space group of the crystalline structure of the lithium nickelate cathode material is R-3m type. In the crystalline structure of the lithium nickelate cathode material, Li, which is in excess of Ni in stoichiometric ratio, occupies octahedral voids in the Ni layer of the layered structure and is randomly distributed in these octahedral voids.

[0006] The molar ratio of Li to Ni in the above lithium nickelate cathode material is slightly greater than 1:1, and the cathode material is in a state of slight lithium excess.

[0007] In some embodiments, 0.03 ≤ x ≤ 0.06.

[0008] In some embodiments, 0.04 ≤ x ≤ 0.05.

[0009] In some embodiments, neutron diffraction has not detected the presence of Li2NiO3 units with a space group of c / 2m in the crystal structure.

[0010] The present invention further provides a lithium nickelate cathode material, wherein the lithium nickelate cathode material has the chemical formula Li 1+x Ni 1-x The material is O2, where 0.02 ≤ x ≤ 0.08, and the lithium nickelate cathode material has a crystal structure of the α-NaFeO2 type hexagonal layered structure, and the space group of the crystal structure is of the R-3m type.

[0011] In some embodiments, 0.03 ≤ x ≤ 0.06.

[0012] In some embodiments, 0.04 ≤ x ≤ 0.05.

[0013] In some embodiments, in the crystal structure of the lithium nickelate cathode material, Li in excess of Ni in a stoichiometric ratio occupies octahedral voids in the Ni layer of the layered structure and is randomly distributed in these octahedral voids.

[0014] In some embodiments, neutron diffraction has not detected the presence of Li2NiO3 units with a space group of c / 2m in the crystal structure.

[0015] In this invention, when surface evaluation is performed by neutron diffraction testing, no peaks of the superstructure can be observed, that is, Li2NiO3 units with space group c / 2m are not detected, so it can be determined that the crystal structure of the lithium nickelate cathode material does not contain Li2NiO3 units with space group c / 2m.

[0016] The present invention further provides a lithium nickelate cathode material, wherein the lithium nickelate cathode material has the chemical formula Li 1+x Ni 1-xwhich is O₂, wherein 0.02≦x≦0.08, and the lithium nickelate cathode positive electrode material is produced and obtained by a manufacturing method comprising: (1) a step of reacting a nickel source and a lithium source with oxygen in the presence of a molten salt additive to obtain a lithium nickelate-containing product; and (2) a step of purifying said lithium nickelate-containing product to obtain a powder containing lithium nickelate, and placing said powder in an oxygen environment to obtain said lithium nickelate cathode positive electrode material.

[0017] In the present invention, the molten salt additive refers to an additive capable of forming a eutectic mixture having a lower eutectic point together with a lithium source in reaction raw materials, and the molten salt additive may be a lithium-containing molten salt or a lithium-free molten salt.

[0018] The present invention further provides a method for manufacturing the aforementioned lithium nickelate cathode positive electrode material, which can stably manufacture a lithium nickelate cathode positive electrode material with a slight excess of lithium. Said manufacturing method comprises: (1) a step of reacting a nickel source and a lithium source with oxygen in the presence of a molten salt additive to obtain a lithium nickelate-containing product; (2) a step of purifying said lithium nickelate-containing product to obtain a powder containing lithium nickelate, and placing said powder in an oxygen environment to obtain said lithium nickelate cathode positive electrode material.

[0019] In addition to lithium nickelate, the lithium nickelate-containing product obtained in the aforementioned step (1) usually also contains an excess lithium source and the molten salt additive.

[0020] In the purification step of the aforementioned step (2), excess lithium source and molten salt additive can be removed, but this process may damage the surface structure of lithium nickelate. In step (2), placing the powder in an oxygen environment repairs the surface structure of lithium nickelate, so that the crystal structure of the finally obtained lithium nickelate cathode positive electrode material has a perfect layered structure whose space group is only R-3m.

[0021] In some embodiments, the nickel source is one or more selected from the group consisting of NiO, Ni(OH)₂ and NiCO₃.

[0022] In some embodiments, the lithium source is selected from LiOH or LiOH·H₂O.

[0023] The molten salt additive is one or more selected from the group consisting of Li₂SO₄, Na₂SO₄ and K₂SO₄.

[0024] In some embodiments, the molten salt additive is Li₂SO₄.

[0025] In some embodiments, the molar ratio of the lithium source to the nickel source is 1.1~1.7:1.

[0026] In some embodiments, the molar ratio of the lithium source to the nickel source is 1.3~1.5:1.

[0027] In some embodiments, the molar ratio of the molten salt additive to the nickel source is 0.1~0.5:1.

[0028] In some embodiments, the molar ratio of the molten salt additive to the nickel source is 0.27~0.5:1.

[0029] In some embodiments, in step (1), the temperature of the reaction is 550~650°C.

[0030] In some embodiments, in step (1), the reaction time is 10 to 20 hours.

[0031] In some embodiments, in step (2), the temperature of the oxygen atmosphere is 450~550°C.

[0032] In some embodiments, in step (2), the residence time under the oxygen atmosphere is 2 to 5 hours.

[0033] In some embodiments, step (2) includes washing and filtration.

[0034] In some embodiments, the method further includes a step of grinding the lithium nickelate-containing product before the purification.

[0035] In some embodiments, the method is (1) Mix the nickel source, lithium source and molten salt additive uniformly to obtain a mixture, place the mixture in a reactor, inject oxygen into the reactor, raise the temperature and react, nickel A process for obtaining lithium oxide-containing products, (2) The process includes the steps of crushing, washing, and filtering the lithium nickelate-containing product to obtain a lithium nickelate-containing powder, placing the powder in a reactor, injecting oxygen into the reactor, raising the temperature, and obtaining the lithium nickelate cathode material. The washing described above can remove excess lithium source and molten salt additives.

[0036] In some embodiments, the oxygen injection flow rate in step (1) is 0.1 to 0.5 L / min.

[0037] In some embodiments, the heating rate in step (1) is 2 to 10°C / min.

[0038] In some embodiments, after the reaction in step (1), the mixture is cooled, preferably at a cooling rate of 2 to 10°C / min.

[0039] In some embodiments, in step (2), the oxygen injection flow rate is 0.1 to 0.5 L / min.

[0040] In some embodiments, in step (2), the heating rate is 2 to 10°C / min.

[0041] In some embodiments, step (2) involves further cooling after the heating, preferably with a cooling rate of 2 to 10°C / min.

[0042] In some embodiments, the reactor is a tube furnace.

[0043] The present invention further provides the use of the aforementioned lithium nickelate cathode material in lithium-ion batteries.

[0044] The present invention further provides a lithium-ion battery comprising a cathode containing the lithium nickelate cathode material described above. In some embodiments, the lithium-ion battery has an initial discharge energy density of 904 Wh / kgV or more at a 0.1C multiplier.

[0045] In some embodiments, the lithium-ion battery has a discharge ratio capacity retention rate of 92.3% or more after 100 charge-discharge cycles in a voltage range of 4.3 to 2.8V at a 1C multiplier.

[0046] In some embodiments, the T2 temperature (the temperature at which the temperature rise due to self-heating exceeds 1°C / min), which is the thermal runaway temperature of the lithium-ion battery, is 253.2°C or higher.

[0047] Compared to the prior art, the present invention has the following technical advantages.

[0048] The lithium nickelate cathode material of the present invention has a thermodynamically stable α-NaFeO2 type hexagonal layered structure, and its crystal structure has a space group of R-3m type, and does not contain Li2NiO3 units with a space group of c / 2m. This overcomes the shortcomings of conventional cathode materials that cannot simultaneously satisfy excellent cycle stability and high magnification performance, and the lithium nickelate cathode material of the present invention simultaneously possesses high cycle stability, high magnification performance and high thermal stability.

[0049] In this invention, lithium ions in a slightly excess stoichiometric ratio are introduced into the nickel layer in the layered structure of lithium nickelate by a molten salt chemistry method, thereby altering the layered crystal structure. When a lithium nickelate cathode material with a slight excess of lithium is obtained and used as the cathode of a lithium-ion battery, the lithium-ion battery will have a voltage of 4.3V (vsLi + When charged to 1 / Li, it can achieve an energy density of >900Wh / kg, while also exhibiting excellent cycle stability and multiplier performance. [Brief explanation of the drawing]

[0050] [Figure 1] This shows the neutron diffraction test results for cathode material 1 in Example 1. [Figure 2] This is a scanning transmission electron microscope image of the positive electrode material 1 in Example 1. [Figure 3] These are the electrochemical charge-discharge test results for positive electrode material 1 in Example 1 and comparative positive electrode material 1 in Comparative Example 1. [Figure 4] This shows the magnification test results for cathode material 1 in Example 1 and comparative cathode material 1 in Comparative Example 1. [Figure 5] This is the initial charge-discharge curve of positive electrode material 1 in Example 1. [Figure 6] This shows the thermal safety test results for the charged state of positive electrode material 1 in Example 1 and comparative positive electrode material 1 in Comparative Example 1. [Figure 7] This shows the oxygen release test results for cathode material 1 in Example 1 and conventional lithium-deficient lithium nickelate. [Figure 8] This is a scanning transmission electron microscope image of the positive electrode material 1 in Example 1. [Figure 9] This is a neutron diffraction pattern of the cathode material in Comparative Example 6. [Modes for carrying out the invention]

[0051] Lithium nickelate (LiNiO₂) has a high energy density (>900Wh / kg), but it is difficult for this type of material to obtain a phase matching the theoretical stoichiometric ratio during synthesis, and the material is usually lithium-deficient (the molar ratio of lithium to nickel is less than 1). In the electrochemical cycling process, this material is prone to structural transformation from a layered phase to a rock salt phase and tends to lose lattice oxygen, resulting in low cycling stability and deteriorated rate performance caused by the structural transformation.

[0052] Conventional lithium nickelate is usually produced by solid-state reaction, and the obtained product is lithium-deficient lithium nickelate with a chemical formula of Li 1-y Ni 1+y O₂. To improve the performance of the lithium nickelate, the structure is usually modified by lattice doping or surface coating.

[0053] The slightly lithium-excess lithium nickelate cathode material with the chemical formula Li 1+x Ni 1-x O₂ cannot be produced and obtained by conventional solid-state reaction production methods. Even if it can be predicted from the Li-Ni-O phase diagram that the phase of this material is a feasible phase, it cannot actually be produced and obtained through experiments.

[0054] In the prior art, there are other types of lithium-excess cathode materials. For this type of material, the molar ratio of Li to transition metal is usually greater than 1.1:0.9, but in the crystal structure of this type of material, in addition to the R-3m structural unit of the layered structure, there is also a c / 2m (monoclinic structure Li₂NiO₃) structural unit. Therefore, although this type of material can achieve high energy density at high voltage, its cycling stability is poor.

[0055] In the present invention, when creatively synthesizing lithium nickelate by the molten salt chemistry method, a molten salt additive is added, so that a slightly lithium-excess lithium nickelate cathode material with a layered structure containing only R-3m structural units can be produced and obtained, and its chemical formula is Li 1+x Ni 1-xIt is O2. When this positive electrode material is used in a lithium-ion battery, the lithium-ion battery simultaneously has high energy density and excellent cycling stability and thermal stability.

[0056] Example 1 Ni(OH)2 is uniformly mixed with LiOH and Li2SO4 (with a molar ratio of 1:1.3:0.27), and then the mixed powder is placed in a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.2 L / min, and the temperature is raised to 600°C at a heating rate of 5°C / min. After maintaining the temperature at 600°C for 15 hours, the temperature is lowered to room temperature at a cooling rate of 5°C / min.

[0057] Then, the cooled powder is removed, mechanically ground, added to deionized water to dissolve excess LiOH and Li2SO4, filtered, and the solid portion is removed and blast-dried at 60°C. The dried powder is again added to a corundum porcelain boat and placed in a tube furnace, pure oxygen is injected at a flow rate of 0.2 L / min, the temperature is raised to 500°C at a heating rate of 5°C / min, the temperature is maintained at 500°C for 5 hours, and then the temperature is lowered to room temperature at a cooling rate of 5°C / min to obtain cathode material 1.

[0058] The crystal structure of the positive electrode material 1 was evaluated by neutron diffraction (Figure 1), confirming that it has a layered structure, a space group of R-3m, and does not contain c / 2mLi2NiO3 units. Since no superstructure peaks were observed, the superstructure here refers to an in-plane superstructure formed by the regular arrangement of Li and Ni to form Li@Ni6, and this superstructure corresponds to a Li2NiO3 unit with c / 2m symmetry. Furthermore, scanning transmission electron microscopy imaging confirmed that excess Li ions are randomly distributed in the Ni layer. The results of the scanning transmission electron microscopy imaging are shown in Figure 8. Li is lighter than Ni, and the contrast is darker. As can be seen in Figure 8, the relatively dark points correspond to the presence of Li atoms that have replaced Ni in the Ni layer, and are randomly distributed (indicated by arrows in Figure 8). The scanning transmission electron microscopy image also confirms that the material has a layered structure (Figure 2). The elemental composition of the material was analyzed by ICP, and the ratio of the molar amounts of Li to Ni was found to be 1.04:0.96 (i.e., the chemical formula Li 1+x Ni 1-x The results were confirmed at O2 with x = 0.04, and are shown in Table 1.

[0059] Example 2 Ni(OH)2 is uniformly mixed with LiOH and Li2SO4 (with a molar ratio of 1:1.1:0.27), and then the mixed powder is placed in a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.5 L / min, and the temperature is raised to 650°C at a heating rate of 2°C / min. After maintaining the temperature at 650°C for 15 hours, the temperature is lowered to room temperature at a cooling rate of 2°C / min.

[0060] The cooled powder is then removed, mechanically ground, added to deionized water to dissolve excess LiOH and Li2SO4, filtered, and the solid portion is removed and blast-dried at 60°C. The dried powder is again added to a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.5 L / min, and the temperature is raised to 450°C at a heating rate of 2°C / min. After being maintained at 450°C for 2 hours, the temperature is lowered to room temperature at a cooling rate of 2°C / min to obtain cathode material 2. The results of the elemental composition analysis of the material by ICP are shown in Table 1.

[0061] Example 3 Ni(OH)2 is uniformly mixed with LiOH and Li2SO4 (with a molar ratio of 1:1.7:0.27), and then the mixed powder is placed in a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.1 L / min, and the temperature is raised to 550°C at a heating rate of 10°C / min. After being maintained at 550°C for 15 hours, the temperature is lowered to room temperature at a cooling rate of 10°C / min.

[0062] Then, the cooled powder is removed, mechanically ground, added to deionized water to dissolve excess LiOH and Li2SO4, filtered, and the solid portion is removed and blast-dried at 60°C. The dried powder is then added again to a corundum porcelain boat and placed in a tube furnace, and pure acid The element was injected at a flow rate of 0.1 L / min, the temperature was raised to 550°C at a heating rate of 10°C / min, and after being maintained at 550°C for 4 hours, the temperature was lowered to room temperature at a cooling rate of 10°C / min to obtain cathode material 3. The results of the elemental composition analysis of the material by ICP are shown in Table 1.

[0063] Example 4 Ni(OH)2 is uniformly mixed with LiOH and Li2SO4 (with a molar ratio of 1:1.5:0.1), and then the mixed powder is placed in a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.2 L / min, and the temperature is raised to 600°C at a heating rate of 5°C / min. After maintaining the temperature at 600°C for 15 hours, the temperature is lowered to room temperature at a cooling rate of 5°C / min.

[0064] The cooled powder is then removed, mechanically ground, added to deionized water to dissolve excess LiOH and Li2SO4, filtered, and the solid portion is removed and blast-dried at 60°C. The dried powder is again added to a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.2 L / min, and the temperature is raised to 500°C at a heating rate of 5°C / min. After being kept at 500°C for 5 hours, the temperature is lowered to room temperature at a cooling rate of 5°C / min to obtain cathode material 4. The results of the elemental composition analysis of the material by ICP are shown in Table 1.

[0065] Example 5

[0066] Ni(OH)2 is uniformly mixed with LiOH and Li2SO4 (with a molar ratio of 1:1.5:0.5), and then the mixed powder is placed in a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.2 L / min, and the temperature is raised to 600°C at a heating rate of 5°C / min. After maintaining the temperature at 600°C for 15 hours, the temperature is lowered to room temperature at a cooling rate of 5°C / min.

[0067] The cooled powder is then removed, mechanically ground, added to deionized water to dissolve excess LiOH and Li2SO4, filtered, and the solid portion is removed and blast-dried at 60°C. The dried powder is again added to a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.2 L / min, and the temperature is raised to 500°C at a heating rate of 5°C / min. After being kept at 500°C for 5 hours, the temperature is lowered to room temperature at a cooling rate of 5°C / min to obtain cathode material 5. The results of the elemental composition analysis of the material by ICP are shown in Table 1.

[0068] Example 6 NiO is uniformly mixed with LiOH·H2O and Li2SO4 (with a molar ratio of 1:1.3:0.27), and then the mixed powder is placed in a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.2 L / min, and the temperature is raised to 600°C at a heating rate of 5°C / min. After maintaining the temperature at 600°C for 15 hours, the temperature is lowered to room temperature at a cooling rate of 5°C / min.

[0069] Then, the cooled powder is removed, mechanically ground, added to deionized water to dissolve excess LiOH·H2O and Li2SO4, filtered, and the solid portion is removed and blast-dried at 60°C. The dried powder is again added to a corundum porcelain boat and placed in a tube furnace, pure oxygen is injected at a flow rate of 0.2 L / min, the temperature is raised to 500°C at a heating rate of 5°C / min, and after being maintained at 500°C for 5 hours, it is cooled to room temperature at a cooling rate of 5°C / min to obtain cathode material 6. The results of the elemental composition analysis of the material by ICP are shown in Table 1.

[0070] Example 7 NiCO3 was uniformly mixed with LiOH and Li2SO4 (the ratio of the three substances being 1:1.3:0.27), and then the mixed powder was added to a corundum porcelain boat and heated in a tube furnace. Place the sample inside, inject pure oxygen at a flow rate of 0.2 L / min, raise the temperature to 600°C at a heating rate of 5°C / min, maintain the temperature at 600°C for 15 hours, and then cool the sample to room temperature at a cooling rate of 5°C / min.

[0071] The cooled powder is then removed, mechanically ground, added to deionized water to dissolve excess LiOH and Li2SO4, filtered, and the solid portion is removed and blast-dried at 60°C. The dried powder is again added to a corundum porcelain boat and placed in a tube furnace. Pure oxygen is injected at a flow rate of 0.2 L / min, and the temperature is raised to 500°C at a heating rate of 5°C / min. After being maintained at 500°C for 5 hours, the temperature is lowered to room temperature at a cooling rate of 5°C / min to obtain cathode material 7. The results of the elemental composition analysis of the material by ICP are shown in Table 1.

[0072] Comparative Example 1 Ni(OH)2 was homogeneously mixed with LiOH (with a molar ratio of 1:1.02), and the mixed powder was then added to a corundum porcelain boat and placed in a tube furnace. Pure oxygen was injected at a flow rate of 0.2 L / min, and the temperature was raised to 485°C at a heating rate of 5°C / min, maintained for 3 hours, then raised to 700°C, maintained for 20 hours, and finally cooled to room temperature at a cooling rate of 5°C / min. Comparative cathode material 1 was obtained. The results of the elemental composition analysis of the material by ICP are shown in Table 1.

[0073] Performance testing: Electrochemical cycle stability: The positive electrode material 1 of Example 1 was assembled as a button cell in an argon-protected glove box with a lithium sheet, diaphragm, and electrolyte (a solution of lithium hexafluoride phosphate dissolved in dimethyl carbonate and fluoroethylene carbonate in a 1:1 volume ratio, with a lithium hexafluoride phosphate concentration of 1 mol / L), and charged and discharged at a 1C multiplier in the voltage range of 4.3 to 2.8V. The positive electrode material 1 of Comparative Example 1 was operated in the same manner, and the electrochemical cycle stability results are shown in Figure 3.

[0074] Magnification performance: Separately, the magnification performance of both materials was evaluated using the same button cell described above. After charging to 4.3V at a magnification of 0.2C, the cells were discharged at a magnification of 0.5 to 10C, and the test results are shown in Figure 4. Here, the initial discharge energy density of the battery corresponding to positive electrode material 1 of Example 1 was obtained by integrating the charging and discharging curves and is 904 Wh / kg (Figure 5).

[0075] Example 8 (Thermal Safety Test) A soft pack battery will be assembled using positive electrode material 1 from Example 1, and thermal safety will be evaluated. Assembly method: (1) Manufacturing of positive electrode pieces: The active substance (positive electrode material 1 from Example 1), conductive agent (carbon black), and adhesive (5 wt% polyvinylidene fluoride / N-methylpyrrolidone solution) are mixed in a mass ratio of 94:3:3, N-methylpyrrolidone (NMP) is added, the solid content concentration is adjusted to 65%, and the mixture is applied to 13 μm aluminum foil. After drying, 55 mm * 35 mm (H * W) pieces are punched out using a punching machine, and after rolling, 1 (2) Manufacturing of negative electrode pieces: Mix an active substance (graphite), a conductive agent (carbon black), and an adhesive (5 wt% polyvinylidene fluoride / N-methylpyrrolidone solution) in a mass ratio of 94:3:3, add NMP to adjust the solid content concentration to 45%, coat it onto 10 μm copper foil, dry it, punch out 57 mm x 37 mm (H x W) pieces with a punching machine, roll them out, and then vacuum dry them at 80 °C for 12 hours. (3) Manufacturing of soft pack battery cells: Assemble a battery cell by stacking a 16 μm PE diaphragm and positive and negative electrodes, ensuring that each positive electrode corresponds to a negative electrode, wrap the outermost layer with a diaphragm, and then seal it with polyamide tape. Weld aluminum and nickel tabs to the exposed tabs of the positive and negative electrodes using an ultrasonic welding machine. Apply polyamide tape to the soldered parts. The outer layer of the battery cell is wrapped in an aluminum-plastic film, leaving an opening for electrolyte injection. The manufactured battery cells are vacuum-dried at 60°C for 6 hours. The capacity is set to 30mAh. (4) Battery manufacturing: Inject 0.5g of electrolyte (the electrolyte component is a 1.2M lithium hexafluoride phosphate solution, and the solvent is a mixed solvent of ethylene carbonate EC and ethyl methyl carbonate EMC in a weight ratio of 3:7, and the solvent also contains 2% by mass of vinylene carbonate VC) into the battery cell using a pipette, and seal the injection port using a sealing machine. After letting it stand for 10 hours in a flat position, test it. (5) Cell formation and testing: Secure the battery with clamps and test it with a charge / discharge tester, charge it to 4.25V with a constant current of 0.1C (22mA / g of positive electrode active material mass, the same applies below), and perform constant voltage charging to 0.05C. Discharge it to 2.75V at 0.1C, and repeat the above process three times to complete cell formation.

[0076] Thermal safety evaluation method: Two manufactured soft pack batteries are each charged with a constant current of 0.1C up to 4.25V, then voltage charged to 0.05C and left in standby mode. The chamber of the accelerating calorimeter is opened, the tip of the thermocouple is attached to the center of one battery with aluminum tape, then the other battery is placed on top, the two batteries are taped together with aluminum tape, and secured to the dedicated test rack inside the chamber. The cover of the accelerating calorimeter is closed, and the accelerating calorimeter process is started to perform the test. Specific test process: The test starts at 25°C, first switching to heating mode, heating the chamber, heating by 5°C (10 minutes) each time, and monitoring the battery temperature. After that, it is left to stand for 30 minutes and then switched to search mode. During this time, if the rate of temperature rise is lower than 0.02°C / min, heating is resumed after the standing period ends. If the rate of temperature rise is higher than 0.02°C / min, it switches to cooling mode, the chamber is no longer heated, and only the temperature change is recorded. The system switches to cooling mode until the temperature exceeds 300°C, and the test is completed. The test results are shown in Figure 6. The battery with positive electrode material 1 from Example 1 attached has a relatively high T2 temperature (thermal runaway temperature, the temperature at which the temperature rise due to self-heating exceeds 1°C / min), which is 253.2°C.

[0077] Comparative Example 2 (Thermal Safety Test) The assembly method and thermal safety evaluation method for the soft pack battery are the same as in Example 8, except that the positive electrode material 1 of Example 1 is replaced with comparative positive electrode material 1 of Comparative Example 1. The test results are shown in Figure 6, and the T2 temperature (thermal runaway temperature, the temperature at which the temperature rise due to self-heating exceeds 1°C / min) is 179.0°C. Therefore, Comparative Example 2 is more prone to thermal runaway than Example 8.

[0078] Using in-situ differential electrochemical mass spectrometry (DEMS), oxygen and carbon dioxide emission tests were conducted on the lithium nickelate cathode material of Example 1 and the lithium-deficient lithium nickelate cathode material of the prior art. The test conditions were one charge with a charge ratio of 0.1C. The results are shown in Figure 7, where A is general lithium nickelate (LNO) and B is lithium nickelate of Example 1 (lithium-slightly excess LR-LNO). As can be seen, general lithium nickelate generates 4.2 μmol / g of O2 and 86.5 μmol / g of CO2 when lithium is removed, but the lithium nickelate of Example 1 basically does not release oxygen.

[0079] Example 9 This is almost identical to Example 1, the only difference being that Li2SO4 is simply replaced with Na2SO4.

[0080] Example 10 This is almost identical to Example 1, the only difference being that Li2SO4 is simply replaced with K2SO4.

[0081] Comparative Example 3 This is almost identical to Example 1, the only difference being that Li2SO4 is not added.

[0082] Comparative Example 4 This example is almost identical to Example 1, the only difference being that the ratio of the amounts of Ni(OH)2, LiOH, and Li2SO4 is 1:1.05:0.27.

[0083] Comparative Example 5 This example is almost identical to Example 1, the only difference being that the ratio of the amounts of Ni(OH)2, LiOH, and Li2SO4 is 1:2:0.27.

[0084] Comparative Example 6 The solution described in the example in JP2015082345A (Japanese Patent Publication No. 2015-82345) is specifically as follows:

[0085] Using lithium peroxide (Li2O2) and nano-sized nickel oxide as starting materials, these raw materials are crushed and mixed in a molar ratio of Li / Ni = 1.9. The mixture is then packed into a platinum tank and sintered at 700°C for 1 hour at a pressure of 4 GPa using a cubic anvil type high-pressure apparatus to obtain lithium-rich lithium nickelate. The average particle size is around 50-100 nm, and the amount of each element is analyzed by emitting a spectrum using ICP, and the composition is determined to be Li 1.30 Ni 0.70 This is confirmed as O2. Figure 9 shows Figure 2 (neutron diffraction diagram) of the patent, and as can be seen from this, the cathode material has a layered structure, and the space group includes c / 2m Li2NiO3 units in addition to R-3m, and there is a very prominent superstructure peak in Figure 9 (where 2θ is in the range of 20~25° and corresponds to the dotted box), which corresponds to c / 2m Li2NiO3 (where M=Ni) units, that is, the regular arrangement of Li@Ni6 is within the Ni layer.

[0086] The elemental components of the materials in Examples 9-10 and Comparative Examples 3-5 were analyzed by ICP, and the results are shown in Table 1.

[0087] [Table 1]

Claims

1. Lithium nickelate cathode material, The lithium nickelate cathode material has the chemical formula Li １＋ｘ Ni １－ｘ O ２ Here, 0.02 ≤ x ≤ 0.08, and the lithium nickelate cathode material has a crystal structure of α-NaFeO ２ The lithium nickelate cathode material has a hexagonal layered structure, and the space group of its crystal structure is of the R-3m type. In the crystal structure of the lithium nickelate cathode material, Li, which is in excess of Ni in stoichiometric ratio, occupies the octahedral voids in the Ni layer of the layered structure and is randomly distributed in the octahedral voids. Neutron diffraction has not detected the presence of Li₂NiO₃ units with a space group of c / 2m in the crystal structure. A lithium nickelate cathode material characterized by the following features.

2. 0.03 ≤ x ≤ 0.06 The lithium nickelate cathode material according to feature 1.

3. 0.04 ≤ x ≤ 0.05 The lithium nickelate cathode material according to feature 1.

4. A method for producing a lithium nickelate cathode material according to any one of claims 1 to 3, The aforementioned method, (1) A process to obtain a lithium nickelate-containing product by reacting a nickel source and a lithium source with oxygen in the presence of a molten salt additive, (2) A step of purifying the lithium nickelate-containing product to obtain a powder containing lithium nickelate, and placing the powder in an oxygen environment to obtain the lithium nickelate cathode material. A method characterized by the following:

5. The nickel source is NiO, Ni(OH) ２ and NiCO ３ Selected from the group consisting of 1 There are one or more The method according to feature 4.

6. The lithium source is LiOH or LiOH·H ２ Selected from O The method according to feature 4.

7. Said molten salt additive is Li ２ SO ４ , Na ２ SO ４ and K ２ SO ４ one or more selected from the group consisting of The method according to feature 4.

8. The molten salt additive is Li ２ SO ４ That is The method according to feature 4.

9. The ratio of the amount of substance of the lithium source to the nickel source is 1.1 to 1.7:1, and / or the ratio of the amount of substance of the molten salt additive to the nickel source is 0.1 to 0.5:

1. The method according to feature 4.

10. The ratio of the amount of substance of the lithium source to the nickel source is 1.3 to 1.5:1, and / or the ratio of the amount of substance of the molten salt additive to the nickel source is 0.27 to 0.5:

1. The method according to feature 4.

11. In step (1), the reaction temperature is 550 to 650°C, and / or, the reaction time in step (1) is 10 to 20 hours, and / or, in step (2), the temperature of the oxygen environment is 450 to 550°C, and / or, in step (2), the residence time in the oxygen environment is 2 to 5 hours. The method according to feature 4.

12. In step (2), the purification includes washing and filtration, and / or the method further includes a step of grinding the lithium nickelate-containing product before the purification. The method according to feature 4.

13. The aforementioned method, (1) A step of uniformly mixing a nickel source, a lithium source and a molten salt additive to obtain a mixture, placing the mixture in a reactor, injecting oxygen into the reactor, raising the temperature of the mixture to cause a reaction, and obtaining a lithium nickelate-containing product. (2) The process includes the steps of: crushing the lithium nickelate-containing product, washing it with water, filtering it to obtain a powder containing lithium nickelate, placing the powder in a reactor, injecting oxygen into the reactor, raising the temperature, and obtaining the lithium nickelate cathode material. The method according to feature 4.

14. In step (1), the oxygen injection flow rate is 0.1 to 0.5 L / min, and / or, in step (1), the heating rate is 2 to 10°C / min. The method according to the present invention, characterized by the present invention.

15. In step (2), the oxygen injection flow rate is 0.1 to 0.5 L / min, and / or, in step (2), the heating rate is 2 to 10°C / min. The method according to the present invention, characterized by the present invention.

16. Use of the lithium nickelate cathode material according to any one of claims 1 to 3 in a lithium-ion battery.

17. The positive electrode comprises the lithium nickelate positive electrode material described in any one of claims 1 to 3. A lithium-ion battery containing a positive electrode characterized by the following features.

18. The energy density of the lithium-ion battery during its initial discharge at a 0.1C multiplier is 904 Wh / kgV or higher, and / or the discharge ratio capacity retention rate of the lithium-ion battery after 100 charge-discharge cycles in a voltage range of 4.3 to 2.8V at a 1C multiplier is 92.3% or higher. The lithium-ion battery according to feature 17.

Images