A lithium-rich nickel-based lithium ion battery cathode material and a preparation method thereof

Abstract

The application provides a lithium-rich nickel-based lithium ion battery positive electrode material, and the structural formula of the positive electrode material is xLi2NiO3·(1-x)LiMO2, wherein 0.4<=x<=0.6; M=Ni in the LiMO2 y Co z Mn 1‑y‑z , wherein 0.3<=y<=1, 0<=z<=0.7, y+z<=1. The positive electrode material as a whole shows a layered crystal structure, and two characteristic small peaks exist between 33-34 and 56-57, and the positive electrode material is a new type of positive electrode material. The positive electrode material has special material and structural composition, has high specific capacity, and has the advantages of good structural stability, good thermal stability, high capacity retention rate, low voltage attenuation rate and the like, and does not need to be charged to above 4.5V, the safety is greatly improved, and has wide market application prospect.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, specifically to a lithium-rich nickel-based lithium-ion battery cathode material and its preparation method. Background Technology

[0002] As the market development of new energy vehicles enters a new stage, the lithium-ion battery industry has also ushered in rapid development. Because the cathode material needs to provide the lithium required for the repeated insertion / extraction of lithium-ion batteries during charging and discharging, and also needs to bear the lithium required to form the SEI film on the surface of the anode material, the cathode material has become the key to restricting the capacity of lithium-ion batteries.

[0003] Currently proposed cathode materials for lithium-ion batteries include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFePO4, and Li x MPO4 (M=Mn, Co, Ni), Li3V2 (PO4)3, Li2MSiO4 (M=Fe, Mn, Co, Ni), LiNi x Co y Mn 1-x-y O2(NCM), LiNi x Co y Al 1-x-y O2 (NCA), and lithium-rich manganese-based cathode material xLi2MnO3·(1-x)LiMO2 (M=Co、Ni、Mn).

[0004] Existing lithium-rich manganese-based cathode materials are composite materials composed of Li₂MnO₃ and LiMO₂ (M = Co, Ni, Mn). They stabilize the electrochemically active LiMO₂ (M = Co, Ni, Mn) within the electrochemically inactive Li₂MnO₃. Li₂MnO₃ belongs to the monoclinic crystal system, C² / m space group; LiMO₂ (M: Co, Ni, Mn) has an α-NaFeO₂ structure, belongs to the trigonal crystal system, R⁻³m space group. However, lithium-rich manganese-based cathode materials require charging to above 4.5V to activate Li₂MnO₃, with a charging cutoff voltage of 4.8V. During the initial charging process, there are two distinct stages: when the charging voltage is below 4.5V, a gradually rising charging curve is observed; as the charging voltage continues to rise, a long charging plateau appears at 4.5V, followed by a rapid rise to 4.8V. Although the material can achieve a specific capacity of over 200 mAh / g, its excessively high charging voltage poses safety risks and limits its commercial application.

[0005] Studies have shown that the higher the Ni content in NCM cathode materials, the greater the specific capacity, thus high-nickel materials have received increasing attention. However, high Ni content in cathode materials can affect their stability. Furthermore, due to the similar ionic radii of Li+ (0.076 nm) and Ni2+ (0.069 nm) during charge and discharge, ion mixing easily occurs, leading to gradual structural collapse and a rapid decrease in cycle life. Therefore, developing a lithium-ion battery cathode material with high specific capacity, high stability, high capacity retention, and low voltage decay is a pressing issue that needs to be addressed. Summary of the Invention

[0006] To address the aforementioned problems, this invention innovatively proposes a lithium-rich nickel-based material, prepared by combining Li2NiO3 and LiMO2 (M: Co, Ni, Mn), exhibiting a high Ni content. The cathode material displays a layered crystal structure and exhibits two characteristic small peaks between 33° and 34° and between 56° and 57°, representing a novel cathode material.

[0007] The first aspect of the present invention provides a lithium-rich nickel-based lithium-ion battery cathode material, characterized in that: the cathode material is composed of Li2NiO3 and LiMO2, and the structural formula of the cathode material is xLi2NiO3·(1-x)LiMO2, wherein 0.4≤x≤0.6;

[0008] In LiMO2, M = Ni y Co z Mn 1-y-z , where 0.3≤y≤1, 0≤z≤0.7, and y+z≤1.

[0009] Preferably, in the LiMO2, M = Ni y Co z Mn 1-y-z , where 0.7≤y≤0.95, 0.05≤z≤0.3, and y+z≤1.

[0010] Preferably, in the LiMO2, M = Ni y Co z Mn 1-y-z , where 0.8≤y≤0.95, 0.05≤z≤0.2, and y+z≤1.

[0011] Preferably, the X-ray diffraction pattern of the cathode material shows an overall layered crystal structure, with two characteristic diffraction peaks between 33° and 34° and between 56° and 57°.

[0012] This invention uses Li2NiO3 and LiMO2 (M=Ni) y Co z Mn1-y-z The lithium-rich nickel-based lithium-ion battery cathode material, composed of composite materials, features a high nickel content and exhibits high specific capacity. The inventors have discovered that the lithium-rich nickel-based lithium-ion battery cathode material described in this invention, while possessing high specific capacity, also exhibits high stability, high capacity retention, and low voltage decay. The inventors believe this is likely due to the novel crystal structure of the composite cathode material, where the two materials form a conjugated lattice, allowing for effective coexistence and reducing the cation mixing and instability issues caused by the strong reducing power of tetravalent nickel ions. Furthermore, the inventors speculate that when the two materials coexist, the tetravalent nickel ions in the system consume oxygen, resulting in more oxygen vacancies, facilitating lithium insertion / extraction and leading to higher conductivity in the resulting cathode material.

[0013] Preferably, the metal salt raw materials used in the cathode material include lithium salt, nickel salt, cobalt salt, and manganese salt.

[0014] Preferably, the lithium salt is at least one of lithium hydroxide and its hydrate, lithium carbonate and its hydrate, and lithium nitrate and its hydrate; the nickel salt is at least one of Ni(CH3COO)2 and its hydrate, Ni(NO3)2 and its hydrate, and NiSO4 and its hydrate; the cobalt salt is at least one of Co(CH3COO)2 and its hydrate, Co(NO3)2 and its hydrate, and CoSO4 and its hydrate; and the manganese salt is at least one of Mn(CH3COO)2 and its hydrate, Mn(NO3)2 and its hydrate, and MnSO4 and its hydrate.

[0015] Another aspect of the present invention provides a method for preparing a lithium-rich nickel-based lithium-ion battery cathode material, characterized by comprising the following steps:

[0016] S1: Mix a 2 mol / L solution of nickel, cobalt and manganese salts and add it to the reaction vessel. Add sodium hydroxide and ammonia solution and react for 35-45 h. Then age for 10-14 h. Then filter, wash and dry to obtain precursor A.

[0017] S2: After mixing precursor A with lithium salt and grinding them evenly, the mixture is placed in a tube furnace and calcined with oxygen. It is sintered at the first sintering temperature for 4-4.5 hours and at the second sintering temperature for 14-16 hours. Then it is cooled with the furnace to obtain the lithium-rich nickel-based lithium-ion battery cathode material.

[0018] Preferably, in step S1, the reaction conditions are a water bath with stirring; the water bath temperature is 40-55℃, and the stirring rate is 500-700 rpm.

[0019] Preferably, in step S1, nitrogen gas is simultaneously introduced into the reaction vessel during the reaction.

[0020] Preferably, in step S1, the pH of the reaction system is controlled to be 11-12.

[0021] More preferably, the pH is 11.5.

[0022] Preferably, in step S2, the first sintering temperature is 480-520℃; the second sintering temperature is 750-850℃.

[0023] Preferably, in step S2, the lithium salt and precursor A are mixed in a molar ratio of (1+a):1, wherein 0.4≤a≤0.6.

[0024] More preferably, in step S2, the lithium salt and precursor A are mixed in a molar ratio of (1.5-1.6):1.

[0025] More preferably, in step S2, the lithium salt and precursor A are mixed at a molar ratio of 1.575:1.

[0026] Preferably, in step S2, the oxygen-assisted calcination is positive pressure oxygen-assisted sintering.

[0027] More preferably, the oxygen is pressurized to 0.1-2 MPa during the positive pressure oxygen calcination.

[0028] More preferably, the oxygen is pressurized to 0.15-1 MPa during the positive pressure oxygen calcination.

[0029] In the above preparation process, by strictly controlling the ratio of metal salts, reaction temperature, and pH of the reaction system, Li₂NiO₃ and LiMO₂ (M=Ni) were prepared. y Co z Mn 1-y-z Li₂NiO₃ is a composite material that cannot exist alone due to its unstable material properties, making it very difficult to prepare. This invention eliminates the need to prepare Li₂NiO₃ separately; instead, it prepares Li₂NiO₃ and LiMO₂ (M=Ni) composites in a single step by mixing lithium salt with a precursor. y Co z Mn 1-y-z This is a composite lithium-rich nickel-based lithium-ion battery cathode material. The coexistence of the two effectively avoids the problem of high activity but poor stability when Li2NiO3 exists alone.

[0030] Another aspect of the present invention provides a method for preparing a lithium-rich nickel-based lithium-ion battery cathode material, characterized by comprising the following steps:

[0031] Nickel salt, cobalt salt, and manganese salt are mixed with ethanol and added to a ball mill jar. The mixture is ball-milled for 11-13 hours and then dried at 75-85°C for 11-15 hours to obtain a powder material. The powder material is then ground and sintered at 480-510°C for 4 hours, followed by sintering at 750-850°C for 12 hours. Finally, it is cooled in the furnace to obtain the lithium-rich nickel-based lithium-ion battery cathode material.

[0032] The lithium-rich nickel-based lithium-ion battery cathode material described in this invention can be used as a cathode material in the preparation of lithium-ion batteries.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention innovatively proposes a lithium-rich nickel-based lithium-ion battery cathode material, which is prepared by combining Li₂NiO₃ and LiMO₂ (M: Co, Ni, Mn) and has a high Ni content. The cathode material exhibits a layered crystal structure and has two characteristic small peaks between 33° and 34° and between 56° and 57°, making it a novel cathode material. The cathode material of this invention possesses a unique material and structural composition, exhibiting high specific capacity while also demonstrating good structural stability, good thermal stability, high capacity retention, and low voltage decay rate. Furthermore, it does not require charging to above 4.5V, significantly improving safety and possessing broad market application prospects. Attached Figure Description

[0035] Figure 1 This is the X-ray diffraction pattern of the cathode material in Embodiment 1 of the present invention.

[0036] Figure 2 This is a scanning electron microscope image of the positive electrode material in Embodiment 1 of the present invention.

[0037] Figure 3 This is the first charge-discharge curve of the positive electrode material in Embodiment 1 of the present invention.

[0038] Figure 4 This is the 20th charge-discharge curve of the positive electrode material in Embodiment 1 of the present invention. Detailed Implementation

[0039] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a lithium-rich nickel-based lithium-ion battery cathode material and its preparation method, as well as the application of the material as a cathode material in lithium-ion batteries. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures, only to further illustrate the features and advantages of the present invention, and not to limit the scope of protection of the claims of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0040] Example

[0041] Example 1

[0042] The lithium-rich nickel-based lithium-ion battery cathode material prepared in this embodiment has the structural formula 0.5Li₂NiO₃·0.5LiNi 0.8 Co 0.1 Mn 0.1 O2 can also be written as Li 1.5 Ni 0.9 Co 0.05 Mn 0.05 O 2.5 .like Figure 1 As shown, the cathode material prepared in this embodiment exhibits a layered crystal structure, and there are two characteristic small peaks between 33° and 34° and between 56° and 57°, which is a novel cathode material.

[0043] In this embodiment, the molar ratio of Li:Ni:Co:Mn is 30:18:1:1.

[0044] The specific preparation method of the cathode material in this embodiment is as follows:

[0045] NiSO4·6H2O, CoSO4·H2O, and MnSO4·H2O were weighed in a molar ratio of 18:1:1. Each reagent was dissolved in deionized water to prepare a 2 mol / L metal salt solution. The three metal salt solutions were then mixed and simultaneously added dropwise to a reaction vessel along with sodium hydroxide and ammonia solutions using a peristaltic pump. The pH of the reaction system was controlled at 11.50, the water bath temperature at 50℃, and the stirring speed at 600 rpm. Nitrogen gas was introduced into the reaction vessel for protection. The reaction was carried out for 36 hours, followed by aging for 12 hours. The mixture was then filtered, washed twice, and finally dried at 110℃ for 12 hours to obtain precursor A: Ni. 0.9 Co 0.05 Mn 0.05 (OH)2;

[0046] The obtained precursor A was mixed and ground uniformly with LiOH·H2O in a molar ratio of 1.5:1 (with LiOH·H2O in 5% excess). The mixture was then placed in a tube furnace and calcined under oxygen. Pre-sintering was performed at 500℃ for 4 hours, followed by sintering at 800℃ for 15 hours. Finally, the mixture was cooled in the furnace to obtain the prepared 0.5Li2NiO3·0.5LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material. Its structural characteristics were determined by XRD, see attached image. Figure 1 It exhibits an overall layered crystal structure, with two characteristic small peaks between 33° and 34° and between 56° and 57°. Its surface morphology was analyzed using scanning electron microscopy (see attached image). Figure 2Its secondary particles are regular spheres with a size of about 10 μm, and the primary particles are uniform and fine with good crystallinity.

[0047] Example 2

[0048] The lithium-rich nickel-based lithium-ion battery cathode material prepared in this example has the structural formula 0.5Li₂NiO₃·0.5LiNi 0.6 Co 0.2 Mn 0.2 O2 can also be written as Li 1.5 Ni 0.8 Co 0.1 Mn 0.1 O 2.5 .

[0049] In this example, the molar ratio of Li:Ni:Co:Mn is 15:8:1:1.

[0050] The specific preparation method of the cathode material in this embodiment is as follows:

[0051] NiSO4·6H2O, CoSO4·H2O, and MnSO4·H2O were weighed according to a molar ratio of 8:1:1. Each reagent was dissolved separately in deionized water to prepare a 2 mol / L metal salt solution. The three metal salt solutions were then mixed and simultaneously added dropwise to a reaction vessel along with sodium hydroxide solution and ammonia solution using a peristaltic pump. The pH of the reaction system was controlled at 11.50, the water bath temperature at 50℃, and the stirring speed at 600 rpm. Nitrogen gas was simultaneously introduced into the reaction vessel for protection. The reaction was carried out for 36 hours, followed by aging for 12 hours, then filtration and washing twice, and finally drying at 110℃ for 12 hours to obtain the precursor Ni. 0.8 Co 0.1 Mn 0.1 (OH)2;

[0052] The obtained precursor was mixed and ground uniformly with LiOH·H2O at a molar ratio of 1.5:1 (with an excess of 5% LiOH·H2O to compensate for calcination losses). The mixture was then placed in a tube furnace and calcined under oxygen. Pre-sintering was performed at 500℃ for 4 hours, followed by sintering at 800℃ for 15 hours. Finally, the mixture was cooled in the furnace to obtain the prepared 0.5Li2NiO3·0.5LiNi 0.6 Co 0.2 Mn 0.2 O2 cathode material.

[0053] Example 3

[0054] The lithium-rich nickel-based lithium-ion battery cathode material prepared in this example has the structural formula 0.4Li₂NiO₃·0.6LiNi 0.5 Co 0.2 Mn 0.3O2 can also be written as Li 1.4 Ni 0.7 Co 0.12 Mn 0.18 O 2.4 .

[0055] In this embodiment, the molar ratio of Li:Ni:Co:Mn is 70:35:6:9.

[0056] Analytical grade lithium hydroxide, nickel acetate, cobalt acetate, and manganese acetate were weighed according to a molar ratio of 70:35:6:9. Ethanol was added at a mass ratio of 1:2, and the mixture was poured into a ball mill jar. Milling beads were added, and the mixture was ball-milled at 120 rpm for 12 hours. After milling, the mixture was dried in an 80℃ forced-air drying oven for 12 hours to allow complete evaporation of the ethanol, yielding a powder material. The obtained powder material was manually ground for half an hour and then placed in a crucible. It was sintered in air at 500℃ for 4 hours, followed by sintering at 850℃ for 12 hours. Finally, it was cooled in the furnace to obtain the prepared 0.4Li₂NiO₃·0.6LiNi 0.5 Co 0.2 Mn 0.3 O2 cathode material.

[0057] Performance testing

[0058] The positive electrode materials obtained in Examples 1-3 were fabricated into electrode sheets and assembled into coin cells for performance testing. The specific steps are as follows:

[0059] The positive electrode material was dried under vacuum at 120℃ for 12 hours, then mixed with Super P and PVDF in a mass ratio of 80:10:10 to prepare a slurry. This slurry was coated onto aluminum foil to prepare a positive electrode sheet, which was then assembled with lithium metal sheets to form a coin cell for performance testing. The electrolyte was 1 mol / L LiPF6 + EC / DMC / EMC (volume ratio 1:1:1). The test process used a nominal specific capacity of 180 mAh / g, first cycling 5 times at 0.1C, then cycling 20 times at 1C, with a voltage range of 2.75V to 4.3V.

[0060] The test data of the cathode materials in Examples 1-3 are shown in Table 1.

[0061] Table 1

[0062]

[0063] The initial charge-discharge curve of the cathode material obtained in Example 1 is shown below. Figure 3 As shown; the 20th charge-discharge curve is as follows. Figure 4As shown in the figure. The results show that the specific capacity of the material during the first 0.1C cycle is 253.3 mAh / g, the specific capacity during discharge is 192.2 mAh / g, and the median discharge voltage is 3.83V; the specific capacity during the first 1C cycle (the 6th cycle overall) is 190.5 mAh / g, which is less than 2 mAh / g lower than that during 0.1C, demonstrating excellent rate performance. The specific capacity during the 20th cycle is 187.8 mAh / g, and the median discharge voltage is still 3.83V, indicating high capacity retention and low voltage decay.

[0064] The test results of Example 2 show that the specific capacity of the material during the first 0.1C cycle is 236.7 mAh / g, the specific capacity during discharge is 183.9 mAh / g, and the median discharge voltage is 3.84V. The specific capacity during the first 1C cycle (the 6th cycle overall) is 177.1 mAh / g, which is only about 7 mAh / g lower than that during 0.1C, showing excellent rate performance. The specific capacity during the 20th cycle is 176.8 mAh / g, and the median discharge voltage is still 3.84V, indicating high capacity retention and low voltage decay.

[0065] The test results of Example 3 show that the material's charge specific capacity is 237.8 mAh / g and discharge specific capacity is 179.9 mAh / g in the first 0.1C cycle, with a median discharge voltage of 3.85V. The discharge specific capacity in the first 1C cycle (the 6th cycle overall) is 173.5 mAh / g, which is only about 6 mAh / g lower than that in the 0.1C cycle, demonstrating excellent rate performance. In the 20th cycle, the discharge specific capacity is 173.3 mAh / g, and the median discharge voltage is still 3.85V, indicating high capacity retention and low voltage decay.

[0066] As can be seen from the above data, the lithium-rich nickel-based lithium-ion battery cathode material of the present invention has the advantages of high specific capacity, high capacity retention rate, and low voltage decay rate, and does not need to be charged to above 4.5V, which greatly improves safety.

Claims

1. A lithium-rich nickel-based lithium-ion battery cathode material, characterized in that, The cathode material is composed of Li₂NiO₃ and LiMO₂, and its structural formula is xLi₂NiO₃·(1-x)LiMO₂, where 0.4≤x≤0.6; in LiMO₂, M=Ni y Co z Mn 1-y-z Where 0.3≤y≤1, 0≤z≤0.7, and y+z≤1; the X-ray diffraction pattern of the cathode material shows an overall layered crystal structure, and there are two characteristic diffraction peaks between 33°~34° and 56°~57°.

2. The lithium-rich nickel-based lithium-ion battery cathode material according to claim 1, characterized in that, The metal salt raw materials used in the cathode material include lithium salt, nickel salt, cobalt salt, and manganese salt.

3. The lithium-rich nickel-based lithium-ion battery cathode material according to claim 2, characterized in that, The lithium salt is at least one of lithium hydroxide and its hydrate, lithium carbonate and its hydrate, and lithium nitrate and its hydrate; the nickel salt is at least one of Ni(CH3COO)2 and its hydrate, Ni(NO3)2 and its hydrate, and NiSO4 and its hydrate; the cobalt salt is at least one of Co(CH3COO)2 and its hydrate, Co(NO3)2 and its hydrate, and CoSO4 and its hydrate; and the manganese salt is at least one of Mn(CH3COO)2 and its hydrate, Mn(NO3)2 and its hydrate, and MnSO4 and its hydrate.

4. The method for preparing the lithium-rich nickel-based lithium-ion battery cathode material according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Mix a 2 mol / L solution of nickel, cobalt and manganese salts and add it to the reaction vessel. Add sodium hydroxide and ammonia solution and react for 35-45 h. Then age for 10-14 h. Then filter, wash and dry to obtain precursor A. S2: After mixing and grinding the precursor A with the lithium salt, it is placed in a tube furnace and calcined with oxygen. It is sintered at the first sintering temperature for 4-4.5 hours and at the second sintering temperature for 14-16 hours. Then it is cooled with the furnace to obtain the lithium-rich nickel-based lithium-ion battery cathode material.

5. The method for preparing the lithium-rich nickel-based lithium-ion battery cathode material according to claim 4, characterized in that, In step S1, the pH of the reaction system is controlled to be 11-12.

6. The method for preparing the lithium-rich nickel-based lithium-ion battery cathode material according to claim 4, characterized in that, In step S2, the first sintering temperature is 480-520℃; the second sintering temperature is 750-850℃.

7. The method for preparing the lithium-rich nickel-based lithium-ion battery cathode material according to claim 4, characterized in that, In step S2, the lithium salt is mixed with precursor A in a molar ratio of (1+a):1, where 0.4≤a≤0.

6.

8. The method for preparing the lithium-rich nickel-based lithium-ion battery cathode material according to claim 4, characterized in that, In step S2, the oxygen-assisted calcination is positive pressure oxygen-assisted sintering.

9. The method for preparing the lithium-rich nickel-based lithium-ion battery cathode material according to any one of claims 1-3, characterized in that, Includes the following steps: Lithium salt, nickel salt, cobalt salt, and manganese salt are mixed in ethanol, and the mixture is added to a ball mill jar and ball-milled for 11-13 hours. Then, it is dried at 75-85℃ for 11-15 hours to obtain a powder material. The obtained powder material is ground and sintered at 480-510℃ for 4 hours, then sintered at 750-850℃ for 12 hours. Finally, it is cooled in the furnace to obtain the lithium-rich nickel-based lithium-ion battery cathode material.

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