A high-voltage, low-cobalt ternary cathode material, its preparation method and use

Abstract

The present invention provides a high voltage low cobalt ternary cathode material, which has the general formula Li a Ni b Co c Mn d O2, wherein 0.97≤a≤1.1, 0.5≤b≤0.76, 0≤c≤0.1, 0.24≤d≤0.5, b+c+d=1, and c<0.35d. Compared with the prior art, the positive electrode material can be used at a higher voltage than other ternary positive electrode materials with the same nickel content. While improving the energy density, the positive electrode material has a smaller volume change, which avoids cracking and pulverization of the positive electrode material, extends the service life of the material, and improves the safety performance of the material. In addition, since the nickel and cobalt content of the positive electrode material is relatively lower and the manganese content is relatively higher, the positive electrode material has better cycle performance and high voltage performance while reducing its use cost.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion battery positive electrode materials, and in particular to a high-voltage, low-cobalt ternary positive electrode material, a preparation method thereof, and uses thereof. Background Art

[0002] Lithium-ion batteries, the world's mainstream energy storage medium, have seen increasing adoption since their invention in the 1990s. Currently, nickel-cobalt-manganese ternary cathode materials hold a significant position in the cathode material market, both in power and non-power lithium-ion batteries, due to their excellent cycle performance, high capacity, and high voltage.

[0003] In nickel-cobalt-manganese ternary cathode materials, predecessors generally believed, as described in ACS Energy Lett., 2017, 2, 196-223, that the role of nickel is to increase the capacity of the material, but a high nickel content, that is, a high-nickel ternary cathode material, will lead to lithium-nickel mixing, thereby causing lithium precipitation; the role of cobalt is to stabilize the layered structure of the material, reduce lithium-nickel mixing, and improve the stability of the material during long cycles; the role of manganese is to reduce material cost, improve material safety and structural stability.

[0004] In order to further improve the energy density of batteries and thus increase the range of electric vehicles, major power battery manufacturers are gradually developing in the direction of high capacity and high voltage.

[0005] One key approach to achieving high capacity is to increase the nickel content of ternary cathode materials. High-nickel materials are generally considered to have a nickel-to-lithium molar ratio greater than 0.8, and development is currently moving toward ultra-high nickel (greater than 0.9). However, the cycling and safety performance of batteries made with high-nickel materials are also receiving increasing attention.

[0006] The primary factor affecting the cycling performance of high-nickel ternary cathode materials is cracking and pulverization. Numerous scientists have conducted extensive research on the causes of pulverization in high-nickel ternary cathode materials. The consensus in the industry is that, at the commonly used 4.3V cutoff voltage, high-nickel materials can achieve higher capacity than low-nickel materials. However, excessive delithiation in high-nickel materials leads to irreversible phase transitions, causing more dramatic volume shrinkage and resulting in cracks within and between primary particles. These cracks gradually widen with continuous cycling, becoming eroded by the electrolyte and accompanied by the release of reactive oxygen species. This leads to electrolyte consumption, electrolyte oxidation, the continuous formation of new cathode solid electrolyte layers (CEIs), and gassing (ACS Energy Lett., 2017, 2, 1150; J. Electrochem. Soc., 2019, 166, A429; ACS Appl. Mater. Interfaces, 2020, 12, 10240), resulting in decreased cycling performance and worsening safety performance.

[0007] Among the high-voltage ternary positive electrode materials, the materials that can be commercialized currently include NCM523, NCM622, etc., and the cobalt content accounts for more than 0.1. Unlike lithium iron phosphate, the capacity of the ternary positive electrode material is positively correlated with the cut-off voltage. For example, an NCM523 material can only exert a capacity of 162mAh / g when its cut-off voltage is 4.2V, but when the voltage is increased to 4.4V, its capacity can reach 175mAh / g. This positive correlation between capacity and voltage is determined by the electronic energy level structure of the three elements of nickel, cobalt and manganese in the ternary positive electrode material. Simply put, the higher the charging voltage applied to the positive electrode material, the more low-energy d-orbital electrons on nickel and cobalt can be forced to escape and transfer to the negative electrode through the external circuit. At the same time, more lithium ions are released from the inside of the positive electrode material and transferred to the negative electrode through the electrolyte. However, as the voltage increases, more lithium ions are released, which will cause problems similar to those of high-nickel materials: volume shrinkage, collapse of the crystal layered structure, and then cracking and powdering of the material, resulting in poor cycle performance.

[0008] In ternary positive electrode materials, cobalt has always been considered to be very important for the cycle stability of the material. For example, J. Electrochem. Soc., 1999, 146, 3571, observed that with the increase of Co content, the cycle stability of lithium nickelate becomes better and better. Due to the high price of cobalt, both the scientific and industrial communities are trying to reduce the cobalt content as much as possible, or even to zero, to develop cobalt-free materials. However, the industry still recognizes that cobalt plays an indispensable role in maintaining the stability of the material during long cycles, such as ACS Energy Lett., 2020, 5, 1814-1824; CN113764653A, etc., and this is even more important under high-voltage conditions. In order to solve the cycle stability of low-cobalt or even cobalt-free materials, the structural stability or interface stability of the material is enhanced by optimizing the selection of coating agents (such as CN111276691A, CN114808127A, CN114853088A, CN114843472A), doping with multiple elements (such as CN112993239A, CN114759183A, CN114709378A), and using other elements such as Al / W / Ti / Mg / Fe to replace Co (such as CN113800574A, CN111816877A). However, these methods require the introduction of new elements, making the process more complicated, and the small amount of other doped elements cannot completely make up for the lack of cycle stability caused by the lack of cobalt, because it does not solve the fundamental problem of the collapse of the layered structure caused by excessive delithiation due to the increase in voltage. Recently, Tesla's chief scientist Jeff Dahn wrote in the article Li[Ni 0.5 Mn 0.3 Co 0.2 O2 as a Superior Alternative to LiFePO4 for Long-Lived Low Voltage Li-Ion Cells has proposed a new solution that is believed to improve the cycling stability of ternary cathode materials. This solution cycles cells using NCM523 cathode material only at 3.65V or below 3.8V, and the cells can cycle for over 100 years at 20°C. However, the charge and discharge voltage of this solution is too low, and the NCM523 material can only achieve a capacity of less than 110mAh / g at 3.8V, which is not conducive to improving energy density.

[0009] In the application of ternary cathode materials, lithium-nickel intermixing has long been considered detrimental to cycling (Nat. Comm. 2014, 5, 3529; Chem. Mater. 2007, 19, 1790). Recent patents such as CN113584590A, CN113809320A, CN113707874A, and CN104409700A all suggest the need to reduce the degree of lithium-nickel intermixing in cathode materials through methods such as doping with different elements or special steps such as staged lithium sintering.

[0010] Therefore, how to reduce the cobalt content to reduce costs while maintaining high energy density of the ternary positive electrode material and maintaining high cycle stability has become a difficult problem. Summary of the Invention

[0011] The inventors have found that, unlike traditional cognition, in the ternary positive electrode material, by controlling the nickel content, reducing the cobalt content, increasing the manganese content to a certain extent, regulating the electronic energy level structure of the low-cobalt ternary positive electrode material to increase its operating voltage, limiting the amount of lithium ions released at high voltage, and preventing the structural collapse caused by excessive delithiation, the low-cobalt positive electrode material can be made to play a higher capacity at high voltage, thereby obtaining a high energy density while maintaining excellent cycle stability. Further, by regulating the lithium-nickel mixing to a certain extent (rather than the lower the better), the nickel in the lithium layer can play a role in maintaining the integrity and stability of the layered structure under high-voltage cycling conditions. Compared with the cobalt-rich positive electrode material containing the same nickel content, the cycle stability of the low-cobalt positive electrode material at high voltage is further improved.

[0012] Therefore, in view of the shortcomings of the prior art, the object of the present invention is to provide a high-voltage, low-cobalt ternary positive electrode material, which has excellent cycle performance and high voltage performance compared with other ternary positive electrode materials containing the same nickel content.

[0013] In order to achieve the above-mentioned purpose, the present invention provides a high voltage low cobalt ternary cathode material, which has the general formula Li a Ni b Co c Mn d O2, where 0.97≤a≤1.1, 0.5≤b≤0.76, 0≤c≤0.1, 0.24≤d≤0.5, b+c+d=1, and c<0.35d.

[0014] According to the positive electrode material of the present invention, the positive electrode material has a lithium-nickel mixing ratio (σ) 2 ≤ σ ≤ 7. The lithium-nickel mixing ratio is defined as the molar percentage of the lithium content in the nickel layer to the total lithium content.

[0015] According to the positive electrode material of the present invention, in terms of capacity, within the operating voltage range of 3-4.3V, the 0.1C capacity of the positive electrode material is not higher than 185mAh / g; within the operating voltage range of 3-4.5V, the 0.1C capacity is not higher than 210mAh / g.

[0016] According to the positive electrode material of the present invention, the positive electrode material is used at an operating voltage greater than or equal to 4.3V, preferably, at an operating voltage greater than or equal to 4.35V, and more preferably, at an operating voltage greater than or equal to 4.40V.

[0017] According to the positive electrode material of the present invention, wherein the positive electrode material has a lower cobalt content and a higher manganese content compared to the conventionally used ternary positive electrode material with the same nickel content, and the cobalt content is less than 0.35 times the manganese content, and the lithium nickel mixing ratio is between 2-7. On the one hand, when the nickel, cobalt and manganese content of the positive electrode material falls within the above range, the d orbital electron energy of the nickel and cobalt elements moves toward a lower energy level, making it more different from the p orbital electron energy level of lithium, thereby increasing the charge and discharge voltage, and increasing the energy density by increasing the charge and discharge voltage of the positive electrode material. The charge and discharge voltage applicable to the positive electrode material can be as high as 4.5V. At a charge and discharge voltage not higher than 4.5V, the positive electrode material has a smaller volume change, thereby preventing cracking or pulverization inside the primary particles and between the primary particles, extending the service life of the positive electrode material, and improving the safety performance of the material. On the other hand, when the nickel, cobalt and manganese content of the positive electrode material falls within the above range, the low-cobalt ternary positive electrode material limits the number of lithium ions that can be intercalated and deintercalated at a given voltage relative to the cobalt-rich ternary positive electrode material with the same nickel content but a cobalt content greater than 0.1, so that the low-cobalt ternary positive electrode material can exert an appropriately high capacity and prevent the degradation of the cycle performance caused by the collapse of the layered structure of the positive electrode material due to excessive delithiation.

[0018] Another object of the present invention is to provide a method for preparing the high-voltage, low-cobalt ternary cathode material as described above, comprising the following steps:

[0019] Step 1: Dissolve NiSO4·6H2O, MnSO4·H2O, and CoSO4·7H2O in deionized water to obtain a salt solution;

[0020] Step 2: Add deionized water to the reaction container, and add concentrated ammonia water to the deionized water to prepare a base liquid containing ammonia water; add the salt solution obtained in step 1, as well as the sodium hydroxide solution and the concentrated ammonia water dropwise to the base liquid at the same time; set an overflow port in the reaction container, and overflow continuously as the salt solution, sodium hydroxide solution and concentrated ammonia water are added dropwise until the particle size D in the reaction container is 50 Achieve target particle size;

[0021] Step 3: taking out all the slurry in the reaction container and performing solid-liquid separation, washing with deionized water, and drying to obtain a nickel-cobalt-manganese hydroxide precursor;

[0022] Step 4: Mix the nickel-cobalt-manganese hydroxide precursor with LiOH·H2O or lithium carbonate;

[0023] Step 5: Sinter the mixture obtained in step 4 under an oxygen atmosphere to obtain a low-cobalt ternary positive electrode material.

[0024] According to the preparation method of the present invention, in step 2, the dripping speed of the salt solution is controlled to be 300 mL / h to 500 mL / h, for example, 300 mL / h, 350 mL / h, 400 mL / h, 450 mL / h, 500 mL / h; the dripping speed of the concentrated ammonia solution is controlled to be 6 mL / h to 10 mL / h, for example, 6 mL / h, 7 mL / h, 8 mL / h, 9 mL / h, 10 mL / h, and the dripping speed of the sodium hydroxide solution is controlled so that the pH of the overall reaction solution is 10.00 to 13.00, for example, the pH is 10.00, 10.50, 11.00, 11.50, 12.00, 12.50, 13.00.

[0025] According to the preparation method of the present invention, the base liquid containing ammonia water used in step 2 is a base liquid containing 0.1-0.8M ammonia water, preferably a base liquid containing 0.3-0.5M ammonia water; the concentrated ammonia water used in step 2 is an ammonia water solution with a concentration of 20%-28%, preferably an ammonia water solution with a concentration of 25%; the sodium hydroxide solution used in step 2 is a sodium hydroxide solution with a concentration of 30%-42%, for example, a sodium hydroxide solution with a concentration of 30%-32%, or a sodium hydroxide solution with a concentration of 40%-42%, preferably a sodium hydroxide solution with a concentration of 32%.

[0026] According to the preparation method of the present invention, the particle size D obtained in step 2 is 50 The target particle size is 3-20 μm, preferably 5-15 μm.

[0027] According to the preparation method of the present invention, the molar ratio of the nickel-cobalt-manganese hydroxide precursor to LiOH·H2O or lithium carbonate in step 4 is 1:1.01 to 1:1.10, preferably 1:1.02 to 1:1.05, for example, 1:1.02, 1:1.03, 1:1.04, 1:1.05.

[0028] According to the preparation method of the present invention, the sintering temperature in step 5 is 700°C to 1000°C, for example, 700°C, 750°C, 800°C, 820°C, 850°C, 890°C, 900°C, 920°C, 940°C, 970°C, 1000°C; and the sintering time is 10 hours to 14 hours, preferably 11 hours to 13 hours.

[0029] According to the preparation method of the present invention, the doping treatment is performed in step 4, including adding one or more compounds containing Ca, Mg, Zr, Sr, Na, Si, Al, La, W, B, Fe, Cu, K, Ge, Nd, Nb, Mo, Y or Ce elements in step 4.

[0030] According to the preparation method of the present invention, a coating treatment is performed after step 5, including adding one or more compounds containing Ca, Mg, Zr, Sr, Na, Si, Al, La, W, B, Fe, Cu, K, Ge, Nd, Nb, Mo, Y or Ce elements after step 5, and sintering the mixture again.

[0031] Through doping and / or coating treatment, the positive electrode material maintains a more excellent layered structure during the cycle process, provides better solvation for lithium ions, or enhances the electronic conductivity and ionic conductivity of the positive electrode material, thereby further specifically improving its cycle, high and low temperature, rate, storage and other performances.

[0032] The above method disclosed in the present invention is only used to illustrate the method used to realize the low-cobalt ternary positive electrode material described in the present invention. The low-cobalt ternary positive electrode material described in the present invention should not be limited by the steps and parameters in the above method.

[0033] Another object of the present invention is to provide a use of the above-mentioned high-voltage, low-cobalt ternary positive electrode material in the preparation of a positive electrode for a lithium-ion battery.

[0034] Technical Effects

[0035] The high voltage low cobalt ternary cathode material provided by the present invention has the general formula Li a Ni b Co c Mn d O2, wherein, 0.97≤a≤1.1, 0.5≤b≤0.76, 0≤c≤0.1, 0.24≤d≤0.5, b+c+d=1, and c<0.35d, and the positive electrode material has a lithium nickel mixing rate (σ): 2≤σ≤7. Compared with the prior art, the positive electrode material can be used at a higher voltage than other ternary positive electrode materials with the same nickel content. While improving the energy density, the positive electrode material has a smaller volume change, which avoids cracking and pulverization of the positive electrode material, extends the service life of the material, and improves the safety performance of the material. In addition, since the nickel and cobalt content of the positive electrode material is relatively lower and the manganese content is relatively higher, the positive electrode material has better cycle performance and high voltage performance while reducing its use cost. DETAILED DESCRIPTION

[0036] Hereinafter, the present invention will be further described through examples, but the present invention is not limited to the examples.

[0037] The main raw material information is as follows:

[0038] Nickel sulfate hexahydrate NiSO4·6H2O, 262.85 g / mol, battery grade, Jinchuan Group;

[0039] Cobalt sulfate heptahydrate CoSO4·7H2O, 281.15 g / mol, battery grade, Huayou Cobalt;

[0040] Manganese sulfate monohydrate MnSO4·H2O, 169.016 g / mol, battery grade, Guizhou Dalong Huicheng New Materials Co., Ltd.

[0041] Nickel cobalt manganese hydroxide precursor Ni b Co c Mn d (OH)2, homemade;

[0042] Lithium hydroxide monohydrate LiOH·H2O, 41.96 g / mol, Shandong Ruifu Lithium Industry Co., Ltd.

[0043] Lithium carbonate Li2CO3, 73.89 g / mol, Shandong Ruifu Lithium Industry Co., Ltd.;

[0044] Polyvinylidene fluoride (PVDF), analytical grade, Aladdin;

[0045] Nitromethylpyrrolidone (NMP), analytical grade, Aladdin;

[0046] Ammonia water (20%-28%), analytical grade, Aladdin;

[0047] Sodium hydroxide solution (32%), analytical grade, Aladdin.

[0048] The main test equipment information is as follows:

[0049] XRD: Malvern Panalytical Aeris X-ray diffractometer

[0050] Electrochemical testing equipment: Shenzhen Xinwei button cell testing system;

[0051] Calcination equipment: Hefei Kejing tube furnace, model OTF-1500X.

[0052] The lithium nickel mixed test method is as follows:

[0053] The cathode material powder was subjected to back pressure tableting treatment, and powder XRD measurement was performed using a Malvern Panalytical Aeris XRD tester with a test angle 2θ of 10°-80°, a step length of 2θ=0.0108°, and a test time of 100 s per step.

[0054] The XRD spectrum obtained from the test was refined using HighScore software. The refinement steps were as follows:

[0055] 1. Perform the Default operation, automatically fit twice, and perform background correction;

[0056] 2. Load the CIF card and select the 96-400-2444 card;

[0057] 3. Convert the card into a photo and perform two automatic refinements;

[0058] 4. Enter the manual refinement mode and refine the background parameters, peak variables, preferred orientation, asymmetry type and spectrum variables in turn;

[0059] 5. Modify the atomic temperature factors, where Li is set to 0.0527, Ni / Co / Mn is set to 0.01232, and O is set to 0.031663;

[0060] 6. Assign atomic occupancy values ​​according to the element content of the embodiment. First, the initial lithium-nickel mixing ratio σ is set to 5, that is, the lithium-nickel mixing ratio is defined as the percentage of lithium content in the nickel layer to the total lithium content is 5%. For example, the LiNi in Example 1 0.52 Co 0.10 Mn 0.38 O2, then Li1 is 0.95, Li2 is 0.05 (that is, the lithium-nickel mixing rate σ), Ni1 is 0.47, Ni2 is 0.05, Co is 0.1, Mn is 0.38, and O is 2.

[0061] 7. Modify the atomic position constraint relationship, using the LiNi of Example 1 0.52 Co 0.10 Mn 0.38 Taking O2 as an example, the constraint relationship is set to Li1+Ni2=1, Li2+Li1=1, Ni1+Li2=0.52, and then the Li1 / Li2 / Ni1 / Ni2 occupancy rate is checked and manually refined.

[0062] Continue the refinement operation until the Weighted R Profile (Rwp) value and the R expected (Rp) value are both lower than 10 (the smaller the value, the closer the measured spectrum and the simulated spectrum are), and the Goodness of Fit (GOF) value is less than 1.5, which means that the refinement is completed. At this time, the lithium nickel mixing rate σ of the material can be read on the software interface.

[0063] The electrochemical performance test method is as follows:

[0064] The positive electrode material and lithium sheet obtained in the embodiment were used as the positive and negative active materials, respectively, to assemble button batteries; the positive electrode slurry in the positive electrode sheet was composed of positive electrode active material, acetylene black (conductive agent) and PVDF (binder), and the mass ratio of the three was 80:12:8; Shenzhen Xinwei's button battery testing system was used for testing, and the charge and discharge voltage was within a set voltage range, such as 3.0–4.5 V. The button batteries assembled with the positive electrode materials were subjected to electrochemical performance tests at room temperature. The mass specific capacity of the positive electrode material was tested at a current density of 0.02 A / g (0.1C), and then its 100-cycle cycle performance was tested at a current density of 0.2 A / g (1C), and its cycle retention rate was calculated.

[0065] The DSC test method is as follows:

[0066] The fully charged battery was disassembled, and the positive electrode material soaked in electrolyte was scraped off from the positive electrode sheet. It was placed in a DSC testing device (TOPEMTMDSC) and heated to 800°C at a heating rate of 10°C / min. The temperature-exotherm curve was obtained, and the exotherm temperature was recorded according to the peak position.

[0067] The particle size D50 test method is as follows:

[0068] The material powder was taken and tested using a Malvern Mastersizer 3000 laser particle size analyzer with a wet sampler to obtain particle size distribution data.

[0069] Example 1

[0070] Weigh 2.73 kg NiSO4·6H2O, 1.284 kg MnSO4·H2O, and 562 g CoSO4·7H2O and dissolve them in 6 L deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0071] 9L of deionized water was added to a 10L reactor, and about 200mL of concentrated ammonia water was added to the water to prepare a base liquid containing 0.3M ammonia water. A peristaltic pump was used to drop the salt solution, 32% sodium hydroxide solution and 25% ammonia solution into the reactor at the same time. The dripping rate of the salt solution was controlled to 400mL / h, the dripping rate of the ammonia water was 8mL / h, and the dripping rate of the sodium hydroxide was controlled by an online pH meter so that the pH of the overall reaction solution was 11.50. The reactor was provided with an overflow port, which continued to overflow as the solution was added until the particle size D50 in the reactor was 10μm. After that, all the slurry in the reactor was taken out, solid-liquid separation was performed using a centrifuge, and washed with deionized water. The washed wet solid was transferred to an oven and dried at 120°C for 10 hours to obtain 885g of Ni 0.52 Co 0.10 Mn 0.38 (OH)2.

[0072] 100gNi 0.52 Co 0.10 Mn 0.38 (OH)2 and 40.9g lithium carbonate were mixed evenly using a high-speed mixer in a molar ratio of 1:1.03. The mixture was put into a sagger and placed in a tube furnace. It was sintered at 920°C for 12 hours under a pure oxygen atmosphere to obtain 102g of positive electrode material LiNi 0.52 Co 0.10 Mn 0.38 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0073] Example 2

[0074] Weigh 3.15 kg of NiSO₄·6H₂O, 1014 g of MnSO₄·H₂O, and 562 g of CoSO₄·7H₂O and dissolve them in 6 L of deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0075] 860 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.6 Co 0.1 Mn 0.3 (OH)2.

[0076] 100gNi 0.6 Co 0.1 Mn 0.3 (OH)2 and 40.9g lithium carbonate were mixed evenly using a high-speed mixer in a molar ratio of 1:1.03. The mixture was placed in a sagger and placed in a tube furnace. It was sintered at 890°C for 12 hours in a pure oxygen atmosphere to obtain 102g of positive electrode material LiNi0.6 Co 0.1 Mn 0.3 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0077] Example 3

[0078] Weigh 3.15 kg of NiSO₄·6H₂O and 1352 g of MnSO₄·H₂O and dissolve them in 6 L of deionized water. Then dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0079] 855 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.6 Mn 0.4 (OH)2.

[0080] 100gNi 0.6 Mn 0.4 (OH)2 and 40.9g lithium carbonate were mixed evenly using a high-speed mixer in a molar ratio of 1:1.03. The mixture was placed in a sagger and placed in a tube furnace. It was sintered at 890°C for 12 hours in a pure oxygen atmosphere to obtain 102g of positive electrode material LiNi 0.6 Mn 0.4 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0081] Example 4

[0082] Weigh 3.668 kg of NiSO₄·6H₂O, 845 g of MnSO₄·H₂O, and 281 g of CoSO₄·7H₂O and dissolve them in 6 L of deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0083] 872 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.70 Co 0.05 Mn 0.25 (OH)2.

[0084] 100gNi 0.70 Co 0.05 Mn 0.25 (OH)2 and 46.80g LiOH·H2O were mixed evenly in a high-speed mixer at a molar ratio of 1:1.03. The mixture was put into a sagger and placed in a tube furnace. It was sintered at 820°C for 12 hours under a pure oxygen atmosphere to obtain 102g of positive electrode material LiNi 0.70 Co 0.05 Mn 0.25O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0085] Example 5

[0086] Weigh 3.15 kg of NiSO₄·6H₂O, 1014 g of MnSO₄·H₂O, and 562 g of CoSO₄·7H₂O and dissolve them in 6 L of deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0087] 860 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.6 Co 0.1 Mn 0.3 (OH)2.

[0088] 100gNi 0.6 Co 0.1 Mn 0.3 (OH)2 and 40.9g lithium carbonate were mixed evenly in a high-speed mixer at a molar ratio of 1:1.03, and 0.1g aluminum oxide and 0.3g zirconium oxide were added to the high-speed mixer and mixed evenly. The mixture was then placed in a sagger and placed in a tube furnace. It was sintered at 890°C for 12 hours in a pure oxygen atmosphere to obtain 102g of LiNi positive electrode material doped with trace amounts of aluminum and zirconium. 0.6 Co 0.1 Mn 0.3 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0089] Example 6

[0090] Weigh 3.15 kg of NiSO₄·6H₂O, 1014 g of MnSO₄·H₂O, and 562 g of CoSO₄·7H₂O and dissolve them in 6 L of deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0091] 860 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.6 Co 0.1 Mn 0.3 (OH)2.

[0092] 100gNi 0.6 Co 0.1 Mn 0.3(OH)2 and 40.9g lithium carbonate were mixed evenly in a high-speed mixer at a molar ratio of 1:1.03. The mixture was put into a sagger and placed in a tube furnace. It was sintered at 890°C for 12 hours under a pure oxygen atmosphere to obtain 102g of positive electrode material LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0093] 100g of the positive electrode material was taken and mixed with 0.3g of aluminum oxide in a high-speed mixer. The mixture was put into a sagger and placed in a tube furnace. The mixture was sintered at 400°C for 12 hours under a pure oxygen atmosphere to obtain 100g of positive electrode material LiNi coated with aluminum. 0.6 Co 0.1 Mn 0.3 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0094] Comparative Example 1

[0095] Weigh 2.625 kg NiSO4·6H2O, 1.014 kg MnSO4·H2O, and 1.124 kg CoSO4·7H2O and dissolve them in 6 L deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0096] 880 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.5 Co 0.2 Mn 0.3 (OH)2.

[0097] 100gNi 0.5 Co 0.2 Mn 0.3 (OH)2 and 40.9g lithium carbonate were mixed evenly using a high-speed mixer at a molar ratio of 1:1.03. The mixture was placed in a sagger and placed in a tube furnace. It was sintered at 920°C for 12 hours under an oxygen atmosphere to obtain 102g of positive electrode material LiNi 0.5 Co 0.2 Mn 0.3 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0098] Comparative Example 2

[0099] Weigh 3.15 kg of NiSO₄·6H₂O, 676 g of MnSO₄·H₂O, and 1124 g of CoSO₄·7H₂O and dissolve them in 6 L of deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0100] 866 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.6 Co 0.2 Mn 0.2 (OH)2.

[0101] 100gNi 0.6 Co 0.2 Mn 0.2 (OH)2 and 40.9g lithium carbonate were mixed evenly using a high-speed mixer at a molar ratio of 1:1.03. The mixture was placed in a sagger and placed in a tube furnace. It was sintered at 890°C for 12 hours under a pure oxygen atmosphere to obtain 100g of positive electrode material LiNi 0.6 Co 0.2 Mn 0.2 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0102] Comparative Example 3

[0103] Weigh 3.15 kg of NiSO₄·6H₂O and 1352 g of MnSO₄·H₂O and dissolve them in 6 L of deionized water. Then dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0104] 891 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.6 Mn 0.4 (OH)2.

[0105] 100gNi 0.6 Mn 0.4 (OH)2 and 40.9g lithium carbonate were mixed evenly using a high-speed mixer in a molar ratio of 1:1.03. The mixture was placed in a sagger and placed in a tube furnace. It was sintered at 940°C for 12 hours under a pure oxygen atmosphere to obtain 101g of positive electrode material LiNi 0.6 Mn 0.4 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0106] Comparative Example 4

[0107] Weigh 3.93 kg of NiSO₄·6H₂O, 507 g of MnSO₄·H₂O, and 562 g of CoSO₄·7H₂O and dissolve them in 6 L of deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0108] 876 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.75 Co 0.1 Mn 0.15 (OH)2.

[0109] 100gNi 0.75 Co 0.1 Mn 0.15 (OH)2 and 46.80gLiOH·H2O were mixed evenly in a high-speed mixer according to a lithiation ratio of 1:1.03. The mixture was put into a sagger and placed in a tube furnace. It was sintered at 820℃ for 12 hours under a pure oxygen atmosphere to obtain 102g of positive electrode material LiNi 0.75 Co 0.1 Mn 0.15 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0110] Comparative Example 5

[0111] Weigh 4.2 kg NiSO4·6H2O, 338 g MnSO4·H2O and 562 g CoSO4·7H2O, dissolve in 6 L deionized water, and then dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution for later use. 894 g Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0112] 100gNi 0.8 Co 0.1 Mn 0.1 (OH)2 and 46.80g LiOH·H2O were mixed evenly in a high-speed mixer at a molar ratio of 1:1.03. The mixture was put into a sagger and placed in a tube furnace. It was sintered at 800℃ for 12 hours under a pure oxygen atmosphere to obtain 101g of positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0113] Comparative Example 6

[0114] Weigh 4.2 kg of NiSO₄·6H₂O, 507 g of MnSO₄·H₂O, and 281 g of CoSO₄·7H₂O and dissolve them in 6 L of deionized water. Then, dilute the salt solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0115] 857 g of Ni with a particle size of 10 μm was synthesized using the same method as in Example 1. 0.8 Co 0.05 Mn 0.15 (OH)2.

[0116] 100gNi 0.8 Co 0.05 Mn 0.15 (OH)2 and 46.80g LiOH·H2O were mixed evenly in a high-speed mixer at a molar ratio of 1:1.03. The mixture was put into a sagger and placed in a tube furnace. It was sintered at 800℃ for 12 hours under a pure oxygen atmosphere to obtain 101g of positive electrode material LiNi 0.8 Co 0.05 Mn 0.15 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0117] Comparative Example 7

[0118] Weigh 2.1 kg NiSO₄·6H₂O, 1.521 kg MnSO₄·H₂O, and 843 g CoSO₄·7H₂O and dissolve them in 6 L deionized water. Then dilute the solution to 10 L. Prepare 32% sodium hydroxide solution and 25% ammonia solution and set aside.

[0119] 823 g of 5Ni with a particle size of 10 μm was synthesized using the same method as in Example 1 0.4 Co 0.15 Mn 0.45 (OH)2.

[0120] 100gNi 0.4 Co 0.15 Mn 0.45 (OH)2 and 40.9g lithium carbonate were mixed evenly using a high-speed mixer at a molar ratio of 1:1.03. The mixture was placed in a sagger and placed in a tube furnace. It was sintered at 800°C for 12 hours under a pure oxygen atmosphere to obtain 102g of positive electrode material LiNi 0.4 Co 0.15 Mn 0.45 O2. The electrochemical specific capacity and cycle performance of the positive electrode material were then tested, and the data are shown in Table 1.

[0121] 10 test cases of electrochemical performance test

[0122] Relevant tests were performed according to the electrochemical performance test method, lithium nickel mixing test method and DSC test method as described above, and the test results are shown in Table 1.

[0123] Table 1

[0124]

[0125] As can be seen from Table 1:

[0126] Comparing Example 1 with Comparative Example 1, since the lithium-nickel mixing ratio of Comparative Example 1 is too low, its cycle retention rate is low and the DSC exothermic starting temperature is low, indicating that a suitable lithium-nickel mixing ratio helps maintain the stability of the structure.

[0127] Comparing Example 2 with Comparative Example 2, since the lithium-nickel mixing ratio of Comparative Example 2 is too low, its cycle retention rate is low and the DSC exothermic starting temperature is low, indicating that a suitable lithium-nickel mixing ratio helps maintain the stability of the structure.

[0128] Comparing Example 3 with Comparative Example 3, since the lithium-nickel mixing rate of Comparative Example 3 is too high, its cycle retention rate is low and its capacity is too low.

[0129] Comparing Example 4 with Comparative Example 4, since the lithium-nickel mixing ratio of Comparative Example 4 is too low, its cycle retention rate is low and the DSC exothermic starting temperature is low, indicating that a suitable lithium-nickel mixing ratio helps maintain the stability of the structure.

[0130] In Comparative Examples 5 and 6, although the lithium-nickel mixing ratio is within an appropriate range, the cycle retention rates are low due to the excessively high nickel content and capacity.

[0131] The nickel content in Comparative Example 7 is too low and the lithium-nickel mixing rate is too high. Although the exothermic starting temperature is improved, the capacity is too low and the cycle retention rate is low.

[0132] In summary, the high voltage low cobalt ternary cathode material provided by the present invention has the general formula Li a Ni b Co c Mn dO2, wherein, 0.97≤a≤1.1, 0.5≤b≤0.76, 0≤c≤0.1, 0.24≤d≤0.5, b+c+d=1, and c<0.35d, and the positive electrode material has a lithium nickel mixing rate (σ): 2≤σ≤7. The high-voltage, low-cobalt ternary positive electrode material provided by the present invention can be used at an operating voltage greater than or equal to 4.3V, and can even be used at an operating voltage of up to 4.5V. While improving the energy density, since the positive electrode material has a smaller volume change, the cracking and pulverization of the positive electrode material are avoided, the service life of the material is extended, which is manifested as a better capacity retention rate during the cycle, and the safety performance of the material is improved, which is manifested as a higher exothermic temperature in the DSC test. In addition, since the nickel and cobalt content of the positive electrode material is relatively lower and the manganese content is relatively higher, the positive electrode material has more excellent cycle performance and high voltage performance while reducing its use cost.

Claims

1. A high voltage low cobalt ternary cathode material having the general formula Li a Ni b Co c Mn d O2, where 0.97≤a≤1.1, 0.5≤b≤0.76, 0≤c≤0.1, 0.24≤d≤0.5, b+c+d=1, and c<0.35d, and the positive electrode material has a lithium nickel mixing rate (σ)2≤σ≤7.

2. The positive electrode material according to claim 1, wherein In terms of capacity, within the operating voltage range of 3-4.3V, the 0.1C capacity of the positive electrode material is not higher than 185mAh / g; within the operating voltage range of 3-4.5V, the 0.1C capacity is not higher than 210mAh / g.

3. The positive electrode material according to claim 1 or 2, wherein The positive electrode material is used at an operating voltage greater than or equal to 4.3V.

4. The positive electrode material according to claim 3, wherein The positive electrode material is used at an operating voltage greater than or equal to 4.35V.

5. The positive electrode material according to claim 3, wherein The positive electrode material is used at an operating voltage greater than or equal to 4.40V.

6. The method for preparing the high-voltage, low-cobalt ternary cathode material according to any one of claims 1 to 5, comprising the following steps: Step 1: Dissolve NiSO4·6H2O, MnSO4·H2O, and CoSO4·7H2O in deionized water to obtain a salt solution; Step 2: Add deionized water to the reaction container, and add concentrated ammonia water to the deionized water to prepare a base liquid containing ammonia water; add the salt solution obtained in step 1, as well as the sodium hydroxide solution and the concentrated ammonia water dropwise to the base liquid at the same time; set an overflow port in the reaction container, and overflow continuously as the salt solution, sodium hydroxide solution and concentrated ammonia water are added dropwise until the particle size D in the reaction container is 50 Achieve target particle size; Step 3: taking out all the slurry in the reaction container and performing solid-liquid separation, washing with deionized water, and drying to obtain a nickel-cobalt-manganese hydroxide precursor; Step 4: Mix the nickel-cobalt-manganese hydroxide precursor with LiOH·H2O or lithium carbonate; Step 5: Sinter the mixture obtained in step 4 under an oxygen atmosphere to obtain a low-cobalt ternary positive electrode material.

7. The preparation method according to claim 6, wherein in step 2, the dropping rate of the salt solution is controlled to be 300 mL / h to 500 mL / h; the dropping rate of the concentrated ammonia solution is controlled to be 6 mL / h to 10 mL / h, and the dropping rate of the sodium hydroxide solution is controlled so that the pH of the overall reaction solution is 10.00 to 13.

00.

8. according to the preparation method described in claim 6 or 7, the end liquid containing ammoniacal liquor that wherein uses in step 2 is the end liquid containing 0.1-0.8M ammoniacal liquor; The concentrated ammoniacal liquor that uses in step 2 is an ammoniacal liquor with a concentration of 20%-28%; The sodium hydroxide solution that uses in step 2 is a sodium hydroxide solution with a concentration of 30%-42%.

9. preparation method according to claim 8, wherein the ammoniacal end liquid that uses in step 2 is the end liquid that contains 0.3-0.5M ammoniacal end liquid; The concentrated ammoniacal liquor that uses in step 2 is an ammoniacal liquor with a concentration of 25%; The sodium hydroxide solution that uses in step 2 is a sodium hydroxide solution with a concentration of 32%.

10. The preparation method according to claim 6 or 7, wherein the particle size D obtained in step 2 50 The target particle size is 3-20 μm.

11. The preparation method according to claim 6 or 7, wherein in step 4, the molar ratio of the nickel-cobalt-manganese hydroxide precursor to LiOH·H2O or lithium carbonate is 1:1.01 to 1:1.

10.

12. The preparation method according to claim 11, wherein in step 4, the molar ratio of the nickel-cobalt-manganese hydroxide precursor to LiOH·H2O or lithium carbonate is 1:1.02 to 1:1.

05.

13. The preparation method according to claim 6 or 7, wherein in step 5, the sintering temperature is 700°C to 1000°C; and the sintering time is 10 hours to 14 hours.

14. The preparation method according to claim 6 or 7, wherein In step 4, a doping treatment is performed, including adding one or more compounds containing Ca, Mg, Zr, Sr, Na, Si, Al, La, W, B, Fe, Cu, K, Ge, Nd, Nb, Mo, Y or Ce elements in step 4.

15. The preparation method according to claim 6 or 7, wherein After step 5, a coating treatment is performed, including adding one or more compounds containing Ca, Mg, Zr, Sr, Na, Si, Al, La, W, B, Fe, Cu, K, Ge, Nd, Nb, Mo, Y or Ce elements after step 5, and sintering the mixture again.

16. Use of the high-voltage, low-cobalt ternary cathode material according to any one of claims 1 to 5 in preparing a positive electrode for a lithium-ion battery.

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