Positive electrode material, method for producing the same, and lithium-ion secondary battery including the same

Abstract

The present invention relates to a positive electrode material, a method for producing the same, and a lithium ion secondary battery comprising the same. Specifically, the present invention relates to a high-nickel material and a coating layer on the surface of the high-nickel material, wherein the coating layer comprises a compound C of formula (I): x H y-n O z Li n (I) and a compound C of formula (II) x H y-n-1 O z Li n+1 (II) wherein x, y, z, and n are integers such that 1≦x≦10, 2≦y≦20, 2≦z≦12, and 1≦n≦3, respectively. The present invention also relates to a method for producing the cathode material, and to a battery containing the cathode material.

Description

[Technical Field]

[0001] The present invention relates to the field of lithium ion secondary batteries, and in particular to a positive electrode material for lithium batteries, a method for producing the same, and a lithium ion secondary battery comprising the same. [Background technology]

[0002] In recent years, the ever-evolving nature of electronic technology has led to an increasing demand for battery devices to power electronic devices. Currently, there is a demand for batteries that can store more power and output higher power. Traditional lead-acid batteries and nickel-metal hydride batteries are no longer able to meet the needs of new electronic products. Therefore, lithium batteries have attracted widespread attention. The development of lithium batteries has effectively improved their capacity and performance.

[0003] In lithium battery technology, high-nickel materials, due to their high energy density, are currently the main development direction for cathode materials and are widely used in the field of power batteries. However, as the nickel content increases, the amount of residual alkali (including LiOH and Li2CO3) on the surface of high-nickel materials increases, reducing processability. Furthermore, the residual alkali causes gas generation in batteries, and the higher the lithium impurities, the more serious the gas generation. Therefore, reducing the amount of residual alkali on the surface of high-nickel materials is the focus of current research.

[0004] While the currently mainstream water-washed modified high-nickel materials do indeed significantly reduce residual alkalinity on the surface, NiO-based substances are formed on the surface of the water-washed modified materials, increasing the impedance of the battery. In addition, the precipitation of lattice lithium within the material destabilizes the material structure, significantly reducing cycle characteristics. Summary of the Invention [Problem to be solved by the invention]

[0005] The main object of the present invention is to provide a positive electrode material for a lithium battery, a method for manufacturing the same, and a lithium ion secondary battery including the same, in order to solve the problem that the methods used in the prior art for reducing the amount of residual alkali on the surface of high-nickel materials lead to an increase in battery impedance and a decrease in cycle characteristics. [Means for solving the problem]

[0006] To solve the above problems, the present invention provides a novel high-nickel material, which has an extremely small amount of residual alkali on its surface and has a coating layer of RCOOLi-type substances on its surface. This coating layer stabilizes the structure of the material, reduces impedance, and can significantly improve the cycling characteristics of the material.

[0007] According to one aspect of the present invention, the present invention comprises: High nickel materials and a coating layer on the surface of the high nickel material, the coating layer comprising: A positive electrode material for a lithium ion battery is provided, comprising a compound of formula (I) and a compound of formula (II).

[0008] C x H y-n O z Li n (I) C x H y-n-1 O z Li n+1 (II)

[0009] (wherein x, y, z, and n are each independently an integer of 1≦x≦10, 2≦y≦20, 2≦z≦12, and 1≦n≦3.) Furthermore, in the above positive electrode material, the compound of formula (I) and the compound of formula (II) are Li salts of an organic acid, and the organic acid is represented by the general formula C x H y O z(Here, x, y, and z are each independently an integer such that 1 ≤ x ≤ 10, 2 ≤ y ≤ 20, and 2 ≤ z ≤ 12), and the organic acid contains 1 to 3 carboxyls and 0 to 1 C=C double bond.

[0010] Furthermore, in the above positive electrode material, the organic acid includes one or more of maleic acid, acrylic acid, fumaric acid, malonic acid, oxalic acid, malic acid, glycolic acid, succinic acid, citric acid, tricarballylic acid, and aconitic acid, preferably one or more of maleic acid, malonic acid, and oxalic acid, and most preferably maleic acid.

[0011] Furthermore, in the above positive electrode material, the molar percentage a of the compound of the formula (I) in the coating layer is 50% ≤ a < 100%, and the molar percentage b of the compound of the formula (II) in the coating layer is 0% < b ≤ 50%, preferably 1 ≤ a / b ≤ 3.

[0012] Furthermore, in the above positive electrode material, the coating layer is uniformly coated on the surface of the high-nickel material.

[0013] Furthermore, in the above positive electrode material, the thickness of the coating layer is 1 to 100 nm, and the mass percentage of the coating layer in the positive electrode material is 0.1 to 10 wt%, preferably 1 to 5 wt%.

[0014] Furthermore, in the above positive electrode material, the coating layer is present simultaneously on both the surface of the secondary particles and the grain boundaries of the primary particles of the high-nickel material.

[0015] Furthermore, in the above positive electrode material, the high-nickel material has the general formula LiNi m M n O2 (where m + n = 1, 0.6 ≤ m ≤ 1, 0 ≤ n ≤ 0.4, and M is one or more of Co, Mn, Al, Mg, Ti, Fe, Cu, Zn, Ga, Zr, Mo, Nb, and W).

[0016] According to another aspect of the present invention, there is provided a method for producing a cathode material according to any one of the above aspects, comprising the steps of: mixing an organic acid with a non-aqueous solvent to obtain an organic acid solution; adding the high-nickel material to the organic acid solution and stirring to obtain a mixed solution; suction-filtering the mixed solution to obtain a mixture; and vacuum-drying the mixture, polishing, and sieving to obtain the cathode material, wherein the coating layer is formed by a reaction between the organic acid and LiOH and / or Li2CO3 contained in the high-nickel material.

[0017] Furthermore, in the above method, the organic acid has a pKa of 1-5.

[0018] Further, in the above method, the organic acid comprises one or more of maleic acid, acrylic acid, fumaric acid, malonic acid, oxalic acid, malic acid, glycolic acid, succinic acid, citric acid, tricarballylic acid, and aconitic acid.

[0019] Furthermore, in the above method, the organic acid is one or more of maleic acid, malonic acid, and oxalic acid, preferably maleic acid.

[0020] Furthermore, in the above method, the non-aqueous solvent comprises one or more of methanol, ethanol, isopropyl alcohol, ethylene glycol, and glycerin.

[0021] Furthermore, in the above method, the mass percentage of the organic acid in the organic acid solution is 0.1 wt% to 35 wt%, the mass ratio of the high-nickel material to the organic acid solution is 1:0.2 to 1:5, and the molar ratio of the total Li amount in LiOH and / or Li2CO3 contained in the high-nickel material to the organic acid in the organic acid solution is 1:0.1 to 1:4.

[0022] Furthermore, in the above method, the stirring is carried out at a speed of 50 to 500 rpm for 0.1 to 8 hours, the vacuum drying is carried out at a temperature of 60 to 150°C for 0.1 to 12 hours, and the size of the sieve used is 50 to 500 mesh.

[0023] According to another aspect of the present invention, there is provided a lithium ion secondary battery including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte solution, The positive electrode plate provides a lithium ion secondary battery comprising the positive electrode material according to any one of the above claims or a positive electrode material produced by the method according to any one of the above claims. [Effects of the Invention]

[0024] The positive electrode material for lithium batteries, the method for producing the same, and the lithium-ion secondary battery including the same of the present invention have the effects of reducing residual alkali in high-nickel positive electrode materials and improving impedance and cycle characteristics. [Brief explanation of the drawings]

[0025] The drawings in the specification that form a part of this application are intended to provide a further understanding of the invention, and the schematic embodiments of the invention and their descriptions are intended to illustrate the invention and are not intended to unduly limit the invention. [Figure 1] FIG. 1 is a schematic diagram of a reaction process between an organic acid and a residual alkali in an embodiment according to the present invention. [Figure 2] FIG. 1 is a graph showing cycle retention rates versus the number of cycles of batteries manufactured in examples and comparative examples according to the present invention. [Figure 3] 1 is a ToF-SIMS spectrum of a positive electrode material produced in Example 1 according to the present invention. [Figure 4] 10 is a ToF-SIMS spectrum of a positive electrode material produced in Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0026] The embodiments and features of the present application may be combined with each other as long as they are not contradictory. The present application will be described in detail below based on the embodiments with reference to the drawings.

[0027] In order to help those skilled in the art better understand the configuration of the present application, the technical solutions in the embodiments of the present application will be described below clearly and completely with reference to the drawings in the embodiments of the present application, but it is clear that the described embodiments are only a part of the embodiments of the present application, and do not represent all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without any creative work should fall within the scope of protection of the present application.

[0028] As described in the Background Art section, in the prior art, high-nickel materials are subjected to water-washing modification to reduce residual alkali on their surfaces. However, this results in the formation of NiO-based substances on the surface of the water-washed modified material, which increases the impedance of the battery. In addition, the precipitation of lattice lithium in the material destabilizes the structure of the material, significantly reducing cycle characteristics.

[0029] In response to the above problems, the present invention provides a positive electrode material for lithium batteries, which is made by washing a high-nickel material with an organic acid solution, and then reacting the organic acid with the residual alkali on the material surface to remove the residual alkali and produce a material with an RCOOLi structure that can be coated on the surface of the high-nickel material. The high-nickel positive electrode material of the present invention has been washed with organic acid, leaving only trace amounts of alkaline material on the surface, and is highly stable. The RCOOLi material produced by the reaction of the organic acid and alkali can reduce impedance and significantly improve cycle characteristics.

[0030] According to an exemplary embodiment of the present application, there is provided a positive electrode material for a lithium ion battery, comprising: a high-nickel material; and a coating layer on a surface of the high-nickel material, wherein the coating layer of the R—Li structure comprises a compound of formula (I) and a compound of formula (II).

[0031] C x H y-n O z Li n (I) C x H y-n-1 O z Li n+1 (II)

[0032] (wherein x, y, z, and n are each independently an integer of 1≦x≦10, 2≦y≦20, 2≦z≦12, and 1≦n≦3.) In a preferred embodiment, the high nickel material has the general formula LiNi m M n O2 (where m+n=1, 0.6≦m≦1, 0≦n≦0.4, and M is one or more of Co, Mn, Al, Mg, Ti, Fe, Cu, Zn, Ga, Zr, Mo, Nb, and W).

[0033] In the manufacturing process of high-nickel materials, the ratio of lithium to metal is slightly increased (i.e., the lithium salt is appropriately in excess) to compensate for losses that occur during the sintering process, so that the Li in the manufactured high-nickel material is in excess and exists mainly as Li2O, which easily reacts with CO2 and H2O in the air to produce Li2CO3 and LiOH. Also, the higher the nickel content of the high-nickel material, the more LiNiO2 there is in the material, and LiNiO2 can also react with H2O to produce LiOH, resulting in the production of more LiOH.

[0034] The inventors have unexpectedly discovered that in order to reduce the residual alkali in a high-nickel material, the residual alkali on the surface of the high-nickel material can be removed by washing the high-nickel material with a specific organic acid, and that the compound produced by the reaction between the organic acid and the residual alkali can form a coating layer of an RCOOLi substance on the surface of the high-nickel material, and that the coating layer according to the present invention can reduce impedance and improve cycle characteristics.

[0035] Here, the RCOOLi material is a mixture of the complete reaction product (i.e., the compound of formula (II)) and the incomplete reaction product (i.e., the compound of formula (I)) of the organic acid and alkali. When both are present simultaneously, the optimal coating effect is achieved. If all the RCOOLi materials are complete reaction products, the reaction consumes lithium in the positive electrode material lattice, reducing the active lithium in the material itself, resulting in a decrease in capacity. If all the RCOOLi materials are incomplete reaction products, their ionic conductivity is lacking, affecting impedance characteristics.

[0036] For example, as shown in Figure 1, when the remaining alkali is reacted with maleic acid, a complete reaction product and an incomplete reaction product are produced as shown in the figure.

[0037] In some embodiments of the present application, the compound of formula (I) and the compound of formula (II) are Li salts of an organic acid, and the organic acid has the general formula C x H y O z (wherein x, y, and z are each independently an integer of 1≦x≦10, 2≦y≦20, and 2≦z≦12), and the organic acid contains 1 to 3 carboxy groups and 0 to 1 C═C double bonds.

[0038] As described above, the coating layer of the present invention is a reaction product of an organic acid with residual lithium (including Li2CO3 and LiOH), i.e., a Li salt of the organic acid, and the organic acid has the general formula C x H y O z The present inventors have also found that organic acids containing 1 to 3 carboxyls and 0 to 1 C═C double bonds are useful in forming the coating layer of the present invention.

[0039] In a preferred embodiment of the present application, the organic acid comprises one or more of maleic acid, acrylic acid, fumaric acid, malonic acid, oxalic acid, malic acid, glycolic acid, succinic acid, citric acid, tricarballylic acid, and aconitic acid, preferably one or more of maleic acid, malonic acid, and oxalic acid, most preferably maleic acid.

[0040] In some embodiments of the present application, the molar percentage a of the compound of formula (I) in the coating layer satisfies 50% ≤ a < 100%, and the molar percentage b of the compound of formula (II) in the coating layer satisfies 0% < b ≤ 50%, preferably 1 ≤ a / b ≤ 3.

[0041] As described above, by the reaction of an organic acid and an alkali, a complete reaction product (i.e., the compound of formula (II)) and an incomplete reaction product (i.e., the compound of formula (I)) are formed. The inventors have discovered that an appropriate ratio of the two helps to achieve an optimal coating effect. When the ratio a / b is less than 1, it means that the complete reaction product is in a large amount. Due to the complete reaction product, lithium in the crystal lattice of the cathode material is consumed excessively, and the capacity of the material decreases. When the ratio a / b is greater than 3, it means that the incomplete reaction product is in a large amount. Due to the incomplete reaction product, the ionic conductivity of the coating layer decreases, affecting the impedance.

[0042] In some embodiments of the present application, the coating layer has characteristic peaks in the range of 1600 - 1800 cm -1 in FTIR, characteristic peaks in the range of 288 - 290 eV in XPS C1s, and shows fragment peaks of C x H y-n-1 O z Li n - and C x-1 H y-n-1 O z-2 Li n - in a ToF - SIMS test. The fragment peaks indicate that in the two - dimensional imaging spectrum (also called an elemental distribution spectrum or a mapping spectrum) tested by ToF - SIMS, they are uniformly coated on the surface of the high - nickel material.

[0043] The present inventors have performed FTIR, XPS C1s, and ToF-SIMS tests on the cathode material produced according to the present invention. -1 In XPS, the peak at 285-287 eV represents C=O, and the peak at 288-290 eV represents CO═O. Therefore, the above test proved that the compounds of formulas (I) and (II) above are present in the coating layer of the positive electrode material produced by the present invention, and that the coating layer is uniformly coated on the surface of the high-nickel material.

[0044] In some embodiments of the present application, the coating layer has a thickness of 1 to 100 nm and a mass percentage of the high-nickel material of 0.1 to 10 wt%, preferably 1 to 5 wt%. In a preferred embodiment, the coating layer is present simultaneously on both the surfaces of the secondary particles of the high-nickel material and on the grain boundaries of the primary particles.

[0045] Through testing, the inventors discovered that a mass percentage of the coating layer in the high-nickel material of 1 to 10 wt% is most advantageous for the material's properties. Furthermore, through electron microscope observation, the inventors found that the thickness of the coating layer produced according to the embodiment of the present invention is 1 to 100 nm. High-nickel material particles are large particles formed by the aggregation of multiple small particles, the small particles being called primary particles and the large particles being called secondary particles. Observation revealed that the coating layer of the present invention is present simultaneously on both the surface of the secondary particles of the high-nickel material and on the grain boundaries of the primary particles, which also indicates that the coating layer is uniformly coated on the surface of the high-nickel material particles.

[0046] Another exemplary embodiment of the present invention provides a method for producing the cathode material according to any one of the above aspects, including the steps of: mixing an organic acid with a non-aqueous solvent to obtain an organic acid solution; adding the high-nickel material to the organic acid solution and stirring to obtain a mixed solution; suction-filtering the mixed solution to obtain a mixture; and vacuum-drying the mixture, polishing, and sieving to obtain the cathode material, wherein the coating layer is formed by a reaction between the organic acid and LiOH and / or Li2CO3 contained in the high-nickel material.

[0047] As described above, the inventors have unexpectedly discovered that washing a high-nickel material with an organic acid, which reacts with residual alkali in the material to form a coating layer on the surface of the high-nickel material, removes the residual alkali while also improving the impedance and cycling characteristics of the material.

[0048] In some embodiments of the present application, the organic acid has a pKa of 1-5.

[0049] In a preferred embodiment, the organic acid comprises one or more of maleic acid, acrylic acid, fumaric acid, malonic acid, oxalic acid, malic acid, glycolic acid, succinic acid, citric acid, tricarballylic acid, and aconitic acid.

[0050] In a preferred embodiment, the organic acid is one or more of maleic acid, malonic acid, and oxalic acid, preferably maleic acid.

[0051] In some embodiments of the present application, the non-aqueous solvent comprises one or more of methanol, ethanol, isopropyl alcohol, ethylene glycol, and glycerin.

[0052] The inventors have discovered that cleaning high-nickel materials using maleic, malonic or oxalic acid, especially maleic acid, results in relatively good material properties, and that using a non-aqueous solvent to prepare the organic acid solution can reduce the impact on the impedance of the material.

[0053] In some embodiments of the present application, the mass percentage of the organic acid in the organic acid solution is 0.1 wt % to 35 wt %, the mass ratio of the high-nickel material to the organic acid solution is 1:0.2 to 1:5, and the molar ratio of the total Li amount in LiOH and / or Li2CO3 contained in the high-nickel material to the organic acid in the organic acid solution is 1:0.1 to 1:4.

[0054] The inventors have discovered that when the amounts of organic acid and high-nickel material used for washing satisfy the above ratio range, it is helpful in producing a material with better properties. If the mass ratio of the high-nickel material to the organic acid solution is too low, the amount of solvent used will be large, resulting in waste and increasing costs. If the mass ratio is too high, it will be difficult for the high-nickel positive electrode material to disperse uniformly in the solution, affecting the uniformity of the reaction.

[0055] In some embodiments of the present application, the stirring is performed at a speed of 50 to 500 rpm for 0.1 to 8 hours, the vacuum drying is performed at a temperature of 60 to 150°C for 0.1 to 12 hours, and the size of the sieve used is 50 to 500 mesh.

[0056] The inventors have discovered that the process conditions for producing a positive electrode material have a certain effect on the properties of the produced material. If the process parameters of the process satisfy the above ranges, it will be helpful to produce a material with better properties.

[0057] According to another exemplary embodiment of the present invention, there is provided a lithium ion secondary battery including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte solution, The positive electrode plate provides a lithium ion secondary battery comprising the positive electrode material according to any one of the above claims or a positive electrode material produced by the method according to any one of the above claims.

[0058] The present invention will now be described in more detail with reference to specific examples, but these examples should not be construed as limiting the scope of the present invention.

[0059] Example Example 1 The high nickel materials and lithium ion batteries used in the examples were fabricated by the following steps.

[0060] (1) 2 g of maleic acid was weighed into a beaker, and ethanol was added up to 100 g. The mixture was stirred for 1 hour to obtain a maleic acid solution. (2) A high-nickel positive electrode material (LiNi 0.8 Co 0.1 Al 0.1 (O2) 100 g was weighed and added to the solution from step (1) and stirred at 350 rpm for 1 hour to obtain a mixed solution. (3) The mixed solution from step (2) was suction filtered, and the resulting solid material was placed in a vacuum oven, dried at 120°C for 8 hours, polished, and sieved (200 mesh) to obtain a pickled high-nickel material. (4) 90 g of the pickled high-nickel material produced in step (3), 5 g of conductive carbon black as a conductive agent, and 5 g of polyvinylidene fluoride (PVDF) as a binder were used to prepare an electrode plate. A half-cell was fabricated using the electrode plate and subjected to measurement of the electrochemical properties of the battery.

[0061] Example 2 A high-nickel material and a battery were produced in the same manner as in Example 1, except that maleic acid was replaced with the same mass of oxalic acid.

[0062] Example 3 A high-nickel material and a battery were produced in the same manner as in Example 1, except that maleic acid was replaced with the same mass of malonic acid.

[0063] Example 4 A high-nickel material and a battery were produced in the same manner as in Example 1, except that the amount of maleic acid used in step (1) was 4 g.

[0064] Example 5 A high-nickel material and a battery were produced in the same manner as in Example 1, except that in step (1) ethanol was added up to 67 g.

[0065] Example 6 A high-nickel material and a battery were produced in the same manner as in Example 1, except that the stirring speed in step (2) was 200 rpm.

[0066] Example 7 A high-nickel material and a battery were produced in the same manner as in Example 1, except that the drying temperature in step (3) was 80°C.

[0067] Example 8 The high-nickel material and battery were manufactured in the same manner as in Example 1, except that the size of the sieve in step (3) was 300 mesh.

[0068] As described above, FTIR, XPS C1s, and ToF-SIMS tests were carried out on the cathode materials prepared according to the examples of the present invention. -1 XPS shows a peak at 285-287 eV, which indicates C=O, and a peak at 288-290 eV, which indicates CO₂OR. ToF-SIMS testing shows that C x H y-n-1 O z Li n - and C x-1 H y-n-1 O z-2 Li n -The fragment peaks of the compounds of formulas (I) and (II) are shown. The two-dimensional imaging spectrum of the fragment peaks obtained by ToF-SIMS indicates that the compounds are uniformly coated on the surface of the high-nickel material (see Figure 3). Therefore, the above test demonstrated that the compounds of formulas (I) and (II) are present in the coating layer of the positive electrode material prepared in the present example, and that the coating layer is uniformly coated on the surface of the high-nickel material. The test also revealed that the mass percentage of the coating layer in the high-nickel material prepared in the present example is 1 to 10 wt%. Electron microscope observation revealed that the coating layer had a thickness of 1 to 100 nm and was present simultaneously on both the surface of the secondary particles of the high-nickel material and on the grain boundaries of the primary particles.

[0069] Comparative Example 1 A high-nickel material and a battery were produced in the same manner as in Example 1, except that the untreated high-nickel material was used as is to produce a positive electrode plate and a battery.

[0070] Comparative Example 2 A high-nickel material and a battery were produced in the same manner as in Example 1, except that the organic acid solution in step (1) was changed to 100 g of deionized water.

[0071] Comparative Example 3 A high-nickel material and a battery were produced in the same manner as in Example 1, except that: (4) after step (3), 100 g of the pickled high-nickel material obtained in step (3) was added to 100 g of deionized water, and steps (2) and (3) were repeated to obtain a pickled and then water-washed high-nickel material; and (5) an electrode plate was produced using 90 g of the material produced in step (4), 5 g of conductive carbon black as a conductive agent, and 5 g of polyvinylidene fluoride (PVDF) as a binder, and a half-cell was produced using the above electrode plate.

[0072] The half-cells of the above examples and comparative examples were first subjected to a single cycle test at 25°C and 0.1C, followed by measurement of the initial impedance. Then, a cycle test was performed 100 times at 60°C, charging at 1C and discharging at 5C, to determine the capacity retention rate of the battery after 100 cycles, and then the impedance after cycling was measured. The test results are shown in Table 1 below.

[0073] [Table 1] * Impedance increase factor = Impedance after cycling / Initial impedance

[0074] Comparison of the results in Table 1 between Examples 1-8 and Comparative Examples 1-3 reveals that the positive electrode materials according to the present invention and the positive electrode materials produced according to the method of the present invention have a coating layer on the surface of the high-nickel material, which contains the compounds of Formula (I) and Formula (II). Compared with untreated high-nickel materials, water-washed high-nickel materials, and high-nickel materials that were pickled and then water-washed, the residual alkali levels were lower, and the impedance increase and capacity retention were significantly improved. Such high-nickel positive electrode materials with a coating layer of a specific composition on the surface have not been described in the prior art. Furthermore, Figure 2 also shows the capacity retention versus cycle number graphs for Example 1 and Comparative Example 1. This graph clearly shows that the positive electrode materials according to the present invention have significantly improved capacity retention compared with untreated high-nickel materials, water-washed high-nickel materials, and high-nickel materials that were pickled and then water-washed. Figure 4 also shows the ToF-SIMS spectrum of the positive electrode material produced according to Comparative Example 3. This graph indicates that when the pickled high-nickel material is further washed with water, the surface of the high-nickel material does not have the coating layer of the present invention on its surface. Considering that conventional methods for removing residual alkali on the surface of high-nickel materials involve either rinsing the high-nickel material with water or rinsing a high-nickel material that has been pickled with water, the method of producing a modified high-nickel material by pickling in the present invention has achieved an unexpectedly improved increase in impedance and capacity retention.

[0075] Furthermore, Examples 1-3 demonstrate that specific organic acids specified in the present invention can achieve the technical effects of reducing residual alkali, increasing impedance, and improving capacity retention, with maleic acid achieving the optimal technical effects. Examples 1, 4, and 5 demonstrate that the mass percentage of the organic acid in the solution and the mass ratio of the high-nickel material to the organic acid solution within the specific ranges specified in the present invention can achieve better technical effects. Examples 1 and 6-8 demonstrate that the stirring speed, drying temperature, and sieve size within the specific ranges specified in the present invention can achieve better technical results.

[0076] In summary, the use of the cathode material according to the present invention and cathode materials produced according to the method of the present invention improves impedance gain and capacity retention while reducing the level of residual alkalinity compared to cathode materials according to the prior art.

[0077] The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and variations are possible for those skilled in the art to make. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. High nickel materials and a coating layer on a surface of the high nickel material, The coating layer comprises a compound of formula (I) and a compound of formula (II). C ｘ H ｙ－ｎ O ｚ Li ｎ (I) C ｘ H ｙ－ｎ－１ O ｚ Li ｎ＋１ (-I) (wherein x, y, z, and n are each independently an integer of 1≦x≦10, 2≦y≦20, 2≦z≦12, and 1≦n≦3.)

2. The compound of formula (I) and the compound of formula (II) are Li salts of an organic acid, and the organic acid is represented by the general formula C ｘ H ｙ O ｚ (wherein x, y, and z are each independently integers satisfying 1≦x≦10, 2≦y≦20, and 2≦z≦12), and the organic acid contains 1 to 3 carboxy groups and 0 to 1 C═C double bonds.

3. 3. The cathode material of claim 2, wherein the organic acid comprises one or more of maleic acid, acrylic acid, fumaric acid, malonic acid, oxalic acid, malic acid, glycolic acid, succinic acid, citric acid, tricarballylic acid, and aconitic acid, preferably one or more of maleic acid, malonic acid, and oxalic acid, and most preferably maleic acid.

4. 2. The cathode material according to claim 1, wherein the molar percentage a of the compound of formula (I) in the coating layer is 50%≦a<100%, and the molar percentage b of the compound of formula (II) in the coating layer is 0%<b≦50%, preferably 1≦a / b≦3.

5. 2. The positive electrode material according to claim 1, wherein the coating layer is uniformly coated on the surface of the high-nickel material.

6. The cathode material according to claim 1, characterized in that the coating layer has a thickness of 1 to 100 nm, and the mass percentage of the coating layer in the cathode material is 0.1 to 10 wt %, preferably 1 to 5 wt %.

7. 2. The positive electrode material according to claim 1, wherein the coating layer is present simultaneously on both the surfaces of the secondary particles of the high-nickel material and on the grain boundaries of the primary particles.

8. The high nickel material has the general formula LiNi ｍ M ｎ O ２ 2. The cathode material of claim 1, having a metal saturation group consisting of Co, Mn, Al, Mg, Ti, Fe, Cu, Zn, Ga, Zr, Mo, Nb, and W, wherein m+n=1, 0.6≦m≦1, 0≦n≦0.4, and M is one or more of Co, Mn, Al, Mg, Ti, Fe, Cu, Zn, Ga, Zr, Mo, Nb, and W.

9. A method for producing the cathode material according to any one of claims 1 to 8, comprising the steps of: mixing an organic acid with a non-aqueous solvent to obtain an organic acid solution; adding the high-nickel material to the organic acid solution and stirring to obtain a mixed solution; suction-filtering the mixed solution to obtain a mixture; and vacuum drying the mixture, grinding and sieving the mixture to obtain the positive electrode material. The organic acid and the LiOH and / or Li contained in the high nickel material ２ CO ３ The coating layer is formed by reaction of

10. 10. The method according to claim 9, wherein the organic acid has a pKa of 1 to 5.

11. 11. The method of claim 9 or 10, wherein the organic acid comprises one or more of maleic acid, acrylic acid, fumaric acid, malonic acid, oxalic acid, malic acid, glycolic acid, succinic acid, citric acid, tricarballylic acid, and aconitic acid.

12. 12. The method of claim 11, wherein the organic acid is one or more of maleic acid, malonic acid, and oxalic acid, preferably maleic acid.

13. 10. The method of claim 9, wherein the non-aqueous solvent comprises one or more of methanol, ethanol, isopropyl alcohol, ethylene glycol, and glycerin.

14. The mass percentage of the organic acid in the organic acid solution is 0.1 wt % to 35 wt %, the mass ratio of the high-nickel material to the organic acid solution is 1:0.2 to 1:5, and the LiOH and / or Li ２ CO ３ 10. The method according to claim 9, wherein the molar ratio of the total amount of Li in the organic acid solution to the amount of the organic acid in the organic acid solution is 1:0.1 to 1:

4.

15. 10. The method according to claim 9, wherein the stirring is performed at a speed of 50 to 500 rpm for 0.1 to 8 hours, the vacuum drying is performed at a temperature of 60 to 150°C for 0.1 to 12 hours, and the size of the sieve used is 50 to 500 mesh.

16. A lithium ion secondary battery including a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, The positive electrode plate comprises the positive electrode material according to any one of claims 1 to 8, or a positive electrode material produced by the method according to any one of claims 9 to 15. A lithium ion secondary battery.

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