Positive electrode material, manufacturing method thereof, and battery

Abstract

The present invention provides a positive electrode material, a method for producing the same, and a battery. [Solution] The positive electrode material is a lithium nickel-cobalt oxide-based composite oxide, which includes a core and a shell reconstruction layer located outside the core. The shell reconstruction layer is a region etched from the positive electrode material by dissolving the positive electrode material in a 100-fold diluted aqua regia solution at an ambient temperature of 300°C for 30 minutes. The core is the region remaining in the positive electrode material after the shell reconstruction layer is etched. When m1 is the molar content of Li in the core and m2 is the molar content of Li in the shell reconstruction layer, the relationship m2 / m1 satisfies 1.3≦m2 / m1≦4.0. The positive electrode material according to the present invention has high capacity, improved crystal structure stability, and can further improve the cycle stability and voltage resistance of the positive electrode material.

Description

[Technical Field]

[0001] The present invention relates to the technical field of positive electrode materials, and more particularly to a positive electrode material, a method for producing the same, and a battery. [Background technology]

[0002] In recent years, lithium-ion batteries have been widely used in modern portable electronic devices. Their advantages, such as high specific energy, high operating voltage, long cycle life, no memory effect, and environmental friendliness, have led to a widespread market for them in hybrid and pure electric vehicles. The cathode material is typically the bottleneck affecting the battery's energy density. Layered ternary cathode materials, combining high discharge capacity, good cycle life, and low cost, are highly promising cathode materials. Increasing the nickel content of the cathode material improves the reversible specific capacity and cycling stability of the cathode material, making it more suitable for high-specific-energy power batteries.

[0003] However, as the Ni content increases, the structural stability also deteriorates, and the particle phase structure undergoes an irreversible phase transition during the charge and discharge process, resulting in a layered structure, spinel structure, and inactive rock salt phase, which causes a decline in capacity and cycle performance. + is released from the positive electrode material, the interlayer spacing increases, and the crystal grains expand. + is absorbed in the positive electrode material, reducing the interlayer spacing and shrinking the crystal grains. As the charge / discharge cycle progresses, the crystal grains of the positive electrode material expand / shrink more rapidly, causing the internal stress of the positive electrode material particles to become more severe, making the positive electrode material particles more susceptible to cracking and powdering, which affects the cycle life and safety performance of the battery. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a positive electrode material that has high capacity, improves the stability of its crystal structure, and further improves the cycle stability and voltage resistance of the positive electrode material; a method for producing the same; and a battery. [Means for solving the problem]

[0005] In a first aspect, the present invention provides a positive electrode material that is a lithium nickel-cobalt oxide-based composite oxide, the lithium nickel-cobalt oxide-based composite oxide including a core and a shell reconstruction layer located outside the core, the shell reconstruction layer being a region that is etched from the positive electrode material by dissolving 0.3 g of the positive electrode material in 0.4 ml of aqua regia diluted 100 times for 30 minutes, the environmental temperature during dissolution being controlled to 300°C, the core being a region that remains in the positive electrode material after the shell reconstruction layer has been etched, and the positive electrode material satisfying 1.3≦m2 / m1≦4.0, where m1 is the molar content of Li in the core and m2 is the molar content of Li in the shell reconstruction layer.

[0006] In a second aspect, the present invention provides a positive electrode material that is a lithium nickel-cobalt oxide-based composite oxide, the lithium nickel-cobalt oxide-based composite oxide including a core and a shell reconstruction layer located outside the core, the shell reconstruction layer being a region that is etched from the positive electrode material by dissolving 0.3 g of the positive electrode material for 30 minutes after diluting it 100 times with 0.4 ml of aqua regia, the environmental temperature during dissolution being controlled to 300°C, the core being a region that remains in the positive electrode material after the shell reconstruction layer has been etched, the molar content of Li in the shell reconstruction layer being m2, and the total molar content of Li in the positive electrode material being m Li When totaled, 1.1≦m2 / m Li A positive electrode material is further provided, which satisfies the total≦3.0.

[0007] In a third aspect, the present invention provides a method for producing a cathode material by subjecting a first mixture containing a precursor of the cathode material and a lithium-containing compound to a primary firing treatment to produce a lithium-containing compound. 1- δNi a Co bM c M1 1-a-b-c O2 (wherein, -0.05≦δ≦0.05, 0.3≦a<1.0, 0.01≦b≦0.3, 0≦c≦0.5, 0≦1-abc≦0.05 are satisfied, M is Mn and / or Al, and M1 is a metal element), and Ni r Co p M q M3 1-r-p-q (OH)2, Ni r Co p M q M3 1-r-p-q OOH and (Ni r Co p M q M3 1-r-p-q )O d (wherein 0≦r≦0.5, 0.3≦p≦1, 0≦q≦0.5, 0≦1−rpq≦0.2, 1≦d≦2 are satisfied, M is Mn and / or Al, and M3 is a metal element), and a second mixture containing the core substrate, and the core substrate, is subjected to a secondary firing treatment to obtain a positive electrode material.

[0008] In a fourth aspect, the present invention provides a battery comprising a cathode material according to the first or second aspect. [Effects of the Invention]

[0009] Compared with the prior art, the present invention has at least the following beneficial effects:

[0010] In the cathode material provided by the present invention, the molar content of Li in the core is lower than the molar content of Li in the shell reconstruction layer. This results in a lithium ion concentration gradient between the core and shell of the cathode material. During charge / discharge, the deintercalation activity of lithium ions in the core is lower than that in the shell reconstruction layer, resulting in preferential deintercalation of lithium ions in the shell reconstruction layer. The degree of deintercalation of lithium ions in the core is lower than that in the shell reconstruction layer, and the change in the lattice constant of the core is smaller than that of the shell reconstruction layer. This reduces the lattice expansion / contraction stress in the core, making it easier for the lattice expansion / contraction stress in the shell reconstruction layer to be released to the outside of the cathode material particles. This effectively reduces cracking and pulverization of the cathode material particles, improving the cycle life and voltage endurance of the cathode material. Furthermore, a high lithium ion molar content in the shell reconstruction layer can also improve the lithium ion conductivity and rate performance of the cathode material.

[0011] In the positive electrode material provided by the present invention, the molar content of Li in the shell reconstruction layer of the positive electrode material is higher than the total molar content of Li in the positive electrode material, i.e., the molar content of lithium ions in the shell reconstruction layer of the positive electrode material is higher than in other regions of the positive electrode material, forming a lithium ion concentration gradient between the core and shell of the positive electrode material. During charge and discharge, the deintercalation reaction activity of lithium ions in the core is lower than that of lithium ions in the shell reconstruction layer, and lithium ions are preferentially deintercalated in the shell reconstruction layer. The deintercalation rate of lithium ions in the core is lower than that in the shell reconstruction layer, and the change in the lattice constant of the core is smaller than that of the shell reconstruction layer. This reduces the lattice expansion / contraction stress in the core and makes it easier for the lattice expansion / contraction stress in the shell reconstruction layer to be released outside the positive electrode material particles. This effectively reduces cracking and pulverization of the positive electrode material particles, improving the cycle life of the positive electrode material and increasing the withstand voltage of the positive electrode material. A high lithium ion molar content in the shell reconstruction layer can also improve the lithium ion conductivity and rate performance of the cathode material.

[0012] The present invention also provides a method for producing a positive electrode material by mixing a shell reconstructing material with a core substrate and sintering the mixture to obtain a positive electrode material. The compositional elements of the shell reconstructing material are highly identical to those of the core substrate, and the difference in lattice constant is small. Furthermore, the binding ability of the shell reconstructing material with Li is stronger than that of the core substrate, the molar content of Ni is lower than that of the core substrate, and the molar content of Co and / or M is higher than that of the core substrate. The binding ability of Co and M with Li is stronger than that of Ni with Li. Therefore, during the sintering process, Co and M in the shell reconstructing material can extract some of the Li from the core substrate and participate in the shell reconstructing of the positive electrode material, thereby performing a function similar to "pumping." The molar content of Li in the shell reconstructing layer of the resulting positive electrode material is greater than the molar content of Li in the core. [Brief explanation of the drawings]

[0013] The present invention will now be further described with reference to the following drawings and examples. [Figure 1] 1 is a structural schematic diagram of a positive electrode material according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram of a discharge state of a battery according to an embodiment of the present invention. [Figure 3a] FIG. 1 is an SEM image of a positive electrode material produced in Example 1 of the present invention. [Figure 3b] FIG. 2 is an SEM image of the substrate produced in Example 1 of the present invention. [Figure 4] FIG. 2 is a comparison diagram of cycle performance of the positive electrode materials produced in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] In order to better understand the technical solution of the present invention, the following detailed description of embodiments of the present invention will be given with reference to the accompanying drawings.

[0015] It should be clear that the described embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, any other embodiments that a person skilled in the art can make without inventive efforts fall within the scope of protection of the present invention.

[0016] The terms used in the embodiments of the present invention are used only to describe specific embodiments and are not intended to limit the present invention. The singular forms "a," "the," and "the" used in the embodiments and claims of the present invention are intended to include the plural forms as well, unless the context clearly dictates otherwise.

[0017] It should be understood that the term "and / or" used herein is only a relational relationship describing related objects, and indicates that three types of relationships may exist, for example, A and / or B can indicate three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the symbol " / " in this specification generally indicates that the related objects before and after it have an "or" relationship.

[0018] Currently, in common multi-element positive electrode materials, the concentration distribution of each element between the core and shell of the positive electrode material particles is uniform, the deintercalation degree of the core and external Li+ during the charge and discharge process is similar, the change range of the lattice constant is similar, and the stress of the shell can be effectively released to the outside, but the internal stress of the positive electrode material particles is easily accumulated and cannot be effectively released.

[0019] Furthermore, due to differences in the lattice constants of lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide in multi-component positive electrode materials, the ease of lithium ion deintercalation varies in different crystal structures, with lithium ions most easily deintercalated in lithium nickel oxide and least easily deintercalated in lithium manganese oxide. Therefore, core-shell structures with different Ni, Co, and Mn content gradients typically result in different lithium ion deintercalation rates. The core has a higher nickel molar content, making it easier to deintercalate lithium than the shell. The core also experiences greater changes in lattice size, resulting in greater lattice expansion / contraction stress, which can lead to particle cracking and shattering of the multi-component positive electrode material, severely impacting the lifespan of the positive electrode material and hindering its full potential.

[0020] In a first aspect, the present invention provides a positive electrode material that is a lithium nickel-cobalt oxide-based composite oxide, as shown in FIG. 1 , wherein the lithium nickel-cobalt oxide-based composite oxide includes a core and a shell reconstruction layer located outside the core, the shell reconstruction layer being a region that is etched from the positive electrode material by dissolving 0.3 g of the positive electrode material in 0.4 ml of aqua regia diluted 100 times for 30 minutes, the environmental temperature during dissolution being controlled to 300°C, the core being a region that remains in the positive electrode material after the shell reconstruction layer has been etched, and the positive electrode material satisfies 1.3≦m2 / m1≦4.0, where m1 is the molar content of Li in the core and m2 is the molar content of Li in the shell reconstruction layer.

[0021] In the cathode material provided by the present invention, the molar content of Li in the core is lower than the molar content of Li in the shell reconstruction layer, resulting in a lithium ion concentration difference between the core and shell of the cathode material. During charge / discharge, the deintercalation reaction activity of lithium ions in the core is lower than that in the shell reconstruction layer, resulting in preferential deintercalation of lithium ions in the shell reconstruction layer. Because the degree of deintercalation of lithium ions in the core is lower than that in the shell reconstruction layer, and the change in the lattice constant of the core is smaller than that of the shell reconstruction layer, the lattice expansion / contraction stress in the core is reduced, and the lattice expansion / contraction stress in the shell reconstruction layer is easily released to the outside of the cathode material particles. This effectively reduces cracking and pulverization of the cathode material particles, improving the cycle life and voltage resistance of the cathode material. Furthermore, a high lithium ion molar content in the shell reconstruction layer can also improve the lithium ion conductivity and rate performance of the cathode material.

[0022] In some embodiments, m2 / m1 may be, for example, 1.3, 1.5, 1.6, 1.8, 2.0, 2.5, 2.8, 2.9, 3.0, 3.2, 3.5, 3.8, or 4.0, and may also be other values ​​within the above ranges, without being limited thereto. If m2 / m1 is too high, i.e., if the Li molar content in the shell reconstruction layer is too high, the alkali content remaining on the surface of the positive electrode material will increase significantly, which is detrimental to improving the initial effect of the positive electrode material and also reduces the processing performance of the material. If m2 / m1 is too low, i.e., if the Li molar content in the core is too high, the overall lithium molar concentration of the positive electrode material will increase, which will significantly increase the gas expansion rate of cells manufactured with the positive electrode material and reduce safety performance. If m2 and m1 are too low, the gram capacity and cycle life of the positive electrode material will be affected.

[0023] In some embodiments, the molar content of Li in the shell reconstruction layer is m and the total molar content of Li in the positive electrode material is m Li When totaled, 1.1≦m2 / m Li The total must be less than 3.0, specifically, m2 / m Li The total may be 1.1, 1.15, 1.2, 1.5, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.5, 2.9, 3.0, etc., and may of course be other values ​​within the above range and are not limited thereto. When the molar content of Li in the shell reconstruction layer of the positive electrode material is higher than the total molar content of Li in the positive electrode material, i.e., when the molar content of lithium ions in the shell reconstruction layer of the positive electrode material is higher than the molar content of lithium ions in the core, a lithium ion concentration difference is formed between the core and shell of the positive electrode material. During the charge / discharge process, the deintercalation reaction activity of lithium ions in the core is lower than that of lithium ions in the shell reconstruction layer, and lithium ions are preferentially deintercalated in the shell reconstruction layer, thereby effectively releasing the expansion / contraction stress caused by deintercalation.

[0024] In the present invention, the molar content of Li refers to the amount of Li material in the entire lattice structure (however, the amount of free lithium Li on the surface of the positive electrode material is not included). + The ratio of the amount of all metallic elements other than Li to the total amount of all metallic elements other than Li, i.e., m Li =n(Li):n(Ni+Co+Mn+M1). The free lithium on the surface may specifically include lithium ions in substances such as Li2CO3 and LiOH remaining on the surface of the positive electrode material. Furthermore, the lithium nickel cobalt oxide-based positive electrode material, which is a lithium nickel cobalt oxide-based composite oxide in the present invention, may be a lithium nickel cobalt manganese oxide (NCM) positive electrode material or a lithium nickel cobalt aluminate (NCA) positive electrode material.

[0025] In some embodiments, the general formula of the shell reconstruction layer is Li 1+ λNi x Co y M z M1 1-x-y-z O2 (wherein 0.01≦λ≦2, 0≦x≦0.5, 0.3≦y≦1, 0≦z≦0.5, 0≦1−xyz≦0.2 are satisfied, M is Mn and / or Al, and M1 is a metal element).

[0026] In this invention, 0.3 g of positive electrode material was weighed and diluted 100 times with 0.4 mL of aqua regia. The solution was then added to the positive electrode material and heated to dissolve. The ambient temperature was controlled to 300°C and the dissolution time was 30 minutes. The resulting solution was filtered, washed, and diluted to a constant volume. After diluting 100 times with 0.4 mL of aqua regia, the molar contents of Li, Ni, Co, M, and M1 were measured. The Li molar content m2 was the Li molar content in the shell reconstruction layer. It can be seen that after diluting 100 times with 0.4 mL of aqua regia, due to the low concentration and amount of material, only the shell reconstruction layer of the positive electrode material particles was dissolved.

[0027] 0.3 g of the positive electrode material was weighed and diluted 5 times with 8 mL of aqua regia. The diluted solution was added to the positive electrode material and heated to dissolve. The ambient temperature was controlled to 300°C and the dissolution time was 30 minutes. The resulting solution was filtered, washed, and diluted to a constant volume. After that, the molar contents of Li, Ni, Co, M, and M1 were measured through ICP measurement. The molar content of Li was measured. Li Total is the total molar content of Li in the cathode material, and the molar content of Li in the core is m = (m Li (Total * w1 - m2 * w2) / (w1 - w2) (where w1 is the total amount of 0.3 g of positive electrode material, and w2 is the amount of material in the shell reconstruction layer.) After diluting 8 mL of aqua regia five times, it can be seen that the high concentration of aqua regia and the high amount of material can completely dissolve the particles of the positive electrode material.

[0028] In some embodiments, the general formula of the shell reconstruction layer is Li 1+ λNi x Co y M z M1 1-x-y-z The value of λ may be 0.01, 0.02, 0.05, 0.08, 0.1, 0.15, 0.18, 0.2, 0.25, 0.5, 0.8, 1, 1.25, 1.5, 1.8, or 2, etc. The value of x may be 0, 0.1, 0.12, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, etc.; the value of y may be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc.; the value of z may be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, etc.; and the molar content of M1 may be 0, 0.001, 0.002, 0.005, 0.01, 0.05, 0.1, 0.15, 0.18, or 0.2, etc.

[0029] In some embodiments, the metal element M1 includes at least one of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy. Specifically, the metal element M1 may be present in the positive electrode material as both a metal element and a coating element.

[0030] The content of each element in the positive electrode material can be measured using a known instrument for performing qualitative and / or quantitative analysis of each element, such as ICP or ICP-MS.

[0031] In some embodiments, the molar content of Ni in the core is greater than the molar content of Ni in the shell reconstruction layer. It is understood that a low molar content of Ni in the shell reconstruction layer can reduce the occurrence of side reactions between the positive electrode material and the electrolyte, thereby improving the cycle life of the positive electrode material. The low molar content of Li and the high molar content of Ni in the core of the positive electrode material of the present invention reduce the expansion / contraction effect during lithium deintercalation in the core of the positive electrode material, which is beneficial to improving the stability of the particle structure. At the same time, the high molar content of Li and the low molar content of Ni in the shell reconstruction layer of the positive electrode material effectively releases the expansion / contraction stress of the positive electrode material, reduces side reactions between the positive electrode material and the electrolyte, which is beneficial to improving the cycle stability of the positive electrode material, thereby enabling the positive electrode material to combine high voltage, high rate, and good cycle performance.

[0032] In some embodiments, the molar content of all metal elements other than Li and Ni in the core is lower than the molar content of all metal elements other than Li and Ni in the shell reconstruction layer. The molar content of Co and M in the core is lower than the molar content of Co and M in the shell reconstruction layer. The higher molar content of Co and M in the shell reconstruction layer can inhibit the H2 to H3 crystalline phase transition of the positive electrode material, thereby improving the stability of the crystalline phase structure of the shell reconstruction layer of the positive electrode material. Furthermore, a higher concentration of the metal element M1 in the shell reconstruction layer can reduce the reactivity of the positive electrode material with the electrolyte. The positive electrode material of the present invention has a gradient of molar content of multiple elements, and the synergistic effects of each element further improve the electrochemical properties of the positive electrode material and enhance the performance of the positive electrode material.

[0033] In some embodiments, m1 satisfies 0.6≦m1<1, and specifically, m1 may be 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, or 0.99, etc., but is not limited thereto. Tests have shown that controlling the molar content of Li in the core within the above range results in excellent electrochemical properties of the positive electrode material.

[0034] In some embodiments, the general formula of the shell reconstruction layer is Li 1+ λNi x Co y M z M1 1-x-y-z When it is O2, 0.1≦λ≦2 is satisfied, that is, the molar ratio of n(Li):n(Ni+Co+M+M1) is 1.1 to 3.

[0035] In some embodiments, the molar ratio of lithium to all other metal elements (Me) in the positive electrode material is (0.95-1.05): 1. Specifically, the n(Li) / n(Me) ratio can be 0.95: 1, 0.96: 1, 0.98: 1, 1.0: 1, 1.02: 1, 1.03: 1, or 1.05: 1, etc., where Me represents the molar content of all metals other than Li in the positive electrode material.

[0036] By controlling the value of n(Li):n(Ni+Co+M+M1) in the shell reconstruction layer to 1.1 to 3 and controlling the ratio of n(Li) / n(Me) in the particles of the entire positive electrode material to the range of (0.95 to 1.05):1, the stress caused by changes in the lattice constant of the positive electrode material can be maximally transferred from the core to the shell reconstruction layer and released to the outside, which is advantageous for comprehensive improvement of the electrochemical properties of the positive electrode material.

[0037] In some embodiments, the mass percentage of the shell reconstruction layer in the positive electrode material is 5 wt% to 50 wt%, specifically, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, or 50 wt%, and may be other values ​​within the above range, without limitation. If the mass percentage of the shell reconstruction layer in the positive electrode material is too low, the shell reconstruction layer of the positive electrode material may have difficulty effectively protecting the core, and the core and shell reconstruction layer may have difficulty forming an effective lithium element concentration difference. If the mass percentage of the shell reconstruction layer in the positive electrode material is too high, the thickness of the shell reconstruction layer of the positive electrode material increases, and the thick shell reconstruction layer makes it difficult to effectively transfer and release the expansion stress of the core, resulting in a decrease in the cycle performance of the positive electrode material. By controlling the mass percentage content of the shell reconstruction layer in the range of 5 wt% to 40 wt%, the expansion / contraction stress inside the positive electrode material can be effectively released, and an appropriate lithium ion concentration gradient is advantageous for improving the stability of the cycle structure of the positive electrode material. More preferably, the mass percentage of the shell reconstruction layer in the positive electrode material is 7 wt% to 40 wt%.

[0038] In some embodiments, the mass percentage of free lithium in the positive electrode material is 200 ppm to 1000 ppm. Specifically, the mass percentage may be 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 800 ppm, or 1000 ppm, and of course, other values ​​within the above range are also possible and are not limited thereto. The free lithium in the positive electrode material is mainly derived from alkaline impurities, such as Li2CO3 and LiOH, on the surface of the positive electrode material. Controlling the content of free lithium in the positive electrode material reduces the corrosion effect of alkaline impurities on the positive electrode material, protects the structural stability of the positive electrode material, and is advantageous for improving the cycle stability of the positive electrode material. The mass percentage of free lithium in the positive electrode material increases with increasing Ni content, and preferably is 200 ppm to 600 ppm.

[0039] In some embodiments, the specific surface area of ​​the positive electrode material is 0.2 m 2 / g~2.0m 2 / g. Specifically, 0.2m 2 / g, 0.5m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 1.8m 2 / g or 2.0m 2 / g, etc., and of course, other values ​​within the above range may also be used, and are not limited thereto. By controlling the specific surface area of ​​the positive electrode material within the above range, the occurrence of side reactions between the positive electrode material and the electrolyte can be reduced, and the positive electrode material can exhibit better cycle stability.

[0040] In some embodiments, the true density of the positive electrode material is 4.6 g / cm 3 ~4.8g / cm 3 Specifically, 4.6g / cm 3 , 4.65g / cm 3 , 4.68g / cm 3 , 4.70g / cm 3 , 4.72g / cm 3 , 4.75g / cm 3 , 4.78g / cm 3 , 4.79g / cm 3 or 4.8 g / cm 3 etc., and is not limited thereto.

[0041] In the second embodiment, a first mixture containing a precursor of a positive electrode material and a lithium-containing compound is subjected to a primary firing treatment to form a compound represented by the general formula Li 1- δNi a Co b M c M1 1-a-b-c a step S10 of obtaining a core substrate made of NiO2 (wherein, -0.05≦δ≦0.05, 0.3≦a<1.0, 0.01≦b≦0.3, 0≦c≦0.5, and 0≦1-abc≦0.05 are satisfied, M is Mn and / or Al, and M1 is a metal element); r Co p M q M3 1-r-p-q(OH)2, Ni r Co p M q M3 1-r-p-q OOH and (Ni r Co p M q M3 1-r-p-q )O d and a step S20 of subjecting a second mixture containing the core substrate and a shell reconstructing material containing at least one of the following (wherein 0≦r≦0.5, 0.3≦p≦1, 0≦q≦0.5, 0≦1−rpq≦0.2, and 1≦d≦2 are satisfied; M is Mn and / or Al; and M3 is a metal element) to a secondary firing treatment to obtain a positive electrode material.

[0042] In the above technical solution, a shell reconstructing material and a core substrate are used for a secondary firing process, and the compositional elements of the shell reconstructing material and the compositional elements of the core substrate are highly identical, resulting in a small difference in lattice constant. Furthermore, the shell reconstructing material of the present invention has a strong bonding ability with Li, a lower Ni molar content than that of the core substrate, a higher Co and / or M molar content than that of the core substrate, and the bonding ability between Co and M and Li is stronger than that between Ni and Li. Therefore, during the secondary firing process, Co and M in the shell reconstructing material can extract some Li from the core substrate and participate in the shell reconstruction of the positive electrode material, and the shell reconstructing material can perform a function similar to "pumping," and the molar content of Li in the shell reconstructing layer of the produced positive electrode material is greater than that in the core.

[0043] The molar content of Li in the core of the positive electrode material produced by the present invention is lower than the molar content of Li in the core substrate (manufacturing material). This is because some Li is extracted from the core substrate and participates in the shell reconstruction of the positive electrode material. Experiments have shown that when the molar content m1 of Li in the core of the final positive electrode material is in the range of 0.6 to 1.0, the electrochemical properties of the positive electrode material are excellent, and the surface reconstruction material and the Li extracted from the core substrate combine to form a Li-containing compound (i.e., a shell reconstruction layer). The molar content of Li in the shell reconstruction layer of the produced positive electrode material is higher than the molar content of Li in the core.

[0044] Furthermore, the lithium ion concentration in the shell reconstruction layer of the cathode material produced by the present invention is greater than that in the core. This difference in lithium ion concentration is not formed during the precursor production process, nor during the solid-state reaction between the precursor and the lithium-containing compound after primary firing to produce a layered structure material, but rather by performing shell reconstruction on the core substrate. Therefore, the shell reconstruction process for the substrate of the present invention is not limited by the type of substrate or the primary firing temperature, and can be applied to polycrystalline or single-crystalline substrates. By expressing differences in the concentrations of each constituent element in the core and shell of the produced cathode material, the rate performance, high-voltage resistance, cycle life, material resistance, and other performances of the cathode material are further improved.

[0045] The production method of the present invention will be specifically described below with reference to examples.

[0046] In step S10, a mixture containing a precursor of a positive electrode material and a lithium-containing compound is subjected to a primary firing treatment to form a compound represented by the general formula Li 1- δNi a Co b M c M1 1-a-b-c A core substrate of O2 (wherein -0.05≦δ≦0.05, 0.3≦a<1.0, 0.01≦b≦0.3, 0≦c≦0.5, and 0≦1-abc≦0.05 are satisfied, M is Mn and / or Al, and M1 is a metal element) is obtained.

[0047] In some embodiments, the general formula of the precursor of the positive electrode material is Ni a1 Co b1 M1 c1 (OH)2 (where 0.3≦a1<1.0, 0.01≦b1≦0.3, 0≦c1≦0.5 are satisfied).

[0048] In some embodiments, the lithium-containing compound includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium fluoride, and lithium acetate. Preferably, the lithium-containing compound includes lithium hydroxide. Specifically, the lithium hydroxide includes at least one of anhydrous lithium hydroxide and lithium hydroxide monohydrate.

[0049] In some embodiments, the molar ratio of metal Me in the precursor of the positive electrode material to Li in the lithium-containing compound satisfies 1:1≦Li / Me≦1:1.3, and may be specifically, but not limited to, 1:1, 1:1.02, 1:1.05, 1:1.08, 1:1.09, 1:1.1, 1:1.2, 1:1.25, or 1:1.3.

[0050] In some embodiments, the first mixture further comprises a first dopant, wherein the metal element M1 in the first dopant comprises at least one of Zr, Sr, Nb, Mo, Y, Co, Ti, Zr, Mg, B, and W.

[0051] In some embodiments, the mass proportion of the first dopant added in the first mixture is controlled to be 0.001 wt% to 2 wt%, which may be, for example, 0.001 wt%, 0.005 wt%, 0.007 wt%, 0.009 wt%, 0.01 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, or 2 wt%, or may be any other value within the above range, and is not limited to this specification.

[0052] In some embodiments, the mixing speed of the first mixture is 300 rpm / min or more, and the mixing time is 15 minutes or more.

[0053] In some embodiments, the temperature of the primary firing treatment is 700° C. to 1000° C. Specifically, the temperature of the primary firing treatment is, but is not limited to, 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., or 1000° C., and may of course be other values ​​within the above range.

[0054] In some embodiments, the time for the primary firing treatment is 4 hours to 10 hours. Specifically, the time for the primary firing treatment is 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc., and may of course be other values ​​within the above range, and is not limited to this specification.

[0055] In some embodiments, the primary firing treatment is performed in an oxygen-containing atmosphere, and the oxygen content of the oxygen-containing gas is 90% or more. Specifically, the oxygen content of the oxygen-containing gas may be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 100%, etc., and may of course be other values ​​within the above range, and is not limited thereto. Preferably, the oxygen content of the oxygen-containing gas is 95% or more.

[0056] In some embodiments, the primary firing treatment equipment includes a static box furnace, a roller hearth continuous furnace, or the like.

[0057] In some embodiments, the product after the primary firing treatment is subjected to pulverization, sieving, and demagnetization treatment to obtain a core substrate having an appropriate particle size.

[0058] In step S20, the second mixture containing the shell reconstructing material and the core substrate is subjected to a second firing process to obtain a positive electrode material.

[0059] In some embodiments, the core substrate and the shell reconstructing material are mixed in a CO2-containing atmosphere to obtain the second mixture, and the CO2 concentration in the mixed atmosphere is 80% or more. The second mixture is mixed in a CO2-containing atmosphere because carbon dioxide gas easily reacts with lithium-containing compounds, such as Li2O or LiOH, on the surface of the core substrate in the second mixture to form Li2CO3, which adheres to the surface of the core substrate particles. This allows the subsequently added shell reconstructing material to easily react with the core substrate to form a Li-containing compound, thereby reconstructing the shell of the core substrate.

[0060] In some embodiments, the CO2 atmosphere contains 5% to 10% by volume of water to further enhance the rate and extent of the reaction.

[0061] In the present invention, by controlling the mixing conditions and mixing atmosphere of the second mixture, the shell reconstructing material in the second mixture can be more uniformly and firmly attached to the surface of the core substrate, and corresponding adjustments may be made during the actual mixing process according to the actual situation.

[0062] During the secondary firing process, the second mixture of the shell reconstructing material and the core substrate is fired, and it is understood that the identity of the constituent elements of the shell reconstructing material and the constituent elements of the core substrate is high, resulting in a small difference in lattice constant. Furthermore, the bonding ability of the shell reconstructing material with Li is stronger than that of the core substrate, the molar content of Ni is lower than that of the core substrate, the molar content of Co and / or M is higher than that of the core substrate, and the bonding ability of Co and M with Li is stronger than that of Ni with Li. Therefore, during the secondary firing process, Co and M in the shell reconstructing material can extract some of the Li in the core substrate and participate in the shell reconstruction of the positive electrode material, and the shell reconstructing material can perform a function similar to "pumping," and the molar content of Li in the shell reconstructing layer of the produced positive electrode material is greater than the molar content of Li in the core.

[0063] In some embodiments, the shell reconstructing material is Ni r Co p M q M3 1-r-p-q (OH)2, Ni r Co p M q M3 1-r-p-q OOH and (Ni r Co p M q M3 1-r-p-q )O d (wherein 0≦r≦0.5, 0.3≦p≦1, 0≦q≦0.5, 0≦1−rpq≦0.2, 1≦d≦2 are satisfied, M is Mn and / or Al, and M3 is a metal element.) The bonding ability of Co and M in the shell reconstructed material to lithium ions is stronger than the bonding ability of Ni to lithium ions in the core substrate.

[0064] In some embodiments, the metal element M3 comprises at least one of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy.

[0065] In some embodiments, the median diameter of the shell reconstructing material particles is 10 nm to 1000 nm, and may be, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 80 nm, 100 nm, 300 nm, 500 nm, 800 nm, or 1000 nm, or may be any other value within the above range, and is not limited to this specification.

[0066] In some embodiments, the deflated bulk density of the shell reconstituting material is 0.6 g / cm 3 Specifically, 0.6 g / cm 3 , 0.5g / cm 3 , 0.4g / cm 3 , 0.3g / cm 3 , 0.35g / cm 3 , 0.25g / cm 3 , 0.2g / cm 3 , 0.15g / cm 3 , 0.1g / cm 3etc., and of course, other values ​​within the above ranges may also be used, and are not limited to the present specification.

[0067] In some embodiments, the specific surface area of ​​the shell reconstructing material is 20 m 2 / g or more. Specifically, 20m 2 / g, 30m 2 / g, 50m 2 / g, 80m 2 / g, 100m 2 / g, or 120m 2 / g, etc., and of course, other values ​​within the above ranges may also be used, and are not limited to the present specification.

[0068] In the present invention, by controlling the particle size, lightly packed bulk density, specific surface area, etc. of the shell reconstruction material, it is possible to control the size of the shell reconstruction material to the nanometer order, which makes it easier for the fine particles of the shell reconstruction material to adhere uniformly to the surface of the core substrate, improves the reaction activity of the shell reconstruction, and is advantageous for forming a shell reconstruction layer with a high lithium molar content in the positive electrode material, thereby improving the cycle stability of the positive electrode material.

[0069] In some embodiments, the molar ratio of the core substrate to the shell reconstruction material is 1:(0.01-0.1). Specifically, the molar ratio may be 1:0.01, 1:0.03, 1:0.05, 1:0.08, 1:0.09, 1:0.1, etc., and of course, other values ​​within the above range are also possible and are not limited to this specification. The addition of the shell reconstruction material effectively forms a shell reconstruction layer of the positive electrode material and effectively creates a Li concentration difference between the core and shell. If the amount added is too large, the shell reconstruction layer becomes too thick, significantly increasing the time it takes for Li+ to diffuse from the core to the shell and reducing the effect of the Li concentration difference between the core and shell. At the same time, the shell reconstruction layer becomes too thick, preventing effective transfer of stress during the charge and discharge process of the core substrate to the shell. Preferably, the molar ratio of the core substrate to the shell reconstruction material is 1:(0.02-0.05).

[0070] In some embodiments, the second mixture further comprises a second dopant, and the metal element M1 in the second dopant comprises at least one of Zr, Sr, Nb, Mo, Y, Co, Ti, Zr, Mg, B, and W.

[0071] In some embodiments, the mass proportion of the second dopant in the second mixture is controlled to be 0.01 wt % to 2 wt %, which may be, for example, 0.01 wt %, 0.05 wt %, 0.08 wt %, 0.1 wt %, 0.5 wt %, 0.8 wt %, 1 wt %, 1.2 wt %, 1.5 wt %, 1.8 wt %, or 2 wt %, or may be any other value within the above range, and is not limited to this specification.

[0072] In some embodiments, the mixing speed of the second mixture is 300 rpm / min or more and the mixing time is 15 minutes or more.

[0073] The present invention aims to achieve a uniform mixture of the components in the second mixture by controlling the mixing conditions of the second mixture, and corresponding adjustments may be made during the actual mixing process depending on the actual situation.

[0074] In some embodiments, the temperature of the secondary firing treatment is 600°C to 900°C. Specifically, the temperature of the secondary firing treatment may be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, or 900°C, and may of course be other values ​​within the above range and is not limited thereto. As the temperature of the secondary firing treatment increases, the concentration of lithium element at the grain boundaries near the coating layer on the surface of the substrate increases. After the lithium element is extracted in excess into the shell, the layered structure of the positive electrode material in the core undergoes a phase transformation to spinel and / or rock salt, which causes a structural change in the positive electrode material and affects the discharge capacity of the positive electrode material.

[0075] In some embodiments, the time for the secondary baking treatment is 4 hours to 10 hours. Specifically, the time for the secondary baking treatment is 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc., and may of course be other values ​​within the above range, and is not limited to this specification.

[0076] In some embodiments, the secondary firing treatment is performed in an oxygen-containing atmosphere, and the oxygen content of the oxygen-containing gas is 20% or more. Specifically, the oxygen content of the oxygen-containing gas may be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%, etc., and may of course be other values ​​within the above range, and is not limited thereto. Preferably, the oxygen content of the oxygen-containing gas is 40% or more.

[0077] In some embodiments, the secondary firing treatment equipment includes a static box furnace, a roller hearth continuous furnace, or the like.

[0078] An embodiment of the present invention further provides a battery. FIG. 2 is a schematic diagram showing a discharged state of a battery according to an embodiment of the present invention. As shown in FIG. 2, the battery includes a case and an electrode assembly having a positive electrode sheet 1, a negative electrode sheet 2, and a separator 3 disposed between the positive electrode sheet 1 and the negative electrode sheet 2. The electrode assembly may have a laminated structure in which the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 are alternately stacked in order. In some other embodiments, the electrode assembly may have a wound structure in which the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order and then wound.

[0079] In some embodiments, the positive electrode sheet 1 has a positive electrode current collector 101 and a positive electrode active material layer 102 provided on at least one surface of the positive electrode current collector 101 .

[0080] In some embodiments, the positive electrode current collector 101 may be an aluminum foil or a nickel foil, or may be any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining a conductive foil (such as an aluminum foil or a nickel foil) with a polymer base. The positive electrode active material layer 102 includes a positive electrode active material including the positive electrode material described above.

[0081] In some embodiments, the negative electrode sheet 2 has a negative electrode current collector 201 and a negative electrode active material layer 202 provided on at least one surface of the negative electrode current collector.

[0082] In some embodiments, the negative electrode current collector 201 may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, or may be any composite current collector disclosed in the prior art, such as a current collector formed by combining a conductive foil with a polymer base, but is not limited to these. The negative electrode active material layer 202 includes a negative electrode material, which may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be at least one selected from elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloys. However, the present invention is not limited to these materials, and other conventional materials usable as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination. The battery according to the present invention has advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery may be a lithium ion battery, a sodium ion battery, a solid electrolyte battery, etc., but is not limited thereto.

[0083] The above is merely a preferred embodiment of the present invention, and does not limit the present invention. Any modifications, equivalent replacements, and improvements made within the concept and principles of the present invention should be included within the protection scope of the present invention.

[0084] Measurement method: 1) Measurement of the specific surface area of ​​the positive electrode material The nitrogen gas adsorption specific surface area is measured by nitrogen gas adsorption analysis and calculated by the BET (Brunauer Emmett Teller) method. The nitrogen gas adsorption specific surface area is measured using a Tri Star II type specific surface and pore analyzer manufactured by Micromeritics, Inc., USA.

[0085] 2) SEM measurement The surface morphology photographs of the materials are obtained by a cold field emission scanning electron microscope (model number Regulus8100) manufactured by HITACHI Corporation, Japan.

[0086] 3) Measurement of the molar content of each element in the positive electrode material The content of each element in the positive electrode material is measured using a known instrument for performing qualitative and / or quantitative analysis of each element, such as ICP or ICP-MS.

[0087] 4) A method for measuring the molar content of Li in the core and shell reconstruction layers in a positive electrode material includes the following steps: First, 0.3 g of cathode material was weighed and diluted 5-fold with 8 mL of aqua regia. This was then added to the cathode material and heated to dissolution. The ambient temperature was controlled at 300°C and the dissolution time was 30 minutes. The resulting solution was filtered, washed, and diluted 100-fold. After that, ICP measurement was performed to measure the molar contents of Li, Ni, Co, M, and M1. Aqua regia was prepared by preparing concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1. The concentration of concentrated hydrochloric acid used in the preparation was 12 mol / L, and the concentration of concentrated nitric acid was 14.5 mol / L. The molar contents of each element in the fully dissolved cathode material were calculated. (1) The total amount of material of Ni, Co, M, and M1 is w1, and after normalization, we obtain n(Ni), n(Co), and n(M). (2)[n(Li):n(Ni+Co+Mn+M1)]=m Li Total. (3) [n(N): n(Ni + Co + M + M1)] = b1N (where N = Ni, Co, or M). (4)[n(M1+M2):n(Ni+Co+M+M1)]=c1.

[0088] Next, 0.3 g of the positive electrode material was weighed and diluted 100 times with 0.4 mL of aqua regia. This was then added to the positive electrode material and heated to dissolve. The ambient temperature was controlled to 300°C and the dissolution time was controlled to 30 minutes. The resulting solution was filtered, washed, and diluted to a constant volume 100 times. After that, ICP measurement was performed to measure the molar contents of Li, Ni, Co, M, and M1 in the shell reconstruction layer. The molar content of each element in the dissolved state of the positive electrode material shell was calculated. (1) The total amount of substance of Ni, Co, M, and M1 is w2, and after normalization, we obtain n(Ni), n(Co), and n(M). (2) Within the shell reconstruction layer, [n(Li):n(Ni+Co+M+M1)] = m2. (3) [n(N):n(Ni+Co+M+M1)] = b2N (where N = Ni, Co, or M). (4)[n(M1+M2): n(Ni+Co+M+M1)]=c2. (5) The mass percentage of the shell reconstruction layer is η = w2 / w1. The molar content of each element in the core of the positive electrode material is calculated from the molar content of each element corresponding to the whole material and the shell reconstruction layer, and the calculation process is as follows:

[0089] Third, calculate the molar contents of Li, Ni, Co, M, and M1 in the core. (1) The total molar content of Ni, Co, M, and M in the core is w3 = w1 - w2, and after normalization, we obtain n(Ni), n(Co), and n(M). (2)[n(Li):n(Ni+Co+M+M1)]=[(m Li total*w1-m2*w2) / w3]=m1; (3) [n(N):n(Ni+Co+M+M1)] = [(b1N*w1-b2N*w2) / w3] = vN (where N = Ni, Co, or M). (4)[n(M1+M2):n(Ni+Co+M+M1)]=[(c1*w1-c2*w2) / w3]=x. When |m2 - m1| is 0.01 or greater, it can be determined that the measured positive electrode material has a Li concentration difference between the shell reconstructed layer and the core. A larger calculated |m2 - m1| value indicates a more significant change in the Li molar content difference of the corresponding positive electrode material. When |b1N-b2N| is 0.01 or more, it can be determined that the measured positive electrode material has a difference in concentration of Ni and / or Co and / or M between the shell reconstructed layer and the core, and a larger calculated value of |b1N-b2N| indicates a more significant difference in the molar content of Ni and / or Co and / or M in the corresponding positive electrode material. When |c1-c2| is 0.001 wt% or more, it can be determined that the measured positive electrode material has a difference in concentration of the metal element between the shell reconstruction layer and the core.

[0090] 5) Measurement of the mass content of free lithium 5g of positive electrode material is dispersed in 100ml of deionized water, stirred magnetically for 10 minutes, and kept at a water temperature of 25°C to obtain a solid-liquid mixture of the remaining eluted lithium carbonate and lithium hydroxide. The solid-liquid mixture is suction filtered to obtain a filtrate, and the hydrochloric acid solution is added to an automatic potentiometric titrator and titrated using the equivalence point titration method. The lithium content of the lithium carbonate and lithium hydroxide in the positive electrode material is calculated according to the state of the titration jump point and the degree of consumption of the hydrochloric acid solution. [Example]

[0091] Example 1 This example provides a method for producing a positive electrode material, which includes the following steps: (1) Ni precursor 0.80 Co 0.01 Mn 0.098(OH)2, LiOH·H2O, and the dopant ZrO2 were charged into a high-speed mixer in a molar ratio of 1:1.02:0.002 and mixed uniformly to obtain a first mixture, where the stirring speed was 1000 rpm and the stirring time was 30 minutes. (2) The mixture was fired in a pure oxygen atmosphere at a firing temperature of 880°C for 8 hours. The fired product was cooled, roller crushed, air-flow crushed, and then passed through a 400-mesh sieve and demagnetized to obtain Li as the base material. 1.02 Ni 0.8 Co 0.1 Mn 0.098 Zr 0.002 Got O2. (3) Li, the core substrate 1.02 Ni 0.8 Co 0.1 Mn 0.098 Zr 0.002 O2 and Ni, a shell reconstruction material 0.08 Co 0.8 Mn 0.08 Al 0.04 The mixture was uniformly mixed with OOH in a molar ratio of 1:0.02 using a high-speed mixer. The stirring speed was 1000 rpm and the stirring time was 30 minutes in a mixed atmosphere containing 95% carbon dioxide gas and 0.05% water vapor by volume, to obtain a second mixture. (4) The second mixture was fired at 730°C for 8 hours in a pure oxygen atmosphere. The mixture was then cooled, roller crushed, sieved through a 400 mesh screen, and demagnetized to obtain a positive electrode material.

[0092] The chemical composition of the positive electrode material is Li 0.986 Ni 0.8 Co 0.1 Mn 0.098 Zr 0.002 O2 0.02Li 1.70 Ni 0.08 Co 0.8 Mn 0.08 Al 0.04 It is O2.

[0093] Based on the process of Example 1, Examples 2 to 17 (abbreviated as S1-S17) and Comparative Examples (abbreviated as D1-D2) were prepared. The differences in the preparation processes are shown in Table 1, and the performance of the prepared positive electrode materials is shown in Table 2.

[0094] [Table 1]

[0095] [Table 2] TIFF2026507299000004.tif229146

[0096] Preparation of positive electrode sheet The cathode material prepared in the Examples or Comparative Examples, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were dissolved in N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 93:5:2. After thorough stirring, the resulting cathode slurry was applied to aluminum foil, dried, and tableted to obtain a cathode sheet. A 2032 coin battery was assembled using a lithium metal sheet as the anode sheet, a polyethylene film as the separator, 1 mol / L lithium hexafluorophosphate, and a 1:1 volumetric solution of diethyl carbonate and ethylene carbonate as the electrolyte.

[0097] The charge / discharge test was performed using the LAND test system CT2001A, with the voltage range of 2.5V to 4.3V to measure the capacity, initial efficiency, and rate performance.

[0098] The coin batteries manufactured in the above Examples and Comparative Examples were cycled at a charge / discharge rate of 0.1C in a charge / discharge range of 2.5V to 4.3V in a room temperature environment (25°C), and the initial discharge capacity and initial coulombic efficiency were measured. The ratio of the capacity after 50 cycles to the initial discharge capacity was defined as the room temperature cycle performance.

[0099] The assembled coin battery was cycled for two weeks at room temperature (25°C) with a charge / discharge rate of 0.1C and a charge / discharge range of 2.5V to 4.3V until it was fully charged to 4.3V. Electrochemical impedance spectroscopy (EIS) was then performed using a Shanghai Chenhua CHI600E electrochemical workstation, with a frequency of 100kHz to 10mHz and an amplitude of 5mV, to obtain the electrochemical impedance performance.

[0100] [Table 3]

[0101] As can be seen from the experimental data of Examples 1 to 4, as the molar ratio of the shell reconstruction material to the substrate increases, the lithium molar content m2 in the shell reconstruction layer of the positive electrode material decreases, and the lithium molar content m1 in the core increases. This is because the thicker the surface reconstruction material, the lower its ability to extract lithium. Here, in Examples 2 and 4, adding too much or too little shell reconstruction material reduces the capacity per gram of the positive electrode material. Adding too little shell reconstruction material in Example 2 reduces the cycle retention rate of the positive electrode material and increases the expansion rate.

[0102] As can be seen from the experimental data of Examples 5 to 13, the performance effects of core substrates with different Ni, Co, and M contents on the positive electrode material were investigated. With a decrease in Ni content, the gram capacity of the positive electrode material gradually decreased, the cycle retention rate gradually improved, and the expansion rate gradually decreased.

[0103] As can be seen from the experimental data of Examples 14 and 15, different baking temperatures and times do not significantly affect the electrochemical properties of the positive electrode material.

[0104] As can be seen from the experimental data of Examples 16-17, different shell reconstruction layers do not significantly affect the electrochemical properties of the positive electrode materials.

[0105] As can be seen from the experimental data for the Example and Comparative Example 1, the Comparative Example did not use a shell reconstruction layer and underwent a secondary calcination treatment, resulting in significantly lower electrochemical properties of the cathode material compared to all the Examples. Figures 3a and 3b are SEM images of the cathode material and substrate of Example 1, respectively. After the shell reconstruction, the particles of the cathode material of Example 1 became more rounded and were able to withstand higher stresses without fracture. The substrate particles without the shell reconstruction exhibited an irregular structure, with pronounced angularity, lower particle strength, and were prone to fracture and shattering during cycling. Figure 4 compares the cycle performance of the cathode materials of Example 1 and Comparative Example 1. It can be seen that the cycle performance of the cathode material of Example 1 was superior to that of Comparative Example 1.

[0106] As can be seen from the experimental data of the example and comparative example 2, the surface of the substrate in comparative example 2 was coated with B2O3, which improved the performance compared to comparative example 1. However, since the molar contents of each type of element in the positive electrode material particles were not distributed in a stepwise manner, the cycle performance of the positive electrode material was inferior to all the examples.

[0107] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited thereto. Within the technical scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining each technical feature in any other suitable manner, and these simple modifications and combinations should also be considered as the contents disclosed in the present invention, and all fall within the protection scope of the present invention.

Claims

1. A positive electrode material that is a nickel-cobalt oxide-based lithium composite oxide, The lithium nickel cobalt oxide-based composite oxide includes a core and a shell reconstructed layer located outside the core, the shell reconstruction layer is a region that is etched from the cathode material by dissolving 0.3 g of the cathode material in 0.4 ml of aqua regia diluted 100 times at an ambient temperature of 300° C. for 30 minutes; the core is the remaining area of ​​the cathode material after the shell reconstruction layer is etched; A positive electrode material, characterized in that, when the molar content of lithium in the core is m1 and the molar content of lithium in the shell reconstruction layer is m2, 1.3≦m2 / m1≦4.0 is satisfied.

2. A positive electrode material that is a nickel-cobalt oxide-based lithium composite oxide, The lithium nickel cobalt oxide-based composite oxide includes a core and a shell reconstructed layer located outside the core, the shell reconstruction layer is a region that is etched from the cathode material by dissolving 0.3 g of the cathode material in 0.4 ml of aqua regia diluted 100 times at an ambient temperature of 300° C. for 30 minutes; the core is the remaining area of ​​the cathode material after the shell reconstruction layer is etched; The molar content of Li in the shell reconstruction layer is m2, and the total molar content of Li in the positive electrode material is m Li When the total is 1.1 ≦ m2 / m Li A positive electrode material characterized by satisfying a total of ≦3.

0.

3. 3. The positive electrode material according to claim 1, wherein the molar content of Ni in the core is greater than the molar content of Ni in the shell reconstruction layer.

4. 3. The positive electrode material according to claim 1, wherein the total molar content of all metal elements other than Li and Ni in the core is smaller than the total molar content of all metal elements other than Li and Ni in the shell reconstruction layer.

5. The general formula of the shell reconstruction layer is Li 1+ λNi x Co y M z M1 1-x-y-z O 2 (wherein 0.01≦λ≦2, 0≦x≦0.5, 0.3≦y≦1, 0≦z≦0.5, 0≦1−x−y−z≦0.2 are satisfied, M is Mn and / or Al, and M1 is a metal element).

6. 6. The positive electrode material according to claim 5, wherein 0.6≦m1<1, 0.1≦λ≦2 are satisfied, and / or the molar ratio of lithium element to all other metal elements in the positive electrode material is (0.95 to 1.05):

1.

7. 6. The positive electrode material according to claim 5, wherein the metal element M1 comprises at least one of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy.

8. The positive electrode material according to claim 1 or 2, wherein a mass percentage of the shell reconstruction layer in the positive electrode material is 5 wt % to 50 wt %.

9. 3. The positive electrode material according to claim 1, wherein the mass content of free lithium in the positive electrode material is 200 ppm to 1000 ppm.

10. The positive electrode material has a specific surface area of ​​0.2 m 2 / g to 2.0m 2 / g and / or a true density of 4.6 g / cm 3 ~4.8g / cm 3 3. The positive electrode material according to claim 1, wherein

11. A first mixture containing a precursor of a positive electrode material and a lithium-containing compound is subjected to a primary firing treatment to form a compound represented by the general formula Li 1- δNi a Co b M c M1 1-a-b-c O 2 (wherein, -0.05≦δ≦0.05, 0.3≦a<1.0, 0.01≦b≦0.3, 0≦c≦0.5, 0≦1-a-b-c≦0.05 are satisfied, M is Mn and / or Al, and M1 is a metal element), and Ni r Co p M q M3 1-r-p-q (OH) 2 , Ni r Co p M q M3 1-r-p-q OOH and (Ni r Co p M q M3 1-r-p-q ) O d (wherein 0≦r≦0.5, 0.3≦p≦1, 0≦q≦0.5, 0≦1−r−p−q≦0.2, 1≦d≦2 are satisfied, M is Mn and / or Al, and M3 is a metal element) and a second mixture containing the core base material, to obtain a positive electrode material.

12. The method of claim 11, wherein the shell reconstructing material satisfies at least one of the following characteristics (1) to (3): (1) The median diameter of the shell reconstructing material is 10 nm to 1000 nm. (2) The lumped bulk density of the shell reconstructing material is 0.6 g / cm 3 The following is the result. (3) The specific surface area of ​​the shell reconstructing material is 20 m 2 / g or more.

13. 12. The method of claim 11, wherein the metal elements M1 and M3 each independently include at least one of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy.

14. The manufacturing method according to claim 11 or 12, characterized in that at least one of the following characteristics (1) to (3) is satisfied: (1) The molar ratio of the core substrate to the shell reconstructing material is 1:(0.01 to 0.1). (2) The core substrate and the shell reconstructing material are mixed in a mixed atmosphere containing carbon dioxide to obtain the second mixture. (3) The temperature of the secondary firing treatment is 600° C. to 900° C., and the time of the secondary firing treatment is 4 hours to 10 hours.

15. A battery comprising the positive electrode material according to any one of claims 1 to 10, or a positive electrode material produced by the production method according to any one of claims 11 to 14.

Images