Positive electrode material, secondary battery and electric equipment

Abstract

The embodiment of the invention provides a positive electrode material, a secondary battery and electric equipment, and the positive electrode material provided by the embodiment of the invention comprises an inner core which comprises a first lithium nickel cobalt manganese oxide, and in the first lithium nickel cobalt manganese oxide, the molar weight ratio of a nickel element is greater than or equal to 60% according to the total molar weight of transition metal elements except lithium; the first film layer comprises a second lithium nickel cobalt manganese oxide and is arranged on at least part of the surface of the inner core, and in the second lithium nickel cobalt manganese oxide, according to the total molar weight of transition metal elements except lithium, the molar weight ratio of cobalt is larger than or equal to 60%; and the width of the line defect at the interface of the first film layer and the inner core is less than 10 atomic intervals. Wherein the width of the line defect at the interface of the cobalt-rich first film layer and the nickel-rich inner core is controlled to be smaller than 10 atom spacing, so that the first film layer and the inner core are tightly combined, the structure is stable, the cycle life of the battery can be prolonged, the first charge-discharge efficiency of the battery can be improved, and the problem of rapid cycle attenuation or cycle diving is solved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode material, a secondary battery, and an electrical device. Background Art

[0002] Currently, automakers are gradually improving the user experience of fast charging and high-speed driving by improving the dynamic characteristics of power batteries.

[0003] The cobalt in nickel-cobalt-manganese ternary materials improves the material's electronic and ionic conductivity, thereby enhancing its power performance. Furthermore, cobalt's unique chemical properties can slow the migration of nickel, thereby delaying the exothermic oxygen release reaction and improving the thermal stability of ternary batteries. Therefore, based on interdiffusion theory, reconstructing a cobalt-rich coating on the surface of the ternary material can improve the material's power and structural stability.

[0004] However, the cobalt-rich coating currently prepared in the ternary material has poor lattice matching with the substrate surface and many defects during the sintering interdiffusion process. At the same time, the cobalt oxide in the cobalt-rich layer, as an inactive substance, easily reduces the capacity of the material and accelerates the oxidative decomposition of the electrolyte, resulting in deterioration of the battery's storage and cycle performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a positive electrode material, a secondary battery and an electrical device to solve the problem that the existing method of reconstructing a cobalt-rich coating on the surface of the ternary material cannot effectively improve the rapid decay of the cycle performance of the ternary battery.

[0006] In order to solve the above problems, the present invention is achieved through the following technical solutions:

[0007] The present invention provides a positive electrode material, comprising:

[0008] A core comprising a first lithium nickel cobalt manganese oxide, wherein the molar amount of nickel element in the first lithium nickel cobalt manganese oxide is ≥ 60% based on the total molar amount of transition metal elements excluding lithium;

[0009] The first film layer includes a second lithium nickel cobalt manganese oxide, which is disposed on at least a portion of the surface of the core, wherein the molar amount of cobalt element in the second lithium nickel cobalt manganese oxide is ≥ 60% based on the total molar amount of transition metal elements excluding lithium;

[0010] The width of the line defect at the interface between the first film layer and the core is less than 10 atomic distances.

[0011] Furthermore, in the positive electrode material, the first film layer has an area close to the core and an area away from the core. The cobalt content of the area close to the core of the first film layer is A1, and the nickel content is B1. The cobalt content of the area away from the core of the first film layer is A2, and the nickel content is B2, satisfying: A1<A2, B1>B2.

[0012] Furthermore, in the positive electrode material, the cobalt content of the first film layer is distributed in a decreasing gradient from the side away from the core to the side close to the core; the nickel content of the first film layer is distributed in an increasing gradient from the side away from the core to the side close to the core.

[0013] Furthermore, the positive electrode material further includes a second film layer provided on the surface of the first film layer, and the second film layer includes a fast ion conductor material.

[0014] Furthermore, in the positive electrode material, the first lithium nickel cobalt manganese oxide comprises a chemical formula of Li x1 Ni a1 Co b1 Mn c1 N d1 At least one compound in O2, N contains one or more of Zr, Al, Ba, Sr, Y, Ti, Mg, Mo, B, Sn, Ce, Sb, W, 1.0≤x1≤1.2, 0.6≤a1≤0.8, 0.02≤b1≤0.2, 0.2≤c1≤0.5, 0.003≤d1≤0.015, a1+b1+c1+d1=1.

[0015] Furthermore, in the positive electrode material, the second lithium nickel cobalt manganese oxide comprises a chemical formula of Li x2 Ni a2 Co b2 Mn c2 M d2 At least one compound in O2, M contains one or more of Zr, Al, Ba, Sr, Y, Ti, Mg, Mo, B, Sn, Ce, Sb, W, 0.9≤x2≤1.2, 0.02≤a2≤0.2, 0.6≤b2≤0.98, 0.01≤c2≤0.2, 0.005≤d2≤0.015, and a2+b2+c2+d2=1.

[0016] Furthermore, in the positive electrode material, the thickness of the first film layer is greater than the thickness of the second film layer.

[0017] Furthermore, in the positive electrode material, the thickness of the first film layer is 10 to 50 nm; and / or

[0018] The thickness of the second film layer is 0.5-8 nm.

[0019] Furthermore, in the positive electrode material, the fast ion conductor material includes one or more of Li3PO4, LiZrP2O7, LiAlPO4, Li3BO3, Li4Ti5O or Li2WO4.

[0020] Furthermore, the lithium-nickel mixed ratio of the positive electrode material is less than 0.7%.

[0021] Furthermore, the positive electrode material satisfies at least one of the following conditions:

[0022] 1) A1 is 60-68%;

[0023] 2) A2 is 70-85%;

[0024] 3) B1 is 30-60%;

[0025] 4) B2 is 5-20%.

[0026] Furthermore, the Dv50 of the positive electrode material is 2.5 to 6.0 μm.

[0027] The present invention also provides a secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode material as described above.

[0028] The present invention further provides an electric device, comprising the above-mentioned secondary battery, wherein the secondary battery serves as a power supply for the electric device.

[0029] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0030] In an embodiment of the present invention, by controlling the cobalt-rich first film layer to coat the nickel-rich core, not only can a higher capacity be provided by the core, but the first film layer can also be used to prevent surface phase changes and interface side reactions of the high-nickel core, thereby maintaining a relatively high capacity inside. Moreover, the film layer has good dynamics and a stable structure, which can significantly improve the interface impedance of the material. In addition, the width of the line defect at the interface between the cobalt-rich first film layer and the nickel-rich core is controlled to be less than 10 atomic spacings, so that the first film layer is tightly combined with the core and has a stable structure, which can improve the cycle life of the battery and the initial charge and discharge efficiency, thereby solving the problem of rapid cycle attenuation or cycle diving of the battery.

[0031] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the positive electrode material provided in the embodiment of the present application.

[0033] Description of reference numerals:

[0034] 11-core, 12-first film layer, 13-second film layer. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0036] The inventors of this application discovered that the cobalt in the existing nickel-cobalt-manganese ternary material has the property of improving the electronic and ionic conductivity of the material, thereby improving the power performance of the material; in addition, cobalt has unique chemical properties that can delay the migration of nickel elements, thereby delaying the oxygen release and exothermic reaction, and improving the thermal stability of the ternary battery. Therefore, according to the mutual diffusion theory, reconstructing a cobalt-rich coating on the surface of the ternary material can improve the power and structural stability of the material.

[0037] The present application embodiment provides a positive electrode material, such as Figure 1 As shown, it includes: a core 11, including a first lithium nickel cobalt manganese oxide, in which the molar amount of nickel element accounts for ≥60% based on the total molar amount of transition metal elements other than lithium; a first film layer 12, including a second lithium nickel cobalt manganese oxide, which is arranged on at least a portion of the surface of the core 11, in which the molar amount of cobalt element accounts for ≥60% based on the total molar amount of transition metal elements other than lithium; the width of the line defect at the interface between the first film layer and the core is less than 10 atomic distances.

[0038] Among them, in the first lithium nickel cobalt manganese oxide, the molar amount of nickel element accounts for ≥60% based on the total molar amount of transition metal elements other than lithium, that is, the material of the core 11 is nickel-rich lithium nickel cobalt manganese oxide; in the second lithium nickel cobalt manganese oxide, the molar amount of cobalt element accounts for ≥60% based on the total molar amount of transition metal elements other than lithium, that is, the material of the first film layer 12 is cobalt-rich lithium nickel cobalt manganese oxide.

[0039] Line defects on a material refer to those defects that are very small in two dimensions but extend longer in the third dimension. These defects are characterized by being very small in two directions but extending longer in another direction, so they are also called one-dimensional defects. The main manifestation of line defects is dislocation, which is caused by the displacement of atomic planes in the crystal. By adjusting the preparation temperature and other coating agents / dopants, the width of the line defect at the interface between the first film layer 12 and the core 11 can be controlled to be less than 10 atomic spacings. In an embodiment of the present application, the width of the line defect at the interface between the first film layer and the core can be in the range of one or both of 2 atomic spacings, 3 atomic spacings, 5 atomic spacings, 7 atomic spacings, and 8 atomic spacings. The width of 1 atomic spacing is

[0040] In the embodiment of the present application, the cobalt-rich first film layer is controlled to cover the nickel-rich core, which can not only provide a higher capacity through the core, but also utilize the first film layer to prevent surface phase changes and interface side reactions of the high-nickel core, thereby maintaining a relatively high capacity inside. In addition, it has good dynamics and a stable structure, which can significantly improve the interface impedance of the material. In addition, by controlling the width of the line defect at the interface between the cobalt-rich first film layer 12 and the nickel-rich core 11 to be less than 10 atomic spacings, the first film layer 12 is tightly combined with the core 11 and the structure is stable, which can improve the cycle life of the battery and the initial charge and discharge efficiency, thereby solving the problem of fast cycle attenuation or cycle diving.

[0041] To further improve the comprehensive electrochemical performance of the battery, optionally, the width of the line defect at the interface between the first film layer 12 and the core 11 is 2 to 6.

[0042] To further improve the comprehensive electrochemical performance of the battery, optionally, the width of the line defect at the interface between the first film layer 12 and the core 11 is 3 to 5.

[0043] Alternatively, in one embodiment, the chemical formula of the first lithium nickel cobalt manganese oxide is Li x1 Ni a1 Co b1 Mn c1 N d1O2, N contains one or more of Zr, Al, Ba, Sr, Y, Ti, Mg, Mo, B, Sn, Ce, Sb, and W, 1.0≤x1≤1.2, 0.6≤a1≤0.8, 0.02≤b1≤0.2, 0.2≤c1≤0.5, 0.003≤d1≤0.015, a1+b1+c1+d1=1, which not only makes the nickel content of the core 11 higher, but also ensures the integrity of the crystal structure of the material, and at the same time can provide excess lithium to react in situ with the cobalt layer in the outer first film layer 12 to form a good bonding layer, so that the core 11 material is easily coated with the cobalt-rich first film layer 12, thereby improving the cycle performance and the initial charge and discharge efficiency of the battery.

[0044] In the embodiment of the present application, the width of the salt rock phase or spinel phase on the surface of the second lithium nickel cobalt manganese oxide is less than 10 atomic spacings, that is, the surface of the second lithium nickel cobalt manganese oxide serving as the first film layer 12 is lithium-deficient lithium nickel cobalt manganese oxide, thereby forming a spinel structure or a rock salt phase structure, which has better stability and limits its phase change width to 10 atomic spacings, which can effectively isolate the core 11 material from direct contact with the electrolyte, thereby reducing the surface side reactions of the positive electrode and improving the cycle and initial charge and discharge efficiency of the battery.

[0045] That is, because the material of the first film layer 12 is a cobalt-rich ternary material, and a cobalt rock salt phase layer is provided on the surface to affect the rate and capacity of the material, it can increase the surface structural strength of the positive electrode material, improve the structural stability of the material, reduce the degree of cracking of the material and the interface side reaction, make the surface CEI film thinner and more stable, improve the cycle retention rate of the material and inhibit the growth of the battery DCR.

[0046] Optionally, in one embodiment, the first film layer 12 has a region close to the core 11 and a region away from the core 11. The cobalt content in the region close to the core 11 of the first film layer 12 is A1, and the nickel content is B1. The cobalt content in the region away from the core 11 of the first film layer 12 is A2, and the nickel content is B2. Both the cobalt content and the nickel content refer to molar content, satisfying: A1<A2, B1>B2, that is, the cobalt content in the region of the first film layer 12 facing the core 11 is lower and the nickel content is higher, while the cobalt content in the region of the first film layer 12 away from the core 11 is higher and the nickel content is lower, so that the side of the first film layer 12 facing the core 11 is easy to combine with the nickel-rich core 11, while the side of the first film layer 12 away from the core 11 can make full use of the rich cobalt to improve the electronic and ionic conductivity of the material, thereby improving the power performance of the battery, and utilizing the unique chemical properties of cobalt to delay the migration of nickel elements, postpone the oxygen release exothermic reaction, and improve the thermal stability of the battery. In this embodiment, the area of ​​the first film layer close to the core side refers to the area ranging from the interface of the first film layer close to the core to one tenth of the thickness of the first film layer, and the area of ​​the first film layer away from the core side refers to the area ranging from the interface of the first film layer away from the core to one tenth of the thickness of the first film layer.

[0047] In some embodiments, A1 is 60-68%, for example, it can be one of 60%, 62%, 65%, 68% or any two of the range values, A2 is 70-85%, for example, it can be one of 70%, 72%, 75%, 78%, 82%, 85% or any two of the range values, B1 is 30-60%, for example, it can be one of 30%, 35%, 50%, 60% or any two of the range values, B2 is 5-20%, for example, it can be one of 5%, 10%, 15%, 20% or any two of the range values. In practical applications, the above-mentioned A1, B1, A2, and B2 can be obtained by performing X-ray sectioning on the positive electrode material powder and then performing TEM (transmission electron microscopy test) and EELS (electron energy loss spectroscopy) analysis to determine the content of nickel and cobalt at different positions of the positive electrode material.

[0048] Optionally, in a specific embodiment, the cobalt content of the first film layer 12 is distributed in a decreasing gradient from the region away from the core 11 to the region near the core 11, and the nickel content of the first film layer 12 is distributed in an increasing gradient from the region away from the core 11 to the region near the core 11. That is, the cobalt content of the first film layer 12 gradually decreases and the nickel content gradually increases from the outside to the inside, and there is a uniform structural transition between the phases, so that the crystal structure of the cobalt-rich first film layer 12 matches the crystal structure of the core 11. Optionally, during the preparation process, by controlling different amounts of cobalt compounds and sintering temperatures, the cobalt content of the first film layer 12 gradually decreases and the nickel content gradually increases from the outside to the inside, ultimately being consistent with the nickel, cobalt and manganese content of the core 11 material.

[0049] In the positive electrode material provided in the embodiment of the present application, since the first film layer 12 is a cobalt-rich material and the cobalt content gradient decreases from the outside to the inside and the nickel content gradient increases, cobalt acts as a non-magnetic cation to replace the Ni in the transition metal layer. 3+ Come with you 2+ The formation of a 90° superexchange interaction effectively reduces the interplanar spacing of the octahedron or tetrahedron, thereby inhibiting the Ni 2+ Migration of lithium prevents it from migrating to Ni 2+ Position, that is, it can effectively reduce the Li / Ni mixing degree in the material, so that the positive electrode material has a more stable internal structure and can improve the surface dynamics, so that the battery's charge and discharge capacity and charge and discharge efficiency are high, thereby improving the battery's energy density and power performance.

[0050] Alternatively, in one embodiment, the lithium-nickel intermixing ratio of the positive electrode material is less than 0.7%. This low intermixing ratio results in a more complete crystal structure, more lithium storage sites, and smoother lithium ion diffusion pathways, thereby increasing the material's capacity and kinetics. In some embodiments, the lithium-nickel intermixing ratio of the positive electrode material is 0.30% to 0.65%.

[0051] Alternatively, in one embodiment, the chemical formula of the second lithium nickel cobalt manganese oxide is Li x2 Ni a2 Co b2 Mn c2 M d2O2, M contains one or more of Zr, Al, Ba, Sr, Y, Ti, Mg, Mo, B, Sn, Ce, Sb, and W, 0.9≤x2≤1.2, 0.02≤a2≤0.2, 0.6≤b2≤0.98, 0.01≤c2≤0.2, 0.005≤d2≤0.015, and a2+b2+c2+d2=1, which not only makes the cobalt content of the first film layer 12 higher than that of the core 11, thereby improving the resistance of lithium ions in the outer layer, increasing the amount of lithium ions released from the inside, and improving the capacity and rate performance of the material, but also can effectively maintain the integrity of the crystal structure of the first film layer 12 and prevent excessive residual alkali.

[0052] Optionally, in one embodiment, the thickness of the first film layer 12 is 10 to 50 nm. For example, the thickness of the first film layer 12 can be one of 10 nm, 12 nm, 15 nm, 20 nm, 30 nm, 40 nm, and 50 nm, or a range value between any two of them. This can effectively coat the core 11 and effectively isolate the core 11 material from direct contact with the electrolyte. It can also effectively take into account the battery capacity and suppress the difficulty of lithium ion escape and the increase in the initial DCR of the material.

[0053] Optionally, in one embodiment, the positive electrode material also includes a second film layer 13 arranged on the surface of the first film layer 12, and the second film layer 13 includes a fast ion conductor material, so that the above-mentioned positive electrode material has a three-layer structure of an internal nickel-rich region (i.e., the inner core 11) providing high capacity, an intermediate layer (i.e., the first film layer 12) providing a cobalt-rich region with fast electron / ion conductivity and stable structure, and a surface layer (i.e., the second film layer 13) increasing the wettability of the material with the electrolyte, making it a positive electrode material with high power, high capacity, long cycle, low impedance, low gas production and excellent storage performance.

[0054] Optionally, in a specific embodiment, the fast ion conductor material includes one or more of Li3PO4, LiZrP2O7, LiAlPO4, Li3BO3, Li4Ti5O or Li2WO4, which can effectively prevent the first film layer from contacting the electrolyte and improve the interface stability of the first film layer.

[0055] Optionally, in a specific embodiment, the thickness of the second film layer 13 is 0.5 to 8 nm, for example, it can be one of 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm or a range value between any two of them, which can effectively improve the wettability of the material and the electrolyte while ensuring the capacity.

[0056] Optionally, in a specific embodiment, the thickness of the first film layer 12 is greater than the thickness of the second film layer 13. In this way, both the conductivity and energy density of the positive electrode material are taken into consideration.

[0057] Optionally, the average particle size of the positive electrode material provided in the embodiment of the present application is 0.5 to 2.5 μm, for example, it can be one of 0.5 μm, 0.6 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or a range value between any two of them. In practical applications, the average particle size of the particles in the SEM image of the positive electrode material can be measured using measure software. The average particle size of the positive electrode material is within the above range, so that the positive electrode sheet has a suitable compaction density, which is beneficial to improving the energy density of the battery.

[0058] The present embodiment also provides a method for preparing the above-mentioned positive electrode material, including steps 101 to 104:

[0059] Step 101: preparing a ternary hydroxide precursor;

[0060] Step 102: Mix the ternary hydroxide precursor, the lithium source, and the first dopant and then sinter for the first time to obtain a first lithium nickel cobalt manganese oxide, wherein the molar ratio of nickel in the first lithium nickel cobalt manganese oxide is greater than or equal to 60 mol %;

[0061] Step 103 : Evenly mix the first lithium nickel cobalt manganese oxide, the cobalt source, and the second dopant, and then sinter the mixture for the second time to coat the surface of the first lithium nickel cobalt manganese oxide with the second lithium nickel cobalt manganese oxide to form a positive electrode material body.

[0062] In some embodiments, step 103 further includes:

[0063] Step 104 : Mix the positive electrode material and the fast ion coating agent and then sinter for a third time to obtain a positive electrode material having a fast ion conductor coated on the surface.

[0064] The preparation method provided in the embodiment of the present application combines the experimental formula design, process and the selection of the type and amount of the cobalt source, so that the above-mentioned positive electrode material has a three-layer structure in which the interior provides a high-capacity nickel-rich region, the middle layer (i.e., the first film layer) provides a cobalt-rich region with fast electron / ion conductivity and stable structure, and the surface layer (i.e., the second film layer) increases the wettability of the material with the electrolyte. Between each phase is an in-situ grown transition layer, thereby improving the material's power performance while also improving the material's cycle and storage properties, making it a positive electrode material with high power, high capacity, long cycle, low impedance, low gas production and excellent storage performance.

[0065] By controlling the width of the line defect at the interface between the cobalt-rich first film layer and the nickel-rich core to be less than 10 atomic spacings, the first film layer is tightly bonded to the core and the structure is stable, which can improve the battery cycle and initial charge and discharge efficiency, thereby solving the problem of rapid cycle attenuation or cycle drop.

[0066] Optionally, in the above step 101, a ternary hydroxide precursor can be prepared by co-precipitation, and its particle Dv50 is between 3.0 and 8.0 μm, which has better long-term performance and less material agglomeration.

[0067] Optionally, in the step 102, the ternary hydroxide precursor, the lithium source, and the first dopant are mixed uniformly in a certain proportion and then sintered for the first time, and then the sintered material is crushed to obtain the first lithium nickel cobalt manganese oxide.

[0068] In some embodiments, the lithium salt is selected from one or more of LiOH·H2O, Li2CO3, Li2C2O4 or LiNO3; and the first dopant is selected from at least one of ZrO2, Al2O3, Co3O4, BaO, SrO, Y2O3, TiO2, MgO, MoO2, B2O3, SnO2, CeO2, Sb2O3 or WO3.

[0069] In some embodiments, in the above step 102, the ternary hydroxide precursor and the lithium source are controlled to be mixed according to the molar ratio of the metal element in the ternary hydroxide precursor to lithium being 1: (1 to 1.20). This not only ensures the structural strength of the material, but also avoids the problem of excessive residual alkali leading to an increase in subsequent negative reactions and affecting product performance.

[0070] In some embodiments, in step 102, the mass of the doping element in the first dopant is 0.1-0.8 wt % of the mass of the ternary hydroxide precursor, which can ensure easier crystallization during sintering and obtain a more stable material structure and morphology.

[0071] In some embodiments, the first sintering process is as follows: the flow rate is 3 to 10 m 3 / h of air or oxygen, and raising the temperature to 800-950°C at a heating rate of 0.5-5.0°C / min for sintering for 6-18 hours, followed by natural cooling to room temperature to obtain a sintered block material. The sintered block material is crushed to obtain a first lithium nickel cobalt manganese oxide. The first lithium nickel cobalt manganese oxide has a Dv50 of 2.0-5.0 μm, which effectively takes into account both the material capacity and the subsequent coating effect.

[0072] Optionally, in the above step 103, the first lithium nickel cobalt manganese oxide, the cobalt source, and the second dopant are mixed, sintered for a second time, crushed and sieved to obtain a second lithium nickel cobalt manganese oxide coated on the surface of the first lithium nickel cobalt manganese oxide to form a positive electrode material.

[0073] In some embodiments, the cobalt source is selected from one or more of CoOOH, Co(OH)2, Co3O4 or CoO, and the BET of the cobalt source is ≥40m 2 / g, and the particle size Dv50 is selected to be 0.1 to 2.5 μm, which is suitable for uniform coating on the surface of the first lithium nickel cobalt manganese oxide.

[0074] In some embodiments, in step 103, the amount of cobalt added to the cobalt source is controlled to be 1-3 wt % of the content of the first lithium nickel cobalt manganese oxide, and the thickness of the formed first film layer is suitable for balancing the capacity, kinetics and interface side reactions in the battery.

[0075] In some embodiments, the second dopant is selected from at least one of ZrO2, Al2O3, BaO, SrO, Y2O3, TiO2, MgO, MoO2, B2O3, SnO2, CeO2, Sb2O3 or WO3.

[0076] In some embodiments, in step 103, the mass of the doping element in the second dopant is 0.05-0.3 wt % of the mass of the second lithium nickel cobalt manganese oxide, so that a more stable material structure can be obtained.

[0077] In some embodiments, the second sintering process is as follows: the flow rate is 3 to 10 m 3 / h of air or oxygen, and raise the temperature to 700-880°C at a heating rate of 0.5-5.0°C / min for 6-12 hours, followed by natural cooling to room temperature to obtain a sintered block material. The sintered block material is crushed to obtain a second lithium nickel cobalt manganese oxide coated on the surface of the first lithium nickel cobalt manganese oxide, forming a positive electrode material. The Dv50 of the positive electrode material is 2.5-6.0μm, which can effectively balance the material capacity and subsequent coating effect.

[0078] Optionally, in the above step 104, the fast ion capping agent is selected from at least one of Li3PO4, LiZrP2O7, LiAlPO4, Li3BO3, Li4Ti5O or Li2WO4.

[0079] In some embodiments, in step 104, the amount of the fast ion coating agent added is controlled to be 0.1-1 wt % of the positive electrode material, so that the battery capacity can be guaranteed while effectively isolating the electrolyte from the first film layer and improving lithium ion transmission.

[0080] In some embodiments, the third sintering process is as follows: the flow rate is 3 to 10 m 3 / h of air or oxygen, and raise the temperature to 400-600°C at a heating rate of 0.5-5.0°C / min for sintering for 3-8h, and then naturally cool to room temperature to obtain a sintered block material. The sintered block material is crushed and sieved to obtain the target product positive electrode material.

[0081] The present application also proposes an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0082] For the above-mentioned secondary battery embodiments and electrical equipment embodiments, their positive electrode plates include a positive electrode active material layer, and the above-mentioned positive electrode active material layer includes the above-mentioned positive electrode material, and can achieve the same technical effects. To avoid repetition, they will not be described here. For relevant matters, please refer to the partial description of the positive electrode material embodiment.

[0083] In order to make the invention purpose, technical solution and beneficial effects of this application clearer, the present application is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate this application and are not used to limit the scope of this application.

[0084] The present application is described in detail below through examples.

[0085] Example 1

[0086] (1) Preparation of positive electrode materials:

[0087] a. Prepare the ternary hydroxide precursor Ni with a particle size Dv50 of 4.0 μm by co-precipitation method 0.621 Co 0.069 Mn 0.31 (OH)2;

[0088] b. The lithium salt Li2CO3, the first dopant (ZrO2, Al2O3) and the ternary hydroxide precursor are uniformly mixed, wherein the molar ratio of Li / (Ni+Co+Mn) is 1.08, and the total content of the first doping elements Zr and Al is 0.3wt% of the ternary hydroxide precursor; then, the mixture is heated to 100 ℃ and heated to 300 ℃ under a ventilation volume of 8 m 3 / h oxygen box furnace, sintered at 930 ° C for 12 hours, and finally crushed into the first lithium nickel cobalt manganese oxide LiNi with a Dv50 of 3.5 μm (with Zr and Al doping) 0.621 Co 0.069 Mn 0.31 O2.

[0089] c. Evenly mix the first lithium nickel cobalt manganese oxide, the cobalt source CoOOH, and the second dopant (WO3 and Al2O3), wherein the Co content is the first lithium nickel cobalt manganese oxide LiNi 0.621 Co 0.069 Mn 0.31 O2 2.0wt%, the second doping element (W and Al) total content is 0.2wt% of the first lithium nickel cobalt manganese oxide content; then the mixed material is placed in a ventilation volume of 6m 3 / h in an oxygen box furnace, the temperature was raised to 820℃ at a heating rate of 2.5℃ / min and pre-sintered for 6h to obtain a positive electrode material coated with a second lithium nickel cobalt manganese oxide (with W and Al doping) as the first film layer and with a Dv50 of 4.0μm.

[0090] d. Mix the cathode material obtained in step c with the fast ion coating agent LiAlPO4 to obtain a mixed material, and then place the mixed material in a 6m 3 / h oxygen box furnace, the temperature was raised to 450℃ at a heating rate of 2.5℃ / min and sintered for 6h. After cooling, it was passed through a 300-mesh sieve to obtain a positive electrode material coated with a fast ion material as the second film layer. The Dv50 of the positive electrode material was 4.0μm.

[0091] (2) Preparation of positive electrode sheet

[0092] The above-mentioned positive electrode material, binder polyvinylidene fluoride (PVDF), conductive agent acetylene black, and conductive agent carbon nanotubes were fully mixed in a mass ratio of 97:1.5:1:0.5, and N-methylpyrrolidone (NMP) was added and stirred evenly under the action of a stirrer to obtain a positive electrode slurry in which the positive electrode active material, binder, and conductive agent were evenly dispersed. The positive electrode slurry was evenly coated on an aluminum foil with a thickness of 12 μm, and the coating was completed on one side and then on the other side. The single-sided slurry coating surface density was 10 mg / cm 2 The coated electrode is dried in an oven at 100-130°C. The dried electrode is rolled and cut into positive electrode sheets.

[0093] (3) Preparation of negative electrode sheet

[0094] The negative electrode active material hard carbon, thickener sodium carboxymethyl cellulose, binder styrene butadiene rubber, and conductive agent acetylene black were mixed in a mass ratio of 96:0.8:1.2:2, and deionized water was added. Under the action of a stirrer, a negative electrode slurry in which the negative electrode active material, thickener sodium carboxymethyl cellulose, binder styrene butadiene rubber, and conductive agent acetylene black were evenly dispersed was obtained. The negative electrode slurry was evenly coated on a copper foil of a certain thickness, and the slurry coating surface density was 7.3 mg / cm 2 ; Transfer the coated electrode to a 100-120°C oven for drying;

[0095] The other side of the electrode is coated with the same surface density, and then cold pressed and cut to obtain the negative electrode.

[0096] (4) Preparation of electrolyte

[0097] The organic solvent is a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 1:1:1; the lithium salt LiPF6 is dissolved in the organic solvent and mixed evenly to obtain an electrolyte; wherein the concentration of the lithium salt is 1.0 mol / L.

[0098] (5) Preparation of diaphragm

[0099] A polyethylene diaphragm with a thickness of 12 μm was selected.

[0100] (6) Preparation of batteries

[0101] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an isolate. After being wound into a square bare cell, it is placed in an outer package, baked to remove water, injected with the corresponding electrolyte, and sealed. After standing, hot and cold pressing, formation, capacity division and other processes, a secondary battery is obtained.

[0102] Example 2

[0103] The preparation process is the same as that of Example 1, except that:

[0104] In step a, the ternary hydroxide precursor is adjusted to Ni 0.66 Co 0.055 Mn 0.285 (OH)2;

[0105] In step b, the total content of the first doping element is adjusted to 0.35 wt % of the ternary hydroxide precursor content, and the sintering temperature is adjusted to 920° C.;

[0106] In step c, the second dopant is adjusted to Al2O3.

[0107] Example 3

[0108] The preparation process is the same as that of Example 1, except that:

[0109] In step c, the Co content of the first lithium nickel cobalt manganese oxide is adjusted to 1.0 wt %, and the sintering temperature is adjusted to 780° C.

[0110] Example 4

[0111] The preparation process is the same as that of Example 1, except that:

[0112] In step c, the Co content of the first lithium nickel cobalt manganese oxide is adjusted to 3.0 wt %, and the sintering temperature is adjusted to 840°C.

[0113] Example 5

[0114] The preparation process is the same as that of Example 1, except that:

[0115] In step c, the Co content of the first lithium nickel cobalt manganese oxide is adjusted to 2.0 wt %, and the sintering temperature is adjusted to 790° C.

[0116] Example 6

[0117] The preparation process is the same as that of Example 1, except that:

[0118] In step c, the Co content of the first lithium nickel cobalt manganese oxide is adjusted to 2.0 wt %, and the sintering temperature is adjusted to 840°C.

[0119] Example 7

[0120] The preparation process is the same as that of Example 1, except that:

[0121] In step c, the total content of the second doping element (W and Al) is 0.6 wt % of the content of the first lithium nickel cobalt manganese oxide, and the sintering temperature is adjusted to 850°C.

[0122] Example 8

[0123] The preparation process is the same as that of Example 1, except that:

[0124] In step c, the second dopant is adjusted to ZrO2 and Al2O3.

[0125] Example 9

[0126] The preparation process is the same as that of Example 1, except that:

[0127] In step a, the particle size Dv50 of the ternary hydroxide precursor is adjusted to 6.0 μm;

[0128] In step b, the sintering temperature is adjusted to 940°C.

[0129] Example 10

[0130] The preparation process is the same as that of Example 1, except that:

[0131] In step d, the fast ion coating agent LiAlPO4 is replaced with Li2WO2. The sieve mesh size is adjusted to obtain a positive electrode material with a Dv50 of 2.5 μm.

[0132] Example 11

[0133] The preparation process was the same as that of Example 1, except that the fast ion coating agent LiAlPO4 was replaced by Li4Ti5O. The sieve mesh size was adjusted to obtain a positive electrode material with a Dv50 of 6.0 μm.

[0134] Example 12

[0135] The preparation process is the same as that of Example 1, except that:

[0136] In step c, the Co content of the first lithium nickel cobalt manganese oxide is adjusted to 0.5 wt %, and the sintering temperature is adjusted to 760° C., so that the thickness of the first film layer is 10 nm.

[0137] Example 13

[0138] The preparation process is the same as that of Example 1, except that:

[0139] In step c, the Co content of the first lithium nickel cobalt manganese oxide is adjusted to 4.0 wt %, and the sintering temperature is adjusted to 860° C., so that the thickness of the first film layer is 50 nm.

[0140] Example 14

[0141] The preparation process is the same as that of Example 1, except that:

[0142] In step d, the positive electrode material is mixed with a fast ion coating agent LiAlPO4, wherein the Al content is 0.05 wt% of the positive electrode material;

[0143] Example 15

[0144] The preparation process is the same as that of Example 1, except that:

[0145] In step d, the positive electrode material is mixed with a fast ion coating agent LiAlPO 4 , wherein the Al content is 0.7 wt % of the positive electrode material.

[0146] Examples 16 to 18

[0147] The preparation process is the same as that of Example 1, except that in step a, the ternary hydroxide precursors are adjusted to be LiNi 0.60 Co 0.154 Mn 0.246 O2、LiNi 0.72 Co 0.025 Mn 0.255 O2、LiNi 0.80 Co 0.054 Mn 0.146 O2.

[0148] Comparative Example 1

[0149] The preparation process is the same as that of Example 1, except that:

[0150] The preparation process is the same as that of Example 1, except that steps b to d are omitted, and in step (2), the first lithium nickel cobalt manganese oxide is used as the positive electrode material.

[0151] Comparative Example 2

[0152] The preparation process is the same as that of Example 1, except that:

[0153] In step c, the Co content is adjusted to 2.0 wt % of the first lithium nickel cobalt manganese oxide, and the sintering temperature is adjusted to 500° C.

[0154] Comparative Example 3

[0155] The preparation process is the same as that of Example 1, except that:

[0156] In step c, the Co content of the first lithium nickel cobalt manganese oxide is adjusted to 4.0 wt %, and the sintering temperature is adjusted to 650°C.

[0157] The positive electrode materials and secondary batteries prepared in the above examples and comparative examples were tested for relevant characteristics and performances. The testing methods are as follows:

[0158] (1) First cycle capacity and first charge and discharge efficiency test:

[0159] At 25±1℃, discharge the secondary battery at 1 / 3C constant current to 2.8V, let it stand for 30 minutes, charge it at 1 / 3C constant current to 4.4V, and charge it at constant voltage to a current of 0.05C to obtain the initial charge capacity of the battery. Let it stand for 30 minutes, discharge it at 1 / 3C constant current to 2.8V to obtain the initial discharge capacity;

[0160] Initial charge and discharge efficiency = initial discharge capacity / initial charge capacity*100%.

[0161] (2) Capacity retention test:

[0162] At 25±1°C, the secondary battery was subjected to charge and discharge cycle test at a charge and discharge rate of 1C / 1C in the range of 2.8-4.4V. The discharge capacity in the first cycle and the discharge capacity after 2000 cycles were recorded. The capacity retention rate after 2000 cycles was calculated as follows: discharge capacity in 2000 cycles / discharge capacity in the first cycle * 100%.

[0163] (3) Lithium-nickel mixed ratio test:

[0164] The material was subjected to XRD testing, and the obtained XRD data was refined to obtain the lithium-nickel mixed arrangement of the positive electrode material. The refinement software was fullprof;

[0165] Among them, the XRD test light source X-RAY has a scanning angle of 5 to 90° and a scanning speed of 5° / min.

[0166] (4) Line defect width test:

[0167] The positive electrode material is sliced ​​by X-RAY to expose the interface between the core and the first film layer. Then, the area of ​​the core and the first film layer is magnified to the atomic level through TEM testing and the interface defect width is marked as several atomic distances.

[0168] (5) Test of nickel and cobalt content in the film:

[0169] The cathode material powder was X-ray sliced, and then subjected to TEM and EELS analysis to determine the nickel and cobalt contents at different locations, thereby obtaining the nickel and cobalt contents in the film layer.

[0170] (6) Film thickness test:

[0171] X-ray sectioning is performed on the cathode material powder, followed by TEM and EELS analysis, and the film thickness is directly calibrated based on the element changes in EELS.

[0172] Table 1

[0173]

[0174]

[0175] Table 2

[0176]

[0177]

[0178] To sum up, in this embodiment, the cobalt-rich first film layer is controlled to cover the nickel-rich core, which can not only provide a higher capacity through the core, but also use the first film layer to prevent the surface phase change and interface side reactions of the high-nickel core, thereby maintaining a relatively high capacity inside. In addition, its good kinetics and structural problems can significantly improve the interface impedance of the material. In addition, the width of the line defect at the interface between the cobalt-rich first film layer and the nickel-rich core is controlled to be less than 10 atomic spacings, so that the first film layer is tightly combined with the core and the structure is stable, which can improve the cycle life of the battery and the initial charge and discharge efficiency, thereby solving the problem of fast cycle attenuation or cycle diving.

[0179] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0180] The above is a detailed introduction to a positive electrode material, a secondary battery and an electrical device provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, according to the ideas of the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A positive electrode material, characterized in that include: A core comprising a first lithium nickel cobalt manganese oxide, wherein the molar amount of nickel element in the first lithium nickel cobalt manganese oxide is ≥ 60% based on the total molar amount of transition metal elements excluding lithium; The first film layer includes a second lithium nickel cobalt manganese oxide, which is disposed on at least a portion of the surface of the core, wherein the molar amount of cobalt element in the second lithium nickel cobalt manganese oxide is ≥ 60% based on the total molar amount of transition metal elements excluding lithium; The width of the line defect at the interface between the first film layer and the core is less than 10 atomic distances.

2. The positive electrode material according to claim 1, characterized in that The first film layer has an area close to the core and an area away from the core. The cobalt content of the area close to the core of the first film layer is A1, and the nickel content is B1. The cobalt content of the area away from the core of the first film layer is A2, and the nickel content is B2, satisfying: A1<A2, B1>B2.

3. The positive electrode material according to claim 2, characterized in that The cobalt content of the first film layer is distributed in a decreasing gradient from the side away from the core to the side close to the core; the nickel content of the first film layer is distributed in an increasing gradient from the side away from the core to the side close to the core.

4. The positive electrode material according to claim 1, characterized in that The positive electrode material further includes a second film layer disposed on the surface of the first film layer, and the second film layer includes a fast ion conductor material.

5. The positive electrode material according to claim 1, characterized in that The first lithium nickel cobalt manganese oxide comprises a chemical formula of Li x1 Ni a1 Co b1 Mn c1 N d1 O2 compound, N contains one or more of Zr, Al, Ba, Sr, Y, Ti, Mg, Mo, B, Sn, Ce, Sb, W, 1.0≤x1≤1.2, 0.6≤a1≤0.8, 0.02≤b1≤0.2, 0.2≤c1≤0.5, 0.003≤d1≤0.015, a1+b1+c1+d1=1.

6. The positive electrode material according to claim 1, characterized in that The second lithium nickel cobalt manganese oxide includes a chemical formula of Li x2 Ni a2 Co b2 Mn c2 M d2 O2 compound, M contains one or more of Zr, Al, Ba, Sr, Y, Ti, Mg, Mo, B, Sn, Ce, Sb, W, 0.9≤x2≤1.2, 0.02≤a2≤0.2, 0.6≤b2≤0.98, 0.01≤c2≤0.2, 0.005≤d2≤0.015, and a2+b2+c2+d2=1.

7. The positive electrode material according to claim 4, characterized in that The thickness of the first film layer is greater than the thickness of the second film layer.

8. The positive electrode material according to claim 4, characterized in that The thickness of the first film layer is 10 to 50 nm; and / or The thickness of the second film layer is 0.5-8 nm.

9. The positive electrode material according to claim 4, characterized in that The fast ion conductor material includes one or more of Li3PO4, LiZrP2O7, LiAlPO4, Li3BO3, Li4Ti5O or Li2WO4.

10. The positive electrode material according to claim 1, characterized in that The lithium-nickel mixed ratio of the positive electrode material is less than 0.7%.

11. The positive electrode material according to claim 2, characterized in that At least one of the following conditions is met: 1) A1 is 60-68%; 2) A2 is 70-85%; 3) B1 is 30-60%; 4) B2 is 5-20%.

12. The positive electrode material according to any one of claims 1 to 11, characterized in that The Dv50 of the positive electrode material is 2.5 to 6.0 μm.

13. A secondary battery comprising a positive electrode plate, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode material according to any one of claims 1 to 12.

14. An electrical device, characterized in that: The secondary battery according to claim 13 is included, and the secondary battery serves as a power supply for the electrical device.

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