Secondary battery, battery module, battery pack, and device

Abstract

The invention provides a secondary battery, a battery module, a battery pack and a device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive active material layer located on the surface of the positive current collector, the positive active material layer comprises a positive active material, and the positive active material comprises a first lithium-nickel transition metal oxide and a second lithium-nickel transition metal oxide, the first lithium-nickel transition metal oxide comprises a first base material and a first coating layer located on the surface of the first base material, the first base material is secondary particles, and the second lithium-nickel transition metal oxide is single-crystal or single-crystal-like particles. The secondary battery has the characteristics of high energy density, low gas production rate, low pole piece expansion rate and the like, and has a good industrialization prospect.

Description

[0001] This application is a divisional application based on the invention with application number 201980100742.2, application date December 2, 2019, applicant being Contemporary Amperex Technology Co., Ltd., and invention name being “A positive electrode sheet, secondary battery, battery module, battery pack and device for secondary batteries”. Technical Field

[0002] The present invention relates to the field of electrochemistry, and in particular to a secondary battery, a battery module, a battery pack and a device. Background Art

[0003] Electric vehicles are increasingly demanding on range, which places higher demands on the energy density of power batteries. The improvement of power battery energy density depends largely on the choice of positive electrode materials. Based on the principle of selecting a high-capacity, high-discharge voltage platform, lithium nickel transition metal oxides (for example, nickel-cobalt-manganese ternary materials) are increasingly being used. Among them, increasing nickel content can significantly increase gram capacity, thereby increasing energy density. Therefore, lithium nickel transition metal oxides with high nickel content are currently a popular choice.

[0004] However, increasing the nickel content in lithium-nickel transition metal oxides makes their preparation more difficult: high temperatures lead to severe lithium volatilization; low temperatures prevent the grains from fully growing, resulting in poor processing performance. The current mainstream high-nickel lithium-nickel transition metal oxides are composed of small primary grains aggregated into large secondary polycrystalline particles. However, due to the large volume changes along the c-axis during charge and discharge, high-nickel lithium-nickel transition metal oxides are prone to cracking between primary grains, which deteriorates cycle performance.

[0005] In addition, the increase in nickel content in lithium nickel transition metal oxide also affects the stability of the material structure, intensifies the transformation of the surface layered structure to the rock salt phase, and the surface oxygen release also intensifies the side reactions of the electrolyte on the material surface. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a secondary battery, a battery module, a battery pack and a device to solve the problems in the prior art.

[0007] To achieve the above objectives and other related objectives, the first aspect of the present invention provides a secondary battery, including a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode active material layer located on the surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including a first lithium nickel transition metal oxide and a second lithium nickel transition metal oxide, the first lithium nickel transition metal oxide including a first substrate and a first coating layer located on the surface of the first substrate, the first substrate is a secondary particle, and the chemical formula of the first substrate is shown in Formula I:

[0008] Li 1+a1 Ni x1 Co y1 Mn z1 M b1 O 2-e1 X e1 (I)

[0009] In formula (I), -0.1 < a1 < 0.1, 0.5 ≤ x1 ≤ 0.95, 0.05 ≤ y1 ≤ 0.2, 0.03 ≤ z1 ≤ 0.4, 0 ≤ b1 ≤ 0.05, 0 ≤ e1 ≤ 0.1, and x1 + y1 + z1 + b1 = 1; wherein, M is selected from one or more combinations of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, B, Co, and Mn, and X is selected from F and / or Cl;

[0010] The first coating layer is selected from metal oxides and / or non-metal oxides;

[0011] The second lithium nickel transition metal oxide is in the form of single crystal or near single crystal particles;

[0012] The D v 50(L) of the first lithium nickel transition metal oxide and the D v 50(S) of the second lithium nickel transition metal oxide satisfy D v [[ID=3�]]50(L) is 5 μm to 18 μm and 2 ≤ D v 50(L) / D v 50(S) ≤ 5;

[0013] The tap density TD of the positive electrode active material is 2.2 g / cm 3 ~2.8 g / cm 3 ;

[0014] When the compaction density of the positive electrode sheet is 3.3 g / cm 3 ~3.5 g / cm 3 the OI of the positive electrode sheet is 10 to 40.

[0015] The second aspect of the present invention provides a battery module, which includes the secondary battery described in the first aspect of the present invention.

[0016] The third aspect of the present invention provides a battery pack, which includes the battery module described in the second aspect of the present invention. [[ID=5९]]

[0017] The fourth aspect of the present invention provides a device, which includes the secondary battery described in the first aspect of the present invention, and the secondary battery is used as the power source of the device.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] In the secondary battery of the present invention, the positive electrode active material includes a first lithium nickel transition metal oxide and a second lithium nickel transition metal oxide, wherein the first lithium nickel transition metal oxide is a secondary particle that has been coated, and the second lithium nickel transition metal oxide is a single particle with a single crystal or quasi-single crystal structure. By regulating the particle size distribution of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide, the tap density of the mixed positive electrode active material and the OI value of the electrode, the prepared secondary battery (for example, a lithium ion battery) has the characteristics of high energy density, low gas production, low electrode expansion rate, etc., and has good industrialization prospects.

[0020] The battery module, battery pack, and device of the present invention include the secondary battery, and thus have at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a perspective view of one embodiment of a battery.

[0022] Figure 2 is an exploded view of one embodiment of a battery.

[0023] Figure 3 This is a perspective view of one embodiment of a battery module.

[0024] Figure 4 This is a perspective view of one embodiment of a battery pack.

[0025] Figure 5 yes Figure 4 Exploded diagram of .

[0026] Figure 6 This is a schematic diagram of an embodiment of a device using a battery as a power source.

[0027] The description of the accompanying drawings is as follows:

[0028] 1 battery pack

[0029] 2 upper box

[0030] 3 lower cabinets

[0031] 4 battery modules

[0032] 5 batteries

[0033] 51 shell

[0034] 52 electrode assembly

[0035] 53 top cover assembly DETAILED DESCRIPTION

[0036] In order to make the object, technical solution and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the embodiments described in this specification are only for explaining the present invention and are not intended to limit the present invention.

[0037] Positive electrode plate

[0038] The first aspect of the present invention provides a positive electrode plate for a secondary battery. The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer located on the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes a first lithium nickel transition metal oxide and a second lithium nickel transition metal oxide. The first lithium nickel transition metal oxide includes a first substrate and a first coating layer located on the surface of the first substrate. The first substrate is a secondary particle. The chemical formula of the first lithium nickel transition metal oxide is shown in Formula I:

[0039] Li 1+a1 Ni x1 Co y1 Mn z1 M b1 O 2-e1 X e1 (I)

[0040] In Formula I, -0.1 < a1 < 0.1, 0.5 ≤ x1 ≤ 0.95, 0.05 ≤ y1 ≤ 0.2, 0.03 ≤ z1 ≤ 0.4, 0 ≤ b1 ≤ 0.05, 0 ≤ e1 ≤ 0.1, and x1 + y1 + z1 + b1 = 1; wherein, M is selected from one or more combinations of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, B, Co, Mn, and X is selected from F and / or Cl;

[0041] The first coating layer is selected from metal oxides and / or non-metal oxides;

[0042] The second lithium nickel transition metal oxide is a single crystal or quasi-single crystal morphology particle;

[0043] The particle size distribution characteristics of the positive electrode active material satisfy: 40 < D v 90 / D v 10 * D v 50 < 80, unit: μm;

[0044] When the tap density of the positive electrode plate is 3.3 g / cm 3 ~3.5 g / cm 3 the OI of the positive electrode plate is 10 - 40.

[0045] In the present invention, D v 10 is the particle size (unit: μm) corresponding to when the volume cumulative distribution percentage of the positive electrode active material reaches 10%; Dv 50 is the particle size corresponding to the cumulative volume distribution percentage of the sample reaching 50% (unit: μm); D v 90 is the particle size corresponding to the cumulative volume distribution percentage of the sample reaching 90% (unit: μm). The OI of the positive electrode sheet is the ratio of the diffraction peak area corresponding to the (003) crystal plane and the (110) crystal plane of the positive electrode active material in the XRD diffraction spectrum of the positive electrode sheet.

[0046] In the positive electrode sheet for a secondary battery provided by the present invention, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes a first lithium nickel transition metal oxide and a second lithium nickel transition metal oxide, the first substrate of the first lithium nickel transition metal oxide has a polycrystalline morphology (secondary particles composed of primary particles) and is coated with a metal oxide and / or a non-metallic oxide, and the second lithium nickel transition metal oxide has a single crystal or quasi-single crystal morphology. In the present invention, quasi-single crystal generally refers to primary particles with a size greater than 1 μm, but with some agglomeration of the primary particles; single crystal generally refers to primary particles with a size greater than 1 μm and no obvious agglomeration. The present invention effectively suppresses the cracking of the positive electrode active material particles by regulating the particle size distribution of the mixed positive electrode active material and the OI value of the positive electrode plate. While improving the compressive strength of the positive electrode active material particles in the positive electrode plate, the relative amount of the (003) crystal plane of the positive electrode active material in the positive electrode plate is reduced, effectively solving the problems of plate expansion rate and gas production, thereby obtaining an electrochemical energy storage device with high energy density, low plate expansion rate and low gas production.

[0047] The positive electrode sheet provided by the present invention has a compaction density of 3.3 g / cm 3 ~3.5g / cm 3 When the OI of the positive electrode sheet is 10-15, 15-20, 20-25, 25-30, 30-35, or 35-40, preferably 10-20. Generally speaking, the OI value of the positive electrode sheet reflects the overall orientation of the crystal planes of the positive electrode active material in the sheet, and is closely related to various process parameters of the sheet manufacturing process, such as coating speed, drying, and cold pressing. If the OI value of the positive electrode sheet is too high, it means that the relative amount of (003) crystal planes perpendicular to the length direction of the positive electrode sheet is too high, reflecting that the positive electrode sheet has a more serious texture after cold pressing, and the sheet is prone to expansion during the battery charging and discharging process; however, if the OI value of the positive electrode sheet is too low, it indicates that the positive electrode active material in the positive electrode sheet has no obvious orientation, the particle strength is too low, and the particles are prone to breakage during cold pressing and in the later stages of the cycle, causing gas production problems.

[0048] In the positive electrode plate provided by the present invention, the second lithium nickel transition metal oxide includes a second substrate, and the chemical formula of the second substrate is shown in Formula II:

[0049] Li1+a2 Ni x2 Co y2 Mn z2 M’ b2 O 2-e2 X’ e2 (II)

[0050] In formula II, -0.1 < a2 < 0.1, 0.5 ≤ x2 ≤ 0.95, 0.05 ≤ y2 ≤ 0.2, 0.03 ≤ z2 ≤ 0.4, 0 ≤ b2 ≤ 0.05, 0 ≤ e2 ≤ 0.1, and x2 + y2 + z2 + b2 = 1; wherein, M’ is selected from one or more combinations of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, B, Co, and Mn, and X’ is selected from F and / or Cl.

[0051] In the positive electrode sheet provided by the present invention, the molecular formulas of the first substrate and the second substrate may independently include, but are not limited to, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.55 Co 0.15 Mn 0.3 O2, LiNi 0.55 Co 0.1 Mn 0.35 O2, LiNi 0.55 Co 0.05 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O\(_2\), LiNi 0.65 Co 0.15 Mn 0.2 O\(_2\), LiNi 0.65 Co 0.12 Mn 0.23 O\(_2\), LiNi 0.65 Co 0.1 Mn 0.25 O\(_2\), LiNi 0.65 Co 0.05 Mn 0.3 O\(_2\), LiNi 0.7 Co 0.1 Mn 0.2 O\(_2\), LiNi 0.75 Co 0.1 Mn 0.15 O\(_2\), LiNi 0.8 Co 0.1 Mn 0.1 O\(_2\), LiNi0.85 Co 0.05 Mn 0.1 O2, LiNi 0.88 Co 0.05 Mn 0.07 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.92 Co 0.03 Mn 0.05 O2, LiNi 0.95 Co 0.02 Mn 0.03 O2, etc., or it can also be a substance obtained by partially substituting and modifying the above substances with doping elements M, M', X, X'. M and M' are each independently selected from one or more combinations of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, B, Co, and Mn. X and X' are each independently selected from F and / or Cl.

[0052] In some preferred embodiments of the present invention, the relative content x1 of Ni element in the molecular formula of the first substrate can satisfy: 0.8 ≤ x1 ≤ 0.95, 0.8 ≤ x1 ≤ 0.85, 0.85 ≤ x1 ≤ 0.9, or 0.9 ≤ x1 ≤ 0.95. The relative content x2 of Ni element in the molecular formula of the second substrate can satisfy: 0.8 ≤ x2 ≤ 0.95, 0.8 ≤ x1 ≤ 0.85, 0.85 ≤ x1 ≤ 0.9, or 0.9 ≤ x1 ≤ 0.95. And the relative contents x1 and x2 of Ni element in the first substrate and the second substrate can satisfy: |x1 - x2| ≤ 0.1. Both the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide in the present invention are selected as layered lithium transition metal oxides with a relatively high nickel content, which can effectively improve the energy density of the battery. At the same time, the difference between the relative contents x1 and x2 of Ni element in the first substrate and the second substrate is not greater than 0.1, which can achieve that when under the same charge-discharge voltage, the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide have a relatively close degree of lithium deintercalation / insertion, which is beneficial to improving the charge-discharge cycle life of the battery.

[0053] In some more preferred embodiments of the present invention, the relative contents x1 and x2 of Ni element in the first substrate and the second substrate satisfy: 0 < x1 - x2 < 0.1. The Ni element content x1 of the first lithium nickel transition metal oxide in the present invention is slightly higher than x2 of the second lithium nickel transition metal oxide, which is beneficial for the battery to exhibit a relatively high energy density while effectively balancing the degree of lithium deintercalation / insertion of the two cathode active materials.

[0054] In the positive electrode sheet provided by the present invention, the particle size and the tapped density TD of the positive electrode active material satisfy: 4.4 < (D v 90 - Dv 10) / TD<8. Specifically, (D v 90-D v The value range of (D) / TD can be 7.5-8, 7-7.5, 6.5-7, 6-6.5, 5.5-6, 5-5.5, 4.4-5. Preferably, 4.6<(D v 90-D v 10) / TD<6.5. Among them, D v 10. D v 90 is in μm; TD is the tap density of the positive electrode active material (unit: g / cm 3 ). In the present invention, when the positive electrode active material further satisfies (D v 90-D v When the value of 10) / TD is within the above range, the particle size distribution of particles of different morphologies of the positive electrode active material is moderate and the gap volume between the particles is low, which is conducive to improving the compaction density of the positive electrode sheet.

[0055] In the positive electrode sheet provided by the present invention, the tap density TD of the positive electrode active material can be 2.2 g / cm 3 ~2.8g / cm 3 , 2.2g / cm 3 ~2.3g / cm 3 , 2.3g / cm 3 ~2.4g / cm 3 , 2.4g / cm 3 ~2.5g / cm 3 , 2.5g / cm 3 ~2.6g / cm 3 , 2.6g / cm 3 ~2.7g / cm 3 , or 2.7g / cm 3 ~2.8g / cm 3 . In the present invention, TD is the powder tap density of the positive electrode active material, and the specific measurement method of the powder tap density may include: filling the powder in a container (for example, a 25 mL container, and for another example, the container used may be a measuring cylinder), vibrating the container (for example, the specific conditions of the vibration may be: a vibration frequency of 250 times / min, an amplitude of 3 mm, and 5000 vibrations), and the mass of the powder per unit volume is the powder tap density. Generally speaking, the larger the TD, the more conducive it is to achieving a high tap density, but TD is affected by factors such as the compactness of individual particles of the material, the particle size distribution of the material, and the morphology of the particles, and has a certain upper limit.

[0056] In the positive electrode sheet provided by the present invention, the first lithium nickel transition metal oxide may be a spherical particle, and the sphericity γ of the first lithium nickel transition metal oxide may be 0.7 to 1. Specifically, the sphericity γ of the first lithium nickel transition metal oxide may be 0.7 to 0.9, 0.7 to 0.8, 0.8 to 0.9, or 0.9 to 1. In the present invention, the sphericity may be measured by the following method: in the SEM photograph of the cross section of the positive electrode sheet, select at least 30 cross-sectional diameters within the positive electrode active material D v For secondary particles with a value of 10 or higher, measure the maximum inscribed circle radius (R max ) and the minimum circumscribed circle radius (R min ) and averaging the ratios to obtain γ. In the present invention, the first lithium nickel transition metal oxide is a secondary particle. When the sphericity of the secondary particles is within the above range, it indicates that the primary particles within the secondary particles are uniform in size and distribution, the secondary particles are compact, and have high mechanical strength.

[0057] In the positive electrode provided by the present invention, the longest diameter L of the second lithium nickel transition metal oxide is max With the shortest path L min The size ratio satisfies: 1≤L max / L min ≤3, 1≤L max / L min ≤1.5, 1.5≤L max / L min ≤2, 2≤L max / L min ≤2.5, or 2.5≤L max / L min ≤3. In the present invention, the L max / L min It can be measured in the following way: In the SEM photo of the cross section of the positive electrode sheet, select at least 30 cross-sectional diameters within the positive electrode active material D v For single crystal or single crystal-like particles with a value of 10 or above, measure the longest diameter (L max ) and the shortest diameter (L min ) ratio, find the average value, and we can get L max / L min In the present invention, the second lithium nickel transition metal oxide is a single crystal or single crystal-like particle. max / L minWhen within the above range, after mixing with secondary particles with a sphericity between 0.7 and 1, it can better fill the gap volume of the secondary particles, while improving the compaction density of the positive electrode sheet and the volume energy density of the battery. It can also effectively inhibit the volume expansion rate of the positive electrode sheet during the cycle and improve the cycle performance.

[0058] In the positive electrode provided by the present invention, the D v 50(L) may be 5 μm to 18 μm, 5 μm to 6 μm, 6 μm to 8 μm, 8 μm to 10 μm, 10 μm to 12 μm, 12 μm to 14 μm, 14 μm to 16 μm, or 16 μm to 18 μm, preferably 8 μm to 12 μm. The D of the second lithium nickel transition metal oxide v 50(S) can be 1 μm to 5 μm, 1 μm to 2 μm, 2 μm to 3 μm, 3 μm to 4 μm, or 4 μm to 5 μm. The substrate in the first lithium nickel transition metal oxide is a polycrystalline form (secondary particles formed by agglomeration of multiple primary particles), the second lithium nickel transition metal oxide is a single crystal or quasi-single crystal morphology particle, the first lithium nickel transition metal oxide has a larger particle size distribution than the second lithium nickel transition metal oxide as a whole, and the particle size distribution D between the two is greater. v 50(L) and D v 50(S) can more preferably satisfy: 2≤D v 50(L) / D v 50(S)≤7、2≤D v 50(L) / D v 50(S)≤3, 3≤D v 50(L) / D v 50(S)≤4, 4≤D v 50(L) / D v 50(S)≤5, 5≤D v 50(L) / D v 50(S)≤6, or 6≤D v 50(L) / D v 50(S)≤7. In the present invention, the first lithium nickel transition metal oxide D v 50(L) and the second lithium nickel transition metal oxide D v When the ratio of 50(S) is within the above range, it is beneficial to suppress the particle cracking problem of secondary particle high-nickel materials with larger particle size, ensure that the positive electrode active material can exert a higher gram capacity, and at the same time improve the mechanical strength and compaction density of the overall positive electrode sheet.

[0059] In the positive electrode provided by the present invention, the weight percentage content of the first lithium nickel transition metal oxide may be 50% to 90%, 85% to 90%, 80% to 85%, 75% to 80%, 70% to 75%, 65% to 70%, 60% to 65%, 55% to 60%, or 50% to 55%, preferably 60% to 85%. The weight percentage content of the second lithium nickel transition metal oxide may be 10% to 50%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%, 40% to 45%, or 45% to 50%, preferably 15% to 40%. In the present invention, the weight percentages of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide in the positive electrode plate are controlled within the above range, which can regulate the OI value of the positive electrode plate to a certain extent, while improving the compaction density and mechanical strength of the plate.

[0060] In the positive electrode plate provided by the present invention, the second lithium nickel transition metal oxide may further include a second coating layer located on the surface of the second substrate, and the second coating layer is a metal oxide and / or a non-metal oxide.

[0061] In the positive electrode sheet provided by the present invention, the first coating layer and / or the second coating layer may be a metal oxide and / or a non-metal oxide, for example, an oxide containing only a metal element or a non-metal element, or an oxide containing both metal elements and non-metal elements. Among the above-mentioned oxides, the metal element may generally be, for example, aluminum, zirconium, zinc, titanium, silicon, tin, tungsten, yttrium, cobalt, barium, etc., and the non-metal element may generally be, for example, phosphorus, boron, etc. Specifically, the first coating layer and / or the second coating layer may be, but is not limited to, a combination of one or more of aluminum oxide, zirconium oxide, zinc oxide, titanium oxide, silicon oxide, tin oxide, tungsten oxide, yttrium oxide, cobalt oxide, barium oxide, phosphorus oxide, boron oxide, and lithium aluminum oxide, lithium zirconium oxide, lithium zinc oxide, lithium magnesium oxide, lithium tungsten oxide, lithium yttrium oxide, lithium cobalt oxide, lithium barium oxide, lithium phosphorus oxide, or lithium boron oxide. In the present invention, the coating layer of the positive electrode active material is selected from the above-mentioned metal oxides and / or non-metallic oxides. The oxide coating layer has good bonding strength with the substrate and is not easy to fall off during the charge and discharge process. The portion of the contact area between the substrate and the electrolyte is reduced, which can effectively modify the surface of the high-nickel positive electrode material and reduce the side reaction between the positive electrode material and the electrolyte, thereby effectively suppressing the gas production of the battery.

[0062] In the positive electrode material provided herein, the first coating layer preferably contains at least one metal element oxide and one non-metal element oxide. The oxides of these elements not only enhance the coating layer's adhesion stability to the secondary particle substrate but also impart both ionic and electronic conductivity to the coating layer, thereby minimizing its impact on the polarization of the positive electrode material.

[0063] Preparation method of positive electrode sheet

[0064] The second aspect of the present invention provides a method for preparing the positive electrode sheet for a secondary battery provided in the first aspect of the present invention. Suitable methods for preparing the positive electrode sheet should be known to those skilled in the art. For example, the positive electrode sheet may include:

[0065] Providing a positive electrode active material including a first lithium nickel transition metal oxide and a second lithium nickel transition metal oxide;

[0066] The positive electrode active material, binder, and conductive agent are mixed to form a slurry, which is then coated on the positive electrode current collector.

[0067] In the preparation method of the positive electrode material provided by the present invention, the first lithium nickel transition metal oxide and / or the second lithium nickel transition metal oxide can be surface-modified. For example, the first lithium nickel transition metal oxide and / or the second lithium nickel transition metal oxide can be surface-modified separately and then mixed. The surface modification methods of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide can be the same or different. Alternatively, the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide can be mixed first and then subjected to a surface modification process together.

[0068] The preparation method of the positive electrode plate provided by the present invention may include: providing a first lithium nickel transition metal oxide. The method of providing the first lithium nickel transition metal oxide should be known to those skilled in the art. For example, it may include: mixing and sintering the raw materials of the substrate of the first lithium nickel transition metal oxide to provide a first substrate; coating the first substrate to provide a first lithium nickel transition metal oxide. Those skilled in the art can select suitable raw materials and proportions according to the elemental composition of the first lithium nickel transition metal oxide to further prepare the first substrate. For example, the raw materials of the first lithium nickel transition metal oxide may include a precursor of the first lithium nickel transition metal oxide, a lithium source, an M source, an X source, etc. The ratio between the raw materials is usually proportioned with reference to the ratio of each element in the first lithium nickel transition metal oxide. More specifically, the precursor of the first lithium nickel transition metal oxide may include but is not limited to Ni 0.5 Co 0.2 Mn 0.3 (OH)2、Ni 0.5 Co0.25 Mn 0.25 (OH)2、Ni 0.55 What 0.15 Mn 0.3 (OH)2、Ni 0.55 What 0.1 Mn 0.35 (OH)2、Ni 0.55 What 0.05 Mn 0.4 (OH)2、Ni 0.6 What 0.2 Mn 0.2 (OH)2、Ni 0.65 What 0.15 Mn 0.2 (OH)2、Ni 0.65 What 0.12 Mn 0.23 (OH)2、Ni 0.65 What 0.1 Mn 0.25 (OH)2、Ni 0.65 What 0.05 Mn 0.3 (OH)2、Ni 0.7 What 0.1 Mn 0.2 (OH)2、Ni 0.75 What 0.1 Mn 0.15 (OH)2、Ni 0.8 What 0.1 Mn 0.1 (OH)2、Ni 0.88 What 0.05 Mn 0.07 (OH)2、Ni 0.92 What 0.03 Mn 0.05 (OH)2、Ni 0.95 What 0.02 Mn 0.03The lithium source can be a lithium-containing compound, which can include but is not limited to LiOH·H2O, LiOH, Li2CO3, Li2O, and a combination thereof. The M source can generally be a compound containing the element M, which can include one or more oxides, nitrates, or carbonates containing at least one of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, Co, and Mn. The X source can be a compound containing the element X, which can include but is not limited to a combination of one or more LiF and NaCl. The raw materials for the first lithium nickel transition metal oxide substrate can be sintered at 700°C to 900°C with an oxygen concentration ≥20%. The method of coating the first substrate may specifically include: sintering the first substrate in the presence of a compound containing a coating element. The compound containing the coating element may be an oxide, nitrate, phosphate, carbonate, etc. containing one or more elements of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, etc. The amount of the coating element used may be generally ≤2wt%, and the sintering conditions in the coating treatment may be 200°C to 700°C.

[0069] The preparation method of the positive electrode plate provided by the present invention may include: providing a second lithium nickel transition metal oxide. The method of providing the second lithium nickel transition metal oxide should be known to those skilled in the art. For example, it may include: mixing and sintering the raw materials of the substrate of the second lithium nickel transition metal oxide to provide a second substrate; coating the second substrate to provide a second lithium nickel transition metal oxide. Those skilled in the art can select suitable raw materials and proportions according to the elemental composition of the second lithium nickel transition metal oxide to further prepare the second substrate. For example, the raw materials of the second lithium nickel transition metal oxide may include a precursor of the second lithium nickel transition metal oxide, a lithium source, an M' source, an X' source, etc. The ratio between the raw materials is usually proportioned with reference to the ratio of each element in the second lithium nickel transition metal oxide. More specifically, the precursor of the second lithium nickel transition metal oxide may include but is not limited to Ni 0.5 Co 0.2 Mn 0.3 (OH)2、Ni 0.5 Co 0.25 Mn 0.25 (OH)2、Ni 0.55 Co 0.15 Mn 0.3 (OH)2、Ni 0.55 Co 0.1 Mn 0.35 (OH)2、Ni 0.55 Co 0.05 Mn 0.4(OH)2、Ni 0.6 Co 0.2 Mn 0.2 (OH)2、Ni 0.65 Co 0.15 Mn 0.2 (OH)2、Ni 0.65 Co 0.12 Mn 0.23 (OH)2、Ni 0.65 Co 0.1 Mn 0.25 (OH)2、Ni 0.65 Co 0.05 Mn 0.3 (OH)2、Ni 0.7 Co 0.1 Mn 0.2 (OH)2、Ni 0.75 Co 0.1 Mn 0.15 (OH)2、Ni 0.8 Co 0.1 Mn 0.1 (OH)2、Ni 0.88 Co 0.05 Mn 0.07 (OH)2、Ni 0.92 Co 0.03 Mn 0.05 (OH)2、Ni 0.95 Co 0.02 Mn 0.03 (OH)2, etc. The lithium source can be a lithium-containing compound, which can include but is not limited to a combination of one or more of LiOH·H2O, LiOH, Li2CO3, Li2O, etc. The M' source can generally be a compound containing the M element, which can be one or more of an oxide, nitrate, or carbonate containing at least one of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, Co, and Mn. The X' source can be a compound containing the X' element, which can include but is not limited to a combination of one or more of LiF, NaCl, etc. The sintering conditions of the raw materials for the second lithium nickel transition metal oxide substrate can be 750°C to 950°C with an oxygen concentration of ≥20%. The method of coating the second substrate may specifically include: sintering the second substrate in the presence of a compound containing a coating element. The compound containing the coating element may be an oxide, nitrate, phosphate, carbonate, etc. containing one or more elements of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, etc. The amount of the coating element used may be generally ≤2wt%, and the sintering conditions in the coating treatment may be 200°C to 700°C.

[0070] In the preparation method of the positive electrode plate provided by the present invention, the binder generally includes a fluorinated polyolefin binder. Water is generally a good solvent relative to the fluorinated polyolefin binder, that is, the fluorinated polyolefin binder generally has good solubility in water. For example, the fluorinated polyolefin binder may include but is not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers, etc., or their modified derivatives (for example, carboxylic acid, acrylic acid, acrylonitrile, etc.). In the positive electrode active material layer, the mass percentage content of the binder may be due to the poor conductivity of the binder itself, so the amount of the binder cannot be too high. Preferably, the mass percentage content of the binder in the positive electrode active material layer is less than or equal to 0.5wt% to 3wt% to obtain a lower electrode impedance.

[0071] In the method for preparing the positive electrode sheet provided by the present invention, the conductive agent of the positive electrode sheet can be any conductive agent suitable for lithium-ion (secondary) batteries in the art, for example, it can be a combination of one or more of acetylene black, conductive carbon black, carbon fiber (VGCF), carbon nanotubes (CNT), Ketjen black, etc. The weight of the conductive agent can account for 1wt% to 10wt% of the total mass of the positive electrode active material layer. More preferably, the weight ratio of the conductive agent to the positive electrode active material in the positive electrode sheet is 1.0wt% to 5.0wt%.

[0072] In the preparation method of the positive electrode sheet provided by the present invention, the positive electrode current collector of the positive electrode sheet can generally be a layer body, and the positive electrode current collector is generally a structure or part that can collect current. The positive electrode current collector can be various materials in the field that are suitable for use as a positive electrode current collector for lithium-ion batteries. For example, the positive electrode current collector can include but is not limited to metal foil, and more specifically can include but is not limited to copper foil, aluminum foil, etc.

[0073] secondary batteries

[0074] A third aspect of the present invention provides a secondary battery comprising the positive electrode sheet provided by the first aspect of the present invention.

[0075] In the secondary battery provided by the present invention, it should be noted that the secondary battery can be a supercapacitor, a lithium-ion battery, a lithium metal battery or a sodium-ion battery. In the embodiments of the present invention, only the embodiment of the secondary battery being a lithium-ion battery is shown, but the present invention is not limited thereto.

[0076] Figure 1 It is a perspective view of a specific embodiment of a lithium-ion battery. Figure 2 yes Figure 1 Exploded view of . Figures 1 to 2The battery 5 includes a housing 51, an electrode assembly 52, a top cover assembly 53, and an electrolyte (not shown). The electrode assembly 52 is housed in the housing 51. The number of electrode assemblies 52 is not limited and can be one or more.

[0077] It should be noted that Figure 1 The battery 5 shown is a can-type battery, but is not limited thereto. The battery 5 may be a pouch-type battery, that is, the housing 51 is replaced by a metal plastic film and the top cover assembly 53 is eliminated.

[0078] A lithium-ion battery may include a positive electrode sheet, a negative electrode sheet, a separator between the positive and negative electrode sheets, and an electrolyte. The positive electrode sheet may be the positive electrode sheet provided by the first aspect of the present invention. Methods for preparing lithium-ion batteries should be known to those skilled in the art. For example, the positive electrode sheet, separator, and negative electrode sheet can each be a layered body, which can be cut to a target size and stacked in sequence. They can also be wound to a target size to form a battery cell, which can be further combined with an electrolyte to form a lithium-ion battery.

[0079] In lithium-ion batteries, the negative electrode sheet typically includes a negative electrode current collector and a negative electrode active material layer located on the surface of the negative electrode current collector. The negative electrode active material layer typically includes a negative electrode active material. The negative electrode active material can be any material suitable for use in lithium-ion batteries. For example, it can include, but is not limited to, one or more combinations of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. Graphite can be selected from a combination of one or more of artificial graphite, natural graphite, and modified graphite; silicon-based materials can be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and tin-based materials can be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is typically a structure or component that collects current. It can be any material suitable for use as a negative electrode current collector in lithium-ion batteries. For example, it can include, but is not limited to, metal foil, and more specifically, copper foil.

[0080] In lithium-ion batteries, the separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be a combination of one or more materials including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0081] In a lithium-ion battery, the electrolyte generally includes an electrolyte and a solvent. Suitable electrolytes suitable for lithium-ion batteries should be known to those skilled in the art. For example, the electrolyte generally includes a lithium salt, and more specifically, the lithium salt may be an inorganic lithium salt and / or an organic lithium salt, and specifically may include but is not limited to a combination of one or more of LiPF6, LiBF4, LiN(SO2F)2 (LiFSI), LiN(CF3SO2)2 (LiTFSI), LiClO4, LiAsF6, LiB(C2O4)2 (LiBOB), LiBF2C2O4 (LiDFOB), etc. For another example, the concentration of the electrolyte may be between 0.8 mol / L and 1.5 mol / L. For another example, the solvent used in the electrolyte may be any solvent suitable for lithium-ion battery electrolytes in the art, and is generally a non-aqueous solvent, and preferably an organic solvent, and specifically may include but is not limited to a combination of one or more of ethylene carbonate, propylene carbonate, butylene carbonate, pentyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, etc., or halogenated derivatives thereof.

[0082] battery module

[0083] In a fourth aspect of the present application, a battery module is provided, comprising the secondary battery provided in the third aspect of the present application. A battery module generally includes one or more secondary batteries, and the battery module can be used as a power source or energy storage device. The number of batteries in the battery module can be adjusted according to the application and capacity of the battery module.

[0084] Figure 3 is a perspective view of a specific embodiment of a battery module.

[0085] Reference Figure 3 The battery module 4 includes a plurality of batteries 5. The plurality of batteries 5 are arranged in a longitudinal direction.

[0086] battery pack

[0087] In a fifth aspect of the present application, a battery pack is provided, which includes the secondary battery provided in the third aspect of the present application, or the battery module block provided in the fourth aspect.

[0088] Figure 4 It is a three-dimensional diagram of a specific embodiment of the battery pack 1. Figure 5 yes Figure 4 Exploded diagram of .

[0089] Reference Figure 4 and Figure 5 The battery pack 1 includes an upper box 2, a lower box 3 and a battery module 4.

[0090] The upper and lower housings 2 and 3 are assembled together to form a space for accommodating the battery modules 4. The battery modules 4 are placed within this space. The output terminals of the battery modules 4 extend from one or both of the upper and lower housings 2 and 3 to provide external power or charging. The number and arrangement of the battery modules 4 used in the battery pack 1 can be determined based on actual needs. The battery pack 1 can function as a power source or energy storage device.

[0091] Device

[0092] A sixth aspect of the present invention provides a device comprising the secondary battery provided by the third aspect of the present invention, wherein the secondary battery serves as a power source for the device.

[0093] Figure 6 It is a three-dimensional diagram of a specific embodiment of the above device. Figure 6 In the embodiment, the device using the battery 5 is an electric vehicle. Of course, it is not limited thereto. The device using the battery 5 can be any electric vehicle other than an electric vehicle (such as an electric bus, an electric tram, an electric bicycle, an electric motorcycle, an electric scooter, an electric golf cart, an electric truck), an electric ship, an electric tool, an electronic device, and an energy storage system. The electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. Of course, depending on the actual form of use, the device provided in the sixth aspect of the present application may include the battery module 4 provided in the fourth aspect of the present application. Of course, the device provided in the sixth aspect of the present application may also include the battery pack 1 provided in the fifth aspect of the present application.

[0094] The beneficial effects of the present invention are further illustrated below with reference to the examples.

[0095] In order to make the invention objectives, technical solutions and beneficial technical effects of the present invention clearer, the present invention is further described in detail below with reference to the examples. However, it should be understood that the examples of the present invention are only for the purpose of explaining the present invention and are not intended to limit the present invention, and the examples of the present invention are not limited to the examples given in the specification. In the examples, where no specific experimental conditions or operating conditions are specified, the products were prepared under conventional conditions or under the conditions recommended by the material supplier.

[0096] Furthermore, it should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before or after the combination step, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified. It should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the presence of other devices / apparatuses before or after the combination device / apparatus, or the insertion of other devices / apparatuses between two explicitly mentioned devices / apparatuses, unless otherwise specified. Furthermore, unless otherwise specified, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the present invention.

[0097] In the following examples, all reagents, materials and instruments used are commercially available unless otherwise specified.

[0098] Example 1

[0099] 1. Preparation of positive electrode active material

[0100] 1) Preparing the precursors of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide: nickel sulfate, manganese sulfate, and cobalt sulfate are prepared into a 1 mol / L solution in a molar ratio of 8:1:1, and a hydroxide coprecipitation technique is used to prepare a particle size D v 50(L) is a 9.7μm precursor for a first lithium nickel transition metal oxide; nickel sulfate, manganese sulfate, and cobalt sulfate are prepared in a molar ratio to a 1 mol / L solution, and a second lithium nickel transition metal oxide precursor with a particle size of 2.9μm is prepared using hydroxide coprecipitation technology. During the precursor preparation process, the particle size and morphology of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide precursors are controlled by controlling the reaction time, the pH value during coprecipitation, and the ammonia concentration.

[0101] 2) The first lithium nickel transition metal oxide (polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2) preparation method:

[0102] The precursor of the first lithium nickel transition metal oxide Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and the lithium-containing compound LiOH·H2O are mixed in a mixing device at a molar ratio of 1:1.05, and then sintered in an atmosphere furnace at 830°C. After cooling, the substrate of the first lithium nickel transition metal oxide is obtained by mechanical grinding;

[0103] The substrate of the first lithium nickel transition metal oxide is mixed with 0.2 wt% of Al2O3, a compound containing a coating element Al, and 0.2 wt% of boric acid, a compound containing a coating element B, in a mixing device, and then sintered at 500°C for 5 hours in an atmosphere furnace to form a first coating layer of the first lithium nickel transition metal oxide, that is, to obtain a surface-coated first lithium nickel transition metal oxide. The D of the above material is v 50. Sphericity and coating materials are shown in Table 1.

[0104] 3) The second lithium nickel transition metal oxide (single crystal LiNi 0.8 Co 0.1 Mn 0.1 O2) preparation method:

[0105] The precursor of the second lithium nickel transition metal oxide Ni 0.8 Co 0.1 Mn 0.1 (OH)2 and the lithium-containing compound LiOH·H2O are mixed in a mixing device at a molar ratio of 1:1.05, and then sintered at 870°C for 4 hours in a furnace with an oxygen concentration of 30%. After cooling, the powder is ground by air flow to obtain a second lithium nickel transition metal oxide substrate;

[0106] The substrate of the second lithium nickel transition metal oxide and 0.2 wt% of the compound Al2O3 containing the coating element Al are placed in a mixing device for mixing, and then placed in an atmosphere furnace for sintering at 500°C for 5 hours to form a coating layer of the lithium nickel transition metal oxide B, that is, to obtain a surface-modified second lithium nickel transition metal oxide. The material D v 50. L max / L min The ratios and coating materials are shown in Table 1.

[0107] 4) The surface-modified first lithium nickel transition metal oxide and the surface-modified second lithium nickel transition metal oxide were mixed uniformly at a mass ratio of 7:3 to obtain the positive electrode active material of Example 1. The TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0108] 2. Preparation of batteries

[0109] 1) Preparation of positive electrode sheet

[0110] Step 1: The positive electrode active material obtained above, the binder polyvinylidene fluoride, and the conductive agent acetylene black were mixed in a mass ratio of 98:1:1, N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on an aluminum foil with a thickness of 12 μm;

[0111] Step 2: Dry the coated electrode in an oven at 100°C to 130°C, and then cold press and cut to obtain the positive electrode.

[0112] 2) Negative electrode preparation

[0113] The negative electrode active material graphite, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black were mixed in a mass ratio of 97:1:1:1, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on a copper foil with a thickness of 8 μm; the copper foil was dried at room temperature and transferred to a 120°C oven for drying for 1 hour, and then cold pressed and slit to obtain a negative electrode sheet.

[0114] 3) Electrolyte preparation

[0115] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with the volume ratio of EC, EMC, and DEC being 20:20:60. In an argon atmosphere glove box with a water content of <10 ppm, fully dried lithium salt is dissolved in the organic solvent and mixed thoroughly to obtain an electrolyte solution. The concentration of the lithium salt is 1 mol / L.

[0116] 4) Preparation of isolation membrane

[0117] A 12μm thick polypropylene isolation film was selected.

[0118] 5) Preparation of batteries

[0119] 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 serve as an isolation. After being wound into a square bare battery cell, an aluminum-plastic film is placed in it. After being baked at 80°C to remove water, the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity separation and other processes, the finished battery is obtained.

[0120] Example 2

[0121] The preparation method of the positive electrode sheet and the battery in Example 2 is similar to that in Example 1, except that the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 9:1, and the TD, (D v 90-D v 10) / TD、D v 90 / Dv 10*D v 50 and the positive electrode OI are shown in Table 1.

[0122] Example 3

[0123] The preparation method of the positive electrode sheet and the battery in Example 3 is similar to that in Example 1, except that the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 6:4, and the TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0124] Example 4

[0125] The preparation method of the positive electrode sheet and the battery in Example 4 is the same as that in Example 1, except that the Ni:Co:Mn element ratio in the second lithium nickel transition metal oxide is 5:2:3, and the particle size D of the second lithium nickel transition metal oxide is 1:1. v 50(S)=4.3μm,L max / L min =1.5, the coating elements are Al and Ti, the compounds used in the sintering process are aluminum oxide and titanium oxide, the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 8:2, and the TD and (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0126] Example 5

[0127] The preparation method of the positive electrode plate and the battery in Example 5 is the same as that in Example 1, except that the Ni:Co:Mn element ratio in the first lithium nickel transition metal oxide is 6:2:2, and the particle size D of the first lithium nickel transition metal oxide is 1:1. v 50(L)=9.6μm, sphericity γ=0.81, TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0128] Example 6

[0129] The preparation method of the positive electrode plate and the battery in Example 6 is the same as that in Example 1, except that the Ni:Co:Mn element ratio in the second lithium nickel transition metal oxide is 9:0.5:0.5, the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 8:2, and the TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0130] Example 7

[0131] The preparation method of the positive electrode plate and the battery in Example 7 is the same as that in Example 1, except that the coating element of the first lithium nickel transition metal oxide is B, that is, no compound corresponding to Al is used for sintering, and the TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0132] Example 8

[0133] The preparation method of the positive electrode plate and the battery in Example 8 refers to Example 1, except that the coating element of the first lithium nickel transition metal oxide is B, that is, no compound corresponding to Al is used for sintering, the coating elements of the second lithium nickel transition metal oxide are Al and B, and the compounds used in the sintering process are aluminum oxide and boron oxide. The TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0134] Example 9

[0135] The preparation method of the positive electrode plate and the battery in Example 9 is the same as that in Example 1, except that the Ni:Co:Mn element ratio in the first lithium nickel transition metal oxide is 8.3:1.4:0.3, and the particle size D of the first lithium nickel transition metal oxide is 0.1:1. v 50(L)=12.3μm, sphericity γ=0.85, the coating element is Ba, the corresponding coating compound is barium oxide, the particle size of the second lithium nickel transition metal oxide is D v 50(S)=2.2μm,L max / Lmin =1.7, the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 6:4, and the TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0136] Example 10

[0137] The preparation method of the positive electrode plate and the battery in Example 10 is the same as that in Example 1, except that the Ni:Co:Mn element ratio in the first lithium nickel transition metal oxide is 8.3:1.4:0.3, and the particle size D of the first lithium nickel transition metal oxide is 0.1:1. v 50(L)=12.3μm, sphericity γ=0.85, the corresponding compound used in the coating is barium oxide, the Ni:Co:Mn element ratio in the second lithium nickel transition metal oxide is 5:2:3, and the particle size D of the second lithium nickel transition metal oxide is v 50(S)=4.3μm, Lmax / Lmin=1.5, the coating elements are Al and Ti, the compounds used in the sintering process are aluminum oxide and titanium oxide, the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 5:5, the TD and (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0138] Comparative Example 1

[0139] The preparation method of the positive electrode plate and the battery in Comparative Example 1 is the same as that in Example 1. The particle size D of the first lithium nickel transition metal oxide is v 50(L)=7.8μm, sphericity γ=0.77, the Ni:Co:Mn element ratio in the second lithium nickel transition metal oxide is 5:2:3, and the particle size D of the second lithium nickel transition metal oxide is v 50(S)=4.3μm,L max / L min =1.5, the coating elements are Al and Ti, the compounds used in the sintering process are aluminum oxide and titanium oxide, and the TD and (D v 90-D v 10) / TD、D v 90 / D v 10*D v50 and the positive electrode OI are shown in Table 1.

[0140] Comparative Example 2

[0141] The preparation method of the positive electrode sheet and the battery in Comparative Example 2 refers to Example 1, except that the second lithium nickel transition metal oxide is not used in the preparation method of the positive electrode active material, and the TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0142] Comparative Example 3

[0143] The preparation method of the positive electrode plate and the battery in Comparative Example 3 refers to that in Example 1, except that the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 4:6, and the TD, (Dv90-Dv10) / TD, Dv90 / Dv10*Dv50 and positive electrode plate OI of the prepared positive electrode active material are shown in Table 1.

[0144] Comparative Example 4

[0145] The preparation method of the positive electrode sheet and the battery in Comparative Example 4 is the same as that in Example 9, except that the particle size D of the first lithium nickel transition metal oxide is v 50(L)=16.8 μm, the particle size D of the second lithium nickel transition metal oxide v 50(S)=2.9μm,L max / L min =2, the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 9:1, and the TD, (D v 90-D v 10) / TD、D v 90 / D v 10*D v 50 and the positive electrode OI are shown in Table 1.

[0146] Comparative Example 5

[0147] The preparation method of the positive electrode sheet and the battery in Comparative Example 5 refers to Example 1, except that the first lithium nickel transition metal oxide is not used in the process of preparing the positive electrode sheet. The TD, (Dv90-Dv10) / TD, Dv90 / Dv10*Dv50 and positive electrode sheet OI of the prepared positive electrode active material are shown in Table 1.

[0148] Comparative Example 6

[0149] The preparation method of the positive electrode plate and the battery in Comparative Example 6 refers to Example 1, except that no coating treatment is performed during the preparation of the first lithium nickel transition metal oxide. The TD, (Dv90-Dv10) / TD, Dv90 / Dv10*Dv50 and positive electrode plate OI of the prepared positive electrode active material are shown in Table 1.

[0150] Detection method

[0151] (1) Test method for secondary particle sphericity:

[0152] Take SEM photos of the cross section of the positive electrode sheet, and select at least 30 cross-sectional diameters within the positive electrode active material D v For secondary particles with a value of 10 or above, measure the maximum inscribed circle radius (R max ) and the minimum circumscribed circle radius (R min ) and find the average value to get the sphericity γ of the secondary particles.

[0153] (2) Test method for Lmax / Lmin of single crystal / quasi-single crystal particles:

[0154] In the SEM photos of the cross section of the positive electrode sheet, select at least 30 cross-sectional diameters within the positive electrode active material D v For single crystal or single crystal-like particles with a value of 10 or above, measure the longest diameter (L max ) and the shortest diameter (L min ) ratio, find the average value, and we can get L max / L min The test results of the embodiments and comparative examples are shown in Table 2.

[0155] (3) Test method for tap density TD:

[0156] 10 g of powder was placed in a 25 mL graduated cylinder. The filled cylinder was vibrated 5000 times at a frequency of 250 vibrations / min and an amplitude of 3 mm. The volume occupied by the powder in the cylinder was read. This was used to calculate the mass of the powder per unit volume, which is the powder tap density (TD). The test results for the Examples and Comparative Examples are shown in Table 2.

[0157] (4) Test method for positive electrode OI value:

[0158] The prepared positive electrode was placed horizontally in an XRD diffractometer to measure its XRD diffraction pattern. The ratio of the diffraction peak areas corresponding to the (003) crystal plane and the (110) crystal plane of the positive electrode active material in the XRD diffraction pattern was calculated to obtain the OI value of the positive electrode. The test results for each embodiment and comparative example are shown in Table 2.

[0159] (5) Test method for compaction density:

[0160] 1) Cut the electrode into 1000mm long membranes;

[0161] 2) The positive electrode sheet is rolled under a certain pressure. Due to the ductility of the aluminum foil, the length of the membrane is 1006mm;

[0162] 3.) Punching 1540.25mm 2 The compacted density can be calculated by measuring the weight and thickness of the small disc;

[0163] The test results of each embodiment and comparative example are shown in Table 2.

[0164] (6) Test method for capacity retention after 400 cycles at 45°C:

[0165] At 45°C, charge the lithium-ion battery at a constant current of 1C to a voltage of 4.2V, then charge at a constant voltage of 4.2V to a current of 0.05C. Then discharge at a constant current of 1C until the final voltage reaches 2.8V. Record the discharge capacity of the first cycle. Repeat the above charge and discharge cycles for 400 cycles, and record the discharge capacity after 400 cycles. Calculate the capacity retention rate after 400 cycles at 45°C based on the discharge capacity of the first cycle and the discharge capacity after 400 cycles.

[0166] The test results of each embodiment and comparative example are shown in Table 2.

[0167] (7) Cyclic DCR growth test:

[0168] At 25°C, charge the battery to 100% SOC at 1C constant current / constant voltage (charge at 1C constant current to 4.2V, then charge at 4.2V constant voltage to 0.05C), then discharge at 1C constant current for 30 minutes, let it rest for 60 minutes, and record the voltage U1 after the rest; then discharge at 4C constant current for 30 seconds, and record the voltage U2 after discharge;

[0169] Calculate the DC resistance of a lithium-ion battery according to the formula: DCR = (U2-U1) / (4C-1C).

[0170] The test results of each embodiment and comparative example are shown in Table 2.

[0171]

[0172] Table 2

[0173]

[0174] Comparison of the Examples and Comparative Examples shows that by mixing a first lithium nickel transition metal oxide in the form of secondary particles with a second lithium nickel transition metal oxide in the form of single crystal or quasi-single crystal particles, and controlling the particle size distribution of the mixed positive electrode active material and the OI value of the positive electrode sheet, while improving the compaction density, particle cracking during cycling, cycle life, and DCR growth during cycling can be improved. Surface-coated metal oxides and non-metal oxides can significantly improve cycle life and cycle DCR growth.

[0175] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A secondary battery, comprising a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode active material layer located on the surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including a first lithium nickel transition metal oxide and a second lithium nickel transition metal oxide, the first lithium nickel transition metal oxide including a first substrate and a first coating layer located on the surface of the first substrate, the first substrate being a secondary particle, and the chemical formula of the first substrate being as shown in Formula I: Li 1+a1 Ni x1 Co y1 Mr z1 M b1 O 2-e1 X e1 (I) In Formula I, -0.1 < a1 < 0.1, 0.5 ≤ x1 ≤ 0.95, 0.05 ≤ y1 ≤ 0.2, 0.03 ≤ z1 ≤ 0.4, 0 ≤ b1 ≤ 0.05, 0 ≤ e1 ≤ 0.1, and x1 + y1 + z1 + b1 = 1; wherein, M is selected from one or more combinations of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, B, Co, and Mn; X is selected from F and / or Cl; The first coating layer is selected from metal oxides and / or non-metal oxides; The second lithium nickel transition metal oxide is a single crystal or a quasi-single crystal morphology particle; The first lithium nickel transition metal oxide D v 50(L) and the second lithium nickel transition metal oxide D v 50(S) satisfies D v 50(L) is 5μm~18μm and 2≤D v 50(L) / D v 50(S)≤5; The tap density TD of the positive electrode active material is 2.2 g / cm 3 ~2.8g / cm 3 ; The compaction density of the positive electrode sheet is 3.3 g / cm 3 ~3.5g / cm 3 When the positive electrode sheet has an OI of 10 to 40.

2. The secondary battery according to claim 1, wherein The second lithium nickel transition metal oxide includes a second substrate, and the chemical formula of the second substrate is as shown in Formula II: Li 1+a2 Ni x2 Co y2 Mr z2 M' b2 O 2-e2 X' e2 (II) In Formula II, -0.1 < a2 < 0.1, 0.5 ≤ x2 ≤ 0.95, 0.05 ≤ y2 ≤ 0.2, 0.03 ≤ z2 ≤ 0.4, 0 ≤ b2 ≤ 0.05, 0 ≤ e2 ≤ 0.1, and x2 + y2 + z2 + b2 = 1; wherein, M' is selected from one or more combinations of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, B, Co, and Mn; X' is selected from F and / or Cl; Preferably, the relative contents x1 and x2 of the Ni element in the molecular formulas of the first substrate and the second substrate satisfy: 0.8 ≤ x1 ≤ 0.95, 0.8 ≤ x2 ≤ 0.95, and |x1 - x2| ≤ 0.1; More preferably, x1 and x2 satisfy: 0 < x1 - x2 < 0.

1.

3. The secondary battery according to claim 1 or 2, wherein: The compaction density of the positive electrode sheet is 3.3 g / cm 3 ~3.5g / cm 3 When the positive electrode sheet has an OI of 10 to 20.

4. The secondary battery according to any one of claims 1 to 3, wherein The particle size distribution of the positive electrode active material satisfies: 40 <D v 90 / D v 10*D v 50<80, unit is μm.

5. The secondary battery according to any one of claims 1 to 4, wherein The positive electrode active material satisfies: 4.4<(D v 90-D v 10) / TD<8, preferably, 4.6<(D v 90-D v 10) / TD<6.5, Among them, D v 10. D v 90 is in μm; TD is the tap density of the positive electrode active material, in g / cm 3 .

6. The secondary battery according to any one of claims 1 to 5, wherein The first lithium nickel transition metal oxide is a spherical particle, and the sphericity γ of the first lithium nickel transition metal oxide particles is 0.7 to 1.

7. The secondary battery according to any one of claims 1 to 6, wherein The longest diameter L of the second lithium nickel transition metal oxide particle max With the shortest path L min The size ratio satisfies: 1≤L max / L min ≤3.

8. The secondary battery according to any one of claims 1 to 7, wherein The second lithium nickel transition metal oxide D v 50(S) is 1 μm to 5 μm; and / or, The D v 50(L) and D v 50(S) satisfies: 2≤D v 50(L) / D v 50(S)≤4.

9. The secondary battery according to any one of claims 1 to 8, wherein In the positive electrode active material, the weight percentage content of the first lithium nickel transition metal oxide is 50% to 90%, preferably 60% to 85%; And the weight percentage content of the second lithium nickel transition metal oxide is 10% to 50%, preferably 15% to 10. The secondary battery according to claim 2, wherein ​ 11. A battery module, characterized in that: ​ 12. A battery pack, characterized in that: ​ 13. A device, characterized in that: ​

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