A positive electrode sheet for a secondary battery, a secondary battery, a battery module, a battery pack, and a device

Abstract

A positive electrode sheet for a secondary battery, a secondary battery (5), a battery module (4), a battery pack (1), and a device. The positive electrode sheet 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, and the second lithium nickel transition metal oxide is a single crystal or quasi-single crystal morphology particle. By regulating the particle size distribution of the positive electrode active material after mixing and the OI value of the electrode sheet, the compressive strength of the positive electrode active material particles in the positive electrode sheet is improved, and the problem of particle cracking of the positive electrode active material particles is effectively inhibited.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry, and particularly to a positive electrode sheet for a secondary battery, a secondary battery, a battery module, a battery pack, and a device. Background Art

[0002] Electric vehicles have an increasingly high requirement for cruising range, which poses a higher requirement for the energy density of power batteries. The improvement of the energy density of power batteries depends to a large extent on the selection of positive electrode materials. According to the selection principle of high capacity and high discharge voltage platform, the application of lithium nickel transition metal oxides (for example, nickel cobalt manganese ternary materials) is increasing. Among them, the increase in nickel content can significantly increase the specific capacity per gram, thereby improving the energy density. Therefore, lithium nickel transition metal oxides with high nickel content are the current popular choice.

[0003] However, the increase in nickel content in lithium nickel transition metal oxides makes the preparation more difficult: at high temperatures, lithium volatilizes severely; at low temperatures, the grains cannot grow sufficiently, and the processing performance is poor. The current mainstream lithium nickel transition metal oxides with high nickel content are secondary polycrystalline large particles aggregated by primary small grains. However, due to the large volume change in the c-axis direction during the charge and discharge process of lithium nickel transition metal oxides with high nickel content, cracks are easily generated between primary grains, thereby deteriorating the cycle performance.

[0004] In addition, the increase in nickel content in lithium nickel transition metal oxides also affects the stability of the material structure, exacerbates the transformation of the surface layer structure to the rock salt phase, and the oxygen evolution on the surface also exacerbates the side reaction of the electrolyte on the material surface. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a positive electrode sheet for a secondary battery, a secondary battery, a battery module, a battery pack, and a device to solve the problems in the prior art.

[0006] To achieve the above object and other related objects, a first aspect of the present invention provides a positive electrode sheet for a secondary battery. The positive electrode sheet 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, and the chemical formula of the first substrate is as shown in Formula I:

[0007] Li 1+a1 Ni x1 Co y1 Mn z1 M b1 O 2-e1 Xe1 (I)

[0008] 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 a combination of more than one of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, B, Co, Mn; X is selected from F and / or Cl;

[0009] The first coating layer is selected from metal oxides and / or non-metal oxides;

[0010] The second lithium nickel transition metal oxide is in the form of single crystal or pseudo single crystal particles;

[0011] The particle size distribution of the positive electrode active material satisfies: 40 < Dv90 / Dv10 * Dv50 < 80, unit: μm;

[0012] The tap density of the positive electrode sheet is 3.3 g / cm 3 ~3.5 g / cm 3 When it is, the OI of the positive electrode sheet is 10 - 40.

[0013] 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.

[0014] The third aspect of the present invention provides a secondary battery, which includes the positive electrode sheet described in the first aspect of the present invention.

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

[0016] The fifth aspect of the present invention provides a battery pack, which includes the battery module described in the fourth aspect of the present invention.

[0017] The sixth aspect of the present invention provides a device, which includes the secondary battery described in the third 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 positive electrode sheet for a 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. The first lithium nickel transition metal oxide is a secondary particle subjected to a coating treatment, and the second lithium nickel transition metal oxide is a single crystal or quasi-single crystal structure single particle. By regulating the particle size distribution of the positive electrode active material after mixing and the OI value of the sheet, the compressive strength of the positive electrode active material particles in the positive electrode sheet is improved, the problem of particle cracking of the positive electrode active material particles is effectively suppressed, and at the same time, the relative content of the (003) crystal plane perpendicular to the positive electrode sheet is reduced, so that the prepared secondary battery (for example, a lithium ion battery) has characteristics such as high energy density, low gas generation amount, and low sheet expansion rate, and has good industrialization prospects.

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

[0021] Figure 1 is a perspective view of an embodiment of the battery.

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

[0023] Figure 3 is a perspective view of an embodiment of the battery module.

[0024] Figure 4 is a perspective view of an embodiment of the battery pack.

[0025] Figure 5 is Figure 4 an exploded view of

[0026] Figure 6 is a schematic view of an embodiment of the device with the battery as a power source.

[0027] Among them, the reference numerals are explained as follows:

[0028] 1 Battery pack

[0029] 2 Upper box body

[0030] 3 Lower box body

[0031] 4 Battery module

[0032] 5 Battery

[0033] 51 Housing

[0034] 52 Electrode assembly

[0035] 53 Top cover assembly DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] To make the object, technical solutions and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below with reference to 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 sheet

[0038] In a first aspect of the present invention, there is provided a positive electrode sheet for a secondary battery. The positive electrode sheet 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 < Dv90 / Dv10 * Dv50 < 80, unit: μm;

[0044] When the tap 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 - 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%; D v50 is the particle size (unit: μm) corresponding to when the cumulative volume distribution percentage of the sample reaches 50%; D v 90 is the particle size (unit: μm) corresponding to when the cumulative volume distribution percentage of the sample reaches 90%. The OI of the positive electrode sheet is 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 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, and the positive electrode active material includes a first lithium nickel transition metal oxide and a second lithium nickel transition metal oxide. The first substrate in 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-metal oxide. The second lithium nickel transition metal oxide is a single crystal or near-single crystal morphology particle. In the present invention, near-single crystal generally means that the size of the primary particles is greater than 1 μm, but there is a certain degree of aggregation of the primary particles; single crystal generally means that the size of the primary particles is greater than 1 μm and there is no obvious aggregation. By regulating the particle size distribution of the positive electrode active material and the OI value of the positive electrode sheet after mixing, the present invention effectively inhibits the problem of particle cracking of the positive electrode active material particles, while increasing the compressive strength of the positive electrode active material particles in the positive electrode sheet, reducing the relative amount of the (003) crystal plane of the positive electrode active material in the positive electrode sheet, effectively solving the problems of the pole piece expansion rate and gas generation, and thus obtaining an electrochemical energy storage device with high energy density, low pole piece expansion rate, and low gas generation.

[0047] In the positive electrode sheet provided by the present invention, the tap density of the positive electrode sheet is 3.3 g / cm 3 ~3.5 g / cm 3 When it is, the OI of the positive electrode sheet can be 10 - 15, 15 - 20, 20 - 25, 25 - 30, 30 - 35, or 35 - 40, and preferably can be 10 - 20. Generally speaking, the OI value of the positive electrode sheet reflects the overall orientation degree of the crystal planes of the positive electrode active material in the pole piece, and is closely related to various process parameters such as the coating speed, drying, and cold pressing in the pole piece manufacturing process. If the OI value of the positive electrode sheet is too high, it means that the relative amount of the (003) crystal plane perpendicular to the length direction of the positive electrode sheet is too high, reflecting that a relatively serious texture appears in the positive electrode sheet after cold pressing, and the pole piece is prone to expansion during the charge and discharge process of the battery; however, if the OI value of the positive electrode sheet is too low, it indicates that there is no obvious orientation of the positive electrode active material in the positive electrode sheet at this time, the particle strength is too low, and particle breakage is likely to occur during cold pressing and in the later stage of cycling, leading to gas generation problems.

[0048] In the positive electrode sheet 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 as shown in Formula II:

[0049] Li 1+a2 Nix2 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 O2, LiNi 0.65 Co 0.15 Mn 0.2 O2, LiNi 0.65 Co 0.12 Mn 0.23 O2, LiNi 0.65 Co 0.1 Mn 0.25 O2, LiNi 0.65 Co 0.05 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.75 Co 0.1 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co0.05 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 may 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 may 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 may 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 may 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 to 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 - D v10) / TD < 8. Specifically, (D v 90 - D v The value range of 10) / 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 has the unit of μm; TD is the tapped 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 10) / TD takes values within the above range, the particle size distribution of different morphologies of the positive electrode active material is moderate, and the interstitial volume between particles is low, which is beneficial to improving the compaction density of the positive electrode sheet.

[0055] In the positive electrode sheet provided by the present invention, the tapped density TD of the positive electrode active material can be 2.2 g / cm 3 ~2.8 g / cm 3 , 2.2 g / cm 3 ~2.3 g / cm 3 , 2.3 g / cm 3 ~2.4 g / cm 3 , 2.4 g / cm 3 ~2.5 g / cm 3 , 2.5 g / cm 3 ~2.6 g / cm 3 , 2.6 g / cm 3 ~2.7 g / cm 3 , or 2.7 g / cm 3 ~2.8 g / cm 3 . In the present invention, TD is the tapped density of the powder of the positive electrode active material. The specific measurement method of the tapped density of the powder can include: filling the powder into a container (for example, a 25 mL container, and for another example, the container used can be a graduated cylinder), after vibrating the container (for example, the specific vibration conditions can be: the vibration frequency is 250 times / minute, the amplitude is 3 mm, and vibrate 5000 times), the mass of the powder per unit volume is the tapped density of the powder. Generally speaking, the larger TD is, the more beneficial it is to achieve a high compaction 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 there is a certain upper limit.

[0056] In the positive electrode sheet provided by the present invention, the first lithium nickel transition metal oxide can be spherical particles, and the sphericity γ of the first lithium nickel transition metal oxide can be 0.7 to 1. Specifically, the sphericity γ of the first lithium nickel transition metal oxide can 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 can be measured in the following manner: in the SEM photograph of the cross-section of the positive electrode sheet, at least 30 secondary particles with a cross-sectional diameter greater than the positive electrode active material D v by a value of 10 are selected, and the ratio of the maximum inscribed circle radius (R max ) to the minimum circumscribed circle radius (R min ) of each secondary particle in the cross-sectional SEM image is measured, and the average value is obtained, and thus γ can be obtained. In the present invention, the first lithium nickel transition metal oxide is a secondary particle. When the sphericity of the secondary particle is within the above range, it indicates that the sizes of the primary particles in the secondary particle are uniform and the distribution is relatively uniform, the secondary particle is relatively compact, and the mechanical strength is relatively high.

[0057] In the positive electrode sheet provided by the present invention, the ratio of the longest diameter L max to the shortest diameter L min of the second lithium nickel transition metal oxide 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 can be measured in the following manner: in the SEM photograph of the cross-section of the positive electrode sheet, at least 30 single crystal or single crystal-like morphology particles with a cross-sectional diameter greater than the positive electrode active material D v by a value of 10 are selected, and the ratio of the longest diameter (L max ) to the shortest diameter (L min ) of each particle in the cross-sectional SEM image is measured, and the average value is obtained, and thus L max / L min can be obtained. In the present invention, the second lithium nickel transition metal oxide is a particle with a single crystal or single crystal-like morphology. When the L max / L minWhen within the above range, after being mixed with secondary particles having a sphericity between 0.7 and 1, it can better fill the interstitial volume of the secondary particles. While improving the compaction density of the positive electrode sheet and the volumetric energy density of the battery, it can also effectively suppress the volume expansion rate of the positive electrode sheet during cycling and improve the cycling performance.

[0058] In the positive electrode sheet provided by the present invention, the D v 50(L) of the first lithium nickel transition metal oxide can 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 v 50(S) of the second lithium nickel transition metal oxide 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 in a polycrystalline form (secondary particles formed by aggregation of multiple primary particles), the second lithium nickel transition metal oxide is a single crystal or quasi-single crystal morphology particle, and the first lithium nickel transition metal oxide has a relatively large particle size distribution as a whole relative to the second lithium nickel transition metal oxide. The particle size distribution D v 50(L) and D v 50(S) 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, when the ratio of 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 is within the above range, it is beneficial to suppress the particle cracking problem of the secondary particle high-nickel material with a relatively large particle size, ensure that the positive active material can exhibit a relatively high specific capacity, and at the same time improve the mechanical strength and compaction density of the overall positive electrode sheet.

[0059] In the positive electrode tab provided by the present invention, the weight percentage content of the first lithium nickel transition metal oxide can be 50% - 90%, 85% - 90%, 80% - 85%, 75% - 80%, 70% - 75%, 65% - 70%, 60% - 65%, 55% - 60%, or 50% - 55%, and preferably can be 60% - 85%. The weight percentage content of the second lithium nickel transition metal oxide can be 10% - 50%, 10% - 15%, 15% - 20%, 20% - 25%, 25% - 30%, 30% - 35%, 35% - 40%, 40% - 45%, or 45% - 50%, and preferably can be 15% - 40%. In the present invention, by controlling the weight percentages of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide in the positive electrode tab within the above ranges, the OI value of the positive electrode tab can be adjusted to a certain extent, and at the same time, the compaction density and mechanical strength of the tab can be improved.

[0060] In the positive electrode tab provided by the present invention, the second lithium nickel transition metal oxide may further include a second coating layer 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 tab provided by the present invention, the first coating layer and / or the second coating layer can be a metal oxide and / or a non-metal oxide. For example, it can be an oxide containing only a metal element or a non-metal element, or an oxide containing both a metal element and a non-metal element. Among the above oxides, the metal element can usually be, for example, aluminum, zirconium, zinc, titanium, silicon, tin, tungsten, yttrium, cobalt, barium, etc., and the non-metal element can usually be, for example, phosphorus, boron, etc. Specifically, the first coating layer and / or the second coating layer can be one or a combination of more than one of, but not limited to, 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, etc. In the present invention, the coating layer of the positive active material is selected from the above metal oxides and / or non-metal oxides. The oxide coating layer has a good bonding force with the substrate, and the coating layer is not easily detached during the charge and discharge process. By reducing the part of the contact area between the substrate and the electrolyte, the surface of the high-nickel cathode material can be effectively modified, the side reaction between the cathode material and the electrolyte can be reduced, and thus the gas generation phenomenon of the battery can be effectively inhibited.

[0062] In the positive electrode material provided by the present invention, the first coating layer preferably contains at least one metal element oxide and one non-metal element oxide simultaneously. The oxides containing the above elements can not only improve the adhesion stability of the coating layer on the surface of the secondary particle substrate, but also endow the coating layer with certain ionic conductivity and electronic conductivity, reducing the influence of the coating layer on the polarization problem of the positive electrode material.

[0063] Preparation method of positive electrode sheet

[0064] In the second aspect of the present invention, a preparation method of a positive electrode sheet for a secondary battery provided in the first aspect of the present invention is provided. A suitable method for preparing a 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] After mixing the positive electrode active material, a binder, and a conductive agent to form a slurry, it is coated on a 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] In the preparation method of the positive electrode sheet provided by the present invention, it may include: providing a first lithium nickel transition metal oxide. The method for 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; performing a coating treatment on the first substrate to provide the first lithium nickel transition metal oxide. Those skilled in the art can select appropriate raw materials and ratios according to the element 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 formulated 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 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, and the lithium-containing compound can be a combination of one or more of, including but not limited to, LiOH·H2O, LiOH, Li2CO3, Li2O, etc. The M source can generally be a compound containing the M element. The above-mentioned compound containing the M element can be one or several of oxides, nitrates, and carbonates containing at least one element among Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, Co, and Mn. The X source can be a compound containing the X element. The above-mentioned compound containing the X element can be a combination of one or more of, including but not limited to, LiF, NaCl, etc. The sintering conditions for the raw materials of the substrate of the first lithium nickel transition metal oxide can be sintering conditions of 700°C to 900°C and an oxygen concentration ≥ 20%. The method for coating the first substrate can specifically include: sintering the first substrate in the presence of a compound containing a coating element. The compound containing the coating element can be an oxide, nitrate, phosphate, carbonate, etc. containing one or more elements among Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, P, etc. The usage amount of the coating element can generally be ≤ 2 wt%. The sintering conditions in the coating treatment can be 200°C to 700°C.

[0069] In the method for preparing the positive electrode sheet provided by the present invention, it can include: providing a second lithium nickel transition metal oxide. The method for providing the second lithium nickel transition metal oxide should be known to those skilled in the art. For example, it can include: mixing and sintering the raw materials of the substrate of the second lithium nickel transition metal oxide to provide a second substrate; performing a coating treatment on the second substrate to provide a second lithium nickel transition metal oxide. Those skilled in the art can select appropriate raw materials and ratios according to the elemental composition of the second lithium nickel transition metal oxide to further prepare and obtain the second substrate. For example, the raw materials of the second lithium nickel transition metal oxide can 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 formulated 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 can be, including but 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, and the lithium-containing compound can be a combination of one or more of, including but not limited to, LiOH·H2O, LiOH, Li2CO3, Li2O, etc. The M' source can generally be a compound containing the M element. The above-mentioned compound containing the M' element can be one or several of oxides, nitrates, and carbonates containing at least one element among Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, Co, and Mn. The X' source can be a compound containing the X' element. The above-mentioned compound containing the X' element can be a combination of one or more of, including but not limited to, LiF, NaCl, etc. The sintering conditions for the raw materials of the substrate of the second lithium nickel transition metal oxide can be sintering conditions of 750 °C to 950 °C and an oxygen concentration ≥ 20%. The method for coating the second substrate can specifically include: sintering the second substrate in the presence of a compound containing a coating element. The compound containing a coating element can be one or more of oxides, nitrates, phosphates, carbonates, etc. containing elements such as Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, and P. The usage amount of the coating element can generally be ≤ 2 wt%. The sintering conditions in the coating treatment can be 200 °C to 700 °C.

[0070] In the method for preparing the positive electrode plate provided by the present invention, the binder usually includes a fluorinated polyolefin binder. Relative to the fluorinated polyolefin binder, water is usually a good solvent, that is, the fluorinated polyolefin binder usually has good solubility in water. For example, the fluorinated polyolefin binder can be, including but not limited to, polyvinylidene fluoride (PVDF), vinylidene fluoride copolymer, etc. or their modified (such as carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives. In the positive electrode active material layer, the mass percentage content of the binder can be due to the poor conductivity of the binder itself, so the dosage 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% - 3wt% to obtain a lower electrode plate impedance.

[0071] In the method for preparing the positive electrode plate provided by the present invention, the conductive agent of the positive electrode plate can be various conductive agents applicable to 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 nanotube (CNT), Ketjen black, etc. The weight of the conductive agent can account for 1wt% - 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 plate is 1.0wt% - 5.0wt%.

[0072] In the method for preparing the positive electrode plate provided by the present invention, the positive electrode current collector of the positive electrode plate can usually be a laminate. The positive electrode current collector is usually a structure or part that can collect current. The positive electrode current collector can be various materials applicable to be used as the positive electrode current collector of a lithium ion battery in the art. For example, the positive electrode current collector can be, including but not limited to, metal foil, etc., and more specifically can be, including but not limited to, copper foil, aluminum foil, etc.

[0073] Secondary battery

[0074] The third aspect of the present invention provides a secondary battery, including the positive electrode plate 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 embodiments in which the secondary battery is a lithium ion battery are shown, but the present invention is not limited thereto.

[0076] Figure 1 is a perspective view of a specific embodiment of a lithium ion battery. Figure 2 is Figure 1 exploded view of. Refer to Figures 1 to 2, the 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 received within the housing 51. The number of the electrode assemblies 52 is not limited and may be one or more.

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

[0078] In a lithium-ion battery, it may include a positive electrode tab, a negative electrode tab, a separator interposed between the positive electrode tab and the negative electrode tab, and an electrolyte. Among them, the positive electrode tab may be the positive electrode tab provided in the first aspect of the present invention. The method for preparing a lithium-ion battery should be known to those skilled in the art. For example, the positive electrode tab, the separator, and the negative electrode tab may each be a laminate, so that they can be cut into a target size and stacked in sequence, or wound to a target size to form an electrode core, and further combined with the electrolyte to form a lithium-ion battery.

[0079] In a lithium-ion battery, the negative electrode tab generally may include 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 generally includes a negative electrode active material. The negative electrode active material may be various materials suitable for negative electrode active materials of lithium-ion batteries in the art. For example, it may be a combination of one or more of, including but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form an alloy with lithium. Among them, the graphite may be selected from a combination of one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based materials may be selected from a combination of one or more of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; the tin-based materials may be selected from a combination of one or more of elemental tin, tin oxides, and tin alloys. The negative electrode current collector is generally a structure or part for collecting current. The negative electrode current collector may be various materials suitable for being a negative electrode current collector of a lithium-ion battery in the art. For example, the negative electrode current collector may be, including but not limited to, a metal foil, and more specifically, it may be, including but not limited to, a copper foil, etc.

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

[0081] In a lithium-ion battery, the electrolyte typically includes an electrolyte salt and a solvent. Suitable electrolytes for lithium-ion batteries should be known to those skilled in the art. For example, the electrolyte salt usually includes lithium salts, etc. More specifically, the lithium salt can be an inorganic lithium salt and / or an organic lithium salt, etc. Specifically, it can include one or a combination of more than one of, but not limited to, 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 can be between 0.8 mol / L and 1.5 mol / L; for another example, the solvent used in the electrolyte can be the solvent of various electrolytes suitable for lithium-ion batteries in the art, usually a non-aqueous solvent, preferably an organic solvent. Specifically, it can include one or a combination of more than one of, but not limited to, ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, etc. or their halogenated derivatives.

[0082] Battery module

[0083] In the fourth aspect of the present application, a battery module is provided, which includes the secondary battery provided in the third aspect of the present application. The battery module usually can include one or more secondary batteries. The battery module can be used as a power source or an 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 the battery module.

[0085] Refer to Figure 3 , the battery module 4 includes a plurality of batteries 5. The plurality of batteries 5 are arranged longitudinally.

[0086] Battery pack

[0087] In the 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 provided in the fourth aspect.

[0088] Figure 4 is a perspective view of a specific embodiment of the battery pack 1. Figure 5 is Figure 4 exploded view of.

[0089] Refer to Figure 4 and Figure 5 , the battery pack 1 includes an upper box body 2, a lower box body 3, and a battery module 4.

[0090] The upper box body 2 and the lower box body 3 are assembled together to form a space for accommodating the battery module 4. The battery module 4 is placed in the space of the assembled upper box body 2 and lower box body 3. The output pole of the battery module 4 passes through one or both of the upper box body 2 and the lower box body 3 to supply power to the outside or charge from the outside. The number and arrangement of the battery modules 4 used in the battery pack 1 can be determined according to actual needs. The battery pack 1 can be used as a power source or an energy storage device.

[0091] Device

[0092] The sixth aspect of the present invention provides a device, which includes the secondary battery provided by the third aspect of the present invention, and the secondary battery is used as the power source of the device.

[0093] Figure 6 is a perspective view of a specific embodiment of the above device. In Figure 6 , 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, according to the actual usage form, the device provided by the sixth aspect of the present application may include the battery module 4 provided by the fourth aspect of the present application. Of course, the device provided by the sixth aspect of the present application may also include the battery pack 1 provided by the fifth aspect of the present application.

[0094] The beneficial effects of the present invention will be further described below in conjunction with embodiments.

[0095] In order to make the invention purpose, 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. However, it should be understood that the embodiments of the present invention are only for explaining the present invention and are not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. For the embodiments without specific experimental conditions or operation conditions, they are made according to conventional conditions or according to the conditions recommended by the material suppliers.

[0096] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between the clearly mentioned steps, unless otherwise specified; it should also be understood that the combined connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before and after the combined devices / apparatuses or the insertion of other devices / apparatuses between the two clearly mentioned devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbers of the method steps are only convenient tools for identifying the method steps, rather than restricting the arrangement order of the method steps or limiting the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of the present invention.

[0097] In the following examples, the reagents, materials and instruments used can be obtained commercially without special instructions.

[0098] Example 1

[0099] 1. Preparation of the positive electrode active material

[0100] 1) Preparation of the precursors of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide: A 1 mol / L solution is prepared by mixing nickel sulfate, manganese sulfate, and cobalt sulfate in a molar ratio of 8:1:1, and the precursor of the first lithium nickel transition metal oxide with a particle size D v 50 (L) of 9.7 μm is prepared by using the hydroxide co-precipitation technique; a 1 mol / L solution is prepared by mixing nickel sulfate, manganese sulfate, and cobalt sulfate in a molar ratio, and the precursor of the second lithium nickel transition metal oxide with a particle size of 2.9 μm is prepared by using the hydroxide co-precipitation technique. During the preparation of the precursors, the particle size and morphology of the precursors of the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide are regulated by controlling the reaction time, pH value during co-precipitation, and ammonia concentration;

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

[0102] The above-mentioned precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2 of the first lithium nickel transition metal oxide and the Li compound LiOH·H2O are mixed in a molar ratio of 1:1.05, placed in a mixing device for mixing, and then sintered in an atmosphere furnace at 830 °C. After cooling, it is mechanically ground to obtain the substrate of the first lithium nickel transition metal oxide;

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

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

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

[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 h to form the coating layer of lithium nickel transition metal oxide B, that is, the surface-modified second lithium nickel transition metal oxide. The D v 50, L max / L min ratio 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 are mixed evenly 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, Dv90 / Dv10*Dv50 and the positive electrode sheet OI of the positive electrode active material of Example 1 are shown in Table 1.

[0108] 2. Preparation of the battery

[0109] 1) Preparation of the positive electrode sheet

[0110] Step 1: Mix the above-obtained positive electrode active material, binder polyvinylidene fluoride, and conductive agent acetylene black in a mass ratio of 98:1:1, add N-methylpyrrolidone (NMP), and stir evenly under a vacuum mixer to obtain a positive electrode paste; evenly coat the positive electrode paste on an aluminum foil with a thickness of 12 μm;

[0111] Step 2: Dry the coated electrode sheet in an oven at 100 °C to 130 °C, and obtain a positive electrode sheet through cold pressing and slitting.

[0112] 2) Preparation of negative electrode sheet

[0113] Mix the negative electrode active material graphite, thickening agent sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black in a mass ratio of 97:1:1:1, add deionized water, and obtain a negative electrode paste under a vacuum mixer; evenly coat the negative electrode paste on a copper foil with a thickness of 8 μm; dry the copper foil at room temperature and then transfer it to an oven at 120 °C for drying for 1 h, and then obtain a negative electrode sheet through cold pressing and slitting.

[0114] 3) Preparation of electrolyte

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

[0116] 4) Preparation of separator

[0117] Select a polypropylene separator with a thickness of 12 μm.

[0118] 5) Preparation of battery

[0119] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, so that the separator is between the positive and negative electrode sheets to play a role in isolation. After winding into a square bare battery core, put it into an aluminum-plastic film, then bake it at 80 °C to remove water, inject the corresponding non-aqueous electrolyte, seal it, and after processes such as standing, hot and cold pressing, formation, clamping, and grading, obtain a finished battery.

[0120] Example 2

[0121] The preparation methods of the positive electrode sheet and the battery in Example 2 refer to Example 1, the difference is 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 and (D of the obtained positive electrode active material v 90-D v10) / TD, Dv90 / Dv10*Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0122] Example 3

[0123] In Example 3, the preparation methods of the positive electrode sheet and the battery refer to 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. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10*Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0124] Example 4

[0125] In Example 4, the preparation methods of the positive electrode sheet and the battery refer to Example 1, except that the element ratio of Ni:Co:Mn in the second lithium nickel transition metal oxide is 5:2:3, and the particle size D v 50(S) = 4.3 μm, L max / L min = 1.5, the coating elements are Al and Ti, the compounds used in the sintering process are alumina and titanium oxide, and the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 8:2. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10*Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0126] Example 5

[0127] In Example 5, the preparation methods of the positive electrode sheet and the battery refer to Example 1, except that the element ratio of Ni:Co:Mn in the first lithium nickel transition metal oxide is 6:2:2, and the particle size D v 50(L) = 9.6 μm, the sphericity γ = 0.81. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10*Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0128] Example 6

[0129] In Example 6, the preparation methods of the positive electrode sheet and the battery refer to Example 1, except that the element ratio of Ni:Co:Mn in the second lithium nickel transition metal oxide is 9:0.5:0.5, and the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 8:2. The TD, (D v90 - D v 10) / TD, Dv90 / Dv10 * Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0130] Example 7

[0131] In Example 7, the preparation methods of the positive electrode sheet and the battery refer to Example 1, except that the coating element of the first lithium nickel transition metal oxide is B, that is, the compound corresponding to Al is not used for sintering. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10 * Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0132] Example 8

[0133] In Example 8, the preparation methods of the positive electrode sheet and the battery refer to Example 1, except that the coating element of the first lithium nickel transition metal oxide is B, that is, the compound corresponding to Al is not used for sintering, and the coating element of the second lithium nickel transition metal oxide is Al and B. The compounds used in the sintering process are aluminum oxide and boron oxide. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10 * Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0134] Example 9

[0135] In Example 9, the preparation methods of the positive electrode sheet and the battery refer to Example 1, except that the element ratio of Ni:Co:Mn in the first lithium nickel transition metal oxide is 8.3:1.4:0.3, the particle size D v 50(L) = 12.3 μm, the sphericity γ = 0.85, the coating element is Ba, and the corresponding compound used for coating is barium oxide. The particle size D v 50(S) = 2.2 μm, L max / L min = 1.7, and the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 6:4. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10 * Dv50, and the OI of the positive electrode sheet are shown in Table 1.

[0136] Example 10

[0137] The preparation methods of the positive electrode plate and the battery in Example 10 refer to Example 1, the difference is that the element ratio of Ni:Co:Mn in the first lithium nickel transition metal oxide is 8.3:1.4:0.3, and the particle size D v 50(L) of the first lithium nickel transition metal oxide is 12.3 μm, the sphericity γ is 0.85, the compound used for coating is barium oxide, the element ratio of Ni:Co:Mn in the second lithium nickel transition metal oxide is 5:2:3, and the particle size D v 50(S) of the second lithium nickel transition metal oxide is 4.3 μm, Lmax / Lmin = 1.5, the coating elements are Al and Ti, the compounds used in the sintering process are alumina 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, and the TD, (D v 90 - D v 10) / TD, Dv90 / Dv10 * Dv50 of the prepared positive electrode active material and the OI of the positive electrode plate are shown in Table 1.

[0138] Comparative Example 1

[0139] The preparation methods of the positive electrode plate and the battery in Comparative Example 1 refer to Example 1. The particle size D v 50(L) of the first lithium nickel transition metal oxide is 7.8 μm, the sphericity γ is 0.77, the element ratio of Ni:Co:Mn in the second lithium nickel transition metal oxide is 5:2:3, and the particle size D v 50(S) of the second lithium nickel transition metal oxide is 4.3 μm, L max / L min = 1.5, the coating elements are Al and Ti, the compounds used in the sintering process are alumina and titanium oxide, and the TD, (D v 90 - D v 10) / TD, Dv90 / Dv10 * Dv50 of the prepared positive electrode active material and the OI of the positive electrode plate are shown in Table 1.

[0140] Comparative Example 2

[0141] The preparation methods of the positive electrode plate and the battery in Comparative Example 2 refer to Example 1. The difference is that in the preparation method of the positive electrode active material, the second lithium nickel transition metal oxide is not used. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10 * Dv50 of the prepared positive electrode active material and the OI of the positive electrode plate are shown in Table 1.

[0142] Comparative Example 3

[0143] The preparation methods of the positive electrode sheet and the battery in Comparative Example 3 refer to Example 1, the difference is 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 of the obtained positive electrode active material and the OI of the positive electrode sheet are shown in Table 1.

[0144] Comparative Example 4

[0145] In Comparative Example 4, the preparation methods of the positive electrode sheet and the battery refer to Example 9, the difference is that the particle size D v 50(L) of the first lithium nickel transition metal oxide is 16.8 μm, and the particle size D v 50(S) of the second lithium nickel transition metal oxide is 2.9 μm, L max / L min = 2, and the mass ratio between the first lithium nickel transition metal oxide and the second lithium nickel transition metal oxide is 9:1. The TD, (D v 90 - D v 10) / TD, Dv90 / Dv10*Dv50 of the obtained positive electrode active material and the OI of the positive electrode sheet are shown in Table 1.

[0146] Comparative Example 5

[0147] In Comparative Example 5, the preparation methods of the positive electrode sheet and the battery refer to Example 1, the difference is that the first lithium nickel transition metal oxide is not used during the preparation of the positive electrode sheet. The TD, (Dv90 - Dv10) / TD, Dv90 / Dv10*Dv50 of the obtained positive electrode active material and the OI of the positive electrode sheet are shown in Table 1.

[0148] Comparative Example 6

[0149] In Comparative Example 6, the preparation methods of the positive electrode sheet and the battery refer to Example 1, the difference is that during the preparation of the first lithium nickel transition metal oxide, the coating treatment is not carried out. The TD, (Dv90 - Dv10) / TD, Dv90 / Dv10*Dv50 of the obtained positive electrode active material and the OI of the positive electrode sheet are shown in Table 1.

[0150] Detection method

[0151] (1) Test method for the sphericity of secondary particles:

[0152] Take SEM photos of the cross-section of the positive electrode sheet, select at least 30 secondary particles with a cross-sectional diameter above the D v 10 value of the positive electrode active material, and measure the maximum inscribed circle radius (R max ) and the minimum circumscribed circle radius (R min) ratio, calculate the average value, and the sphericity γ of the secondary particles can be obtained.

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

[0154] In the SEM photos of the cross-section of the positive electrode sheet, select at least 30 single crystal or single crystal-like particles with a cross-sectional diameter above the value of D of the positive electrode active material v 10. Measure the ratio of the longest diameter (L max ) to the shortest diameter (L min ) of each particle in the SEM image, calculate the average value, and L max / L min can be obtained. The test results of each example and comparative example are shown in Table 2.

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

[0156] Fill 10 g of powder into a graduated cylinder with a range of 25 mL. Vibrate the filled graduated cylinder at a vibration frequency of 250 times / minute, an amplitude of 3 mm, and vibrate 5000 times. Read the volume occupied by the powder in the graduated cylinder at this time, and the mass of the powder per unit volume can be calculated, which is the tapped density TD of the powder. The test results of each example and comparative example are shown in Table 2.

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

[0158] Place the prepared positive electrode sheet horizontally in an XRD diffractometer to test the XRD diffraction spectrum of the positive electrode sheet, and calculate 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, which is the OI value of the positive electrode sheet. The test results of each example and comparative example are shown in Table 2.

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

[0160] 1) Cut the electrode sheet into a membrane with a length of 1000 mm;

[0161] 2) Roll the positive electrode sheet under a certain pressure. Since the aluminum foil has ductility, the length of the membrane becomes 1006 mm;

[0162] 3.) Punch a small round piece of 1540.25 mm 2 . Measure the weight and thickness of the small round piece, and the tap density can be calculated;

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

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

[0165] At 45 °C, the lithium-ion battery is charged at a constant current of 1C until the voltage reaches 4.2V, then charged at a constant voltage of 4.2V until the current reaches 0.05C, and then discharged at a constant current of 1C until the final voltage is 2.8V. Record the discharge capacity of the first cycle. Then, charge and discharge the battery according to the above operation 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 example and comparative example are shown in Table 2.

[0167] (7) Test of cyclic DCR growth:

[0168] At 25 °C, the battery is charged at a constant current / constant voltage of 1C (charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C) to 100% SOC, then discharged at a constant current of 1C for 30 minutes, left idle for 60 minutes, and record the voltage U1 after idling; then discharge at a constant current of 4C for 30 seconds, and record the voltage U2 after discharge;

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

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

[0171] Table 1

[0172]

[0173] Table 2

[0174]

[0175]

[0176] By comparing the examples and comparative examples, it can be seen that by mixing the first lithium nickel transition metal oxide with a secondary particle morphology and the second lithium nickel transition metal oxide with a single crystal or quasi-single crystal morphology, and controlling the particle size distribution of the positive active material and the OI value of the positive electrode sheet after mixing, while improving the tap density, it is possible to improve particle cracking during cycling, improve the cycle life, and the DCR growth during cycling. The surface-coated metal oxides and non-metal oxides can significantly improve the cycle life and the cyclic DCR growth.

[0177] The above is only a preferred embodiment of the present invention and does not impose any formal or substantial limitations on the present invention. It should be noted that for those of ordinary skill in the art of this technology, several improvements and supplements can still be made without departing from the method of the present invention, and these improvements and supplements should also be regarded as within the protection scope of the present invention. Any equivalent changes in the form of minor modifications, decorations, and evolutions that can be made by those skilled in the art without departing from the spirit and scope of the present invention by using the technical content disclosed above are 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 still fall within the scope of the technical solution of the present invention.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode plate, and 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, and 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, and the chemical formula of the first substrate is as shown in Formula I: Li 1+a1 Ni x1 Co y1 Mn z1 M b1 O 2-e1 X e1 (I) In Formula I, -0.1 < a1 < 0.1, 0.8 ≤ 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; The first coating layer is selected from metal oxides and / or non-metal oxides; The first lithium nickel transition metal oxide is spherical particles, and the sphericity γ of the first lithium nickel transition metal oxide particles is 0.7 to 1; The second lithium nickel transition metal oxide is single crystal or quasi-single crystal morphology particles; 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 Mn z2 M’ b2 O 2-e2 X’ e2 (II) In Formula II, -0.1 < a2 < 0.1, 0.8 ≤ 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, Mn, and X' is selected from F and / or Cl; The longest diameter L of the second lithium nickel transition metal oxide particles max and the shortest diameter L min satisfy the dimensional ratio: 1 ≤ L max / L min ≤3; The particle size distribution of the positive electrode active material satisfies: 40 < Dv90 / Dv10 * Dv50 < 80, with the unit of μm; The tap density of the positive electrode sheet is 3.3 g / cm 3 ~3.5 g / cm 3 When it is, the OI of the positive electrode sheet is 10 to 40.

2. The secondary battery according to claim 1, wherein The relative contents x1 and x2 of Ni element in the molecular formulas of the first substrate and the second substrate satisfy: |x1 - x2| ≤ 0.

1.

3. The secondary battery according to claim 2, wherein The x1 and x2 satisfy: 0 < x1 - x2 < 0.

1.

4. The secondary battery according to claim 1, wherein The tap density of the positive electrode sheet is 3.3 g / cm 3 ~3.5 g / cm 3 When it is, the OI of the positive electrode sheet is 10 to 20.

5. The secondary battery according to claim 1, wherein The positive electrode active material satisfies: 4.4 < (D v 90 - D v 10) / TD<8, Among them, D v 10. D v 90 has the unit of μm; TD is the tap density of the positive electrode active material, with the unit of g / cm 3 .

6. The secondary battery according to claim 5, wherein, 4.6 < (D v 90 - D v (10) / TD < 6.5。 7. The secondary battery according to claim 5, wherein The tapped density TD of the positive active material is 2.2 g / cm 3 to 2.8 g / cm 3 .

8. The secondary battery according to claim 1, wherein 1.5 ≤ L max / L min ≤ 3.

9. The secondary battery according to claim 1, wherein The D of the first lithium nickel transition metal oxide v 50(L) is 5 μm to 18 μm, and the D of the second lithium nickel transition metal oxide v 50(S) is 1 μm to 5 μm.

10. The secondary battery according to claim 9, wherein Said D v 50 (L) and D v 50 (S) satisfy: 2 ≤ D v 50(L) / D v 50(S) ≤ 7 11. The secondary battery according to claim 1, wherein In the positive electrode active material, the weight percentage content of the first lithium nickel transition metal oxide is 50% to 90%; And the weight percentage content of the second lithium nickel transition metal oxide is 10% to 50%.

12. The secondary battery according to claim 11, wherein The weight percentage content of the first lithium nickel transition metal oxide is 60% to 85%.

13. The secondary battery according to claim 11, wherein, The weight percentage content of the second lithium nickel transition metal oxide is 15% to 40%.

14. The secondary battery according to claim 1, characterized in that, The second lithium nickel transition metal oxide further includes 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.

15. The secondary battery according to claim 14, characterized in that, The second coating layer material is a metal oxide.

16. A battery module, characterized in that, Including the secondary battery according to any one of claims 1 to 15.

17. A battery pack, characterized in that, Including the battery module according to claim 16.

18. A device, characterized in that, Including the secondary battery according to any one of claims 1 to 15, and the secondary battery is used as the power source of the device.

19. The device according to claim 18, characterized in that, The device includes an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, an electric ship, and an energy storage system.

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