Patent Application
20230299281
The present disclosure claims priority to and benefits of Chinese Patent Application No. 202010821206.6, filed on Aug. 14, 2020. The entire content of the above-referenced application is incorporated herein by reference.
The present invention relates to the technical field of batteries, and in particular to a composite positive electrode material, a positive electrode plate and a preparation method thereof, and a battery.
Ternary materials, due to their high energy density, are widely used as a positive electrode material in electric vehicle batteries. Moreover, as the energy density requirement for electric vehicles continues to increase, ternary materials used have transitioned from LiNi1/3Co1/3Mn1/3O2 to LiNi0.5Co0.2Mn0.3O2, and even LiNi0.6Co0.2Mn0.2O2, LiNi0.8Co0.1Mn0.1O2, LiNiO2, NCA (Lithium-Nickel-Cobalt-Aluminum-Oxide) and other high-nickel materials.
However, the ternary high-nickel material has problems such as a poor cycle performance at a room temperature, increased DCIR (DC resistance at a specific load and discharge current) after cycles, serious gas production after cycles, and a poor safety performance. To solve the above problems of ternary high-nickel materials, the currently available technical solution is to improve the structural stability of the materials as much as possible, slow down the capacity decrease due to the phase transition of the materials during the long-term cycle process, and improve the safety of the materials, by optimization of coating, doping and sintering. This technical solution cannot essentially solve the change in the phase transition of the materials in a fixed charge/discharge voltage window, but only improves the structural stability of the materials.
To resolve at least one of the above technical problems, the present invention is provided. Specifically, in one aspect of the present invention, a composite positive electrode material is provided, which includes:
In an embodiment of the present invention, the ternary material has a nanohardness of 0.2-1.4 GPa, and the phase-transition material has a nanohardness of 1.5-3.5 GPa.
In an embodiment of the present invention, the ternary material has a tap density of 2.0-2.8 g/cm3, and the phase-transition material has a tap density of 0.8-1.5 g/cm3.
In an embodiment of the present invention, the ternary material has a D50 of 3.5-5.0 μm, and the primary particles in the phase-transition material have a D50 of 20-40 nm.
In an embodiment of the present invention, the ternary material has a chemical formula of LiNixCoyMz, where x+y+z=1, and M includes Mn, Al, Zr, Ti, Y, Sr or W.
In an embodiment of the present invention, the ternary material includes a nickel-cobalt-manganese ternary material or a nickel-cobalt-aluminum ternary material.
In an embodiment of the present invention, the phase-transition material has an olivine structure, and the phase-transition material has a chemical formula of LiAvBwPO4, where v+w=1, A comprises Fe, Co, Mn, Ni, Cr or V, and B comprises Fe, Co, Mn, Ni, Cr or V.
In an embodiment of the present invention, the phase-transition material comprises lithium manganese iron phosphate, lithium manganese vanadium phosphate, or lithium chromium iron phosphate.
In another aspect of the present invention, a method for preparing a composite positive electrode material according to the present invention is provided, which includes
In an embodiment of the present invention, the rotational speed of the mechanical blender is 4000-7000 r/min, and the blending time is 10-30 min.
In an embodiment of the present invention, the rotational speed of the mechanical blender is 4500-6500 r/min, and the blending time is 15-25 min.
In an embodiment of the present invention, the baking temperature of the composite material is 80-120° C., and the baking time is 0.5-2.5 hrs.
In an embodiment of the present invention, the baking temperature of the composite material is 95-105° C., and the baking time is 1-2 hrs.
In another aspect of the present invention, a positive electrode plate is provided, which includes a current collector and a composite positive electrode material according to the present invention provided on the current collector.
In an embodiment of the present invention, the intensity ratio of crystallographic orientation 003 to crystallographic orientation 110 is 10-100 after the positive electrode plate is compacted.
In another aspect of the present invention, a method for preparing the positive electrode plate according to the present invention is provided, which includes
In an embodiment of the present invention, before the final slurry is obtained, the method further includes adding an amount of lithium carbonate to the slurry.
In another aspect of the present invention, a battery is provided, which includes a positive electrode plate according to the present invention, a negative electrode plate, and a separator provided between the positive electrode plate and the negative electrode plate.
In the composite positive electrode material, the positive electrode plate and the preparation method thereof, and the battery proposed in the present invention, the positive electrode material includes a ternary single crystal material and a phase-transition material coated on the surface of the ternary single crystal material. On the one hand, the ternary single crystal material itself has the advantages of a good high-temperature performance, less gas production, and good safety. On the other hand, the phase-transition material coated on the surface of the ternary material increases the start temperature of thermal runaway of the ternary material and the battery and reduces the heat release during the thermal runaway process, thereby improving the safety. Moreover, by means of the phase-transition material, the phase transition of the ternary material in the charge/discharge voltage window is slowed down or delayed, and the capacity decrease caused by the phase transition of the ternary material during the long-term cycle process is slowed down, thereby improving the cycle performance of the battery, reducing the impedance increase of the material during the aging process, and improving the safety of the battery.
Further, in the embodiment of the present invention, the orientation of the ternary material in the 003 crystallographic orientation is restricted by defining the nanohardnesses of the ternary material and the phase-transition material, and higher electrode compacted density of the positive electrode plate is realized by defining the tap densities of the ternary material and the phase-transition material, thus ensuring the energy density of the battery.
To describe the technical solutions in the embodiments of the present invention more clearly, the following briefly describes the accompanying drawings required for describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.
In the following description, numerous specific details are given to facilitate a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, to avoid confusion with the present invention, some technical features known in the art are not described
It should be understood that the present invention can be implemented in different forms and should not be construed as being limited to the embodiments presented herein. Conversely, these embodiments are provided for the purpose of making the disclosure thorough and complete, and conveying the scope of the present invention fully to those skilled in the art. In the drawings, for the sake of clarity, the sizes and relative sizes of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout the present invention.
It should be understood that when an element or layer is referred to as being “on”, “adjacent to”, “connected to” or “coupled to” other elements or layers, it can be directly located on, adjacent, connected or coupled to the other elements or layers, or there may be an intervening element or layer. Conversely, when an element is referred to as being “directly on”, “directly adjacent to”, “directly connected to” or “directly coupled to” other elements or layers, no intervening element or layer is present. It should be understood that although the terms first, second, and third, etc. can be used to describe various elements, components, regions, layers and/or portions, these elements, components, regions, layers and/or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or portion from another element, component, region, layer or portion. Therefore, without departing from the teachings of the present invention, the first element, component, region, layer or portion discussed below may be expressed as a second element, component, region, layer or portion.
Terms indicating the spatial relationships such as “under”, “below”, “lower”, “beneath”, “above”, and “upper” are used herein for the convenience of description, to describe the relationship between one element or feature and other elements or features shown in the figure. It can be understood that in addition to the orientations shown in the figures, the terms indicating the spatial relationships include different orientations of a device in use and operation. For example, if the device in the figure is upside down, then an element or feature described as being “under”, “beneath” or “below” other elements will be oriented to be “above” the other elements or features. Therefore, the exemplary terms “under” and “below” may include both an upper and a lower orientation. The device can be otherwise oriented (rotated by 90 degrees or in other orientations) and the spatial descriptions used here are interpreted accordingly.
The terms are used herein merely for purpose of describing specific embodiments and not as a limitation of the present invention. When used herein, the singular forms “a”, “an” and “the” are also meant to include the plural form, unless otherwise clearly indicated. It should also be understood that the terms “consisting of” and/or “including”, when used in this specification, confirm the existence of the described features, integers, steps, operations, elements and/or components, but do not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components and/or groups. As used herein, the term “and/or” includes any and all combinations of related listed items.
For the purpose of thoroughly understanding the present invention, a detailed structure will be presented in the following description to explain the technical solution proposed in the present invention. Optional embodiments of the present invention are described in detail as follows. However, besides these detailed descriptions, the present invention may also have other implementations.
As described above, the ternary high-nickel material has problems such as a poor cycle performance at the room temperature, increased DCIR (DC resistance at a specific load and discharge current) after cycles, serious gas production after cycles, and a poor safety performance. To solve the above problems of ternary high-nickel materials, the currently available technical solution is to improve the structural stability of the materials as much as possible, slow down the capacity decrease due to the phase transition of the materials during the long-term cycle process, and improve the safety of the materials, by optimization of coating, doping and sintering. However, this technical solution cannot essentially solve the change in phase transition of the materials in a fixed charge/discharge voltage window, but only improves the structural stability of the materials. In the present invention, from the perspective of a plate design and a battery design, the cycle and safety performances of the materials are improved to overcome the current problems on the basis of improving the stability of the materials.
The idea of the present invention is to coat a phase-transition material on the surface of a ternary material to improve the cycle and safety performances of the ternary material on the basis of improving the structural stability of the main material. The general idea is to share more charge and discharge tasks on a charge and discharge stage of a ternary high-nickel material of about 4.25 V (relative to the potential of Li) and to slow down or delay the phase transition in the charge/discharge voltage window of the material by taking advantage of the charge and discharge characteristics of different materials. Moreover, the phase-transition material is evenly coated on the surface of the ternary material, and the coating layer has a heat isolation effect to increase the start temperature of thermal runaway of the material and reduce the heat released during the thermal runaway process.
As shown in
In an embodiment, the weight ratio of the ternary material to the phase-transition material is 80:20-99.8:0.2, for example, the weight ratio of the ternary material to the phase-transition material is 90:10 to 95:5.
In an embodiment of the present invention, the ternary material has a chemical formula of LiNixCoyMz, where x+y+z=1 and M includes, but is not limited to, Mn, Al, Zr, Ti, Y, Sr or W. For example, the ternary material includes a nickel-cobalt-manganese ternary material (i.e. NCM (Lithium-Nickel-Cobalt-Manganese-Oxide)) or a nickel-cobalt-aluminum ternary material (i.e. NCA). For example, the ternary material is a high-nickel ternary material of LiNixCoyMz where x is greater than 0.6.
The phase-transition material has a single crystal structure or a poly-crystalline structure. In an embodiment, the phase-transition material has an olivine structure, and the phase-transition material has a chemical formula of LiAvBwPO4, where v+w=1, A includes, but is not limited to, Fe, Co, Mn, Ni, Cr or V, and B includes, but is not limited to, Fe, Co, Mn, Ni, Cr or V. For example, the phase-transition material includes lithium manganese iron phosphate, lithium manganese vanadium phosphate, or lithium chromium iron phosphate. For example, the phase-transition material is lithium manganese iron phosphate (LMFP) having a structure of LiMnxFeyPO4, where x is a value in the range of 0.05-0.95, and preferably in the range of 0.5-0.85; y is a value in the range of 0.05-0.95, and preferably in the range of 0.15-0.5; and the material is a single crystal material.
In this embodiment, the phase-transition material may undergo phase transition between 4.0 and 2.0 V. When the phase-transition material and the ternary high-nickel material form a composite positive electrode material, the structural phase transition of the ternary high-nickel material at 4.25 V (relative to the potential of Li) can be weakened or delayed.
For example, the ternary material is NCM811, and the composite material is an LMFP coated ternary material, the CV curves of the positive electrode plates prepared therewith are shown in
Further, to better improve the cycle performance and safety of the battery in the present invention, the ternary material is a single crystal material, and the composite material is coated with a layer of phase-transition material, such as LMFP, on the surface of the single crystal ternary material. On the one hand, the ternary single crystal material itself has the advantages of a good high-temperature performance, less gas production, and good safety. On the other hand, the phase-transition material is evenly coated on the surface of the ternary material, and the coating layer has a heat isolation effect, to increase the start temperature of thermal runaway of the material and reduce the heat released during the thermal runaway process, thereby improving the safety performance of the material.
Furthermore, because the ternary material is a single crystal material, and the single crystal ternary material has the characteristic of orientation in (003) crystallographic orientation after the positive electrode plate is compacted. As shown in
Further, to better restrict the orientation of the ternary single crystal material in the 003 crystallographic orientation, in an embodiment of the present invention, the nanohardnesses of the ternary material and the coating material is defined. In an embodiment, the ternary material has a nanohardness of 0.001-5 GPa, and the coating material has a nanohardness of 0.01-10 GPa. In an embodiment, the ternary material has a nanohardness of 0.2-1.4 GPa, and the coating material has a nanohardness of 1.5-3.5 GPa. By defining the nanohardnesses of the ternary material and the coating material, the orientation of the ternary single crystal material in the 003 crystallographic orientation can be restricted, thus reducing the expansion of the ternary material and the positive electrode plate in the thickness direction, and improving the battery performance.
Further, in this embodiment, since the coating material is a material such as LMFP and the compacted density of LMFP is low, the energy density of the battery is affected. In the embodiment of the present invention, the tap densities of the ternary material and the coating material are defined, to realize higher an electrode compacted density of the positive electrode plate and ensure the energy density of the battery. In an embodiment of the present invention, the ternary material has a tap density of 2.0-2.8 g/cm3, and the phase-transition material has a tap density of 0.8-1.5 g/cm3.
Further, in this embodiment, to achieve a uniform distribution of the coating material on the surface of the ternary single crystal material, the coating material is a material including nano-scale primary particles. The ternary material has a D50 (median particle diameter) of 3.0-6.0 μm, and the primary particles in the coating material has a D50 of 10-50 nm.
Further, in an embodiment of the present invention, in order to improve the safety performance of the material and the battery, an amount of lithium carbonate can be added to the slurry of the composite positive electrode material. Since lithium carbonate can produce a gas when the battery fails, the reversal and the valve opening time of CID (current interrupt device) and an explosion-proof valve are advanced to prevent more serious thermal runaway. In an embodiment, relative to the composite positive electrode material, the content of lithium carbonate is 2-10%.
In the composite positive electrode material according to the embodiment of the present invention, a ternary single crystal material is employed and the surface of the ternary single crystal material is coated. On the one hand, the ternary single crystal material itself has the advantages of a good high-temperature performance, less gas production, and good safety. On the other hand, the coating material coated on the surface of the ternary material has a heat isolation effect, which increases the start temperature of thermal runaway of the ternary material and the battery and the heat release during the thermal runaway process, thereby improving the safety. Moreover, by means of the coating material, the phase transition of the ternary material in the charge/discharge voltage window is slowed down or delayed, and the capacity decrease caused by the phase transition of the ternary material during the long-term cycle process is slowed down, thereby improving the cycle performance of the battery, reducing the impedance increase of the material during the aging process, and improving the safety of the battery.
Further, in the embodiment of the present invention, the orientation of the ternary material in the 003 crystallographic orientation is restricted by defining the nanohardnesses of the ternary material and the coating material, and a higher compacted density of the positive electrode plate is realized by defining the tap densities of the ternary material and the coating material, thus ensuring the energy density of the battery.
In another aspect of the present invention, a method for preparing a composite positive electrode material according to the present invention is provided, which includes, as shown in
Step 101: Feed a ternary material, a phase-transition material and NMP (N-methyl-2-pyrrolidone) at a certain weight ratio to a mechanical blender and blend to form a composite material.
In this embodiment, the ternary material is a single crystal material, and the ternary material has a D50 of 3.0-6.0 The phase-transition material is a single crystal material or a secondary spherical material, and the primary particles in the phase-transition material have a D50 of 10-50 nm. The weight ratio of the ternary material to the phase-transition material is 80:20-99.8:0.2. The ternary material has a nanohardness of 0.001-5 GPa, and the phase-transition material has a nanohardness of 0.01-10 GPa.
Examples of the ternary material and the phase-transition material are as described above, and will not be repeated here.
The ternary material and the phase-transition material can be prepared by methods commonly used in the art. For example, the ternary material is NCM, and the phase-transition material is LMFP, and the preparation methods therefor are provided below.
A ternary material precursor (NixCoyMnz(OH)2) and a lithium source are mixed and subjected to pre-sintering, first sintering, first crushing, second sintering, and second crushing to obtain a ternary material.
The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium nitrate and lithium acetate.
The sintering conditions for pre-sintering include a sintering temperature of 200-500° C., and a sintering time of 4-6 hrs.
The first sintering includes a constant-temperature stage, a heating stage and a cooling stage. The constant-temperature stage includes a first constant-temperature stage that occurs at a temperature of 800-1000° C. for a time of 5-8 hrs, a second constant-temperature stage that occurs at a temperature of 1000-1100° C. for a time of 8-10 hrs, and a third constant-temperature stage that occurs at a temperature of 1100-1200° C. for a time of 5-10 hrs.
The heating stage includes a first heating stage that occurs at a temperature of 200-800° C. for a heating time of 1.5-3.5 hrs, a second heating stage that occurs at a temperature of 800-1000° C. for a heating time of 1.5-3.5 hrs, and a third heating stage that occurs at a temperature of 1000-1200° C. for a heating time of 1.0-2.5 hrs.
The cooling stage includes a first cooling stage that occurs at a temperature of 1200-800° C. for a cooling time of 1.5-3 hrs, and a second cooling stage that occurs at a temperature of 800-200° C. for a cooling time of 0.5-2 hrs.
The first crushing includes the following. The poly-crystalline material is subjected to first ball milling for preliminary crushing, where the rotation speed in the first ball milling is 4000-8000 r/min, and preferably 5500-7500 r/min, followed by pneumatic crushing under a pressure of 5-10 MPa, and preferably 6.5-8.5 MPa.
Before the second sintering, a coating agent is added to the crushed material, where the coating agent contains one or more of Ti3O4, Mg(OH)2, W2O3, Al2O3, Co(OH)2, and H3BO3.
The sintering conditions for second sintering include a second sintering temperature of 500-800° C. and preferably 550-750° C.
The second crushing includes the following: The second crushing is performed by mechanical milling where the rotation speed in the mechanical milling is 2000-4000 r/min, and preferably 2500-3500 r/min.
A ternary positive electrode material is obtained by the above process.
Preparation method of LMFP material
FePO4, Li2CO3, glucose and water are mixed at a certain ratio, and the mixed material is treated by rough grinding and fine grinding to form an aqueous solution; the aqueous solution is spray dried to form a mixture of three materials; solid-phase sintering is carried out at a high temperature, and the material obtained after the first sintering is subjected to pneumatic crushing to obtain an LMFP material.
In an embodiment of the present invention, the rotation speed of the mechanical blender is 4000-7000 r/min, and the blending time is 10-30 min. In another embodiment, the rotation speed of the mechanical blender is 4500-6500 r/min, and the blending time is 15-25 min.
Step 102: Bake the blended composite material at a certain temperature to obtain a composite positive electrode material.
In an embodiment of the present invention, the baking temperature of the composite material is 80-120° C., and the baking time is 0.5-2.5 hrs. In another embodiment, the baking temperature of the composite material is 95-105° C., and the baking time is 1-2 hrs.
In another aspect of the present invention, a positive electrode plate for a battery is also provided, which includes a current collector and a composite positive electrode material according to the present invention provided on the current collector.
In an embodiment, the current collector is, for example, an aluminum foil.
In an embodiment, the intensity ratio of the crystallographic orientation 003/110 after the positive electrode plate is compacted is 10-100.
Due to the use of the composite positive electrode material according to the embodiment of the present invention, the positive electrode plate according to the present invention has similar advantages, that is, it can improve the cycle performance of the battery, reduce the impedance increase of the material during the aging process, and improve the safety of the battery.
In another aspect of the present invention, a battery is also provided, which includes a positive electrode plate according to an embodiment of the present invention, a negative electrode plate, a separator provided between the positive electrode plate and the negative electrode plate, and an electrolyte.
In an embodiment, the positive electrode plate includes a current collector and a composite positive electrode material according to an embodiment of the present invention provided on the current collector. In an embodiment, the positive electrode current collector includes an aluminum foil. It should be understood that a conductive agent and a binder are also provided on the positive electrode current collector. For example, the weight ratio of the composite positive electrode material: binder: conductive agent is 100:2.0:2.2.
In an embodiment, the composite positive electrode material is a single-crystal NCM of which the surface is coated with a layer of LMFP material which is formed of nano-scale primary particles, and the binder is PVDF (polyvinylidene fluoride) with a special functional group on a polymer chain thereof. The special functional group is, for example, an F-containing group or a carboxyl group, an ester group or an amino group added to the polymer chain. The addition of an F-containing group can increase the gelatin resistance, and the addition of a carboxyl group, an ester group or an amino group can improve the adhesive force. The conductive agent is a combination of conductive agents including conductive carbon black, CNTs (carbon nanotubes) with different diameters, and graphene. These conductive agents enable mutual conduction between points and points, points and lines, and lines and lines, to better form a complete conductive network. Because the two materials are respectively nanoscale and microscale, dotted, linear or even planar conductive agent are needed to form a complete conductive network.
In an embodiment, the negative electrode plate includes a current collector and a negative electrode material provided on the current collector. In an embodiment, the negative electrode current collector includes a copper foil, and the negative electrode material is graphite. For example, the weight ratio of graphite: binder: CMC (carboxymethyl cellulose): conductive agent is 100:1.9:1.6:1.2. In an embodiment, the negative electrode graphite is artificial graphite formed of carbon-coated secondary particles. The secondary particles are formed of smaller primary particles aggregated together, and then coated with carbon on the surfaces thereof to improve the conductivity. This can increase the rate performance and the low-temperature performance, and reduce the inherent expansion of graphite itself.
In an embodiment, the electrolyte includes one or more of EC, DMC, EMC, DEC, VC, and PS, where EC is the abbreviation of ethylene carbonate, DMC is the abbreviation of dimethyl carbonate, EMC is the abbreviation of ethyl methyl carbonate, DEC is the abbreviation of diethyl carbonate, VC is the abbreviation of vinylene carbonate, and PS is the abbreviation of polystyrene.
In an embodiment, the separator is a composite structure composed of PE, ceramic, and glue.
Due to the use of the composite positive electrode material according to the embodiment of the present invention, the battery according to the present invention has similar advantages, that is, it can improve the cycle performance of the battery, reduce the impedance increase of the material during the aging process, and improve the safety of the battery.
In another aspect of the present invention, a method for preparing a positive electrode plate according to an embodiment of the present invention is provided, which includes the following step.
Step 201: Adding PVDF to a certain amount of NMP to form a PVDF solution, that is, the PVDF is dissolved. The PVDF is specially used for ternary high-nickel materials, for example, PVDF with an F-containing group and a carboxyl group, an ester group or an amino group on a polymer chain thereof, which has an increased gelatin resistance. NMP (N-methyl-2-pyrrolidone) can prevent the agglomeration of the binder. The content of NMP is determined according to the needs, and is not particularly limited.
Step 202: Adding an amount of a conductive agent to the PVDF solution, and stirring to form a slurry.
In an embodiment, a certain amount of a conductive agent is added to the PVDF solution, and then fully stirred on a vacuum high-speed blending device such as a vacuum high-speed planetary disperser to form a slurry.
In an embodiment, the stirring time is, for example, 10-50 min.
In an embodiment, the conductive agent is a combination of conductive agents including conductive carbon black, CNTs with different diameters and graphene.
Step 203: After a period of time, adding the composite positive electrode material according to the present invention to the slurry and fully stirring to obtain a final slurry.
In an embodiment, after 10-50 min, a composite positive electrode material is added to the slurry and fully stirred to obtain a final slurry. The composite positive electrode material is as described above, and will not be repeated here.
Step 204: Coating the final slurry onto a current collector, removing the NMP in the slurry by high-temperature baking, rolling, and slicing to obtain a positive electrode plate.
In an embodiment, before the final slurry is obtained, the method further includes adding an amount of lithium carbonate to the slurry to improve the safety performance of the battery and the material.
In the present invention, experimental tests are also performed on the positive electrode plate prepared by the above method and the battery using the positive electrode plate to verify the battery performance.
Positive electrode plate: composite positive electrode material:binder:conductive agent=100:2.0:2.2. The composite positive electrode material is a ternary single crystal material of which the surface is coated with a layer of LMFP material which is formed of nano-scale primary particles, the binder is PVDF with a special functional group on a polymer chain thereof, and the conductive agent is a combination of conductive agents including conductive carbon black, CNTs with different diameters and graphene.
Negative electrode plate: graphite:binder:CMC:conductive agent =100:1.9:1.6:1.2. The negative electrode graphite is artificial graphite formed of carbon-coated secondary particles.
The electrolyte is a mixed solution of EC, DMC, EMC, DEC, VC, and PS.
The separator is PE (polyethylene)+ceramic+glue.
Experiment procedure
The components and percentages by weight thereof in the slurry mentioned in this experiment are as follows: PVDF5130: 2.1%; conductive agent 1.9%; composite positive electrode material (Ni83 of which the surface is coated with a layer of LMFP material which is formed of nano-scale primary particles) 96%. The preparation process includes dissolution of the PVDF, addition of different kinds of conductive materials, and addition of the composite positive electrode material. The ratio of composite positive electrode material, PVDF and conductive agent in the slurry is 96:2.1:1.9.
The experimental parameters and performance test results are shown in Tables 1 and 2.
The parameter explanation and the performance test methods in the above table are as follows.
Ratio of crystallographic orientation (003) to crystallographic orientation (110) after the plate is compacted: The XRD pattern of the plate prepared with uncoated positive electrode material has an intensity ratio of 003/110 ranging from 5 to 200; and the XRD pattern of the plate prepared with a composite positive electrode material of coated ternary material has an intensity ratio of 003/110 ranging from 10 to 100.
Electrode compacted density of plate: The electrode compacted density of the plate having the ternary material is generally above 3.0 g/cm3. Due to process limitations and the possibility of material crushing, the electrode compacted density generally does not exceed 3.8 g/cm3.
45° C.-0500 refers to the capacity retention rate of the battery. The upper limit of this range is 100% without decrease. There may also be a sudden drop during the cycle process of the battery, and in this case, the capacity retention rate is very low and is below 50%.
Thickness change rate of battery % at 60° C. for 28 Days: This parameter is mainly provided for evaluating the gas production of the battery. The change rate is preferably 0, that is, no gas is produced in the battery. If the battery produces a large amount of gas, the change rate may exceed 100%.
Rate performance (ratio of discharge capacity at 5C to that at 0.2 C): This parameter is provided for evaluating the discharge capacity of the battery at a large rate and is generally 50%-98%.
Low-temperature performance (ratio of discharge capacity at −20° C. to that at 25° C.): This parameter is provided for evaluating the discharge capacity of the battery at a low temperature, and fluctuates greatly depending on the battery, which can be 5%-90%.
Test methods and results in the above experiment
Particle size: 1) Test instrument: Laser particle size analyzer, reference model Malvern 2000/3000.
2) Test method: Dispersion in deionized water and ultrasonication for 10 min. Refractive index of the particles: 1.74. Data such as D0.01, D10, D50, D90, and D99 in the volume distribution and the original data are required.
Tap density: The tap density is tested by Dandong Bettersize (BT-1001) intelligent powder comprehensive tester. The powder is placed in a 100 ml measuring cylinder, and weighed. The measuring cylinder is vibrated on the tester for 300 times at a vibration frequency of 300 times/mi. The volume of the powder in the measuring cylinder is measured after the vibration is over. According to the weight and volume of the powder, the tap density is calculated.
Nanohardness: The nanohardness is tested by a nanoindenter, which controls the continuous load change by a computer and monitors the indentation depth online. A complete indentation process includes two steps, that is, the so-called loading process and unloading process. During the loading process, an external load is applied to an indenter to press it into the sample surface. As the load increases, the depth of the indenter into the sample increases accordingly. When the load reaches the maximum, the external load is removed. An indentation mark is remained on the surface. The nanohardness is calculated from the applied pressure and the area of the indentation mark. Nanohardness is related to the selected crystal plane.
Ratio of crystallographic orientation (003) to crystallographic orientation (110) after the plate is compacted: This parameter is determined according to JY/T 009-1996 General rules for X-ray polycrystalline diffractometry.
Electrode compacted density of plate: An uncompacted positive electrode plate is prepared into a size of 40*100 mm, and compacted by Daye compacting machine, and the electrode compacted density of the plate is calculated according to the areal density and the thickness after compaction of the plate.
45° C.-0500: Test method: At a temperature condition of 45±5° C., the battery is charged to 4.2 V at a constant current of 1C and then discharged to 2.5 V at a constant current of 1C; and the capacity retention rate after 500 cycles, that is, C500, is calculated with the discharge capacity Cl of the first cycle as a reference.
Thickness change rate of battery % at 60° C. for 28D: The battery is charged to 4.2 V at a constant current of 0.2 C, and placed at room temperature for 2 hrs. The initial thickness of the battery is recorded. The battery is stored in a constant-temperature cabinet at 60° C. for 28 days, and the thickness after storage is recorded. The thickness change is calculated.
Rate performance (ratio of discharge capacity at 5C to that at 0.2 C): The battery is charged to 4.2 V at 25° C. and a constant current of 0.2 C; and then constant-current discharged to 2.5 V at different rates of 0.2 C and 5 C. The ratio of the discharge capacity at 5 C to that at 0.2 C is calculated.
Low-temperature performance (ratio of discharge capacity at −20° C. to that at 25° C.): The battery is stored for 6 hrs in a constant-temperature incubator at 25° C., and at -20° C. for 12 hrs. At 25° C., the battery is charged to 4.2 V/cell at a constant current of 0.2 C, and then discharged to 2.5 V/cell at a constant current of ⅓ C at 25° C. and −20° C. The ratio of the discharge capacity at −20° C. to that at 25° C. is calculated.
The composite positive electrode materials in Examples 1-14 all have excellent performance. Specifically, in terms of the orientation of the compacted plate after the composite positive electrode material is prepared into a positive electrode plate, the greater the ratio of the peak intensities (003) to (110) is, the higher the degree of orientation of the composite positive electrode material will be, and the more obvious the orientation of the C-axis of the composite positive electrode material perpendicular to the current collector will be. The smaller the ratio is, the weaker the orientation of the C-axis of the positive electrode composite material perpendicular to the current collector will be, and the distribution of the layered structure is irregular, which is beneficial to slowing down the thickness change of the positive electrode plate caused by the contraction and expansion of the unit cell volume during the charge and discharge process. The ratio of the peak intensities 004 to 110 can reach a minimum of 11.5, and a maximum of only 20, indicating that the composite positive electrode materials prepared in the examples has a poor orientation, which slows down the expansion of the positive electrode plate during the charge and discharge process. In terms of the electrode compacted density after the composite positive electrode material is prepared into the positive electrode plate, a higher electrode compacted density is conducive to the improvement of the energy density of the battery, and a lower density goes against the energy density of the battery. In the examples, the electrode compacted density of the positive electrode plate has a maximum reaching 3.62 g/cm3 and a minimum reaching 3.45 g/cm3. Therefore, the positive electrode plate has a higher electrode compacted density, since the main material and the coating material in the composite positive electrode material both have a high tap density. After a battery is prepared with the composite positive electrode material, the capacity retention rate after 500 cycles at 45° C., the thickness change rate after storage at 60° C. for 28 Days, the rate performance and the low-temperature discharge performance of the battery are mainly related to the particle size of NCM in the composite positive electrode material, the particle size of the primary particles in the coating material, and the weight ratio of the main material to the coating material in the composite material. The larger the particle size of NCM in the composite material is, the larger the particle size of the primary particles in the coating material is, the lower the degree of side reactions between the material and the electrolyte, the less the gas is produced by the material, the less the dissolved Mn content of the coating material is, the better the cycle performance and the smaller the thickness change rate of the battery after storage will be. Moreover, due to the increase of the particle size, the diffusion path of lithium ions becomes longer, so the rate performance and low-temperature performance of the battery will deteriorate. The composite positive electrode material in the embodiments have a maximum capacity retention rate of 94% and a minimum capacity retention rate of 86% after 500 cycles at 45° C. The thickness change rate of the battery after storage at 60° C. for 28 Days is as low as 5% and 12% at most. The positive electrode material has good high-temperature performance. The ratio of discharge capacities at a rate of 5C has a maximum of 95%, and a minimum of 85%. The ratio of discharge capacities at a low temperature of −20° C. has a maximum of 85%, and a minimum of 78%. The composite positive electrode material has good low-temperature performance and rate performance.
In Comparative Example 1, the proportion of LMFP in the composite positive electrode material is too high. The two materials have different structures. During the charge and discharge process, the diffusion resistance of lithium ions is very large, the high-temperature cycle performance, and the rate and low-temperature performance of the battery deteriorate, and the electrode compacted density of the positive electrode plate decreases.
In Comparative Example 2, the positive electrode material is not coated, and the crystallographic orientation of the compacted plate cannot be well suppressed. The expansion and contraction of the plate during the charge and discharge process will cause the uneven distribution of the electrolyte inside the battery, leading to lithium plating inside the battery and deteriorated cycle performance of the battery.
In Comparative Example 3, the particle size of the main NCM material in the composite positive electrode material is too large, the diffusion path of lithium ions is too long during the charge and discharge process, and the low-temperature and rate performances of the battery deteriorate.
In Comparative Example 4, the particle size of the coating material LMFP in the composite positive electrode material is too large, which will also deteriorate the low-temperature and rate performances of the battery.
In Comparative Example 5, the particle size of the main NCM material in the composite positive electrode material is too small, the specific surface area increases, the side reaction with the electrolyte increases, the cycle performance of the battery becomes worse, the gas production after storage increases, and the electrode compacted density of the positive electrode plate decreases accordingly.
In Comparative Example 6, the particle size of the coating material LMFP in the composite positive electrode material is too small, the amount of dissolved Mn increases, the electrode compacted density of the positive electrode plate decreases, and the high-temperature cycle performance deteriorates.
In Comparative Example 7, the hardness of the main NCM material in the composite positive electrode material is too low, and it is preferentially compacted when the positive electrode plate is compacted, the orientation of the crystal cannot be suppressed, and the hardness is too low, after the positive electrode plate is compacted, the particles are easy to break, causing exposure of large fresh surfaces to the electrolyte, so the side reactions increase, and the cycle performance of the material deteriorates.
In Comparative Example 8, the hardness of the main NCM material in the composite positive electrode material is too high, and LMFP cannot inhibit the orientation of the crystal. The positive electrode plate expands and contracts during the charge and discharge process, causing uneven electrolyte distribution in the battery. This causes lithium plating inside the battery, the cycle performance of the battery deteriorates, and the electrode compacted density of the positive electrode plate decreases accordingly.
In Comparative Example 9, the hardness of LMFP in the composite positive electrode material is too high, and the LMFP material is also a nano-particle material. When the positive electrode plate is compacted, the nano-material enters NCM, so LMFP cannot inhibit the orientation of the crystal. At the same time, the surface of the NCM material is destroyed, and the cycle performance of the battery deteriorates.
Although some embodiments have been described with reference to accompanying drawings, it should be understood that the above embodiments are only illustrative, and do not limit the scope of the present invention thereto. Various changes and modifications can be made by a person of ordinary skill in the art without departing from the scope and spirit of the present invention. All these changes and modifications are embraced in the scope of the present invention as defined in the appended claims.
Numerous specific details are set forth in the specification provided herein. However, it can be understood that, the embodiments of the present invention may be practiced without the specific details. In some examples, known methods, structures, and technologies are not disclosed in detail, so as not to mix up understanding on the specification.
Similarly, it should be understood that to simplify the present invention and help to understand one or more of disclosure aspects, in the descriptions of the above embodiments of the present invention, features of the present invention are sometimes grouped into a single embodiment or figure, or descriptions thereof. However, the methods in the present invention should not be construed as reflecting the following intention: that is, the present invention claimed to be protected is required to have more features than those clearly set forth in each claim. More definitely, as reflected in the corresponding claims, the inventiveness of the disclosure lies in resolving the corresponding technical problem using features less than all features of a single embodiment disclosed above. Therefore, the claims following the Detailed Description are hereby expressly incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment of the present invention.
A person skilled in the art may understand that, all features disclosed in this specification (including the accompanying claims, abstract and drawings), and all processes or units of any method or device disclosed herein may be combined in any combination, unless features are mutually exclusive. Unless otherwise explicitly stated, each feature disclosed in this specification (including the accompanying claims, abstract and drawings) may be replaced with an alternative feature serving the same, equivalent or similar purpose.
In addition, those skilled in the art can understand that, although some embodiments herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the present invention and to form different embodiments. For example, in the claims, any one of the claimed embodiments may be used in any combination.
It should be noted that the above-mentioned embodiments illustrate rather than limit the present invention, and those skilled in the art may devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claims. The present invention can be implemented by way of hardware including several different elements and an appropriately programmed computer. In the unit claims enumerating several apparatuses, several of these apparatuses can be specifically embodied by the same item of hardware. The use of the words such as “first”, “second”, “third”, and the like does not denote any order. These words can be interpreted as names.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202010821206.6 | Aug 2020 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/110587 | 8/4/2021 | WO |
