CN111916664A - Positive plate, preparation method and battery - Google Patents
Positive plate, preparation method and battery Download PDFInfo
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- CN111916664A CN111916664A CN202010933332.0A CN202010933332A CN111916664A CN 111916664 A CN111916664 A CN 111916664A CN 202010933332 A CN202010933332 A CN 202010933332A CN 111916664 A CN111916664 A CN 111916664A
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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Abstract
The invention provides a positive plate, a preparation method and a battery, wherein the positive plate comprises the following components: the current collector comprises a current collector body, wherein a protective layer is arranged on the surface of at least one side of the current collector body, an active layer is arranged on one side, far away from the current collector body, of the protective layer, and the active layer comprises a first positive electrode active material; the protective layer includes a second positive electrode active material having a first particle size and a second particle size, a ratio of the first particle size to the second particle size being greater than or equal to 1.5, and the first particle size being smaller than the particle size of the first positive electrode active material. In the positive plate, the protective layer is arranged on at least one side surface of the current collector and is positioned between the surface of the current collector and the active layer, the strength of the positive plate can be enhanced through the protective layer, so that the positive plate is not easy to damage, the short circuit problem is prevented when the battery is pierced by a hard object and impacted by a heavy object, the battery is prevented from burning or generating heat, the safety of the battery is improved, and the cycle performance and the energy density of a battery core are improved.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a positive plate, a preparation method and a battery.
Background
The lithium ion battery has the advantages of high energy density, high working voltage, light weight, small volume and the like, and the lithium ion battery has long cycle life and is also a necessary condition for wide application of the lithium ion battery with environmental protection. The lithium ion battery has wider application in daily electronic products, electric vehicles and other energy storage power supply systems. Because of the particularity of the materials and the structure of the lithium ion battery, a plurality of potential safety hazards exist at present, and particularly when the lithium ion battery is pierced by a hard object and impacted by a heavy object, the safety of the lithium ion battery becomes one of the most important reasons for restricting the large-scale industrial application of the lithium ion battery, so that the requirement of people on the safety performance of the lithium ion battery is higher and higher, and how to improve the safety of the lithium ion battery becomes the focus of attention at home and abroad.
Four short circuit modes occur when a lithium ion battery is pierced by a sharps: the anode and the cathode are in short circuit, the anode and the copper foil are in short circuit, the aluminum foil and the copper foil are in short circuit, and the aluminum foil and the cathode are in short circuit, wherein the power of the short circuit between the aluminum foil and the cathode is the maximum, and a large amount of heat can be generated instantly. When the lithium ion battery is pierced by a hard object and impacted by a heavy object, the problem of short circuit easily occurs, so that the battery burns or generates heat, and the safety of the battery is reduced.
Disclosure of Invention
In view of the above, the invention provides a positive plate, a preparation method thereof and a battery, which are used for solving the problem that the safety of the battery is reduced due to the fact that the battery is easily short-circuited when the battery is pierced by a hard object and impacted by a heavy object, and the battery burns or generates heat.
In order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, a positive electrode sheet according to an embodiment of the present invention includes:
the current collector comprises a current collector body, wherein a protective layer is arranged on the surface of at least one side of the current collector body, an active layer is arranged on one side, far away from the current collector body, of the protective layer, and the active layer comprises a first positive electrode active material;
the protective layer comprises a second positive electrode active material, the second positive electrode active material has a first particle size and a second particle size, and the ratio of the first particle size to the second particle size is greater than or equal to 1.5;
and the first particle diameter is smaller than a particle diameter of the first positive electrode active material.
Wherein, be equipped with respectively on the both sides surface of mass flow body the protective layer.
Wherein the particle size of the first positive electrode active material is 10-30 μm.
The second positive electrode active material comprises at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, a lithium-rich manganese-based material, lithium nickel cobalt aluminate or lithium titanate.
Wherein the first particle size is 0.15-25 μm, and the second particle size is 0.1-7 μm.
Wherein the mass ratio of the second positive electrode active material having the second particle size in the protective layer to the second positive electrode active material in the protective layer is 35% to 85%.
Wherein the protective layer comprises a second conductive agent and a second binder, and the mass of the second positive electrode active material in the protective layer is greater than or equal to the sum of the mass of the second binder and the second conductive agent in the protective layer; and/or
The active layer further comprises a first conductive agent and a first binder; and/or
The protective layer further comprises a second conductive agent and a second adhesive.
Wherein the porosity of the protective layer is 12-30%.
In a second aspect, a method for manufacturing a positive electrode sheet according to an embodiment of the present invention includes:
providing a current collector;
forming a protective layer on at least one side surface of the current collector;
forming an active layer on one side, far away from the current collector, of the protective layer, wherein the active layer comprises a first positive electrode active material;
the protective layer comprises a second positive electrode active material, the second positive electrode active material has a first particle size and a second particle size, and the ratio of the first particle size to the second particle size is greater than or equal to 1.5;
and the first particle diameter is smaller than a particle diameter of the first positive electrode active material.
In a third aspect, a battery according to an embodiment of the present invention includes a positive electrode tab as described in the above embodiments.
The technical scheme of the invention has the following beneficial effects:
according to the positive plate, the surface of at least one side of the current collector is provided with the protective layer, one side, far away from the current collector, of the protective layer is provided with the active layer, and the active layer comprises the first positive active material; the protective layer includes a second positive electrode active material therein, the second positive electrode active material having a first particle diameter and a second particle diameter, a ratio of the first particle diameter to the second particle diameter being greater than or equal to 1.5, and the first particle diameter being smaller than the particle diameter of the first positive electrode active material. In the positive plate, the protective layer is arranged on at least one side surface of the current collector and is positioned between the surface of the current collector and the active layer, so that the strength of the positive plate can be enhanced through the protective layer, the positive plate is not easy to damage, the short circuit problem is prevented when the battery is pierced by a hard object and impacted by a heavy object, the combustion or heat generation of the battery is avoided, the safety of the battery is improved, and the service performance of the battery is improved; due to the grain diameter difference of the second anode active material in the protective layer, the lithium ion transmission in pores is facilitated, the grains in the active layer are better embedded into the protective layer, and the cycle performance and the energy density of the battery cell can be improved.
Drawings
Fig. 1 is a schematic view of a protective layer on a current collector;
fig. 2 is a schematic structural view of a positive electrode sheet according to an embodiment of the present invention.
Reference numerals
A current collector 10; a protective layer 11; an active layer 12.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.
The positive electrode sheet according to an embodiment of the present invention is specifically described below.
As shown in fig. 1 and fig. 2, a positive electrode sheet according to an embodiment of the present invention includes a current collector 10, a protective layer 11 is disposed on at least one side surface of the current collector 10, an active layer 12 is disposed on one side of the protective layer 11 away from the current collector 10, and the active layer 12 includes a first positive electrode active material; the protective layer 11 includes a second positive electrode active material having a first particle diameter and a second particle diameter, a ratio of the first particle diameter to the second particle diameter is greater than or equal to 1.5, and the first particle diameter is smaller than the particle diameter of the first positive electrode active material.
The second positive electrode active material referred to in the present invention has a first particle diameter and a second particle diameter, and means that the second positive electrode active material has two large particle diameter distribution peaks, and the particle diameter corresponding to the peak value of the particle diameter distribution peak having a larger particle diameter is the first particle diameter, and the particle diameter corresponding to the peak value of the particle diameter distribution peak having a smaller particle diameter is the second particle diameter.
That is to say, the positive plate mainly comprises a current collector 10, wherein a protective layer 11 is disposed on a surface of one side of the current collector 10, or protective layers 11 are disposed on surfaces of two sides of the current collector 10, respectively, the thickness of the protective layer 11 can be reasonably set as required, the thickness of the protective layer 11 can be 5-20 μm, for example, 9 μm, an active layer 12 can be disposed on one side of the protective layer 11 away from the current collector 10, the active layer 12 can include a first positive active material, and the first positive active material can include at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganese manganate, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium manganese rich base material, lithium nickel cobalt aluminate or lithium titanate; the protective layer 11 may include therein a second positive electrode active material having a first particle diameter and a second particle diameter, a ratio of the first particle diameter to the second particle diameter being greater than or equal to 1.5, and the first particle diameter being smaller than the particle diameter of the first positive electrode active material; the second positive active material may include at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, a lithium rich manganese-based material, lithium nickel cobalt aluminate, or lithium titanate, for example, the second positive active material may include lithium cobaltate or lithium iron phosphate. In the positive plate, the protective layer 11 is arranged on at least one side surface of the current collector 10, the protective layer 11 is positioned between the surface of the current collector 10 and the active layer 12, the strength of the positive plate can be enhanced through the protective layer 11, so that the positive plate is not easy to damage, when a battery is pierced by a hard object and impacted by a heavy object, the particle size of the second positive active material is smaller than that of the first positive active material, and a compact protective layer is formed on the current collector to prevent an aluminum foil from contacting with a negative electrode. Due to the grain diameter difference of the second anode active material in the protective layer, the lithium ion transmission in pores is facilitated, the grains in the active layer are better embedded into the protective layer, and the cycle performance and the energy density of the battery cell can be improved.
In some embodiments, as shown in fig. 2, protective layers 11 may be respectively disposed on both side surfaces of the current collector 10, and active layers 12 are respectively disposed on the protective layers 11 on each side surface of the current collector 10, so as to enhance the strength of the positive plate, so that the positive plate is not easily damaged, and when the battery is pierced by a hard object and impacted by a heavy object, the short circuit problem is prevented, and the battery is prevented from burning or generating heat.
In other embodiments, the active layer 12 may further include a first conductive agent and a first binder. Wherein the first conductive agent may include at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, or metal powder; the first binder may include at least one of styrene-butadiene rubber, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and polyvinylidene fluoride, and the types and amounts of the first positive electrode active material, the first conductive agent, and the first binder in the active layer 12 may be reasonably selected according to actual needs.
In some embodiments, a second conductive agent and a second binder may also be included in the protective layer 11.
The second conductive agent may include at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, or metal powder; the second binder may include at least one of styrene-butadiene rubber, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyvinylidene fluoride. The first positive electrode active material and the second positive electrode active material may be the same or different, the first conductive agent and the second conductive agent may be the same or different, the first binder and the second binder may be the same or different, and the components and contents in the protective layer 11 and the active layer 12 may be reasonably selected according to actual needs.
In some embodiments, the second positive electrode active material in the protective layer 11 has a first particle size and a second particle size, which are different, for example, the first particle size may be 0.15 to 25 μm and the second particle size may be 0.1 to 7 μm. The first particle size and the second particle size may be set as desired, for example, the first particle size is 1.05 μm and the second particle size is 700 nm. Alternatively, the particle size of the first positive electrode active material may be 10 to 30 μm. The particles with different particle sizes are mutually doped to form pores, so that the porosity in the protective layer 11 is increased, the transmission of lithium ions in the pores is facilitated, the diffusion of electrolyte among the particles is facilitated, and the cycle performance of the battery cell is improved; meanwhile, due to the particle size difference of the second anode active material in the protective layer 11, the protective layer 11 can present an uneven interface, so that particles in the active layer 12 can be better embedded into the protective layer 11, the protective layer 11 and the active layer 12 are fully connected, the space utilization rate is higher, and the energy density of the battery cell can be improved.
In the embodiment of the present invention, the mass ratio of the second positive electrode active material with the second particle size in the protection layer 11 to the second positive electrode active material in the protection layer 11 is 35% to 85%, preferably, the mass ratio is 50% to 70%, which can increase the porosity in the protection layer 11, facilitate the diffusion of the electrolyte between particles, and improve the cycle performance of the battery cell.
In some embodiments, a second conductive agent and a second binder may be included in the protective layer 11, and the mass of the second positive active material in the protective layer 11 is greater than or equal to the sum of the masses of the second binder and the second conductive agent in the protective layer 11, so that the protective layer 11 facilitates the transmission of lithium ions; and/or, the active layer 12 may further include a first conductive agent and a first binder; and/or, the protective layer 11 may further include a second conductive agent and a second binder.
The protective layer 11 has pores, the porosity of the protective layer 11 may be 12% to 30%, preferably, the porosity of the protective layer 11 is 14% to 22%, and the pores can accommodate the electrolyte, so that diffusion of the electrolyte among particles is facilitated, the cycle performance of the battery core is improved, the capacity loss of the battery is reduced, and the energy density loss of the lithium ion battery is reduced.
The embodiment of the invention provides a preparation method of a positive plate.
The preparation method of the positive plate comprises the following steps:
providing a current collector 10;
forming a protective layer 11 on at least one side surface of the current collector 10;
forming an active layer 12 on the protective layer 11 on a side away from the current collector 10, wherein the active layer 12 comprises a first positive electrode active material;
the protective layer 11 includes a second positive electrode active material having a first particle diameter and a second particle diameter, a ratio of the first particle diameter to the second particle diameter being greater than or equal to 1.5;
and the first particle size is smaller than a particle size of the first cathode active material.
That is, the current collector 10 is selected first, the protective layer 11 is formed on one side surface of the current collector 10, or the protective layers 11 are formed on both side surfaces of the current collector 10, respectively, the active layer 12 may be formed on the protective layer 11 on the side away from the current collector 10, and the first positive active material may be included in the active layer 12; the protective layer 11 includes a second positive electrode active material having a first particle diameter and a second particle diameter, a ratio of the first particle diameter to the second particle diameter is greater than or equal to 1.5, and the first particle diameter is smaller than the particle diameter of the first positive electrode active material. The first positive active material may include at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, a lithium-rich manganese-based material, lithium nickel cobalt aluminate, or lithium titanate. According to the positive plate prepared by the method, the protective layer 11 is positioned between the surface of the current collector 10 and the active layer 12, the strength of the positive plate can be enhanced through the protective layer 11, so that the positive plate is not easy to damage, the short circuit problem is prevented when the battery is pierced by a hard object and impacted by a heavy object, the battery is prevented from burning or generating heat, the safety of the battery is improved, and the service performance of the battery is improved; due to the grain diameter difference of the second anode active material in the protective layer, the lithium ion transmission in pores is facilitated, the grains in the active layer are better embedded into the protective layer, and the cycle performance and the energy density of the battery cell can be improved.
In some embodiments, the protective layers 11 may be formed on both side surfaces of the current collector 10, and the active layers 12 are formed on the protective layers 11 on each side surface of the current collector 10, so that the strength of the positive plate can be enhanced, the positive plate is not easily damaged, and when the battery is pierced by a hard object and impacted by a heavy object, the problem of short circuit is prevented, and the battery is prevented from burning or generating heat.
In an embodiment of the present invention, a first conductive agent and a first binder may also be included in the active layer 12.
Optionally, a second conductive agent and a second binder may also be included in the protective layer 11. Alternatively, the second positive electrode active material in the protective layer 11 has a first particle size and a second particle size, for example, the first particle size is 0.15 to 25 μm, and the second particle size is 0.1 to 7 μm. The particle size of the first positive electrode active material may be 10 to 30 μm, and the mass ratio of the second positive electrode active material having the second particle size in the protective layer 11 to the second positive electrode active material in the protective layer is 35 to 85%, preferably 50 to 70%.
In some embodiments, the protective layer 11 includes a second conductive agent and a second binder, and the mass of the second positive electrode active material in the protective layer 11 is greater than or equal to the sum of the mass of the second binder and the second conductive agent in the protective layer 11; the active layer 12 may further include a first conductive agent and a first binder; and/or
The protective layer 11 may further include a second conductive agent and a second binder.
Optionally, the protective layer 11 has pores therein, and the porosity of the protective layer 11 may be 12% to 30%, and preferably, the porosity of the protective layer 11 is 14% to 22%.
The preparation method of the positive plate in the embodiment of the present invention corresponds to the positive plate in the above embodiment, and reference may be made to the positive plate in the above embodiment, which is not described herein again.
An embodiment of the present invention provides a battery, and the battery includes the positive electrode sheet described in the above embodiment. The battery can be a lithium ion battery, and the battery with the positive plate in the embodiment prevents the short circuit problem when the battery is pierced by a hard object and impacted by a heavy object, avoids the combustion or heat generation of the battery, improves the safety of the battery, and improves the service performance of the battery.
The invention is further illustrated by the following specific examples.
Example 1
Mixing lithium iron phosphate, polyvinylidene fluoride and carbon black according to a mass ratio of 65:32:3, wherein the lithium iron phosphate has a first particle size D1 and a second particle size D2, the first particle size D1 is 1.05 mu m, the second particle size D2 is 700nm, the mass of lithium iron phosphate (LFP) with the second particle size is 35% of the total mass of the lithium iron phosphate, dissolving all the components in N-methylpyrrolidone (NMP), uniformly stirring to prepare a protective layer slurry, coating the protective layer slurry on the two side surfaces of an aluminum foil with the thickness of 10 mu m, drying to remove the NMP to obtain the aluminum foil with the protective layer, and the thickness of the protective layer can be 9 mu m;
mixing lithium iron phosphate, polyvinylidene fluoride and conductive carbon fiber according to a mass ratio of 96:2:2, dissolving all the components in N-methyl pyrrolidone, stirring uniformly, preparing active slurry, coating the active slurry on the surface of one side, far away from an aluminum foil, of a protective layer, drying to remove NMP, rolling and slitting to obtain the positive plate with the protective layer and the active layer.
Example 2
Example 2 differs from example 1 in that: and (3) adjusting the mixing ratio of the lithium iron phosphate, the polyvinylidene fluoride and the carbon black in the protective layer slurry to 30:65: 5.
Example 3
Example 3 differs from example 1 in that: the mixing ratio of the lithium iron phosphate, the polyvinylidene fluoride and the carbon black in the protective layer slurry is adjusted to 0:98: 2.
Example 4
Example 4 differs from example 1 in that: the lithium iron phosphate in the protective layer slurry only has the second particle size D2.
Example 5
Example 5 differs from example 1 in that: the lithium iron phosphate in the protective layer slurry only has the first particle size D1, and the first particle size D1 is 2 μm.
Example 6
Example 6 differs from example 1 in that: the lithium iron phosphate has a first particle size D1 and a second particle size D2, the first particle size D1 is 2 μm, the second particle size D2 is 700nm, and the mass of the lithium iron phosphate having the second particle size is 35% of the total mass of the lithium iron phosphate.
Example 7
Example 7 differs from example 1 in that: the mass of the lithium iron phosphate having the second particle diameter is 50% of the total mass of the lithium iron phosphate.
Example 8
Example 8 differs from example 1 in that: the mass of the lithium iron phosphate having the second particle diameter is 70% of the total mass of the lithium iron phosphate.
Example 9
Example 9 differs from example 1 in that: the mass of the lithium iron phosphate having the second particle diameter is 85% of the total mass of the lithium iron phosphate.
Example 10
Example 10 differs from example 1 in that: the second positive electrode active material in the protective layer is lithium cobaltate.
Example 11
Example 11 differs from example 1 in that: the mass of the lithium iron phosphate having the second particle diameter is 95% of the total mass of the lithium iron phosphate.
Comparative example 1
Mixing lithium iron phosphate, polyvinylidene fluoride and conductive carbon fiber according to a mass ratio of 96:2:2, dissolving all the components in N-methylpyrrolidone (NMP), uniformly stirring to prepare active slurry, coating the active slurry on the two side surfaces of a 10-micron aluminum foil, drying to remove NMP, rolling and cutting to obtain the positive plate only with the active layer.
The positive electrode sheets prepared in the above embodiments 1 to 11 and comparative example 1, a conventional negative electrode sheet, a diaphragm and an electrolyte are manufactured into a lithium ion battery according to a conventional lithium battery manufacturing process, and the battery capacity is about 4970 mAh.
And (3) performance testing: the prepared lithium ion battery was subjected to 4.45V full electro-acupuncture, 4.45V weight impact and energy density tests.
The test method is as follows:
1. nail penetration testing method
And (3) placing the lithium ion battery in a normal temperature environment, charging the lithium ion battery at a constant current of 0.5 ℃ until the voltage is 4.45V, then charging at a constant voltage until the current is reduced to 0.025C, and stopping charging. And vertically penetrating the central position of the lithium ion battery at the speed of 30mm/s by using a steel nail with the diameter of 4mm, keeping for 300s, and recording that the lithium ion battery passes through when the lithium ion battery does not catch fire and explode. Each example tests 15 lithium ion batteries, and the nail penetration test passing rate is used as an index for evaluating the safety of the lithium ion batteries.
2. Weight impact test method
Placing the lithium ion battery in a normal temperature environment, charging the lithium ion battery at a constant current of 0.2C until the voltage is 4.45V, then charging at a constant voltage until the current is reduced to 0.025C, stopping charging, then discharging at a constant current of 0.5C, and discharging to 3.0V, circulating for 5T in the way, and performing a weight impact test within 24 hours after the last battery cell is fully charged: the battery core is placed on a plane, a steel column with the diameter of 15.8 +/-0.2 mm is placed in the center of the battery core, the longitudinal axis of the steel column is parallel to the plane, a weight with the mass of 9.1 +/-0.1 kg freely falls onto the steel column above the center of the battery from the height of 610 +/-25 mm, and the lithium ion battery is observed for 6 hours after the test is finished, and the lithium ion battery is not fired and not exploded and is recorded as passing. 10 lithium ion batteries are tested in each case, and the passing rate of the weight impact test is used as an index for evaluating the safety of the lithium ion batteries.
3. Volume energy density testing method
And (3) placing the lithium ion battery at 25 ℃ and room temperature, charging at a constant current of 0.5 ℃ until the voltage is 4.45V, then charging at a constant voltage of 4.45V until the current is 0.05C, discharging at 0.5C until the voltage is 3.0V, and recording the discharge capacity.
Volume energy density (discharge capacity) plateau voltage/(lithium ion battery length width thickness); wherein, the length, the width and the thickness refer to the length, the width and the thickness of the packaged lithium ion battery.
The lithium ion batteries prepared from the positive electrode sheets of examples 1 to 11 and comparative example 1, which were tested by the above method, had the test results shown in table 1 below.
TABLE 1 test results for different lithium ion batteries
| Sample (I) | Penetration rate of acupuncture | Impact passing rate of heavy object | Rate of energy density loss |
| Example 1 | 10/15 | 5/10 | 2.54％ |
| Example 2 | 11/15 | 7/10 | 3.11％ |
| Example 3 | 14/15 | 7/10 | 5.03％ |
| Example 4 | 12/15 | 6/10 | 2.21％ |
| Example 5 | 9/15 | 4/10 | 2.52％ |
| Example 6 | 11/15 | 6/10 | 2.62％ |
| Example 7 | 13/15 | 7/10 | 2.21％ |
| Example 8 | 15/15 | 8/10 | 2.12％ |
| Example 9 | 14/15 | 8/10 | 2.08％ |
| Example 10 | 12/15 | 7/10 | 2.14％ |
| Example 11 | 13/15 | 6/10 | 1.94％ |
| Comparative example 1 | 0/15 | 0/10 | Datum |
As can be seen from table 1, compared with comparative example 1, the needling passage rate, the weight impact rate and the energy density loss rate in examples 1 to 11 are higher, and when the mass of lithium iron phosphate is greater than the sum of the mass of polyvinylidene fluoride and the mass of carbon black, the energy density loss rate can be controlled within 3%, so that short circuit can be prevented in the using process, the battery can be prevented from burning or generating heat, the safety of the battery is good, and the service performance is good.
Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A positive electrode sheet, comprising:
the current collector comprises a current collector body, wherein a protective layer is arranged on the surface of at least one side of the current collector body, an active layer is arranged on one side, far away from the current collector body, of the protective layer, and the active layer comprises a first positive electrode active material;
the protective layer comprises a second positive electrode active material, the second positive electrode active material has a first particle size and a second particle size, and the ratio of the first particle size to the second particle size is greater than or equal to 1.5;
and the first particle diameter is smaller than a particle diameter of the first positive electrode active material.
2. The positive electrode sheet according to claim 1, wherein the protective layers are provided on both side surfaces of the current collector, respectively.
3. The positive electrode sheet according to claim 1, wherein the particle diameter of the first positive electrode active material is 10 to 30 μm.
4. The positive electrode sheet according to claim 1, wherein the second positive electrode active material comprises at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, a lithium rich manganese-based material, lithium nickel cobalt aluminate, or lithium titanate.
5. The positive electrode sheet according to claim 1, wherein the first particle size is 0.15 to 25 μm, and the second particle size is 0.1 to 7 μm.
6. The positive electrode sheet according to claim 1, wherein the second positive electrode active material having the second particle diameter in the protective layer accounts for 35% to 85% by mass of the second positive electrode active material in the protective layer.
7. The positive electrode sheet according to claim 1, wherein the protective layer includes a second conductive agent and a second binder therein, and the mass of the second positive electrode active material in the protective layer is greater than or equal to the sum of the mass of the second binder and the second conductive agent in the protective layer; and/or
The active layer further comprises a first conductive agent and a first binder; and/or
The protective layer further comprises a second conductive agent and a second adhesive.
8. The positive electrode sheet according to claim 1, wherein the porosity of the protective layer is 12% to 30%.
9. A method for preparing a positive plate is characterized by comprising the following steps:
providing a current collector;
forming a protective layer on at least one side surface of the current collector;
forming an active layer on one side, far away from the current collector, of the protective layer, wherein the active layer comprises a first positive electrode active material;
the protective layer comprises a second positive electrode active material, the second positive electrode active material has a first particle size and a second particle size, and the ratio of the first particle size to the second particle size is greater than or equal to 1.5;
and the first particle diameter is smaller than a particle diameter of the first positive electrode active material.
10. A battery comprising the positive electrode sheet according to any one of claims 1 to 8.
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