CN116207383A - Dry functional layer for lithium battery, preparation method, composite electrode and preparation method - Google Patents
Dry functional layer for lithium battery, preparation method, composite electrode and preparation method Download PDFInfo
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- CN116207383A CN116207383A CN202310492262.3A CN202310492262A CN116207383A CN 116207383 A CN116207383 A CN 116207383A CN 202310492262 A CN202310492262 A CN 202310492262A CN 116207383 A CN116207383 A CN 116207383A
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/52—Removing gases inside the secondary cell, e.g. by absorption
- H01M10/526—Removing gases inside the secondary cell, e.g. by absorption by gas recombination on the electrode surface or by structuring the electrode surface to improve gas recombination
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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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- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
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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
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Abstract
The invention provides a dry functional layer for a lithium battery, a preparation method of the dry functional layer, a composite electrode and a preparation method of the composite electrode, and particularly relates to the technical field of lithium batteries. The dry-method functional layer for the lithium battery comprises a functional material and a dry-method binder, wherein the dry-method binder is fibrous and is crosslinked to form a reticular framework of the dry-method functional layer, and the functional material is uniformly dispersed in the reticular framework; the functional material mainly comprises a porous material and a functional additive, wherein the functional additive is used for absorbing oxidative gas generated in the lithium battery. The dry functional layer does not use solvent, so that the gas oxygen can be absorbed better; meanwhile, the electrode plate deformation does not exist, the surface of the obtained functional layer has no crack, the smoothness is better, the functional layer can be better attached to the surface of the electrode plate, the solid-solid contact effect is improved, the interface impedance is smaller, meanwhile, the crosstalk of gas in the battery core is better avoided while the good heat insulation function is achieved, and the electrical property and the safety of the lithium battery are improved.
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a dry functional layer for a lithium battery, a preparation method, a composite electrode and a preparation method.
Background
With the increasing wide application of lithium batteries in production and life, the rapid improvement of battery energy density is also increasingly important for the safety performance of lithium batteries. In particular, lithium batteries can undergo thermal runaway due to external or internal factors, resulting in serious life and property losses. The solving path of the current industry technology comprises modification of anode and cathode materials to enhance stability, or use of high temperature resistant diaphragms, electrolyte additives and the like. The temperature of thermal runaway is often outside the range that can be controlled by the above means. As the research is further advanced, researchers find that the main cause of thermal runaway of the high-nickel ternary cell is oxygen release of the positive electrode material, and for this reason, researchers propose to coat a layer of gas absorbent on the alignment side of the separator, but it still cannot solve the shrinkage of the separator from the fundamental level and short-circuit occurs, thereby causing thermal runaway to occur.
Therefore, in the prior art, the functional coating with the three-dimensional skeleton structure is formed through the three-dimensional porous micro powder, and the three-dimensional porous micro powder can absorb the oxidative gas generated by the anode under the condition that the energy density, the ion transmission path and the internal resistance of the lithium ion battery are not influenced while providing reliable attachment points for the gas absorbent, so that the gas crosstalk is prevented, the problem of thermal runaway of lithium ions is comprehensively solved on the whole, the safety of the lithium ion battery is greatly improved, and the defect that the prior art can only solve the problem of thermal runaway from a certain aspect is overcome.
However, the functional coating is prepared by a wet method, in the preparation process, toxic organic solvents are used for homogenate, recovery equipment is expensive and has huge energy consumption, and if the functional coating leaks into the environment, the functional coating is harmful to human health and the environment; on the other hand, no matter what kind of solvent is adopted, the functional coating needs to be subjected to secondary evaporation by the oven, so that a large amount of field space is occupied, and the energy consumption is huge. At the same time, the solvent in the freshly applied functional coating may penetrate into the underlying dried electrode, thereby affecting the adhesion of the electrode material. Meanwhile, the wet-process coated functional coating is extremely easy to crack on the surface, so that the safety of the battery cell is greatly reduced.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide a dry functional layer for a lithium battery, and aims to solve the technical problems of pollution, difficult recovery, surface cracking and lower cell safety caused by the use of an organic solvent in the existing wet functional layer.
The second purpose of the invention is to provide a preparation method of the dry functional layer for the lithium battery.
It is a further object of the present invention to provide a composite electrode.
The fourth object of the invention is to provide a preparation method of the composite electrode.
The fifth object of the invention is to provide an application of the composite electrode in a lithium battery.
In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:
the first aspect of the invention provides a dry functional layer for a lithium battery, which comprises a functional material and a dry binder, wherein the dry binder is fibrous, the dry binder is crosslinked to form a reticular framework of the dry functional layer, and the functional material is uniformly dispersed in the reticular framework;
wherein the functional material mainly comprises a porous material and a functional additive, and the functional additive is used for absorbing oxidative gas generated in the lithium battery.
Further, the porous material includes at least one of silica, alumina, zirconia, titania, and magnesia;
the functional additive comprises at least one of an ester of an anhydride having an unsaturated alicyclic structure, an amide of an anhydride having an unsaturated alicyclic structure, an imide of an anhydride having an unsaturated alicyclic structure, a dicarboxylic acid of an anhydride having an unsaturated alicyclic structure, and an anhydride polymer having an unsaturated alicyclic structure;
the dry binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, poly (vinylidene fluoride-CO-hexafluoropropylene), polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid.
Further, the mass ratio of the functional material to the dry binder is 1.5-4.5:1;
the mass ratio of the porous material to the functional additive is 5.5-14:1;
the D50 particle size of the porous material is 1-30 mu m, the porosity is more than or equal to 50%, and the average pore diameter is 10-150 nm.
The second aspect of the invention provides a preparation method of the dry functional layer for the lithium battery, wherein the functional material and the dry binder are crushed to obtain a fibrous raw material; and carrying out first heating rolling on the fibrillated raw materials to obtain the dry functional layer.
Further, the thickness of the dry functional layer is 5-40 μm;
the crushing mode comprises jet milling or high-speed dispersion;
the rotating speed of the high-speed dispersion is 2000rpm-4000rpm;
the temperature of the first heating calendaring is 45-300 ℃.
The third aspect of the invention provides a composite electrode, comprising an electrode and a dry functional layer for a lithium battery, wherein the dry functional layer is arranged on the surface of the electrode;
the dry functional layer for a lithium battery is the dry functional layer for a lithium battery according to the first aspect.
The fourth aspect of the present invention provides a method for manufacturing a composite electrode, wherein the electrode is manufactured and then rolled; and attaching a dry functional layer for the lithium battery on the surface of the electrode, and carrying out second heating and calendaring to obtain the composite electrode.
Further, the temperature of the second heated calendaring is 45 ℃ to 150 ℃.
The composite electrode comprises a positive electrode and a negative electrode, wherein the compacted density of the negative electrode is 1g/cm 3 -1.8g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The positive electrode has a compacted density of 2.2g/cm 3 -3.7g/cm 3 。
Further, after rolling and before the dry functional layer is attached, the compacted density of the electrode is 85% -99% of that of the composite electrode.
A fifth aspect of the invention provides the use of the composite electrode in a lithium battery.
Further, the electrode comprises a first composite electrode, a second composite electrode, an electrolyte, a diaphragm and a shell.
Compared with the prior art, the invention has at least the following beneficial effects:
the dry-method functional layer for the lithium battery provided by the invention has the function of bonding all components, and meanwhile, an elastic open net support is formed in the dry-method functional layer. Compared with the finished product prepared by the wet method, the porous material can be better and evenly dispersed in the three-dimensional space of the dry functional layer, the condensation problem does not exist between the porous material and the functional additive, and the electrical property and the safety of the prepared lithium battery are higher. The pores in the porous material in the dry functional layer can not be blocked by residual solvent and glue solution to block the ion path, so that the battery cell has good electrical performance. The dry functional layer and the pole piece active material layer do not have the penetration of solvent, so that the electrical performance of the battery core is not affected, and the pole piece is not deformed. The surface of the functional layer prepared by the dry film forming process has no cracks, the surface smoothness is better, the functional layer can be better attached to the surface of the pole piece, the solid-solid contact effect is improved, the interface impedance is smaller, meanwhile, the complete functional film form has a good heat insulation function, meanwhile, the crosstalk of gas in the battery cell is better avoided, and the safety is also improved.
According to the preparation method of the dry-method functional layer for the lithium battery, the functional material and the dry-method binder are mixed, fibrillated and calendered to obtain the functional layer. The adopted dry film forming process is solvent-free, nontoxic and harmless, does not increase or decrease additional solvent treatment equipment, saves a great amount of drying equipment and process time required by the wet process, greatly reduces the manufacturing cost of the battery cell and improves the manufacturing efficiency of the battery cell.
The composite electrode provided by the invention reduces gas crosstalk caused by oxygen release and solves the problem of thermal runaway of lithium ions.
The preparation method of the composite electrode provided by the invention has the advantages of continuous process and high degree of mechanization, and is convenient for large-scale industrialization.
The application of the composite electrode in the lithium battery improves the safety of the lithium ion battery, promotes the development of the lithium battery and widens the application places and conditions of the lithium battery.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a diagram of a lithium battery structure according to the present invention;
FIG. 2 is a schematic view of another lithium battery according to the present invention;
FIG. 3 is a graph showing voltage and temperature curves during the cell needling process of example 7;
FIG. 4 is a graph showing voltage and temperature during the cell lancing process of comparative example 10;
FIG. 5 is a first discharge capacity test result of example 7 and comparative example 10;
FIG. 6 is an SEM image of the surface of a pole piece of example 7;
fig. 7 is an SEM image of the surface of the pole piece of comparative example 11.
Icon: 10-positive electrode current collector; 20-positive electrode; 30-a dry functional layer; 40-a membrane; 50-negative electrode current collector; 60-negative electrode.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments of the present invention.
The terms "comprises," "comprising," "including," or any other variation thereof, are intended to cover a specific feature, number, step, operation, element, component, or combination of the foregoing, which may be used in various embodiments of the present invention, and are not intended to first exclude the presence of or increase the likelihood of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing.
Furthermore, the terms "first," "second," "third," and the like are used merely to distinguish between descriptions and should not be construed as indicating or implying relative importance.
The first aspect of the invention provides a dry functional layer for a lithium battery, which comprises a functional material and a dry binder, wherein the dry binder is fibrous, the dry binder is crosslinked to form a reticular framework of the dry functional layer, and the functional material is uniformly dispersed in the reticular framework;
wherein the functional material mainly comprises a porous material and a functional additive, and the functional additive is used for absorbing oxidative gas generated in the lithium battery.
The dry-method functional layer for the lithium battery provided by the invention has the function of bonding all components, and meanwhile, an elastic open net support is formed in the dry-method functional layer. Compared with the finished product prepared by the wet method, the porous material can be better and evenly dispersed in the three-dimensional space of the dry functional layer, the condensation problem does not exist between the porous material and the functional additive, and the electrical property and the safety of the prepared lithium battery are higher. The pores in the porous material in the dry functional layer can not be blocked by residual solvent and glue solution to block the ion path, so that the battery cell has good electrical performance. The dry functional layer and the pole piece active material layer do not have the penetration of solvent, so that the electrical performance of the battery core is not affected, and the pole piece is not deformed. The surface of the functional layer prepared by the dry film forming process has no cracks, the surface smoothness is better, the functional layer can be better attached to the surface of the pole piece, the solid-solid contact effect is improved, the interface impedance is smaller, meanwhile, the complete functional film form has a good heat insulation function, meanwhile, the crosstalk of gas in the battery cell is better avoided, and the safety is also improved.
Further, the porous material includes at least one of silica, alumina, zirconia, titania, and magnesia;
the functional additive comprises at least one of an ester of an anhydride having an unsaturated alicyclic structure, an amide of an anhydride having an unsaturated alicyclic structure, an imide of an anhydride having an unsaturated alicyclic structure, a dicarboxylic acid of an anhydride having an unsaturated alicyclic structure, and an anhydride polymer having an unsaturated alicyclic structure; in the present invention, the function additive functions to facilitate film formation and gas absorption.
The dry binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, poly (vinylidene fluoride-CO-hexafluoropropylene), polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid.
Further, the mass ratio of the functional material to the dry binder is 1.5-4.5:1; typically, but not by way of limitation, the functional material and dry binder are present in a mass ratio of 1.5:1, 2.5:1, 3.5:1 or 4.5:1.
The mass ratio of the porous material to the functional additive is 5.5-14:1; typically, but not by way of limitation, the mass ratio of porous material to functional additive is 5.5:1, 6:1, 7:1, 8:1, 9:1, 11:1 or 14:1.
The D50 particle size of the porous material is 1-30 mu m, the porosity is more than or equal to 50%, and the average pore diameter is 10-150 nm.
The second aspect of the invention provides a preparation method of the dry functional layer for the lithium battery, wherein the functional material and the dry binder are crushed to obtain a fibrous raw material; and carrying out first heating rolling on the fibrillated raw materials to obtain the dry functional layer.
According to the preparation method of the dry-method functional layer for the lithium battery, the functional material and the dry-method binder are mixed, fibrillated and calendered to obtain the functional layer. The adopted dry film forming process is solvent-free, nontoxic and harmless, does not increase or decrease additional solvent treatment equipment, saves a great amount of drying equipment and process time required by the wet process, greatly reduces the manufacturing cost of the battery cell and improves the manufacturing efficiency of the battery cell.
Further, the thickness of the dry functional layer is 5-40 μm; when the thickness of the dry functional layer is less than 5 mu m, the heat insulation effect is poor due to the fact that the thickness is too small, meanwhile, the heat conduction effect is poor, and the risk of short circuit after needling is further increased; when the thickness of the dry functional layer is greater than 40 μm, the coating layer will have an effect on the rate performance and cycle performance of the cell when the thickness is greater than 40 μm, while reducing the overall energy density of the cell. In some embodiments of the present invention, the thickness of the dry functional layer is typically, but not limited to, 5 μm, 10 μm, 20 μm, 30 μm or 40 μm.
The crushing mode comprises jet milling or high-speed dispersion;
the rotating speed of the high-speed dispersion is 2000rpm-4000rpm;
the temperature of the first heating calendaring is 45-300 ℃. When the temperature of the first heating and rolling is less than 45 ℃, film formation cannot be better performed; when the temperature of the first heated rolling is more than 300 ℃, the adhesive effect of the adhesive is destroyed to be unfavorable for film formation. In some embodiments of the present invention, the temperature of the first heated calender is typically, but not limited to, 45 ℃, 80 ℃, 150 ℃, 200 ℃, 250 ℃, or 300 ℃.
The third aspect of the invention provides a composite electrode, comprising an electrode and a dry functional layer for a lithium battery, wherein the dry functional layer is arranged on the surface of the electrode;
the dry functional layer for a lithium battery is the dry functional layer for a lithium battery according to the first aspect.
The composite electrode provided by the invention reduces gas crosstalk caused by oxygen release and solves the problem of thermal runaway of lithium ions.
The fourth aspect of the present invention provides a method for manufacturing a composite electrode, wherein the electrode is manufactured and then rolled; and attaching a dry functional layer for the lithium battery on the surface of the electrode, and carrying out second heating and calendaring to obtain the composite electrode.
The preparation method of the composite electrode provided by the invention has the advantages of continuous process and high degree of mechanization, and is convenient for large-scale industrialization.
The fabrication of the electrode belongs to the conventional steps, and is not limited in the present invention. The NP ratio of the electrode serving as the positive electrode and the electrode serving as the negative electrode is prepared according to a set value.
Further, the temperature of the second heated calendaring is 45 ℃ to 150 ℃. When the temperature of the second heating calendaring is less than 45 ℃, the second heating calendaring cannot be attached to a current collector better; when the temperature of the second heating calendaring is greater than 150 ℃, the adhesive property of the adhesive is destroyed to affect the attaching effect with the current collector. In some embodiments of the present invention, the temperature of the second heated calender is typically, but not limited to, 45 ℃, 55 ℃, 80 ℃, 100 ℃, 120 ℃, or 150 ℃.
The composite electrode comprises a positive electrode and a negative electrode, wherein the compacted density of the negative electrode is 1g/cm 3 -1.8g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The positive electrode has a compacted density of 2.2g/cm 3 -3.7g/cm 3 。
When the dry functional layer is not attached to the electrode surface, the first roll press directly presses the electrode to the target compacted density. When the dry functional layer is attached to the surface of the electrode, the compaction density of the electrode is 85% -99% of the compaction density (target compaction density) of the composite electrode after rolling and before the dry functional layer is not attached, and the composite electrode is manufactured after the dry functional layer is attached and then compacted for the second time to the target compaction density. This prevents the second voltage delay electrode from being over-voltage. Because the electrode material may be crushed under the condition of overvoltage, gaps are generated inside the electrode, and the ion conducting performance of the electrode is reduced.
In some embodiments of the invention, the positive and negative electrodes are both composite electrodes, and the compacted density of the negative electrode is 1g/cm 3 -1.8g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The positive electrode has a compacted density of 2.2g/cm 3 -3.7g/cm 3 。
In other embodiments of the present invention, only one of the positive electrode and the negative electrode is a composite electrode, and the other electrode is an electrode, so that the electrode does not need to be attached with a dry functional layer in the preparation process, and the electrode is directly rolled to a compacted density after being manufactured.
A fifth aspect of the invention provides the use of the composite electrode in a lithium battery.
The application of the composite electrode in the lithium battery improves the safety of the lithium ion battery, promotes the development of the lithium battery and widens the application places and conditions of the lithium battery.
Further, the electrode comprises a first composite electrode, a second composite electrode, an electrolyte and a diaphragm.
In some embodiments of the present invention, as shown in fig. 1, the lithium battery includes a positive electrode current collector 10, a positive electrode 20, a dry functional layer 30, a separator 40, a dry functional layer 30, a negative electrode 60, and a negative electrode current collector 50, where the surfaces of the positive electrode 20 and the negative electrode 60 are each provided with the dry functional layer 30 for absorbing an oxidizing gas.
In other embodiments of the present invention, the dry functional layer 30 may be provided only on the surface of the positive electrode 20 or the negative electrode 60. As shown in fig. 2, the lithium battery includes a positive electrode current collector 10, a positive electrode 20, a dry functional layer 30, a separator 40, a negative electrode 60, and a negative electrode current collector 50, in which only the dry functional layer 30 for absorbing the oxidative gas generated from the positive electrode is provided on the surface of the positive electrode 20.
The invention is further illustrated by the following specific examples and comparative examples, however, it should be understood that these examples are for the purpose of illustration only in greater detail and should not be construed as limiting the invention in any way. The raw materials used in the examples and comparative examples of the present invention were conducted under conventional conditions or conditions recommended by the manufacturer, without specifying the specific conditions. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
Example 1
The embodiment provides a dry functional layer for a lithium battery, and the preparation method comprises the following steps:
1. 140g of a silica porous material (specific surface area 1400 m) 2 Per g, a porosity of 95% and a density of 0.08g/cm 3 The D50 particle size is 10 mu m, the pore diameter is 40 nm), 20g of polyvinylidene fluoride and 40g of polytetrafluoroethylene PTFE are mixed and then put into a jet mill for jet milling to obtain fibrous functional powder;
2. the fibrillated functional powder is put into a hot rolling and calendering device for rolling, and the rolling temperature is 150 ℃ to obtain a dry functional layer with 25 mu m.
Example 2
The present embodiment provides a dry functional layer for a lithium battery, which is different from embodiment 1 in that the thickness of the dry functional layer is 30 μm, and the other preparation methods and raw materials are the same as those of embodiment 1, and are not described herein.
Example 3
The present embodiment provides a dry functional layer for a lithium battery, which is different from embodiment 1 in that the thickness of the dry functional layer is 50 μm, and the other preparation methods and raw materials are the same as those of embodiment 1, and are not described herein.
Example 4
The present embodiment provides a dry functional layer for a lithium battery, which is different from embodiment 1 in that the amount of the silica porous material is 160g, and the other preparation methods and raw materials are the same as embodiment 1, and are not described herein.
Example 5
The dry functional layer for a lithium battery is provided in this embodiment, and is different from embodiment 1 in that the amount of polyvinylidene fluoride is 10g, and the other preparation methods and raw materials are the same as those in embodiment 1, and are not described here again.
Example 6
The present embodiment providesUnlike example 1, the dry functional layer for lithium battery uses alumina porous material (specific surface area of 1000m 2 Per g, a porosity of 95% and a density of 0.05g/cm 3 The D50 particle size was 20 μm and the pore diameter was 60 nm), and the other preparation methods and raw materials were the same as those of example 1, and will not be described here again.
Comparative example 1
The comparative example provides a dry functional layer for a lithium battery, which is different from example 1 in that the addition amount of the silica porous material is 35g, the addition amount of polyvinylidene fluoride is 5g, and the other preparation methods and raw materials are the same as example 1, and are not described here again.
Comparative example 2
This comparative example provides a dry functional layer for lithium batteries, which is different from example 1 in that no silica porous material is used, the amount of polyvinylidene fluoride added is 100g, the amount of polytetrafluoroethylene added is 160g, and the other preparation methods and raw materials are the same as those of example 1, and are not described here again.
Comparative example 3
This comparative example provides a dry functional layer for a lithium battery, which is different from example 1 in that a general silica is used instead of a silica porous material, and the other preparation methods and raw materials are the same as example 1, and are not described here again.
Comparative example 4
This comparative example provides a dry functional layer for lithium batteries, which is different from example 1 in that polyvinylidene fluoride is not added, and the other preparation methods and raw materials are the same as example 1, and are not described here again.
Comparative example 5
This comparative example provides a functional layer slurry for lithium batteries, 140g of a silica porous material (specific surface area 1400m 2 Per g, a porosity of 95% and a density of 0.08g/cm 3 The D50 particle size was 10 μm and the pore diameter was 40 nm), and 20g of polyvinylidene fluoride and 400g of dimethylacetamide solvent were mixed and stirred sufficiently to obtain a functional layer slurry for lithium batteries.
Examples 7 to 12
These examples provide some lithium batteries, specifically prepared as follows:
1. preparing a positive electrode plate: according to the active materials: conductive agent: binder = 97:1:2 at a solids content of 70%, and according to 470g/m 2 Is coated and dried, and then the positive electrode sheet is coated according to the surface density of 3.37g/cm 3 The positive electrode plate to be attached with the dry functional layer is obtained by rolling the electrode plate with the compacted density.
2. Preparing a negative electrode plate: according to the active materials: conductive agent: binder = 94.7:2:3.3 amount A negative electrode slurry was prepared at 47% solids and was prepared at 226.9g/m 2 Is coated and dried, and then the negative electrode sheet is coated according to the surface density of 1.5g/cm 3 And (3) rolling the pole piece by the compaction density to obtain the final negative pole piece.
3. The dry functional layer films obtained in examples 1-6 are adhered to the surface of the positive electrode sheet, and are put into a hot rolling device for rolling, the rolling temperature is 100 ℃, and the rolling is carried out until the compacted density of the electrode sheet is 3.50g/cm 3 And obtaining the positive electrode plate with the dry functional layer.
4. And die-cutting or slitting the positive and negative electrode plates obtained by the belt, and then assembling the positive and negative electrode plates with a diaphragm, electrolyte and a shell to form the lithium ion battery.
Example 13
This example provides a lithium battery, unlike example 7, in which the positive electrode sheet was 3.55g/cm in step 1 3 Is rolled into a pole piece; in step 2, the negative electrode sheet was subjected to a process of 1.43g/cm 3 Is rolled into a pole piece; in step 3, the dry functional layer film obtained in example 1 is attached to the surface of the negative electrode plate, and the plate is rolled to a compaction density of 1.47g/cm 3 And obtaining the negative electrode plate with the dry functional layer. The other materials and methods are the same as in example 7, and will not be described here again.
Example 14
The embodiment provides a lithium ion battery, wherein the positive electrode adopts the positive electrode plate with the dry-method functional layer of the embodiment 7, the negative electrode adopts the negative electrode plate with the dry-method functional layer of the embodiment 13, and the obtained positive electrode plate is die-cut or striped, and then assembled with a diaphragm, electrolyte and a shell.
Comparative examples 6 to 9
These comparative examples provide some lithium batteries, and unlike example 7, the dry functional layer films obtained in comparative examples 1 to 4 are correspondingly attached to the surface of the positive electrode sheet, and the remaining methods and steps are the same as example 7, and are not described here again.
Comparative example 10
These comparative examples provide lithium batteries, unlike example 7, in which the positive electrode sheet in step 1 was 3.37g/cm 3 Is rolled into a pole piece; step 3 is omitted; the other methods and steps are the same as those of example 7, and will not be described here again.
Comparative example 11
The comparative example provides a lithium battery, which is different from example 7 in that the functional layer slurry for a lithium battery obtained in comparative example 5 is coated on the surface of the positive electrode sheet, and the other raw materials and steps are the same as those in example 7, and are not described herein.
Test example 1
The lithium batteries obtained in examples 7 to 14 and comparative examples 6 to 10 were subjected to standard tests including a first-week charge capacity test, a first-week discharge capacity test, a first-week coulombic efficiency and an internal resistance. The results obtained are shown in Table 1 below.
TABLE 1
As can be seen from table 1:
(1) It can be seen from examples 7-14 that the uniformity of cell performance is high within the scope of the present invention. Comparing the cells of examples 7-14 with the dry layer with the cells of comparative example 10 without the dry layer, the data were highly consistent, and the capacity, initial efficiency, and internal resistance were all at one level, which shows that the dry layer of the present invention has no effect on the electrical properties of the cells. This demonstrates that the dry porous layer of the present invention can be applied to the electrode surface of a lithium ion battery as a dry functional layer.
(2) Comparative example 6 reduced the functional material below the lower limit and comparative example 9 had no significant effect on the cell electrical properties without additives, but had significant effects in the safety test results listed in table 2.
(3) Example 9 is a case where the dry functional layer is too thick, which has exceeded the scope defined by the present invention, and since the thicker dry functional layer, although its initial effect is slightly reduced but not significantly, the excessively thick functional layer has a significant adverse effect on the internal resistance of the cell.
(4) Comparative example 7 was free of porous material, resulting in a functional layer that was composed of binder and functional additive directly, which resulted in a dry functional layer without sufficient voids to provide good ion paths for the cells, resulting in a significant decrease in cell discharge capacity, initial coulombic efficiency, and discharge voltage uniformity, while at the same time, an increase in internal resistance.
(5) Although the chemical components of the porous material exist in comparative example 8, but the porous structure of the porous material is not provided, and a good ion path is not provided in the construction process of the dry functional layer as in comparative example 7, the solid silica material added in comparative example 8 has a certain pore between particles after the formation of the dry functional layer, and thus the electrical properties are greatly affected, but slightly better than in comparative example 7.
(6) Compared with comparative example 6, the first effect of the battery cell of comparative example 11 is obviously lower than that of example 7, and the internal resistance is obviously higher than that of example 7, and in the process of preparing the functional coating by surface wet coating, the surface tension of the solvent in the porous structure enables the coating to have extremely strong capillary force in the drying process, and the hydroxyl groups in the porous structure have extremely strong condensation action, so that the two reasons jointly lead to cracking of the coating and collapse of the porous structure (figure 6), and the residual solvent, the adhesive solution, the active material failure caused by penetration into the active material layer and other various reasons lead to the increase of the internal resistance of the battery cell of comparative example 11, and the first effect is reduced.
Test example 2
The lithium batteries obtained in examples 7 to 14 and comparative examples 6 to 10 were subjected to safety performance tests according to GB T31485-2015, and the test results obtained are shown in Table 2.
TABLE 2
As can be seen from table 2:
(1) From the test results of examples 7 to 14 and comparative example 10, the cells of examples 7 to 14 having the dry functional layer of the present invention all passed the respective safety tests, while the cell of comparative example 10 having no dry functional layer of the present invention failed the respective safety tests. Therefore, the dry functional layer of the invention has obvious improvement on the safety performance of the lithium ion battery.
(2) As can be seen from comparative example 6, too little functional material will have a significant effect on the safety performance of the battery cell, and the dry functional layer produced by combining the data of comparative example 6 in table 1, although it has no effect on the electrical performance of the battery cell, cannot better improve the safety performance of the battery cell when the functional material is below the lower limit of the present invention.
(3) As can be seen from example 9, when the functional layer is thicker, the battery cells pass each safety test, and the data in table 1 show that although the lithium ion battery manufactured in example 9 can pass each safety index, the electrical performance of the lithium ion battery is significantly reduced.
(4) The surfaces of example 14 and example 8, either without porous material or replaced with non-porous material, not only had their electrical properties reduced but their safety performance was also compromised.
(5) In example 10, the electrical performance of the cells in table 1 was not significantly affected by the non-functional additives, but it is evident from the safety test results in table 2 that the safety performance was also reduced without the functional additives.
(6) The test results of comparative example 11 demonstrate that the wet coated functional layer has no significant improvement in safety performance due to the presence of cracking.
The full electric acupuncture test results of example 7 and comparative example 10 are shown in fig. 3 and 4. From this, it is clear that the cell with the dry functional layer in example 7 can be needled without significant changes in voltage and temperature; in contrast, the cells without the dry functional layer in comparative example 10 failed the needling test, and the voltage was drastically attenuated in several tens of seconds while the temperature was drastically increased to more than 900 ℃.
The first discharge curves of example 7 and comparative example 10 are, as shown in fig. 5, substantially identical for the cell discharge curve with the dry functional layer in example 7 and the cell discharge curve without the dry functional layer in comparative example 10, i.e., the dry functional layer has substantially no effect on the electrical properties of the cell.
The pole pieces obtained in example 7 and comparative example 11 were subjected to scanning electron microscopy, and the results are shown in fig. 6 and 7. As can be seen from fig. 6 and 7, the functional layer prepared using the dry method of example 7 had no crack, whereas the functional layer prepared using the wet coating of comparative example 11 had a surface with its obvious crack.
Finally, it should be noted that: the above examples are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention, but it should be understood by those skilled in the art that the present invention is not limited thereto, and that the present invention is described in detail with reference to the foregoing examples: any person skilled in the art may modify or easily conceive of the technical solution described in the foregoing embodiments, or perform equivalent substitution of some of the technical features, while remaining within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. The dry-method functional layer for the lithium battery is characterized by comprising a functional material and a dry-method binder, wherein the dry-method binder is fibrous, the dry-method binder is crosslinked to form a net-shaped framework of the dry-method functional layer, and the functional material is dispersed in the net-shaped framework;
wherein the functional material mainly comprises a porous material and a functional additive, and the functional additive is used for absorbing oxidative gas generated in the lithium battery.
2. The dry functional layer for a lithium battery according to claim 1, wherein the porous material comprises at least one of silica, alumina, zirconia, titania, and magnesia;
the functional additive comprises at least one of an ester of an anhydride having an unsaturated alicyclic structure, an amide of an anhydride having an unsaturated alicyclic structure, an imide of an anhydride having an unsaturated alicyclic structure, a dicarboxylic acid of an anhydride having an unsaturated alicyclic structure, and an anhydride polymer having an unsaturated alicyclic structure;
the dry binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, poly (vinylidene fluoride-CO-hexafluoropropylene), polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid.
3. The dry functional layer for a lithium battery according to claim 1, wherein a mass ratio of the functional material to the dry binder is 1.5-4.5:1;
the mass ratio of the porous material to the functional additive is 5.5-14:1;
the D50 particle size of the porous material is 1-30 mu m, the porosity is more than or equal to 50%, and the average pore diameter is 10-150 nm.
4. A method for producing a dry functional layer for a lithium battery according to any one of claims 1 to 3, characterized in that the functional material and the dry binder are crushed to obtain a fibrillated raw material; and carrying out first heating rolling on the fibrillated raw materials to obtain the dry functional layer.
5. The method of claim 4, wherein the dry functional layer has a thickness of 5 μm to 40 μm;
the crushing mode comprises jet milling or high-speed dispersion;
the rotating speed of the high-speed dispersion is 2000rpm-4000rpm;
the temperature of the first heating calendaring is 45-300 ℃.
6. The composite electrode is characterized by comprising an electrode and a dry functional layer for a lithium battery, wherein the dry functional layer is arranged on the surface of the electrode;
wherein the dry functional layer for a lithium battery is the dry functional layer for a lithium battery according to any one of claims 1 to 3.
7. A method of manufacturing a composite electrode according to claim 6, wherein the electrode is manufactured and then rolled; and attaching a dry functional layer for the lithium battery on the surface of the electrode, and carrying out second heating and calendaring to obtain the composite electrode.
8. The method of claim 7, wherein the second heated calender has a temperature of 45 ℃ to 150 ℃;
the composite electrode comprises a positive electrode and a negative electrode, wherein the compacted density of the negative electrode is 1g/cm 3 -1.8g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The positive electrode has a compacted density of 2.2g/cm 3 -3.7g/cm 3 。
9. The method of claim 7, wherein the compacted density of the electrode after rolling and before the dry functional layer is attached is 85% -99% of the compacted density of the composite electrode.
10. Use of a composite electrode according to claim 6 or a composite electrode prepared by a method according to any one of claims 7 to 9 in a lithium battery.
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