CN116053406A - Lithium ion battery negative electrode plate, battery and preparation method - Google Patents
Lithium ion battery negative electrode plate, battery and preparation method Download PDFInfo
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Abstract
The invention discloses a lithium ion battery negative electrode piece, a battery and a preparation method thereof, wherein the battery comprises a porous foil, a lithium supplementing material coating, a silicon negative electrode material coating and a graphite coating; wherein the porosity of the porous foil is 20% -50%, and the aperture is 0.1-4 mm; the lithium supplementing material layers are attached to two side surfaces of the porous foil and are filled in holes of the porous foil; the silicon negative electrode material coating is attached to the outer side of the lithium supplementing material layer; the graphite coating is attached to the outside of the silicon-based anode material coating.
Description
Technical Field
The invention belongs to the technical field of electrochemistry, and particularly relates to a lithium ion battery negative electrode plate, a battery and a preparation method thereof.
Background
The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.
Because the lithium ion battery has irreversible capacity loss when being charged for the first time, lithium is generally needed to be supplemented when the negative electrode plate is prepared, and the conventional lithium supplementing method at present uses lithium plates or lithium powder to be placed on the surface of the negative electrode plate.
In addition, in the practical application process, the existing silicon-based anode material is easy to change in volume during lithium intercalation or deintercalation, so that the overall cycle performance of the lithium ion battery is poor. At present, the expansion of the anode material is improved by using an excellent binder, but when the expansion of the silicon anode material reaches a certain degree along with the increase of the cycle times, no redundant space is needed to digest the expansion stress and the volume change generated by the silicon anode, and the anode material still can be greatly damaged.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a lithium ion battery negative electrode plate, a battery and a preparation method.
In order to achieve the above object, the present invention is realized by the following technical scheme:
in a first aspect, the invention provides a lithium ion battery negative electrode plate, which comprises a porous foil, a lithium supplementing material coating, a silicon negative electrode material coating and a graphite coating;
wherein the porosity of the porous foil is 20% -50%, and the aperture is 0.1-4 mm;
the lithium supplementing material layers are attached to two side surfaces of the porous foil and are filled in holes of the porous foil;
the silicon negative electrode material coating is attached to the outer side of the lithium supplementing material layer;
the graphite coating is attached to the outside of the silicon-based anode material coating.
As described in the background art, in the practical application process, the existing silicon-based anode material is easy to change in volume during lithium intercalation or deintercalation, resulting in deterioration of the overall cycle performance of the lithium ion battery.
The inventors tried various methods to solve the above technical problems, one of which is to coat a lithium supplementing coating on a porous foil, fill the lithium supplementing coating into the through holes of the porous foil, and then coat a silicon-based negative electrode material coating on the surface of the lithium supplementing coating to obtain a negative electrode sheet. However, when the silicon-based anode material coating was subjected to a charge-discharge test, it was found that most of the expansion direction was away from the porous foil during charge-discharge expansion.
The inventors have further studied this phenomenon, and found that the overall expansion stress release direction of the silicon-based anode material coating is disordered, that is, the expansion tendency is toward the periphery without difference, and the porous foil is provided with a large number of holes, but when the silicon-based anode material coating expands toward the porous foil, the following resistance needs to be overcome: when the porous foil is not provided with a resistance at the hole position and the hole is filled by expansion, the resistance is large when expanding toward the porous foil due to frictional resistance of the inner wall of the hole against the silicon negative electrode material, and the like.
When the coating layer of the silicon-based negative electrode material expands in a direction away from the porous foil, the expansion resistance to the silicon-based negative electrode material is small because the separator is soft in texture and high in elasticity even if the separator can be touched. Therefore, the overall expansion direction of the silicon-based anode material coating layer is outward, and in this case, the porosity utilization ratio to the porous foil is low, and it is difficult to achieve a good effect of reducing the expansion failure effect of the silicon anode.
The inventors have therefore demanded further improvements in the technical solutions.
Based on the above findings, the inventors tried to apply a stopper layer on the outer side of the silicon-based anode material coating layer, which can apply a pressing force toward the inner side to the silicon-based anode material when it expands outwardly, to restrict the outward expansion of the silicon-based anode material.
Because the prepared product is a negative electrode plate, the limiting layer needs to have the following properties: the conductive material has better conductivity so as to ensure the normal operation of the negative electrode plate; has high strength and can effectively inhibit the outward expansion of the silicon negative electrode material. The coating is also preferably a negative electrode active material coating-if not, to reduce the overall energy density of the cell; the coating is not capable of blocking lithium ion conduction.
Proved by repeated experiments, the graphite coating can meet the requirements, so that the outer side of the silicon negative electrode material coating is coated with a graphite layer, the surface density of the graphite layer is 0.5-5 times of that of the silicon negative electrode coating, the graphite coating contains a binder, graphite is layered and parallel to the foil surface during rolling, and finally the graphite coating has stress for extruding the silicon coating towards the foil surface.
The effect of the graphite coating is analyzed in detail as follows:
1. the graphite coating itself is a negative electrode active material, and has a gram capacity lower than that of a silicon-based negative electrode, relative to a silicon-based coating. But its expansion is much smaller than that of a silicon-based negative electrode/silicon & graphite composite negative electrode.
2. The graphite coating acts as a structural coating. The negative electrode active material has two coatings, wherein the silicon coating has larger expansion and smaller expansion, when the lithium supplementing material in the porous foil is consumed, the porous foil has a plurality of gaps, the flexibility of the graphite coating (with a binder) is far lower than that of a diaphragm, and meanwhile, the graphite in the graphite coating is layered and parallel to the foil after the lithium battery pole piece is rolled. The graphite coating itself expands, and the stress generated by the expansion presses the silicon negative electrode coating against the foil surface. Therefore, when the silicon negative electrode expands, the resistance of the surface facing the foil is far smaller than the resistance of the surface facing the graphite, the silicon negative electrode releases the expansion stress into the gaps of the porous foil preferentially, and the internal gaps of the porous foil are fully utilized.
The working principle of the negative electrode plate of the invention is as follows:
when the lithium battery is charged for the first time, the lithium supplementing coating in the porous foil can supplement lithium for the silicon anode material, so that the first efficiency of the battery is improved, and the energy density of the battery is increased. After the lithium powder in the lithium supplementing coating is consumed, the pores filled by the lithium supplementing material of the original porous foil can be provided with a lot of space. The silicon negative electrode material coating expands in volume when being charged, and expands towards the two directions of the porous foil and the graphite coating, because a plurality of gaps are formed in the porous foil due to consumption of the lithium supplementing material, the expansion stress and volume change of the silicon negative electrode material coating can be preferentially released into the gaps of the porous foil under the limit effect of the graphite coating, so that the gaps of the porous foil well solve the problem of the expansion stress and volume change of the silicon negative electrode material coating during charging and discharging, and finally the whole negative electrode plate is not influenced by the expansion.
Based on the above working principle, the expanded silicon-based anode material is limited by the graphite coating layer, and is expanded in the direction of the inner porous foil, so as to inhibit the outward expansion of the silicon-based anode material. This requires that the porous foil can provide sufficient voids to satisfy the expansion volume of the silicon-based anode material.
In addition, the inventors have found that when the pore diameter of the porous foil is small, the resistance to be overcome when the silicon-based anode material is deformed to fill the pores is larger, but the strength of the graphite coating is limited, so that the pore diameter of the porous foil needs to be limited to effectively reduce the deformation filling resistance, and as described in the examples, the pore diameter is 0.1 to 4mm, the resistance smaller than 0.1mm is larger, and the strength of the porous foil is difficult to maintain when larger than 4 mm.
In some embodiments, the pores of the porous foil are through-holes. When the silicon negative electrode fills the gap of the foil material during the through hole, the stress on two sides of the foil material is balanced because the active substances are communicated; meanwhile, the silicon negative electrode is communicated when the through hole is formed, and the lithium battery is similar to the action mechanism of a porous foil, so that the lithium battery is better in conductivity and more beneficial to the cycle rate and other electrical properties of the lithium battery.
In some embodiments, the graphite layer comprises graphite, a conductive agent and a binder, wherein the mass ratio of the graphite, the conductive agent and the binder is 84-98:1-6:1-10. Graphite is also a negative electrode active material, which also participates in charge and discharge of the battery, so that graphite is both a functional coating and a part of the negative electrode, and a conductive agent is added to the coating like a normal negative electrode active material coating.
The graphite is artificial graphite or natural graphite.
Preferably, the binder is selected from one or a combination of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polymethacrylic acid, polyacrylate and sodium carboxymethyl cellulose or polyvinylidene fluoride.
Preferably, the conductive agent is selected from one or a combination of Super P, SFG, ketjen black, VGCF, CNTs and graphene.
In some embodiments, the graphite layer has a thickness of 40 to 150 μm.
In some embodiments, the lithium supplementing material layer has a thickness of 0-3 μm on the surface of the porous foil. To increase the energy density of the cell, the space for coating the active material is not occupied as much as possible.
In some embodiments, the porous foil has a thickness of 8 to 20 μm.
In a second aspect, the invention provides a preparation method of the lithium ion battery negative electrode plate, which comprises the following steps:
uniformly mixing metal lithium powder, a conductive agent and a binder according to a proportion to prepare a lithium supplementing material;
coating a lithium supplementing material on the porous foil, and filling the holes of the porous foil to obtain a lithium supplementing material layer;
uniformly mixing a silicon-based negative electrode material, a conductive agent and a binder in proportion, and coating the obtained slurry on a lithium supplementing material layer to obtain a silicon-based negative electrode material coating;
graphite, a conductive agent and a binder are mixed according to the mass ratio of 84-98:1-6:1-10, the obtained graphite slurry is coated on a silicon negative electrode material coating to obtain a graphite coating, and the binder in the graphite coating is selected from one or a combination of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polymethacrylic acid, polyacrylate, sodium carboxymethylcellulose and polyvinylidene fluoride.
In some embodiments, the lithium-compensating material is applied to the porous foil by spray coating or magnetron sputtering deposition.
In a third aspect, the present invention provides the lithium ion battery, which includes the negative electrode tab.
The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:
the negative electrode plate has strong practicability, and a complex and difficult-to-operate method of covering the lithium plate is not needed. The invention can obviously reduce the damage of expansion to the pole piece when the silicon anode material is used, and safely and reasonably supplements lithium to the silicon anode.
The invention perfectly utilizes the porous and negative electrode multilayer coating structure of the porous foil, and improves the initial effect and expansion of the silicon negative electrode.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a plan view of a porous foil of an embodiment of the invention;
FIG. 2 is a cross-sectional view of an embodiment of the present invention after lithium supplementing material;
fig. 3 is a schematic cross-sectional view of a negative electrode plate of a lithium ion battery prepared in an embodiment of the invention.
Wherein, 1, porous foil; 100. a through hole;
2. a lithium supplementing material coating; 3. a silicon-based negative electrode material coating; 4. and (3) a graphite coating.
Detailed Description
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The invention is further illustrated below with reference to examples.
Example 1
As shown in fig. 1-3, a lithium ion battery negative electrode plate comprises a porous foil 1, a lithium supplementing material layer 2, a silicon negative electrode material coating 3 and a graphite coating 4;
the porosity of the porous foil 1 is 20% -50%, and the aperture is 0.1-4 mm;
the lithium supplementing material layers 2 are attached to two side surfaces of the porous foil material 1 and are filled in the through holes 100 of the porous foil material 1;
the silicon-based negative electrode material coating 3 is attached to the outer side of the lithium supplementing material layer 2;
the graphite coating 4 is attached to the outside of the silicon-based anode material coating 3.
And (3) manufacturing a lithium supplementing material layer 2: the surface density of the silicon negative electrode material coating 3 is P 3 ＝7mg/cm 2 Gram volume of C 3 =500 mAh/g, first coulomb efficiency L 3 =80% graphite coating 4 surface density P 4 ＝7mg/cm 2 Gram volume of C 4 =350 mAh/g, first coulomb efficiency L 4 =90%, pole piece area s=120 cm 2 Design capacity of pre-lithiation C 0 80% of irreversible capacity of the cathode, and gram capacity of metal lithium powder is C Lithium ion battery =3600 mAh/g, the positive-negative NP ratio is 1.12, i.e. the negative balance is y=12%. Thereby calculating the required quantity of the lithium metal powder as M Lithium ion battery ：
M Lithium ion battery ＝((P 3 *S*C 3 *(1-L 3 )*80％*Y)+(P 4 *S*C 4 *(1-L 4 )*80％*Y))/C Lithium ion battery ＝
((7*120*500*(1-80％)*80％*12％)+(7*120*350*(1-90％)*80％*12％))/3600mg＝3.024mg。
According to 97% of metal lithium powder mass, 1.5% of conductive agent KS-6 mass fraction and 1.5% of binder polyacrylic acid mass fraction are uniformly mixed in tetrahydrofuran solution, and lithium supplementing slurry is coated on the porous copper foil by spraying. The thickness of the porous copper foil is 8 mu m, and the porosity is 30%.
The lithium metal density is known to be 534mg/cm 3 The theoretical thickness of the lithium supplementing layer is D Lithium supplement ＝M Lithium ion battery Lithium density/S100000/97% = 3.024/534/120 x 100000 μm = 4.719 μm.
The lithium supplementing layer is coated on the surface of the foil with the thickness of D Surface of the body ＝(D Theory of Copper foil thickness porosity)/2=1.16 μm.
And (3) manufacturing a silicon-based anode material coating 3: the negative electrode active material silicon oxide material, the conductive agent Super-P and the binder polyvinylidene fluoride are uniformly mixed in NMP according to the weight ratio of 97 percent to 1.5 percent to form slurry, and the slurry is coated on the front side and the back side of the lithium supplementing material layer 2.
And (3) preparing a graphite coating 4: the negative electrode active material artificial graphite, the conductive agent Super-P and the binder polyvinylidene fluoride are uniformly mixed into slurry in NMP according to the weight ratio of 96.5 percent to 1.5 percent to 2.0 percent, and the slurry is coated on the front side and the back side of the silicon negative electrode material coating 3.
The negative electrode sheet is produced as shown in fig. 3, and is rolled after being dried. Cutting to obtain the required negative electrode plate.
And (3) manufacturing a positive plate: the positive electrode ternary material, the conductive agent and the binder are mixed according to the mass ratio of 96.5 percent: 2.0%: and (3) uniformly mixing 1.5 percent, and coating the mixture on the positive electrode current collector. Rolling and cutting to obtain the required positive pole piece.
And (3) manufacturing a battery: and laminating, baking, packaging and injecting the liquid to obtain the required battery.
Comparative example one (a) preparation: the comparative example positive electrode was the same positive electrode as that of the example; the negative electrode was prepared by using a silicon oxide material having a gram capacity of 425mAh/g (the total capacity of the negative electrode coating was equivalent to that of the negative electrode of example 1), mixing the negative electrode material with a conductive agent Super-P and a binder polyvinylidene fluoride in an amount of 97.0%:1.5% of the powder is uniformly mixed and then the powder has an areal density of 14mg/cm 2 The lithium-supplementing porous foil was coated with the same lithium-supplementing porous foil as in example 1 (i.e., the same porous foil 1 and the same lithium-supplementing material layer 2 shown in the figure). The two subsequent material processes are identical. And comparing the two batteries. The relevant properties of the fabricated batteries are shown in table 1.
TABLE 1
The data in table 1 shows that the full-charge rebound rate of the negative electrode plate is effectively reduced in the examples, and the gaps of the foil are better utilized in the examples compared with the comparative examples, so that the charging expansion of the silicon negative electrode is better improved, and the cycle performance is further improved.
Comparative example one (two) preparation: the comparative example positive electrode was the same positive electrode as in example 1; the negative electrode was made of a silicon oxide material having a gram capacity of 425mAh/g (the total capacity of the negative electrode coating is equivalent to that of the exampleA total capacity of the negative electrode), uniformly mixing the negative electrode material with the conductive agent Super-P and the binder polyvinylidene fluoride according to the proportion of 97.0 percent to 1.5 percent, and then obtaining the negative electrode material with the surface density of 14mg/cm 2 The porous foil is coated on a porous foil, and the porous foil adopts a carbon-coated porous foil which is conventional in the industry. The two subsequent material processes are identical. And comparing the two batteries. The relevant properties of the fabricated batteries are shown in table 2.
TABLE 2
From the data in table 2, it can be seen that the example effectively reduces the full-charge rebound rate of the negative electrode sheet compared with the conventional battery, thereby well improving the charge expansion of the silicon negative electrode, further improving the cycle performance, and simultaneously improving the initial effect and increasing the gram capacity.
Example 2
The surface density of the silicon negative electrode material coating 3 is P 3 ＝7mg/cm 2 Gram volume of C 3 =550 mAh/g, first coulomb efficiency L 3 =79% and graphite coating 4 surface density of P 4 ＝8mg/cm 2 Gram volume of C 4 =350 mAh/g, first coulomb efficiency L 4 =90%, pole piece area s=120 cm 2 Design capacity of pre-lithiation C 0 80% of irreversible capacity of the cathode, and gram capacity of metal lithium powder is C Lithium ion battery =3600 mAh/g, the positive-negative NP ratio is 1.12, i.e. the negative balance is y=12%. Thereby calculating the required quantity of the lithium metal powder as M Lithium ion battery ：
M Lithium ion battery ＝((P 3 *S*C 3 *(1-L 3 )*80％*Y)+(P 4 *S*C 4 *(1-L 4 )*80％*Y))/C Lithium ion battery
＝((7*120*550*(1-79％)*80％*12％)+(8*120*350*(1-90％)*80％*12％))/3600mg＝3.483mg。
According to 97% of metal lithium powder mass, 1.5% of conductive agent KS-15 mass fraction and 1.5% of binder polyvinylidene fluoride mass fraction, uniformly mixing in tetrahydrofuran solution, and coating lithium supplementing slurry by sprayingOn the porous copper foil. The thickness of the porous copper foil is 8 mu m, and the porosity is 30%. The lithium metal density is known to be 534mg/cm 3 The theoretical thickness of the lithium supplementing layer is D Lithium supplement ：
D Lithium supplement ＝M Lithium ion battery Lithium density/S100000/97% = 3.483/534/120 x 100000 μm
＝5.438μm。
The lithium supplementing layer is coated on the surface of the foil with the thickness of D Surface of the body ＝(D Theory of Copper foil thickness porosity)/2=1.518 μm.
And (3) manufacturing a silicon-based anode material coating 3: the negative electrode active material silicon oxide material, the conductive agent KS-6 and the binder polyvinylidene fluoride are uniformly mixed in NMP according to the weight ratio of 97 percent to 1.5 percent to form slurry, and the slurry is coated on the front side and the back side of the lithium supplementing material layer 2.
And (3) preparing a graphite coating 4: the negative electrode active material artificial graphite, a conductive agent KS-6 and a binder polyvinylidene fluoride are uniformly mixed in NMP according to the weight ratio of 96.5 percent to 1.5 percent to 2.0 percent to form slurry, and the slurry is coated on the front side and the back side of the silicon negative electrode material coating 3.
The negative electrode sheet is produced as shown in fig. 3, and is rolled after being dried. Cutting to obtain the required negative electrode plate.
And (3) manufacturing a positive plate: the positive electrode ternary material, the conductive agent and the binder are mixed according to the mass ratio of 96.0 percent: 2.5%: and (3) uniformly mixing 1.5 percent, and coating the mixture on the anode porous current collector. Rolling and cutting to obtain the required positive pole piece.
And (3) manufacturing a battery: and laminating, baking, packaging and injecting the liquid to obtain the required battery.
Production of comparative example two (one): the comparative example positive electrode was the same positive electrode as in example two; the negative electrode adopts silicon oxide material with the gram capacity of 444mAh/g (the total capacity of a negative electrode coating is equal to that of a second negative electrode in the embodiment), and the negative electrode material, a conductive agent Super-P and a binder polyvinylidene fluoride are mixed according to 96.8 percent: 1.5% to 1.7% and 15mg/cm in surface density 2 The coating is coated on a lithium supplementing porous foil, and the lithium supplementing porous foil adopts the same lithium supplementing foil as the second embodiment (namely foil 1 and lithium supplementing material shown in the attached drawings)Layer 2, as well). The two subsequent material processes are identical. And comparing the two batteries. The relevant properties of the fabricated batteries are shown in table 3.
TABLE 3 Table 3
The data in table 3 shows that the full-charge rebound rate of the negative electrode plate is effectively reduced in the examples, and the gaps of the foil are better utilized in the examples compared with the comparative examples, so that the charging expansion of the silicon negative electrode is better improved, and the cycle performance is further improved.
Comparative example two (two) preparation: the comparative example positive electrode was the same positive electrode as in example two; the negative electrode adopts silicon oxide material with the gram capacity of 444mAh/g (the total capacity of a negative electrode coating is equal to that of a second negative electrode in the embodiment), and the negative electrode material, a conductive agent Super-P and a binder polyvinylidene fluoride are mixed according to 96.8 percent: 1.5% to 1.7% and 15mg/cm in surface density 2 The carbon-coated porous foil was coated with the same foil as in example 2, but the carbon-coated layer did not contain lithium powder (i.e., carbon-coated porous foil was used as normal in the industry). The two subsequent material processes are identical. And comparing the two batteries. The relevant properties of the fabricated batteries are shown in table 4.
TABLE 4 Table 4
As can be seen from the data of comparative example 2 and comparative example two, the battery prepared by the lithium supplementing method can maintain the primary efficiency and gram capacity as long as the lithium supplementing amount is sufficient when the silicon content of the negative electrode is increased. Meanwhile, the battery manufactured in the embodiment 2 is superior to the common battery in the aspects of primary efficiency, gram capacity exertion and negative pole piece rebound.
Example 3
The production method and materials used in example 3 were the same as those used in example 2, but the lithium-supplemented porous copper foil having a negative electrode of 10 μm was used, and the available porosity of the foil was increased relative to that of example 2. The same procedure was used for comparative example three (one) and comparative example two (one), but the foil thickness was changed from 8 μm to 10 μm. Full-electrode negative electrode tab rebound ratios of comparative examples one, two, and three.
The relevant data are shown in table 5:
TABLE 5
From the data in Table 5, when the anode foil has sufficient gaps available, the battery prepared by the method can well utilize the gaps of the porous foil, so that under the condition that the silicon content is increased, the expansion of the anode silicon material is still ensured to be obviously improved; however, it is apparent from the comparative example that when the structural formula of the present invention is not adopted, the thickened gap of the foil becomes large and the expansion of the anode is not improved much.
Example 4
The surface density of the silicon negative electrode material coating 3 is P 3 ＝7mg/cm 2 Gram volume of C 3 =600 mAh/g, first coulomb efficiency L 3 =75% graphite coating 4 surface density P 4 ＝8mg/cm 2 Gram volume of C 4 =350 mAh/g, first coulomb efficiency L 4 =90%, pole piece area s=120 cm 2 Design capacity of pre-lithiation C 0 80% of irreversible capacity of the cathode, and gram capacity of metal lithium powder is C Lithium ion battery =3600 mAh/g, the positive-negative NP ratio is 1.12, i.e. the negative balance is y=12%. Thereby calculating the required amount M lithium of the metal lithium powder:
m lithium= ((P) 3 *S*C 3 *(1-L 3 )*80％*Y)+(P 4 *S*C 4 *(1-L 4 ) 80% Y))/C lithium
＝((7*120*600*(1-75％)*80％*12％)+(8*120*350*(1-90％)*80％*12％))/3600mg＝4.256mg。
According to 97% of metal lithium powder mass, 1.5% of conductive agent KS-15 mass fraction and 1.5% of binder polyvinylidene fluoride mass fraction are uniformly mixed in tetrahydrofuran solution, and lithium supplementing slurry is coated on a porous copper foil through magnetron sputtering deposition. The thickness of the porous copper foil is 8 mu m, and the porosity is 30%. The lithium metal density is known to be 534mg/cm 3 The theoretical thickness of the lithium supplementing layer is D Lithium supplement ：
D Lithium supplement ＝M Lithium ion battery Lithium density/S100000/97% = 3.483/534/120 x 100000 μm
＝6.642μm。
The lithium supplementing layer is coated on the surface of the foil with the thickness of D Surface of the body ＝(D Theory of Copper foil thickness porosity)/2= 2.121 μm.
And (3) manufacturing a silicon-based anode material coating 3: the negative electrode active material silicon oxide material, the conductive agent super-P and the binder polyvinylidene fluoride are uniformly mixed in NMP according to the weight ratio of 97 percent to 1.5 percent to form slurry, and the slurry is coated on the front side and the back side of the lithium supplementing material layer 2.
And (3) preparing a graphite coating 4: the negative electrode active material artificial graphite, a conductive agent KS-6 and a binder polyvinylidene fluoride are uniformly mixed in NMP according to the weight ratio of 96.5 percent to 1.5 percent to 2.0 percent to form slurry, and the slurry is coated on the front side and the back side of the silicon negative electrode material coating 3.
The negative electrode sheet is produced as shown in fig. 3, and is rolled after being dried. Cutting to obtain the required negative electrode plate.
And (3) manufacturing a positive plate: the positive electrode ternary material, the conductive agent and the binder are mixed according to the mass ratio of 96.0 percent: 2.5%: and (3) uniformly mixing 1.5 percent, and coating the mixture on the anode porous current collector. Rolling and cutting to obtain the required positive pole piece.
And (3) manufacturing a battery: and laminating, baking, packaging and injecting the liquid to obtain the required battery.
Comparative example four (one) preparation: the comparative example positive electrode was the same positive electrode as in example 4; the negative electrode was made of a silicon oxide material having a gram capacity of 467mAh/g (the total capacity of the negative electrode coating is equivalent to that of the exampleFour negative electrode total capacity), the negative electrode material and the conductive agent Super-P and the binder polyvinylidene fluoride are mixed according to 96.8 percent: 1.5% to 1.8% and 15mg/cm in surface density 2 The lithium-supplementing porous foil is coated with the same lithium-supplementing foil as in example 4 (namely, foil 1 and lithium-supplementing material layer 2 shown in the drawings). The two subsequent material processes are identical. And comparing the two batteries. The performance data of the cells are shown in table 6.
TABLE 6
From the data in table 6, it can be seen that example 4 effectively reduces the full-charge rebound rate of the negative electrode sheet, and that example 4 better utilizes the gaps of the foil material compared with the comparative example, thereby better improving the charge expansion of the silicon negative electrode and further improving the cycle performance.
Comparative example four (two) preparation: the comparative example positive electrode was the same positive electrode as in example four; the negative electrode adopts a silicon oxide material with gram capacity of 467mAh/g (the total capacity of a negative electrode coating is equal to that of a fourth negative electrode in the embodiment), and the negative electrode material, a conductive agent Super-P and a binder polyvinylidene fluoride are mixed according to 96.8 percent: 1.5% to 1.7% and 15mg/cm in surface density 2 The carbon-coated porous foil is coated on the carbon-coated porous foil, and the carbon-coated porous foil adopts the foil which is the same as that of the fourth embodiment, but the carbon-coated layer does not contain lithium powder (namely the carbon-coated porous foil is normally used in the industry). The two subsequent material processes are identical. The relevant performance data of the cells fabricated by comparing the two are shown in table 7.
TABLE 7
When the silicon content continues to be increased to the most advanced level in the industry, the battery manufactured by the method can still ensure that the expansion of the cathode is obviously improved compared with the common battery.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The utility model provides a lithium ion battery negative pole piece which characterized in that: comprises a porous foil, a lithium supplementing material coating, a silicon negative electrode material coating and a graphite coating;
wherein the porosity of the porous foil is 20% -50%, and the aperture is 0.1-4 mm;
the lithium supplementing material layers are attached to two side surfaces of the porous foil and are filled in holes of the porous foil;
the silicon negative electrode material coating is attached to the outer side of the lithium supplementing material layer;
the graphite coating is attached to the outside of the silicon-based anode material coating.
2. The lithium ion battery negative electrode tab of claim 1, wherein: the holes of the porous foil are through holes.
3. The lithium ion battery negative electrode tab of claim 1, wherein: the graphite layer comprises graphite, a conductive agent and a binder, wherein the mass ratio of the graphite to the conductive agent to the binder is 84-98:1-6:1-10.
4. A lithium ion battery negative electrode tab according to claim 3, wherein: the binder is selected from one or a combination of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polymethacrylic acid, polyacrylate and sodium carboxymethyl cellulose or polyvinylidene fluoride.
5. A lithium ion battery negative electrode tab according to claim 3, wherein: the conductive agent is selected from one or a combination of Super P, SFG, ketjen black, VGCF, CNTs and graphene.
6. The lithium ion battery negative electrode tab of claim 1, wherein: the thickness of the graphite layer is 40-150 mu m.
7. The lithium ion battery negative electrode tab of claim 1, wherein: the thickness of the lithium supplementing material layer on the surface of the porous foil is 0-3 mu m.
8. A preparation method of a lithium ion battery negative electrode plate is characterized by comprising the following steps: the method comprises the following steps:
uniformly mixing metal lithium powder, a conductive agent and a binder according to a proportion to prepare a lithium supplementing material;
coating a lithium supplementing material on the porous foil, and filling the holes of the porous foil to obtain a lithium supplementing material layer;
uniformly mixing a silicon-based negative electrode material, a conductive agent and a binder in proportion, and coating the obtained slurry on a lithium supplementing material layer to obtain a silicon-based negative electrode material coating;
graphite, a conductive agent and a binder are mixed according to the mass ratio of 84-98:1-6:1-10, the obtained graphite slurry is coated on a silicon negative electrode material coating to obtain a graphite coating, and the binder in the graphite coating is selected from one or a combination of styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, polymethacrylic acid, polyacrylate, sodium carboxymethylcellulose and polyvinylidene fluoride.
9. The method for preparing the lithium ion battery negative electrode plate according to claim 8, wherein the method comprises the following steps: the lithium supplementing material is coated on the porous foil by spraying or magnetron sputtering deposition.
10. A lithium ion battery, characterized in that: comprising the negative electrode sheet of any one of claims 1-7.
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