CN117334835A - Lithium ion battery and electronic device comprising same - Google Patents
Lithium ion battery and electronic device comprising same Download PDFInfo
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- CN117334835A CN117334835A CN202311287877.9A CN202311287877A CN117334835A CN 117334835 A CN117334835 A CN 117334835A CN 202311287877 A CN202311287877 A CN 202311287877A CN 117334835 A CN117334835 A CN 117334835A
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 58
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 58
- 239000011148 porous material Substances 0.000 claims abstract description 15
- 239000003575 carbonaceous material Substances 0.000 claims description 44
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 42
- 239000006229 carbon black Substances 0.000 claims description 40
- 229910021389 graphene Inorganic materials 0.000 claims description 27
- 239000010410 layer Substances 0.000 claims description 23
- 239000002048 multi walled nanotube Substances 0.000 claims description 23
- 239000002109 single walled nanotube Substances 0.000 claims description 22
- 239000007774 positive electrode material Substances 0.000 claims description 15
- 239000002003 electrode paste Substances 0.000 claims description 14
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 13
- 239000013543 active substance Substances 0.000 claims description 13
- 229910052744 lithium Inorganic materials 0.000 claims description 13
- 239000011247 coating layer Substances 0.000 claims description 12
- 239000007773 negative electrode material Substances 0.000 claims description 7
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 5
- 239000002210 silicon-based material Substances 0.000 claims description 5
- 239000011366 tin-based material Substances 0.000 claims description 5
- 229910021383 artificial graphite Inorganic materials 0.000 claims description 4
- 229910021385 hard carbon Inorganic materials 0.000 claims description 4
- 229910021382 natural graphite Inorganic materials 0.000 claims description 4
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 claims description 3
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 claims description 3
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 claims description 3
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 3
- DVATZODUVBMYHN-UHFFFAOYSA-K lithium;iron(2+);manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[Fe+2].[O-]P([O-])([O-])=O DVATZODUVBMYHN-UHFFFAOYSA-K 0.000 claims description 3
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- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
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- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 description 1
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- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 229920003063 hydroxymethyl cellulose Polymers 0.000 description 1
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- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000004005 microsphere Substances 0.000 description 1
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- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 1
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 1
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 description 1
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- 229910052718 tin Inorganic materials 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
Classifications
-
- H—ELECTRICITY
- 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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- 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
-
- H—ELECTRICITY
- 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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
-
- H—ELECTRICITY
- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
The invention discloses a lithium ion battery and an electronic device, wherein the lithium ion battery comprises a positive plate and a negative plate, and the positive plate and the negative plate satisfy the following relation:R c is the resistivity of the positive plate, P c Is the porosity of the positive plate, τ c Is the tortuosity of the pore gap of the positive plate, R a For the resistivity of the negative plate, P a For the porosity of the negative electrode sheet, τ a Negative is tortuosity of the pore of the negative electrode sheet. The lithium ion battery prepared by the invention meets the above relation, thereby realizing the reduction of the resistance of the electrode slice layer, forming a good conductive network between electrode material layers, ensuring the perfection of the conductive network in the circulation process and improving the performance of the batteryThe lithium ion battery assembled by the positive and negative plates not only improves the internal resistance, but also improves the comprehensive electrochemical performance.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery and an electronic device containing the same.
Background
The lithium ion battery has been widely used in the fields of consumer electronics, new energy automobiles, energy storage and the like due to the advantages of long service life, high average output voltage, low environmental pollution and the like. In use, lithium ion batteries are used, and lithium ions and electrons are transmitted inside the battery pole pieces, so that good transmission of the lithium ions and the electrons is an important factor for determining the performance of the lithium ion batteries.
In the electrode, electrons are transported mainly through the solid phase. On the positive electrode side, the positive electrode active material is generally a transition metal oxide having poor conductivity, so that the sheet resistance is extremely large, and an additional conductive agent is required to be added to form an electron conductive path. The factors influencing the final sheet resistance of the positive electrode sheet are directly and closely related to the distribution state of the conductive agent, the contact state between solid particles, the interface condition of the current collector and the coating layer, and the like besides the type of the conductive agent. For the negative electrode side, the conventional graphite negative electrode has better conductivity due to the intrinsic characteristic, but the electrode resistance is increased to a certain extent due to the introduction of high polymer materials such as a binder SBR, a thickener CMC and the like, and the electron conduction is affected. For silicon anodes, due to their semiconducting properties, it is also necessary to add a conductive agent to ensure a good electron conduction path.
The lithium ion battery is an integral, the performance in operation is the result of the comprehensive operation of the whole system, lithium ions and electrons are continuously separated from or inserted into the anode and the cathode, the lithium ions and the electrons are continuously changed between the electrodes, the lithium ion battery faces to the complex chemical system change, the integral internal resistance of the battery is difficult to be effectively reduced by independently regulating and controlling the anode or the cathode, and the integral battery performance is difficult to be improved.
For example, in the positive electrode sheet, the content of the novel high-efficiency conductive agent material is continuously increased by adjusting the proportion, the sheet resistivity of the positive electrode side is continuously reduced, and although the internal resistance of the battery is reduced in the initial stage, the later change is not great, because the electronic and lithium ion conduction rate of the positive electrode side is continuously increased by adjusting the formula, but the electronic and lithium ion conduction of the negative electrode side is mainly restricted, and the single increase of the positive electrode side cannot effectively play a role in improving the overall performance of the battery.
That is, the requirement that the positive and negative polarities are independently improved cannot be met, the matching of the positive electrode and the negative electrode of the battery is extremely critical, and lithium ions and electrons are well transmitted between the positive electrode and the negative electrode, so that the performance of the whole battery is favorably exerted, and the service life of the battery is prolonged. When the positive electrode and the negative electrode are not matched, more adverse effects are brought to the battery, and the lithium ion battery can face the problems of high internal resistance, obviously reduced cycle life, poor rate capability and the like, so that how to simply and effectively design the lithium ion battery to ensure that the positive electrode and the negative electrode are obviously optimized is a technical problem to be solved urgently.
Disclosure of Invention
In order to solve the problems, the invention provides a lithium ion battery, which comprises a positive plate and a negative plate, wherein the positive plate comprises a current collector and a positive paste layer coated on at least one side of the current collector, and the positive paste layer comprises a positive active substance and a carbon material; the negative electrode sheet comprises a current collector and a negative electrode paste coating layer coated on at least one side of the current collector, wherein the negative electrode paste coating layer comprises a negative electrode active substance and a carbon material; the performance parameters of the positive plate and the negative plate meet the relation:
wherein R is c Is the resistivity of the positive plate, P c Is the porosity of the positive plate, τ c Is the tortuosity of the pore gap of the positive plate, R a For the resistivity of the negative plate, P a For the porosity of the negative electrode sheet, τ a Is the tortuosity of the pore gap of the negative electrode sheet.
In one embodiment of the present invention, the performance parameters of the positive electrode sheet and the negative electrode sheet satisfy the relation:
preferably, the positive electrode sheet and the negative electrode sheet satisfy the relation:
by way of example only, and in an illustrative,is 3.31,5.05,2.06,1.62,8.12 or any point in the range of any two points described above.
Wherein, the relation between the pore tortuosity tau and the porosity P is expressed by a relation formula of Bruggeman: τ=p (1-α) Wherein, alpha is more than or equal to 1.0 and less than or equal to 3.5.α=1.5 in a uniform porous electrode; the performance parameters of the positive plate and the negative plate meet the relation:
in one embodiment of the invention, 10% < P c ＜100％，15％＜P a ＜100％，0.05KΩ.cm＜R c ＜6.8KΩ.cm，1Ω.cm＜R a ＜50Ω.cm；100％＜τ c ＜316％，100％＜τ a ＜258％。
Preferably, 15% < P c ＜60％，20％＜P a ＜80％，0.05KΩ.cm＜R c ＜2.4KΩ.cm，1Ω.cm＜R a ＜20Ω.cm，129％＜τ c ＜258％，111％＜τ a ＜224％。
In one embodiment of the invention, the carbon material comprises one or more of carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphene.
In one embodiment of the present invention, the positive electrode active material includes one or more of lithium cobaltate, lithium manganate, lithium titanate, lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate.
Preferably, the negative active material includes one or more of a silicon-based material, a tin-based material, artificial graphite, natural graphite, or hard carbon.
In one embodiment of the present invention, the content of the carbon material in the positive electrode sheet satisfies one of the following conditions:
(a) When the carbon material in the positive plate is only carbon black, the content of the carbon black in the positive paste layer is 1.2-3wt%;
(b) When the carbon material in the positive plate contains carbon black and at least one of multi-wall carbon nano tubes, single-wall carbon nano tubes and graphene, the total content of the carbon material in the positive paste layer is 0.6-3wt%; the content of the carbon black is 0.1 to 2.9 weight percent of the positive electrode paste layer.
(c) When the carbon material in the positive plate is single-walled carbon nanotube and/or graphene, the total content of the carbon material in the positive electrode paste coating layer is 0.4-1.5 wt%; when the carbon material in the positive plate is single-walled carbon nanotube and graphene, the mass ratio of the single-walled carbon nanotube to the graphene is 1:5.
If the carbon material in the positive plate is too much, the addition amount of the active substance can be reduced, so that the energy density is lost, and the addition amount can cause difficult dispersion in the stirring process, agglomeration of the carbon material and influence the electronic conductivity due to the fact that the specific surface area of the carbon material is relatively high. The invention controls the content of the carbon material in the range, can reduce the surface resistance better and improve the energy density.
In one embodiment of the present invention, the carbon material content in the negative electrode sheet is 0% to 2% by weight, preferably 0.2% to 1% by weight.
Too much carbon material content in the negative plate can also reduce the addition amount of active substances, and the stirring is difficult; the addition amount is too small, which affects the conductivity of ions and electrons, so that the control of the carbon material content in the negative electrode sheet can more effectively reduce the surface resistance and improve the negative electrode dynamics.
In one embodiment of the present invention, the specific surface area of the carbon black is 60 to 900m 2 /g; preferably 60 to 300m 2 /g; more preferably 60 to 180m 2 /g。
Illustratively, the carbon black has a specific surface area of 60m 2 /g、80m 2 /g、100m 2 /g、120m 2 /g、140m 2 /g、160m 2 /g、180m 2 /g or any range between any two values.
In one embodiment of the invention, the multiwall carbon nanotubes satisfy at least one of the following conditions:
(i) The average length of the multi-wall carbon nanotubes is 1-100 μm, preferably 50-100 μm;
(ii) The average diameter of the multi-walled carbon nanotubes is 3nm to 2 μm, preferably 3nm to 500nm.
In one embodiment of the present invention, the single-walled carbon nanotubes have an average diameter of 1.6 μm and an average length of 1 μm to 1000 μm.
Preferably, the graphene satisfies at least one of the following conditions:
(I) The average layer number of the graphene is 1-10;
(II) D of the graphene 50 From 1 μm to 10. Mu.m.
In one embodiment of the invention, the positive plate and the negative plate are rolled plates.
Preferably, the positive plate is rolled once, and the negative plate is rolled twice.
Preferably, at least one side of the current collector of the positive electrode sheet is coated with a paste layer.
According to an aspect of the present invention, there is also provided an electronic device including the above lithium ion battery.
In particular, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD-player, a mini-compact disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable audio recorder, a radio, a stand-by power supply, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flash lamp, a camera, and the like.
The invention has the beneficial effects that:
considering that the electrode material is continuously expanded and contracted along with the charge and discharge of the electrode in the battery circulation process, the conductive network is damaged at the later period of the circulation so as to influence the performance of the battery, in order to solve the problems, the invention provides a lithium ion battery, wherein the performance parameters such as the resistivity, the porosity and the pore tortuosity in the positive and negative electrode plates satisfy the relationThe resistance of the electrode plate layer is reduced, a good conductive network is formed between electrode material layers, the perfection of the conductive network in the circulation process is ensured, the performance of the battery is improved, and the lithium ion battery assembled by adopting the positive and negative electrode plates not only improves the internal resistance, but also improves the comprehensive electrochemical performance.
Under the condition of ensuring smaller internal resistance of the lithium ion battery, reasonable collocation between the anode and the cathode is realized, the design pressure of the battery is relieved, the power performance and the discharge efficiency of the lithium ion battery are improved, and particularly the multiplying power and the cycle life of the lithium ion battery are improved.
Drawings
FIG. 1 is a schematic diagram of a pole piece resistivity test point location according to the present invention.
Fig. 2 is a schematic diagram of the principle of the pole piece resistivity test of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and examples. It should be emphasized that the specific embodiments described herein are merely illustrative of some, but not all embodiments of the invention, and are not intended to limit the invention. Further, technical features relating to the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
In lithium ion batteries, the main effect on electron transmission is the resistivity of the electrode sheet, which is an intrinsic barrier to electrons, and the lower the electrode sheet resistance, the lower the resistance to electrons. The main effect of ion transmission is the porosity of the pole piece, which provides a path for ion transmission, and the higher the porosity of the pole piece is, the lower the resistance of the pole piece to ions is. Therefore, the resistivity of the pole piece has a large influence on the electronic impedance, and the porosity of the pole piece has a large influence on the ionic impedance. The internal resistance of the battery can be reduced by reducing the resistivity of the positive and negative pole pieces and improving the porosity of the pole pieces.
However, the positive and negative plates are balanced in electron transmission and lithium ion intercalation-deintercalation, and the electronic impedance or the ion impedance of a certain polar plate is reduced independently, so that the overall impedance of the battery cannot be reduced effectively, and therefore, the design between the positive and negative plates needs to be balanced. For example, in order to reduce the internal resistance of the lithium ion battery, the resistivity of the positive electrode sheet is continuously reduced by means of reducing the resistivity of the positive electrode sheet, improving the porosity of the positive electrode sheet and the like, and by adjusting the electrode material and the electrode proportion, the resistivity of the positive electrode sheet is continuously reduced, but the internal resistance of the battery is hardly reduced after the internal resistance of the battery is reduced to a certain extent, because the resistivity of the positive electrode sheet is not the bottleneck of the battery impedance at this time, the continuous reduction of the resistivity of the positive electrode sheet does not obviously contribute to the reduction of the internal resistance of the battery, and therefore, the parameter in the positive electrode sheet or the negative electrode sheet is independently adjusted, so that the requirement of integral regulation of the battery cannot be met.
In order to solve the problems, the invention provides a lithium ion battery, which comprises a positive plate and a negative plate, wherein the positive plate comprises a current collector and a positive paste layer coated on at least one side of the current collector, and the positive paste layer comprises a positive active substance and a carbon material; the negative electrode sheet comprises a current collector and a negative electrode paste coating layer coated on at least one side of the current collector, wherein the negative electrode paste coating layer comprises a negative electrode active substance and a carbon material; the performance parameters of the positive plate and the negative plate meet the relation:
wherein R is c Is the resistivity of the positive plate, P c Is the porosity of the positive plate, τ c Is the tortuosity of the pore gap of the positive plate, R a For the resistivity of the negative plate, P a For the porosity of the negative electrode sheet, τ a Is the tortuosity of the pore gap of the negative electrode sheet.
According to the invention, the specific matching relation is satisfied by adjusting the resistivity, the porosity and the pore tortuosity in the positive and negative plates, so that the matching degree between the positive and negative plates is higher, the reasonable matching between the positive and negative plates is realized under the condition of smaller internal resistance of the lithium ion battery, the design pressure of the battery is relieved, and the power performance and the discharge efficiency of the lithium ion battery are improved.
Preferably, the performance parameters of the positive plate and the negative plate satisfy the relation:
more preferably, the performance parameters of the positive electrode sheet and the negative electrode sheet satisfy the relation:
according to the invention, 10% < P c ＜100％，15％＜P a ＜100％，0.05KΩ.cm＜R c ＜6.8KΩ.cm，1Ω.cm＜R a ＜50Ω.cm；100％＜τ c ＜316％，100％＜τ a ＜258％。
Preferably, 15% < P c ＜60％，20％＜P a ＜80％，0.05KΩ.cm＜R c ＜2.4KΩ.cm，1Ω.cm＜R a ＜20Ω.cm，129％＜τ c ＜258％，111％＜τ a ＜224％。
The current collectors of the positive and negative electrode sheets are not particularly limited in the present invention as long as they have conductivity without causing chemical changes in the battery. Such as copper, stainless steel, aluminum, nickel, titanium, or a metal current collector surface treated with carbon or other substances. The positive and negative electrode current collectors may have fine irregularities formed on the surfaces thereof to improve the adhesion of the positive electrode active material. For example, positive electrode current collectors of various shapes such as films, sheets, foils, nets, porous bodies, foams and non-woven fabrics may be used.
According to the present invention, the carbon material includes one or more of carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphene.
The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, and preferably, the positive electrode active material includes one or more of lithium cobaltate, lithium manganate, lithium titanate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate; the negative electrode active material includes one or more of silicon-based material, tin-based material, artificial graphite, natural graphite, and hard carbon.
The positive electrode sheet may contain a positive electrode binder and/or a positive electrode conductive material in addition to the positive electrode active material described above. The positive electrode binder is used for binding the positive electrode active material, the conductive material, the current collector and other components together. Specifically, at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber may be contained, with polyvinylidene fluoride being preferred.
The content of the carbon material in the positive plate according to the invention meets one of the following conditions:
(a) When the carbon material in the positive plate is only carbon black, the carbon black content is 1.2-3wt% of the positive electrode paste coating layer;
(b) When the carbon material in the positive plate contains carbon black and at least one of multi-wall carbon nano tubes, single-wall carbon nano tubes and graphene, the total content of the carbon material in the positive paste layer is 0.6-3wt%; the content of the carbon black is 0.1 to 2.9 weight percent of the positive electrode paste layer.
(c) When the carbon material in the positive plate is single-walled carbon nanotube and/or graphene, the total content of the carbon material is 0.4-1.5 wt% of the positive paste layer; when the carbon material in the positive plate is single-walled carbon nanotube and graphene, the mass ratio of the single-walled carbon nanotube to the graphene is 1:5.
Preferably, the content of the carbon material in the negative electrode sheet is 0.01-2 wt% of the negative electrode paste coating layer, and preferably 0.2-1 wt%.
According to the invention, the specific surface area of the carbon black is 60-900 m 2 /g; preferably 60 to 300m 2 /g; more preferably 60 to 180m 2 /g。
Preferably, the multiwall carbon nanotubes satisfy at least one of the following conditions:
(i) The average length of the multi-wall carbon nanotubes is 1-100 μm, preferably 50-100 μm;
(ii) The average diameter of the multi-walled carbon nanotubes is 3nm to 2 μm, preferably 3nm to 500nm.
Preferably, the single-walled carbon nanotubes have an average diameter of 1.6 μm and an average length of 1 μm to 1000 μm.
According to the invention, the graphene at least meets one of the following conditions:
(I) The average layer number of the graphene is 1-10;
(II) D of the graphene 50 Is 1-10 mu m.
The positive electrode sheet may be manufactured by coating a positive electrode slurry including a positive electrode active material and optionally a positive electrode binder, a positive electrode conductive material, and a solvent for forming a positive electrode slurry on a positive electrode current collector, and then drying and rolling.
The negative electrode active material can be one or more of silicon-based materials, tin-based materials, lithium titanate, graphite, soft carbon, hard carbon, carbon fibers and mesophase carbon microspheres. Wherein, the graphite can be one or more of artificial graphite and natural graphite; the silicon-based material can be one or more of elemental silicon, silicon oxygen compound, silicon carbon compound and silicon alloy; the tin-based material can be one or more of elemental tin, tin oxide and tin alloy.
The negative plate also comprises a binder, a conductive agent and a thickening agent. The conductive agent includes, but is not limited to, conductive carbon black, carbon nanotubes, graphene, or the like; the binder includes, but is not limited to, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, styrene-butadiene rubber, or hydroxymethyl cellulose, etc. The thickener is, for example, sodium carboxymethyl cellulose.
The invention provides a preparation method of a positive plate and a negative plate and an assembly method of a lithium ion battery, wherein the preparation method comprises the following steps:
the preparation method of the positive plate comprises the following steps: mixing the positive electrode active material, the conductive agent and the binder according to a certain mass ratio, adding the mixture into a stirring tank, adding a solvent, uniformly stirring to prepare positive electrode slurry, uniformly coating the positive electrode slurry on the surface of a current collector through a coating machine, drying, compacting by a roller press, and cutting to obtain the positive electrode plate.
The preparation method of the negative plate comprises the following steps: adding a negative electrode active material, a conductive agent, a thickening agent and a binder into a stirring tank according to a certain mass ratio, adding deionized water, stirring to obtain uniform-fluidity negative electrode slurry, uniformly coating the negative electrode slurry on the surface of a current collector copper foil, drying, compacting by a roller press, and cutting to obtain a negative electrode plate.
And rolling the prepared positive plate and the negative plate, wherein the positive plate is formed by one-time rolling, and the negative plate is formed by two-time rolling.
Assembling a lithium ion battery:
and winding the prepared positive plate, the isolating film and the negative plate to obtain a bare cell without liquid injection, placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried bare cell, and carrying out the procedures of vacuum packaging, standing, formation, shaping, sorting and the like to obtain the corresponding lithium ion battery.
The technical scheme of the invention is further described below with reference to specific embodiments.
Example 1
Firstly, preparing a positive plate and a negative plate
(1) Preparation of positive electrode slurry and positive electrode plate
Preparing a positive plate: adding positive electrode active substances of lithium cobaltate, carbon black, multi-wall carbon nano tubes, single-wall carbon nano tubes and polyvinylidene fluoride into a stirring tank according to the mass ratio of 97.6:0.9:0.4:0.1:1, wherein the carbon black ratio table is 60m 2 The average diameter and the tube length of the multi-wall carbon nano tube are respectively 10nm and 50 mu m, and the average diameter of the single-wall carbon nano tube is 1.6nm. Then adding a solvent N-methyl pyrrolidone (NMP) solvent, uniformly stirring to prepare positive electrode slurry, uniformly coating the positive electrode slurry on the surface of a current collector aluminum foil by a coating machine, drying and compacting by a roller press to obtain the positive electrode plate.
(2) Preparation of negative electrode slurry and negative electrode sheet
Preparing a negative electrode sheet: adding negative electrode active substance graphite, conductive carbon material carbon black, styrene-butadiene rubber and sodium carboxymethylcellulose into a stirring tank according to the mass ratio of 96.4:1:1:1.3, wherein the specific surface area of the carbon black is 60m 2 And (3) adding deionized water, stirring to obtain uniform-fluidity negative electrode slurry, uniformly coating the negative electrode slurry on a current collector copper foil surface by a coating machine, drying and compacting by a roller press to obtain the negative electrode plate.
And rolling the prepared positive plate and the negative plate, wherein the positive plate is formed by one-time rolling, and the negative plate is formed by two-time rolling.
(3) The electrolyte is selected from conventional electrolyte (1 mol/L LiPF 6 Solvent EC: EMC: pc=20:70:10, additive weight percent: 1% VC+1% PS).
(4) The isolating film is a film coated with 5+3 Zhuo Gaohun film of 8 microns thickness.
(5) Preparation of lithium ion batteries
Winding the prepared positive plate, the isolating film and the negative plate to obtain a bare cell without liquid injection; and placing the bare cell in an outer packaging foil, injecting the prepared corresponding electrolyte into the dried bare cell, and performing the procedures of vacuum packaging, standing, formation, shaping, sorting and the like to obtain the corresponding lithium ion battery.
Example 2
The same preparation method as in example 1 is used, except thatThe method comprises the following steps: the proportion of each component in the preparation of the positive plate is positive electrode active material, carbon black, multi-wall carbon nano tube and polyvinylidene fluoride according to the mass ratio of 97.2:1:0.6:1.2, wherein the specific surface area of the carbon black is 120m 2 The average diameter and tube length of the multiwall carbon nanotubes were 8nm and 50 μm, respectively.
Preparing a negative plate: the negative electrode active material, conductive carbon material carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are formed according to the mass ratio of 96.7:0.5:1.5:1.3, wherein the specific surface area of the carbon black is 60m 2 /g。
Example 3
The same preparation as in example 1 was carried out, except that: the positive electrode ratio is composed of positive electrode active substances of lithium cobaltate, carbon black and polyvinylidene fluoride according to the mass ratio of 96.5:2:1.5, wherein the carbon black ratio table is 120m 2 /g。
The negative electrode ratio is composed of negative electrode active substance graphite, conductive carbon material carbon black, binder styrene-butadiene rubber and thickener sodium carboxymethyl cellulose according to the mass ratio of 96.9:0.5:1.3:1.3, wherein the carbon black ratio table is 60m 2 /g。
Example 4
The preparation method of the positive electrode sheet is the same as that of the positive electrode sheet in example 2; the preparation method of the negative electrode sheet was the same as that of example 3.
Example 5
Preparing a positive plate: comprises a positive electrode active material, carbon black, multi-wall carbon nano tubes, graphene and polyvinylidene fluoride according to the mass ratio of 97.8:0.6:0.3:0.2:1.1, wherein the carbon black ratio table is 120m 2 The average diameter and the tube length of the multiwall carbon nanotubes are 8nm and 50 mu m respectively, and the average layer number and the particle size of the graphene are 10 layers and 5 mu m.
The preparation method of the negative electrode sheet was the same as that of the negative electrode sheet in example 2.
The lithium ion battery provided in embodiments 1-5 adopts the carbon material and the corresponding addition amount in the application for the positive electrode plate and the negative electrode plate so as to achieve lower electrode plate resistivity, and meanwhile, the matching relationship between the positive electrode plate and the negative electrode plate of the lithium ion battery is based on:the specific values of the parameters in (a) are shown in table 1.
Comparative example 1
The preparation method is the same as in example 1, except that:
preparing a positive plate: is composed of positive electrode active material lithium cobaltate, carbon black, multi-wall carbon nano tube, single-wall carbon nano tube and polyvinylidene fluoride according to the mass ratio of 97.3:0.6:0.6:0.5:1, wherein the specific surface area of the carbon black is 60m 2 The average diameter and the tube length of the multi-wall carbon nano tube are respectively 10nm and 50 mu m, and the average tube diameter of the single-wall carbon nano tube is 1.6nm.
Preparing a negative electrode sheet: the negative electrode active material comprises graphite, styrene-butadiene rubber and sodium carboxymethylcellulose according to the mass ratio of 97.2:1.5:1.3, and no conductive carbon material is added.
Comparative example 2
The preparation method is the same as in example 1, except that the positive plate comprises a positive active material, carbon black and polyvinylidene fluoride according to a mass ratio of 97.6:0.6:1.8, wherein the carbon black ratio is 60m 2 /g。
The negative electrode sheet was prepared as in example 2.
Comparative example 3
The positive plate comprises positive electrode active material, carbon black and polyvinylidene fluoride according to the mass ratio of 97:1:2, wherein the carbon black ratio is 120m 2 And/g. The preparation method of the negative electrode sheet is the same as that of example 1.
Comparative example 4
The preparation method of the positive plate is the same as that of comparative example 1; the proportion of the negative electrode plate is composed of negative electrode active substance, carbon black, styrene-butadiene rubber and sodium carboxymethylcellulose according to the mass ratio of 96.5:0.5:1.7:1.3.
Comparative example 5
The positive electrode sheet was prepared in the same manner as in example 2, and the negative electrode sheet was prepared in the same manner as in comparative example 2.
Comparative example 6
The preparation method of the positive electrode sheet was the same as that of the positive electrode sheet in example 3, and the preparation method of the negative electrode sheet was the same as that of the negative electrode sheet of comparative example 2.
The lithium ion batteries provided in comparative examples 1 to 6 were based on the matching relationship between the positive electrode sheet and the negative electrode sheet of the lithium ion battery:the specific values of the parameters in (a) are shown in table 1.
[ Performance characterization ]
The positive and negative electrode sheets prepared in examples 1 to 5 and comparative examples 1 to 6 were tested for resistivity by a double probe surface resistance measurement method:
1) Respectively taking a positive plate and a negative plate to be assembled into a battery, and taking a certain number of points on the plates according to requirements (figure 1); the pole piece point taking requirement is as follows: the back of the pole piece (namely the short surface and the double surface) is provided with a left point, a middle point and a right point, wherein the left point and the right point are required to be separated from the edges of the plaster on the two sides of the pole piece by 2cm.
2) And measuring the sheet resistivity of the point positions of the positive sheet and the negative sheet by using a surface resistance tester, recording specific numerical values, and calculating an average value.
The pole piece resistivity test principle (fig. 2) is: the current loop is sequentially electrode positive-paste-current collector-paste-electrode negative; electrode sheet resistance calculation formula R T Pole piece resistivity ρ= (V/I) ×2h/S, where R T The volume resistance is ρ, the resistivity is h, the thickness of the pole piece is h, the contact area of the probe is S (probe diameter phi 4 mm), the probe surface pressure is set to be 1.0MPa, V is the measurement voltage, and I is the current between the two probes.
(II) porosity test:
and testing the porosity of the target pole piece by a pole piece pore testing method. The pole piece is tiled on a glass tabletop, cut into a certain size, and the thickness of the pole piece is measured by a ten-thousandth ruler to calculate the volume V of the pole piece 1 The method comprises the steps of carrying out a first treatment on the surface of the Then the pole piece is put into test equipment, a gas valve is opened, helium is introduced, and the true volume V of the pole piece is tested 2 The method comprises the steps of carrying out a first treatment on the surface of the According to formula (V 1 -V 2 )/V 1 *100% gives the porosity of the pole piece.
(III) DCR test
And (3) charging the prepared battery to 50% SOC at the temperature of 25 ℃ at 0.7C, standing for 10min, then discharging the battery for 10s at the current of 0.1C (I1) and discharging the battery at the current of 1C (I2) for 5s respectively, and collecting the voltages during and before and after discharging. The DCR value is calculated as follows:
wherein V is 1 To be at current I 1 Terminal voltage after discharge, V 2 Is based on current I 2 Terminal voltage after discharge.
τ c ＝P c (1-α) ，τ a ＝P a (1-α) ，α＝1.5。
TABLE 1
As can be seen from examples 1 to 5 and comparative examples 1 to 6, the matching formula was followed When the calculation result of the positive plate and the negative plate is not in the range of 1.1-196.6, the matching property of the positive plate and the negative plate is poor, and the lithium ion battery assembled by the positive plate and the negative plate with poor matching property has larger DCR internal resistance and has certain influence on the discharge multiplying power of the battery.
As can be seen from examples 1-5 and comparative examples 1 and 4, comparative example 1 has insufficient positive-negative matching properties, mainly due to excessive negative-side electronic impedance, while the design of the positive-side is relatively excessive. The insufficient positive-negative electrode matching of comparative example 4 is mainly due to insufficient porosity and pore tortuosity on the negative electrode sideDegree τ a Too large, in turn, results in too large a negative side lithium ion impedance, as is the positive side design.
Therefore, under the conditions that the design of the positive electrode side is relatively excessive and the ion or electron impedance of the negative electrode side is large, the matching formula in the application can be accurately identified, and the calculated value is larger than 196.6.
As can be seen from examples 1-5 and comparative examples 2, 3, and 6, the positive and negative electrode matching properties of comparative example 2 and comparative example 3 are insufficient, mainly due to the excessive positive electrode side electronic impedance, while the design of the negative electrode side is relatively excessive. The insufficient positive-negative electrode matching of comparative example 6 is mainly due to insufficient porosity at the positive electrode side and pore tortuosity τ a Too large, and thus the positive electrode side lithium ion resistance is too large.
Therefore, the matching formula in the invention can accurately identify the situation that the design of the negative electrode side is relatively excessive and the ion or electron impedance of the positive electrode side is large, and the calculated value is less than 1.1.
There are also cases where the final calculated value of positive and negative electrodes is not in the range of 1.1 to 196.6, but DCR is still small, as in comparative example 5, the final calculated value of 0.68 of comparative example 5 is not in the range, but DCR is also low. This is not an indication of the excellent battery performance of comparative example 5, but rather an indication of poor positive-negative electrode matching. As can be seen from the comparison between example 5 and comparative example 5, the design of the positive electrode side is substantially the same, while the resistivity of the negative electrode sheet of comparative example 5 is reduced by approximately 6 times, the porosity and pore tortuosity are improved correspondingly, but the DCR is hardly improved compared with example 5, and the rate discharge performance is hardly different, which means that the positive and negative electrode of comparative example 5 is insufficient in matching, more specifically, the design of the negative electrode is excessive correspondingly, the cost is increased, and the internal resistance of the battery is further improved, and the improvement of the positive electrode side is emphasized.
(4) 25 ℃ multiplying power discharge test
Using the batteries prepared in the above examples and comparative examples, the voltage, internal resistance, thickness T of the batteries were first tested 1 Then the battery is charged to 4.48V at constant current and constant voltage of 0.7C under the constant temperature environment of 25 ℃, the cut-off current is 0.025C, and the battery is kept stand for 10min. Then respectively placing the materials at 0.2C/1C/2C/3C/4CThe discharge capacity was recorded and divided by the discharge capacity of 0.2C to give a capacity retention rate. The rate discharge capacity retention rate of the lithium battery is shown in table 2.
TABLE 2 lithium cell rate discharge capacity retention rate
As can be seen from the data in table 2, the battery assembled from the positive electrode sheet and the negative electrode sheet satisfying the present invention has good electrical properties. The positive and negative plates obtained by adopting the technical scheme in the application have good matching property, the positive and negative plates with lower plate resistivity are obtained, the lithium ion battery assembled and prepared by the positive and negative plates can cope with a complex system, has lower DCR, and further improves the battery multiplying power.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications should also be considered as being within the scope of the present invention.
Claims (10)
1. The lithium ion battery is characterized by comprising a positive plate and a negative plate, wherein the positive plate comprises a current collector and a positive paste layer coated on at least one side of the current collector, and the positive paste layer comprises a positive active substance and a carbon material; the negative electrode sheet comprises a current collector and a negative electrode paste coating layer coated on at least one side of the current collector, wherein the negative electrode paste coating layer comprises a negative electrode active substance and a carbon material; the performance parameters of the positive plate and the negative plate meet the relation:
wherein R is c Is the resistivity of the positive plate, P c Is the porosity of the positive plate, τ c Is the tortuosity of the pore gap of the positive plate, R a For the resistivity of the negative plate, P a For the porosity of the negative electrode sheet, τ a Is the tortuosity of the pore gap of the negative electrode sheet.
2. The lithium ion battery of claim 1, wherein the performance parameters of the positive and negative electrode sheets satisfy the relationship:
3. the lithium ion battery of claim 2, wherein the performance parameters of the positive and negative electrode sheets satisfy the relationship:
4. a lithium ion battery according to any one of claims 1 to 3, wherein 10% < P c ＜100％，15％＜P a ＜100％，0.05KΩ.cm＜R c ＜6.8KΩ.cm，1Ω.cm＜R a ＜50Ω.cm；100％＜τ c ＜316％，100％＜τ a ＜258％。
Preferably, 15% < P c ＜60％，20％＜P a ＜80％，0.05KΩ.cm＜R c ＜2.4KΩ.cm，1Ω.cm＜R a ＜20Ω.cm，129％＜τ c ＜258％，111％＜τ a ＜224％。
5. The lithium ion battery of any of claims 1-3, wherein the carbon material comprises one or more of carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, and graphene.
6. A lithium ion battery according to any one of claims 1 to 3, wherein the positive electrode active material comprises one or more of lithium cobaltate, lithium manganate, lithium titanate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate;
the negative electrode active material includes one or more of silicon-based material, tin-based material, artificial graphite, natural graphite, and hard carbon.
7. A lithium ion battery according to any one of claims 1 to 3, wherein the content of carbon material in the positive electrode sheet satisfies one of the following conditions:
(a) When the carbon material in the positive plate is only carbon black, the carbon black content is 1.2-3wt% of the positive electrode paste coating layer;
(b) When the carbon material in the positive plate contains carbon black and at least one of multi-wall carbon nano tubes, single-wall carbon nano tubes and graphene, the total content of the carbon material in the positive paste layer is 0.6-3wt%; the content of the carbon black is 0.1 to 2.9 weight percent of the positive electrode paste layer.
(c) When the carbon material in the positive plate is single-walled carbon nanotube and/or graphene, the total content of the carbon material is 0.4-1.5 wt% of the positive paste layer; when the carbon material in the positive plate is single-walled carbon nanotube and graphene, the mass ratio of the single-walled carbon nanotube to the graphene is 1:5.
Preferably, the content of the carbon material in the negative electrode sheet is 0.01-2 wt% of the negative electrode paste coating layer, and preferably 0.2-1 wt%.
8. The lithium ion battery of claim 5, wherein the specific surface area of the carbon black is 60-900 m 2 /g; preferably 60 to 300m 2 /g; more preferably 60 to 180m 2 /g。
Preferably, the multiwall carbon nanotubes satisfy at least one of the following conditions:
(i) The average length of the multi-wall carbon nanotubes is 1-100 μm, preferably 50-100 μm;
(ii) The average diameter of the multi-walled carbon nanotubes is 3nm to 2 μm, preferably 3nm to 500nm.
Preferably, the single-walled carbon nanotubes have an average diameter of 1.6 μm and an average length of 1 μm to 1000 μm.
9. The lithium ion battery of claim 5, wherein the graphene satisfies at least one of the following conditions:
(I) The average layer number of the graphene is 1-10;
(II) D of the graphene 50 Is 1-10 mu m.
10. An electronic device comprising the lithium ion battery according to any one of claims 1 to 9.
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