CN113675400A - Positive electrode, preparation method thereof and lithium ion battery - Google Patents
Positive electrode, preparation method thereof and lithium ion battery Download PDFInfo
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Abstract
The invention relates to the technical field of lithium ion batteries, and discloses a positive electrode, a preparation method thereof and a lithium ion battery. The positive electrode comprises a current collector, and a guide layer and a base layer which are sequentially arranged on the current collector, wherein the guide layer contains a fluorinated modified mesoporous micro-nano material, and the content of fluorine element in the fluorinated modified mesoporous micro-nano material is 0.1-10 wt%. The positive electrode can improve the cycle number of the lithium ion battery under the condition of a precursor with high energy density of the lithium battery.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a positive electrode, a preparation method thereof and a lithium ion battery.
Background
At present, commercial lithium ion batteries mostly adopt an electrolyte prepared from a carbonate solvent and lithium hexafluorophosphate (lithium salt) as a medium for transmitting lithium ions by a positive electrode and a negative electrode. Because the theoretical reduction potential of the carbonate solvent is above the electrochemical window of the main negative electrode such as graphite, silicon, lithium metal and the like, the graphite and silicon negative electrodes can avoid the continuous progress of side reactions by forming a good SEI film.
On the one hand, however, lithium metal and alloy negative electrodes have a very large volume effect, and an electrolyte adopting a carbonate conventional solvent has a serious side reaction with a metal lithium negative electrode, and a fresh specific surface of the lithium metal continuously exposed in a circulation process continuously has a side reaction with the carbonate electrolyte. Therefore, the carbonate electrolyte based electrolyte cannot be used in a lithium metal negative electrode, and the energy density of the battery is difficult to further increase. On the other hand, under the condition that a material system is determined, if the energy density of the battery is to be improved, the amount of auxiliary materials and the compacted density of the positive electrode are generally increased, but the wettability of the carbonate electrolyte is poor, and the carbonate electrolyte cannot fully infiltrate the whole electrode after the thickness and the compacted density reach certain limit values, so that a part of materials cannot exert capacity, rate capability, low-temperature performance and cycle performance.
The electrolyte adopting the ether and fluoroether solvents is matched with the lithium metal negative electrode, so that the energy density of the battery can be effectively improved, and the battery has good cycle performance. In the process of pursuing high energy density, under the condition that the thickness of the lithium metal or alloy negative electrode is not changed, the increase of the surface density (thickness of the positive electrode layer) of the positive electrode has obvious improvement on the energy density of the battery. However, the lithium metal and alloy negative electrodes expand and contract continuously in the circulation process, so that the specific surface of the negative electrode is greatly increased, the negative electrode is easier to absorb the electrolyte in the battery, the absorption energy of the negative electrode is far greater than that of the positive electrode after the negative electrode is circulated for a certain period, the electrolyte on the positive electrode side is extremely deficient, the continuous ion conduction path on the positive electrode side is damaged, and the positive electrode active material cannot be fully exerted.
CN108258174A discloses a separator for lithium ion battery. However, it does not improve the problem of uneven electrolyte distribution in the direction of the internal cross section of the electrode, and the common molecular sieve is not suitable for electrolyte systems based on fluorosulfonate and fluoroether.
CN109742391A discloses a high nickel lithium ion battery, a battery anode material and a preparation method thereof. However, there is no difference in the adsorption capacity of the positive electrode to the electrolyte in the cross-sectional direction, and when the thickness of the electrode reaches a certain upper limit, the problem of electrolyte shortage still exists at the position close to the current collector; in particular, the molecular sieve activated at low temperature has limited adsorption capacity to ether and fluoroether solvents, and cannot be applied to a lithium metal negative electrode system.
Therefore, it is of great interest to research and develop a positive electrode and a lithium ion battery.
Disclosure of Invention
The invention aims to overcome the defect that a high-energy-density lithium battery adopting lithium metal and lithium alloy as a negative electrode in the prior art has poor cycle performance under high energy density of the lithium battery, and provides a positive electrode, a preparation method thereof and a lithium ion battery.
In order to achieve the above object, a first aspect of the present invention provides a positive electrode, where the positive electrode includes a current collector, and a guide layer and a base layer sequentially disposed on the current collector, where the guide layer contains a fluorinated modified mesoporous micro-nano material, and a content of fluorine in the fluorinated modified mesoporous micro-nano material is 0.1-10 wt%.
The second aspect of the present invention provides a method for preparing the aforementioned positive electrode, wherein the method comprises:
(1) carrying out first contact on a positive electrode active material, a binder, a conductive agent and a positive electrode solvent to form base layer slurry;
(2) carrying out second contact on the base layer slurry and the fluorinated modified mesoporous micro-nano material to form a guide layer slurry;
(3) and sequentially coating the guide layer slurry and the base layer slurry on the current collector, and drying and rolling to obtain the positive plate.
A third aspect of the present invention provides a lithium battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is the positive electrode described above.
Through the technical scheme, the invention has the following advantages:
(1) the guide layer close to the positive current collector in the positive electrode contains the fluorinated modified mesoporous micro-nano material, so that the sufficient infiltration and maintenance of electrolyte in the thicker positive electrode can be effectively ensured, and particularly the electrolyte containing ether solvents, fluoroether solvents and fluorocarboxylic acid ester solvents is obtained. The thicker positive electrode is beneficial to increasing the active material proportion of the positive electrode material and improving the energy density of the battery.
(2) In the invention, the ether solvent, the fluoroether solvent and the fluorocarboxylic acid ester solvent are more stable with the metal lithium or lithium alloy, and the side reaction is far less than that of the carbonic acid ester solvent; the use of metallic lithium or lithium alloy can greatly increase the energy density of the battery.
(3) In the present invention, the fluorinated modified mesoporous micro-nano material preferably has good compatibility with fluorinated ethers solvents, fluorinated carboxylic acid esters solvents, and fluorine-containing lithium salts and solvents such as lithium bis-fluorosulfonylimide (LiFSI). Due to the fact that the fluorine-containing group with strong electronegativity is highest in the fluoroether solvent, the fluorocarboxylic acid ester solvent and the fluorine-containing lithium salt, side reaction of other surface groups of the mesoporous micro-nano material and the fluorine-containing group in the electrolyte is avoided through fluorination treatment, and meanwhile the fluorinated modified mesoporous micro-nano material and the fully circulated negative electrode material have similar surface states and liquid absorption and retention capacities. Thus ensuring the continuity of the ion transport channels inside the positive electrode during long-term cycling.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a positive electrode, wherein the positive electrode comprises a current collector, and a guide layer and a base layer which are sequentially arranged on the current collector, wherein the guide layer contains a fluorinated modified mesoporous micro-nano material, and the fluorine content of the fluorinated modified mesoporous micro-nano material is 0.1-10 wt%.
According to the invention, the fluorine content in the fluorinated modified mesoporous micro-nano material is 0.1-10 wt%, specifically, for example, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% and 10 wt%, and any value in the range formed by any two of these points.
According to the invention, preferably, the fluorine content in the fluorinated modified mesoporous micro-nano material is 0.5-9 wt%, more preferably 1-8 wt%, more preferably 2-5 wt%, and even more preferably 2-4 wt%. In the invention, the content of fluorine element in the fluorinated modified mesoporous micro-nano material has an important influence on the compatibility of the electrolyte, the content of fluorine element in the fluorinated modified mesoporous micro-nano material is limited to be within the range, so that the electrolyte has good compatibility, furthermore, a guide layer is arranged in the positive electrode adjacent to the current collector, the liquid absorption and retention capacity of the electrolyte can be effectively improved, and the continuity of the electrolyte in the cross section direction of the positive electrode in the long-term circulation process can be ensured.
According to the invention, the mesoporous micro-nano material comprises one or more of mesoporous molecular sieve, zeolite, aerogel and montmorillonite; wherein the mesoporous molecular sieve is selected from one or more of 5A molecular sieve zeolite powder and silica aerogel.
Wherein the molecular formula of the 5A molecular sieve is 3/4CaO 1/4Na2O·Al2O3·2SiO2·9/2H2O; silicon-aluminum ratio: SiO 22/AI2O3Approximately equal to 2, the effective aperture is about
In the present invention, the mesoporous molecular sieve, zeolite, aerogel and montmorillonite are commercially available, for example, from Nippon Zhongcun super hard company, China ceramic materials or Shandong aluminum works, and the types may be MFI type, AFX type, AFI type, LTL type, CHA type, FAU type, MOR type, AEI type, and the like. Specifically Beta zeolite, ZSM-5 zeolite, ZSM-22 zeolite, ZSM-35 zeolite, ZSM-50 zeolite, ZSM-57 zeolite, MCM-22 zeolite, MCM-56 zeolite, SAPO-17 molecular sieve, SAPO-43 molecular sieve and the like.
According to the invention, the average particle size of the mesoporous micro-nano material is 5-8000nm, preferably 10-6000nm, more preferably 50-5000nm, and still more preferably 400-5000 nm; according to the invention, the average particle size of the mesoporous micro-nano material is too large, so that the mesoporous micro-nano material is difficult to uniformly disperse in a guide layer of a positive electrode, and the average particle size of the mesoporous micro-nano material is too small, so that the mesoporous micro-nano material is easy to agglomerate and difficult to process.
According to the invention, the preparation method of the fluorinated modified mesoporous micro-nano material comprises the following steps: and (3) mixing and soaking the fluoride aqueous solution and the mesoporous micro-nano material, and then drying to obtain the fluorinated modified mesoporous micro-nano material. Wherein the fluoride is selected from one or more of hydrogen fluoride, ammonium bifluoride, boron trifluoride, ammonium fluoroborate and ammonium fluorosilicate; after the mixing and soaking, the moisture may be removed by means of air drying, vacuum drying, spray drying, microwave drying, or the like.
According to the invention, the thickness of the guide layer is 5 to 100. mu.m, preferably 10 to 80 μm, more preferably 30 to 60 μm.
According to the invention, the thickness of the base layer is 10 to 500. mu.m, preferably 20 to 300. mu.m, more preferably 90 to 120. mu.m.
In the invention, the thicknesses of the guide layer and the base layer are limited in the range, which is beneficial to increasing the proportion of active substances of the anode material, thereby improving the energy density of the battery.
According to the present invention, the guide layer further contains a positive electrode active material, a binder, and a conductive agent.
According to the present invention, the foundation layer contains a positive electrode active material, a binder, and a conductive agent.
In the present invention, the positive active material is selected from the group consisting of positive electrode materials conventional in the art, such as lithium cobalt oxide LiCoO2Lithium nickel oxide LiNiO2Lithium manganese oxide LiMnO2An oxide; Li-Ni-Co-O Li (Ni)0.8Co0.2)O2Lithium nickel cobalt manganese oxygen LiNi1/3Co1/3Mn1/3O2、LiNi0.1Co0.1Mn0.8O2And the like; LiFePO4、LixV2(PO4)3、LiMnPO4、Li2FeSiO4、Li2MnSiO4An iso-polyanion system; lixVO2、LixV2O4、Li1+xV3O8And the like.
In the present invention, the binder is selected from one or more of PVDF (polyvinylidene fluoride), Polytetrafluoroethylene (PTFE) and Styrene Butadiene Rubber (SBR), preferably PVDF.
In the present invention, the conductive agent is selected from one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers and graphene, and is preferably acetylene black and/or conductive carbon black.
According to the invention, based on the total weight of the positive electrode active material, the binder and the conductive agent, the content of the positive electrode active material is 90-99 wt%, the content of the binder is 0.2-5 wt%, and the content of the conductive agent is 0.1-5 wt%; preferably, the content of the positive electrode active material is 95 to 97 wt%, the content of the binder is 2 to 3 wt%, and the content of the conductive agent is 1 to 2 wt%.
According to the invention, the weight ratio of the total weight of the positive electrode active substance, the binder and the conductive agent to the fluorinated modified mesoporous micro-nano material is 500: (0.5-30), preferably 500: (1-25). In the invention, on one hand, the weight ratio of the two is limited to be within the range, so that the fluorinated modified mesoporous micro-nano material can be better dispersed in the base layer cathode slurry consisting of the cathode active material, the binder, the conductive agent and the solvent. On the other hand, the problem of agglomeration of the mesoporous micro-nano material can be avoided.
According to the invention, the current collector is an aluminum foil.
The second aspect of the present invention provides a method for preparing the aforementioned positive electrode, wherein the method comprises:
(1) carrying out first contact on a positive electrode active material, a binder, a conductive agent and a positive electrode solvent to form base layer slurry;
(2) carrying out second contact on the base layer slurry and the fluorinated modified mesoporous micro-nano material to form a guide layer slurry;
(3) and sequentially coating the guide layer slurry and the base layer slurry on the current collector, and drying and rolling to obtain the positive plate.
According to the invention, in step (1) and step (2), both the first contacting and the second contacting are carried out in a vacuum stirrer. Preferably, the conditions of the first contacting include: the temperature is 30-70 ℃, the time is 60-300min, and the stirring speed is 200-3000 rpm. The conditions of the second contacting include: the temperature is 30-70 ℃, the time is 60-180min, and the stirring speed is 500-2000 rpm.
According to the present invention, the weight ratio of the total weight of the positive electrode active material, the binder, and the conductive agent to the positive electrode solvent is 1: (0.5-10), preferably 1: (1-3).
According to the invention, in the step (3), the rolling is carried out by adopting a roller press, and the roller press is purchased from Shenzhen, Kezhida, Inc., and has the model number of MSK-2300A.
According to the present invention, in the step (3), the drying is not particularly limited, and may be performed in a simultaneous multilayer coating apparatus at a temperature of 80 to 140 ℃. The synchronous multilayer coating equipment is self-made and has the model of LB-2015B.
In addition, in the present invention, the coating includes at least one of spray coating, curtain coating, blade coating, roll coating, drawing, and dip coating.
A third aspect of the present invention provides a lithium battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is the positive electrode described above.
According to the present invention, the electrolyte contains a lithium salt selected from LiN (SO) and a solvent2F)2Lithium bis (fluorosulfonylimide), LiN (CF)3SO2)2、LiCF3SO3、LiC(CF3SO2)3、LiB(C2O4)2、Li2Al(CSO3Cl4)、LiP(C6H4O2)3、LiPF3(C2F5)3、LiN(CF3SO2)2And LiN (SiC)3H9)2One or more of; preferably, said lithium salt is selected from fluorine-containing organic lithium salts selected from LiN (SO)2F)2、LiN(CF3SO2)2、LiCF3SO3、LiC(CF3SO2)3、LiPF3(C2F5)3And LiN (CF)3SO2)2One or more of (a).
According to the present invention, the solvent is selected from one or more of an ether solvent, a fluorocarboxylic acid ester solvent, and a fluoroether solvent; preferably, the solvent is a mixed solvent of an ether solvent, a fluorinated carboxylic ester solvent and a fluorinated ether solvent; more preferably, the solvent is a mixed solvent containing a fluorinated carboxylic ester solvent and a fluorinated ether solvent.
In the invention, the ether solvent, the fluorinated carboxylic ester solvent and the fluorinated ether solvent as well as the ether solvent, the fluorinated carboxylic ester solvent and the fluorinated ether solvent in a specific ratio are adopted, so that the ether solvent, the fluorinated carboxylic ester solvent and the fluorinated ether solvent are more stable with metal lithium or lithium alloy, and the side reaction is far less than that of the carbonate solvent.
According to the invention, the concentration of the lithium salt is 12 to 70 wt.%, preferably 20 to 66 wt.%.
According to the invention, the ether solvent is selected from one or more of ethylene glycol dimethyl ether (DME), dipropylene glycol dimethyl ether (DMM), tripropylene glycol monomethyl ether (TPM) and tetraethylene glycol dimethyl ether.
According to the invention, the fluorinated carboxylic ester solvent is selected from one or more of ethyl Difluoroacetate (DFEA), ethyl Fluoroacetate (FEA), ethyl 2,2 difluoropropionate and ethyl trifluoropropionate;
according to the present invention, the fluoroether solvent is selected from the group consisting of 1,1,2, 2-tetrafluoroethylether (ETFE), 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE), hexafluoroisopropyl ether (HFPE), tetrafluoroethyl-tetrafluoropropyl ether (HFE), 2,2, 2-trifluoroethyl ether (BTFE), 1,2, 2-tetrafluoroethyl-2, 2, 2-trifluoroethyl ether, difluoromethyl-2, 2,3, 3-tetrafluoropropyl ether, 2,2,3,3, 3-pentafluoropropyl methyl ether, 1,2,3, 3-hexafluoropropyl ether, 1,2,3,3, 3-pentafluoropropyl difluoromethyl ether, 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether, 1,2,2, 2, 3-tetrafluoropropyl ether, One or more of 1H,1H, 5H-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether and bis (2,2, 2-trifluoroethyl) ether.
According to the invention, the negative electrode comprises a current collector and metallic lithium or a lithium alloy attached to the current collector; wherein the lithium alloy is selected from one or more of lithium boron alloy, lithium silicon alloy, lithium magnesium alloy and lithium aluminum alloy. In the present invention, the use of metallic lithium or lithium alloy can greatly increase the energy density of the battery.
According to the invention, the current collector is one or more of a copper foil, a porous copper foil, a copper mesh and a nickel mesh.
According to the invention, the thickness of the metallic lithium or the lithium alloy is 2 to 100. mu.m, preferably 10 to 50 μm.
In the present invention, the lithium metal may be a lithium foil.
According to the invention, the fluorinated modified mesoporous micro-nano material has good compatibility with fluorine-containing lithium salts such as fluoroether solvents, fluorocarboxylic acid ester solvents, lithium bis (fluorosulfonyl) imide (LiFSI) and the like. Due to the fact that the fluorine-containing group with strong electronegativity is highest in the fluoroether solvent, the fluorocarboxylic acid ester solvent and the fluorine-containing lithium salt, side reaction of other surface groups of the mesoporous micro-nano material and the fluorine-containing group in the electrolyte is avoided through fluorination treatment, and meanwhile the fluorinated modified mesoporous micro-nano material and the fully circulated negative electrode material have similar surface states and liquid absorption and retention capacities. Thus ensuring the continuity of the ion transport channels inside the positive electrode during long-term cycling.
The present invention will be described in detail below by way of examples.
In the following examples and comparative examples:
(1) determination of energy density:
the dimensional parameters of the battery are obtained by calculating by measuring the length, width, thickness and the like of each component of the battery. The energy parameter of the battery is obtained by integrating the discharge capacity and the voltage.
(2) Determination of the cycle life of the battery:
on a LAND CT 2001C secondary battery performance testing device, purchased from Wuhan blue electricity, the batteries were subjected to charge-discharge cycle testing at 0.2C at 25 + -1 deg.C.
The method comprises the following steps: standing for 10 min; charging at constant voltage to 4.2V/0.05C, and cutting off; standing for 10 min; constant current discharge to 3.0V, i.e. 1 cycle. Repeating the step, and when the battery capacity is lower than 80% of the first discharge capacity in the circulation process, ending the circulation, wherein the circulation times are the circulation life of the battery, and each group is averaged.
(3) Battery expansion rate:
and testing the size of the battery after the cycle life is finished, and comparing the size with the size before the cycle to calculate the expansion rate of the battery.
(4) The raw material sources are as follows:
in the present invention, the mesoporous molecular sieve, zeolite, aerogel and montmorillonite are commercially available, for example, from Nippon Zhongcun super hard company, China ceramic materials, Shandong aluminum works, etc., in the respective models of MFI type, AFX type, AFI type, LTL type, CHA type, FAU type, MOR type, AEI type, etc. Specifically Beta zeolite, ZSM-5 zeolite, ZSM-22 zeolite, ZSM-35 zeolite, ZSM-50 zeolite, ZSM-57 zeolite, MCM-22 zeolite, MCM-56 zeolite, 5A molecular sieve, SAPO-17 molecular sieve, SAPO-43 molecular sieve and the like.
Example 1
This example is presented to illustrate the preparation of a lithium ion battery using the positive electrode of the present invention.
(1) Production of positive electrode
S1 anode active material LiFePO of 960g4(96%), 30g of binder PVDF (3%), 5g of acetylene black (0.5%) and 5g of conductive agent conductive carbon black (0.5%) were added to 2000g of solvent NMP (N-methylpyrrolidone), and then stirred in a vacuum stirrer at a temperature of 45 ℃ and a stirring rate of 2000rpm for 180min to form a stable and uniform base layer cathode slurry.
500g of basic anode slurry and 10g of Beta zeolite with the grain diameter of 50nm and the fluorine content of 2 percent are uniformly mixed and stirred in a vacuum stirrer to form stable and uniform guide layer anode slurry.
S2, uniformly and sequentially coating the anode slurry of the guide layer and the anode slurry of the base layer on the surface of an aluminum foil (the size of the aluminum foil is 160mm in width and 16 mu m in thickness) by adopting synchronous multilayer coating equipment, wherein the guide layer is close to a current collector, and the base layer is arranged on the guide layer; and then 393K drying, and tabletting by a roller press to obtain the positive plate, wherein the thickness of the single side of the guide layer is controlled to be 30 mu m, and the thickness of the basic layer is controlled to be 90 mu m. The positive plate was cut into rectangular pieces of 48mm by 56mm in size, and tab was spot-welded at the widthwise position.
(2) Preparation of electrolyte
In a glove box filled with argon (H)2O≤5PPM，O2Less than or equal to 5PPM), and ethylene glycol dimethyl ether (DME), ethyl Difluoroacetate (DFEA), 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE). According to DME: DFEA: mixing TTE 20:70:10Then, 60 wt% of lithium bis (fluorosulfonyl) imide LiN (SO) was added to the mixed solution2F)2。
(3) Fabrication of negative electrodes
In a glove box filled with argon (H)2O≤5PPM，O2Less than or equal to 5PPM), cutting commercial lithium foil with copper as a substrate into pole pieces with the size of 49mm to 57mm, and obtaining the negative pole piece, wherein the thickness of the lithium foil is 25 mu m.
(4) Battery fabrication
And (3) sequentially laminating the positive plate obtained in the step (1), the diaphragm and the negative plate obtained in the step (3), and preparing the battery in a lamination mode, wherein the positive plate and the negative plate are isolated by the diaphragm to obtain a dry battery core. And (3) placing the dry electric core in an aluminum plastic film outer package, injecting the electrolyte obtained in the step (2), vacuumizing and sealing, standing at 60 ℃ for 48h, pressurizing at 60 ℃, performing secondary packaging, exhausting and grading to obtain the lithium battery marked as S1 prepared in the embodiment 1.
Example 2
This example is presented to illustrate the preparation of a lithium ion battery using the positive electrode of the present invention.
A lithium ion battery was prepared in the same manner as in example 1, except that: in step (1), "10 g of zeolite having a fluorine content of 2% and a median particle diameter of 50 nm" was replaced with "20 g of 5A molecular sieve having a fluorine content of 3.5% and a median particle diameter of 2 μm".
The result is a lithium battery, designated as S2, prepared in this example 2.
Example 3
This example is presented to illustrate the preparation of a lithium ion battery using the positive electrode of the present invention.
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), the zeolite with 2 percent of fluorine content is replaced by the zeolite with 3.5 percent of fluorine content; and in the step (2), "1, 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE)" is replaced with 1,1,2, 2-tetrafluoroethyl-2, 2, 2-trifluoroethyl ether.
The result is a lithium battery, designated as S3, prepared in this example 3.
Example 4
This example is presented to illustrate the preparation of a lithium ion battery using the positive electrode of the present invention.
A lithium ion battery was prepared in the same manner as in example 1, except that: in step (1), "10 g of zeolite having a fluorine content of 2% and a particle diameter of 50 nm" was replaced with "2 g of MFI-type zeolite having a fluorine content of 3% and a particle diameter of 600 nm".
The result is a lithium battery, designated as S4, prepared in this example 4.
Example 5
This example is presented to illustrate the preparation of a lithium ion battery using the positive electrode of the present invention.
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "10 g of zeolite having a fluorine content of 2% and a particle diameter of 50 nm" was replaced with "20 g of ZSM-35 zeolite having a particle diameter of 5 μm and a fluorine content of 4";
in step (2): "ethylene glycol dimethyl ether (DME), ethyl Difluoroacetate (DFEA), 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE) were added. According to mass ratio, according to DME: DFEA: mixing TTE 20:70:10, and then adding 60 wt% of lithium bis (fluorosulfonyl) imide LiN (SO) to the mixed solution2F)2The 'replacement' solvent is ethylene glycol dimethyl ether (DME) and 1,1,2,2 tetrafluoroethylether (ETFE) which are mixed according to the weight ratio of 2:1, and then 45 wt% of lithium salt lithium bis (fluorosulfonyl imide) LiN (SO) is added into the mixed solution2F)2”。
The result is a lithium battery, designated as S5, prepared in this example 5.
Example 6
This example is presented to illustrate the preparation of a lithium ion battery using the positive electrode of the present invention.
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "10 g of zeolite having a fluorine content of 2% and a particle diameter of 50 nm" was replaced with "2 g of ZSM-50 zeolite having a fluorine content of 2.5% and a particle diameter of 400 nm";
in step (2): mixing "ethylene glycol dimethyl ether (DME), ethyl difluoroacetate(DFEA), 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE). According to mass ratio, according to DME: DFEA: mixing TTE 20:70:10, and then adding 60 wt% of lithium bis (fluorosulfonyl) imide LiN (SO) to the mixed solution2F)2The 'substitution' solvent is ethylene glycol dimethyl ether (DME) and tetrafluoroethyl-tetrafluoropropyl ether (HFE) according to the weight ratio of 7: 3 and then 53 wt% of lithium salt LiN (CF) was added to the mixed solution3SO2)2”。
The result is a lithium battery, designated as S6, prepared in this example 6.
Example 7
This example is presented to illustrate the preparation of a lithium ion battery using the positive electrode of the present invention.
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "10 g of zeolite with a fluorine content of 2% and a particle size of 50 nm" was replaced with "2 g of MCM-22 zeolite with a fluorine content of 7% and a particle size of 500 nm";
in step (2): "ethylene glycol dimethyl ether (DME), ethyl Difluoroacetate (DFEA), 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE) were added. According to mass ratio, according to DME: DFEA: mixing TTE 20:70:10, and then adding 60 wt% of lithium bis (fluorosulfonyl) imide LiN (SO) to the mixed solution2F)2The 'replacement' solvent is ethylene glycol dimethyl ether (DME) and 1,1,2,3,3, 3-pentafluoropropyldifluoromethyl ether which are mixed according to the weight ratio of 1:1, and then 62 wt% of lithium salt LiPF is added into the mixed solution3(C2F5)3”。
The result is a lithium battery, designated as S7, prepared in this example 7.
Comparative example 1
(1) Production of positive electrode
S1 anode active material LiFePO of 960g4(96%), 30g of PVDF (3%) as a binder, 5g of acetylene black (0.5%), 5g of conductive carbon black (0.5%) as a conductive agent were added to 2000g of NMP (N-methylpyrrolidone) as a solvent, and then stirred in a vacuum stirrer at 45 ℃ and 2000rpm for 120min to form a stable and uniform baseAnd (4) layer cathode slurry.
S2, uniformly and intermittently coating the base layer anode slurry on two sides of an aluminum foil (the size of the aluminum foil is 160mm in width and 16 mu m in thickness) by adopting coating equipment; and then 393K drying, and tabletting by a roller press to obtain the positive plate, wherein the single-side coating thickness is controlled to be 120 microns. The positive plate was cut into rectangular pieces of 48mm by 56mm in size, and tab was spot-welded at the widthwise position.
(2) Preparation of electrolyte
In a glove box filled with argon (H)2O≤5PPM，O2Less than or equal to 5PPM), and ethylene glycol dimethyl ether (DME), ethyl Difluoroacetate (DFEA), 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE). According to mass ratio, according to DME: DFEA: mixing TTE 20:70:10, and then adding 60 wt% of lithium bis (fluorosulfonyl) imide LiN (SO) to the mixed solution2F)2。
(3) Fabrication of negative electrodes
And cutting the commercial lithium foil with copper as a substrate into pole pieces with the size of 49mm x 57mm to obtain the negative pole piece, wherein the thickness of the lithium foil is 25 mu m.
(4) Battery fabrication
And (3) alternately laminating the positive plate obtained in the step (1) and the negative plate obtained in the step (3) together with the diaphragm, and preparing the battery in a lamination mode, wherein the positive plate and the negative plate are alternately isolated by the diaphragm to obtain the dry battery core. And (3) placing the dry electric core in an aluminum plastic film outer package, injecting the electrolyte obtained in the step (2), vacuumizing and sealing, standing at 60 ℃ for 48h, pressurizing at 60 ℃ to form a layer, performing secondary packaging, exhausting and grading to obtain the lithium battery marked as DS1 prepared in the comparative example 1.
Comparative example 2
A lithium ion battery was prepared in the same manner as in example 1, except that: replacing the electrolyte prepared in the step (2) with a traditional carbonate electrolyte, specifically: the preparation process is as follows: DEC in a volume ratio of 4: 6 parts of the mixture was used as a solvent, and then 12.5 wt% of LiPF6 was added.
The result was a lithium cell prepared according to comparative example 2 labeled as DS 2.
Comparative example 3
A lithium ion battery was prepared in the same manner as in example 1, except that: in step (1), "10 g of zeolite Beta having a fluorine content of 2% and having a particle size of 50 nm" was replaced with "10 g of zeolite Beta having a fluorine content of 500nm11% of Boiling at BetaStone ".
The result was a lithium cell prepared according to comparative example 3 labeled as DS 3.
Comparative example 4
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "the thickness of the guide layer on one side is 30 μm and the thickness of the base layer is 90 μm" is replaced with "the thickness of the guide layer on one side is 5 μm and the thickness of the base layer is 9 μm".
The result was a lithium cell prepared according to comparative example 4 labeled as DS 4.
Comparative example 5
A lithium ion battery was prepared in the same manner as in example 1, except that: in step (3), "the commercial copper-based lithium foil is cut into pieces of 49mm × 57mm in size, and then the negative electrode piece is obtained, wherein the thickness of the lithium foil is 25 μm", and the graphite negative electrode of 186 μm is replaced.
The result was a lithium cell prepared according to comparative example 5 labeled as DS 5.
Test example
The lithium batteries prepared in examples 1 to 7 and comparative examples 1 to 5 were subjected to tests for the energy density of the battery and the number of cycles of the lithium battery.
The test results are shown in table 1.
TABLE 1
As can be seen from the results in table 1, examples 1 to 7 of lithium batteries using the positive electrode of the present invention can increase the cycle number of the lithium battery and increase the cycle life of the lithium battery under the precursor of high energy density of the lithium battery.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. The positive electrode is characterized by comprising a current collector, and a guide layer and a base layer which are sequentially arranged on the current collector, wherein the guide layer contains a fluorinated modified mesoporous micro-nano material, and the content of fluorine element in the fluorinated modified mesoporous micro-nano material is 0.1-10 wt%.
2. The positive electrode according to claim 1, wherein the fluorine content in the fluorinated modified mesoporous micro-nano material is 0.5 to 9 wt%, preferably 1 to 8 wt%, and more preferably 2 to 5 wt%.
3. The positive electrode according to claim 1 or 2, wherein the mesoporous micro-nano material comprises one or more of a mesoporous molecular sieve, a zeolite, an aerogel, and a montmorillonite;
preferably, the mesoporous molecular sieve is selected from one or more of a 5A molecular sieve, zeolite powder and silica aerogel;
preferably, the average particle size of the mesoporous micro-nano material is 5-8000 nm.
4. The positive electrode of claim 1, wherein the thickness of the lead layer is 5-100 μ ι η and the thickness of the base layer is 10-500 μ ι η;
preferably, the guide layer further contains a positive electrode active material, a binder, and a conductive agent;
preferably, the foundation layer contains a positive electrode active material, a binder, and a conductive agent.
5. The positive electrode according to claim 4, wherein in the guide layer, the weight ratio of the total weight of the positive electrode active material, the binder and the conductive agent to the fluorinated modified mesoporous micro-nano material is 500: (0.5-30), preferably 500: (1-25).
6. A method for preparing a positive electrode according to any one of claims 1 to 5, characterized in that it comprises:
(1) carrying out first contact on a positive electrode active material, a binder, a conductive agent and a positive electrode solvent to form base layer slurry;
(2) carrying out second contact on the base layer slurry and the fluorinated modified mesoporous micro-nano material to form a guide layer slurry;
(3) and sequentially coating the guide layer slurry and the base layer slurry on the current collector, and drying and rolling to obtain the positive plate.
7. A lithium battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode is a positive electrode according to any one of claims 1 to 5.
8. The lithium battery of claim 7, wherein the electrolyte comprises a lithium salt selected from LiN (SO) and a solvent2F)2、LiN(CF3SO2)2、LiCF3SO3、LiC(CF3SO2)3、LiB(C2O4)2、Li2Al(CSO3Cl4)、LiP(C6H4O2)3、LiPF3(C2F5)3、LiN(CF3SO2)2And LiN (SiC)3H9)2One or more of;
preferably, the lithium salt is selected from LiN (SO)2F)2、LiN(CF3SO2)2、LiCF3SO3、LiC(CF3SO2)3、LiPF3(C2F5)3And LiN (CF)3SO2)2One or more of;
preferably, the concentration of the lithium salt is 12 to 70 wt%.
9. The lithium battery according to claim 8, wherein the solvent is selected from one or more of ether solvents, fluorocarboxylic acid ester solvents, and fluoroether solvents.
10. The lithium battery of claim 7, wherein the negative electrode comprises a current collector and metallic lithium or a lithium alloy attached to the current collector;
preferably, the lithium alloy is selected from one or more of lithium boron alloy, lithium silicon alloy, lithium magnesium alloy and lithium aluminum alloy;
preferably, the thickness of the metallic lithium or the lithium alloy is 2 to 100 μm.
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