CN115524377A - Method for testing expansion rate of silicon-based negative electrode material - Google Patents
Method for testing expansion rate of silicon-based negative electrode material Download PDFInfo
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- CN115524377A CN115524377A CN202211221263.6A CN202211221263A CN115524377A CN 115524377 A CN115524377 A CN 115524377A CN 202211221263 A CN202211221263 A CN 202211221263A CN 115524377 A CN115524377 A CN 115524377A
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 69
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 69
- 239000010703 silicon Substances 0.000 title claims abstract description 69
- 239000007773 negative electrode material Substances 0.000 title claims abstract description 52
- 238000012360 testing method Methods 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims abstract description 32
- 239000000463 material Substances 0.000 claims abstract description 27
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 55
- 229910002804 graphite Inorganic materials 0.000 claims description 36
- 239000010439 graphite Substances 0.000 claims description 36
- 239000002210 silicon-based material Substances 0.000 claims description 29
- 239000011230 binding agent Substances 0.000 claims description 21
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 20
- 238000001035 drying Methods 0.000 claims description 19
- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical compound [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 claims description 16
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 14
- 239000000654 additive Substances 0.000 claims description 13
- 230000000996 additive effect Effects 0.000 claims description 13
- 239000006258 conductive agent Substances 0.000 claims description 13
- 239000002002 slurry Substances 0.000 claims description 12
- 239000002904 solvent Substances 0.000 claims description 12
- 238000005096 rolling process Methods 0.000 claims description 10
- 239000002041 carbon nanotube Substances 0.000 claims description 8
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 8
- 238000004080 punching Methods 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 238000002156 mixing Methods 0.000 claims description 7
- 238000004140 cleaning Methods 0.000 claims description 6
- 238000005520 cutting process Methods 0.000 claims description 6
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 6
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 239000010405 anode material Substances 0.000 claims description 5
- 239000011248 coating agent Substances 0.000 claims description 5
- 238000000576 coating method Methods 0.000 claims description 5
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 4
- 230000003213 activating effect Effects 0.000 claims description 4
- 229910021389 graphene Inorganic materials 0.000 claims description 4
- 229910000676 Si alloy Inorganic materials 0.000 claims description 3
- 239000003273 ketjen black Substances 0.000 claims description 3
- 239000005543 nano-size silicon particle Substances 0.000 claims description 3
- 229920001084 poly(chloroprene) Polymers 0.000 claims description 3
- 238000002360 preparation method Methods 0.000 claims description 3
- 238000001291 vacuum drying Methods 0.000 claims description 3
- 238000007599 discharging Methods 0.000 abstract description 4
- 238000010998 test method Methods 0.000 abstract description 4
- 238000011160 research Methods 0.000 abstract description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 2
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 12
- 229910052744 lithium Inorganic materials 0.000 description 12
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 7
- 239000011889 copper foil Substances 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 4
- 239000010406 cathode material Substances 0.000 description 4
- 239000000919 ceramic Substances 0.000 description 4
- 239000003792 electrolyte Substances 0.000 description 4
- -1 lithium hexafluorophosphate Chemical compound 0.000 description 4
- 238000007789 sealing Methods 0.000 description 4
- 230000004913 activation Effects 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 238000004364 calculation method Methods 0.000 description 2
- 238000005056 compaction Methods 0.000 description 2
- 238000005034 decoration Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- 239000011149 active material Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000007770 graphite material Substances 0.000 description 1
- 239000002153 silicon-carbon composite material Substances 0.000 description 1
- 238000007581 slurry coating method Methods 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention belongs to the technical field of lithium ion batteries, and discloses a method for testing the expansion rate of a silicon-based negative electrode material. The button cell is assembled by pole pieces prepared from different silicon-based negative electrode materials, the required thickness of the component is measured by ten-thousandth scale after the button cell is disassembled before the button cell is assembled and in a full-electricity state (or in any step in a circulation process), the expansion rate of the silicon-based negative electrode material in the charging and discharging or circulation process can be measured by directly measuring the thickness by using the method, and the expansion rate rapid test method is provided. Meanwhile, the expansion rate of the silicon-based negative electrode material can be obtained only by assembling the material into a button battery to test the specific discharge capacity, and a foundation is laid for the research on the test method of the expansion rate of the silicon-based negative electrode material.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a method for testing the expansion rate of a silicon-based negative electrode material.
Background
When a battery is designed, no matter the negative electrode adopts a graphite material or a silicon-carbon composite material, the expansion rate parameter of the negative electrode is one of the key parameters in the battery design. Meanwhile, in the development process of the cathode material, the silicon-based cathode material enters the visual field of people with high capacity and low electrode potential, but the volume expansion occurs in the discharge process, and the volume expansion brings problems of subsequent cycle capacity attenuation, low coulombic efficiency, poor rate capability and the like, so that the expansion problem of the silicon-based cathode material is a problem which is difficult to solve by the existing silicon-based material, and the expansion analysis of the silicon-based cathode material is very important. And through the test analysis of the expansion of the silicon-based negative electrode material, the advantages and the disadvantages of different silicon-based negative electrode materials can be evaluated on one aspect. Therefore, establishing an analysis method of the expansion of the anode material is of great significance.
The existing testing method is mainly a pole piece expansion testing method, the method is complicated and high in cost, a special method for quickly testing the expansion rate of the silicon-based negative electrode material does not exist, and a technology for estimating the expansion rate of the silicon-based negative electrode material according to the method does not exist. Therefore, it is highly desirable in the art to provide a specific test method capable of rapidly analyzing the expansion rate of a silicon-based negative electrode material.
Disclosure of Invention
In view of the above, the invention provides a method for testing the expansion rate of a silicon-based negative electrode material, so as to solve the problems that the existing analysis method is complicated and has high implementation cost, and meanwhile, the research of a proprietary method for testing the expansion rate of the silicon-based negative electrode material is blank.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for testing the expansion rate of a silicon-based negative electrode material, which comprises the following steps:
(1) Cutting and punching sheet of pole piece material made of silicon-based materialRolling to obtain pole piece, measuring thickness H of pole piece 1 And current collector thickness H 0 (ii) a Baking the pole piece, and measuring the thickness H of the baked pole piece 2 ；
(2) Assembling the baked pole pieces into a battery, activating the battery, and testing the battery to be in a full-charge state, wherein the discharge specific capacity is Q;
(3) Disassembling the battery tested to the full-charge state to obtain a pole piece, cleaning the pole piece, and measuring the thickness H of the cleaned pole piece 3 ；
(4) And (3) calculating the expansion rate of the silicon-based negative electrode material according to the formula 1:
expansion ratio = (H) 2 -H 1 )/(H 1 -H 0 )×100％+(H 3 -H 2 )/(H 2 -H 0 ) X 100% of formula 1;
(5) Establishing a standard curve by taking the discharge specific capacity Q as a horizontal coordinate and the expansion rate of the silicon-based negative electrode material as a vertical coordinate; and obtaining the expansion rate of the silicon-based negative electrode material of the battery sample to be tested according to the discharge capacity and the standard curve of the battery sample to be tested assembled by the pole pieces made of the silicon-based material.
Preferably, the silicon-based material is one or more of a mixed material of graphene and silicon, a mixed material of graphite and silicon oxide, a mixed material of graphite and silicon carbon, a mixed material of carbon and nano graphite, nano silicon, a silicon alloy, carbon-coated silicon and silicon oxide.
Preferably, the pole piece obtained after the punching sheet is cut is a circular sheet, and the diameter of the circular sheet is 11-15 mm; the rolling pressure is 1-15 MPa, and the compacted density of the rolled pole piece is 1-1.2 g/cm 3 。
Preferably, the baking temperature is 60-120 ℃, and the baking time is 2-48 h.
Preferably, when the baked pole pieces are assembled into batteries, the number of the batteries assembled by the pole pieces made of the same silicon-based material is more than or equal to 2; the discharge specific capacity Q is the average discharge specific capacity.
Preferably, the solvent used for cleaning is dimethyl carbonate.
Preferably, the preparation method of the pole piece material made of the silicon-based material comprises the following steps:
a. mixing a silicon-based material, a conductive agent, a binder, an additive and a solvent to obtain slurry;
b. and coating the slurry on a current collector and drying to obtain the pole piece material.
Preferably, the conductive agent is one or more of conductive carbon black, conductive graphite, ketjen black and carbon nanotubes; the binder is an aqueous binder; the additive is carbon nano tube, chloroprene rubber or N-methyl pyrrolidone; the solvent is water.
Preferably, the mass ratio of the silicon-based material to the conductive agent to the binder to the additive is 1-3: 0.05 to 0.4:1 to 15:0 to 10; the addition amount of the solvent is 6-10% of the total mass of the silicon-based material, the conductive agent, the binder and the additive.
Preferably, the slurry is applied to a thickness of 50 to 200 μm; the drying is vacuum drying, the drying temperature is 80-100 ℃, the drying time is 8-24 h, and the drying vacuum degree is-0.05 to-0.2 MPa.
According to the technical scheme, compared with the prior art, the invention has the following beneficial effects:
the method for testing the expansion rate of the silicon-based negative electrode material can accurately and quickly test the expansion rate of the silicon-based negative electrode material, can estimate the expansion rate of the silicon-based negative electrode material, and lays a foundation for the research on the method for testing the expansion rate of the silicon-based negative electrode material.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a flow chart of a method for testing the expansion rate of a silicon-based negative electrode material according to the invention;
FIG. 2 is a flow chart of the battery assembly according to examples 1 and 2 of the present invention;
fig. 3 is a graph showing the specific discharge capacity of the battery obtained in example 1 of the present invention and the expansion rate of the silicon-based negative electrode material;
fig. 4 is a graph showing the specific discharge capacity of the battery obtained in example 2 of the present invention and the expansion rate of the silicon-based negative electrode material.
Detailed Description
The invention provides a method for testing the expansion rate of a silicon-based negative electrode material, which comprises the following steps:
(1) Cutting, punching and rolling a pole piece material made of a silicon-based material to obtain a pole piece, and measuring the thickness H of the pole piece 1 And current collector thickness H 0 (ii) a Baking the pole piece, and measuring the thickness H of the baked pole piece 2 ；
(2) Assembling the baked pole pieces into a battery, activating the battery, and testing the battery to be in a full-charge state, wherein the discharge specific capacity is Q;
(3) Disassembling the battery tested to the full-charge state to obtain a pole piece, cleaning the pole piece, and measuring the thickness H of the cleaned pole piece 3 ；
(4) And (3) calculating the expansion rate of the silicon-based negative electrode material according to the formula 1:
expansion ratio = (H) 2 -H 1 )/(H 1 -H 0 )×100％+(H 3 -H 2 )/(H 2 -H 0 ) X 100% of formula 1;
(5) Establishing a standard curve by taking the discharge specific capacity Q as an abscissa and the expansion rate of the silicon-based negative electrode material as an ordinate; and obtaining the expansion rate of the silicon-based negative electrode material of the battery sample to be tested according to the discharge capacity and the standard curve of the battery sample to be tested assembled by the pole pieces made of the silicon-based material.
In the present invention, the expansion ratio calculation method is: total expansion = pole piece rebound (physical expansion) + full electrical expansion (chemical expansion). Pole piece rebound rate (physical expansion) = (H) 2 -H 1 )/(H 1 -H 0 ) X 100%, full electrical expansion ratio (chemical expansion) = (H) 3 -H 2 )/(H 2 -H 0 )×100％。
In the present invention, the silicon-based material is preferably one or more of a mixed material of graphene and silicon, a mixed material of graphite and silica, a mixed material of graphite and silicon-carbon, a mixed material of carbon and nanographite, nanosilicon, a silicon alloy, carbon-coated silicon, and silica, and is more preferably one or more of a mixed material of graphene and silicon, a mixed material of graphite and silica, a mixed material of graphite and silicon-carbon, and a mixed material of carbon and nanographite.
In the invention, the pole piece obtained after the punching sheet is cut is a circular sheet, and the diameter of the circular sheet is preferably 11-15 mm, and further preferably 13-14 mm; the rolling pressure is preferably 1 to 15MPa, and more preferably 5 to 10MPa; the compaction density of the rolled pole piece is preferably 1 to 1.2g/cm 3 More preferably 1.12 to 1.18g/cm 3 ；
The calculation formula of the compacted density of the rolled pole piece is shown as the formula 2:
compacted density of pole piece after rolling =1000 × (m-m) 0 )/[(H 1 -H 0 )×πr 2 ]Formula 2
Wherein: m is the weighed mass of the negative pole piece after cutting and punching, namely the mass of the pole piece before assembling into a battery; m is 0 The blank copper foil quality of the cut and stamped sheet; r is the radius of the pole piece, the pole piece used in the invention is a wafer, so the active material area of the pole piece is calculated as pi r 2 ，H 0 Is the thickness of the current collector, H 1 The thickness of the pole piece;
the thickness of the rolled pole piece is preferably 60 to 90 μm, and more preferably 70 to 80 μm, without considering the rebound.
According to the invention, the influence of the initial thickness on the expansibility of the silicon-based negative electrode material is eliminated by controlling the compaction density and the thickness, and the accuracy of the testing method is improved.
In the invention, the baking temperature is preferably 60-120 ℃, and more preferably 80-100 ℃; the baking time is preferably 2 to 48 hours, and more preferably 24 to 40 hours.
In the invention, when the baked pole pieces are assembled into the battery, the number of the batteries assembled by the pole pieces made of the same silicon-based material is preferably more than or equal to 2, and more preferably 3-4; the specific discharge capacity Q is preferably an average specific discharge capacity.
In the present invention, the activation period is preferably 1 to 5 cycles, and more preferably 2 to 3 cycles; the full-power state is as follows: discharging the battery to a full charge state at a multiplying power of 0.01-5 ℃;
the magnification is preferably 0.02 to 2C, and more preferably 0.05 to 0.5C.
In the present invention, the solvent used for the washing is preferably dimethyl carbonate.
In the invention, the preparation method of the pole piece material made of the silicon-based material comprises the following steps:
a. mixing a silicon-based material, a conductive agent, a binder, an additive and a solvent to obtain slurry;
b. and coating the slurry on a current collector and drying to obtain the pole piece material.
In the present invention, the conductive agent is preferably one or more of conductive carbon black, conductive graphite, ketjen black and carbon nanotubes, and is further preferably conductive graphite and/or carbon nanotubes; the binder is preferably an aqueous binder, and is further preferably one or more of aqueous binder LA133, aqueous binder LA132 and aqueous binder LA 136D; the additive is preferably carbon nano tube, chloroprene rubber or N-methyl pyrrolidone, and is further preferably carbon nano tube or N-methyl pyrrolidone; the solvent is preferably water.
In the present invention, the mass ratio of the silicon-based material, the conductive agent, the binder and the additive is preferably 1 to 3:0.05 to 0.4:1 to 15:0 to 10, more preferably 1.5 to 2.5:0.1 to 0.3:2 to 5:1 to 8; the addition amount of the solvent is preferably 6-10% of the total mass of the silicon-based material, the conductive agent, the binder and the additive, and is further preferably 8-9% of the total mass of the silicon-based material, the conductive agent, the binder and the additive.
In the present invention, the thickness of the slurry coating is preferably 50 to 200 μm, and more preferably 100 to 150 μm; the drying is vacuum drying, and the drying temperature is preferably 80-100 ℃, and more preferably 90-95 ℃; the drying time is preferably 8 to 24 hours, and more preferably 10 to 20 hours; the degree of vacuum of drying is preferably-0.05 to-0.2 MPa, more preferably-0.08 to-0.15 MPa.
The button cell is assembled by pole pieces prepared from different silicon-based negative electrode materials, the required thickness of the component is measured by ten-thousandth scale after the button cell is disassembled before the button cell is assembled and in a full-electricity state (or in any step in a circulation process), the expansion rate of the silicon-based negative electrode material in the charging and discharging or circulation process can be measured by directly measuring the thickness by using the method, and the expansion rate rapid test method is provided. Meanwhile, the expansion rate of the silicon-based negative electrode material can be obtained only by assembling the material into a button battery to test the specific discharge capacity.
The technical solutions provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Step 1, preparing a silicon-based anode material: pure silicon-carbon (not mixed with graphite), pure silicon-carbon mixed with 10% of graphite, pure silicon-carbon mixed with 20% of graphite, pure silicon-carbon mixed with 30% of graphite, pure silicon-carbon mixed with 40% of graphite, pure silicon-carbon mixed with 50% of graphite, pure silicon-carbon mixed with 60% of graphite, pure silicon-carbon mixed with 70% of graphite, pure silicon-carbon mixed with 80% of graphite, and pure silicon-carbon mixed with 90% of graphite;
step 2, weighing 2.275g of the silicon-based material mixed with graphite and silicon carbon in different proportions in the step 1, respectively mixing with SP0.075g of conductive carbon black, 3g of a water-based binder LA132 (with the concentration of 5%) and 0.5g of pure water, and stirring and mixing to obtain 10 kinds of slurry;
step 3, respectively and uniformly coating the obtained slurry on copper foils, drying the copper foils in a blast oven at 80 ℃ for 8 hours, rolling the copper foils after drying, then cutting the punched sheets, selecting pole pieces with the diameter of 13mm, respectively measuring the thicknesses of the pole pieces at the moment and recording the thicknesses as H 1 And the thickness of the blank copper foil is marked as H 0 (ii) a Wherein H 0 、H 1 Are all average values;
among them, requirements of rolling: the requirements of the compacted density of the rolled pole piece are as follows:the compacted density of the rolled pole piece is controlled to be 1g/cm 3 (ii) a The requirements on the thickness of the rolled pole piece are as follows: the thickness of the rolled pole piece is required to be controlled at 60 mu m (under the condition of not considering rebound);
step 4, putting the pole piece into an oven to be baked for 8 hours at the temperature of 80 ℃, sending the pole piece into a glove box after baking, and recording the thickness of the baked pole piece as H 2 (ii) a Wherein H 2 Is an average value;
step 5, repeating the steps 3 and 4 for 4 times to respectively obtain 11 groups (4 parallel sample pole pieces in each group) of pole pieces;
and 6, respectively assembling each pole piece into a lithium battery, wherein the assembling steps are as follows:
step S01: transferring the prepared pole piece, the ceramic diaphragm, the lithium piece, the negative electrode shell, the positive electrode shell, the spring piece and the gasket into a glove box;
step S02: placing the cathode shell on the bottommost layer, and sequentially placing the spring piece, the gasket and the lithium piece above the cathode shell;
step S03: 0.1g of lithium hexafluorophosphate electrolyte is dropwise added into the lithium sheet manufactured in the step S02, then a ceramic diaphragm is placed, then 0.2g of lithium hexafluorophosphate electrolyte is dropwise added again, and then a pole piece is placed and covered with a positive shell, so that the battery is assembled;
step S04: and (5) placing the battery assembled in the step S03 on a clamping groove of a sealing machine, and sealing to obtain the lithium battery.
Step 7, sending the lithium battery out of the glove box, testing the battery to a full state after activating the battery in a test cabinet, recording the discharge specific capacity Q at the moment, taking down the battery, and sending the battery into the glove box for disassembly;
wherein, the activation stage is 2 circles before, and then the battery is taken down when the battery is discharged to a full state under the multiplying power of 0.1C;
step 8, cleaning the silicon-based negative pole piece obtained after the battery is disassembled in a glove box by using DMC (DMC), and then measuring the thickness of the pole piece after the pole piece is naturally dried and recording the thickness as H 3 (ii) a Wherein H 3 Is an average value;
step 9, the data obtained in the step are processed according to an expansion rate formula (H) 2 -H 1 )/(H 1 -H 0 )×100％+(H 3 -H 2 )/(H 2 -H 0 ) Calculating the product by multiplying by 100 percent to obtain a result;
the data obtained in this example are shown in Table 1:
TABLE 1 data for 7 Si-based materials as described in example 1
According to the data in table 1, the specific discharge capacity Q is used as an abscissa, and the corresponding expansion rate Y of the silicon-based negative electrode material is used as an ordinate, so that the curve Q and the curve Y are in an approximate linear relationship. As shown in fig. 3, Q and Y have the relationship Y =0.1148Q-22.444; wherein, the linear correlation coefficient R 2 The specific discharge capacity of the button battery can be rapidly estimated by only assembling the silicon-based negative electrode material into the button battery to test the expansion rate of the silicon-based negative electrode material by using the relational expression subsequently, wherein the specific discharge capacity is not less than 0.9916, the slope K is 0.1148, namely Y is not more than 0.1148Q.
Example 2
Step 1, preparing a silicon-based negative electrode material: silicon oxide (graphite not mixed), graphite mixed with 10% of silicon oxide, graphite mixed with 20% of silicon oxide, graphite mixed with 30% of silicon oxide, graphite mixed with 40% of silicon oxide, graphite mixed with 50% of silicon oxide, graphite mixed with 60% of silicon oxide, graphite mixed with 70% of silicon oxide, graphite mixed with 80% of silicon oxide and graphite mixed with 90% of silicon oxide;
step 2, respectively weighing 1.875g of the silicon-based material mixed with graphite and silicon carbon in different proportions in the step 1, respectively mixing with 0.125g of conductive carbon black SP, 5g of aqueous binder LA132 (the concentration is 5%), 60.25g of conductive carbon black SFG and 0.5g of pure water, and stirring and mixing to obtain 11 types of slurry;
step 3, respectively and uniformly coating the obtained slurry on copper foils, drying for 8 hours in a blast oven at the temperature of 80 ℃, rolling after drying,and (4) cutting the punching sheet, selecting pole pieces with the diameter of 13mm, respectively measuring the thickness of the pole pieces at the moment and recording the thickness as H 1 And the thickness of the blank copper foil is recorded as H 0 (ii) a Wherein H 0 、H 1 Are all average values;
among them, requirements of rolling: the requirements of the compacted density of the rolled pole piece are as follows: the compacted density of the rolled pole piece is controlled to be 1g/cm 3 (ii) a The requirements on the thickness of the rolled pole piece are as follows: the thickness of the rolled pole piece is required to be controlled to be 60 mu m (under the condition of not considering rebound);
step 4, putting the pole piece into an oven to be baked for 8 hours at the temperature of 80 ℃, sending the pole piece into a glove box after baking, and recording the thickness of the baked pole piece as H 2 (ii) a Wherein H 2 Is an average value;
step 5, repeating the steps 3 and 4 for 4 times to respectively obtain 11 groups (4 parallel sample pole pieces in each group) of pole pieces;
and 6, respectively assembling each pole piece into a lithium battery, wherein the assembling steps are as follows:
step S01: transferring the prepared pole piece, the ceramic diaphragm, the lithium piece, the negative electrode shell, the positive electrode shell, the spring piece and the gasket into a glove box;
step S02: placing the cathode shell on the bottommost layer, and sequentially placing the spring piece, the gasket and the lithium piece above the cathode shell;
step S03: 0.1g of lithium hexafluorophosphate electrolyte is dripped into the lithium sheet manufactured in the step S02, then the ceramic diaphragm is placed, 0.2g of lithium hexafluorophosphate electrolyte is dripped again, and then the positive electrode shell is covered on the pole piece, thus the battery is assembled;
step S04: and (5) placing the battery assembled in the step S03 on a clamping groove of a sealing machine, and sealing to obtain the lithium battery.
Step 7, the lithium battery is sent out from the glove box, the battery is activated in the test cabinet, then the battery is tested to be in a full state, the discharging specific capacity Q is recorded, and meanwhile, the battery is taken down and sent into the glove box for disassembly;
wherein, the activation stage is 2 circles before, and then the battery is taken down when the battery is discharged to a full state under the multiplying power of 0.1C;
step 8, in the glove boxCleaning a silicon-based negative pole piece obtained after the battery is disassembled by using DMC, then measuring the thickness of the pole piece after the pole piece is naturally dried, and recording the thickness as H 3 (ii) a Wherein H 3 Is an average value;
step 9, the data obtained in the step are processed according to an expansion rate formula (H) 2 -H 1 )/(H 1 -H 0 )×100％+(H 3 -H 2 )/(H 2 -H 0 ) Calculating the product by multiplying by 100 percent to obtain a result;
the data obtained in this example are shown in Table 2:
TABLE 2 data for 7 Si-based materials as described in example 2
According to the data in table 2, the specific discharge capacity Q is taken as the abscissa, and the corresponding expansion rate Y of the silicon-based negative electrode material is taken as the ordinate, so that the curve Q and Y are in an approximate linear relationship. As shown in fig. 4, Q and Y have a relationship Y =0.065Q-8.4085; wherein, the linear correlation coefficient R 2 The slope K is 0.065, namely Y is in the range of oc to 0.065Q, and the expansion rate of the silicon-based anode material can be rapidly estimated only by assembling the silicon-based anode material into a button battery to test the discharge specific capacity by using the relational expression subsequently.
From the embodiments 1 and 2, the testing method is simple, convenient and quick, and can quickly estimate the expansion rate of the silicon-based negative electrode material.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A method for testing the expansion rate of a silicon-based negative electrode material is characterized by comprising the following steps:
(1) Cutting and punching a pole piece material made of a silicon-based material, rolling to obtain a pole piece, and measuring the thickness H of the pole piece 1 And current collector thickness H 0 (ii) a Baking the pole piece, and measuring the thickness H of the baked pole piece 2 ；
(2) Assembling the baked pole pieces into a battery, activating the battery, and testing the battery to be in a full-charge state, wherein the discharge specific capacity is Q;
(3) Disassembling the battery tested to the full charge state to obtain a pole piece, cleaning the pole piece, and measuring the thickness H of the cleaned pole piece 3 ；
(4) And (3) calculating the expansion rate of the silicon-based negative electrode material according to the formula 1:
expansion ratio = (H) 2 -H 1 )/(H 1 -H 0 )×100％+(H 3 -H 2 )/(H 2 -H 0 ) X 100% of formula 1;
(5) Establishing a standard curve by taking the discharge specific capacity Q as an abscissa and the expansion rate of the silicon-based negative electrode material as an ordinate; and obtaining the expansion rate of the silicon-based negative electrode material of the battery sample to be tested according to the discharge capacity and the standard curve of the battery sample to be tested assembled by the pole pieces made of the silicon-based material.
2. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in claim 1, wherein the silicon-based material is one or more of a mixed material of graphene and silicon, a mixed material of graphite and silicon oxide, a mixed material of graphite and silicon carbon, a mixed material of carbon and nano graphite, nano silicon, a silicon alloy, carbon-coated silicon and silicon oxide.
3. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in claim 2, wherein the pole piece obtained after the punching is cut is a circular piece, and the diameter of the circular piece is 11-15 mm; the rolling pressure is 1-15 MPa, and the compacted density of the rolled pole piece is 1-1.2 g/cm 3 。
4. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in any one of claims 1 to 3, wherein the baking temperature is 60 to 120 ℃ and the baking time is 2 to 48 hours.
5. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in claim 4, wherein when the baked pole pieces are assembled into a battery, the number of the batteries assembled by the pole pieces made of the same silicon-based material is more than or equal to 2; the discharge specific capacity Q is the average discharge specific capacity.
6. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in claim 5, wherein the solvent used for cleaning is dimethyl carbonate.
7. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in claim 1, 5 or 6, wherein the preparation method of the pole piece material made of the silicon-based material comprises the following steps:
a. mixing a silicon-based material, a conductive agent, a binder, an additive and a solvent to obtain slurry;
b. and coating the slurry on a current collector and drying to obtain the pole piece material.
8. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in claim 7, wherein the conductive agent is one or more of conductive carbon black, conductive graphite, ketjen black and carbon nanotubes; the binder is an aqueous binder; the additive is carbon nano tube, chloroprene rubber or N-methyl pyrrolidone; the solvent is water.
9. The method for testing the expansion rate of the silicon-based negative electrode material as claimed in claim 8, wherein the mass ratio of the silicon-based material to the conductive agent to the binder to the additive is 1-3: 0.05 to 0.4:1 to 15:0 to 10; the adding amount of the solvent is 6-10% of the total mass of the silicon-based material, the conductive agent, the binder and the additive.
10. The method for testing the expansion rate of the silicon-based anode material according to the claim 8 or 9, wherein the slurry is coated to a thickness of 50-200 μm; the drying is vacuum drying, the drying temperature is 80-100 ℃, the drying time is 8-24 h, and the drying vacuum degree is-0.05 to-0.2 MPa.
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