Three-dimensional porous negative electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium batteries, in particular to a three-dimensional porous negative electrode as well as a preparation method and application thereof, and the three-dimensional porous negative electrode is obtained by performing electrochemical treatment on a carbon-containing electrode by utilizing electrolyte; the electrolyte comprises a solvent containing sulfolane and a lithium salt; the carbon-containing negative electrode is subjected to intercalation treatment through an electrochemical method, the three-dimensional porous negative electrode material with lithium storage and lithium affinity functions is prepared, and the porous structure not only retains the lithium storage capability of a carbon material, but also serves as a lithium affinity skeleton to provide additional lithium storage and lithium deposition space, so that lithium ions are more uniformly deposited on the surface of the negative electrode, and the lithium ion storage capacity is improved. Therefore, the growth of lithium dendrites is effectively inhibited; the carbon material is subjected to intercalation treatment by using a sulfolane-based electrolyte, the graphite is not stripped after intercalation, and the negative electrode structure is kept complete; the preparation process is simple to operate, easy to realize large-scale production, low in energy consumption and small in equipment loss.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, in particular to a three-dimensional porous negative electrode and its preparation method and application. Background Art

[0002] Due to the rapid development of various electronic devices, the demand for high-energy density chemical batteries is increasing day by day. The theoretical specific capacity of the currently widely used graphite negative electrode is 372 mAh / g, which cannot meet the requirements of high-energy density batteries. The theoretical specific capacity of lithium metal is 3860 mAh / g. Developing lithium metal negative electrodes is expected to replace graphite negative electrodes and be used in fields such as new energy vehicles and drones.

[0003] However, there are still many problems with lithium metal as the negative electrode. Among them, when lithium ions are deposited on the surface of the negative electrode copper foil or lithium foil, it is easy to form needle-shaped or mossy dendrites. The growth of lithium dendrites may pierce the separator, resulting in internal short circuit of the battery, triggering thermal runaway and bringing potential safety hazards. In addition, the formation of lithium dendrites will also lead to dead lithium, reducing the active lithium in the battery, and decreasing the battery cycle life and energy density.

[0004] In order to overcome the lithium dendrite problem, modifying the current collector has become one of the means to control the growth of dendrites. Among them, effective ways include: using a current collector with a three-dimensional porous structure to provide a larger surface area, evenly distribute the current, and inhibit the growth of lithium dendrites. Currently, patents for improving the preparation method of porous copper foil include CN102943187A, CN101596598A, CN103046088A, CN103132111A, CN104057099A, etc. However, copper foil has poor lithium affinity and is not suitable as a lithium metal deposition substrate. Moreover, these methods are complex to prepare. Both CN102943187A and CN101596598A use alloys as raw materials. In addition to strict component control, they also involve high-temperature melting and dealloying steps, with high energy consumption; CN103046088A and CN103132111A are prepared by electrodeposition methods, involving the use of corrosive reagents and hydrogen protection treatment, with high energy consumption and large equipment loss; CN104057099A uses high-pressure and high-temperature reactions, with high energy consumption.

[0005] Therefore, a simple and lithium-affine three-dimensional porous negative electrode has a positive effect on controlling the growth of dendrites and inhibiting the formation of needle-shaped or mossy dendrites, and is of great significance for constructing a high-safety and high-specific-energy lithium metal battery. Summary of the Invention

[0006] The present invention aims at the deficiencies of the prior art and provides a three-dimensional porous negative electrode and its preparation method and application.

[0007] Specifically, it is realized through the following technical solutions:

[0008] A three-dimensional porous negative electrode is obtained by electrochemically treating a carbon-containing electrode sheet with an electrolyte; the electrolyte includes a solvent containing sulfolane and a lithium salt.

[0009] Further, the thickness of the three-dimensional porous negative electrode is 1-100 μm.

[0010] Further, the electrode active material of the carbon-containing electrode sheet is one of graphite, hard carbon, soft carbon, silicon carbon or a mixture of multiple ones in any ratio.

[0011] Further, the volume dosage of sulfolane is 0-100% of the volume of the solvent containing sulfolane and does not take zero.

[0012] The lithium salt is one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide or a mixture of multiple ones in any ratio.

[0013] Still further, the concentration of the lithium salt in the electrolyte is 0.01-10 mol / L.

[0014] Further, the electrochemcial treatment is carried out with the carbon-containing electrode sheet as the positive electrode and metallic lithium as the negative electrode. Then, a separator is placed between the positive and negative electrodes. After assembling into a battery, the electrolyte is injected. After charge and discharge cycle treatment, it is taken out, washed with dimethyl carbonate and dried to obtain the product.

[0015] The present invention also provides a preparation method of a three-dimensional porous negative electrode, including the following steps:

[0016] (1) Electrolyte preparation: Mix a solvent containing sulfolane and a lithium salt evenly to obtain an electrolyte with a lithium salt concentration of 0.01-10 mol / L;

[0017] (2) Carbon-containing electrode sheet production: Coat a carbon-containing electrode material slurry on the surface of a current collector, and after compaction and roll cutting, a carbon-containing electrode sheet is obtained; the carbon-containing electrode material slurry is divided into a dry electrode material slurry or a wet electrode material slurry; the dry electrode material slurry is obtained by mixing an electrode active material, a binder and a conductive agent evenly; the wet electrode material slurry is obtained by mixing an electrode active material, a binder, a conductive agent and a solvent evenly;

[0018] (3) Battery assembly: Using the carbon-containing electrode sheet prepared in step (2) as the positive electrode and lithium foil as the negative electrode, place a separator between the positive and negative electrodes and assemble into a battery;

[0019] (4) Electrochemical treatment: Inject the electrolyte into the battery prepared in step (3), after charge and discharge treatment, take it out, wash it with dimethyl carbonate and dry it to obtain the three-dimensional porous negative electrode.

[0020] Further, the electrode active material is one of graphite, hard carbon, soft carbon, and silicon carbon, or a mixture of multiple types in any ratio.

[0021] The conductive agent is conductive carbon black.

[0022] The current collector is an aluminum current collector, a copper current collector, a nickel current collector, a stainless steel current collector, a composite material current collector, a conductive polymer current collector, a laminated composite film material current collector, a conductive resin current collector, a carbon-coated metal foil current collector, and a flexible conductive material current collector.

[0023] Still further, the graphite is artificial graphite or natural graphite.

[0024] The present invention also provides an application of the three-dimensional porous negative electrode in the preparation of a lithium-ion battery or a lithium metal battery.

[0025] Further, the lithium-ion battery or the lithium metal battery includes a positive electrode, a negative electrode, a shrapnel, a gasket, and a separator.

[0026] Still further, the active material used in the positive electrode is lithium iron phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium cobaltate, lithium nickelate, or sulfur.

[0027] Still further, the separator is a single-layer polypropylene separator.

[0028] Beneficial effects:

[0029] (1) By electrochemically intercalating the carbon negative electrode, the present invention prepares a three-dimensional porous negative electrode material with lithium storage and lithium-philic functions. The porous structure not only retains the lithium storage capacity of the carbon material but also serves as a lithium-philic skeleton, providing additional lithium storage and lithium deposition spaces, making the deposition of lithium ions on the negative electrode surface more uniform, thereby effectively suppressing the growth of lithium dendrites; this lithium storage and lithium-philic regulation mechanism greatly improves the safety of the battery and reduces the risks of internal short circuit and thermal runaway caused by the growth of lithium dendrites.

[0030] (2) The present invention uses a sulfolane-based electrolyte to intercalate the carbon material. After intercalation, the carbon material is not peeled off, and the negative electrode structure remains intact. When the prepared three-dimensional porous negative electrode material is used as the negative electrode of a lithium metal battery and a lithium-ion battery, it provides a larger surface area and a more uniform current distribution, is conducive to the wetting of the electrolyte, and can accommodate the deposition of lithium.

[0031] (3) The preparation process of the present invention is simple in operation, easy to realize large-scale production, low in energy consumption, and small in equipment loss. Description of the Drawings

[0032] Figure 1 SEM image of the three-dimensional porous negative electrode prepared by the method of Example 1;

[0033] Figure 2 SEM image of the three-dimensional porous negative electrode prepared by the method of Comparative Example 1;

[0034] Figure 3 SEM image of the three-dimensional porous negative electrode prepared by the method of Comparative Example 2;

[0035] Figure 4 SEM image of the three-dimensional porous negative electrode prepared by the method of Comparative Example 3;

[0036] Figure 5 and Figure 6 Voltage-capacity curve of the three-dimensional porous negative electrode prepared in Example 1;

[0037] Figure 7 Partial enlarged SEM image of the three-dimensional porous negative electrode prepared by the method of the present invention;

[0038] Figure 8 SEM image of the three-dimensional porous negative electrode prepared by the method of the present invention. Detailed Description of the Invention

[0039] The following further details the specific embodiments of the present invention. However, the present invention is not limited to these embodiments. Any improvement or substitution based on the basic spirit of this embodiment still falls within the scope protected by the claims of the present invention.

[0040] Example 1

[0041] A method for preparing a three-dimensional porous negative electrode includes the following steps:

[0042] (1) Electrolyte preparation: Take sulfolane (abbreviated as SL), LiPF6, and DMC and mix them evenly to obtain an electrolyte with a LiPF6 concentration of 1 mol / L; the volume ratio of sulfolane to DMC is 1:1;

[0043] (2) Preparation of the carbon-containing electrode sheet: Take 96 g of graphite, 2 g of binder, and 2 g of conductive carbon black, mix them evenly, and stir evenly with water as a solvent to obtain a carbon-containing electrode material slurry; then coat the carbon-containing electrode material slurry on the surface of a copper current collector, and after compaction and slitting, a carbon-containing electrode sheet is obtained;

[0044] (3) Battery assembly: In an argon glove box with an oxygen pressure and a water pressure both less than 0.1 ppm, use the electrode sheet prepared in step (2) as the positive electrode and a lithium foil as the negative electrode, and place a single-layer polypropylene film between the positive and negative electrodes to assemble a battery;

[0045] (4) Electrochemical treatment: Inject the electrolyte into the battery prepared in step (3), charge and discharge at a current density of 0.1 A / g in the voltage range of 0.01 V to 1.5 V for one week, then take it out, wash it with dimethyl carbonate and dry it to obtain a three-dimensional porous negative electrode with a thickness of 50 μm.

[0046] Example 2

[0047] A preparation method of a three-dimensional porous negative electrode, comprising the following steps:

[0048] (1) Electrolyte preparation: Take SL and lithium bis(trifluoromethanesulfonyl)imide and mix them evenly to obtain an electrolyte with a concentration of 0.1 mol / L of bis(fluorosulfonyl)imide;

[0049] Steps (2) and (3): The same as Example 1;

[0050] (4) Electrochemical treatment: Inject the electrolyte into the battery prepared in step (3), after charging and discharging at a current density of 0.2 A / g in the voltage range of 0.01 V to 1.5 V for one week, take it out, wash it with dimethyl carbonate and dry it to obtain a three-dimensional porous negative electrode with a thickness of 30 μm.

[0051] Example 3

[0052] A preparation method of a three-dimensional porous negative electrode, comprising the following steps:

[0053] (1) Electrolyte preparation: Take SL, lithium perchlorate, and DMC and mix them evenly to obtain an electrolyte with a concentration of 1.2 mol / L of lithium perchlorate, and the volume ratio of SL to DMC is 2:1;

[0054] Steps (2) and (3): The same as Example 1;

[0055] (4) Electrochemical treatment: Inject the electrolyte into the battery prepared in step (3), charge and discharge at a current density of 0.1 A / g in the voltage range of 0.01 V to 1.5 V for one week, take it out, wash it with dimethyl carbonate and dry it to obtain a three-dimensional porous negative electrode with a thickness of 50 μm.

[0056] Example 4

[0057] A preparation method of a three-dimensional porous negative electrode, comprising the following steps:

[0058] (1) Electrolyte preparation: Take SL, lithium bis(oxalato)borate, and DMC and mix them evenly to obtain an electrolyte with a concentration of 1.5 mol / L of lithium bis(oxalato)borate, and the volume ratio of SL to DMC is 1:3;

[0059] Steps (2) and (3): The same as Example 1;

[0060] (4) Electrochemical treatment: Inject the electrolyte into the battery prepared in step (3), charge and discharge at a current density of 0.1 A / g in the voltage range of 0.01 V to 1.5 V for one week, take it out, wash it with dimethyl carbonate and dry it to obtain a three-dimensional porous negative electrode with a thickness of 50 μm.

[0061] Example 5

[0062] A method for preparing a three-dimensional porous negative electrode, comprising the following steps:

[0063] (1) Electrolyte preparation: Take SL, lithium bis(trifluoromethanesulfonyl)imide, and DMC and mix them evenly to obtain an electrolyte with a concentration of 1.5 mol / L of lithium bis(trifluoromethanesulfonyl)imide, and the volume ratio of SL to DMC is 1:1;

[0064] (2) Preparation of carbon-containing electrode sheet: Take 96 g of hard carbon, 2 g of binder, and 2 g of conductive carbon black and mix them evenly to obtain a carbon-containing electrode material slurry; then spray the carbon-containing electrode material slurry on the surface of a copper current collector, and after compaction and roll cutting, a carbon-containing electrode sheet is obtained;

[0065] Step (3): The same as in Example 1;

[0066] (4) Electrochemical treatment: Inject the electrolyte into the battery prepared in step (3), and after charging and discharging at a current density of 0.1 A / g in a voltage range of 0.01 V to 1.5 V for one week, take it out, wash it with dimethyl carbonate and dry it to obtain a three-dimensional porous negative electrode with a thickness of 50 μm.

[0067] Comparative Example 1

[0068] The difference from Example 1 is that: Replace sulfolane with ethylene carbonate (EC).

[0069] Comparative Example 2

[0070] The difference from Example 1 is that: Replace sulfolane with propylene carbonate (PC).

[0071] Comparative Example 3

[0072] The difference from Example 1 is that: Replace sulfolane with fluoroethylene carbonate (FEC).

[0073] Figure 1 SEM image of the three-dimensional porous negative electrode prepared by the method of Example 1; Figure 2 SEM image of the three-dimensional porous negative electrode prepared by the method of Comparative Example 1; Figure 3 SEM image of the three-dimensional porous negative electrode prepared by the method of Comparative Example 2; Figure 4 SEM image of the three-dimensional porous negative electrode prepared by the method of Comparative Example 3; It can be seen from Figures 1 - 4 that after cycling in EC and FEC electrolytes, the graphite particles still maintain integrity, while after cycling in PC, all the graphite particles are damaged. In contrast, after cycling in SL electrolyte, the graphite particles have a shape like an accordion, and their particle integrity is between that of PC and EC or FEC. Therefore, when the graphite negative electrode prepared in Example 1 expands in volume, it will not be damaged or fall off, and thus can be used as a three-dimensional current collector to accommodate lithium metal deposition.

[0074] According to the traditional process, lithium iron phosphate was selected as the positive electrode active material, and a positive electrode sheet was made with a conductive agent and a binder. A single-layer polypropylene separator was used as the separator. The treated electrode sheet of Example 1 and the treated electrode sheet of Comparative Example 1 were used as the negative electrodes of the treated graphite group and the untreated graphite group respectively to assemble a battery. The electrolyte of Comparative Example 1 (i.e., the electrolyte was composed of a solvent of EC and DMC with an equal volume ratio and 1 mol / L of LiPF6) was injected, and discharge tests were carried out at currents of 0.27 mA and 0.904 mA respectively, and Figure 5 and Figure 6 .

[0075] At a current density of 0.27 mA, the treated graphite and the untreated graphite had similar electrochemical platforms, indicating that the structure of the graphite was not damaged after treatment with sulfolane and it still maintained the original lithium intercalation ability; the lithium deposition overpotential of the untreated graphite negative electrode was 19 mV and the platform potential was 12 mV. In contrast, the lithium deposition overpotential of the treated graphite negative electrode was 17 mV and the platform potential was 10 mV. The treated graphite had a larger surface area, which helped to promote lithium deposition.

[0076] At a current density of 0.904 mA, the treated graphite and the untreated graphite had similar charge-discharge curves, indicating that the structure of the graphite was not damaged after treatment with sulfolane and it still maintained the original lithium intercalation ability; the lithium deposition overpotential of the untreated graphite negative electrode was 27 mV, the platform potential was 17 mV, and the de-lithiation platform potential was 16 mV. The discharge specific capacity and the charge specific capacity were 4.52 and 4.44 mAh respectively. In contrast, the lithium deposition overpotential of the treated graphite negative electrode was 22 mV, the platform potential was 14 mV, and the de-lithiation platform potential was 10 mV. The discharge specific capacity and the charge specific capacity were 4.52 and 4.47 mAh respectively. The treated graphite had a larger surface area, which increased the reaction rate, helped the lithium deposition / delithiation behavior, and improved the reversible specific capacity of the three-dimensional porous negative electrode.

[0077] The three-dimensional porous negative electrodes obtained from Example 2 - Example 5 and other technical solutions within the protection scope of the present invention were scanned by an electron microscope. The results showed that: when the carbon material electrode was subjected to an electrochemical reaction with sulfolane, the carbon particles presented an accordion-like shape, and the particle integrity was good. They would not fall off and were not easily damaged when the volume expanded. Select Figure 7 、 Figure 8 as representatives to prove it.

Claims

1. A three-dimensional porous negative electrode, characterized in that, The three-dimensional porous negative electrode is obtained by electrochemically treating a carbon-containing electrode with an electrolyte; the electrolyte includes a solvent containing sulfolane and a lithium salt.

2. The three-dimensional porous negative electrode according to claim 1, wherein The thickness of the three-dimensional porous negative electrode is 1-100 μm.

3. The three-dimensional porous negative electrode according to claim 1, wherein The electrode active material of the carbon-containing electrode sheet is one of graphite, hard carbon, soft carbon, silicon carbon or a mixture of multiple kinds in any ratio.

4. The three-dimensional porous negative electrode according to claim 1, wherein The volume dosage of the sulfolane is 0-100% of the volume of the solvent containing sulfolane and does not take zero.

5. The three-dimensional porous negative electrode according to claim 1, wherein The lithium salt is one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide or a mixture of multiple kinds in any ratio.

6. The three-dimensional porous negative electrode according to claim 1, wherein, The concentration of the lithium salt in the electrolyte is 0.01-10 mol / L.

7. The three-dimensional porous negative electrode according to claim 1, wherein, The electrochemcial treatment is carried out by using the carbon-containing electrode as the positive electrode and metallic lithium as the negative electrode, then placing a separator between the positive and negative electrodes, assembling into a battery, injecting the electrolyte, and after charge and discharge cycling treatment, taking it out, washing with dimethyl carbonate and drying to obtain.

8. A method for preparing a three-dimensional porous negative electrode according to any one of claims 1-7, characterized in that, It includes the following steps: (1) Electrolyte preparation: Mix the solvent containing sulfolane and the lithium salt evenly to obtain an electrolyte with a lithium salt concentration of 0.01-10 mol / L; (2) Preparation of the carbon-containing electrode sheet: Coat the carbon-containing electrode material slurry on the surface of the current collector, and after compaction and roll cutting, the carbon-containing electrode sheet is obtained; The carbon-containing electrode material slurry is divided into a dry electrode material slurry or a wet electrode material slurry; the dry electrode material slurry is obtained by mixing the electrode active material, the binder and the conductive agent evenly; the wet electrode material slurry is obtained by mixing the electrode active material, the binder, the conductive agent and the solvent evenly; (3) Battery assembly: Using the carbon-containing electrode sheet prepared in step (2) as the positive electrode and lithium foil as the negative electrode, place a separator between the positive and negative electrodes and assemble into a battery; (4) Electrochemical treatment: Inject the electrolyte into the battery prepared in step (3), after charge and discharge treatment, take it out, wash with dimethyl carbonate and dry to obtain the three-dimensional porous negative electrode.

9. The application of a three-dimensional porous negative electrode according to any one of claims 1-7 or a three-dimensional porous negative electrode prepared by the preparation method according to claim 8 in the preparation of a lithium-ion battery or a lithium metal battery.

Images