Lithium sheet reference electrode, lithium ion battery and preparation method of lithium sheet reference electrode

Abstract

The invention relates to the technical field of batteries, in particular to a lithium sheet reference electrode, a lithium ion battery and a preparation method of the lithium sheet reference electrode. The lithium sheet reference electrode comprises a folded lithium sheet, a metal wire arranged in the folded lithium sheet and a protective layer deposited on the surface of the lithium sheet. The preparation method of the lithium sheet reference electrode is simple, the lithium sheet reference electrode obtained through in-situ generation of the protective layer is stable in monitoring potential, the protective layer and the lithium sheet are stably combined through chemical bonds, the protective layer is uniform and compact, the ionic conductivity is good, and the service life of the lithium sheet reference electrode is obviously prolonged under the use working conditions of high temperature, low temperature, normal temperature and the like.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a lithium reference electrode, a lithium-ion battery, and a method for preparing the same. Background Technology

[0002] With the excessive consumption of fossil fuels and the increasing severity of global warming, the use and promotion of green energy has become an inevitable trend. Lithium-ion batteries, as the main power source for new energy vehicles, play a crucial role in green travel and the green economy. However, the slow lithium intercalation at the negative electrode during fast charging of lithium-ion batteries poses a risk of lithium plating. Therefore, accurately assessing the lithium intercalation capability of the negative electrode and the lithium plating potential boundary has become a critical research issue that urgently needs to be addressed in fast charging technology. Existing evaluation methods typically use lithium sheet reference electrodes for testing; however, lithium sheet reference electrodes suffer from problems such as easy side reactions with the electrolyte, unstable reference potential, and short service life. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a lithium reference electrode, a lithium-ion battery and a method for preparing the same.

[0004] To achieve the above objectives, this application adopts the following solution:

[0005] A lithium reference electrode includes a folded lithium sheet, a metal wire disposed within the folded lithium sheet, and a protective layer deposited on the surface of the lithium sheet.

[0006] The thickness of the lithium sheet is 0.01mm to 0.2mm, and the size of the lithium sheet before folding is (0.5 to 50mm) * (0.5 to 50mm).

[0007] The metal wire is any one of insulating enameled copper wire, silver wire or gold wire, and the insulation layer is removed at 3±2mm from both ends of the metal wire; one end of the metal wire extends out of the folded lithium sheet.

[0008] The folded lithium sheet also contains polyester fibers; the length of the polyester fibers does not exceed the length of the lithium sheet.

[0009] The present invention also includes a method for preparing the lithium sheet reference electrode, comprising the following steps: 1) taking a lithium sheet and placing a metal wire, preferably, and a polyester fiber on the geometric center of the lithium sheet surface, folding the lithium sheet in half to cover the metal wire, preferably, and the polyester fiber, and cutting the lithium sheet to the required size;

[0010] 2) Place the lithium sheet with metal wire prepared above into an electrolytic cell containing a treatment solution, with the lithium sheet as the negative electrode and lithium iron phosphate, ternary lithium, or lithium cobalt oxide as the positive electrode, and pass a current of 1 to 200 uA to uniformly generate a protective layer on the surface of the lithium sheet. Preferably, the energizing treatment time is 0.05 to 24 h and the treatment temperature is 5 to 60 °C.

[0011] The treatment liquid comprises a solvent and a salt additive, wherein the mass fraction of the solvent is 60wt% to 80wt% and the mass fraction of the salt additive is 20wt% to 40wt%.

[0012] The solvents mentioned include one or more of the following: dimethyl ethylene glycol (DME), 1,3-dioxolane (DOL), vinyl sulfite (ES), succinate (SN), 2,4-bis(2-fluoroethoxy)tetrafluorocyclotriphosphazene (DFEPN), trifluoromethoxybenzene (PhOCF3), tetrafluorophthalonitrile (o-TFPN), and 1,3-dithiane;

[0013] Preferably, the solvent is a mixture of DOL, DME, ES, and 1,3-dithiane, wherein the mass ratio of DOL, DME, ES, and 1,3-dithiane is (4-8):(4-8):(2-5):1; preferably 5:5:4:1.

[0014] The salt additives include one or more of lithium nitrate (LiNO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), and silver trifluoromethanesulfonate (AgTFMS);

[0015] Preferably, the salt additive is a mixture of LiTFSI, AgTFMS, and LiNO3, wherein the mass ratio of LiTFSI, AgTFMS, and LiNO3 is (1-5):(0.5-2):(0.5-2); preferably 3:1:1.

[0016] The present invention also includes a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a lithium sheet reference electrode as described in any one of claims 1-4; wherein the lithium sheet reference electrode is disposed between the positive electrode and the separator, or between the negative electrode and the separator.

[0017] A membrane coating is provided at the position where the lithium reference electrode contacts the positive or negative electrode.

[0018] The present invention also includes a method for preparing the lithium-ion battery, comprising the following steps: 1) preparing a lithium-ion battery electrode assembly by forming a positive electrode, a separator, and a negative electrode; 2) placing a lithium reference electrode into the unfilled lithium-ion battery electrode assembly obtained in step 1), and then covering the lithium reference electrode and the electrode with a separator coating layer, with the insulating end of the metal wire extending beyond the battery encapsulation material and fixed with tape; 3) subsequently performing normal assembly, electrolyte filling, and capacity testing of the battery electrode assembly.

[0019] Compared with the prior art, the beneficial effects of this application are as follows:

[0020] The lithium reference electrode preparation method of this application is simple. The lithium reference electrode obtained by in-situ generation of protective layer has stable monitoring potential. The protective layer and lithium sheet are chemically bonded and stable. The protective layer is uniform and dense, with good ionic conductivity. The service life is significantly improved under operating conditions such as high temperature, low temperature and room temperature. Attached Figure Description

[0021] Figure 1 This is an overall schematic diagram of the unfolded lithium-ion battery of the present invention;

[0022] Figure 2 This is an overall schematic diagram of the lithium-ion battery of the present invention with and without a lithium-sheet reference electrode. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] Example 1:

[0025] 1. Fabrication of lithium reference electrode: Take a lithium sheet, place the metal wire and polyester fiber on the surface of the lithium metal sheet, fold the lithium sheet in half to cover the metal wire and polyester fiber, and cut the lithium sheet into 2mm*10mm pieces.

[0026] The reference electrode treatment solution had a solvent mass fraction of 60 wt%, with DOL:DME:ES:1,3-dithiaane in a ratio of 5:5:4:1; and a salt additive mass fraction of 40 wt%, with LiTFSI:AgTFMS:LiNO3 in a ratio of 3:1:1. A lithium sheet was used as the negative electrode, and lithium iron phosphate as the positive electrode. The electrodes were placed in an electrolytic cell containing the treatment solution, and a current of 10 μA was applied to uniformly form a dense protective layer on the lithium sheet surface. The temperature was set at 25 °C, and the treatment lasted for 1 hour.

[0027] Remove the lithium reference electrode 1 prepared in the previous step and place it into the unfilled single lithium-ion battery cell (the placement process is as follows). Figure 2 As shown, the lithium-ion battery includes a positive electrode 3, a negative electrode 4, a separator 2, and a lithium reference electrode 1, as illustrated in the unfolded diagram below. Figure 1 As shown, a lithium reference electrode is placed between the positive electrode and the separator, and then a separator coating layer 21 is used to cover the lithium reference electrode and the electrode. The battery is then injected with electrolyte and sealed; subsequently, normalization and capacity testing are performed. The stability of the positive and negative electrode potentials during long-term cycling is monitored using the reference electrode at 1C rate and 10 / 25 / 45°C.

[0028] Example 2:

[0029] Take a lithium metal sheet, place the metal wire and polyester fiber on the surface of the lithium metal sheet, fold the lithium sheet in half to cover the metal wire and polyester fiber, and cut the lithium sheet into 2mm*10mm pieces.

[0030] The reference electrode treatment solution had a solvent mass fraction of 80 wt%, with DOL:DME:ES:1,3-dithiaane in a ratio of 5:5:4:1; and a salt additive mass fraction of 20 wt%, with LiTFSI:AgTFMS:LiNO3 in a ratio of 3:1:1. A lithium sheet was used as the negative electrode, and lithium iron phosphate as the positive electrode. The electrodes were placed in an electrolytic cell containing the treatment solution, and a current of 10 μA was applied to uniformly form a dense protective layer on the lithium sheet surface. The temperature was set at 25 °C, and the treatment lasted for 1 hour.

[0031] The prepared lithium reference electrode 1 is removed from the previous step and placed into a single-cell lithium-ion battery (including positive electrode 3, negative electrode 4, and separator 2) that has not been filled with electrolyte. The lithium reference electrode is placed between the positive electrode 3 and the separator 2. Then, a separator coating layer is used to cover the lithium reference electrode and the electrode. The battery is then filled with electrolyte and sealed. Subsequently, normalization and capacity testing are performed. The stability of the positive and negative electrode potentials during long-term cycling is monitored through the reference electrode at 1C rate and 10 / 25 / 45℃.

[0032] Example 3:

[0033] Take a lithium metal sheet, place the metal wire and polyester fiber on the surface of the lithium metal sheet, fold the lithium sheet in half to cover the metal wire and polyester fiber, and cut the lithium sheet into 2mm*10mm pieces.

[0034] The reference electrode treatment solution had a solvent mass fraction of 60 wt%, with DOL:DME:ES:1,3-dithiaane in a ratio of 5:5:4:1; and a salt additive mass fraction of 40 wt%, with LiTFSI:AgTFMS:LiNO3 in a ratio of 3:1:1. A lithium sheet was used as the negative electrode, and lithium iron phosphate as the positive electrode. The electrodes were placed in an electrolytic cell containing the treatment solution, and a current of 10 μA was applied to uniformly form a dense protective layer on the lithium sheet surface. The temperature was set at 45 °C, and the treatment lasted for 1 hour.

[0035] The prepared lithium reference electrode from the previous step was placed into a single lithium-ion battery without electrolyte filling. The lithium reference electrode was positioned between the positive electrode and the separator, and then the separator was used to cover the lithium reference electrode and the electrode. The battery was then filled with electrolyte and sealed. Subsequently, normalization and capacity testing were performed. The stability of the positive and negative electrode potentials during long-term cycling was monitored through the reference electrode at 1C rate and 10 / 25 / 45℃.

[0036] Example 4:

[0037] Take a lithium metal sheet, place the metal wire and polyester fiber on the surface of the lithium metal sheet, fold the lithium sheet in half to cover the metal wire and polyester fiber, and cut the lithium sheet into 2mm*10mm pieces.

[0038] The reference electrode treatment solution had a solvent mass fraction of 60 wt%, with DOL:DME:ES:1,3-dithiaane in a ratio of 5:5:4:1; and a salt additive mass fraction of 40 wt%, with LiTFSI:AgTFMS:LiNO3 in a ratio of 3:1:1. A lithium sheet was used as the negative electrode, and lithium iron phosphate as the positive electrode. The electrodes were placed in an electrolytic cell containing the treatment solution, and a current of 10 μA was applied to uniformly form a dense protective layer on the lithium sheet surface. The temperature was set at 25 °C, and the treatment lasted for 6 hours.

[0039] The prepared lithium reference electrode from the previous step was placed into a single lithium-ion battery without electrolyte filling. The lithium reference electrode was positioned between the positive electrode and the separator, and then the separator was used to cover the lithium reference electrode and the electrode. The battery was then filled with electrolyte and sealed. Subsequently, normalization and capacity testing were performed. The stability of the positive and negative electrode potentials during long-term cycling was monitored through the reference electrode at 1C rate and 10 / 25 / 45℃.

[0040] Comparative Example 1:

[0041] Take a lithium metal sheet, place the metal wire and polyester fiber on the surface of the lithium metal sheet, fold the lithium sheet in half to cover the metal wire and polyester fiber, and cut the lithium sheet into 2mm*10mm pieces.

[0042] The prepared lithium reference electrode from the previous step was placed into a single lithium-ion battery without electrolyte filling. The lithium reference electrode was positioned between the positive electrode and the separator, and then the separator was used to cover the lithium reference electrode and the electrode. The battery was then filled with electrolyte and sealed. Subsequently, normalization and capacity testing were performed. The stability of the positive and negative electrode potentials during long-term cycling was monitored through the reference electrode at 1C rate and 10 / 25 / 45℃.

[0043] Table 1 Comparison of Reference Electrode Stability

[0044]

[0045] Table 1 compares the stability and service life of the lithium reference electrodes in Examples 1-4 and Comparative Example 1. It can be seen that the service life and stability of the lithium reference electrodes in each example are significantly improved compared with the comparative example at various temperatures.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0047] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0048] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A lithium-ion reference electrode, characterized in that, It includes a folded lithium sheet, metal wires disposed within the folded lithium sheet, and a protective layer deposited on the surface of the lithium sheet.

2. The lithium reference electrode according to claim 1, characterized in that, The thickness of the lithium sheet is 0.01mm to 0.2mm, and the size of the lithium sheet before folding is (0.5 to 50mm) * (0.5 to 50mm).

3. The lithium reference electrode according to claim 1, characterized in that, The metal wire is any one of insulating enameled copper wire, silver wire or gold wire, and the insulation layer is removed at 3±2mm from both ends of the metal wire; one end of the metal wire extends out of the folded lithium sheet.

4. The lithium reference electrode according to claim 1, characterized in that, The folded lithium sheet also contains polyester fibers; the length of the polyester fibers does not exceed the length of the lithium sheet.

5. A method for preparing a lithium-ion reference electrode according to any one of claims 1-4, characterized in that, The steps include: 1) Take a lithium sheet and place the metal wire, preferably, and polyester fiber on the geometric center of the lithium sheet surface, fold the lithium sheet in half to cover the metal wire, preferably, and polyester fiber, and cut the lithium sheet to the required size; 2) Place the lithium sheet with metal wire prepared above into an electrolytic cell containing a treatment solution, using the lithium sheet as the negative electrode and lithium iron phosphate, ternary lithium, or lithium cobalt oxide as the positive electrode, and pass a current of 1 to 200 uA, preferably 10 uA, to uniformly generate a protective layer on the surface of the lithium sheet. Preferably, the energizing treatment time is 0.05 to 24 h, preferably 1 to 6 h, and the treatment temperature is 5 to 60 °C, preferably 25 to 45 °C.

6. The preparation method according to claim 5, characterized in that, The treatment liquid comprises a solvent and a salt additive, wherein the mass fraction of the solvent is 60wt% to 80wt% and the mass fraction of the salt additive is 20wt% to 40wt%.

7. The preparation method according to claim 5, characterized in that, The solvents mentioned include one or more of the following: ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), vinyl sulfite (ES), succinate (SN), 2,4-bis(2-fluoroethoxy)tetrafluorocyclotriphosphazene (DFEPN), trifluoromethoxybenzene (PhOCF3), tetrafluorophthalonitrile (o-TFPN), and 1,3-dithiaane. Preferably, the solvent is a mixture of DOL, DME, ES, and 1,3-dithiane, and the mass ratio of DOL, DME, ES, and 1,3-dithiane is (4-8):(4-8):(2-5):1; more preferably 5:5:4:

1.

8. The preparation method according to claim 5, characterized in that, The salt additives include one or more of lithium nitrate (LiNO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), and silver trifluoromethanesulfonate (AgTFMS). Preferably, the salt additive is a mixture of LiTFSI, AgTFMS, and LiNO3, wherein the mass ratio of LiTFSI, AgTFMS, and LiNO3 is (1-5):(0.5-2):(0.5-2); preferably 3:1:

1.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and a lithium reference electrode as described in any one of claims 1-4; the lithium reference electrode is disposed between the positive electrode and the separator, or between the negative electrode and the separator; preferably, a separator coating layer is provided at the position where the lithium reference electrode contacts the positive electrode or the negative electrode.

10. A method for preparing a lithium-ion battery according to claim 9, characterized in that, The process includes the following steps: 1) Preparing a lithium-ion battery electrode assembly by forming a positive electrode, a separator, and a negative electrode; 2) Placing a lithium reference electrode into the unfilled lithium-ion battery electrode assembly obtained in step 1), and then covering the lithium reference electrode with a separator coating layer between the lithium reference electrode and the electrode, with the insulating end of the metal wire extending beyond the battery encapsulation material and fixed with tape; 3) Subsequently performing normal assembly, electrolyte filling, and capacity testing of the battery electrode assembly.

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