Reference electrode battery and preparation method thereof

Abstract

The invention discloses a reference electrode battery and a preparation method thereof, the method comprises the following steps: S1, a double-sided lithium pole piece and a single-sided graphite electrode lamination form a soft package battery, the double-sided lithium pole piece is located in the middle, the two sides of the double-sided lithium pole piece are separated by a diaphragm, a copper / nickel pole piece and a graphite pole piece are respectively placed, and a unit battery can be formed; s2, carrying out mixing treatment on the unit battery and an electrolyte to obtain a mixed battery; s3, carrying out electroplating treatment and charging treatment on the mixed battery to obtain a charged battery; s4, disassembling the charged battery to obtain a lithium-plated copper sheet / lithium-plated nickel sheet and a lithium-embedded graphite sheet; and S5, implanting the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet into a battery cell. The method is easy to operate, and the problems that the reference electrode is low in manufacturing success rate, difficult in standardization process, limited in use scene and poor in effect are solved.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a reference electrode battery and a preparation method thereof. Background Art

[0002] As a representative product of current battery technology, lithium-ion batteries are widely used in new energy vehicles, portable electronic devices and other fields due to their advantages such as high energy density, long cycle life and low self-discharge rate. However, traditional two-electrode lithium-ion batteries have limitations in electrochemical performance analysis. When it is necessary to deeply study the specific behavior of the positive and negative electrodes in the full battery, such as potential changes, capacity decay mechanisms, etc., the traditional two-electrode system seems to be unable to cope with it. Therefore, the introduction of a reference electrode has become a necessary means to improve battery performance analysis and research.

[0003] The advantages of three-electrode lithium-ion batteries in electrochemical analysis are mainly reflected in two aspects. First, by introducing a reference electrode, independent electrochemical measurements of the entire battery and the positive and negative electrodes can be achieved, thereby more accurately evaluating the overall performance of the battery and the contribution of each electrode. This analytical capability is of great significance for battery design optimization, material selection, and performance evaluation. Secondly, the three-electrode structure helps to improve the electrochemical stability and safety of the battery. The presence of a reference electrode can monitor the potential changes inside the battery in real time, promptly detect and prevent potential electrochemical imbalance problems, thereby extending the battery life and promptly warning of safety risks.

[0004] Traditional reference electrodes for lithium-ion batteries are lithium metal and lithium-plated metal wires. The advantage of such reference electrodes is that the lithium metal potential is stable and accurate. It is usually used as the zero potential point and can directly reflect the electrochemical behavior of the positive and negative electrode materials of lithium-ion batteries. However, due to the active chemical properties of lithium metal, it is easy to react in the air environment. The process of making lithium metal reference electrodes is demanding. After being placed inside the battery, it is easy to react with the electrolyte, resulting in the inability to maintain a stable reference potential. The method of implanting metal wires for lithium plating also has certain defects. The lithium plating conditions are difficult to reasonably control, and it is easy to over-deposit lithium dendrites, which then pierce the diaphragm and affect the normal operation of the battery itself. The metal wire is generally controlled to be extremely thin, the lithium loading is limited, and the time to maintain continuous monitoring during the battery cycle is short. In addition, the metal wire itself is not strong enough and is very easy to break. The conductive segment is easy to cause internal shorts inside the battery, and the success rate of manufacturing is low. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the present invention provides a battery reference electrode manufacturing technology, adopts a new reference electrode manufacturing idea, proposes a solution that is superior to the traditional reference electrode, and solves the problems of low reference electrode manufacturing success rate, difficult standardized process, limited use scenarios, and poor effect.

[0006] In one aspect of the present invention, the present invention provides a method for preparing a reference electrode. According to an embodiment of the present invention, the method comprises:

[0007] S1: A double-sided lithium electrode sheet and a single-sided graphite electrode stack form a soft-pack battery. The double-sided lithium electrode sheet is located in the middle, and the two sides are separated by a diaphragm. The copper / nickel electrode sheet and the graphite electrode sheet are placed separately to form a unit battery.

[0008] S2: mixing the unit cell with an electrolyte to obtain a mixed cell;

[0009] S3: performing electroplating and charging treatments on the mixed battery to obtain a charged battery;

[0010] S4: disassembling the battery after the charging process to obtain a lithium-plated copper sheet / lithium-plated nickel sheet and a lithium-embedded graphite sheet;

[0011] S5: implanting the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-intercalated graphite sheet into the battery cell. The method is simple to operate and solves the problems of low success rate of reference electrode production, difficult standardized process, limited use scenarios, and poor effect.

[0012] According to an embodiment of the present invention, the above method may further include at least one of the following additional technical features:

[0013] According to an embodiment of the present invention, the single-sided graphite electrode stack is obtained by loading a copper or nickel sheet on the back side of the single-sided graphite electrode sheet.

[0014] According to an embodiment of the present invention, the graphite is selected from natural graphite, artificial graphite or a mixture of a composite graphite material, a conductive agent and a binder.

[0015] According to an embodiment of the present invention, the copper or nickel sheet has a thickness of 6-15 um.

[0016] According to an embodiment of the present invention, the thickness of the single-sided graphite electrode stack is 20-80 um.

[0017] According to an embodiment of the present invention, the copper sheet is selected from rolled copper foil, electrolytic copper foil, copper wire or foam copper.

[0018] According to an embodiment of the present invention, the nickel sheet is selected from nickel foil, nickel mesh or nickel foam.

[0019] According to an embodiment of the present invention, the double-sided lithium pole sheet is selected from a double-sided lithium iron phosphate pole sheet, a lithium sheet or a double-sided lithium pole sheet made of other lithium-containing compound materials.

[0020] According to an embodiment of the present invention, the size of the double-sided lithium electrode sheet is consistent with the size of the single-sided graphite electrode stack.

[0021] According to an embodiment of the present invention, the electrolyte is selected from a mixture of a carbonate solvent, a carboxylate solvent and a lithium salt.

[0022] According to an embodiment of the present invention, the carbonate solvent is selected from ethylene carbonate, propylene carbonate, dimethyl carbonate or diethyl carbonate.

[0023] According to an embodiment of the present invention, the carboxylic acid ester solvent is selected from ethyl acetate, propargyl alcohol or epichlorohydrin.

[0024] According to an embodiment of the present invention, the lithium salt is selected from LiPF6 or LiFSI.

[0025] According to an embodiment of the present invention, the electrolyte further includes an additive, and the additive is selected from vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate or vinyl sulfate.

[0026] According to an embodiment of the present invention, the electroplating process is to use an electrochemical workstation or a charge and discharge test cabinet to connect the copper foil and the lithium iron phosphate tab, and use a current of 0.04C-0.5C for electroplating.

[0027] According to an embodiment of the present invention, the electroplating treatment time is 1-6 hours.

[0028] According to an embodiment of the present invention, the charging process is to transfer the negative electrode clip of the battery after the electroplating process to the graphite tab, and use a current of 0.1C-0.5C to insert lithium into the graphite sheet to full charge, 0.2V, 0.12V or 0.08V.

[0029] According to an embodiment of the present invention, the disassembly process is performed in an environment without water or oxygen.

[0030] According to an embodiment of the present invention, the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet is not cut after step S4, and the implantation in step S5 is performed by directly stacking the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet together with a common stacked soft package and placing it between the outermost negative electrode sheet and the aluminum-plastic film.

[0031] According to an embodiment of the present invention, after step S4, the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet are evenly cut into narrow strips with a width of 0.1-2 mm from the width direction, and the implantation in step S5 is carried out by wrapping the two narrow strips with fixed films on the upper and lower ends of the diaphragm, welding the pole ear sheet on the upper end, and placing them between the positive and negative pole pieces of the battery cell, or on the upper and lower ends and sides of the outside of the battery cell.

[0032] In another aspect of the present invention, the present invention provides a reference electrode. According to an embodiment of the present invention, the reference electrode is prepared by the method described above.

[0033] In another aspect of the present invention, the present invention proposes the use of a reference electrode prepared according to the method described above or the reference electrode described above in the preparation of a lithium battery.

[0034] In one aspect of the present invention, the present invention provides a method for preparing a reference electrode. According to an embodiment of the present invention, the method comprises:

[0035] 1. Take the coated single-sided graphite (including: natural graphite, artificial graphite, a mixture of composite graphite materials and conductive agents and binders) electrode, and leave a blank substrate copper foil (rolled copper foil or electrolytic copper foil) on the back. The thickness of the copper foil here is 6-15um, and the thickness of the electrode after coating is controlled at 20-80um. In addition to copper foil loaded with graphite negative electrode materials, the substrate can also use copper wire, foam copper, nickel foil, nickel mesh, foam nickel, etc.;

[0036] 2. Take the coated double-sided lithium iron phosphate electrode (which can be replaced by other lithium compound materials or lithium sheets), the size of which is consistent with the above-mentioned graphite negative electrode;

[0037] 3. Cut pure copper foil of the same size and combine it with the double-sided lithium iron phosphate electrode sheet and single-sided graphite electrode stack obtained in the above two steps to form a soft-pack battery. The lithium iron phosphate electrode sheet is located in the middle, separated by a diaphragm on both sides, and copper foil and graphite electrode sheets are placed separately to form a unit battery. This unit structure can be repeated to mass-produce reference electrodes;

[0038] 4. Carry out the conventional drying and injection process for the assembled soft-pack battery. The electrolyte uses a mixture of carbonate solvents (ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), etc.) or carboxylic acid solvents (ethyl acetate (EA)\propargyl alcohol (PA)\epichlorohydrin (EP), etc.) and lithium salts (LiPF6\LiFSI). Common additives (vinyl carbonate (VC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC) and vinyl sulfate (DTD), etc.) can be added. After sealing, let it stand for 12-24 hours;

[0039] 5. Use an electrochemical workstation or a charge and discharge test cabinet to connect the copper foil and the lithium iron phosphate tab, use a current of 0.04C-0.5C for electroplating, and the electroplating time is 1-6h. After the electroplating of the copper foil is completed, transfer the negative electrode clip to the graphite tab, and use a current of 0.1C-0.5C to embed lithium into the graphite sheet until it is fully charged (or three voltage platform areas: 0.2V, 0.12V and 0.08V);

[0040] 6. In an environment without water or oxygen, disassemble the prepared lithium-plated copper foil and lithium-embedded graphite sheet, without cutting or evenly cutting into narrow strips with a width of 0.1-2 mm in the width direction;

[0041] 7. In the case of no cutting, the lithium-plated copper foil and the lithium-embedded graphite sheet are directly stacked together with the ordinary stacked soft package and placed between the outermost negative electrode sheet and the aluminum-plastic film; in the case of cutting, the two narrow strips can be wrapped with the upper and lower ends of the diaphragm fixed with film, and the upper end can be welded with the pole ear sheet, and placed between the positive and negative pole sheets of the battery cell, or at the upper and lower ends and sides of the battery cell. See the specific embodiment for details.

[0042] According to an embodiment of the present invention, the above method may further include at least one of the following additional technical features:

[0043] According to an embodiment of the present invention, the method further comprises: after the implantation is completed, a normal subsequent soft pack production process is performed. The lithium-intercalated graphite reference electrode of the present invention does not need to be activated, and the potential change can be monitored during the formation stage, and the reference electrode end is respectively connected to the positive and negative electrodes of the battery with a voltage collector.

[0044] According to an embodiment of the present invention, the copper foil lithium-plated pole piece and the graphite lithium-embedded pole piece can be implanted at the same time. After the initial formation of the battery cell, part of the lithium in the positive electrode will be consumed to form a film after formation, which is an irreversible consumption. To address this problem, the negative electrode of the battery cell and a fully lithium-embedded or highly lithium-embedded graphite reference electrode can be connected to preferentially form a film on the negative electrode using a small current of 0.1-0.5C. At the same time, the implanted copper foil lithium-plated monitor reference electrode potential changes are used. When the next platform potential is reached, the priority film formation step is stopped. The graphite lithium-embedded reference still has a stable potential monitoring capability at this time. The lithium-plated copper foil left in the battery cell can verify the effectiveness of the lithium-embedded graphite in parallel, and the accuracy of potential monitoring. After the active lithium is consumed in the subsequent battery cycle, all lithium can be sacrificed to improve the performance of the battery cell itself.

[0045] According to an embodiment of the present invention, when only the graphite embedded lithium reference electrode is implanted, there are three feasible graphite reference electrodes corresponding to the three voltage platform areas of graphite embedded lithium at 0.2V, 0.12V and 0.08V, which are implanted in the interlayer of the battery cell or the battery cell shell. After the liquid injection package is made, the reference and the positive and negative electrodes of the battery cell can be connected to the voltage collector respectively to monitor the potential changes during battery operation. In the later stage of battery operation, the internal active lithium loss needs to be supplemented, and the lithium brought in by the sacrificed reference electrode can be used to improve the battery performance.

[0046] According to the embodiments of the present invention, the present invention has at least one of the following technical effects:

[0047] 1) The present invention proposes a stable and efficient preparation scheme for lithium-intercalated graphite reference electrode, which can be produced in batches;

[0048] 2) The lithium-intercalated graphite reference of the present invention can be directly used without activation after being implanted in the core, and the potential change can be monitored at the formation stage;

[0049] 3) The present invention specifically optimizes the implantation method of the lithium-intercalated graphite reference electrode and provides a variety of implantation position schemes, which does not interfere with the normal operation of the battery while playing the role of monitoring the potential;

[0050] 4) The present invention utilizes three graphite lithium-intercalation platforms from a novel perspective, proposes a variety of reference electrode manufacturing schemes, and simultaneously takes into account the lithium replenishment function, integrating multiple functions into one;

[0051] 4) The present invention has good practical applicability in both fresh battery monitoring and failed battery analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0053] Figure 1 It is a schematic diagram of the three voltage platforms of graphite intercalation lithium mentioned in the present invention;

[0054] Figure 2 It is a schematic diagram of the reference electrode preparation process of the present invention, wherein 1. copper foil, 2. double-sided lithium iron phosphate pole piece, 3. single-sided graphite coated copper foil, 4. electrochemical workstation or charge and discharge test cabinet;

[0055] Figure 3 Schematic diagram of a reference electrode implanted in a battery according to a first embodiment of the present invention, wherein 5. a negative electrode sheet of a battery body, 6. a positive electrode sheet of a battery body, 7. a separator, and 8. an outer aluminum-plastic film shell;

[0056] Figure 4 is a reference electrode monitoring data diagram in Example 1 of the present invention;

[0057] Figure 5 Schematic diagram of the reference electrode structure and position in an embodiment of the present invention, wherein 9. nickel tab, 10. tab glue, 11. film, 12. diaphragm, 13. lithium-embedded graphite pole piece. DETAILED DESCRIPTION

[0058] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0059] Embodiment 1

[0060] The graphite lithium-intercalated reference electrode of the present invention is implanted into a fresh soft-pack battery for potential monitoring, and the specific operation is as follows:

[0061] 1. Take a 6um copper foil and coat it on one side with graphite negative electrode material. The main graphite material used here is artificial graphite, and the thickness of the electrode after coating is controlled to be 70um.

[0062] 2. Take the double-sided lithium iron phosphate coated electrode, cut the copper foil of the same size, stack the three sheets with lithium iron phosphate in the middle, and align the copper foil and graphite material on both sides. Figure 2 shown.

[0063] 3. After drying the assembled battery, inject a mixture of carbonate solvent and lithium salt electrolyte, seal it and let it sit for 12 hours to soak, so that the internal electrodes remain moist and connected.

[0064] 4. Use the charge and discharge test cabinet to connect the positive electrode to the lithium iron phosphate tab and the negative electrode to the copper foil tab, set the current to 0.05C for 4 hours. Transfer the negative electrode to the graphite tab and charge it with a current of 0.1C until the graphite is fully charged.

[0065] 5. In the glove box, disassemble the lithium-plated copper foil and lithium-embedded graphite sheet of the above-mentioned battery and place them between the top negative electrode sheet and the aluminum-plastic film of the core to be made, in the following order: the electrode sheet of the battery to be tested, the lithium-embedded graphite sheet, and the lithium-plated copper foil. Figure 3 As shown, the normal stacked sheets are placed and made into a core, and then the subsequent preparation processes such as liquid injection and packaging are carried out.

[0066] 6. Use a charge and discharge test cabinet to connect the fully charged lithium-embedded graphite pole piece to the negative electrode of the battery, and use a voltage collector to connect the lithium-embedded graphite pole piece to the lithium-plated copper foil. Use a 0.02C current to discharge the negative electrode until the potential of the lithium-embedded graphite reference relative to lithium reaches a platform of 0.08V. This operation is equivalent to consuming the lithium carried by the reference electrode in advance to form the initial SEI film, and the reference electrode remains stable when it reaches the platform area.

[0067] 7. Transfer the positive electrode clip of the test cabinet to the positive electrode of the soft pack, start the normal chemical composition process, use a multi-channel acquisition instrument to connect the graphite reference to the positive electrode, the graphite reference to the negative electrode, monitor the voltage state of the battery during normal testing, and connect the lithium-plated copper foil to the positive and negative electrodes of the battery to verify the effectiveness of the graphite reference.

[0068] This example verifies that implanted lithium-intercalated graphite has the function of stabilizing the indicating potential. Figure 4 As shown, the lithium replenishment function also improves the discharge capacity of the battery cell and reduces the irreversible capacity loss of the graphite negative electrode by 3%. Appropriate lithium replenishment operations can still be performed when the battery capacity decays subsequently.

[0069] Embodiment 2

[0070] Take two single-sided coated graphite sheets of the same specifications as those described in Example 1, and place the coated material areas on both sides of the double-sided lithium iron phosphate opposite to each other. Set up three groups of three pole pieces in a group and repeat, and stack the pieces to form a battery cell. After the normal liquid injection and static process, connect the charge and discharge test cabinet and set the charging current to 0.1C, and adjust the charge state to 40%. At this time, the graphite embedded with lithium is located at the center of the 0.12V platform area. After completing the charge adjustment process, remove 6 lithium-embedded graphite electrodes in the glove box, and use anhydrous ethanol to erase the area with a width of 1 cm at the end of the pole piece ear. After erasing, the pole piece is evenly stripped, and the width is divided into narrow areas of 2 mm. Take the copper foil part on the upper end of the pole piece after stripping and weld the nickel ear. The upper and lower ends of the diaphragm wrapped in the material area are fixed with film, such as Figure 5 Schematic diagram of the reference electrode structure. Place the prepared lithium-intercalated graphite reference electrode into the upper end of the fresh coil, and use the core tape to fix the reference electrode to maintain the stability of the reference position inside the battery cell, and perform subsequent production such as liquid injection and sealing to complete the implantation of the reference electrode. In subsequent battery tests, a multi-channel detector is used to connect the reference-positive electrode and the reference-negative electrode to collect voltage results. The initial voltage indication is converted into lithium potential, and the deviation compared with the lithium metal reference is no more than 5%. It can then run stably for more than 100 cycles.

[0071] Embodiment 3

[0072] The preparation process of the graphite lithium intercalation reference electrode is consistent with that in Example 2, the only difference being that the charge state is adjusted to 60%, at which time the graphite lithium intercalation reference is located in the potential platform region of 0.08 V. After the reference is implanted, the same detection method can be used to stably operate and achieve the expected monitoring potential effect.

[0073] Embodiment 4

[0074] The preparation process of the reference electrode is consistent with that in Example 2. When implanted, it is placed in the gap between the right side of the fresh coil and the aluminum-plastic film so as not to interfere with the normal operation of the battery. The test results show that this placement method can operate stably.

[0075] Embodiment 5

[0076] The preparation process of the reference electrode is consistent with that in Example 2. When implanted, it is placed in the gap between the bottom of the fresh coil and the aluminum-plastic film to keep the reference electrode wet and not interfere with the normal operation of the battery. The test results show that this placement method can also achieve stable operation.

[0077] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0078] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a reference electrode, characterized in that: include: S1: A double-sided lithium electrode sheet and a single-sided graphite electrode stack form a soft-pack battery. The double-sided lithium electrode sheet is located in the middle, and the two sides are separated by a diaphragm. The copper / nickel electrode sheet and the graphite electrode sheet are placed separately to form a unit battery. S2: mixing the unit cell with an electrolyte to obtain a mixed cell; S3: performing electroplating and charging treatments on the mixed battery to obtain a charged battery; S4: disassembling the battery after the charging process to obtain a lithium-plated copper sheet / lithium-plated nickel sheet and a lithium-embedded graphite sheet; S5: implanting the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet into the battery cell.

2. The method for preparing a reference electrode according to claim 1, characterized in that: The single-sided graphite electrode laminate is obtained by loading a copper or nickel sheet on the back side of the single-sided graphite electrode sheet; Optionally, the graphite is selected from a mixture of natural graphite, artificial graphite or a composite graphite material and a conductive agent and a binder; Optionally, the copper or nickel sheet has a thickness of 6-15 um; Optionally, the thickness of the single-sided graphite electrode laminate is 20-80 um; Optionally, the copper sheet is selected from rolled copper foil, electrolytic copper foil, copper wire or foam copper; Optionally, the nickel sheet is selected from nickel foil, nickel mesh or nickel foam.

3. The method for preparing a reference electrode according to claim 1, characterized in that: The double-sided lithium pole sheet is selected from a double-sided lithium iron phosphate pole sheet, a lithium sheet or a double-sided lithium pole sheet made of other lithium-containing compound materials; Optionally, the size of the double-sided lithium electrode sheet is consistent with the size of the single-sided graphite electrode stack.

4. The method for preparing a reference electrode according to claim 1, characterized in that: The electrolyte is selected from a mixture of carbonate solvent, carboxylate solvent and lithium salt; Optionally, the carbonate solvent is selected from ethylene carbonate, propylene carbonate, dimethyl carbonate or diethyl carbonate; Optionally, the carboxylic acid ester solvent is selected from ethyl acetate, propargyl alcohol or epichlorohydrin; Optionally, the lithium salt is selected from LiPF6 or LiFSI; Optionally, the electrolyte further comprises an additive selected from vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate or vinyl sulfate.

5. The method for preparing a reference electrode according to claim 1, characterized in that: The electroplating treatment is to use an electrochemical workstation or a charge and discharge test cabinet to connect the copper foil and the lithium iron phosphate tab, and use a current of 0.04C-0.5C for electroplating; Optionally, the electroplating treatment time is 1-6h; Optionally, the charging process is performed by transferring the negative electrode clip of the battery after the electroplating process to the graphite tab, and using a current of 0.1C-0.5C to insert lithium into the graphite sheet to full charge, 0.2V, 0.12V or 0.08V.

6. The method for preparing a reference electrode according to claim 1, characterized in that: The disassembly process is carried out in an environment without water or oxygen.

7. The method for preparing a reference electrode according to claim 1, characterized in that: After step S4, the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet is not cut, and the implantation in step S5 is performed by directly stacking the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet together with a common stacked soft package and placing it between the outermost negative electrode sheet and the aluminum-plastic film.

8. The method for preparing a reference electrode according to claim 1, characterized in that: After step S4, the lithium-plated copper sheet / lithium-plated nickel sheet and / or lithium-embedded graphite sheet are evenly cut into narrow strips with a width of 0.1-2 mm in the width direction. The implantation in step S5 is carried out by wrapping the two narrow strips with the upper and lower ends of the diaphragm with fixed films, welding the pole ear sheet on the upper end, and placing them between the positive and negative pole pieces of the battery cell, or at the upper and lower ends and sides of the outside of the battery cell.

9. A reference electrode, characterized in that The reference electrode is prepared by the method according to any one of claims 1 to 8.

10. Use of the reference electrode prepared by the method according to any one of claims 1 to 8 or the reference electrode according to claim 9 in preparing a lithium battery.

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