A soft package lithium ion battery containing a synchronous lithium plating reference electrode and a preparation method thereof

Abstract

The present application belongs to the technical field of lithium ion batteries, and particularly relates to a soft package lithium ion battery containing a synchronous lithium plating reference electrode and a preparation method thereof. The soft package lithium ion battery comprises a laminated cell and an electrochemical lithium plating structure arranged on the outer side of the laminated cell. The laminated cell comprises a plurality of first positive electrodes and negative electrodes alternately laminated. The electrochemical lithium plating structure comprises two second positive electrodes and a reference electrode current collector between the two second positive electrodes. Blank areas for lithium plating are arranged on the two surfaces of the reference electrode current collector opposite the two second positive electrodes. The blank areas can respectively take the corresponding second positive electrodes as lithium sources, and a lithium layer is synchronously deposited through electrochemical lithium plating to obtain two reference electrodes with lithium plated on the opposite surfaces. The preparation method can realize quick preparation of the reference electrode and ensure the stability and repeated use of the reference electrode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a soft package lithium ion battery containing a synchronous lithium-plated reference electrode and a preparation method thereof. BACKGROUND

[0002] In 1913, Lewis and Keyes et al. carried out electrochemical research on lithium metal, designed a classic three-electrode experiment, accurately calculated the electrode potential of lithium, opened up the electrochemical application of lithium metal, and became a cornerstone of the development of lithium ion batteries. In a two-electrode system, the counter electrode has a dual role, and also plays the role of a reference electrode. However, in a conventional test, due to the current passing through, the counter electrode is often polarized, resulting in a potential shift. At this time, the electrode potential fed back is the relative electrode potential. As a typical representative of a two-electrode system, the lithium ion battery cannot accurately decouple the potential signals from the positive and negative electrodes during the charging and discharging process, making it impossible to accurately interpret the electrochemical behavior of the lithium ion battery during the charging and discharging process, and making the lithium ion battery a black box. By introducing a three-electrode system, the positive and negative electrodes can be accurately decoupled, and the reference electrode becomes a "key" to opening the black box.

[0003] During fast charging, the slow kinetics of lithium intercalation into the graphite negative electrode leads to serious polarization on the graphite negative electrode side, causing the negative electrode potential to drop to 0 V (vs. Li / Li + ), and the graphite lithium intercalation potential is about 0.1 V (vs. Li / Li + ) due to polarization. The threshold value of lithium deposition potential is 0 V (vs. Li / Li + ), and lithium metal deposition occurs on the surface of the graphite negative electrode. In a three-electrode system, the reference electrode is an electrode with a known and stable potential, which is highly compatible with the electrolyte and has no pollution. It can effectively decouple the electrochemical information of the positive and negative electrodes as a potential reference. The three-electrode method monitors the lithium potential of the negative electrode (vs. Li / Li + ) during the charging and discharging process of the battery, and then synchronously determines the lithium deposition behavior. Therefore, the three-electrode system is also an in-situ non-destructive detection method for fast charging lithium deposition, which plays an important role in effectively detecting the lithium deposition boundary in the fast charging process and optimizing the fast charging strategy. The commonly used reference electrodes in the three-electrode system of lithium ion batteries are lithium sheet, in-situ lithium-plated copper wire, lithium and metal alloy materials, etc.

[0004] Chinese patent CN 113889599A provides a method for preparing a reference electrode with a punched copper foil as a lithium supplement part. Multiple rows of circular through holes of the same size and arranged at equal intervals are formed on the copper foil to form a special structure of the copper foil as a reference electrode placed between the positive and negative electrode sheets and separated by a separator. First, a constant current is used to charge and lithium-plating the outer surface of the copper foil close to the positive electrode sheet for 5 hours, and then the same lithium-plating operation is performed on the outer surface close to the negative electrode sheet. Although this method can ensure effective lithium plating and uniform lithium plating thickness, the through holes can also facilitate lithium ion transmission to some extent during the charging and discharging process. However, the areas without through holes will still hinder lithium ion transmission during the charging and discharging process, and this problem cannot be completely avoided. Moreover, the single-sided lithium plating time is as long as 5 hours, and the lithium plating time of the entire reference electrode is relatively long. At the same time, the lithium plating process consumes active lithium of the positive and negative electrodes, causing irreversible loss of lithium on the positive and negative electrodes.

[0005] Chinese patent CN 115132962A provides a method for preparing a reference electrode with a copper foil and a lithium foil stacked to form a composite structure. A fixed pressure is applied to the two sides of the copper foil to roll the lithium foil, obtaining a three-layer composite structure with a lithium foil layer on each side of the copper foil surface. This design ensures sufficient lithium on the reference electrode by rolling the lithium foil onto the copper foil. However, the preparation of lithium foil directly requires more stringent environmental conditions, and the preparation process needs to prevent oxidation of the lithium foil. At the same time, the combination of lithium foil and copper foil is achieved through physical means. If the combination is not effective, the lithium foil may fall off during the subsequent process of the battery preparation, causing the reference electrode to fail. Compared with electrochemical deposition and lithium plating, this scheme cannot be used for secondary lithium plating. Once the combination of lithium foil and copper foil fails, the risk of failure of the entire three-electrode system increases due to unstable potential.

[0006] Therefore, the following problems need to be solved based on the copper foil as the reference electrode of the three-electrode system: 1. It cannot affect the transmission of lithium ions during the charging and discharging process; 2. The efficiency of electrochemical deposition and lithium plating needs to be further improved; 3. Irreversible loss of active lithium from the positive and negative electrodes during the electrochemical deposition and lithium plating process needs to be avoided; 4. The combination between lithium and the copper substrate needs to be tight to avoid the failure of the reference electrode, and the reference electrode needs to be able to be used twice. SUMMARY

[0007] Based on the deficiencies of existing preparation techniques, the present invention provides a soft-pack lithium ion battery containing a synchronous lithium-plated reference electrode and a method for preparing the same. The preparation method of the present invention can achieve fast preparation of the reference electrode of the soft-pack lithium ion battery, effectively shorten the electrochemical lithium plating time by half under the same lithium plating experimental conditions, and improve the efficiency of electrochemical lithium plating.

[0008] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0009] In a first aspect, a soft package lithium ion battery containing a synchronous lithium-plated reference electrode, the inside of the soft package lithium ion battery comprises a laminated cell and an electrochemical lithium-plated structure arranged on the outer side of the laminated cell, the laminated cell comprises a plurality of first positive electrodes and negative electrodes alternately laminated; the electrochemical lithium-plated structure comprises two second positive electrodes and a reference electrode current collector between the two second positive electrodes, the reference electrode current collector is provided with a blank area for lithium plating on both surfaces opposite the two second positive electrodes, the blank area can respectively take its corresponding second positive electrode as a lithium source, and a lithium layer is synchronously deposited through electrochemical lithium plating to obtain two reference electrodes plated with lithium on the opposite surfaces; the first positive electrode, the negative electrode, the second positive electrode, and the reference electrode are separated from each other by a diaphragm, or at least one side of each is covered by a diaphragm to separate each other.

[0010] Further, the first positive electrode is completely identical to the second positive electrode except for the size;

[0011] And / or, the length and width of the diaphragm are 0.2-1.5 mm larger than the length and width of the electrode plate separated and / or covered by the diaphragm.

[0012] Further, the maximum cross-sectional area of the first positive electrode is greater than the maximum cross-sectional area of the second positive electrode, and the maximum cross-sectional area of the second positive electrode is greater than the maximum cross-sectional area of the reference electrode;

[0013] And / or, the diaphragm comprises a first diaphragm, a second diaphragm, and a third diaphragm, the first diaphragm is used to separate / cover the first positive electrode and / or negative electrode; the second diaphragm is used to separate / cover the second positive electrode; and the third diaphragm is used to separate / cover the reference electrode.

[0014] Further, the reference electrode current collector comprises a copper foil and / or a copper wire;

[0015] And / or, the reference electrode is provided with a reference electrode tab;

[0016] And / or, the first positive electrode is provided with a first positive electrode tab;

[0017] And / or, the negative electrode is provided with a negative electrode tab;

[0018] And / or, the second positive electrode is provided with a second positive electrode tab.

[0019] Further, the reference electrode current collector comprises a copper foil and a copper wire;

[0020] And / or, the copper wire is an enameled copper wire, and the wire diameter is 40-60 μm;

[0021] And / or, the thickness of the copper foil is 5μm to 10μm;

[0022] And / or, the portion of the reference electrode current collector, excluding the blank area, is covered with adhesive tape;

[0023] And / or, the first positive electrode tab is parallel to the negative electrode tab, the reference electrode tab is parallel to the second positive electrode tab, and the second positive electrode tab is perpendicular to the first positive electrode tab.

[0024] Furthermore, the blank area is located on the surface of the copper foil at the end away from the copper wire, and the area of ​​the blank area accounts for 1 / 5 to 1 / 2 of the total surface area of ​​the copper foil;

[0025] And / or, the tape material is one of PET, MOPP and PI;

[0026] And / or, the reference electrode tab is made of nickel-plated copper;

[0027] And / or, the material of the second positive electrode tab is aluminum.

[0028] Secondly, a method for preparing the aforementioned soft-pack lithium-ion battery includes the following steps:

[0029] S1. Multiple first positive electrodes, separators and negative electrodes are alternately stacked to form a stacked battery cell;

[0030] S2. Place the blank area of ​​the reference electrode current collector between the two second positive electrodes, and separate the three by a membrane to form an electrochemical lithium plating structure.

[0031] S3. The electrochemical lithium plating structure is disposed on one side of the stacked cell. Before packaging, the reference electrode current collector and the second positive electrode tab are led out to enable electrochemical lithium plating connection. After packaging, an intermediate product is obtained.

[0032] S4. The intermediate product is baked, injected with liquid, left to stand, formed, and divided into volumes; then the reference electrode current collector is electrochemically plated with lithium to obtain the reference electrode, and at the same time, a soft-pack lithium-ion battery is obtained.

[0033] Further, in step S1, after stacking, a first positive electrode tab is set on the first positive electrode and a negative electrode tab is set on the negative electrode, and both the first positive electrode tab and the negative electrode tab are led out from the top of the stacked cell.

[0034] And / or, in step S2, the reference electrode current collector comprises a copper foil provided with a blank area and a copper wire welded on the copper foil, and the second positive electrode is obtained by cutting and reducing two first positive electrodes, and second positive electrode tabs are welded on the two second positive electrodes; in step S3, the electrochemical lithium plating structure is arranged on one side of the jelly-roll, and then the copper wire and the second positive electrode tabs are drawn out from the side of the jelly-roll.

[0035] And / or, in step S4, the working current I selected during the electrochemical lithium plating is Ai, where the current density is i, i = 7.0-10.0 μA / mm 2 , and the area of the blank area is A, A = 0.4-1.2 cm 2 .

[0036] And / or, in step S4, the electrochemical lithium plating time is 1-4 h.

[0037] Further, in step S2, the copper wire is an enameled copper wire, which is subjected to partial paint removal treatment in a strong acid solution, cleaned, and dried for standby use; the copper foil is cut to an appropriate size, cleaned to remove the surface oxide layer, and then dried for standby use; finally, the standby copper wire and copper foil are welded together, and a portion of the top surface of the copper foil away from the copper wire is reserved as a blank area to facilitate subsequent lithium plating, and the remaining area is covered with adhesive tape.

[0038] And / or, before the electrochemical lithium plating, a reference electrode tab is provided on the copper wire.

[0039] Further, the electrochemical lithium plating structure, and / or the reference electrode tab, and / or the first positive electrode tab, and / or the negative electrode tab, and / or the second positive electrode tab, are all fixed by a tab adhesive or adhesive tape.

[0040] Compared with the prior art, the present application has at least the following beneficial effects:

[0041] The soft-pack lithium-ion battery of the present invention has a multi-electrode system. Specifically, based on the stacked cell, two additional second positive electrodes are introduced to construct an electrochemical lithium plating structure system consisting of a second positive electrode, a separator, a reference electrode current collector, a separator, and a second positive electrode, which is placed at the outermost layer of the cell. The system composed of the two second positive electrodes and the reference electrode current collector serves as an auxiliary lithium plating structure to achieve efficient lithium plating of current collectors such as copper foil or copper wire. The soft-pack lithium-ion battery constructed by this invention, which contains a reference electrode with simultaneous lithium plating, solves some problems associated with the preparation of reference electrodes in a three-electrode system based on current collectors such as copper foil. This invention has the following outstanding advantages: First, from the perspective of traditional three-electrode system architecture, most of them place copper foil, copper wire, etc., inside the cell between the positive and negative electrodes and use a separator for isolation. Since the copper wire or copper foil needs to have a layer of lithium deposited on its surface (lithium plating) to serve as a reference electrode with a stable potential, it needs to be charged before deposition so that the negative electrode can embed a certain amount of lithium. This ensures that there is a sufficient lithium source when reverse lithium plating is performed. At the same time, the lithium plating process requires forward lithium plating between the positive electrode and the copper foil. After the forward lithium plating is completed, reverse lithium plating between the negative electrode and the copper foil needs to be performed for the same amount of time. The entire lithium plating process takes a long time. In this invention, by introducing two additional positive electrode plates and placing a current collector such as copper foil between the two positive electrode plates, lithium plating can be performed on different sides of the copper foil simultaneously. Under the premise of ensuring the same lithium layer thickness, the electrochemical lithium plating time can be shortened by half. Secondly, in traditional placement methods, the large area of ​​the copper foil can affect lithium-ion transport during charging and discharging. In particular, during high-rate (high-current) fast charging tests, the copper foil can hinder the lithium-ion transport rate between the positive and negative electrodes, thus affecting the lithium plating test results. In this invention, the reference electrode is placed on the outside of the main cell, avoiding its influence on the charging and discharging process. Thirdly, by introducing an additional positive electrode, the entire auxiliary lithium plating structure is placed on the outside of the main cell. During lithium plating, the lithium source comes from the introduced positive electrode, avoiding the loss of active lithium in the main cell. Lithium plating with copper foil or copper wire can reduce the cell's capacity, affecting its performance. This solution effectively avoids this drawback and greatly minimizes the influence of the reference electrode on the main cell. Fourthly, since the lithium layer on the copper foil is deposited in situ through electrochemical deposition in the later stage, compared with other cases where lithium foil and copper foil are combined by physical methods such as rolling, the present invention is more stable in structure. At the same time, in the event of lithium layer detachment, the reference electrode can be restored to stability through secondary electrochemical deposition, thus ensuring the stability and reusability of the reference electrode. Attached Figure Description

[0042] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0043] Figure 1 The appearance structure diagram of the soft package lithium ion battery of the present application;

[0044] Figure 2 The internal structure diagram of the soft package lithium ion battery of the present application;

[0045] Figure 3 The partial structure enlarged diagram of the reference electrode of the present application;

[0046] Figure 4 The lithium plating curve diagram of the reference electrode of the present application;

[0047] Figure 5 The stability test diagram of the reference electrode after lithium plating of the present application;

[0048] Figure 6 The negative electrode potential test diagram of the soft package lithium ion battery of the present application in the charging process.

[0049] Figure: 1-First diaphragm; 2-First positive electrode; 3-Negative electrode; 4-Second positive electrode; 5-Reference electrode; 6-First positive electrode tab; 7-Negative electrode tab; 8-Second positive electrode tab; 9-Tab glue; 10-Reference electrode tab; 11-Third diaphragm; 12-Second diaphragm; 13-Adhesive tape; 14-Copper wire; 15-Copper foil. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the present application more clear, the following will combine the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Those skilled in the art should understand that the embodiments are only to help understanding the present application, and should not be regarded as specific limitation to the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application. The process parameters not specified in the following embodiments are usually according to the conventional conditions.

[0051] In the description of the present application, the terms "opposite", "vertical", "upper", "lower", "parallel" and the like indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application and do not require the present application to be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. The terms "connected", "connected", "provided" used in the present application should be understood broadly, for example, it can be fixedly connected or detachably connected; it can be directly connected or indirectly connected through an intermediate part; it can be wired electrical connection, wireless electrical connection or wireless communication signal connection, and the specific meaning of the above terms can be understood by those skilled in the art according to the specific circumstances.

[0052] The endpoints of the ranges and any values disclosed in the present application are not limited to the precise values recited. The ranges or values should be interpreted as being approximate, and include values near the recited values. For numeric values, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to form one or more new numeric ranges, which should be considered as specifically disclosed in the present application.

[0053] According to the first aspect of the present application, a soft package lithium ion battery containing a synchronous lithium-plated reference electrode, the inside of the soft package lithium ion battery comprises a laminated cell and an electrochemical lithium-plated structure arranged on the outer side of the laminated cell, the laminated cell comprises a plurality of first positive electrodes and negative electrodes alternately laminated; the electrochemical lithium-plated structure comprises two second positive electrodes and a reference electrode current collector between the two second positive electrodes, the reference electrode current collector is provided with a blank area for lithium plating on both surfaces opposite the two second positive electrodes, the blank area can respectively take its corresponding second positive electrode as a lithium source, and a lithium layer is synchronously deposited by electrochemical lithium plating to obtain two reference electrodes plated with lithium on the opposite surfaces; the first positive electrode, the negative electrode, the second positive electrode and the reference electrode are separated from each other by a diaphragm, or at least one side of each is covered by a diaphragm to separate each other.

[0054] The application designs a multi-electrode structure based on reference electrode synchronous lithium plating on the basis of laminated cell soft package lithium ion battery, specifically by introducing two additional positive plates in the space between the laminated cell side, that is, the outermost negative plate of the laminated cell and the shell or the outermost positive plate of the laminated cell and the shell, and placing a reference electrode current collector such as a copper base (copper foil, copper wire, etc.) between the two positive plates, so as to realize the plating of lithium on different surfaces of the copper base to form a reference electrode, achieve the purpose of in-situ synchronous plating of lithium, shorten the electrochemical plating lithium time by half under the premise of ensuring the same lithium layer thickness, and improve the efficiency of electrochemical deposition plating lithium. Moreover, the lithium is loaded on the copper base in-situ by electrochemical deposition, which ensures the close combination of lithium and the copper base. At the same time, the copper base, especially the copper foil, is placed outside the laminated cell, that is, in the space between the laminated cell and the shell such as aluminum plastic film, which solves the problem of hindering lithium ion transmission between the positive and negative electrodes in the charging and discharging process caused by the excessive specific surface area of the copper foil under the premise of ensuring the plating of lithium on the copper foil, and reduces the influence of the introduction of the copper foil on the electrochemical performance of the cell. The introduction of the additional positive plate provides sufficient lithium source for plating lithium, which can reduce the irreversible loss of active lithium caused by electrochemical plating lithium. Further, when the copper base is a copper foil, the platable area of the copper foil is much larger than that of the copper wire, so the plating amount of the copper foil is also much higher than that of the copper wire, and the service life of the reference electrode after plating lithium can be greatly improved.

[0055] In the present application, the diaphragm is used to block the pole piece to avoid the pole piece from contacting short circuit, so its size is not particularly limited, as long as it can completely separate and / or cover (separate / cover) the pole piece, usually the length and width of the diaphragm are 0.2-1.5mm larger than those of the pole piece it separates and / or covers. Considering that one optional embodiment of the soft package lithium ion battery of the present application is: the first positive electrode and the second positive electrode are completely the same except for size (completely the same means that the positive electrode material, area density, current collector thickness, etc. on the second positive electrode piece are completely the same as those in the original battery system (stacked chip), and the maximum cross-sectional area of the first positive electrode piece is larger than that of the second positive electrode piece. Further, the second positive electrode piece is obtained by cutting the first positive electrode piece, specifically, after cutting, the length L1 of the second positive electrode piece is 3.0cm-4.0cm, the width W1 is 3.5cm-4.5cm, so the length L3 of the diaphragm covering one side or both sides is 3.2cm-4.2cm, and the width W3 of the diaphragm is 3.7cm-4.7cm. In this way, not only can the lithium source be provided additionally, but also the original battery packaging production can be changed, which is convenient for the sealing and packaging of the whole battery, so as a further optional embodiment of the soft package lithium ion battery of the present application, the diaphragm comprises a first diaphragm, a second diaphragm and a third diaphragm, the first diaphragm is used to separate / cover the first positive electrode and / or negative electrode; the second diaphragm is used to separate / cover the second positive electrode; the third diaphragm is used to separate / cover the reference electrode. Further, since the maximum cross-sectional area of the first positive electrode is larger than that of the second positive electrode, and the maximum cross-sectional area of the second positive electrode is larger than that of the reference electrode; therefore, the maximum cross-sectional area of the first diaphragm is larger than that of the second diaphragm, the maximum cross-sectional area of the second diaphragm is not less than that of the third diaphragm, further, the maximum cross-sectional area of the second diaphragm is larger than that of the third diaphragm, so that the third diaphragm can not only shield the copper matrix, especially the copper foil, but also facilitate insertion operation to separate the copper matrix and the positive electrode piece.In the present application, the separation and / or coating of the diaphragm to the electrode can be specifically as follows: the structure order from one side to the other side inside the battery shell can be second diaphragm, second positive electrode, second diaphragm, reference electrode, third diaphragm, second positive electrode, first diaphragm, negative electrode, first diaphragm, first positive electrode, first diaphragm, negative electrode, first diaphragm, first positive electrode, …, first diaphragm; or second diaphragm, second positive electrode, second diaphragm, reference electrode, third diaphragm, second positive electrode, first diaphragm, first positive electrode, first diaphragm, negative electrode, first diaphragm, first positive electrode, first diaphragm, negative electrode, …, first diaphragm; or first diaphragm, negative electrode, first diaphragm, first positive electrode, first diaphragm, negative electrode, … first positive electrode, first diaphragm, second positive electrode, second diaphragm, reference electrode, third diaphragm, second positive electrode, second diaphragm; or first diaphragm, first positive electrode, first diaphragm, negative electrode, first diaphragm, first positive electrode, first diaphragm, …, negative electrode, first diaphragm, second positive electrode, second diaphragm, reference electrode, third diaphragm, second positive electrode, second diaphragm.

[0056] As an optional embodiment of the soft package lithium ion battery of the present application, the reference electrode current collector comprises copper foil and / or copper wire. Further, the reference electrode current collector comprises copper foil and copper wire, and the connection mode of the copper foil and the copper wire is not particularly limited, and the two can be conductive to each other, and specifically, ultrasonic welding and other prior art can be used for welding connection. Further, the copper wire is an enameled copper wire, and the diameter of the copper wire is 40 μm to 60 μm; and / or the thickness of the copper foil is 5 μm to 10 μm, and after being cut, the size of the copper foil is 2.5 to 3.5 cm long L4 and 0.5 to 1.0 cm wide W4, and a blank area is reserved thereon to facilitate lithium plating. Further, the blank area is on the surface of the end of the copper foil away from the copper wire, and the area of the blank area accounts for 1 / 5 to 1 / 2 of the entire surface area of the copper foil. Specifically, the size of the blank area is 0.8 to 1.2 m long L5 and 0.5 to 1.0 cm wide W4. Further, the size of the third diaphragm is set according to the size of the copper foil and the blank area, and the length L2 of the diaphragm is 3.8 cm to 4.0 cm, and the width W2 of the diaphragm is 1.5 cm to 2.0 cm.

[0057] As an optional embodiment of the soft package lithium ion battery of the present application, the part of the reference electrode current collector except the blank area is coated with adhesive tape. Further, the material of the adhesive tape is one of PET, MOPP and PI.

[0058] As an optional embodiment of the soft package lithium ion battery of the present application, the reference electrode is provided with a reference electrode tab; and / or the first positive electrode is provided with a first positive electrode tab; and / or the negative electrode is provided with a negative electrode tab.

[0059] And / or, a second positive electrode tab is arranged on the second positive electrode. Further, the first positive electrode tab is parallel to the negative electrode tab, the reference electrode tab is parallel to the second positive electrode tab, and the second positive electrode tab is perpendicular to the first positive electrode tab; that is, the first positive electrode tab and the negative electrode tab are arranged on a first side of the soft-pack lithium ion battery, the reference electrode tab and the second positive electrode tab are arranged on a second side of the soft-pack lithium ion battery, and the first side is perpendicular to the second side.

[0060] And / or, the material of the reference electrode tab is nickel-plated copper; and / or, the material of the second positive electrode tab is aluminum.

[0061] According to a second aspect of the present application, a preparation method of the soft-pack lithium ion battery comprises the following steps:

[0062] S1, alternately stacking a plurality of first positive electrodes, separators and negative electrodes to form a stacked electrode core;

[0063] S2, placing a blank area of a reference electrode current collector between two second positive electrodes, and separating the three by a separator to form an electrochemical lithium plating structure;

[0064] S3, arranging the electrochemical lithium plating structure on one side of the stacked electrode core, leading out the reference electrode current collector and the second positive electrode tab before packaging to enable electrochemical lithium plating connection, and obtaining an intermediate product after packaging.

[0065] S4, baking, liquid injection, standing, formation, and capacity grading the intermediate product; electrochemically plating lithium on the reference electrode current collector to obtain a reference electrode, and simultaneously obtaining a soft-pack lithium ion battery.

[0066] As an optional embodiment of the preparation method of the present application, in step S1, a first positive electrode tab is arranged on the first positive electrode after stacking, and a negative electrode tab is arranged on the negative electrode, and the first positive electrode tab and the negative electrode tab are both led out from the top of the stacked electrode core;

[0067] And / or, in step S2, the reference electrode current collector comprises a copper foil provided with a blank area and a copper wire welded on the copper foil, and the second positive electrode is obtained by cutting and reducing two first positive electrodes, and the second positive electrode tab is welded on the two second positive electrodes; further, the welding mode between the second positive electrode and the second positive electrode tab is ultrasonic welding; in step S3, the electrochemical lithium plating structure is arranged on one side of the stacked electrode core, and then the copper wire and the second positive electrode tab are both led out from the side of the stacked electrode core;

[0068] And / or, in step S4, the working current I selected during electrochemical lithium plating is Ai, where the current density is i, i = 7.0-10.0 μA / mm 2The blank area has an area A, A = 0.4-1.2 cm 2 ;

[0069] And / or, in step S4, the electrochemical lithium plating time is 1-4 h.

[0070] As an optional embodiment of the preparation method of the application, in step S2, the copper wire is a varnished copper wire, which is subjected to partial varnish removal treatment by a strong acid solution, and is cleaned, impurity-removed and dried for standby use; the copper foil is cut to a proper size, cleaned to remove the surface oxide layer, and then dried for standby use; finally, the standby copper wire and copper foil are welded together, and a part of the top surface of the copper foil away from the copper wire is reserved as a blank area for subsequent lithium plating, and the remaining area is covered by adhesive tape; further, the strong acid solution is concentrated sulfuric acid, and the cleaning of impurities and the oxide layer is performed by dilute hydrochloric acid and ultrapure water, and the drying temperature is selected to be 30-50℃.

[0071] And / or, before the electrochemical lithium plating, a reference electrode tab is arranged on the copper wire, and further, the reference electrode tab is welded by a soldering iron.

[0072] As an optional embodiment of the preparation method of the application, the electrochemical lithium plating structure, and / or the reference electrode tab, and / or the first positive electrode tab, and / or the negative electrode tab, and / or the second positive electrode tab, are all fixed by a tab adhesive or adhesive tape.

[0073] The application will be further described in detail below in combination with specific examples and comparative examples.

[0074] Example 1

[0075] A soft-pack lithium ion battery containing a synchronous lithium plating reference electrode, as shown in Figure 1 、 2As shown, the inside of the soft package lithium ion battery includes a laminated cell and an electrochemical lithium plating structure arranged on the outer side of the laminated cell, the laminated cell includes a plurality of first positive electrodes 2 and negative electrodes 3 which are alternately laminated, the first positive electrode 2 is provided with a first positive electrode tab 6, the negative electrode 3 is provided with a negative electrode tab 7, the first positive electrode tab 6 is parallel to the negative electrode tab 7; the electrochemical lithium plating structure includes two second positive electrodes 4 and a reference electrode current collector between the two second positive electrodes 4, the reference electrode current collector is provided with a blank area for lithium plating on the two surfaces opposite the two second positive electrodes 4, the blank area can take the corresponding second positive electrode 4 as the lithium source respectively, and a lithium layer is deposited synchronously through electrochemical lithium plating to obtain two reference electrodes 5 with lithium plated on the opposite surfaces, the reference electrode 5 is provided with a reference electrode tab 10 made of plated nickel-copper, the reference electrode tab 10 is parallel to the second positive electrode tab 8, the second positive electrode 4 is provided with a second positive electrode tab 8 made of aluminum, and the second positive electrode tab 8 is perpendicular to the first positive electrode tab 6; the first positive electrode 2, the negative electrode 3, the second positive electrode 4 and the reference electrode 5 are separated from each other by a separator, or at least one side of each is covered by a separator to separate them from each other, and the length and width of the separator are 0.2-1.5mm larger than those of the electrode plate which is separated and / or covered.

[0076] As shown in detail Figure 2 , the second positive electrode 4 is completely identical to the first positive electrode 2 except for the size, and the maximum cross-sectional area of the second positive electrode 4 is smaller than that of the first positive electrode 2, the length L1 of the electrode plate of the second positive electrode 4 is 3.0cm-4.0cm, and the width W1 is 3.5cm-4.5cm;

[0077] As shown in detail Figure 2 , the maximum cross-sectional area of the reference electrode 5 is smaller than that of the second positive electrode 4, the reference electrode current collector includes a copper foil 15 and a copper wire 14, the copper wire 14 is an enameled copper wire with a wire diameter of 40μm-60μm; the thickness of the copper foil 15 is 5μm-10μm, the length L4 is 2.5-3.5cm, and the width W4 is 0.5-1.0cm; the blank area is on the surface of the copper foil 15 away from the copper wire 14, the size of the blank area is 0.8-1.2m in length L5 and 0.5-1.0cm in width W4; the part of the reference electrode current collector other than the blank area is covered by a tape 13, and the tape 13 is made of one of PET, MOPP and PI;

[0078] As shown in detail Figure 2 , the separator includes a first separator 1, a second separator 12 and a third separator 11, the first separator 1 is used to separate / cover the first positive electrode 2 and / or the negative electrode 3; the second separator 12 is used to separate / cover the second positive electrode 4; the third separator 11 is used to separate / cover the reference electrode 5, and the length L2 of the third separator is 3.8cm-4.0cm, and the width W2 of the separator is 1.5cm-2.0cm.

[0079] The preparation method of the soft package lithium ion battery of the embodiment comprises the following steps:

[0080] S1, a plurality of first positive electrodes 2, first separators 1 and negative electrodes 3 are alternately stacked in the order of first separator 1, negative electrode 3, first separator 1, first positive electrode 2, first separator 1, negative electrode 3, and the like, to form a stacked cell; and after stacking, a first positive electrode tab 6 is arranged on the first positive electrode 2, a negative electrode tab 7 is arranged on the negative electrode 3, and the first positive electrode tab 6 and the negative electrode tab 7 are both led out from the top of the stacked cell;

[0081] S2, the enameled copper wire is partially stripped in a strong acid solution, and after cleaning and drying, it is ready for use; at the same time, the copper foil 15 is cut to an appropriate size, then cleaned to remove the surface oxide layer, and then dried for standby; finally, the standby copper wire 14 and copper foil 15 are ultrasonically welded together, and a part of the blank area is reserved at the top of the copper foil 15 to facilitate subsequent lithium plating, and the rest of the area is covered with adhesive tape 13 to the welding area, to obtain a reference electrode current collector; wherein the strong acid solution is concentrated sulfuric acid, the impurities and oxide layer are cleaned with dilute hydrochloric acid and ultrapure water, and the drying temperature is selected to be 30-50°C;

[0082] The second positive electrode 4 is obtained by cutting and reducing two first positive electrodes 2, and is separated by a second separator 12 to form a stacked structure of second separator 12, second positive electrode 4, second separator 12, and second positive electrode 4; at the same time, the second positive electrode tab 8 is ultrasonically welded to the two second positive electrodes 4;

[0083] The blank area of the reference electrode current collector is placed between the two second positive electrodes 4, separated by a second separator 12 on one side and a third separator 11 on the other side, to form an electrochemical lithium plating structure;

[0084] S3, the electrochemical lithium plating structure is fixed on one side of the stacked cell through the tab adhesive 9, the aluminum plastic film after punching is used to top side seal the stacked cell and the electrochemical lithium plating structure, and the copper wire 14 and the second positive electrode tab 8 are led out from the side to enable electrochemical lithium plating, after packaging, the reference electrode tab 10 is welded to the copper wire 14 by using an electric soldering iron, to obtain an intermediate product;

[0085] S4, the reference electrode tab 10 is fixed by the adhesive tape 13, and the second positive electrode tab 8 is fixed by the tab adhesive 9, then the intermediate product is baked, injected, placed, formed, and divided, and the reference electrode current collector is electrochemically plated with lithium, the working current I=A1 is selected, the current density is i=7.0-10.0μA / mm 2 , the area of the blank area is A=0.4-1.2cm 2 , and the reference electrode 5 is obtained after electrochemical lithium plating for 1-4h, and a soft package lithium ion battery is also obtained.

[0086] Figure 3 In order to synchronize the lithium plating of the reference electrode by using the current size of 0.28mA-1.2mA, the plating curve is stable within the plating time of 0.5h, which indicates that the positive and negative synchronization lithium plating can be realized on the copper foil 15 by the electrochemical deposition method.

[0087] Figure 4 After the lithium plating is completed, the battery is rested for more than 12h, then the open circuit voltage of the negative electrode and the reference electrode is monitored in real time, it is found that the voltage value changes little and is only within 1mV, and is stable at 0.1711V after 19h, which indicates that the potential of the whole reference electrode can be stable, the potential changes little with time, and can meet the use conditions of the reference electrode.

[0088] Figure 5 By using the reference electrode to monitor the negative electrode potential in the whole process of charging, the potential change information of the negative electrode in the charging process is obtained, Table 1 is the negative-reference electrode potential information of the negative electrode in the charging process under different SOC states and different charging rates, the dynamic monitoring of the negative electrode potential is realized, and the negative electrode potential information is effectively decoupled from the whole battery voltage information for analysis. Table 1 is as follows:

[0089] Table 1 Potential under different SOC states

[0090] SOC (%) C-rate (C) Full cell voltage (V) Negative electrode - reference potential (mV) 10％ 1C 3.29 174.5 50％ 1C 3.40 72.5 80％ 1C 3.45 38.0 90％ 1C 3.49 18.0 96％ 0.5C 3.46 31.0 100％ 0.2C 3.65 67.0

[0091] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A soft-pack lithium-ion battery containing a synchronously lithium-plated reference electrode, characterized in that: The soft-pack lithium-ion battery includes a stacked cell and an electrochemical lithium plating structure disposed on the outer side of the stacked cell. The stacked cell includes a plurality of alternating stacked first positive electrode (2) and negative electrode (3). The electrochemical lithium plating structure includes two second positive electrodes (4) and a reference electrode current collector between the two second positive electrodes (4). The reference electrode current collector has blank areas for lithium plating on both surfaces opposite to the two second positive electrodes (4). The blank areas are respectively used as lithium sources with their corresponding second positive electrodes (4). After electrochemical lithium plating, lithium layers are deposited simultaneously to obtain two reference electrodes (5) with lithium plating on their back-to-back surfaces. The first positive electrode (2), negative electrode (3), second positive electrode (4) and reference electrode (5) are separated from each other by a separator, or at least one side of each other is covered by a separator to separate them from each other. The reference electrode current collector includes copper foil (15) and copper wire (14). The blank area is located on the surface of the copper foil (15) away from the copper wire (14), and the area of ​​the blank area accounts for 1 / 5 to 1 / 2 of the total surface area of ​​the copper foil (15). The portion of the reference electrode current collector, excluding the blank area, is covered with tape (13); The electrochemical lithium plating operation current is I=Ai, where the current density is i, i=7.0~10.0μA / mm. 2 The area of ​​the blank region is A, where A = 0.4~1.2 cm². 2 The electrochemical lithium plating time is 1-4 hours.

2. The soft-pack lithium-ion battery according to claim 1, characterized in that: The first positive electrode (2) and the second positive electrode (4) are identical except for their size; And / or, the length and width of the diaphragm are both greater than the length and width of the electrode it separates and / or covers by 0.2-1.5 mm.

3. The soft-pack lithium-ion battery according to claim 2, characterized in that: The maximum cross-sectional area of ​​the first positive electrode (2) is greater than the maximum cross-sectional area of ​​the second positive electrode (4), and the maximum cross-sectional area of ​​the second positive electrode (4) is greater than the maximum cross-sectional area of ​​the reference electrode (5); And / or, the diaphragm includes a first diaphragm (1), a second diaphragm (12) and a third diaphragm (11), wherein the first diaphragm (1) is used to cover the first positive electrode (2) and / or the negative electrode (3); the second diaphragm (12) is used to cover the second positive electrode (4); and the third diaphragm (11) is used to cover the reference electrode (5).

4. The soft-pack lithium-ion battery according to claim 1, characterized in that: The reference electrode (5) is provided with a reference electrode tab (10); And / or, a first positive electrode tab (6) is provided on the first positive electrode (2); And / or, a negative electrode tab (7) is provided on the negative electrode (3); And / or, a second positive electrode tab (8) is provided on the second positive electrode (4).

5. The soft-pack lithium-ion battery according to claim 4, characterized in that: The first positive electrode tab (6) is parallel to the negative electrode tab (7), the reference electrode tab (10) is parallel to the second positive electrode tab (8), and the second positive electrode tab (8) is perpendicular to the first positive electrode tab (6).

6. The soft-pack lithium-ion battery according to claim 5, characterized in that: The tape (13) is made of one of PET, MOPP and PI; And / or, the reference electrode tab (10) is made of nickel-plated copper; And / or, the material of the second positive electrode tab (8) is aluminum.

7. The soft-pack lithium-ion battery according to claim 1, characterized in that: The copper wire (14) is enameled copper wire with a diameter of 40μm~60μm; And / or, the thickness of the copper foil (15) is 5μm~10μm.

8. A method for preparing a soft-pack lithium-ion battery as described in any one of claims 1-7, characterized in that: Includes the following steps: S1. Multiple first positive electrodes (2), separators and negative electrodes (3) are stacked alternately to form a stacked battery cell; S2. Place the blank area of ​​the reference electrode current collector between the two second positive electrodes (4), and separate the three by a membrane to form an electrochemical lithium plating structure. S3. The electrochemical lithium plating structure is placed on one side of the stacked battery cell. Before packaging, the reference electrode current collector and the second positive electrode (4) tab are led out. After packaging, the intermediate product is obtained. S4. The intermediate product is baked, injected with liquid, left to stand, formed, and divided into volumes; then the reference electrode current collector is electrochemically plated with lithium to obtain the reference electrode (5), and a soft-pack lithium-ion battery is obtained at the same time.

9. The preparation method according to claim 8, characterized in that: In step S1, after stacking, a first positive electrode tab (6) is set on the first positive electrode (2), and a negative electrode tab (7) is set on the negative electrode (3). Both the first positive electrode tab (6) and the negative electrode tab (7) are led out from the top of the stacked cell. And / or, in step S2, the reference electrode current collector includes a copper foil (15) with a blank area and a copper wire (14) welded to the copper foil (15), while the second positive electrode (4) is obtained by cutting and shrinking two other first positive electrodes (2), and the two second positive electrodes (4) are welded with second positive electrode tabs (8); in step S3, the electrochemical lithium plating structure is set on one side of the stacked cell, and then the copper wire (14) and the second positive electrode tab (8) are both led out from the side of the stacked cell.

10. The preparation method according to claim 9, characterized in that: In step S2, the copper wire (14) is an enameled copper wire. The enameled copper wire is partially deenamelted by a strong acid solution and then cleaned, cleaned, and dried for later use. The copper foil (15) is cut to a suitable size, cleaned to remove the surface oxide layer, and then dried for later use. Finally, the copper wire (14) and copper foil (15) are welded together. And / or, before the electrochemical lithium plating, a reference electrode tab (10) is provided on the copper wire (14).

11. The preparation method according to claim 10, characterized in that: The electrochemical lithium plating structure, and / or the reference electrode tab (10), and / or the first positive electrode tab (6), and / or the negative electrode tab (7), and / or the second positive electrode tab (8) are all fixed by tab adhesive (9) or tape (13).

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