Lithium-ion battery prelithiation method and lithium-ion battery

Abstract

The present invention relates to a method for prelithiation of a lithium ion battery and a lithium ion battery. The method includes the steps of: placing one or more lithium source composite sheets on a core body and connecting at least one of the lithium source composite sheets to a negative electrode tab of a lithium ion battery before injecting an electrolyte; and injecting an electrolyte to impregnate the lithium source composite sheets with the electrolyte, thereby prelithiating the negative electrode. The lithium ion battery obtained by the prelithiation method of the present invention has a high capacity, with a battery capacity increased by more than 10% compared to the same period last year, and a cycle life increased by more than 100%. The specific energy of a pouch-type lithium iron phosphate core can be more than 230 Wh / Kg, and it is easy to industrialize and has a very low overall cost.

Description

Technical Field

[0001] The present invention relates to a prelithiation method for lithium-ion batteries and lithium-ion batteries, and belongs to the production technical field of lithium-ion batteries.

Background Art

[0002] Currently, the electrification of automobiles has become an irreversible trend worldwide. Therefore, the requirements for lithium-ion batteries, which are the core components of electric vehicles, are increasing. Emphasis is placed on continuously increasing energy density and cycle life. For example, the ternary semi-solid battery is required to have a weight energy density of 350 to 400 Wh / Kg or more, and the lithium iron phosphate single battery is required to have a weight energy density of 230 Wh / Kg or more and a cycle life of 15,000 times or more. At this time, it is necessary to use a silicon-containing negative electrode material, and the application of the prelithiation technology to full-scale industrialization is becoming increasingly urgent. On the other hand, in portable electronic devices (such as mobile phones), high capacity (such as longer standby time) and long life are also required.

[0003] The silicon negative electrode generally refers to metallic silicon (Si) or silicon monoxide (SiO). Si can form a Li4Si alloy at room temperature, and its theoretical gram capacity is 3579 mAh / g, which is 10 times that of the graphite negative electrode. However, in the process of alloy formation, the volume expansion rate of silicon is about 300 to 400%, which causes swelling of the negative electrode and the entire cell. On the other hand, if the swelling is too large, it will cause the collapse of the silicon-containing particle material, and a large amount of new surfaces will be regenerated, consuming a large amount of lithium ions. Generally, for the graphite negative electrode, the irreversible lithium ions consumed for the formation of the SEI film by the negative electrode during the formation process are about 6%, while the silicon-containing negative electrode consumes about 10 to 20% of lithium ions. This is the reason for the low initial efficiency during the formation of the silicon-containing negative electrode.

[0004] ​​To solve this problem, academia and industry have conducted much research on prelithiation technology (or lithium replenishment technology), and the paper "Lithium Replenishment Technology for Lithium-ion Batteries" ("Energy Storage Science and Technology," May 2021, Vol. 10, No. 3) outlines this technology. In summary, the main prelithiation technologies currently available can be divided into metallic lithium powder prelithiation, metallic lithium foil rolling prelithiation, metallic lithium vapor deposition prelithiation, cathode additive prelithiation, and electrochemical prelithiation.

[0005] FMC Company's Chinese patent application (publication number CN1290209C) provides a method for prelithiating metallic lithium powder. However, this method has not yet been industrially applied due to its extremely high process requirements and very high costs for raw materials and processes.

[0006] Chinese patent applications, publication numbers CN112310336A and CN112397682A, disclose an apparatus and method for rolling metallic lithium foil prelithio. The apparatus is extremely complex, requires very high process control, has strict environmental control requirements, and poses significant safety concerns. Furthermore, the method is very costly to manufacture due to the use of specially required lubricants, release agents, and support materials.

[0007] A Chinese patent application with publication number CN111430659A discloses a method for prelithiation by vacuum deposition. This method has the advantage of producing a thin and uniform metallic lithium deposition layer, but it has the significant disadvantage of requiring expensive vacuum deposition equipment, making it difficult to apply industrially.

[0008] Currently, the main lithium replenishment additives used for cathode lithium are Li2O, Li2S, Li3N, Li4FeO5, Li6CoO4, Li2NiO2, and Li4DHBN. However, this method results in residues after prelithiation that affect the energy density and performance of the battery, and also has many side effects (such as gas generation). Therefore, no additive that meets the requirements for industrial applications has yet been identified.

[0009] The patent with publication number CN105845894B provides an electrochemical wet prelithiolation method. In the course of implementation, this method found that the method of prelithiolation on a negative electrode monolith to assemble a battery remains complex and requires further improvement. The patent application with disclosure number CN110224182A discloses an improved means of electrochemical "wet prelithiolation," but this method still involves a step of removing the bare cell after prelithiolation is complete, and is not the simplest process. The patent application with disclosure number CN110061299A discloses a method of electrochemical prelithiolation. This method requires drilling a circular hole in the cell cover plate, placing metal electrodes and metallic lithium inside the cell, performing electrochemical prelithiolation, and then removing the cell. Because it is difficult to drill and reseal the hole after injection, and there is a risk of leakage, this method is not industrially applicable. Furthermore, this method also carries the risk of metallic lithium leaching and localized lithium deposition in the sheet. The patent application with publication number CN111969266A discloses an automated prelithiolation method for cylindrical lithium-ion batteries. This method is limited to cylindrical batteries and automatically completes prelithiolation by placing metallic lithium in the central hole of the cylindrical battery and bringing it into contact with the negative electrode case. However, this method causes localized lithium deposition in the cell due to the localized concentration of lithium metal, which still presents significant limitations to its industrialization. Furthermore, the biggest problems with electrochemical prelithiolation methods are the extremely long time required for prelithiolation, the small amount of prelithiolated material, and the ease with which metallic lithium particles dissolve.

[0010] As described above, current prelithiation methods still have various drawbacks and have not yet reached full-scale industrialization. Therefore, there is a great need to find a prelithiation method that is simple, easy to perform, and low-cost in order to achieve industrial application. [Overview of the project] [Problems that the invention aims to solve]

[0011] The present invention aims to provide a method for prelithiating lithium-ion batteries that have high energy density and long lifespan by enabling the prelithiating process of the negative electrode by installing a lithium source composite sheet connected to the negative electrode inside the cell, thereby solving technical problems such as a long electrochemical prelithiating time, low amount of prelithiating material, non-uniform prelithiating material, and dissolution of metallic lithium particles. [Means for solving the problem]

[0012] To achieve the above objective, the present invention provides a method for prelithiating lithium-ion batteries, which is an electrochemical prelithiating method that is easy to industrialize and has low cost. In the manufacturing process of a typical lithium-ion battery, before injecting the electrolyte, one or more lithium source composite sheets are placed on the core body (e.g., a wound core or a stacked core, hereinafter the same), and at least one of the lithium source composite sheets is connected to the negative electrode tab of the lithium-ion battery. The process includes the steps of injecting an electrolyte, impregnating the lithium source composite sheet with the electrolyte, and prelithiating the negative electrode.

[0013] In a specific embodiment of the present invention, preferably, the lithium source composite sheet is a metal composite lithium sheet formed by combining lithium foil and metal foil (for example, a composite structure of one layer of lithium foil and one layer of metal foil, or a "sandwich" structure in which two layers of lithium foil are placed on the surfaces of both sides of one layer of metal foil), where the metal foil may be a metal foil commonly used as a current collector, such as copper foil, nickel foil, or platinum foil, or the lithium source composite sheet may be made of a lithium-containing material having electrochemical properties similar to metallic lithium.

[0014] According to specific embodiments of the present invention, the shape of the lithium source composite sheet may be as needed, preferably in the form of a sheet, strip, or tape, and may be provided with tabs.

[0015] In a specific embodiment of the present invention, preferably, a blocking member capable of preventing the passage of lithium ions is installed on the surface of the lithium source composite sheet that approaches the core body (for example, the surface facing the positive electrode sheet or the negative electrode sheet). By installing the blocking member, localized deposition of lithium can be prevented. The blocking member may preferably be a metal foil or insulating tape. When using a lithium source composite sheet having a composite structure of one layer of lithium foil and one layer of metal foil, it is possible to block the surface of the metal foil where the lithium foil is not installed toward the positive electrode sheet or the negative electrode sheet.

[0016] The lithium content of the lithium source sheet is appropriate so as not to be excessive enough to cause lithium deposition, and not so insufficient as to fail to meet the requirements for the amount of prelithiation, and the need for lithium replenishment during the cycle process must also be considered. In other words, the thickness of the lithium source sheet is appropriate so as to be able to fit into the space in which it is placed and so as not to fall out during the prelithiation process, and so as to be able to completely consume the lithium after prelithiation is complete. Any thickness in this principle falls within the scope of protection of this patent. Specifically, according to the means of implementing the present invention, preferably the thickness of the lithium source composite sheet does not exceed the thickness of the core body. The thickness of the lithium source composite sheet may be a specific numerical value within the range of 5 to 500 μm, preferably 20 to 300 μm, more preferably 30 to 280 μm, and even more preferably 50 to 250 μm, for example, 50 μm, 80 μm, 150 μm, 200 μm, 220 μm, etc.

[0017] In a specific embodiment of the present invention, preferably, an insulating porous elastic material is provided on the surface of the lithium source composite sheet that is close to the lithium-ion battery case. By providing an insulating porous elastic material, the leaching and detachment of metallic lithium can be avoided, the core body (laminated core or wound core) can be elastically restrained and the structural stability inside the lithium-ion battery can be improved, while ensuring that there is sufficient electrolyte during the prelithiation process. The lithium source composite sheet may be wrapped in an elastic liquid-absorbing material, more preferably the elastic liquid-absorbing material is a separator material. By wrapping it in an elastic material, during the prelithiation process, the elastic material deforms as the lithium source composite sheet is consumed, filling the space after consumption and improving structural stability.

[0018] In a specific means of the present invention, preferably, the lithium source composite sheet is directly connected to the negative electrode tab (for example, integrally welded), or the lithium source composite sheet is connected to the positive or negative electrode via an external circuit through a third electrode. That is, in the technical solution of the present invention, the lithium source composite sheet and the negative electrode may have two types of connection methods.

[0019] In the first type, the lithium source composite sheet is directly connected to the negative electrode tab, for example, by metal leads, metal sheet connections, or direct welding. In this method, after the electrolyte is injected, the negative electrode immediately begins prelithiation without any load being applied, and this method is suitable when the amount of prelithiasis is small, for example when the amount of prelithiasis is 10% SOC or less, or for example when the amount of prelithium is 5% SOC.

[0020] In the second type, the lithium source composite sheet is connected to a third electrode via an external circuit to the negative electrode tab of the lithium-ion battery to prelithiate the negative electrode. After the lithium-ion battery has formed, the third electrode is connected via an external circuit to the positive electrode tab of the lithium-ion electrode to prelithiate the positive electrode. In this method, the progress of prelithiation can be controlled by the external circuit, the rate of prelithiation can be improved, it is suitable when the amount of prelithiation is large, and prelithiation can be replenished by the third electrode as needed during the lithium-ion battery's use. This method is suitable when the amount of prelithiation is large, for example, when the amount of prelithiation is 10% SOC or more.

[0021] According to a specific embodiment of the present invention, preferably, the method for prelithiating the lithium-ion battery is Before injecting the electrolyte, the lithium-ion battery is fitted with one or more lithium source composite sheets and a third electrode, and the lithium source composite sheets are connected to the third electrode. The steps include injecting an electrolyte and impregnating the lithium source composite sheet with the electrolyte, The process includes the step of connecting the lithium source composite sheet to the negative electrode tab via a third electrode in an external circuit, thereby prelithiating the negative electrode.

[0022] In a specific embodiment of the present invention, preferably, after the cell has been properly formed, the lithium source composite sheet is connected to the positive electrode tab via an external circuit through a third electrode to prelithiate the positive electrode. That is, the prelithiatement method of the lithium-ion battery of the present invention further, Before injecting the electrolyte, the lithium-ion battery is fitted with one or more lithium source composite sheets and a third electrode, and the lithium source composite sheets are connected to the third electrode. The steps include injecting the electrolyte and impregnating the lithium source composite sheet with the electrolyte, The process may also include the step of prelithiating the positive electrode by connecting the lithium source composite sheet to the positive electrode tab via an external circuit through a third electrode after the cell has been successfully formed.

[0023] According to a specific embodiment of the present invention, preferably, when the lithium source composite sheet is directly connected to the negative electrode tab, the connection between the lithium source composite sheet and the negative electrode tab is located inside the case of the lithium ion battery. The connection between the lithium source composite sheet and the tab can be realized by a metal lead, a metal sheet connection, welding, etc. For example, the lithium source composite sheet is connected to the negative electrode tab by ultrasonic welding. In the process of cell stacking, the lithium source composite sheet is inserted, and the metal foil (for example, copper foil) of the lithium source composite sheet is welded to the same tab (Tab sheet) as the copper foil of the negative electrode, so that industrial formation production is easy to perform. When the lithium source composite sheet is directly connected to the negative electrode tab, the metal lead, metal sheet, or welding position for the connection is all located inside the case. In this case, the connection being located inside the case improves safety, and problems such as liquid leakage caused by the tab extending from the case can be avoided, and the production process is also greatly simplified. The connection between the lithium source composite sheet and the negative electrode is installed inside the case, and there is no need to install a tab on the lithium source composite sheet and extend it outside the case (of course, in order to facilitate the connection, a tab may be installed on the lithium source composite sheet, but the tab is located inside the case and does not extend outside the case). After prelithiation, the lithium in the lithium source composite sheet is completely consumed. In this way, without changing the structure of the conventional lithium ion battery, it can be applied to more types of lithium ion batteries. In addition, such a prelithiation method for lithium ion batteries of the present invention has good production convenience, small adjustment to the conventional production line, and low overall cost. When the lithium source composite sheet is connected to the negative electrode tab or the positive electrode tab in an external circuit via a third electrode, the third electrode, etc. may be located inside the case, or may extend from a certain position away from the case of the lithium ion battery.

[0024] In a specific embodiment of the present invention, preferably, a liquid injection port is provided in the lithium-ion battery, and the third electrode is in communication with a positive electrode tab or a negative electrode tab via an external circuit through the liquid injection port. The charge / discharge device of the external circuit causes the battery to undergo a prelithiolysis reaction in the discharge state. When it is necessary to prelithiate the negative and positive electrodes, the lithium source composite sheet, the negative electrode tab, and the positive electrode tab are connected to the discharge state of the charge / discharge device via the liquid injection port, and the electrolyte is allowed to flow into the cell, thereby realizing the prelithiolysis operation of the negative or positive electrode. Here, the position of the liquid injection port is not particularly limited and can be understood as a normal arrangement method in the prior art.

[0025] According to a specific embodiment of the present invention, the third electrode is mainly used when there is a large demand for prelithiolation, and preferably the third electrode may be installed in the cell case, or it may be done by prelithiolation of a tab through the injection port.

[0026] According to the specific implementation means of the present invention, preferably, when the prelithiation amount of the battery is less than 5% SOC, no measures are taken to dynamically hold the electrolyte inside the battery; when the prelithiation amount of the battery is more than 10% SOC, measures are taken to dynamically hold the electrolyte inside the battery. That is, in the process of prelithiation of the negative electrode and the positive electrode, by taking measures to make the electrolyte flow inside the cell of the lithium-ion battery, the lithium ions locally eluted by the flowing electrolyte can be embedded in the electrode sheet of the negative electrode or the positive electrode (that is, the lithium ions on the surface of the lithium source composite sheet are made to flow and embedded inside the electrode sheet of the negative electrode or the positive electrode), thereby increasing the prelithiation rate and the prelithiation amount, and improving the uniformity of lithium embedding. This is one of the key points of the present invention. The above "measures to dynamically hold the electrolyte" include, but are not limited to, vibration, rotation, inert gas stirring, electromagnetic stirring, etc. For example, the rotation of the lithium-ion battery, the vibration of the lithium-ion battery, introducing an inert gas into the cell of the lithium-ion battery, or magnetically stirring the electrolyte, etc., are used to realize the flow of the electrolyte inside the cell of the lithium-ion battery. Any method that can realize the flow of the electrolyte is acceptable and is not limited to the methods listed above.

[0027] According to the specific implementation means of the present invention, in addition to the lithium source composite sheet, the lithium-ion battery may further include several other ordinary members, such as a core body composed of a positive electrode sheet, a negative electrode sheet, and a separator, and a case. At least one lithium source composite sheet is installed on the surface of the core body of the lithium-ion battery and / or in other available spaces respectively. Positive electrode tabs and negative electrode tabs are installed on the positive electrode sheet and the negative electrode sheet respectively. The material, size, and installation method of the separator may refer to the ordinary methods in the field of lithium-ion batteries.

[0028] According to a specific embodiment of the present invention, the lithium-ion battery may include an assembly of core bodies, each consisting of several core bodies connected in series or in parallel, wherein at least one lithium source composite sheet is installed on the surface of each core body and / or in other possible spaces within the assembly of core bodies.

[0029] According to specific implementations of the present invention, the lithium-ion battery according to the prelithiolation method of the present invention may be a conventional stacked core battery, a wound core battery, or a JTM (Jellyroll To Module) battery.

[0030] In a specific embodiment of the present invention, preferably, at least one lithium source composite sheet is provided on the surface of the core body of the lithium-ion battery and / or in other spaces where it can be placed, or the lithium-ion battery includes an assembly of core bodies consisting of several core bodies connected in series or parallel, and at least one lithium source composite sheet is provided on the surface of each stacked core in the assembly of core bodies and / or in other spaces where it can be placed.

[0031] In a specific embodiment of the present invention, preferably, the core body of the lithium-ion battery is a laminated core, wherein at least one lithium source composite sheet is provided on at least one surface of the laminated core, or at least one lithium source composite sheet is provided on each of the surfaces of the laminated core, or lithium source composite sheets are provided on the sides and in other possible spaces.

[0032] According to a specific embodiment of the present invention, preferably the core body of the lithium-ion battery is a wound core, and at least one lithium source composite sheet is provided on the side or top surface of the wound core, preferably the lithium source composite sheet covers the side surface of the wound core, and during the prelithiation process, the lithium source composite sheet covering the side surface of the wound core diffuses uniformly, and lithium can be uniformly supplied to the negative electrode.

[0033] In a specific embodiment of the present invention, preferably, the lithium-ion battery includes an assembly of core bodies (e.g., a JTM battery) consisting of several core bodies connected in series or parallel to each other, wherein at least one lithium source composite sheet is provided on at least one surface of each laminated core in the assembly of core bodies. In the lithium-ion battery described above, the core body may be a laminated core or a wound core consisting of a positive electrode sheet and a negative electrode sheet.

[0034] In a specific embodiment of the present invention, preferably, the negative electrode of the core body of the lithium-ion battery is one or more combinations of negative electrodes such as a silicon negative electrode, a graphite negative electrode, a lithium titanate negative electrode, or a tin negative electrode, and more preferably, the negative electrode is a silicon-containing negative electrode, and the lithium source composite sheet is located in a pre-reserved bulge space for the negative electrode within the case of the lithium-ion battery. In a battery using a silicon-containing negative electrode, a certain bulge space is required between the wide surface of the case and the core body to account for the bulging of the silicon-containing negative electrode core body. In the present invention, when prelithiolation of a lithium-ion battery is performed, a lithium source composite sheet (for example, one or two lithium source composite sheets) can be placed in this space, and in this manner, the lithium source composite sheet can be placed in the battery case without affecting the battery structure, and after prelithiolation is completed, the lithium source composite sheet is completely consumed, the pre-reserved bulge space becomes empty again, and does not affect the normal use of the lithium-ion battery.

[0035] In a specific embodiment of the present invention, the electrolyte used in the present invention may be an electrolyte commonly used in the field of lithium-ion batteries, and an amount of electrolyte that can be ensured to impregnate the lithium source composite sheet is injected.

[0036] In a specific embodiment of the present invention, it is preferable to control the current and current method when prelithiating the negative or positive electrode via a third electrode. This allows for an increased prelithiating rate and control of the uniformity of prelithiating to avoid localized lithium deposition.

[0037] According to a specific embodiment of the present invention, preferably, during the cell formation process, a certain amount of lithium is embedded from the positive electrode to the negative electrode, preferably the amount of lithium embedded is 10% to 80% SOC, followed by prelithiation of the positive electrode.

[0038] In a specific embodiment of the present invention, the process of prelithiating the positive electrode via a third electrode is preferably carried out by a constant voltage discharge method, wherein the voltage is preferably 2.5V to 3.5V, more preferably 3.0V to 3.4V, and is within a range such as 2.5V, 2.6V, 2.7V, 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V, 3.4V, 3.5V, or two of these specific voltage values ​​as the upper and lower limits, respectively.

[0039] In a specific embodiment of the present invention, the current used to prelithiate the positive electrode is preferably 0.00001C to 1C, and more preferably 0.0001C to 0.5C.

[0040] In a specific embodiment of the present invention, prelithiation of the positive electrode is preferably performed in an intermittent manner. The current intermittence time can be controlled within a range of 1 to 3600 seconds, preferably 300 to 1800 seconds, more preferably 60 to 600 seconds, for example, 60 seconds, 100 seconds, 200 seconds, 300 seconds, 400 seconds, 500 seconds, 600 seconds, or two of these specific time values ​​as the upper and lower limits, respectively.

[0041] In a specific embodiment of the present invention, the process of prelithiating the negative electrode via the third electrode is preferably carried out by a constant voltage discharge method, where the voltage is preferably 0.1V to 0.3V, and more preferably 0.2V.

[0042] In a specific embodiment of the present invention, the current used to prelithiate the negative electrode is preferably 0.00001C to 1C, more preferably 0.0001C to 0.5C, and even more preferably 0.01C to 0.2C.

[0043] In a specific embodiment of the present invention, prelithiation of the negative electrode is preferably performed in an intermittent manner. The current intermittence time can be controlled within a range of 1 to 3600 seconds, preferably 300 to 1800 seconds, preferably 60 to 600 seconds, for example, 60 seconds, 100 seconds, 200 seconds, 300 seconds, 400 seconds, 500 seconds, 600 seconds, or two of these specific time values ​​as the upper and lower limits, respectively.

[0044] In a specific embodiment of the present invention, preferably, the prelithiation time is 8h to 200h, for example, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, 110h, 120h, 130h, 140h, 150h, 160h, 170h, 180h, 190h, 200h, or a range in which two of these specific time values ​​are set as the upper and lower limits, respectively.

[0045] According to a specific embodiment of the present invention, the lithium content of the lithium source composite sheet is calculated according to the required amount of prelithiation, taking into appropriate consideration the utilization rate. The thickness of the lithium source composite sheet must be controlled as needed to meet the requirements of being able to fit into the corresponding space and not falling out during the prelithiation process, and moreover, the lithium in the lithium source composite sheet is completely consumed after the prelithiation is completed.

[0046] In a specific embodiment of the present invention, preferably, the formula for calculating the theoretical amount of prelithio Y required per Ah is shown below: Y = 1000 nF / 3.6 A Here, n is the number of Li counts, F is the Faraday constant, and A is the atomic weight of lithium. The required Ah number is equal to the initial loss efficiency multiplied by the cell's design capacity.

[0047] The present invention further provides a high-energy-density, long-life lithium-ion battery manufactured by the above-described prelithiation method.

[0048] The prelithiation method provided in the present invention involves directly connecting a lithium source composite sheet to the negative electrode tab, injecting an electrolyte, initiating a prelithiation reaction, and then discharging (for example, connecting the positive and negative electrodes with an external circuit, performing a constant voltage discharge, and allowing lithium ions to enter the positive electrode) to achieve prelithiation of the positive electrode, ultimately achieving prelithiation of the battery. In the prelithiation method provided in the present invention, when prelithiation of the negative electrode is performed, there is no need to apply extra load, and prelithiation can be completed during the process of the core body infiltration, chemical formation, and capacity selection. Moreover, by directly connecting the lithium source composite sheet to the negative electrode and controlling this connection within the case of the lithium-ion battery, it is possible to avoid safety problems that can easily arise by separately installing a prelithiation tab and extending it outside the battery case.

[0049] Conventional electrochemical prelithiation methods all involve prelithiating the electrode sheet, and since the battery is assembled after prelithiation is complete, it leads to problems such as difficulty in cell assembly, high environmental requirements, and high production costs. The method provided in the present invention is performed after the battery assembly is complete, avoiding the impact of prelithiation on the battery assembly, and solving problems such as long electrochemical prelithiation time, low amount of prelithiation, non-uniform prelithiation, and leaching of metallic lithium particles. It has low environmental requirements, is easy to prelithiate, is easily industrializable, and is cost-effective.

[0050] By using the prelithiation method provided in the present invention, the lithium in the lithium source composite sheet is completely consumed during the prelithiation process and does not remain inside the battery, thus avoiding the safety concerns associated with the long-term presence of the lithium source composite sheet inside the lithium-ion battery in conventional technology.

[0051] The prelithiation method provided in this invention allows for the achievement of prelithiation in a simple manner. This method does not fundamentally alter the original process of lithium-ion batteries, but only requires localized modifications to the equipment, such as installing a lithium source composite sheet, including a prelithiation electrolyte, on the surface of the core body, or increasing the number of fixtures that flow the electrolyte during prelithiation. All of these modifications are easily implemented, making industrial production feasible. [Effects of the Invention]

[0052] The beneficial effect of the present invention is that, if the process and equipment of conventional lithium-ion batteries are not significantly altered, the prelithiation method provided by the present invention can realize the industrial application of prelithiation technology at a low cost. Lithium-ion batteries produced by the prelithiation method of the present invention can have their capacity increased by more than 5%, have a high energy density (e.g., more than 370 Wh / kg for ternary batteries, more than 230 Wh / kg for lithium iron phosphate batteries, etc.), have a long cycle life (e.g., more than 15,000 cycles for lithium iron phosphate batteries, etc.), and have a low cost (increasing the amount of electricity while lowering the cost), making it a revolutionary lithium-ion battery process method with great future potential. [Brief explanation of the drawing]

[0053] [Figure 1] This is a schematic diagram of the structure of a lithium source composite sheet. [Figure 2] This is a schematic diagram of the structure of the rectangular battery provided in Example 1. [Figure 3] This is a schematic diagram of the structure of the pouch-type battery provided in Example 2. [Figure 4]This is a schematic diagram of the structure of the pouch-type battery provided in Example 3. [Figure 5] This figure shows the cycle life results for the rectangular battery of Example 1 and the rectangular battery of Control Example 1. [Modes for carrying out the invention]

[0054] In order to more clearly understand the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the technical solutions of the present invention will be provided, but this should not be understood as limiting the scope of the invention's applicability.

[0055] The lithium source composite sheet used in the present invention may be configured as shown in Figure 1, by compounding lithium foil 15 onto one or both sides of a metal foil 14, with an elastic liquid-absorbing material layer 16 wrapped around the outside of the lithium foil 15.

[0056] The lithium source composite sheet may be composited on the side of the laminated core 11 (or any other space containing electrolyte; for example, if a wound core is used, the lithium source composite sheet may be composited on the top of the wound core or cover the side of the wound core), and the two are insulated from each other with insulating tape 13, and the lithium source composite sheet is connected to the negative electrode tab 12 by metal foil 14.

[0057] The manufacturing process of the lithium source composite sheet and the composite process with the core body can be carried out in the following manner: The lithium foil 15 is compounded with the metal foil 14 by a rolling method, allowing the thickness of the metal foil 14 to be controlled within the range of 4 to 100 μm and the thickness of the lithium foil 15 within the range of 0.01 to 10 mm. The lithium foil 15 may be compounded on one side or both sides. A lithium foil 15 is wrapped in an elastic liquid-absorbing material to form an elastic liquid-absorbing material layer 16. An insulating tape 13 having corrosion resistance to the electrolyte is attached to the bonding surface between the laminated core 11 and the lithium source composite sheet. Next, the laminated core 11 is connected to the metal foil 14, which may have a suitable tab installed at its upper end, using the tab 12 of the laminated core 11.

[0058] (Example 1) This embodiment provides a method for prelithiating a prismatic battery, the structure of which is shown in Figure 2. This prismatic battery is, The core body 22 is manufactured by a winding or lamination process from a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet is made of lithium iron phosphate material and the negative electrode sheet is made of graphite material, and positive electrode tabs 26 and negative electrode tabs 24 are installed on the two core body 22, The present invention includes a case 21 used to house a core body 22, with a positive electrode connection portion 27 and a negative electrode connection portion 25 installed on the upper part of the case 21.

[0059] The prelithiation method is The lithium source composite sheet 23 is installed on one side of the core body 22, and the lithium source composite sheet 23 is a lithium copper composite tape with the structure shown in Figure 1, that is, a composite of one layer of copper foil and one layer of lithium foil, with the lithium foil thickness being 0.1 mm and the copper foil thickness being 4.5 μm, and the lithium source composite sheet 23 is connected to the negative electrode tab 24, and before the electrolyte is injected, the lithium copper composite tape is positioned in a position where it can be impregnated with the electrolyte, and The process includes the steps of: placing the laminated core with the lithium source composite sheet inside the case 21; after assembly is complete, injecting electrolyte into the inside of the prismatic battery to impregnate the lithium source composite sheet, thereby initiating the prelithiation process; The prelithiation time is controlled according to the required amount of prelithiation. In this embodiment, the amount of prelithiation is 5%SOC, and the prelithiation time is controlled to 48 hours. This prelithiation time is within the permissible range of the lithium-ion battery manufacturing process. After prelithio is complete, the usual chemical conversion, standing, and volume sorting processes are carried out, specifically as follows: 1. In the chemical process, charge with a current of 0.02C for 4 hours, leave for 10 minutes, then charge with a current of 0.1C for 2 hours. 2. During the aging process, after the chemical conversion is complete, the mixture is left to stand for 12 hours to allow it to age. 3. In capacity selection, the batteries were charged to a voltage of 3.65V with a constant current of 0.33C, then charged to a current of 0.05C with a constant voltage of 3.65V, and after completion, left for 10 minutes. Next, they were discharged to a voltage of 2.0V with a current of 0.33C to complete capacity selection.

[0060] (Contrast example 1) This comparative example differs from Example 1 in that it does not include a lithium source sheet and does not perform prelithiation, but otherwise provides a standard method for manufacturing a prismatic battery that is identical in all other respects.

[0061] Table 1 shows the results of detecting the relevant characteristics of the prismatic batteries manufactured in Example 1 and Control Example 1.

[0062] [Table 1]

[0063] From the contents of Table 1, it was found that the lithium-ion cell obtained by the prelithiation method of Example 1 could achieve a capacity approximately 5% higher than that of Control Example 1, and could achieve a cycle life of approximately 15,000 cycles without decay up to approximately 2,000 cycles, whereas the sample of Control Example 1 had a cycle life of less than 6,000 cycles (shown in Figure 5).

[0064] (Example 2) This embodiment provides a method for prelithiating a pouch-type battery, the structure of which is shown in Figure 3, and its length is 360 mm. This pouch-type battery is, The core body 32 is manufactured by a lamination process from a positive electrode sheet, a negative electrode sheet, and a separator, where the positive electrode sheet is a ternary material NCM, and the negative electrode sheet is a silicon 600 negative electrode, with a positive electrode tab 35 and a negative electrode tab 34 installed on the two respectively, and the core body 32 is installed on the same side of the core body 32, The present invention includes a case 31, which is made of aluminum laminate and is used to house a core body 32.

[0065] The prelithiation method is The lithium source composite sheet 33 is placed on one side of the core body 32, positioned to ensure that the lithium source composite sheet 33 is impregnated with the electrolyte, and the lithium source composite sheet 33 is a lithium copper composite tape having the structure shown in Figure 1, i.e., a composite of one layer of copper foil and one layer of lithium foil, with a lithium foil thickness of 0.1 to 0.2 mm and a copper foil thickness of 4.5 μm, and the lithium copper composite tape can be made into various shapes such as rectangular, strip-shaped, or U-shaped, and The third electrode 36 is placed on the lithium source composite sheet 33, removed through the liquid injection port, and the negative electrode, positive electrode, and lithium source composite sheet 33 are connected as shown in Figure 3, and prelithiolysis is performed on the negative electrode and positive electrode. The core body with the lithium source composite sheet installed is placed inside the case, and after assembly is complete, the electrolyte is injected into the pouch-type battery to impregnate the lithium source composite sheet. The procedure includes the step of connecting the lithium source composite sheet 33 to the negative electrode tab 34 via a third electrode 36 in an external circuit, thereby prelithiating the negative electrode.

[0066] After the prelithiation of the negative electrode is complete, a standard chemical conversion process is carried out, specifically as follows: Charge with a current of 0.02C for 2 hours, leave for 10 minutes, then charge with a current of 0.05C for 2 hours, leave for 10 minutes, and then charge with a current of 0.1C for 1 hour. Next, the third electrode 36 is connected to the positive electrode tab 35, and the positive electrode is prelithiated. The prelithiation current is controlled to 0.01C, and the process can be carried out using a constant voltage, intermittent discharge method, with a voltage of 3.0V and an intermittent time of 60 seconds. During the prelithiation process, the electrolyte inside the core body 32 is circulated through the pouch-type battery by rotation and vibration to increase the prelithiation speed and ensure uniform prelithiation. The rotation is performed alternately in forward and reverse directions of 180°, with a rotation speed of 5 revolutions per minute. The vibration motor rotates at 1000 revolutions per minute, specifically performing intermittent rotations of 180°, remaining still for 60 seconds, and then rotating again by 180°.

[0067] The prelithiation time is controlled according to the required amount of prelithiation. In this embodiment, the amount of prelithiation is 12%SOC, and the prelithiation time is 96 hours.

[0068] After prelithiation is complete, the cells undergo the normal aging and capacity selection processes, specifically as follows: 1. During the aging process, after the chemical conversion is complete, leave it to stand for 24 hours to age. 2. In capacity selection, the batteries were charged to a voltage of 4.25V with a constant current of 0.33C, then charged to a current of 0.05C with a constant voltage of 4.25V, and after completion, left for 10 minutes. Next, they were discharged to a voltage of 2.0V with a current of 0.33C to complete capacity selection.

[0069] (Contrast example 2) This comparative example differs from Example 2 in that it does not include a lithium source sheet and does not perform prelithiation, but otherwise provides a standard method for manufacturing a pouch-type battery that is identical in all other respects.

[0070] Table 2 shows the results of detecting the relevant characteristics of the pouch-type batteries manufactured in Example 2 and Control Example 2.

[0071] [Table 2]

[0072] From the contents of Table 2, it was found that the lithium-ion battery manufactured by the method of Example 2 exhibited high initial charge / discharge efficiency and high capacity, with a specific energy of 370 Wh / kg for the cell, compared to a specific energy of only 320 Wh / kg for the sample of Control Example 2.

[0073] (Example 3) This embodiment provides a method for prelithiating a pouch-type battery, the structure of which is shown in Figure 4, and its length is 357 mm. Its structure is similar to that of the pouch-type battery in Embodiment 2, differing only in that the pouch-type battery in this embodiment has tabs at both ends. This pouch-type battery is, The core body 42 is manufactured by a lamination process from a positive electrode sheet, a negative electrode sheet, and a separator, where the positive electrode sheet is made of lithium iron phosphate material and the negative electrode sheet is made of silicon 600 negative electrode material, and positive electrode tabs 45 and negative electrode tabs 44 are installed on the two respectively, and the core body 42 is installed at both the upper and lower ends of the core body 42, The present invention includes a case 41, which is made of aluminum laminate and is used to house a core body 42.

[0074] The lithium source composite sheet, the prelithiation process, and the aging and capacity selection processes are the same as in Example 2.

[0075] (Contrast example 3) This comparative example differs from Example 3 in that it does not include a lithium source sheet and does not perform prelithiation, but otherwise provides a standard method for manufacturing a pouch-type battery that is identical in all other respects.

[0076] Table 3 shows the results of detecting the relevant characteristics of the prismatic batteries manufactured in Example 3 and Control Example 3.

[0077] [Table 3]

[0078] From the contents of Table 3, it was found that the lithium-ion battery manufactured by the method of Example 3 exhibited high initial charge / discharge efficiency (initial efficiency improved by 19%, which is a groundbreaking breakthrough) and high capacity, with a specific energy of 230.3 Wh / kg for the cell, compared to a specific energy of only 199.6 Wh / kg for the sample of Control Example 3.

Claims

1. In a typical lithium ion battery manufacturing process, before injecting an electrolyte, one or more lithium source composite sheets are installed on a core body, and at least one of the lithium source composite sheets is connected to a negative electrode tab of a lithium ion battery; Injecting an electrolyte solution to impregnate the lithium source composite sheet with the electrolyte solution, and prelithiating the negative electrode. A method for prelithiation of a lithium ion battery.

2. The lithium source composite sheet is a metal composite lithium sheet formed by combining a lithium foil and a metal foil.

2. The method of claim 1 .

3. The metal foil is a copper foil, a nickel foil, or a platinum foil.

3. The method of claim 2.

4. a blocking member capable of blocking the passage of lithium ions is provided on a surface of the lithium source composite sheet that is close to the core body, and an insulating porous elastic material is provided on a surface of the lithium source composite sheet that is close to the lithium ion battery case; 3. The method of claim 2.

5. The blocking member is a metal foil or an insulating tape.

5. The method of claim 4.

6. The thickness of the lithium source composite sheet does not exceed the thickness of the core body; 5. The method of claim 4.

7. The thickness of the lithium source composite sheet is 5 to 500 μm.

7. The method of claim 6.

8. The lithium source composite sheet is directly connected to the negative electrode tab to prelithiate the negative electrode, or the lithium source composite sheet is connected to a third electrode connected to a negative electrode tab of a lithium ion battery by an external circuit to pre-lithiate the negative electrode, and after the lithium ion battery is formed, the third electrode is connected to a positive electrode tab of the lithium ion battery by an external circuit to pre-lithiate the positive electrode; The method according to any one of claims 1 to 7.

9. When the lithium source composite sheet is directly connected to a negative electrode tab, the connection between the lithium source composite sheet and the negative electrode tab is located inside the case of the lithium ion battery.

9. The method of claim 8.

10. The lithium ion battery is provided with a liquid injection port, and the third electrode is connected to a positive electrode tab or a negative electrode tab in an external circuit through the liquid injection port. The charging / discharging device of the external circuit allows the battery to undergo a pre-lithiation reaction in a discharging state.

10. The method of claim 9.

11. When the pre-lithiation amount of the battery is less than 5% SOC, no measures are taken to dynamically maintain the electrolyte inside the battery, and when the pre-lithiation amount of the battery is more than 10% SOC, measures are taken to dynamically maintain the electrolyte inside the battery.

11. The method of claim 10.

12. Measures for dynamically maintaining the electrolyte include rotating the lithium ion battery, vibrating the lithium ion battery, introducing an inert gas into the lithium ion battery cell, or electromagnetically stirring the electrolyte.

12. The method of claim 11 .

13. The core body comprises a positive electrode sheet, a negative electrode sheet, and a separator, and at least one lithium source composite sheet is installed on the surface of the core body of the lithium ion battery and / or in another space where it can be installed, Alternatively, the lithium ion battery includes an assembly of core bodies consisting of several core bodies connected to each other in series or parallel, and at least one lithium source composite sheet is installed on the surface of each core body in the assembly of core bodies and / or in another space where it can be installed.

9. The method of claim 8.

14. The core body comprises a positive electrode sheet, a negative electrode sheet, and a separator, The core body of the lithium ion battery is a laminated core, and at least one lithium source composite sheet is installed on at least one surface of the laminated core, or at least one lithium source composite sheet is installed on each of the surfaces of both sides of the laminated core, or a lithium source composite sheet is installed on the side and in other spaces where it can be installed; Alternatively, the core body of the lithium ion battery is a wound core, and at least one lithium source composite sheet is installed on the side or top surface of the wound core, and preferably, the lithium source composite sheet is coated on the side surface of the wound core; Alternatively, the lithium ion battery includes an assembly of core bodies consisting of several core bodies connected to each other in series or in parallel, and at least one lithium source composite sheet is provided on at least one surface of each core body in the assembly of core bodies.

9. The method of claim 8.

15. The negative electrode of the core body of the lithium ion battery is one or a combination of two or more of a silicon negative electrode, a graphite negative electrode, a lithium titanate negative electrode, and a tin negative electrode. Preferably, the negative electrode is a silicon-containing negative electrode, and the lithium source composite sheet is located in a bulge space reserved in advance for the negative electrode in the case of the lithium ion battery.

9. The method of claim 8.

16. The current for prelithiating the positive electrode is 0.00001 C to 1 C, preferably 0.0001 C to 0.5 C; 12. The method of claim 11 .

17. The pre-lithiation of the positive electrode is carried out by constant voltage discharge, and the voltage is preferably 2.5V to 3.5V, more preferably 3.0V to 3.4V.

12. The method of claim 11 .

18. The prelithiation of the positive electrode is carried out in an intermittent manner, and the time interval between the intermittences is 1 to 3600 seconds, preferably 60 to 600 seconds; 12. The method of claim 11 .

19. The formula for calculating the theoretical amount of pre-lithio Y required per Ah is shown below: Y=1000nF / 3.6A, where n is the Li count, F is the Faraday constant, A is the atomic weight of lithium, and the number of Ah required is equal to the initial efficiency of loss multiplied by the design capacity of the cell.

12. The method of claim 11 .

20. The prelithiation time is 8 h to 200 h; 12. The method of claim 11 .

21. A lithium ion battery produced by the method of any one of claims 1 to 20.

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