A method for diagnosing lithium plating in lithium-ion batteries using electrochemical impedance spectroscopy.

Abstract

The present invention relates to the field of lithium ion batteries, and more particularly to a method for diagnosing lithium plating in lithium ion batteries using electrochemical impedance spectroscopy.

Description

Technical Field

[0001] Technical Field The present invention relates to the field of lithium-ion batteries, and particularly to a method for diagnosing lithium plating of lithium-ion batteries using electrochemical impedance spectroscopy.

Background Art

[0002] Background Art Lithium-ion batteries (LIBs) have been widely used as an energy source for electric vehicles and hybrid electric vehicles, replacing conventional fossil fuels, due to their unique advantages such as high energy density, high power density, low memory effect, and environmental considerations. However, lithium-ion batteries still face important technical issues such as lithium metal plating on the anode (negative electrode). Lithium plating is kinetically favorable because the operating potential of graphite is very close to the deposition potential of metallic lithium. Lithium plating on the anode of a lithium-ion battery is closely related to charging conditions such as low temperature, high charging rate, and overcharging. These conditions cause high polarization of the anode, resulting in an anode potential that reaches the threshold for metallic lithium deposition and causing anode lithium plating. Metallic lithium usually deposits in a dendritic or mossy form, which is one of the main causes of aging and safety accidents such as short circuits due to lithium accumulation. Therefore, research on lithium plating is very important for the operation of lithium-ion batteries under different usage conditions. Many methods are used as common techniques to determine the presence or absence of lithium plating.

[0003] The plating and morphology of lithium metal on the graphite anode can be observed using visual observation techniques such as the naked eye, optical microscopes, SEM, or TEM. Different observation techniques determine whether the lithium-ion battery needs to be disassembled or at least requires special design. Disassembly will cause irreversible damage to the battery. If lithium plating occurs, many measures can be taken to remove it, and the battery can be recycled further for the remainder of its life.

[0004] Electrochemical impedance spectroscopy (EIS) is a widely used tool for characterizing lithium-ion batteries. The results are typically presented in the form of a Nyquist plot. A Nyquist plot contains two "semicircles": a low-frequency semicircle representing charge transfer at the electrode / electrolyte interface, and a high-frequency semicircle representing the interface between the electrode particles and the metal current collector. In a very simple model, Rct is expected to follow the Arrhenius equation:

[0005] 1 / Rct=Ae (-Ea / (kB T)) , Here, Ea represents the activation energy associated with the site where lithium ions transition through the solid electrolyte interface in the material, kB is the Boltzmann constant, T is the temperature, and A is the proportionality constant.

[0006] Conventional electrochemical impedance spectroscopy typically requires careful attention to environmental factors of the electrochemical system, such as temperature control, thereby ensuring only the corresponding causal relationship between the measured signal and interfering signals during the analysis process, thereby eliminating other interfering signals. Therefore, conventional electrochemical impedance spectroscopy of lithium-ion batteries is performed at the same temperature.

[0007] For example, CN106680726A discloses a method for testing the cycle performance of a lithium-ion battery. This method involves subjecting the lithium-ion battery to a set of pre-set charge-discharge cycle test operations for different cycles, and then performing a pre-set test operation in real time. The test operation includes detecting the charge state of the lithium-ion battery in real time. When the charge state of the lithium-ion battery reaches a pre-set charge state value, an electrochemical AC impedance test is performed on the lithium-ion battery, and pre-set AC impedance test parameters are obtained. However, the AC impedance test in this patent application is not performed at different temperatures.

[0008] CN106199451A discloses a method for testing the optimal molding density of lithium iron phosphate cathode plates for lithium-ion batteries. The test steps include performing two electrochemical tests using the IVIUM-n-STAT electrochemical workstation. First, an AC impedance spectroscopy test is performed, followed by a linear sweep test. The specific AC impedance spectroscopy test is performed with a starting voltage of 3.42V to 3.43V, a scanning frequency of 100000 to 0.01Hz, and a current range of 100mA. After the open-circuit voltage stabilizes, a linear sweep is performed with a voltage amplitude of 50mV, a voltage interval of 1mV, a scan speed of 1mV / s, and a current range of 1mA. Finally, the relevant performance of the lithium iron phosphate cathode plate is determined by result analysis. Note that the AC impedance test in this patent application does not include testing at different temperatures. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] CN106680726A [Patent Document 2] CN106199451A [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Summary of the Invention In this field, there is a need for a method to rapidly analyze and / or determine whether lithium plating has occurred on the anode inside a battery without disassembling the battery. [Means for solving the problem]

[0011] The inventors have discovered that it is possible to determine whether or not lithium plating has occurred in a battery without disassembling it, using electrochemical impedance spectroscopy. The inventors have found that electrochemical impedance spectroscopy is temperature-dependent, and that the results differ when measured at different temperatures. Therefore, when electrochemical impedance spectroscopy is performed on lithium-ion batteries with lithium plating and lithium-ion batteries without lithium plating, the results show different trends. Specifically, in the case of lithium-ion batteries without lithium plating, the Nyquist plot curve of electrochemical impedance spectroscopy tends to decrease in the real part (horizontal axis) as the temperature increases, while conversely, in the case of lithium-ion batteries with lithium plating, the Nyquist plot curve of electrochemical impedance spectroscopy tends to increase in the real part (horizontal axis) as the temperature increases. Therefore, these two contradictory results can serve as a criterion for quickly evaluating whether or not lithium plating has occurred in a lithium-ion battery.

[0012] Therefore, the present invention relates to a method for determining whether lithium plating has occurred on the anode of a lithium-ion battery at different temperatures using electrochemical impedance spectroscopy. This method is very effective for diagnosing lithium deposition.

[0013] In one embodiment, the present invention relates to a method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy. This method is characterized by performing electrochemical impedance spectroscopy on complete / unassembled lithium-ion batteries under different temperature conditions and determining the occurrence of lithium plating on the anode of the lithium-ion battery according to the arrangement of curves at different temperatures on the resulting Nyquist plot.

[0014] In another embodiment, the present invention relates to a method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy, characterized in that the occurrence of lithium plating is determined according to the order of the arrangement of electrochemical impedance spectroscopy curves obtained under different temperature conditions.

[0015] In yet another aspect, the present invention relates to a method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy, characterized in that, in Nyquist plots of electrochemical impedance spectroscopy obtained at different temperatures, one or more curves obtained from low temperature to high temperature are arranged from high frequency region to low frequency region, indicating the occurrence of lithium deposition, or one or more curves obtained from low temperature to high temperature are arranged from left to right in the real part, indicating the occurrence of lithium deposition.

[0016] In yet another embodiment, the present invention relates to a method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy, characterized in that the temperature interval between different temperature conditions for performing electrochemical impedance spectroscopy is 5 to 20°C, preferably 5 to 15°C, and more preferably 5 to 10°C.

[0017] In yet another embodiment, the present invention relates to a method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy, characterized in that the temperature change between different temperature conditions for performing electrochemical impedance spectroscopy is continuous.

[0018] In yet another embodiment, the present invention relates to a method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy, characterized in that multiple electrochemical impedance spectroscopy measurements are performed at each test temperature, preferably 1 to 10 times, more preferably 2 to 8 times, most preferably 3 to 5 times, or 3 or 4 times. [Modes for carrying out the invention]

[0019] Embodiment Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Any methods and materials similar or equivalent to those described herein may be used in carrying out or testing the present invention, but preferred methods and materials are described below.

[0020] In this application, a lithium-ion battery is the smallest basic functional unit of a lithium-ion battery pack. In the scope of the present invention, the lithium-ion battery pack represents not only a rechargeable battery pack (secondary battery pack) but also a non-rechargeable battery pack (primary battery pack). A rechargeable lithium-ion battery is synonymous with a lithium-ion secondary battery. Also, these two terms include a lithium battery pack and a lithium-ion storage battery. A battery pack is composed of at least two batteries connected. Usually, in a lithium-ion battery pack, two or more lithium-ion batteries are connected in series or in parallel. Here, a lithium-ion battery includes two opposing electrodes, a negative electrode (anode) and a positive electrode (cathode). These two electrodes are electrically and physically separated by a separator disposed between the electrodes. A lithium-ion battery is usually filled with an electrolyte. Since the separator allows lithium ions to penetrate, ion exchange can occur between the anode and the cathode during charge and discharge.

[0021] In this specification, the term "active material" means the part of the electrode that stores lithium ions. In the case of the cathode, the active material may be a lithium-containing compound such as a lithium metal oxide complex. In the case of the opposite anode electrode, the active material may be silicon or lithiated silicon.

[0022] In this specification, the term "anode" refers to an electrode that can donate electrons during the operation of the battery and is also called the negative electrode in nomenclature.

[0023] As the anode active material, all materials known in the relevant technical field can be used. There is no particular limitation on the anode in the meaning of the present invention. In particular, it is also possible to use a mixture of different anode active materials.

[0024] The anode material can be selected from lithium metal oxides, such as lithium titanium oxide, metal oxides (e.g., Fe2O3, ZnO, ZnFe2O4), carbon-containing materials, such as graphite (synthetic graphite, natural graphite), graphene, mesophase carbon, doped carbon, hard carbon, soft carbon, fullerene, silicon-carbon mixtures, silicon, lithium alloys, lithium metal, and mixtures thereof. Niobium pentoxide, tin alloys, titanium dioxide, tin dioxide, and silicon can also be used as anode materials.

[0025] Furthermore, the anode material may be a material that can be alloyed with lithium. It may be a lithium alloy, or a non-lithified or partially lithified precursor, from which a lithium alloy is formed during the formation process. Preferred materials that can be alloyed with lithium are lithium alloys selected from the group consisting of silicon-based alloys, tin-based alloys, and antimony-based alloys.

[0026] Any material known in the relevant art can be used as the cathode active material. There are no particular limitations on the cathode in the sense of the present invention. In particular, mixtures of different cathode active materials can be used.

[0027] The electrochemical workstation used for electrochemical impedance spectroscopy measurements in the method of the present invention is not particularly limited. It may be any conventional electrochemical workstation in the art, including single-channel electrochemical workstations, multi-channel electrochemical workstations, integrated electrochemical workstations, etc., and various types of electrochemical workstations provided by manufacturers or trademarks such as Zahner, Gamry, and Vertex. It is well known to those skilled in the art to plot the results obtained by the electrochemical workstation onto a corresponding Nyquist plot and analyze it.

[0028] In conjunction with the accompanying drawings, other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments. This disclosure is written for those skilled in the art. This disclosure uses terms that are not generally familiar, but those skilled in the art will be familiar with the terms used herein. This invention includes the following items. [Item 1] A method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy, characterized in that the occurrence of lithium plating is determined according to the arrangement of electrochemical impedance spectroscopy curves obtained under different temperature conditions. [Item 2] The method according to item 1, characterized in that, in Nyquist plots obtained by electrochemical impedance spectroscopy under different temperature conditions, one or more curves obtained from low temperature to high temperature, arranged sequentially from high frequency to low frequency, indicate the occurrence of lithium plating. [Item 3] The method according to item 1, characterized in that one or more curves obtained from low temperature to high temperature, arranged from left to right in the actual part, indicate the occurrence of lithium plating. [Item 4] The method according to any one of items 1 to 3, characterized in that the temperature interval between different temperature conditions for electrochemical impedance spectroscopy is 5 to 20°C, preferably 5 to 15°C, and more preferably 5 to 10°C. [Item 5] The method according to item 4, characterized in that the temperature change between different temperature conditions for electrochemical impedance spectroscopy is continuous. [Item 6] The method according to item 4, characterized in that multiple electrochemical impedance spectroscopy measurements are performed at each test temperature. [Item 7] The method according to item 6, characterized in that measurements are performed 1 to 10 times, preferably 2 to 8 times, more preferably 3 to 5 times, or 3 or 4 times, at each test temperature. [Brief explanation of the drawing]

[0029] Description of the drawing Figure 1 shows curves obtained by electrochemical impedance spectroscopy measurements of the sample at different temperatures. Since the temperature changes continuously, 3 to 4 measurements were performed at each test temperature.

[0030] As can be seen from the figure, each temperature group has multiple curves, and as the temperature increases in increments of approximately 5-10°C, the groups of curves belonging to the same temperature in the electrochemical impedance spectroscopy measurements performed in this study shift to the right along the horizontal axis of the Nyquist plot. In other words, these groups of curves are positioned from lower to higher in the real part as the temperature increases.

[0031] Figure 2 is an SEM image of a graphite electrode sheet plated with lithium metal.

[0032] Figure 3 is an SEM image of a fresh (unplated with lithium) graphite electrode sheet.

[0033] Figure 4 is a photograph of a fresh (unplated with lithium) graphite electrode sheet.

[0034] Figure 5 is a photograph of a graphite electrode sheet plated with lithium metal. [Examples]

[0035] Examples Two commercially available softpack batteries with well-matched graphite anodes were selected in parallel and cycled at 0°C and 0.3°C to induce lithium plating. After 80 cycles, the battery capacity retention rate was approximately 90%.

[0036] Example 1 (Disassembly and inspection for comparison) One of the batteries was disassembled to examine the state of the lithium plating. Visual inspection revealed that the two batteries were in different states. Upon observation, a gray area due to lithium metal plating was visible on the anode (see comparison of Figures 4 and 5). Furthermore, when the surface was photographed using a scanning electron microscope (SEM), changes in the microscopic morphology were observed.

[0037] Example 2 (Electrochemical Impedance Spectroscopy of the present invention) For comparison, instead of disassembling the other battery, electrochemical impedance spectroscopy measurements were performed in potentiometric mode at different temperatures (30°C, 35°C, 45°C, 56°C) using Eco Chemie's Autolab PGSTAT302N electrochemical workstation (test parameters: 5mV / 10 -1 ~10 5Lithium plating was confirmed at Hz. The results are summarized in Figure 1, clearly showing the trend of lithium plating within the battery. As the temperature increased, the curve(s) on the Nyquist plot continued to shift to the right. For impedance, the real part gradually increased. This change does not coincide with the temperature reversal in the case of lithium-ion batteries without lithium plating; that is, the real part decreased with increasing measurement temperature. Therefore, it is considered that the cause of this phenomenon lies in the lithium plating. As the temperature rises, the plated lithium metal is re-encapsulated in graphite. As a result, the electronic conductivity decreases, the internal resistance increases, and the arrangement of curves in electrochemical impedance spectroscopy shows an increase in the real part with increasing temperature.

Claims

1. A method for analyzing the occurrence of lithium plating on the anode of a lithium-ion battery using electrochemical impedance spectroscopy, wherein the occurrence of lithium plating is determined according to the arrangement of electrochemical impedance spectroscopy curves obtained under different temperature conditions. The method is characterized in that two or more curves obtained from low temperature to high temperature, arranged from left to right in the actual section, indicate the occurrence of lithium plating.

2. The method according to claim 1, characterized in that, in Nyquist plots obtained by electrochemical impedance spectroscopy under different temperature conditions, two or more curves obtained from low temperature to high temperature, arranged sequentially from high frequency to low frequency, indicate the occurrence of lithium plating.

3. The method according to claim 1 or 2, characterized in that the temperature interval between different temperature conditions for electrochemical impedance spectroscopy is 5 to 20°C.

4. The method according to claim 3, characterized in that the temperature change between different temperature conditions for electrochemical impedance spectroscopy is continuous.

5. The method according to claim 3, characterized in that multiple electrochemical impedance spectroscopy measurements are performed at each test temperature.

6. The method according to claim 5, characterized in that 1 to 10 measurements are performed at each test temperature.

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