Electrochemical impedance spectroscopy-based lithium plating diagnostic method for lithium-ion batteries

Abstract

The present application relates to the field of lithium ion batteries, and in particular to a method for diagnosing lithium precipitation in lithium ion batteries using electrochemical impedance spectroscopy.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of lithium-ion batteries, in particular, to a method for diagnosing lithium plating in lithium-ion batteries using electrochemical impedance spectroscopy. BACKGROUND

[0002] Due to the unique advantages of lithium-ion batteries (LIBs), such as their high energy and power density, low memory effect, and environmental friendliness, they have been widely used as energy sources for electric and hybrid electric vehicles, replacing conventional fossil fuels. However, lithium-ion batteries still face some key technical challenges, such as lithium metal plating on the anode. Lithium plating is kinetically favorable because the working potential of graphite is very close to the potential of metal lithium deposition. Lithium plating on the anode in lithium-ion batteries is closely related to charging conditions, such as low temperature, high charging rate, and overcharging. These conditions lead to high anode polarization and force the anode potential to reach the threshold for metal lithium plating, thus causing anode lithium plating. Lithium metal is usually deposited in dendritic or mossy form and is one of the main causes of aging and safety incidents, such as short circuits caused by lithium accumulation. Therefore, studying lithium plating is crucial for the operation of lithium-ion batteries under different operating conditions. To determine whether lithium plating occurs, many methods are used as general techniques.

[0003] Visual observation techniques, such as by naked eye, optical microscope, SEM, or TEM, can be used to observe the plating of lithium metal on the graphite anode and its morphology. Different observation techniques determine whether the lithium-ion battery needs to be disassembled or at least needs to be specially designed. Disassembly causes irreversible damage to the battery. When lithium plating occurs, many measures can be taken to eliminate it, and the battery can be further cycled in the remaining life.

[0004] Electrochemical impedance spectroscopy (EIS) is a widely used tool for characterizing lithium-ion batteries. Its results are usually presented in the form of Nyquist plots, which contain two "semicircular" features, where the low-frequency semicircle is attributed to the charge transfer at the electrode / electrolyte interface, and the high-frequency semicircle is attributed to the interface between the electrode particles and the metal current collector. In a very simple model, Rct is expected to follow the Arrhenius formula:

[0005] 1 / Rct = Ae (-Ea / (kB T)) ,

[0006] where Ea is the activation energy related to the site of lithium ion transition through the solid electrolyte interface in the material, kB is the Boltzmann constant, T is the temperature, and A is a proportional constant.

[0007] The conventional electrochemical impedance spectroscopy analysis usually needs to pay attention to meet the environmental factors of the electrochemical system, such as the control of temperature, so as to ensure the unique corresponding causal relationship between the measurement signal and the disturbance signal during the analysis process, thereby excluding any other interference signals; therefore, the electrochemical impedance spectroscopy analysis implemented on the lithium ion battery in the prior art is carried out at the same temperature.

[0008] For example, CN106680726A discloses a method for testing the cycle performance of a lithium ion battery, which includes performing a preset test operation in real time after the lithium ion battery is subjected to a preset different number of charge-discharge cycle test operations, the test operation including detecting the state of charge of the lithium ion battery in real time, when the state of charge of the lithium ion battery reaches a preset state of charge value, performing an electrochemical alternating current impedance test on the lithium ion battery, and obtaining preset alternating current impedance test parameters. However, the alternating current impedance test performed in the patent application file is not carried out at different temperatures.

[0009] CN106199451A discloses a method for testing the optimal compaction density of a lithium iron phosphate positive electrode sheet of a lithium ion battery, wherein the test step involves performing two electrochemical tests using an electrochemical workstation IVIUM-n-STAT, first performing an alternating current impedance spectroscopy test, and then performing a linear sweep test, the specific alternating current impedance spectroscopy test having a starting voltage of 3.42V-3.43V, a scanning frequency of 100000-0.01Hz, and a current range of 100mA; after the open circuit voltage is stabilized, the linear sweep test is performed, with a voltage amplitude of 50mV, a voltage interval of 1mV, a scanning rate of 1mV / s, and a current range of 1mA. Finally, the relevant performance of the lithium iron phosphate positive electrode sheet is obtained through result analysis. The alternating current impedance test performed in the patent application file is also not carried out at different temperatures. SUMMARY

[0010] There is a need in the art for a method for quickly analyzing and / or determining whether lithium deposition occurs on the anode in the battery without disassembling the battery.

[0011] The inventors have found that the occurrence of lithium plating in a lithium-ion battery can be determined without disassembling the battery using electrochemical impedance spectroscopy. The inventors have found that the results of electrochemical impedance spectroscopy are temperature dependent and will show a difference when measured at different temperatures. Thus, when electrochemical impedance spectroscopy is performed on a lithium-ion battery in which lithium plating occurs and on a lithium-ion battery in which lithium plating does not occur, the results of the electrochemical impedance spectroscopy will show different trends. Specifically, for a lithium-ion battery in which lithium plating does not occur, the curve in the Nyquist plot of the electrochemical impedance spectroscopy will show a decreasing trend in the real part (horizontal axis) as the temperature is increased. Conversely, for a lithium-ion battery in which lithium plating occurs, the curve in the Nyquist plot of the electrochemical impedance spectroscopy will show an increasing trend in the real part (horizontal axis) as the temperature is increased. These two opposite results thus provide a criterion for quickly evaluating the occurrence of lithium plating in a lithium-ion battery.

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

[0013] In one 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 plots. The method is characterized in that electrochemical impedance spectroscopy is performed on an intact / non-disassembled lithium-ion battery under different temperature conditions, and the occurrence of lithium plating on the anode of the lithium-ion battery is determined based on the arrangement of the curves on the Nyquist plot obtained at different temperatures.

[0014] In 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 plots, characterized in that the occurrence of lithium plating is determined based on the arrangement order of the electrochemical impedance spectroscopy curves obtained at different temperatures.

[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 plots, characterized in that, in the Nyquist plot of the electrochemical impedance spectroscopy obtained at different temperatures, the one or more curves obtained at low to high temperatures are arranged in sequence from the high frequency region to the low frequency region, indicating the occurrence of lithium plating, or the one or more curves obtained at low to high temperatures are arranged in sequence from left to right in the real part, indicating the occurrence of lithium plating.

[0016] 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 plots, characterized in that the temperature interval between the different temperature conditions under which the electrochemical impedance spectroscopy is performed is 5-20°C, preferably 5-15°C, more preferably 5-10°C.

[0017] In still another aspect, the present application relates to a method of 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 the different temperature conditions at which the electrochemical impedance spectroscopy is performed is performed continuously.

[0018] In still another aspect, the present application relates to a method of 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 the different temperature conditions at which the electrochemical impedance spectroscopy is performed is performed continuously. DETAILED DESCRIPTION

[0019] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are now described.

[0020] In the present application, a lithium-ion cell is the smallest basic functional unit of a lithium-ion battery. In the sense of the present application, a lithium-ion battery denotes not only a rechargeable battery (secondary battery) but also a non-rechargeable battery (primary battery). A rechargeable lithium-ion battery is synonymous with a lithium-ion secondary battery. These two terms also include lithium batteries and lithium-ion accumulators. A battery consists of at least two connected cells. Typically, in a lithium-ion battery, two or more lithium-ion cells are connected in series or in parallel. A lithium-ion cell comprises here two opposite electrodes, a negative anode and a positive cathode. The two electrodes are electrically and physically isolated from each other by a separator arranged between the electrodes. A lithium-ion cell is usually filled with an electrolyte. The separator is permeable to lithium ions, so that ions can be exchanged between the anode and the cathode during the charging process or the discharging process.

[0021] As used herein, "active material" means that part of the electrode which stores lithium ions. In the case of a cathode, the active material can be a lithium-containing compound such as a lithium metal oxide complex. In the case of the opposite anode electrode, the active material can be silicon or lithiumated silicon.

[0022] As used herein, the term "anode" denotes an electrode which is able to give off electrons when the battery is operated, which is also referred to as negative electrode in nomenclature.

[0023] As active material of the anode, it is possible to use all materials known from the relevant art. There are no restrictions with regard to the anode in the sense of the present application. In particular, it is also possible to use mixtures of different active anode 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, meso-carbon, doped carbon, hard carbon, soft carbon, fullerenes, mixtures of silicon and carbon, silicon, lithium alloys, metallic lithium and mixtures thereof. As anode material, also niobium pentoxide, tin alloys, titanium dioxide, tin dioxide, silicon can be used.

[0025] The anode material can also be a material that can alloy with lithium. It can be a lithium alloy or a precursor that is not lithiated or partially lithiated, from which a lithium alloy is generated upon formation. Preferred materials that can alloy with lithium are lithium alloys selected from the group consisting of silicon-based alloys, tin-based alloys and antimony-based alloys.

[0026] As active material for the cathode, all materials known in the relevant art can be used. There is no restriction with respect to the cathode in the sense of the present application. In particular, it is also possible to use mixtures of different active cathode materials.

[0027] The electrochemical workstation used for carrying out the measurement of electrochemical impedance spectroscopy of the method of the present application is not particularly limited and can be an electrochemical workstation conventional in the art, including single-channel electrochemical workstations, multi-channel electrochemical workstations, comprehensive electrochemical workstations and the like, such as various models of electrochemical workstations provided by manufacturers or trademarks Zahner, Gamry, Vertex and the like. The results obtained by the electrochemical workstation are plotted into the corresponding Nyquist plots and the analysis thereof is well known to the person skilled in the art.

[0028] Other objects, advantages and novel features of the present application will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings. The disclosure is written for the skilled in the art. Although the disclosure uses terms that can not be familiar to laymen, the skilled in the art will be familiar with the terms used herein. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 are curves obtained by carrying out electrochemical impedance spectroscopy measurements on one sample at different temperatures; wherein, since the temperature is continuously changed, 3-4 measurements are carried out at each temperature.

[0030] As can be seen from the figure, there are several curves in each temperature group, and as the temperature is increased at intervals of about 5-10°C, each group of curves attributed to the same temperature in the electrochemical impedance spectroscopy determined in this case moves to the right along the horizontal axis in the Nyquist plot, i.e. in the real part as the temperature increases, and these curve groups are arranged from low to high.

[0031] Figure 2is a SEM picture of a graphite electrode sheet where lithium metal is precipitated.

[0032] Figure 3 is a SEM picture of a fresh (no lithium precipitated) graphite electrode sheet.

[0033] Figure 4 is a picture of a fresh (no lithium precipitated) graphite electrode sheet.

[0034] Figure 5 is a picture of a graphite electrode sheet where lithium metal is precipitated.

[0035] Example

[0036] Two commercial soft pack batteries with graphite anodes that showed good consistency were selected in parallel and cycled at 0 °C, 0.3C rate to induce lithium precipitation. After 80 cycles, the batteries retained about 90% capacity retention, respectively.

[0037] Example 1 (disassembly check as a comparison)

[0038] One of the batteries was disassembled to check the lithium precipitation occurrence. By visual observation, it can be seen that both exist in different states. By observation, it was found that on the anode, a grey area (see Figure 4 and Figure 5 ) due to the precipitated lithium metal can be observed visually. After taking pictures of their surfaces using the SEM method, it was observed that both changed in terms of micro-morphology.

[0039] Example 2 (electrochemical impedance spectroscopy of the present invention)

[0040] As a comparison, the other battery was not disassembled, but electrochemical impedance spectroscopy measurements were performed on an Eco Chemie Autolab PGSTAT302N electrochemical workstation in potentiostatic mode (test parameters: 5mV / 10 -1 ~ 10 5 Hz) at different temperatures (30 °C, 35 °C, 45 °C, 56 °C) to check the lithium precipitation. The results obtained are summarized in Figure 1 From this figure, it can be clearly seen that the trend of lithium precipitation of the battery. As the temperature increases, the curve (set) continuously moves to the right on the Nyquist plot. For the impedance, the real part gradually increases. This change does not comply with the temperature inversion in the case of lithium-ion batteries without lithium precipitation, i.e., the real part decreases as the measurement temperature increases. Therefore, the cause of this phenomenon can be attributed to lithium precipitation: as the temperature increases, the precipitated lithium metal will re-embed in the graphite. This reduces the electronic conductivity and increases the internal resistance, and the arrangement of the curve in the electrochemical impedance spectroscopy increases in the real part as the temperature increases.

Claims

1. A method of analyzing occurrence of lithium deposition on an anode of a lithium-ion battery using electrochemical impedance spectroscopy without disassembling the battery, characterized by, The occurrence of lithium plating is determined from the arrangement of the electrochemical impedance spectroscopy curves obtained at different temperature conditions, and also from the arrangement of the Nyquist plots of the electrochemical impedance spectroscopy obtained at different temperature conditions, in which one or more curves obtained at temperatures from low to high are arranged in sequence from the high frequency region to the low frequency region, indicating the occurrence of lithium plating.

2. The method of claim 1, wherein, The occurrence of lithium plating is indicated by the arrangement of one or more curves obtained at temperatures from low to high in sequence from left to right in the real part.

3. The method according to any one of claims 1 to 2, characterized in that, The temperature interval between the different temperature conditions in which the electrochemical impedance spectroscopy analysis is performed is 5-20 °C.

4. The method of claim 3, wherein, The temperature variation between the different temperature conditions in which the electrochemical impedance spectroscopy analysis is performed is continuous.

5. The method of claim 3, wherein, A plurality of electrochemical impedance spectroscopy measurements are performed at each test temperature.

6. The method of claim 5, wherein, 1-10 measurements are performed at each test temperature.

7. The method of claim 3, wherein, The temperature interval between the different temperature conditions in which the electrochemical impedance spectroscopy analysis is performed is 5-15 °C.

8. The method of claim 3, wherein, The temperature interval between the different temperature conditions in which the electrochemical impedance spectroscopy analysis is performed is 5-10 °C.

9. The method of claim 5, wherein, 2-8 measurements are performed at each test temperature.

10. The method of claim 5, wherein, 3-5 measurements are performed at each test temperature.

11. The method of claim 5, wherein, 3 or 4 measurements are performed at each test temperature.

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