Deinterlacing of lithium ions in lithium secondary batteries

In Lifepo4, the deinterlacing of lithium ions in lithium secondary batteries will cause changes in the crystal structure of electrode materials, which can be tracked by changes in the peak position or intensity in the XRD spectrum. Non in-situ XRD is used for observation. After the electrochemical reaction, the electrode material needs to be cleaned and dried. During this process, the electrode material may be transformed into a thermodynamic stable state, which makes it difficult to accurately analyze the structural changes occurred. In situ XRD can monitor the change of crystal structure in real time.

As shown in Chart 4.51, to conduct in situ experiments, we need to prepare a battery for in situ analysis. It should be pointed out that XRD is used for volume analysis [5], and the voltage measured in the experiment is caused by the reaction on the particle surface, so the time required for the particle surface reaction to transmit to the interior and reach the equilibrium state must be reduced to the minimum. In addition, the current density passing through the particles must be evenly distributed, the internal resistance of the battery must be minimized, and the continuous supply of electrolyte must be guaranteed during the cycle [6]. A transparent window is also needed to allow XRD rays to pass through. In order to ensure the complete sealing of liquid electrolyte, corrugated windows with high mechanical strength and good insulation performance are usually used.

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Use a medical blade to directly coat the electrode material to the other window to obtain the in situ battery [7]. Since the oxidation potential of Be is greater than 4.2 V [7], it is difficult to analyze the anode materials that are easy to be oxidized. This problem can be solved by using the Bellcore battery. There is an air gap between the electrodes in the Bellcore battery to prevent Be from directly contacting the electrolyte [5, 8].

Using the in-situ battery, the XRD patterns of CoO2 and NiO2 can be obtained after the complete lithium removal of LiCoO2 and LiNiO2. The changes of crystal structure with different amounts of lithium removal can be identified and analyzed by the XRD patterns in Figure 4.52 and Figure 4.53.

As another example, alloy type Sn based electrode material is deposited on the glass plate by spraying. Figure 4.54 shows the results of its in-situ XRD analysis [10]. The XRD patterns of changes with time and voltage during charging and discharging are displayed at the bottom and the corresponding results are displayed at the top.

As shown in Figure 4.55, another method is to use a battery that allows the X-ray beam to pass through. Although synchrotron radiation X-ray source is required, battery manufacturing is relatively simple, and X-ray penetration can be adjusted by adjusting the incidence angle

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Depth [11, 12]. The peak of Cu or Al collector fluid may be displayed on the XRD spectrum, but this can be solved by reducing the thickness of the collector fluid. This problem does not occur on the commercial collector, because its thickness is 10-25 μ m。

Figure 4.56 shows the diffraction results of in-situ synchrotron radiation of a PLIonTM battery. As lithium is stripped from LiMn2O4 spinel cathode, oxidation reaction occurs, forming a new

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Interphase. With the reduction reaction of lithium intercalation, the mesophase disappears. Through the analysis of these reactions, it can be found that the crystal structure of the mesophase is double hexagonal [13]. In Figure 4.56, a~f is the change of LiMn2O4 diffraction pattern with the charge discharge process.

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