Battery assembling and testing method for in-situ optical microscope detection

Abstract

The invention belongs to the technical field of electrochemical in-situ characterization and battery detection, and discloses a battery assembly and test method for in-situ optical microscope detection. According to the method, a multifunctional in-situ optical observation electrolytic tank is designed, and a synchronous optical-electrochemical test process is combined, so that the dynamic evolution process of a positive electrode, a negative electrode and an electrode-electrolyte interface (EEI) in the battery is monitored in a real-time and associated manner. The electrolytic tank adopts a three-electrode system structure made of a chemical inert insulating material, is provided with double independent transparent observation windows, and can synchronously capture positive and negative electrode interface form change and chemical species migration; through combination with an electrochemical workstation, direct correlation between optical signals (morphology and color) and electrochemical parameters (voltage and current) is established. According to the method, the defects that the dynamic states of the positive and negative electrode interfaces cannot be observed synchronously and an interface reaction visualization means is lacked in the prior art are overcome, the method is suitable for various systems such as lithium metal batteries and iodine / bromine batteries, and a powerful in-situ detection platform is provided for electrode material screening, electrolyte additive evaluation and interface regulation and control strategy optimization.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical in-situ characterization and battery testing technology, specifically involving an in-situ optical microscope detection method for battery assembly and testing, which is particularly suitable for real-time observation of the dynamic evolution process of the positive electrode, negative electrode and electrode-electrolyte interface (EEI) in systems such as lithium metal batteries, iodine cathode batteries and bromine cathode batteries. Background Technology

[0002] Optimizing the performance and extending the lifespan of electrochemical energy storage devices is a core research direction in the energy field. The performance degradation and failure mechanisms of battery systems often stem from complex internal interfacial dynamic processes, which is particularly prominent in multi-electron reaction energy storage systems. In lithium metal batteries, the uncontrolled growth of lithium dendrites on the negative electrode surface can pierce the separator, causing internal short circuits and other safety hazards. In iodine and bromine cathode batteries, soluble polyiodides (I-dioxides) formed at the cathode... x - ) and polybrominated compounds (Br x - A shuttle effect occurs, leading to the loss of active materials and capacity decay. These interface problems severely limit the cycle life and practical application of batteries.

[0003] Traditional research methods primarily rely on electrochemical testing and post-cycling disassembly analysis. Techniques such as electrochemical impedance spectroscopy and cyclic voltammetry can only provide macroscopic electrochemical parameters and cannot reveal the dynamic details of the interface; while disassembly analysis is a destructive test that cannot restore the true state of the battery's operation and is easily influenced by external interference, leading to distorted results. For processes such as the formation and diffusion of polyhalides, which are accompanied by significant color changes, traditional methods struggle to establish a direct correlation between these processes and electrochemical performance.

[0004] Optical microscopy, with its real-time imaging capabilities, has been explored for use in battery research. However, existing techniques have significant limitations: conventional single-window electrolytic cell designs cannot simultaneously monitor the evolution of the positive and negative electrode interfaces; the size and light transmittance of the observation window are insufficient for long-term, high-resolution observations; and there is a lack of a universal platform adaptable to the diverse observation needs of different battery systems (such as lithium metal batteries and iodine / bromine batteries). Therefore, there is an urgent need to develop an in-situ observation method and apparatus capable of simultaneously, comprehensively, and in real-time monitoring of the dynamics of the internal interfaces of batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to solve the following technical problems: existing in-situ optical observation technologies cannot synchronously and correlate the dynamic evolution process of the interface between the positive and negative electrodes inside the battery; it is difficult to obtain intuitive information on interface chemical reactions (such as polyhalogen complexation and transformation) in real time; there is a lack of effective visualization methods for the formation and action mechanism of dynamic interface layers (such as oil phase complexes); existing devices have poor versatility and cannot adapt to the observation needs of various battery systems.

[0006] To achieve the above objectives, the present invention provides a method for detecting batteries based on in-situ optical microscopy, characterized by comprising the following steps: Step 1, Electrolytic Cell Assembly: An electrolytic cell is provided. The main body of the electrolytic cell is made of a chemically inert and insulating material. The main body has parallel positive electrode cells, negative electrode cells, and reference electrode cells, forming a three-electrode system. Independent transparent observation windows are provided above the area of ​​the main body facing the positive electrode cell and above the area facing the negative electrode cell, respectively. The transparent observation windows are sealed to the main body under high pressure by O-rings. Step 2, Electrode and electrolyte assembly: In an inert atmosphere glove box, install the negative electrode, positive electrode and diaphragm into the corresponding electrode slots, inject the appropriate electrolyte and then seal the electrolytic cell. Step 3, Synchronous Testing: Fix the sealed electrolytic cell onto the stage of the inverted optical microscope, connect the three electrodes of the electrolytic cell to the electrochemical workstation, and set the charge-discharge test program; synchronously acquire morphological evolution images of the positive and negative electrode observation windows at preset time intervals using imaging equipment, and simultaneously acquire voltage and current data through the electrochemical workstation. Step 4, Data Correlation Analysis: The collected optical image data and electrochemical parameter data are correlated over time to obtain the correspondence between the dynamic evolution of the battery's internal interface and its electrochemical performance.

[0007] Furthermore, the main tank is made of polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK).

[0008] Furthermore, the transparent observation window is made of sapphire or quartz glass. Furthermore, in step 2, the negative electrode is a lithium metal foil or a zinc foil; the positive electrode is an iodine-carbon composite electrode or a potassium bromide electrode.

[0009] Furthermore, in step 2, the electrolyte is an ether-based electrolyte or an aqueous electrolyte. The ether-based electrolyte is suitable for lithium metal battery systems, and the aqueous electrolyte is suitable for zinc-iodine battery systems.

[0010] Furthermore, in step 3, the imaging device is a digital camera or a high-speed video camera, and the preset time interval is 1-30 seconds.

[0011] This invention also provides an electrolytic cell for in-situ optical microscopy, comprising a main cell body, a transparent observation window, a sealing assembly, and an electrode connection structure; the main cell body is made of a chemically inert and insulating material, and has a positive electrode slot, a negative electrode slot, and a reference electrode slot inside, with the three electrode slots distributed in parallel; there are two transparent observation windows, corresponding to the upper areas of the positive and negative electrode slots respectively, forming independent observation channels with the main cell body; the sealing assembly is an O-ring, disposed on the contact surface between the transparent observation window and the main cell body; the electrode connection structure includes a positive electrode terminal, a negative electrode terminal, and a reference electrode terminal, respectively disposed corresponding to each electrode slot.

[0012] Furthermore, the main cell material is polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK), and the transparent observation window material is sapphire or quartz glass.

[0013] The beneficial effects of this invention are: In the iodine cathode battery system without inhibitors, a light brown electrolyte was clearly observed near the cathode interface during the initial charging phase. The brown area expanded and diffused with increasing charging depth, confirming the formation and migration of polyiodides. Furthermore, the diffusion rate closely correlated with battery capacity decay and coulombic efficiency reduction. With the addition of specific inhibitors, the electrolyte remained transparent during charge-discharge cycles, confining polyiodides near the electrode surface. This directly demonstrates that inhibitors suppress the loss of active materials through complexation or steric hindrance. In the bromine cathode battery system, a bright yellow color rapidly appeared at the cathode interface without inhibitors, forming a concentration gradient diffusion. This diffusion rate was faster than that of polyiodides, revealing the underlying reason for the more severe self-discharge and capacity decay in bromine cathode batteries. In bromine cathode batteries with specific additives, a stable oil-phase complex layer 5-10 micrometers thick was formed at the cathode interface during charging, effectively blocking the diffusion of polybrominates into the bulk phase, providing direct experimental evidence for the mechanism of additive action.

[0014] For the first time, synchronous and correlated observation of the positive and negative electrode interfaces within the same device has been achieved, breaking through the limitations of traditional single-window designs and providing intuitive evidence for understanding the performance degradation mechanism of full cells. Through the direct correlation between optical signals (morphology, color) and electrochemical parameters, key interfacial processes such as multihalide complexation, dendrite suppression, and oil phase layer formation are visualized and confirmed, deepening the understanding of interfacial mechanisms. It is applicable to various liquid battery systems such as lithium metal batteries and iodine / bromine batteries, and allows for flexible replacement of electrode materials and electrolytes to meet the interface research needs of different systems. It provides a reliable in-situ detection platform for screening high-performance electrode materials, evaluating electrolyte additives, and optimizing interfacial modification strategies, accelerating the research and development process of high-performance batteries. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the electrolytic cell device of the present invention.

[0016] Figure 2 This is a schematic diagram of the connection of the synchronous testing system of the present invention.

[0017] Figure 3 These are in-situ observation images of polyiodide shuttle in the iodine cathode battery system of this invention without the addition of inhibitors.

[0018] Figure 4 In-situ observation images of polybromination shuttle in the bromine cathode battery system with added inhibitors for this invention.

[0019] Figure 5 This is an in-situ observation image of the shuttle movement of polybrominates in the bromine cathode battery of this invention.

[0020] Figure 6 In-situ observation images of the formation of the polybrominated interfacial complex layer in the bromine cathode battery system for which inhibitors have been added in this invention. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in further detail below with reference to specific examples. These examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0022] To keep the embodiments concise, only the parts related to the present invention are schematically shown in the embodiments, and they do not represent the actual structure of the product. In addition, to make the embodiments concise and easy to understand, only one of the components with the same structure or function in the embodiments is schematically drawn, or only one of them is marked.

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, specific implementation methods of the present invention will be described below. Obviously, those skilled in the art can obtain other similar structural products and other implementation methods based on this embodiment without any creative effort.

[0024] This invention provides a method for battery assembly and testing using in-situ optical microscopy, the specific technical solution of which is as follows: (I) Electrolytic Cell Structure Design The electrolytic cell includes a main cell body, a transparent observation window, a sealing assembly, and an electrode connection structure. Main cell body: Made of chemically inert and insulating material (polytetrafluoroethylene PTFE or polyether ether ketone PEEK), with parallel positive electrode, negative electrode and reference electrode cells inside, forming a three-electrode system to ensure the accuracy of electrochemical testing; Transparent observation windows: Independent transparent observation windows are set above the areas of the main cell directly opposite the positive and negative electrode cells. The materials used are sapphire or quartz glass to ensure high light transmittance and structural stability, so as to realize synchronous in-situ observation of the positive and negative electrode interfaces. Sealing assembly: O-rings are used for high-pressure sealing between the window and the pool body to prevent electrolyte leakage and ensure the stability of the testing process; Electrode connection structure: Each electrode slot is equipped with a positive electrode connection port, a negative electrode connection port, and a reference electrode connection port for easy connection to an electrochemical workstation.

[0025] (II) Battery Assembly and Testing Procedures Electrolytic cell assembly: Assemble the electrolytic cell according to the above structure, ensuring that the observation window is sealed and the electrode terminals have good contact; Electrode and electrolyte assembly: In an inert atmosphere glove box, the negative electrode (lithium metal foil, zinc foil, etc.), positive electrode (iodine-carbon composite electrode, potassium bromide electrode, etc.) and separator are respectively installed into the corresponding electrode tanks, and a suitable electrolyte is injected (ether-based electrolyte is used for lithium metal batteries, and aqueous electrolyte is used for zinc-iodine batteries). After the assembly is completed, the electrolytic cell is sealed and removed from the glove box. Synchronous optical-electrochemical testing: The electrolytic cell is fixed on the stage of an inverted optical microscope, and the three electrodes are connected to the electrochemical workstation through the electrode terminals. The charge-discharge test program (such as voltage range, number of cycles, etc.) is set. The imaging device (digital camera or high-speed video camera) is started to synchronously acquire morphological evolution images of the positive and negative electrode observation windows at preset time intervals (such as 30 seconds). At the same time, the electrochemical workstation acquires electrochemical data such as voltage and current in real time. Data correlation analysis: The collected optical image data (morphological changes, color changes) and electrochemical parameter data are aligned and correlated over time to establish the correspondence between interface dynamic evolution (such as dendrite growth, polyhalide diffusion, complex layer formation) and electrochemical performance (capacity, coulombic efficiency, etc.).

[0026] Example 1: Multiiodide shuttle observation of iodine cathode battery system Electrolytic cell preparation: The main cell body is made of PTFE material, and the transparent observation window is made of sapphire glass and sealed with an O-ring; Electrode assembly: In an inert atmosphere glove box, zinc foil (100μm thick) is used as the negative electrode, iodine-carbon composite electrode (30wt% iodine content) is used as the positive electrode, glass fiber diaphragm is used as the diaphragm, and 1mol / L Zn(OTf)2 aqueous electrolyte is used as the electrolyte. Test parameter settings: Fix the electrolytic cell on the stage of an inverted optical microscope, connect it to a CHI660E electrochemical workstation, and set the charge / discharge voltage range to 0.4-1.4V and the current density to 0.1mA / cm².2 The imaging device used is a digital camera, with a shooting interval of 30 seconds; Results: In the initial stage of charging (voltage rises to 1.0V), the electrolyte near the positive electrode interface turns light brown. As the voltage rises to 1.4V, the brown area gradually expands and spreads to the entire electrolyte area. Simultaneous electrochemical data show that the capacity decay rate is 25% / 100 cycles and the coulombic efficiency drops to 82%, confirming that polyiodide shuttle causes performance degradation.

[0027] Example 2: Testing of Iodine Cathode Cells with Added Inhibitors The electrolytic cell and electrode configuration are the same as in Example 1, except that 5 wt% of a specific complexing agent is added to the electrolyte. The test parameters are the same as in Example 1; Results: Throughout the entire charge-discharge cycle, the electrolyte remained optically transparent, and only a brief darkening of color was observed at the positive electrode interface. No brown area diffusion was observed. Electrochemical data showed that the capacity decay rate decreased to 3% / 100 cycles, and the coulombic efficiency remained stable at 97%, proving that the inhibitor effectively suppressed polyiodide shuttle.

[0028] Example 3: Observation of the oil phase complex layer in a bromine cathode battery system The preparation of the electrolytic cell is the same as in Example 1; Electrode assembly: Zinc foil is used for the negative electrode, potassium bromide composite electrode (potassium bromide content 40wt%) is used for the positive electrode, and 2mol / L KBr aqueous electrolyte is used with 3wt% interface modifier added. Test parameters: Charge / discharge voltage range 0.6-1.8V, current density 0.2mA / cm² 2 The high-speed camera captures images at 15-second intervals. Results: During charging (voltage rises to 1.7V), a uniform oil phase complex layer gradually forms at the positive electrode interface, with the thickness increasing to 8μm with the charging depth, and the electrolyte remains transparent throughout; after 100 cycles, the capacity retention rate is 92%, which is significantly better than the system without inhibitors (capacity retention rate of 65%).

[0029] 1. In-situ observation of polyiodide shuttle in an iodine cathode battery system: In an iodine cathode battery system without any added inhibitors, the device of this invention clearly recorded the dynamic shuttle process of polyiodides using an in-situ optical microscope. For example... Figure 3 As shown, the electrolyte near the positive electrode interface begins to turn light brown during the initial charging stage. As the charging depth increases, the brown area gradually expands and diffuses downwards to cover the entire electrolyte region. This phenomenon confirms that I... - After being oxidized to form I2, it further reacts with I... - The reaction produces soluble I3 - and I5 -Polyiodides are present. Especially under high-rate charge-discharge conditions, the brown diffusion rate is significantly accelerated, indicating an intensified polyiodide shuttle phenomenon, which is highly consistent with the electrochemical test results of battery capacity decay and coulombic efficiency reduction.

[0030] 2. The inhibitory effect of additives on polyiodide shuttle showed significant differences in observation results when specific inhibitors were added to the same battery system. For example... Figure 4 As shown, the electrolyte remained optically transparent throughout the entire charge-discharge cycle, without any significant color change. Analysis of consecutive images of the window region revealed only a brief darkening of color at the positive electrode interface; however, the polyiodides were effectively confined to the vicinity of the electrode surface and failed to diffuse into the electrolyte phase. This result directly demonstrates that the additives successfully suppressed the dissolution and loss of active materials by forming insoluble complexes with the polyiodides or through steric hindrance, providing direct evidence for improving battery cycle stability.

[0031] 3. Study on the shuttle behavior of polybrominates in bromine cathode batteries. This invention also yielded important findings in the observation of bromine cathode battery systems. For example... Figure 5 As shown, without the addition of inhibitors, a bright yellow area rapidly appears at the positive electrode interface during charging, and gradually forms a significant concentration gradient diffusion over time. This yellowing change is due to the presence of polybrominates (mainly Br3). - The characteristic optical response of polybrominates is noteworthy. It is worth noting that, compared to the brown diffusion of polyiodides, the yellow diffusion of polybrominates is faster and covers a wider area, indicating a more significant shuttle effect. This also explains the fundamental reason why bromine cathode batteries typically face more severe self-discharge and capacity decay problems.

[0032] 4. The most prominent discovery regarding the formation and protection mechanism of the interfacial complex layer appeared in experiments with bromine cathodes containing specific additives. For example... Figure 6 As shown, a stable oil-phase complex layer gradually forms at the positive electrode interface during charging. High-resolution time-series image analysis reveals that this layer exhibits distinct phase interface characteristics, with its thickness increasing with charging depth, reaching a maximum of 5-10 micrometers. Crucially, after this layer forms, the electrolytic liquid phase remains colorless and transparent, indicating that the polybrominates are effectively confined within the interface layer. This synergistic mechanism of physical barrier effect and chemical complexation provides intuitive experimental evidence for understanding the mechanism of action of additives. The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for detecting batteries based on in-situ optical microscopy, characterized in that, Includes the following steps: Step 1, Electrolytic Cell Assembly: An electrolytic cell is provided. The main body of the electrolytic cell is made of a chemically inert and insulating material. The main body has parallel positive electrode cells, negative electrode cells, and reference electrode cells, forming a three-electrode system. Independent transparent observation windows are provided above the area of ​​the main body facing the positive electrode cell and above the area facing the negative electrode cell, respectively. The transparent observation windows are sealed to the main body under high pressure by O-rings. Step 2, Electrode and electrolyte assembly: In an inert atmosphere glove box, install the negative electrode, positive electrode and diaphragm into the corresponding electrode slots, inject the appropriate electrolyte and then seal the electrolytic cell. Step 3, Synchronous Testing: Fix the sealed electrolytic cell onto the stage of the inverted optical microscope, connect the three electrodes of the electrolytic cell to the electrochemical workstation, and set the charge-discharge test program; synchronously acquire morphological evolution images of the positive and negative electrode observation windows at preset time intervals using imaging equipment, and simultaneously acquire voltage and current data through the electrochemical workstation. Step 4, Data Correlation Analysis: The collected optical image data and electrochemical parameter data are correlated over time to obtain the correspondence between the dynamic evolution of the battery's internal interface and its electrochemical performance.

2. The method according to claim 1, characterized in that, The main tank is made of polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK).

3. The method according to claim 1, characterized in that, The transparent observation window is made of sapphire or quartz glass.

4. The method according to claim 1, characterized in that, In step 2, the negative electrode is a lithium metal foil or a zinc foil; the positive electrode is an iodine-carbon composite electrode or a potassium bromide electrode.

5. The method according to claim 1, characterized in that, In step 2, the electrolyte is an ether-based electrolyte or an aqueous electrolyte. The ether-based electrolyte is suitable for lithium metal battery systems, and the aqueous electrolyte is suitable for zinc-iodine battery systems.

6. The method according to claim 1, characterized in that, In step 3, the imaging device is a digital camera or a high-speed video camera, and the preset time interval is 1-30 seconds.

7. An electrolytic cell for in-situ optical microscopy detection, characterized in that, The device includes a main cell body, a transparent observation window, a sealing assembly, and an electrode connection structure. The main cell body is made of a chemically inert and insulating material and has a positive electrode slot, a negative electrode slot, and a reference electrode slot inside, with the three electrode slots distributed in parallel. There are two transparent observation windows, corresponding to the upper areas of the positive and negative electrode slots respectively, forming independent observation channels with the main cell body. The sealing assembly is an O-ring, which is set on the contact surface between the transparent observation window and the main cell body. The electrode connection structure includes a positive electrode terminal, a negative electrode terminal, and a reference electrode terminal, which are respectively set for each electrode slot.

8. The electrolytic cell according to claim 7, characterized in that, The main cell body is made of polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK), and the transparent observation window is made of sapphire or quartz glass.

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