Exploration of the cause of hydrogen in three yuan lithium ion battery

　　Author ：Iflowpower – Portable Power Station Supplier

Abstract: This effort explores the cause of H2 in a ternary lithium-ion battery (Libs) through gas chromatography (GC) and rechargeable symmetric lithium ion battery. In addition to the recognized hydrogen, it is important that the work is important to explore the proton electrolyte oxide (R-H +) and carbonate to form two hydrogen generation mechanisms related to the three yuan lithium ion battery. In view of the associated product of R-H + as the positive and negative poles deposited on the negative surface, graphite / graphite negative electrode soft bag with charge-discharge power, NCM / NCM (lini0.

6co0.2Mn0.2O2 is ncm) Positive soft bag symmetrical battery and graphite / NCM soft bag full battery.

The side surface of this result verifies that the R-H + mechanism is established, i.e., H2 is generated by the positive electrode to deposit the product R-H + reduction, so the individual positive electrode symmetry battery has no H2.

In order to exclude the interference of hydrogen to R-H + mechanism, the normal electrode symmetry battery of the R-H + mechanism is selected, and after the cycle is selected, the GC results were detected after the micro moisture recirculation. Description of the symmetric battery, the original micro moisture is negligible for the result of final hydrogen. Finally, the positive electrode symmetrical battery is selected to verify the carbonate, according to the previous experimental conclusion, this system can exclude the effect of R-H + and moisture on the final hydrogen production results.

After the high temperature storage and high temperature overcharge test, the positive electrode symmetry battery is not detected inside H2 inside, so the carbonate is not established. Key words: gas chromatography; symmetric battery; H2; R-H +; picture lithium ion battery is the core component of green electric cars. However, during the long-term operation of the electric vehicle, due to the failure of the battery structural components due to gas expansion, electrolyte leaks often occur, and the safety accident is often occurred.

In addition, gas chromatography shows that H2 is higher in gas components of the failure battery. Whether it is an incorporated or battery management system (BMS) monitoring in the system, it is urgent to analyze the angle of H2 gasification mechanism. Among them, the electrode, diaphragm and electrolyte moisture exceeding the standard is an important reason for hydrogen in lithium ion batteries.

Because water is easy to generate H2 (H2O + E- → OH- + 1 / 2H2) at 1.2V (vs.li/li +).

Wu et al. Found that when the linear carbonate was sintered at 80 ° C for 120 h, the H2 was detected, and it was important that the carbonate was formed into a picture. In recent years, a new H2 gas mechanism, a high temperature or high potential (R-H +) is proposed from the positive electrode to the negative electrode and then restore to H2 [9, 11], due to BMS to battery system Voltage or temperature monitoring abnormality.

This paper uses a symmetric lithium ion battery having charge and discharge capacity, and the gas chromatography (GC) analysis of the gas that occurs during the successful collection of the softbell battery test using the online gas extraction device. Exploring the proton electrolyte oxide (R-H +) and carbonate is a picture of two hydrogen generation mechanisms related to the three-dimensional lithium ion battery. 1 Experiment 1.

1 Symmetrical Battery Cooking This paper is a fresh electrode sheet, which is from Guoxuan High-tech Power Energy Co., Ltd., three-yuan material NCM and artificial graphite raw materials from suppliers Xiamen Tungsten and Shenzhen Beitry New Energy Materials Co.

, Ltd. The side of the bilateral coating positive and negative pole sheets were respectively wiped with N-methylpyrrolidone (NMP) and deionized water, and 4 h was dried in an oven at 80 ° C, and the negative electrode sheet and the positive electrode sheet were cut into fixed sizes 42 mm × 53 mm and 40mm × 50mm. In order to prevent the polar cirrus from expanding due to negative electrode swelling, a symmetrical battery should be particularly important to take the battery level rubber step on the bare copper foil after the side of the negative electrode plate is wiped off.

Single layer laminate soft bag battery (65mA · h) consists of artificial graphite negative electrode and ternary positive electrode. The electrolyte component is 1 mol / llipf6, Ec: EMC (mass ratio 3: 7, Shenzhen Xinzhibang Technology Co., Ltd.

, EC purity 99.95%, EMC purity 99.9%, water content <20ppm, 1ppm = 10-6).

Before the electrolytic solution is filled, the positive and negative electrode sheet is vacuumped in a dry box at 80 ° C for 10 h. Soft bag battery liquid is 0.5g.

All batteries are cycled in a C / 20 magnification, then cycled with C / 10 magnification for 3 weeks (the voltage range is 3 ~ 4.2V). The battery having an approximate capacity is selected, charged to 4.

2V (100% SOC) without a constant voltage, and discharged from C / 10 to 3V (0% SOC), then dismanting the battery. After the dismantling of the polar film is soaked by DMC, the positive (negative) pole re-assembled from the battery in a 100% SOC and 0% SOC state is reunited into a positive electrode (negative) symmetrical battery. Due to the difference in the internal parallel content of the symmetric battery, the charge and discharge capacity of the lithium-ion battery can be realized.

The above experiment is completed in the dew point of -50 ° C. The detailed process is shown in Figure 1. Figure 1 Rechargeable symmetric battery detailed illustration 1.

2GC online gas test device Due to low gas content of single layer lamination soft bag battery, gas chromatography detection. A polypropylene (PP) tube is inserted into the aluminum plastic film to extract the gas, and seal the PP tube through the T type silica gel. The gas chromatography needle can be pumped through silica gel in multiple times while ensuring sealing.

The successful production of the device should pay attention to the following three points: 1 The tube material is the same as the material of the sealing layer in the aluminum film. It is the PP material; 2PP tube inner diameter (4mm × 2.5mm) is the same as the T-type silicone rubber plug outer diameter (2.

5mm) 3 copper wire (about 0.5 mm diameter) should be inserted into the PP tube to ensure that the pick-up passage is reserved after the PP tube and aluminum plastic film are sealed, and the aluminum plastic film sealing conditions are 185 ° C hot press 20s, and the final online gas collecting device is shown in Figure 2. Figure 2 Soft bag battery online gas picking device 1.

3 parallel experiments Designed to explore H2 in three-yuan lithium ion battery, this paper designed three sets of parallel experiments, and detects the generated gas ingredients of the generated by gas chromatography: 1 Making graphite / graphite negative electrode Symmetric battery, the negative electrode gas component is separated, excluded from the gas component interference from the positive electrode, due to the assembled graphite plate, is disassembled from the whole battery after the circulation, and therefore, the negative surface may remain in the negative electrode Surrounded product R-H +; 2 Making NCM / NCM positive electrode symmetry battery, separating the positive electrode gas content, excluding the interference from the negative gas gas ingredient, and simultaneously monitor the gas components of the oxidation process of the positive electrode symmetry battery; 3 graphite / NCM Soft bag fully battery to see any gas associated with the intersecting of the electrodes between the gaseous components of the graphite negative electrode and NCM positive electrode. The composition of the sampling gas is analyzed by gas chromatography (Shimad GCNexis2030). The detector is the barrier discharge electropper detector (BID).

The temperature of the gas chromatography oven is set to 300 ° C, and helium is used as carrier gas. Gas retention time (RT) is 20 min. After the test test, insert the silicone plug in the soft bag battery PP tube to collect the gas in the soft bag battery PP, then immediately inject the GC equipment test.

2 Results and Discussion 2.1 Determination of a symmetric battery charge voltage range is composed of two batteries from two capacities (capacity Q) but different of SOC. For examples in A and B, if the A battery is 100% SOC, B battery is 0% SOC.

The two batteries are disassembled into a negative symmetry battery, and the negative symmetry battery capacity is Q, the same, the assembled positive symmetry battery capacity is still Q. Therefore, within the selected voltage range, the charge and discharge capacitance of the positive and negative symmetric battery should be similar to the whole battery. The positive electrode symmetry battery consists of a positive electrode sheet of the disassembled 100% SOC and 0% SOC.

When the node symmetry battery is lowered from a half state (ie 50% SOC), the voltage of the positive electrode symmetry battery should be 0V. In order to make full use of additional 50% SOC capacity, negative voltage should be loaded to supply additional energy to promote LI + migration. Therefore, the voltage range of the positive electrode symmetry battery should be symmetrically distributed on both sides of 0V.

When the node symmetry battery is fully charged, the electrode side is completely deesed, and the side is completely embedded in the lithium state, so it can be fully charged (completely delaid) and empty electricity (completely delaid), completely de-lithium state) and empty electricity (completely de-lithium state) and empty electricity (completely delaid) The potential difference between the state is obtained from its substantially voltage range. Similarly, the voltage range of a negative symmetric battery can be obtained. The normal voltage range of the positive and negative buckle semi-battery corresponding to the whole battery 3 ~ 4.

2V is 3 ~ 4.25V and 0.005 ~ 2V, respectively.

The voltage range of the positive and negative symmetric battery is temporarily set to -1.2 ~ 1.2V and -2 ~ 2V.

In summary, symmetrical adjustment voltage range, so that the symmetrical battery capacity is consistent with the full battery capacity. Finally, the voltage range of the positive symmetry battery is -1 to 1V, the voltage range of the negative symmetric battery is -2 to 2V. The corresponding charge and discharge curve is shown in Figure 3.

Figure 3 Fence-Board full-battery, positive symmetric battery, and negative symmetric battery charge and discharge curve Figure 2.2 In order to obtain reliable experimental conclusions, the gas component analysis in different experimental environments is selected. 0.

1C / 0.1C cycle test And abnormal overcharge test. The experimental system consists of a positive symmetrical battery, an negative symmetrical battery, and a full battery.

After 20 times in 0.1c / 0.1c, the gases in the three systems are shown in Figures 4 and 1.

Figure 40.1C / 0.1C magnification 20 weeks, GC chromatography detected full-battery, negative symmetric battery, and positive symmetric cells generated in symmetric cells 10.

1c / 0.1c magnification 20 weeks, GC chromatography detected Detailed gas component shown in each cell, a negative electrode symmetric battery, and a positive electrode symmetric battery, and the value of the Y-axis represents the percentage of the detection gas. H2 has an H2 in the full battery and negative symmetry battery, and the normal symmetry battery has no H2.

In summary, different from the previous result, R-H + can appear in the normal voltage range, excessive or high temperature is not necessary to form the necessary conditions of R-H +. The gas ingredient marked in the figure is determined by the corresponding standard spectrum database. Standard hybrid gases contain 10 kinds of gas in lithium ion batteries, including H2, O2, N2, CH4, CO, CO2, C2H4, C2H6, C3H6 and C3H8.

Among them, the unknown gas volume fraction is less than 0.8%, and the total ratio is calculated. Further, since N2 is not included in the lithium ion battery gas, N2 may detect N2 may be caused by introducing air during gas extraction, so the O2 volume of the O2 in this paper except for the proportion of air (nitrogen and oxygen).

Volume ratio is 81.17:18.83, the details are shown in Table 1).

At the same time, Figure 5 shows the impedance spectrum of 3 strain after 20 weeks of cycle. All EIS tests are completed in 50% SOC. The voltage corresponding to the whole battery, the negative symmetric battery and the positive electrode symmetry battery are 3.

65V, 0V, and 0V, respectively. The high frequency region is caused by the SEI film impedance, and the semicircle located in the intermediate frequency region corresponds to the charge transfer impedance RCT, RCT is an important factor affecting battery performance. Since there are two identical electrodes in the symmetric battery, its value is equal to 2RCT.

As shown in Table 2, the charge transfer resistor RCT of the whole battery, a negatively symmetric battery, and the charge transfer resistor RCT of the positive symmetric battery are 1.98, 1.92 and 0.

86Ω, respectively. Compared with the negative symmetry battery, the whole battery exhibits a high RCT value. Because R-H + is constantly generated and consumed in the full battery, the by-product is constantly accumulated in the negative surface, and the shuttle of lithium ions is largely hindered.

In contrast, there is no R-H + in the positive electrode symmetry battery, so there is no corresponding by-product deposition, the RCT impedance is minimum. Figure 5 Full-cell, negative symmetric battery and positive symmetry battery After 20 weeks of 0.1C / 0.

1C magnification, the half-electricity (corresponding voltage is 3.65V, 0V, and 0V) at room temperature 25 ° C is tested. The whole battery, negatively symmetric battery and positive symmetry battery impedance spectrum fitting results Next, on the basis of these three systems, the transition experiment is continued, and the specific steps of over charge are: the battery charges to 1.

5Vmax in 1C magnification (Vmax For the battery charging upper limit voltage), there is no fire, explode, and leakage, which is passed after standing for 1h. The three systems are overcharted, and the gas is taken to collect gas for GC test. The corresponding GC results in Figures 6 and 3 indicate that H2 is generated in a whole battery and an negative symmetry battery, but there is no in the positive symmetry battery.

The result is consistent with the GC results of the conventional cycle test. This data is calculated exactly the same as the data in Figures 4 and 1. Figure 6GC chromatography detected full battery, negative symmetric battery and positive electrode symmetric tabs 3 full battery, negatively symmetric battery, and positive symmetric battery over charge, each battery generated by the detailed gas component of each battery After the normal temperature cycle and overcharge test, the GC results show that H2 appears in a soft bag full battery and an negative symmetry battery, and the positive electrode symmetry is not.

The side surface of this result verifies that the R-H + mechanism is established, i.e., H2 is generated by the positive electrode to deposit the product R-H + reduction, so the individual positive electrode symmetry battery has no H2.

In order to exclude the interference of hydrogen on R-H + mechanism, hydrogen is selected from the micro moisture reduction in the battery, and the positive electrode symmetry of hydrogen will not appear after the cycle, the syringe is inserted into the silica gel plug to add trace moisture, 0.1C / 0.1C cycle 3 weeks, GC results detection To hydrogen (Figure 7).

Description of the symmetric battery, the original micro moisture is negligible for the result of final hydrogen. Figure 7 Positive Symmetry Battery Injecting Trace Water 0.1C / 0.

1C Cycles 3 weeks After the GC test results Next, further explore the mechanism of carbonate decomposition. According to the literature, H2 is caused by a carbonate solvent at 80 ° C for 120 h. In the previous experimental results, the positive electrode symmetric battery was selected to eliminate moisture and R-H + mechanism for interference of carbonate to form a picture mechanism, and a high temperature storage and high temperature overcharge test of the positive electrode symmetry battery were selected.

Hydrogen. Therefore, the carbonate solution is not established. 3 Conclusions (1) After 20 cycles or overcharge experiments, GC results show that all of the total battery and negatively symmetry batteries have H2, and the positive electrode symmetry battery is not H2.

The side surface demonstrates the presence of proton electrolyte oxide (R-H +), that is, R-H + as an associated product between the positive and negative elements, by the positive electrode production, deposition has hydrogen in the negative electrode, so a separate positive electrode symmetry battery has no H2 appearance. Positive electrode symmetry battery electrode surface by-product deposition amount is small, and the charge transfer impedance is minimized after 20 weeks of cycle. (2) After 20 weeks of the positive electrode symmetry battery, re-injection of micro moisture continued to cycle 3 weeks, GC results detect H2, indicating that the original micro moisture on the inside of the symmetry battery is negligible.

(3) Select the positive symmetry battery to further verify the hydrolysis of the carbonate. In summary, the positive symmetry battery can exclude micro moisture and R-H + on the effect of hydrogen verification results in a picture mechanism of carbonate. Even after high temperature storage and high temperature overcharge test, the positive electrode symmetry battery does not have hydrogen.

Therefore, the carbonate solution is not established. 引用本文：袁雪芹,杨雷.三元锂离子电池氢气出现原因探索[J].

储能科学与技术,2021,10(01):150-155.YUANXueqin,YANGLei.ExplorationofthecauseofhydrogengenerationinNCMlithium-ionbatteries[J].

EnergyStorageScienceandTechnology 2021, 10 (01): 150-155. Corresponding author: Yuan Xueqin (1989-), female, lecturer, research direction is lithium ion battery material, E-mail: 22000023@wxc.edu.

cn. .