CR1632 battery

Research progress of CR1632 battery formation technology

Abstract: CR1632 battery production process needs to be formed to achieve electrode wetting and fully activate electrode materials. At the same time, during the first charging process, as lithium ions are embedded in the negative electrode, the electrolyte components undergo a reduction reaction at the negative electrode to form a stable solid electrolyte interface film (SEI film) to prevent the irreversible consumption of electrolyte and lithium ions in the subsequent cycle. Therefore, this technology is of extraordinary significance to battery performance. The effect of formation directly affects the subsequent performance of lithium batteries, including storage performance, cycle life, rate performance and safety. However, for each single cell in the battery pack of electric vehicles, it takes several days or even weeks to go through the formation and aging process, resulting in lower battery production efficiency; a large number of charging and discharging equipment, temperature control equipment and environmental space increase the production cost of the battery; the traditional formation method cannot fully meet the high performance requirements such as capacity, life and safety. At present, many studies have been conducted to improve battery performance and reduce formation time by optimizing CR1632 battery formation technology, thereby reducing battery production costs. This review reviews the optimization of lithium-ion formation technology, introduces the significance of battery formation, cost analysis, various technical parameters and formation methods, and looks forward to future research and improvement directions.

Keywords: CR1632 battery; formation technology; solid electrolyte interface membrane; production efficiency; production cost

With the widespread use of lithium batteries, electrochemical energy storage has put forward higher requirements on the cost, energy density, cycle life and safety of lithium batteries. Nowadays, researchers have made great efforts to improve the comprehensive performance of batteries. The positive electrode, negative electrode, separator and electrolyte are all developing towards high energy density, high service life, high rate and high safety. However, the production cost of lithium batteries is still high. Controlling battery costs without sacrificing battery performance has become a major problem for current electric vehicle battery pack manufacturers. This review will start from the internal materials of the battery and introduce the formation/aging technology that is essential after the battery is prepared. It is particularly important to reduce the formation and aging time while obtaining high battery performance in the battery production process.

As we all know, in the CR1632 battery production process, after the preparation of the battery cell, there is a continuous process of injection, formation and aging, which has an important impact on the performance and service life of the CR1632 battery. After the aging is over, the defective batteries will be selected out through capacity testing (capacity separation), and some manufacturers will also grade the capacity of their batteries to reduce the differences in the subsequent use of the batteries. Therefore, all battery manufacturers will optimize the formation technology, and the technology between manufacturers varies to achieve the best cost-effective state. Because in addition to the high cost of battery materials, the battery formation/aging process is the most expensive process in battery manufacturing, accounting for up to 6.4% of the total cost.

Wood et al. mentioned that if a low rate is used for charging and discharging, the formation/aging process is a long and costly process. The first is the electrode wetting process. Sufficient and balanced cell wetting is particularly important in the formation/aging process. The porosity of the separator in the battery (the surface energy of polyethylene is 35-36mN/m, while that of polypropylene is only 30.1mN/m), the electrode binder and the conductive carbon black all hinder the wettability of the electrode. It takes a 12-24h cycle to achieve the basic electrode wetting process, and there are still a large number of small pore spaces that are not fully wetted. The wetting rate is closely related to the electrolyte properties (such as viscosity, surface tension), temperature, and porous electrodes (such as porosity and microstructure). Therefore, in order to ensure high-quality lithium batteries with consistent capacity, safety, and long life, the electrode wetting and formation process will consume 3-7 days and then nearly 2 weeks of aging time, which greatly increases the battery production cost. In addition to the time cost, a large number of battery testing systems and temperature control systems must be installed, which will consume a large amount of floor space and heat and electricity consumption and loss. Therefore, some research focuses on reducing the formation time to reduce the battery production cost.

On the other hand, obtaining better battery performance under the same preparation and processing technology is also an important factor in reducing battery costs. Graphite has stable cycle performance and ultra-high safety characteristics relative to lithium metal, and is one of the most common CR1632 battery negative electrode materials. During the first charge, some solvents in the electrolyte, such as alkyl carbonates or electrolyte film-forming additives, can be preferentially reduced and decomposed on the negative electrode surface to form a solid electrolyte interface film (SEI film). This passivation film has high ionic conductivity and electronic insulation, and Li+ can be freely embedded and removed through the passivation layer. The SEI film can inhibit the continuous decomposition of the electrolyte on the electrode and protect the electrode material structure. However, if a dense and stable SEI film cannot be formed in this process, then the exposure of the fresh electrode surface to the electrolyte will lead to the continuous decomposition of the electrolyte in the subsequent cycle process and the co-embedding of solvent molecules to cause graphite exfoliation. Therefore, how to form a stable SEI film during the first charge process, minimize the loss of active lithium and electrolyte decomposition, and effectively improve the cycle stability and safety of the battery during use is a major challenge to the battery formation/aging process.

After the electrolyte fully infiltrates the electrode, the SEI film at the electrode/electrolyte interface is formed in the formation stage and further chemically rearranged and adjusted in the aging stage. In this process, temperature, external mechanical pressure, charge and discharge current, charge and discharge voltage, state of charge, electrolyte composition and properties, battery chemical characteristics and other technical parameters affect the formation effect of the battery, resulting in differences in battery formation time and performance, which directly determines the production cost of the battery, as shown in Figure 1. Although major battery manufacturers now have standardized formation/aging processes, there are relatively few studies and analysis of the process mechanism, and the optimization of CR1632 battery formation/aging conditions is not comprehensive enough. This review summarizes and comments on optimizing the technical parameters and technical methods of CR1632 battery formation/aging, improving production efficiency and reducing production costs. First, an overview of the CR1632 battery formation/aging process and its cost analysis are introduced; secondly, the formation/aging technology and its impact on battery performance are analyzed; finally, the full text is summarized and the future research trend of the CR1632 battery formation/aging process is prospected, aiming to further reduce the production cost of lithium batteries and provide a basis and ideas for the development of an efficient and convenient formation method.

Figure 1 CR1632 battery formation technology

1 Overview of CR1632 battery formation technology and its cost analysis

Lithium batteries must form an excellent SEI film in the formation stage, which plays an irreplaceable role in the battery life and safety. After the electrode is injected, it will go through the active material infiltration stage. The wettability of the electrolyte to the electrode is an important factor that must be considered in the development of high-performance lithium batteries. Uneven electrolyte distribution in the electrode will lead to uneven current density and SEI film formation. Insufficient electrolyte infiltration will lead to a sharp decline in battery performance and lithium deposition on the graphite negative electrode. A CR1632 battery liquid absorption rate test method based on the permeability coefficient (COP) and solid permeability coefficient (SPC) as important parameters has been reported. The larger the electrolyte COP, the easier it is for the electrolyte to wet the electrode; similarly, the larger the electrode SPC, the easier it is to be wetted. The results show that the increase in lithium salt concentration in the electrolyte will lead to a decrease in the electrode wetting rate. The EC-EMC solvent system is more conducive to electrode wetting than the EC-DEC solvent system. The unrolled graphite negative electrode has higher wettability than the unrolled LiNi0.5Co0.2Mn0.3O2. In addition, a lattice-Boltzmann model was used to simulate the electrolyte distribution and wetting characteristics of the positive and negative electrodes of lithium batteries, and the porous electrode model was used to prove the influence of electrode wettability on battery performance and the dependence of capacity on the degree of wetting. The simulation results show that there are still widely distributed unwetted areas after the electrode wetting step. This incomplete wetting comes from the air wrapped in the electrolyte and electrode particles. Among them, the air in the electrolyte can be removed during the high-temperature aging stage, and the air in the negative electrode can be removed by repeated charging and discharging, and the graphite negative electrode expands/contracts. Low positive electrode wetting leads to low battery capacity, while low negative electrode wetting induces metal lithium deposition, which affects battery safety and cycle life.

In addition to the influence of battery material properties on electrode wettability, the formation/aging processes used by most manufacturers are not consistent. Technical parameters include temperature, external mechanical pressure, charge and discharge current, charge and discharge voltage, state of charge, etc. The charging methods include traditional constant current charging, constant voltage charging, currently commonly used step charging formation and high temperature pressure formation, and the latest reported "high rate charging + high voltage shallow cycle". Among the charging methods, constant current charging generally charges from an initial small current to a later large current. This method takes a long time and wastes resources seriously. The initial current of constant voltage charging is large, and then gradually decreases until the charging is completed and the current is zero. This method takes less time, but is more difficult to control. Improper selection of charging voltage will affect the battery. The existing technology of step-by-step charging formation is to vacuum the electrolyte and inject it in batches, seal it, and perform small current step-by-step charging activation, plus intermittent pulse discharge. Although this method can shorten the formation time, it may also cause incomplete electrochemical reaction. The high-temperature pressure formation method is to clamp the battery cell in the fixture cabinet, heat the formation fixture, and perform constant current charging after the battery cell is shelved. The gas inside the battery cell is squeezed out by pressurization. The temperature and applied pressure can be adjusted to complete the formation process. This method enhances the CR1632 battery formation effect and shortens the formation time by virtue of the advantages of simultaneous controllable temperature, external mechanical pressure and charge and discharge current, but the cost is relatively high. Therefore, it is necessary to further develop new formation methods to save time and cost and improve battery performance. In view of the importance of formation to the cost of battery production, Wood et al. counted the cost of electrode wetting and formation process. They believe that in industry, these two processes take 1.5 to 3 weeks, which will result in an unacceptable processing bottleneck and production cost. The typical formation process starts with a 2-3d soaking process at room temperature, followed by the first charge and discharge (a very low charge and discharge rate such as 0.05C/-0.05C), followed by another 1-2d soaking process; followed by a slightly faster charge and discharge (such as 0.1C/-0.1C) and a high temperature (50-60℃) soaking process; the third faster formation charge and discharge (about 0.25C/-0.25C). These formation cycles are often carried out at high temperatures, and the long cycle greatly increases the cost of battery production. The article conducts cost statistics for each link of the formation process, and the results are shown in Table 1. The formation cost of $22.6 per kilowatt-hour of energy accounts for 6.4% of the total battery manufacturing cost. It can be seen that the formation process is important in battery production. If the formation time is shortened by 60% to 75% using scientific and efficient formation technology, then $13.6 to $17 can be saved per kilowatt-hour.

Table 1 Cost distribution of lithium batteries for basic electrode processing conditions (estimated usable energy per kWh assuming 70% cycle discharge depth)

2 Formation technology parameters/methods and their impact on battery performance

2.1 Temperature

The formation and aging temperatures are decisive for the characteristics of the electrode SEI film. There are two opposing research results on the formation temperature. On the one hand, high-temperature formation is reported to have severe capacity loss. German et al. studied the effect of temperature on capacity loss and subsequent electrochemical performance during the formation of Lix(Ni1/3Co1/3Mn1/3)yO2(NCM)/graphite full cells, NCM half cells and graphite half cells, and showed that the sources of capacity loss of the positive and negative electrodes are different, among which the negative electrode capacity loss is mainly due to the formation of SEI film on the graphite surface, while the positive electrode capacity loss is attributed to the inhibition of NCM kinetics. With the increase of formation temperature, the irreversible capacity loss of the positive and negative electrodes increases, and due to the increase of lithium diffusion coefficient of NCM electrode, the capacity loss ratio of the positive and negative electrodes decreases, thus seriously deteriorating the battery performance of graphite. As shown in Table 2, the capacity loss of the electrodes during the two processes of formation at different temperatures and subsequent charge and discharge at room temperature. As the formation temperature rises, the capacity loss of the graphite negative electrode is attributed to the increased degree of decomposition of the electrolyte components. The capacity loss of the NCM positive electrode decreases due to accelerated kinetics, but the capacity loss caused by low-temperature formation can be partially recovered during the subsequent normal temperature cycle. Therefore, high-temperature formation has no advantage for the full battery, and both the positive and negative electrodes show severe lithium loss and decreased cycle stability of the graphite electrode. Similarly, Yan et al. compared the gap between the formation behaviors of graphite half-cells and NCM/graphite full cells at different temperatures and concluded that high-temperature formation leads to severe side reactions, low-temperature formation will form a SEI film with low ionic conductivity, and the SEI film formed by normal temperature formation has the best ionic conductivity and stability. Differently, Huang et al. proved that after high-temperature formation, the battery has a higher discharge capacity and better capacity retention. By investigating the cycling performance of LiNi1/3Co1/3Mn1/3O2/artificial graphite batteries at different formation temperatures (25°C and 45°C), the results show that the irreversible capacity loss decreases from 18.4% at 25°C to 10.5% at 45°C. High-temperature formation at 45°C is beneficial to reducing SEI film impedance and irreversible capacity loss, and the irreversible capacity loss under high-current formation conditions of 1.077mA/cm2 is only 12.8%. Also, with a higher transfer rate under high-temperature formation, a more uniform SEI film can be formed on the graphite negative electrode.

Table 2 (a) State of charge during the formation charging stage and (b) the capacity loss corresponding to the subsequent charge to 100% state of charge

Regarding the aging process, Lopez et al. believe that the most suitable temperature is determined by the previous formation conditions. For example, when formed at room temperature, a long cycle performance can be obtained at an aging temperature of 5°C; while when formed at a low temperature of 5°C, a high-temperature aging of 45°C can obtain the best cycle performance. At the same time, characterizing the composition of the negative electrode SEI film under different aging conditions helps us improve battery performance by optimizing battery aging conditions. After aging at an ambient temperature of 5°C, the SEI film thickness is thinner, the graphite signal peak is stronger, and the signal peaks of oxygen and fluorine are weaker; while the SEI film formed at an aging ambient temperature of 45°C is thicker, and the signal peaks of phosphorus and fluorine are stronger as the aging cycle increases.

2.2 External mechanical pressure

External mechanical pressure on lithium batteries has both advantages and disadvantages in existing literature reports. Advantages include better electrode contact, less lithium deposition, and less gas appearance and distribution. Disadvantages include the possibility of graphite expansion due to lower mechanical pressure and deformation caused by uneven pore closure of the diaphragm under higher pressure, which hinders the internal dynamics of the battery. Heimes et al. set different pressures and temperatures in a formation procedure including constant current charging-constant voltage charging-constant current discharge, and explored the time required for the three stages. The results are shown in Figure 2. When the external mechanical pressure increases from 0.05kN to 1.70kN, the constant voltage charging stage time is significantly reduced, while the constant current charging and discharging stage time is not much different. The whole process can save 14.7% of the formation time by adding external mechanical pressure. The article also proves that high external mechanical pressure has more potential to reduce battery formation time than high ambient temperature, so the possibility of saving battery cost is also greater. In addition, when high temperature and high mechanical pressure are combined, the battery temperature rises., which can inhibit the exothermic reaction of the battery.

Figure 2 Effect of thermal load and mechanical load on the entire formation cycle

2.3 Charge and discharge current

With the continuous exploration and understanding of the SEI film of the graphite negative electrode, its composition and structure and its importance to the electrode have gradually become clear. EIS (electrochemical impedance spectroscopy) studies have found that the impedance of the SEI film of the graphite negative electrode reaches the maximum in the voltage range of 0.8-0.3V, and the SEI film is completely formed during the first lithium insertion process. The SEI film is divided into two layers, the inner layer is mainly composed of inorganic substances, including Li2CO3, Li2O, LiF, etc.; the outer layer is mainly composed of organic products, such as alkyl lithium oxide (ROLi) and alkyl lithium carbonate (ROCO2Li). Ota et al. believed that the reaction on the electrode surface is a competitive process of passivation film formation and charge transfer. Due to the diffusion speed and migration number of different ions, the main electrochemical reactions occurring at different current densities are different, and the generated SEI film also has different properties. Therefore, it is particularly important to control the formation current density to obtain a uniform, dense and thin SEI film. The graphite anode will undergo a 10% volume expansion during the cycle, resulting in the rupture of the SEI film and further electrolyte decomposition. The composition and structure of the SEI film can be adjusted by adjusting the formation charge current, thereby optimizing the electrochemical performance of the graphite anode. Zhu et al. used Li/graphite half-cells to form at three different current densities: 0.02C, 0.1C, and 0.5C (1C=340mA/g). Subsequently, the charge and discharge cycle was performed at 0.5C. After 300 cycles, the capacity of 0.02C stabilized at 366.5mA·h/g, which was higher than 350.1mA·h/g and 338.2mA·h/g of 0.1C and 0.5C. The low current density formation is beneficial to the electrochemical performance, which can be attributed to the effective regulation of the SEI film, as shown in Figure 3. EIS and TEM characterization show that after low current formation, a thick and uniformly dense passivation layer is formed on the negative electrode surface, which effectively stabilizes the electrode/electrolyte interface, buffers the volume change of the graphite electrode in the subsequent cycle process, and prevents the continuous decomposition of the electrolyte caused by the active sites of graphite being exposed to the electrolyte, thereby improving the electrochemical performance of the graphite electrode. XPS shows that compared with high current density, the SEI film formed during the low current density formation process contains more organic lithium salts and less inorganic lithium salts, which can wrap the graphite electrode more evenly and protect the electrode material well.

Figure 3 (a) Formation of SEI film on graphite surface during formation stage and (b) Effect of formation current density on SEI film

2.4 Charge and discharge voltage

In addition to the current that can affect the formation of SEI film during the formation process, the selection of voltage range is also very important. Optimizing the voltage range can reduce battery capacity decay and save formation time. Lee et al. believed that the traditional formation process consumes a lot of time in the process of graphite lithium insertion after the formation of SEI film, so they explored the effect of different charging cut-off voltages on battery performance for LiCoO2/C cylindrical batteries. It was found that when the charge cutoff voltage was 3.6V, the SEI film was not fully formed, resulting in poor cycle performance; when the charge cutoff voltage was 3.7V, the SEI film was fully formed, and if the cutoff voltage was added, the battery electrochemical performance would not be improved. Therefore, 3.7V is the most suitable charge cutoff voltage for LiCoO2/C batteries. Similarly, compared with the formation charge cutoff voltage of 4.2V, when the NMC/graphite or Li/NMC battery was charged to 3.6V or 3.7V (50% SOC), the capacity difference in the subsequent full charge cycle was not obvious. Pathan et al. used NMC111/graphite button cells to explore different formation voltage intervals at 25°C. By taking 10 different voltage intervals between 2.6 and 4.0V for 10 times of charge and discharge, and then using a 0.5C rate in the voltage range of 2.5 to 4.2V for 500 charge and discharge cycles, the results are shown in Figure 4. The best battery performance corresponds to a formation voltage between 3.65 and 4.0 V, and the capacity retention rate after 500 cycles is 86%. Various characterization methods prove that the formation in the voltage range of 3.65 to 4.0 V forms a SEI film with lower impedance. This shows that the selection of the formation voltage range is very important for the battery's cycle performance, especially when the voltage window is at a high voltage (>3.65 V), the electrolyte is more likely to form a stable SEI film on the surface of the positive and negative electrodes.

Figure 4 Average battery capacity corresponding to the number of cycles in all different formation cases

2.5 State of charge

Battery state of charge (SOC) is also often optimized as an important formation technology parameter. It is closely related to the charge and discharge voltage in the previous section. For example, when optimizing the charge cutoff voltage of ordinary LiCoO2 or NMC batteries, charging to 3.6 to 3.7 V represents a charge close to the general battery (i.e., 50% SOC), which is an ideal choice in terms of performance and formation time. Lopez et al. compared the charge states of 25%, 50% and 75% during the formation of NMC-111/graphite soft-pack lithium batteries (for the same target charge state, it is divided into two methods: direct charging to the charge state and charging to 100% SOC first and then discharging to the charge state). They found that different charge states will cause different degrees of reaction during the aging process, affecting the properties of the SEI film and thus affecting the battery performance. The results show that the 25% charge state exhibits a large impedance before and after battery aging, and the capacity retention rate is lower than the other two charge states. The formation method corresponding to the best performance is to charge to 100% SOC first and then discharge 25% SOC, that is, the battery maintains a charge state of 75%, combined with room temperature aging, to obtain the highest first discharge capacity and capacity retention rate.

2.6 Formation method

The above is a summary of the exploration of chemical technical parameters, and the formation charge and discharge method used is relatively simple. Regarding the conventional charge and discharge procedures, Wood's research group believes that the long formation time seriously increases the battery production cost. Therefore, five different formation methods were optimized using LiNi0.8Mn0.1Co0.1O2 (NMC811)/graphite batteries, with cycles ranging from 10 to 86 hours. The shortest time of 10 hours includes a 6-hour soaking time and 0.5C charge and discharge once, and the electrode shows severe lithium deposition and poor electrochemical performance. The longest time of 86 hours includes a 6-hour soaking time and 0.1C charge and discharge 4 times, and the results do not show excellent cycle performance. The low impedance rise accompanied by excellent performance appeared in two medium-time formation methods, namely 26 hours (6 hours soaking time and 0.1C charge and discharge once) and 30 hours (6 hours soaking time and 0.1C charge and discharge once, followed by 0.5C charge and discharge once), especially the 30-hour formation method. Therefore, it is necessary to develop new formation methods to balance the formation time, rate performance, cycle performance and irreversible lithium deposition. Then, the research group proposed that the formation under high SOC state is conducive to the formation of passivation film on the surface of positive and negative electrodes due to the instability of electrolyte; but high SOC cannot simply control the battery at high voltage (at this time the current quickly drops to near 0), so a new formation method is used for NMC/graphite soft pack CR1632 battery. As shown in Figure 5, the three basic formation methods (baseline) include charging and discharging 5 times at C/20, C/10 and C/5, the time is 220h, 107h and 55h respectively, and the new formation method (alternative) is to charge to 4.2V at C/20, C/10 and C/5, and then shallowly cycle 4 times in the high voltage range of 3.9~4.2V at the same current density, and then discharge to 2.5V, the time is 68h, 42h and 21h respectively. Among them, the new 21h formation saves at least 6 times of time compared with the traditional C/20 formation (calculated based on the 3 cycles of C/20 in the production process). It is worth noting that the subsequent cycle performance has not been deteriorated, but the capacity retention rate has been improved. According to EIS, the SEI film formed by the new formation has a smaller impedance. On this basis, Wood et al. further used the high-voltage shallow cycle formation method to increase the formation rate to 1C and shorten the formation time to 14h again. The article believes that high-rate charge and discharge may affect the formation of the SEI film, but repeated shallow cycle formation in the high voltage range can form a robust SEI and CEI (positive electrode electrolyte interface film), because high voltage conditions can easily cause instability of the electrolyte solvent and lithium salt on the surface of the positive and negative electrodes. Therefore, after rapid formation using this method, the battery cycle performance is not affected, but the formation time is greatly reduced, reducing costs.

Figure 5 (a) Voltage curve: the blue line represents the basic formation method, and the orange line represents three new formation methods (the rate is marked as a); (b) The formation time corresponding to different formation methods

3 Summary and Outlook

In the production process of lithium batteries, the formation technology is particularly important. The formation of SEI film and CEI film largely determines the electrochemical performance of the battery, but the long formation time and a large number of equipment increase the battery production cost. The optimization of formation/aging technical parameters and the development of methods are imperative to improve battery performance and save formation time, thereby improving battery production efficiency and reducing production costs. At present, researchers have explored different technical parameters such as formation/aging temperature, external mechanical pressure, charge and discharge current, charge and discharge voltage, and state of charge. With the development of new methods, the understanding of this process is clearer. In different application fields, such as 3C, power or energy storage, the requirements for battery performance are also different, such as cycle, rate or storage. When pursuing different battery performance, the selection of formation conditions is particularly important. For example, in the electrolyte additive direction, if the circulating additive and rate additive are to achieve the best effect, the voltage range and temperature range used must be optimized accordingly. If the temperature is too high, the electrolyte solvent such as ethylene carbonate (EC) will decompose severely, resulting in a thicker film, which may reduce the rate performance of the battery; at the same time, the choice of charge and discharge current will also affect the uniformity of the SEI film. Therefore, for batteries in different application fields, it is necessary to consider the optimization of the formation method to achieve the best battery performance.

In subsequent research, the optimization of formation/aging technical parameters and the development of methods need to be further developed to scientifically and effectively improve the electrochemical performance and production efficiency of batteries, focusing on the following aspects.

(1) The formation/aging technical parameters need to be tailored to the specific battery type. For different battery material types, the technical parameters should be adjusted accordingly to achieve the optimal performance of the reaction and time at the interface of the formation/aging process.

(2) The technical parameters must be optimized in a coordinated manner. In theory, there is an optimal value in a certain parameter type, but if other parameters change, the optimal value may also change. Different parameter types affect each other, so certain parameters cannot be ignored during the optimization process, and the synergistic effect should be followed to obtain the optimal values of various parameters.

(3) Combined with high compaction density, the infiltration of electrolyte into most positive electrode material particles faces great challenges. The electrolyte cannot only infiltrate the electrode surface, but also the electrolyte bridges the inside of the electrode material to improve the ion transfer rate. Therefore, after the technical parameters are optimized, a more effective formation method should be developed to enable the electrolyte to enter the electrode material more effectively and increase the electrode wettability.

(4) Future research directions need to focus on tailoring different formation methods for different electrolyte additives, and maximize the effect of electrolyte additives by optimizing the charging voltage and formation temperature during the formation stage.

(5) The development direction needs to realize the controllability of multiple factors (temperature, external mechanical pressure, charge and discharge current, etc.) of the formation, such as further increasing the temperature and shortening the formation time. At the same time, combining effective electrolyte additives with new formation methods to synergistically build an excellent SEI protective layer and improve the formation efficiency.

Formation technology is very important for cost control of lithium batteries, but there are still many areas to be improved. Improving battery performance and reducing production costs through the development of new formation methods will bring greater benefits in the future.

Cite this article: LIN Yilong, XIAO Min, HAN Dongmei, et al. Research progress information technique for LIBs [J]. Energy Storage Science and Technology, 2021, 10(01): 50-58.

LIN Yilong, XIAO Min, HANDongmei, et al. Research progress information technique for LIBs [J]. Energy Storage Science and Technology, 2021, 10(01): 50-58.

First author: LIN Yilong (1992-), male, doctoral student, important research direction is lithium ion/lithium sulfur battery formation behavior and electrolyte, E-mail: linylong3@mail2.sysu.edu.cn;

Corresponding author: MENG Yuezhong, professor, important research direction is functional polymers, chemical utilization of carbon dioxide and new energy materials, E-mail: mengyzh@mail.sysu.edu.cn.

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