Date: 2026-02-06 hits: 136
Currently, lithium-ion batteries are developing in three directions:
(1) Faster charging speed: The charging rate of current smartphones is generally 1C, while the maximum charging rate has reached 6C, allowing a phone to be fully charged in as little as 16 minutes;
(2) Higher energy density: The 4.45V system platform is already mature and commercially available, and 4.48V and even higher voltage platforms have become popular research directions;
(3) Longer cycle life: In the past few years, the service life requirement for 3C lithium-ion batteries was 500 cycles, but major manufacturers have now increased it to 800 cycles.
Fast charging refers to a charging method that charges the battery to full or near-full capacity at the fastest possible speed in a very short time, while ensuring that the lithium-ion battery meets the specified cycle life, safety performance, and electrical performance. Currently, ordinary commercial lithium-ion batteries can occasionally be charged and discharged at high rates, but long-term high-rate charging and discharging will lead to a significant reduction in their cycle life. Fast-charging lithium-ion batteries require specialized material selection and design to meet customer requirements. This article discusses the design points and relevant influencing factors of fast-charging lithium-ion batteries based on long-term experience in fast-charging battery design.
I. Materials
In lithium-ion batteries, the diffusion process of Li+ mainly includes the extraction of Li+ from the positive electrode material, the migration of Li+ in the electrolyte, the passage of Li+ through the separator, the intercalation of Li+ into the negative electrode, and the diffusion of Li+ within the negative electrode material. Improving the fast-charging performance of lithium-ion batteries requires research in these aspects.
Generally, the solid-phase diffusion coefficient inside the negative electrode material is relatively small, limiting the high-current charge and discharge capacity of the negative electrode material and becoming the controlling step of the electrode reaction. Under the action of electric field and concentration gradient, Li+ migrates and diffuses from the positive electrode to the negative electrode, which involves liquid-phase diffusion. The concentration of the electrolyte also has a significant impact on improving fast-charging performance. The porosity of the separator determines the amount of Li+ migration. If the separator porosity is low, high-current charging can easily cause pore blockage. The thickness of the separator determines the diffusion distance of Li+. The thinner the separator, the shorter the diffusion distance.
1. Anode Material
Graphite materials possess advantages such as a two-dimensional layered structure and a low voltage platform. The interlayer C-C distance can reach 0.340 nm, and Li+ can be embedded between the layers of graphite, forming the interlayer compound LixC6, making it one of the most commonly used anode materials. The layered structure of graphite requires Li+ to be embedded from the ends of the graphite, and then diffuse into the interior of the particles, increasing the diffusion path. The small interlayer spacing results in a low diffusion rate of Li+, and during high-rate charging, Li+ easily deposits on the graphite surface, forming a large number of lithium dendrites, posing a safety hazard.
Currently, surface coating modification is commonly used to improve the performance of the material. The interlayer spacing of soft and hard carbon is slightly larger than that of graphite, which is beneficial for lithium ion diffusion. Usually, soft and hard carbon coatings on the graphite surface improve the electrochemical performance of graphite. That is, through surface modification, an amorphous carbon layer is formed on the graphite surface, increasing the lithium ion channels, improving lithium ion diffusion, and enhancing its rate performance. When designing fast-charging lithium-ion batteries, small particles and soft/hard carbon-coated anode materials are usually used.
2. Electrolyte
High-concentration electrolytes exhibit excellent rate performance. Experimental studies have prepared a phosphate-based electrolyte composed of 5 mol/L lithium bis(fluorosulfonyl)imide (LiFSI) in trimethyl phosphate (TIMP) solvent. It has good compatibility with graphite anode materials and forms a stable LiF-rich SEI layer, effectively hindering the growth of lithium dendrites in lithium metal batteries. Other experimental studies have added propionitrile or butyronitrile co-solvents to traditional ethylene carbonate-based electrolytes, which significantly enhanced the conductivity of the electrolyte and greatly promoted the battery's high-rate charging capability at low temperatures (-20°C). This means that the battery can achieve fast charging at low temperatures. To better achieve fast charging, an electrolyte with high concentration, high conductivity, and low viscosity should be selected.
3. Separator
The quality of the separator determines the interface structure and internal resistance of the battery, directly affecting the battery's rate performance, cycle life, and safety performance. To ensure that the separator possesses properties such as electrical insulation, low resistance, high ionic conductivity, resistance to electrolyte corrosion, and high wettability, the selection of the separator mainly considers indicators such as thickness, porosity, air permeability, wettability, pore size, puncture strength, and thermal stability. Among these, the thickness, porosity, and air permeability of the separator significantly affect the fast charging performance of lithium-ion batteries. When the thickness is thin, the porosity is high, and the air permeability is high, the resistance to lithium ion transport from the positive electrode to the negative electrode is reduced, and the polarization effect during charging is minimized. The thickness and porosity of the separator affect the charging performance of lithium-ion batteries. When designing fast-charging batteries, thin and high-porosity separators are generally preferred.
II. Structural Factors
The internal structure of consumer lithium-ion batteries is mainly divided into four types based on their manufacturing method: ordinary structure, centrally located tab structure, multi-tab structure, and stacked structure. The ordinary structure has only one positive and one negative tab, located at one end of the electrode sheet, and is manufactured by winding; the centrally located tab structure has the tab in the middle of the electrode sheet, generally processed through laser cleaning, intermittent coating, and tape application, resulting in lower internal resistance and better rate performance; the multi-tab winding structure has multiple tabs on the wound electrode sheet, with different tab positions depending on the design, resulting in even lower battery resistance and better rate performance; the stacked battery is made by cutting the electrode sheets into specific shapes and folding them alternately, with a tab in each layer. This structure offers the best rate performance.
1. Centrally Located Tab Structure
Experimental studies have investigated the impact of tab position on the performance of lithium-ion batteries. The tab position significantly affects the internal resistance and rate performance of lithium-ion batteries. When the tab is in the middle of the positive and negative electrodes, the battery's internal resistance and rate performance are optimal, approaching the performance of batteries made with the stacking process.
2. Multi-Tab Winding
Due to higher welding requirements and precision, batteries made with this structure are more expensive. The advantages of the multi-tab structure include: further reducing battery impedance, improving the battery's high-rate charge and discharge performance, supporting 5C~10C discharge; effectively reducing the temperature rise during high-rate discharge, with the surface temperature rise of a 10C discharge battery being less than 20°C; and lower battery temperature, significantly increasing battery cycle life.
Currently, mobile phone manufacturers generally claim that their products can achieve fast charging, but most only limit it to the first 30 minutes. The constant voltage stage in the later part of charging is actually quite long. Multi-tab winding technology can improve this aspect, but because it has more tabs that need to be welded and connected, its energy density is relatively low. Increasing the energy density of multi-tab structure batteries will be the main direction of this technology in the future.
3. Stacking Technology
Compared to multi-tab winding, stacked batteries have a tab in each layer. Batteries made with this structure have the highest fast-charging performance among all current structures. However, due due to limitations in its level of automation, it is currently used less frequently in the consumer electronics sector, and is mainly employed in military and power battery applications. It is believed that with advancements in automation capabilities, stacking technology will become mainstream in the future.
III. Design Factors
The fast-charging performance of lithium-ion batteries is closely related to the battery design. Factors such as electrode coating amount, compaction density, thickness of copper and aluminum foils, size of the tabs, and width of the electrodes all significantly affect the fast-charging performance of the battery. Battery areal density and compaction density have a significant impact on the battery's rate capability and cycle performance. Fast-charging lithium-ion batteries require a low areal density design, while excessively high or low compaction density will lead to poor performance. Excessively high compaction density "compresses" the active material of the electrode, leading to a rapid drop in cycle capacity, while excessively low compaction density results in insufficient contact between the active materials, leading to higher battery impedance and thus poor fast-charging performance.
Experimental studies have investigated the impact of different foil thicknesses on the performance of lithium-ion batteries. Thicker foils, due to their better conductivity, result in better battery resistance and rate capability compared to thinner foils. However, the increased thickness inevitably leads to a decrease in battery energy density. The same principle applies to the tabs and foils: the larger the cross-sectional area, the lower the resistance. Currently, commonly used tab thicknesses are 0.08 or 0.1 mm, with widths of 4-6 mm. Fast-charging lithium-ion batteries typically use tabs with dimensions of 0.1 mm x 6 mm. In addition, copper-plated nickel tabs can also reduce the impedance of the tabs. Furthermore, the length, width, and size of the battery electrodes also have a certain impact on the fast-charging performance of the battery.
IV. Other Factors
1. Construction of the Conductive Network
Typically, materials with better conductivity are used as conductive additives to form a conductive network, which can further improve the fast-charging performance of lithium-ion batteries. Common conductive agents include carbon nanotubes (CNT) and carbon black (SP). The amount of conductive agent added must be appropriate; too little may not form an effective conductive network, while too much will reduce the content of active material in the electrode, leading to a decrease in energy density. Constructing a conductive network can optimize the electrical performance of electrode materials, which is of practical significance for achieving fast-charging lithium-ion batteries.
2. Influence of Binders and Carbon Coating Carriers
Binders, as auxiliary materials in lithium-ion batteries, are used in very small quantities, but they have a significant impact on battery performance. Their main function is to improve the battery's resistance, thereby enhancing its performance and lifespan. By using different synthesis methods and adjusting the surface of SBR, the wettability of the electrolyte to SBR can be improved, achieving the goal of improving the battery's low-temperature and rate performance.
By modifying the current collector of the lithium-ion battery with a conductive coating, the adhesion between the current collector and the active material of the lithium-ion battery is significantly improved, and the battery impedance is significantly reduced, which can significantly improve the high-rate charge and discharge performance of the lithium-ion battery. In addition, in practical use, the use of modified carriers can also improve the problem of large thickness differences between the ends of the electrode, further extending the lifespan of the lithium-ion battery.
3. High-Voltage Overcharging
The charging process of lithium-ion batteries is divided into two steps: the first step is constant-current charging to the battery's maximum voltage, and the second step is constant-voltage charging at that voltage. During constant-voltage charging, the current gradually decreases, and charging ends when the current decreases to a set value. The constant-voltage charging stage is long and charges a small amount of capacity. The idea behind high-voltage overcharging is to reduce constant-voltage charging and increase the proportion of constant-current charging. However, it should be noted that the higher the charging cut-off voltage of the battery, the more serious the impact on battery life. Different models need to be verified before increasing the voltage; otherwise, the battery life will rapidly decline.
4. Multi-Series and Parallel Combination
Currently, to improve the charging efficiency of mobile phones, manufacturers are not only working on the battery itself but also researching different battery combination methods. OPPO is one of the leading manufacturers in fast charging technology in my country. Experimental studies have been conducted on OPPO's SuperVOOC fast charging technology. The increase in charging speed is equivalent to an increase in charging power. Power = voltage x current. For lithium-ion batteries, the maximum voltage they can withstand is around 4.4~4.5V. Even with high-voltage overcharging, the increase is only 0.02~0.03V. Considering conversion efficiency, the input voltage to the phone is generally 5V. However, excessive charging current can cause severe heating of the device, accelerating the aging of various components, seriously affecting the device's lifespan, and even posing safety hazards. OPPO uses a dual-cell connection method, employing a 5A/10V charging system, where each battery withstands a current and voltage of 5V/5A, thus increasing the phone's charging power. However, it should be noted that this method requires fast-charging lithium batteries; otherwise, it will significantly affect the battery's cycle life.
V. Conclusion
This article discusses the manufacturing of fast-charging lithium-ion batteries from a design perspective. Fast-charging lithium-ion batteries should be optimized in terms of materials, design, and structure. In terms of materials, the anode, separator, and electrolyte significantly impact fast charging. When designing fast-charging lithium-ion batteries, small-particle and hard-carbon-coated anode materials are typically used to improve the lithium intercalation/deintercalation rate of the anode. The separator should be a thin separator with high porosity to reduce the distance of lithium ion transport and increase the speed of lithium ion passage. The electrolyte should be one with high conductivity, high concentration, and low viscosity to reduce battery polarization and internal resistance, and increase the migration speed of lithium ions.
In terms of design, it is mainly related to the coating amount and compaction density. Low coating amount and low compaction density are beneficial to both the fast-charging performance and lifespan of lithium-ion batteries.
In terms of structure, the current mainstream central tab structure, multi-tab winding, and stacking technologies can significantly improve the fast-charging capability and cycle life of batteries.
In other aspects, building a conductive network and using binders with higher ionic/electrical conductivity, optimizing the battery charging method, and using high-voltage overcharging technology and multi-series and parallel combinations can also improve the charging speed of the battery.
