1800mah 18650 battery

Research progress of solid-state 1800mah 18650 battery

All-solid-state lithium-ion batteries use solid electrolytes to replace traditional organic liquid electrolytes, which is expected to fundamentally solve the problem of battery safety and is an ideal chemical power source for electric vehicles and large-scale energy storage. In order to achieve large capacity and long life, thereby promoting the practical application of all-solid-state lithium-ion batteries, the development of key battery materials and the optimization of performance are urgent, mainly including the preparation of solid electrolytes with high room temperature conductivity and electrochemical stability, as well as high-energy electrode materials suitable for all-solid-state lithium-ion batteries, and improving the electrode/solid electrolyte interface compatibility. Introduction to solid-state batteries Traditional lithium-ion batteries use organic liquid electrolytes. Under abnormal conditions such as overcharging and internal short circuits, the battery is prone to heat up, causing electrolyte bloating, spontaneous combustion and even explosion, posing serious safety hazards.

All-solid-state 1800mah 18650 battery based on solid electrolytes, which were developed in the 1950s, use solid electrolytes and do not contain flammable and volatile components, completely eliminating safety hazards such as battery smoke and fire caused by battery leakage, and are known as the safest battery system. Regarding energy density, the governments of China, the United States and Japan hope to develop prototype devices with an energy density of 400 to 500 Wh/kg by 2020 and achieve mass production between 2025 and 2030. To achieve this goal, the most likely approach is the use of metallic lithium negative electrodes. In traditional liquid lithium-ion batteries, metallic lithium faces many technical challenges such as dendrites, pulverization, unstable SEI (solid electrolyte interface film), and many surface side reactions. The compatibility of solid electrolytes with metallic lithium makes it possible to use lithium as a negative electrode, thereby significantly improving energy density. Comparison of properties of different types of electrolytes and their lithium-ion battery systems

Research progress of solid electrolytes For solid-state batteries, solid electrolytes are the core components that distinguish them from other battery systems. Ideal solid electrolytes should have high lithium ion conductivity in the working temperature range (especially room temperature); negligible or non-existent grain boundary impedance; match the thermal expansion coefficient of the electrode material; maintain good chemical stability to the positive and negative electrode materials during battery charging and discharging, especially the metal lithium or lithium alloy negative electrode; wide electrochemical width and high decomposition voltage; not easy to absorb moisture, low price, simple preparation process, and environmentally friendly. At present, the material system of polymer electrolytes in mass-produced polymer solid-state batteries is polyethylene oxide (PEO). The characteristics of PEO-type polymer electrolytes are high ion conductivity at high temperatures, easy film formation, easy processing, and can form a continuous ion conduction channel after compounding with the positive electrode, and the positive electrode surface resistance is small. The oxidation potential of PEO is 3.8V, and high energy density positive electrodes such as lithium cobalt oxide, layered oxides, and spinel oxides are difficult to match with it, so they need to be modified; secondly, the operating temperature of PEO-based electrolytes is 60-85℃, and the battery system requires thermal management, which requires a special battery system design for power and energy storage applications; thirdly, this type of battery directly uses metallic lithium, and the uneven deposition at the interface during charging and discharging still has the hidden danger of lithium dendrites passing through the polymer film to cause internal short circuits. In addition, the rate characteristics need to be improved. The development of polymer electrolytes with high voltage resistance, high room temperature ionic conductivity, lithium dendrite blocking mechanism, and good mechanical properties is a key research direction. Inorganic solid electrolytes mainly include oxides and sulfides. The solid-state batteries that have been produced in small batches are mainly thin-film batteries with amorphous LiPON as the electrolyte. The advantages of inorganic solid electrolytes are that some materials have high bulk ionic conductivity, can withstand high voltage, have good electrochemical, chemical, and thermal stability, and have a certain effect in inhibiting lithium dendrites. Compared with oxides, sulfides are relatively soft and easier to process, and all-solid-state 1800mah 18650 battery can be prepared by hot pressing. The solid-state lithium battery recently demonstrated can even work at 60°C at room temperature. Although the volume and mass energy density will drop significantly at this time, at least this result reflects the potential of solid-state batteries in high power output. Sulfide electrolytes are also sensitive to air, easy to oxidize, and easy to produce harmful gases such as hydrogen sulfide when in contact with water. This problem can be improved to a certain extent by compounding oxides or doping in sulfides, but whether it can ultimately meet the requirements of safety and environmentally friendly properties in applications still needs experimental verification. At present, the mass and volume energy density of all-solid-state large-capacity battery cells using inorganic ceramic solid electrolytes are still significantly lower than those of existing liquid lithium-ion batteries. Research progress in positive electrode materials In addition to solid electrolytes, electrode materials are also key factors affecting the performance of all-solid-state batteries. Although there is basically no side reaction of solid electrolyte decomposition at the interface between solid electrolytes and electrode materials, the solid characteristics make the electrode/electrolyte interface poorly compatible, and the high interface impedance seriously affects the transmission of ions, ultimately resulting in low cycle life and poor rate performance of solid-state batteries. In addition, the development and application of all-solid-state lithium-ion batteries will inevitably be extended from small all-solid-state thin-film batteries to large all-solid-state energy storage batteries in the future. However, traditional electrode materials can no longer meet the current requirements for high energy density. Based on the above reasons, the research on electrode materials is mainly focused on two aspects: one is to modify the electrode materials and their interfaces to improve the electrode/electrolyte interface compatibility; the other is to develop new electrode materials to further improve the electrochemical performance of solid-state batteries. High-energy-density positive electrode materials have large lithium insertion capacity and high voltage, and there will be significant volume changes during charging and discharging. When using solid electrolytes, the interface between the positive electrode and the solid electrolyte membrane, as well as the interface between the positive electrode and the solid electrolyte, may have poor contact.

The solution includes in-situ or non-in-situ deposition or hot pressing of a layer of solid electrolyte on the surface of the positive electrode particles; or filling the pores of the positive electrode particles with a solid electrolyte with a certain elasticity to form a continuous ion conductive phase, similar to a liquid electrolyte; or introducing liquid on the positive electrode side to form a solid-liquid composite system. Since it is difficult to inject liquid into the positive electrode alone, whether the solid-state lithium battery can have the advantages of high energy density and safety after the introduction of liquid is the key, which depends on the electrochemical and safety characteristics of the introduced liquid, and whether the metal lithium electrode is fully protected in advance. Since the safety of existing liquid electrolytes has basically met the requirements, adding liquid to reduce the contact resistance on the positive electrode side in solid-state batteries should be a solution that can take into account both dynamics and safety. However, it is not easy to find liquid electrolyte additives that can work at high voltage, have good wettability and good safety. This is itself one of the main research directions and bottleneck technologies of liquid lithium-ion batteries. Progress in research on negative electrode materials Metals have become one of the most important negative electrode materials for all-solid-state batteries due to their advantages of high capacity and low potential. However, metal lithium will produce lithium dendrites during the cycle process, which will not only reduce the amount of lithium available for insertion/extraction, but more seriously, it will cause safety problems such as short circuits.

In addition, metal Li is very active and easily reacts with oxygen and moisture in the air, and metal lithium cannot withstand high temperatures, which brings difficulties to the assembly and application of batteries. Adding other metals to lithium to form alloys is one of the main methods to solve the above problems. These alloy materials generally have high theoretical capacity, and the activity of metallic lithium is reduced by the addition of other metals, which can effectively control the formation of lithium dendrites and the occurrence of electrochemical side reactions, thereby promoting interface stability. However, there are some obvious defects in lithium alloy negative electrodes, mainly the large change in electrode volume during the cycle, which can cause electrode powder failure in severe cases and a significant decrease in cycle performance. At the same time, since lithium is still an electrode active substance, the corresponding safety hazards still exist.

At present, the methods that can improve these problems mainly include synthesizing new alloy materials, preparing ultrafine nano alloys and composite alloy systems (such as active/inactive, active/active, carbon-based composites and porous structures), etc. Carbon-based, silicon-based and tin-based materials of the carbon family are another important negative electrode material for all-solid-state batteries.

Carbon-based materials are typically represented by graphite materials. Graphite carbon has a layered structure suitable for lithium ion embedding and extraction, has a good voltage platform, and a charge and discharge efficiency of more than 90%. However, the low theoretical capacity (only 372 mA˙h/g) is the biggest shortcoming of this type of material, and the current practical application has basically reached the theoretical limit and cannot meet the needs of high energy density. In summary, the use of solid electrolytes to replace traditional organic electrolytes to prepare solid-state batteries can fundamentally solve the safety problems of lithium-ion batteries. At present, a lot of work is focused on the development of all-solid-state lithium-ion batteries with higher energy and power density. In the process of promoting the industrialization of high-safety and high-energy storage batteries, the research and development and preparation of key materials (solid electrolytes, positive and negative electrodes) are a crucial link.

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