Pre-lithiation of the positive electrode material | Solving the correct posture of the lithium supplement problem?

The topic of lithium supplementation is already a commonplace. In the past, we have simply summarized the current mainstream lithium-replenishing process. In general, the use of metal Li powder and Li foil directly to the lithium anode has a higher maturity. The main method adopted by power battery manufacturers, however, the safety problem and high cost are the problems that metal Li can not be avoided. In contrast, the positive lithium supplement process has good safety and does not change the existing process, but the technology maturity is low. Also need related materials manufacturers to launch the corresponding products.

In addition to adding a small amount of high-capacity Li-containing oxide to the positive electrode system, there is also a means to store excess Li in the positive electrode material during the synthesis of the positive electrode material, thereby storing excess Li in the positive electrode material. During the process, excess Li can be released to supplement the Li element consumed by the negative electrode, thereby achieving the purpose of improving the first efficiency.

There are generally two ways to add excess lithium to the positive electrode material. The first one is to insert Li+ into the positive electrode material by electrochemical reaction. Generally, the positive electrode material and the metal Li are first composed of a half-cell, and the positive electrode material is intercalated with lithium. Then, the positive electrode material and the common negative electrode constitute a full battery, thereby achieving the purpose of lithium replenishment. This method is relatively simple, and can also well control the amount of embedded Li, which is suitable for use in a laboratory, but the disadvantages are also obvious, and the operation is compared. Complex, there is no practical value in actual production. Another method is to add excess Li in the process of synthesis through chemical methods. Although the technical difficulty is relatively high, there is no need to add extra process in battery production, so it has more Practical value.

The concept of positive pre-lithiation comes from Giulio Gabrielli, Germany, and Giulio Gabrielli first reported in 2016 the chemical synthesis of Li. _1+XNi _0.5Mn _1.5O₄Material, but at the time Giulio Gabrielli was hoping to synthesize Li _1+XNi _0.5Mn _1.5O₄Material (200mAh/g) improves LiNi _0.5Mn _1.5O₄The reversible capacity of the material (147mAh/g), until 2017, Giulio Gabrielli and other talents discovered Li _1+XNi _0.5Mn _1.5O₄The potential of materials to solve the problem of the first low efficiency of lithium-ion batteries, after the excessive Li out of the first charging process, Li _1+XNi _0.5Mn _1.5O₄The material is transformed into normal LiNi _0.5Mn _1.5O₄Material, by controlling different proportions of Li _1+XNi _0.5Mn _1.5O₄Materials and LiNi _0.5Mn _1.5O₄The mixing of materials and materials can accurately control the excess ratio of Li, thus completely compensating for the irreversible capacity loss of the negative electrode during the first charging process. This is also an innovation and breakthrough in the positive lithium charging process.

Giulio Gabrielli Synthetic Li _1+XNi _0.5Mn _1.5O₄The material is chemically synthesized, and the excess Li is directly added during the synthesis of the material, so it is more practical and is solved by SiO. _xAn effective method for the first-time low efficiency of lithium-ion batteries. However, it is not an easy task to add excess Li to the positive electrode material and form a stable structure, and to ensure that the cycle performance of the material is not affected. Xiaobian also consulted Giulio. All the articles published by Gabrielli have not yet been reported by Giulio Gabrielli in other materials (such as NCA and NCM materials), and it is also reflected that this method is not suitable for all cathode materials.

Recently, Vanchiappan Aravindan from India found that the method can also be applied to LiVPO. ₄In F material, the method adopted by Vanchiappan Aravindan is a relatively simple electrochemical embedding method, that is, LiVPO is first introduced. ₄F and metal Li form a battery, discharge to let Li+ be embedded in LiVPO ₄Li is formed in the F material _1.26VPO ₄F, then dissect the battery, Li _1.26VPO ₄F and anode material (a-Fe used here) ₂O₃) constitute a full battery, using Li _1.26VPO ₄Excessive Li element in F material makes up a-Fe ₂O₃The irreversible capacity of the material during the first lithium insertion process (about 503 mAh/g) greatly increases the energy density of the whole cell. However, this method requires first forming a half-cell, and electrochemically inserting Li+ into the positive electrode material. Therefore, the practical application in actual production is of little significance, so it is necessary to continue to explore how to directly synthesize lithium excess Li by chemical methods. _1.26VPO ₄F material, to achieve positive lithium.

Positive pre-lithiation is to solve SiO _xThe negative irreversible capacity of the negative electrode is an ideal method to increase the energy density of the lithium ion battery. However, it is a big challenge to embed excess Li in the positive electrode and maintain a stable structure. Therefore, the current research on the pre-lithiation of the positive electrode is mainly focused on the spinel. Structure of LiMn ₂O₄And LiNi _0.5Mn _1.5O₄In terms of materials, if pre-lithiation technology can be applied to NCA and NCM materials, embedding excess Li element without affecting the performance of NCA and NCM materials will have great application value.