Lithium replenishment is a frequently discussed topic. We've already summarized the mainstream lithium replenishment processes. Generally speaking, using metallic Li powder and Li foil to directly replenish the negative electrode is a relatively mature technology and is currently the main method used by power battery manufacturers. However, safety issues and high costs are unavoidable problems with metallic Li lithium replenishment. In contrast, positive electrode lithium replenishment offers better safety and doesn't change existing processes, but its technological maturity is lower, and relevant material manufacturers still need to launch corresponding products.
Besides adding a small amount of high-capacity Li oxide to the cathode system, another method for lithium replenishment in the cathode is to add excess Li during the cathode material synthesis process, thereby storing excess Li in the cathode material. During the first charge, the excess Li can be released to replenish the Li consumed by the anode, thus improving the first-charge efficiency.
There are generally two ways to add excess lithium to the cathode material. The first is through an electrochemical reaction that allows Li+ ions to intercalate into the cathode material. This typically involves first forming a half-cell with metallic Li to intercalate the lithium in the cathode material, and then combining this cathode material with a standard anode to form a full cell, thus achieving lithium replenishment. This method is relatively simple and allows for good control of the amount of intercalated Li, making it suitable for laboratory use. However, its drawbacks are also obvious: the operation is complex, and it has no practical value in actual production. The other method is through chemical methods, adding excess Li during the synthesis process. Although technically more challenging, this method does not require additional processes in battery production, making it more practical.
The concept of cathode pre-lithiation originated from Giulio Gabrielli et al. in Germany. In 2016, Giulio Gabrielli first reported the chemical synthesis of Li1+XNi0.5Mn1.5O4 material. However, at that time, Giulio Gabrielli hoped to improve the reversible capacity of LiNi0.5Mn1.5O4 material (147mAh/g) by synthesizing Li1+XNi0.5Mn1.5O4 material (200mAh/g). It wasn't until 2017 that Giulio Gabrielli et al. discovered Li... The potential of 1+XNi0.5Mn1.5O4 material in solving the problem of low initial efficiency in lithium-ion batteries is evident. During the first charge, after excess Li is released, the Li1+XNi0.5Mn1.5O4 material transforms into normal LiNi0.5Mn1.5O4 material. By controlling the mixing ratio of Li1+XNi0.5Mn1.5O4 material with LiNi0.5Mn1.5O4 material, the proportion of excess Li can be precisely controlled, thereby completely compensating for the irreversible capacity loss of the negative electrode during the first charge. This is also an innovation and breakthrough in the lithium replenishment process of the positive electrode.
Giulio Gabrielli synthesized Li1+XNi0.5Mn1.5O4 using a chemical synthesis method, directly adding excess Li during the synthesis process. This method is therefore more practical and an effective way to address the low initial efficiency of SiOx-containing lithium-ion batteries. However, adding excess Li to the cathode material and forming a stable structure while ensuring that the material's cycle performance is not affected is not an easy task. A review of all of Giulio Gabrielli's publications reveals no reports of him applying this method to other materials (such as NCA and NCM), suggesting that this method is not suitable for all cathode materials.
Recently, Vanchiappan Aravindan from India discovered that this method can also be applied to LiVPO4F materials. Vanchiappan Aravindan's method is a relatively simple electrochemical intercalation approach. First, LiVPO4F is combined with metallic Li to form a battery. Discharging allows Li+ to intercalate into the LiVPO4F material, forming Li1.26VPO4F. Then, the battery is dissected, and the Li1.26VPO4F is combined with the negative electrode material (here, α-Fe2O3) to form a full cell. The excess Li in the Li1.26VPO4F material compensates for the irreversible capacity (approximately 503 mAh/g) of the α-Fe2O3 material during the initial lithium intercalation process, significantly improving the energy density of the full cell. However, this method requires first forming a half-cell and then electrochemically intercalating Li+ into the positive electrode material. Therefore, its practical application in actual production is limited. Further research is needed on how to directly synthesize lithium-excess Li1.26VPO4F material through chemical methods to achieve positive electrode lithium replenishment.
Pre-lithiation of the cathode is an ideal method to solve the problem of large irreversible capacity of SiOx anode and improve the energy density of lithium-ion batteries. However, embedding excess Li into the cathode and maintaining a stable structure presents a significant challenge. Therefore, current research on cathode pre-lithiation mainly focuses on spinel-structured LiMn2O4 and LiNi0.5Mn1.5O4 materials. If pre-lithiation technology can be applied to NCA and NCM materials to embed excess Li elements without affecting the performance of NCA and NCM materials, it will have great application value.
