无负极锂金属电池的研究进展

[Background] The lithium metal anode, with almost the highest theoretical capacity (3 860 mAh/g) and the lowest redox potential (-3. 04 V vs standard hydrogen electrode), presents great potentials for next-generation high-energy-density rechargeable battery systems. However, fabricating lithium metal anode requires a complicated and costly process. More importantly, lithium metal anode is prone to react with the electrolyte due to lithium's high reactivity, forming a non-stable solid electrolyte interface (SEI) film of inhomogeneous composition and structure. Hence, anode-free lithium metal batteries (LMBs) constructed by direct matching lithiated cathode with an anode current collector can significantly reduce lithium usage and simplify anode fabrication. Without lithium foil, anode-free LMBs exhibit lower battery mass and thickness, reduced cost, and improved energy density and battery safety, thereby receiving extensive attention. [Progress] Anode-free LMBs still face significant challenges in terms of reversibility, capacity retention and cycling stability. The working principle of the anode-free design is that, during the initial charging process, lithium metal is deposited in-situ on the surface of the anode current collector and then stripped during the subsequent discharging process. This deposition/stripping process is repeated in later cycles. Unfortunately, the deposition is difficult to control and the deposited lithium film also simultaneously reacts with the electrolyte, leading to irreversible loss of finite active lithium and rapid degradation of battery performances. Therefore, improving the reversibility of lithium metal deposition/stripping and reducing the consumption of active lithium are the two major challenges for anode-free LMBs. Several strategies have been proposed and investigated: 1) Combining pre-lithiation of high-capacity cathode materials with the existing battery manufacturing process to build anode-free LMBs. The cathode active material provides active lithium for the whole system as the lithium source, so developing high-capacity and high-loading cathode is essential to improve the cycling stability of anode-free LMBs. 2) Successfully applying dual-salt electrolyte systems in anode-free lithium metal pouch cells. The function of synergizing organic and inorganic components in dual-salt electrolyte to build a stable interface has been confirmed with excellent battery performance even under high current density and low electrolyte/anode capacity ratio conditions. 3) Developing Ag-C anode current collector for all-solid-state batteries of excellent cycling stability. Regulating lithiophilic sites on the current collector effectively refines the lithium deposition behavior, significantly boosting the battery safety and extending the battery life. These advances have greatly promoted the development of anode-free LMBs. In this paper, we summarize the state-of-art progress of anode-free LMBs from the aspects of anode collector, electrolyte, battery test standardization and characterization techniques. [Perspective] There remains a significant gap between the performance of anode-free LMBs and the requirements for commercial application. 1) To narrow the gap, researchers could aim to improve SEI stability in anode-free LMBs by modifying the current collector surface and regulating the SEI composition. Given that commercial metal collectors are becoming thinner and lighter, the challenges lie in ensuring sufficient mechanical strength of the foil to withstand processing and performing surface modification to enhance the affinity of commercial collectors for lithium metal. 2) SEI film composed of desired molecular structure and elemental distribution, with both fast ionic conduction and high stability, is possible to standardize battery test parameters for comparability of results from different studies. 3) It is also necessary to facilitate a smooth and practical transition from coin-type batteries in research laboratories to utility-grade pouch cells. This transition requires the development of advanced characterization technologies for rapid and accurate diagnostics of problems in anode-free LMBs. Incorporating multi-mode, in-situ techniques helps to gain real time data with high spatial, energy and temporal resolution. In addition, artificial intelligence technology should be implemented to identify useful data, establish reliable models, and carry out comprehensive training under complex working conditions. These efforts can ultimately promote the development of anode-free LMBs.