The Institute of Chemistry has made a series of progress in the research and development of high energy density nano solid-state metal lithium batteries and their key materials

Figure 1. Schematic diagram of the (a) deposition process and (b) deposition mechanism of metallic lithium on curved graphitic carbon spheres.

Figure 2. (a) Discharge curve and deposition schematic of graphitized carbon fiber. Electrode surface morphology of (b) original material and (c) after discharge to 0 V, (d) after deposition of 2 mA h cm ⁻² , (e) after deposition of 8 mA h cm ⁻² , (f) after dissolution of 4 mA h cm −2, and (g) when charged to 1 V.

Figure 3. (a) Schematic diagram of the preparation of ipn-PEA electrolyte (top) and lithium deposition (bottom). (b) Modulus diagram of ipn-PEA electrolyte. (c) Voltage photo of Li|ipn-PEA electrolyte|LFP soft pack battery after cutting. The LED device can be lit before (e) and after (f) the soft pack battery bending test.

In order to develop high-energy-density nano solid-state metal lithium batteries and solve the problems of cyclability and safety faced by metal lithium batteries, with the strong support of the Ministry of Science and Technology, the National Natural Science Foundation of China and the Chinese Academy of Sciences, the research team led by Guo Yuguo, a researcher at the Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, has made a series of progress in the research of metal lithium negative electrodes, solid electrolytes and solid-state batteries.

In recent years, the researchers of this research group have been committed to the research of metal lithium negative electrode. In the previous research work, in order to solve the problem of uneven dissolution and deposition (i.e. dendrites) of metal lithium negative electrode during charge and discharge, they proposed to use three-dimensional nano-current collector to guide the uniform deposition and dissolution of metal lithium inside the three-dimensional electrode, and successfully achieved the control of metal lithium dendrites (Nat. Commun., 2015, 6, 8058). The researchers proposed and developed an in-situ treatment technology, which successfully formed a lithium phosphate solid electrolyte interface film with high Young's modulus and fast lithium ion transport capacity on the surface of metal lithium, effectively reducing the side reaction between metal lithium and electrolyte and inhibiting the growth of lithium dendrites (Adv. Mater., 2016, 28, 1853).

To further solve the problem of low utilization rate of metallic lithium negative electrode, the researchers combined the structural advantages of graphite carbon materials and proposed the concept of an efficient and stable "lithium storage room" (Figure 1). Onion-shaped, graphitized spherical carbon particles were grown on a three-dimensional conductive skeleton, achieving uniform regulation of the metallic lithium/electrolyte interface, effectively controlling the growth of metallic lithium dendrites on the surface of carbon spheres and greatly improving the utilization rate of lithium. Under the condition of only 5% excess negative electrode capacity, the battery can still cycle stably for a long time. The research results were recently published in J. Am. Chem. Soc. (2017, 139, 5916).

In order to solve the problems of dendrite growth and poor cycle stability in high-area capacity lithium metal anodes, researchers used electrochemically active graphitized carbon fibers as multifunctional three-dimensional current collectors to obtain a dendrite-free lithium metal anode with an areal capacity of up to 8 mA h cm-2. Since graphitized carbon fibers can reduce local current density and alleviate volume changes, the anode exhibits high Coulomb efficiency, low voltage polarization and long cycle life during the cycle process. The relevant results were recently published in Adv. Mater. (2017, 29, 1700389).

In the preliminary research work on electrolytes for lithium metal batteries, the research group designed a mixed electrolyte system of ether electrolyte plus ionic liquid to improve the deposition behavior and cycle stability of lithium metal anode in order to solve the problem of irreversible degradation of SEI spontaneously formed on the surface of lithium metal during the cycle (Adv. Sci., 2017, 4, 1600400). The researchers proposed a functional electrolyte additive containing Al colloidal particles. By adding AlCl3 to the electrolyte, a uniform, stable and dense SEI film was successfully formed in situ on the surface of lithium metal, stabilizing the interface of lithium metal/electrolyte (Nano Energy, 2017, 36, 411).

In order to improve battery safety and further solve the problem of lithium dendrites in liquid electrolyte systems, researchers designed and constructed a class of bifunctional interpenetrating network structure poly (ether-acrylate) solid electrolytes (Figure 3). This solid electrolyte (ipn-PEA) combines high mechanical strength (about 12 GPa) and high room temperature ionic conductivity (0.22 mS cm−1), making lithium deposition/precipitation balanced. Due to its dual role of reducing interfacial resistance and accelerating lithium ion transport, ipn-PEA electrolyte effectively inhibits lithium dendrite growth and reshapes the feasibility of room temperature solid-state lithium metal batteries (J. Am. Chem. Soc., 2016, 138, 15825).

In view of the leading research of the research group in solid-state metal lithium batteries, the researchers were invited by the editor-in-chief of ACS Energy Lett. to write a perspective article on the research and development prospects of solid-state metal lithium batteries (ACS Energy Lett., 2017, 2, 1385), and were also invited to write a review article on advanced carbon materials in metal lithium anodes (Adv. Energy Mater., 2017, doi: 10.1002/aenm.201700530). In addition, at the invitation of Adv. Sci., the research group also collaborated with Associate Professor Zhang Qiang of Tsinghua University to write a review article, summarizing and looking forward to the electrochemical behavior of metal lithium and electrode design strategies (Adv. Sci. 2017, 4, 1600445).