In-Situ observation of lithium dendrites in lithium metal anodes Tianyao Ding

Lithium metal anode The development of the electronic device results a increasing demand on high performance battery. High energy density battery can meet the demand but currently Li-ion is getting closer to their inherent capability limits. Lithium metal is the ideal choice due to its extremely high theoretical specific capacity (3860mAh g-1), low density (0.59 g cm-3) and the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode).[1][2]

Lithium Dendrite Under charging conditions. Lithium can accumulate on battery’s electrode. Which forms dendrites. Exhibit ramified morphologies [3] Loss capacity when fall off the deposition surface. Penetrate the separator of the battery and cause short circuit which will lead burning and explosion. Effect of the solvents, salts in the electrolyte, additives and other treatments has become the main reason of the dendrite growth. Dendrite grow on the pure lithium electrode

Current methods for lithium dendrite study SEM Optical microscope XPS to analyze the chemical component Basically those are based on different system. There is no general solution for the environment to control the dendrite growth. These set of experiment is designed in order to test the dendrite growth on lithium anode in different systems and conditions.

Experiment setup 6 5 2 1 3 4 7 Schematic set-up of the self-made two-electrode cell in this work. 1, observation glass window; 2, steel current collector for reference/counter electrode; 3, lithium disk of working electrode; 4, electrolyte; 5, lithium metal of reference/counter electrode; 6, steel current collector for working electrode; 7, PTFE body of the cell.

Figure 5. The optical photographs of lithium electrodes with electrochemical deposition of lithium in different electrolytes. In 1 M LiBETFSi/DME/DOL electrolyte with deposition, (A) and (F); in 1 M LiClO4/DME/DOL electrolyte with deposition, (B) and (G); in 1 M LiDFOB/DME/DOL electrolyte with deposition, (C) and (H); in 1 M LiTFS/DME/DOL electrolyte with deposition, (D) and (I); in 1 M LiTFSi/DME/DOL electrolyte with deposition, (E) and (J). All electrolytes contain 0.1 M LiNO3. The deposition condition is 2 mA for 1 hour. From (A) to (E), in 200X magnification; from (F) to (J) in 400X magnification.

It’s reported that Non-lithium cation will form a layer to uniform the dendrite growth. The non-lithium cation used is Cesium. The next few experiment is designed in order to find the metal additive effect to the dendrite structure formation. [4]

(A) (B) (C) (D) (E) (F) (G) (H) (I) (J) (K) (L) (M) (N) (O) Figure 7. The optical photographs of lithium electrodes with and without electrochemical deposition of lithium in different electrolytes. In 1 M LiBETFSi/DME/DOL electrolyte with 0.1 M LiNO3 before and after deposition, (A),(F) and (K); In 1 M LiTSFi/DME/DOL, with 0.1M LiNO3 and 0.05M Bi(NO3)3 before and after deposition, (B),(G) and(L); In 1 M LiTSFi/DME/DOL, with 0.1M LiNO3 and 0.05M In(NO3)3 before and after deposition (C), (H) and (M); In1 M LiTSFi/DME/DOL, with 0.1M LiNO3 and 0.05M Pb(NO3)2 before and after deposition, (D),(I) and (N); In 1 M LiTFSi/DME/DOL, with 0.1M LiNO3 and 0.025M Co(II) phthalocyanine before and after deposition. The deposition condition is 2mA for 1hour. From (A) to (J), in 100X stitching magnification; from (K) to (O) in 200X magnification.

(A) (B) (C) (D) (E) (F) (G) (H) (I) (J) (K) (L) Figure 8. The optical photographs of lithium electrodes with electrochemical deposition of lithium in LiTFSi/DME/DOL, with 0.1M LiNO3, with different current. In 2mA for 1hour, (A) and (D); In 0.8mA for 2.5 hour, (B) and (E); In 0.1mA for 20 hours, (C) AND (F). 0.05M CsNO3 is added to the electrolyte from (G) to (L). In 2mA for 1hour, (G) and (J); In 0.8mA for 2.5 hour, (H) and (K); In 0.1mA for 20 hours, (I) AND (L). From (A) to (C) and (G) to (I), in 100X stitching magnification; from (D) to (F) and (J) to (L) in 200X magnification.

Polycyclic Aromatic Hydrocarbons(PAHs) additive Li metal PAH in solvent PAH in solvent with Li 𝑀+𝐴𝑟 ⇌ ( 𝐴𝑟 − , 𝑀 + ) 𝑖𝑜𝑛 𝑝𝑎𝑖𝑟 ⇌ 𝐴𝑟 − + 𝑀 + Blue solution M can be Li+ K+, Na+, alkali metal ion

Figure 9. The optical photographs of lithium electrodes with and without Polycyclic aromatic hydrocarbon (PAH). Left:1M LiTFSi/DME, without PAH; Right: 1M LiTFSi/DME, with 10mM Phenanthrene. First row: before deposition. Second row: after 1 hr 2mA deposition. Third row: after 1hr 2mA stripping. For the left column are 50X magnification; for the right column are 100X magnification.

Future Work Different polyaromatic hydrocarbons, pure or mixed at different concentration and ratio; Different lithium salts, single or mixed at different ratio and concentration Different solvents for the electrolytes TEM or SEM method beside optic microscope

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