Lithium Insertion into Carbonaceous Anode Materials Prepared by Electrolysis of Molten Li-K-Na Carbonates

Abstract

Carbon powders were prepared by electroreduction of molten lithium-sodium-potassium carbonates at 450°C. The influence of the potential and the heat-treatment after washing in HCl solution on their electrochemical performances when they are used as anode in Li-ions battery were studied. Correlation between the presence of surface disordering ͑Raman spectroscopy͒ and the presence H, Li, K, and Na on the outermost layer on the powder surface ͑secondary ion mass spectroscopy͒, and their electrochemical performances was pointed out: samples having both the higher surface disordering and the lower H, Li, K, and Na content on their surface exhibit the lowest electrochemical performances. The best results were obtained for carbon deposited at Ϫ2.4 V vs. CO 2 -O 2 and heat-treated at 400°C: the reversible capacity obtained in 1 M LiPF 6 -ethylene carbonate:diethyl carbonate:dimethyl carbonate is 1080 mAh g Ϫ1 ͑composition of Li 2.9 C 6 ). This value is 2.9 times higher than the theoretical one observed with graphite (372 mAh g Ϫ1 , composition of LiC 6 ). The potential profile obtained in galvanostatic mode is intermediate between that usually observed for graphite and amorphous carbon, because in the potential range 1.5-0.3 V vs. Li/Li ϩ , the potential profile shows rather continuous charge-discharge curves sloping, and between 0.3 and 0.02 V vs. Li/Li ϩ , phase transformations between different stages occur successively as in the case of pure graphite.Rechargeable lithium-ion batteries are widely used as power sources in electrical equipment. These batteries are commercially available and are composed of LiCoO 2 , LiNiO 2 , or LiMn 2 O 4 as positive electrode, 1-8 and lithiated graphite instead of metallic lithium as negative electrode. 9-17 The use of lithiated graphite avoids growth of metallic Li dendrite usually observed upon chargedischarge cycles with a metallic lithium anode. It exists in numerous carbonaceous materials which exhibit different electrochemical performances when they are used as a reservoir of lithium in lithiumion batteries. Among these carbon materials, graphite or graphitized carbon materials have high reversible capacity, low irreversible capacity, low potential and flat potential profiles, high coulombic efficiency, long life cycle, and high safety level compared to other compounds such as metal oxides, lithium alloys, or lithium metal. Hexagonal graphite has a layered lattice structure with a perfect stacking order of graphene layers ͑sequence of ABAB type͒. Owing to this lamellar structure, Li cations can be easily inserted and deinserted between two carbon sheets. A maximum lithium ion content of one lithium guest atom per six carbon host atoms can be achieved, giving rise to a composition of LiC 6 and to a theoretical specific capacity of 372 mAh g Ϫ1 . The charge-discharge voltage profile in galvanostatic mode exhibits three distinct plateaus appearing approximately at around 0.21, 0.11, and 0.06-0.08 V vs. Li/Li ϩ due to a staging mechanism which involves one or more graphene layers: 1...

Carbonate Reduction and the Properties and Applications of Carbon Formed Through Electrochemical Deposition in Molten Carbonates: A Review

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Electrochemical Behavior of Carbonate Ion in the LiF^|^ndash;NaF^|^ndash;Li2CO3 System

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Graphene/(h-BN) n/X-doped graphene as anode material in lithium ion batteries (X=Li, Be, B and N)

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