Meng Jiang

Lithium Salt of Tetrahydroxybenzoquinone: Toward the Development of a Sustainable Li-Ion Battery

The use of lithiated redox organic molecules containing electrochemically active C=O functionalities, such as lithiated oxocarbon salts, is proposed. These represent alternative electrode materials to those used in current Li-ion battery technology that can be synthesized from renewable starting materials. The key material is the tetralithium salt of tetrahydroxybenzoquinone (Li(4)C(6)O(6)), which can be both reduced to Li(2)C(6)O(6) and oxidized to Li(6)C(6)O(6). In addition to being directly synthesized from tetrahydroxybenzoquinone by neutralization at room temperature, we demonstrate that this salt can readily be formed by the thermal disproportionation of Li(2)C(6)O(6) (dilithium rhodizonate phase) under an inert atmosphere. The Li(4)C(6)O(6) compound shows good electrochemical performance vs Li with a sustained reversibility of approximately 200 mAh g(-1) at an average potential of 1.8 V, allowing a Li-ion battery that cycles between Li(2)C(6)O(6) and Li(6)C(6)O(6) to be constructed.

Identifying the Local Structures Formed during Lithiation of the Conversion Material, Iron Fluoride, in a Li Ion Battery: A Solid-State NMR, X-ray Diffraction, and Pair Distribution Function Analysis Study

The structural transformations that occur when FeF(3) is cycled at room temperature in a Li cell were investigated using a combination of X-ray diffraction (XRD), pair distribution function (PDF) analysis, and magic-angle-spinning NMR spectroscopy. Two regions are seen on discharge. The first occurs between Li = 0 and 1.0 and involves an insertion reaction. This first region actually comprises two steps: First, a two-phase reaction between Li = 0 and 0.5 occurs, and the Li(0.5)FeF(3) phase that is formed gives rise to a Li NMR resonance due to Li(+) ions near both Fe(3+) and Fe(2+) ions. On the basis of the PDF data, the local structure of this phase is closer to the rutile structure than the original ReO(3) structure. Second, a single-phase intercalation reaction occurs between Li = 0.5 and 1.0, for which the Li NMR data indicate a progressive increase in the concentration of Fe(2+) ions. In the second region, the conversion reaction, superparamagnetic, nanosized ( approximately 3 nm) Fe metal is formed, as indicated by the XRD and NMR data, along with some LiF and a third phase that is rich in Li and F. The charge process involves the formation of a series of intercalation phases with increasing Fe oxidation state, which, on the basis of the Li NMR and PDF data, have local structures that are similar to the intercalation phases seen during the first stage of the discharge process. The solid-state NMR and XRD results for the rutile phase FeF(2) are presented for comparison, and the data indicate that an insertion reaction also occurs, which is accompanied by the formation of LiF. This is followed by the formation of Fe nanoparticles and LiF via a conversion reaction.

Structure of aluminum fluoride coated Li[Li1/9Ni1/3Mn5/9]O2 cathodes for secondary lithium-ion batteries

The structural properties of layered Li[Li1/9Ni1/3Mn5/9]O2 positive electrodes nominally coated with aluminum fluoride are studied. Coatings were prepared by using aqueous solutions with various concentrations of aluminum and fluorine and are compared with samples treated under similar conditions but with aqueous HCl solutions. Samples were investigated following heat treatment at 120 °C and 400 °C with powder X-ray diffraction, transmission electron microscopy including energy dispersive X-ray spectroscopy (TEM/EDS), elemental analysis via inductively coupled plasma-optical emission spectroscopy (ICP-EA), and both 6Li and 27Al magic angle spinning NMR spectroscopy. The TEM/EDS and 27Al NMR data provide support for an aluminum-rich amorphous coating that, following drying at 120 °C, comprises six coordinated, partially hydrated aluminum environments. Heat treatment at 400 °C results in a phase that resembles partially fluorinated γ- or γ′-Al2O3, at least locally. An Al : F ratio of 2 : 1 is obtained in stark contrast to the ratio used in the original solution (1 : 3). No AlF3 is detected by PXRD and instead some evidence for a protonated phase (formed by ion exchanging protons for lithium) is detected along with Li[Li1/9Ni1/3Mn5/9]O2 after drying. This phase disappears on heating to 400 °C, suggesting some reorganization of bulk Li[Li1/9Ni1/3Mn5/9]O2 and possibly some incorporation of Al into the structure. This is in agreement with the 6Li NMR spectra, which indicate that the local environments that are found in the Ni-free end member of the series Li[Li(1/3−2x/3)NixMn(2/3−x/3)]O2 (i.e. Li2MnO3) are enhanced on sintering.