Synthesis and Characterization of LiCoO2 from Different Precursors by Sol‑Gel Method

Abstract

Lithium cobalt oxide, LiCoO 2 , widely used as cathode in lithium ion batteries was synthesized and their structural and electronic properties investigated. The crystalline powders were prepared by the sol-gel method with four complexing agents: citric acid, glycine, starch and gelatin. These syntheses were compared with the blank test (without complexing agent). The X-ray diffraction and vibrational spectroscopy allowed the identification of the rhombohedral phase LiCoO 2 ( ) as the only or principal crystalline component in all samples. A small fraction of a second phase of cubic spinel Co 3 O 4 was observed in the samples of starch, gelatin and the blank test. The Rietveld refinements showed small structural variations, indicating reduced influence of the complexing agents on the synthesis. The theoretical HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap values are in agreement to those estimated by diffuse reflectance spectroscopy (DRS). The scanning electron microscopy (SEM) showed morphological pattern regardless of the complexing agent used, showing an alternative method.Keywords: LiCoO 2 , sol-gel method, XRD, Rietveld refinement, lithium ion batteries, DFT IntroductionLithium cobalt oxide, LiCoO 2 , has been the focus of many studies regarding their structural and electronic properties. [1][2][3][4][5][6][7][8] This system has interesting electrochemical features that allows a wide use as cathodes of lithium ion batteries. 2,4 The investigation of the structural aspects of the material is a crucial issue to better understand the electrochemical properties of the LiCoO 2 compound. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] For example, the nature of the crystal, its size and shape, are directly related with its electrochemical characteristics. 2 The LiCoO 2 synthesized at low temperatures (LT), below 500 °C, presents a cubic spinel structure ( ), while the synthesis at high temperatures (HT) (above 500 °C), generates the rhombohedral structure with stratified layers ( ). Therefore, several authors usually classify these structures as LT-LiCoO 2 and HT-LiCoO 2 , respectively . 1,2,7,8,[18][19][20][21][22][23][24] The rhombohedral phase is characterized by a structure with alternating layers of cobalt and lithium cations intercalated with oxygen anions. 22 The lithium and cobalt(III) ions are arranged in intercalated layers (Figure 1a). The cobalt(III) ion is located at the octahedral sites, forming a strong bond with the neighboring oxygen anion to constitute the Co−O layers (Figure 1b). Finally, the lithium layers are intercalated between the CoO 2 plans. 1,3,4 The octahedral sites of these layers are occupied by lithium and cobalt(III) ions alternately that forms a sequential stacking with oxygen ion layers in a close packing of the ABCABC type ( Figure 1c). 4,5 This specific stacking arrangement leads to an environment equivalent for all ions, allowing the maximum charge delocalization and the minimal system energy. 1,3,4 The degree of crystal orde...

Chemical synthesis and steady state characterization of a nanocrystalline lithium cobalt oxide

“…6B-6E). This agrees with Okubo et al results [44,45], in which the electron diffraction patterns revealed the characteristic geometry of an oxide structure along atomic layers.…”

Superior Lithium Ion Storage Performance of LiCoO2 Cathode at 4.5 V Enabled by the Multiple Synergistic Effect of Nano-Silver

“…56 In addition, the characteristic band of the spinel Co 3 O 4 at around the 690 cm −1 is not observed in Raman spectra, which suggests there is no Co 3 O 4 impurity in the as-prepared cathode materials. 58 The Raman spectral results suggest that LiCoO 2 with α-NaFeO 2 layered structure and without any impurity are synthesized, and the crystalline structure and purity of LiCoO 2 is not affected by addition of Ag, agreeing well with XRD results.…”

“…4d are attributed to the Co-O stretching Eg modes and the O-Co-O vibrational A1g modes of LiCoO 2 with ordered α-NaFeO 2 layered structure, respectively. 56,58 While four Raman bands for LiCoO 2 with spinel structure are not observed in the as-prepared products. 56 In addition, the characteristic band of the spinel Co 3 O 4 at around the 690 cm −1 is not observed in Raman spectra, which suggests there is no Co 3 O 4 impurity in the as-prepared cathode materials.…”

A Structural and Morphological Study of LiCo<sub>1-<i>X</i></sub>Sm<sub><i>X</i></sub>O<i><sub>Y</i></sub> Powders Obtained by the Sol-Gel Method

“…These powders exhibit a rhombohedral crystalline structure (ICSD 98-004-8103) characteristic of LiCoO 2 [17] [18] [19] with no secondary phases. The space group associated with this structure is R-3m (166), known as a high-temperature structure, or HT-LiCoO 2 [20]; it is formed of alternating cobalt and lithium layers with oxygen anions, as reported by Bruno et al [21]; a schema of this structure is shown in Figure 1(b).…”