Ni-rich Layed Materials With Core-shell Structured As Cathode For Li-ion Battery

Lithium ion batteries are considered as potential energy storage devices for electric vehicles(EVs). Due to its low cost, less toxicity, larg reversible capacity and especially high energydensity, Ni-rich Li[Ni1-xMx]O2(M=metals) has attracted much interest as lithium storagematerials, and has been considered as one of the most promising cathode materials for lithiumion batteries in recent years. However, Ni-rich Li[Ni1-xMx]O2(M=metals) material still showsstructural unstable during thermal runaway reactions due to the release of oxygen from thehost structure. Yang-Kook Sun synthetized a series of core-shell materials, which improvedthe safety and cycleability compared with the core or shell materials. However, the averagecomposition of the core-shell materials are obviously different from the core or the shellmaterials because of a certain ratio of the shell. Therefore, there was a lack of contrastiveexperiment between the core-shell and non-core-shell materials with the same compositions.In this paper, a novel structure with multi-layers core-shell is put forward in order to replacethe early one-layer core-shell structure and the subsequent concentration-gradient core-shellstructure. In this paper, we use Li[Ni1/3Co1/3Mn1/3]O2and Li [Ni0.45Co0.1Mn0.45]O2for the shellcomponent of core-shell structured (one-layer, multi-layers, concentration-gradient) materialsrespectively, compare with the non-core-shell structure materials without comparisonchange.This can clarify the function of core–shell structure in core–shell structured layeredmaterials by excluding the effects of composition variation.First, we chose Li[Ni0.8Co0.1Mn0.1]O2with high capacity for the core, Li[Ni1/3Co1/3Mn1/3]O2for the shell component of core-shell structured (one-layer, multi-layers,concentration-gradient) materials compare with the non-core-shell structure materials withoutcomparison change. The designed core–shell structure of hydroxide precursor was identifiedby particle size analysis, scanning electron microscopy (SEM) and derivativethermogravimetric analysis (DTG). The obtained core–shell precursor was calcined withstoichiometric Li2CO3(nLi/nM=1.05/1) at820°C for16h to get the lithiated oxide. XRDresults showed that lithiated oxide can be indexed to a typical layered structure with a R-3mspace group. The electrochemical and differential scanning calorimetry (DSC) tests showedthat core–shell structured (one-layer, multi-layers, concentration-gradient) materials displayedremarkably improved cyclability and thermal stability compared with the non-core–shellstructured one.Secondly, we chose Li[Ni0.8Co0.1Mn0.1]O2with high capacity for the core,Li[Ni0.45Co0.1Mn0.45]O2for the shell component of one-layer core-shell structuredLi[(Ni0.8Co0.1Mn0.1)1-x(Ni0.45Co0.1Mn0.45)x](x=0.2), multi-layers core-shell structured,concentration-gradient core-shell structured materials compare with the non-core-shellstructure materials without comparison change. The designed core–shell structure ofhydroxide precursor was identified by particle size analysis, SEM and DTG. The obtained core–shell precursor was calcined with stoichiometric Li2CO3(nLi/nM=1.05/1) at820°C for16h to get the lithiated oxide. XRD results showed that the lithiated oxide can be indexed to atypical layered structure with a R-3m space group. The electrochemical and differentialscanning calorimetry (DSC) tests showed that core–shell structured (one-layer, multi-layers,concentration-gradient) materials displayed remarkably improved cyclability and thermalstability compared with the non-core–shell structured one. Dates shows that one-layercore-shell structured Li[Ni0.73Co0.1Mn0.17]O2has the best cyclability and thermal stability.Finally, we increase the thickness of the shell, compare one-layer core-shell structuredLi[(Ni0.8Co0.1Mn0.1)1-x(Ni0.45Co0.1Mn0.45)x](x=0.3,0.4) materials with the non-core-shellstructure materials with the same compositions. The designed core–shell structure ofhydroxide precursor was identified by particle size analysis, X-ray powder diffraction (XRD),EDS, SEM and DTG. The obtained core–shell precursor was calcined with stoichiometricLi2CO3(nLi/nM=1.05/1) at high temperature for16h to get lithiated oxide. XRD resultsshowed that lithiated oxide can be indexed to a typical layered structure with a R-3m spacegroup. The EDS compositional change from the cross-section of core–shell particles resultssuggest that the core–shell structure is retained after lithiation at a high temperature, but aconcentration-gradient layer is formed from core partto surface of particles.Theelectrochemical and differential scanning calorimetry (DSC) tests showed that core–shellstructured materials displayed remarkably improved cyclability and thermal stabilitycompared with the non-core–shell structured one.