Dynamic behaviour of interphases and its implication on high-energy-density cathode materials in lithium-ion batteries

Undesired electrode-electrolyte interactions prevent the use of many high-energy-density cathode materials in practical lithium-ion batteries. Efforts to address their limited service life have predominantly focused on the active electrode materials and electrolytes. Here an advanced three-dimensional chemical and imaging analysis on a model material, the nickel-rich layered lithium transition-metal oxide, reveals the dynamic behaviour of cathode interphases driven by conductive carbon additives (carbon black) in a common nonaqueous electrolyte. Region-of-interest sensitive secondary-ion mass spectrometry shows that a cathode-electrolyte interphase, initially formed on carbon black with no electrochemical bias applied, readily passivates the cathode particles through mutual exchange of surface species. By tuning the interphase thickness, we demonstrate its robustness in suppressing the deterioration of the electrode/electrolyte interface during high-voltage cell operation. Our results provide insights on the formation and evolution of cathode interphases, facilitating development of in situ surface protection on high-energy-density cathode materials in lithium-based batteries.ope

Controlled three-dimensional polystyrene micro- and nano-structures fabricated by three- dimensional electrospinning

The combination of electrospinning with extrusion based 3D printing technology opens new pathways for micro- and nanofabrication, which can be applied in a wide range of applications. This simple and inexpensive method has been proven to fabricate 3D fibrous polystyrene structures with controlled morphology and micro- to nano-scale fibers diameter. The controllable movement of the nozzle allows precise positioning of the deposition area of the fibers during electrospinning. A programmed circular nozzle pattern results in the formation of controllable 3D polystyrene designed shapes with fiber diameters down to 550 nm. The assembly of the fibrous structures starts instantaneously, and a 4 cm tall and 6 cm wide sample can be produced within a 10 minutes electrospinning process. The product exhibits high stability at ambient conditions. The shape, size, and thickness of fibrous polystyrene structures can be easily controlled by tuning the process parameters. It is assumed that the build-up of 3D fibrous polystyrene structures strongly depends on charge induction and polarization of the electrospun fibers

Nanostructured LiMPO 4

Nanostructured materials are considered to be strong candidates for fundamental advances in efficient storage and/or conversion. In nanostructured materials transport kinetics and surface processes play determining roles. This work describes recent developments in the synthesis and characterization of composites which consist of lithium metal phosphates (LiMPO4, M = Fe, Mn, Co, Ni) coated on nanostructured carbon supports (unordered nanofibers, foams). The composites have been prepared by coating the carbon structures in aqueous (or polyols) solutions containing lithium, metal ions and phosphates. After drying out, the composites have been thermally treated at different temperatures (between 600-780°C) for 5-12 hours under nitrogen. The formation of the olivine structured phase was confirmed by the X-ray diffraction analysis on powders prepared under very similar conditions. The surface investigation revealed the formation of an homogeneous coating of the olivine phase on the carbon structures. The electrochemical performance on the composites showed a dramatic improvement of the discharge specific capacity (measured at a discharge rate of C/25 and room temperature) compared to the prepared powders. The delivered values were 105 mAhg-1 for M = Fe, 100 mAhg-1 for M = Co, 70 mAhg-1 for M = Mn and 30 mAhg-1 for M = Ni respectively

Investigation of the LiCo1−xMgxPO4 (0≤x≤0.1)–graphitic carbon foam composites

LiCo1−xMgxPO4–graphitic carbon foam (LCMP–GCF with 0 ≤ x ≤ 0.1) composites are prepared by Pechini-assisted sol-gel method and annealed with the 2-steps annealing process (T = 300 °C for 5 min in flowing air, then at T = 730 °C for t = 12 h in flowing nitrogen). The XRD analysis, performed on powders reveals LiCoPO4 as major crystalline phase, Co2P and Co2P2O7 as secondary phases. The morphological investigation revealed the formation and growth of microcrystalline “islands” which consist of acicular crystallites with different dimensions (typically 5–50 μm). By addition of Mg-ions, CV-curves of LCMP–GCF composites show a decrease of the surface between anodic and cathodic sweeps by cycling and a stark contribution of faradaic processes due to the graphitic structured foam. The electrochemical measurements, at a discharge rate of C/10 at room temperature, show the decrease of the discharge specific capacity from 100 mAh g−1 for x = 0.0 to ∼35 mAh g−1 for 0.025 ≤ x ≤ 0.05, then an increase to 69 mAh g−1 for x = 0.1. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity at high Mg-ions content into the LiCoPO4 phase (x ≥ 0.025)

Influence of the annealing atmosphere on the properties of LiCoPO4–graphitic carbon foams composites

The investigation on the properties of LiCoPO4–graphitic carbon foams (LCP-GCF) composites is reported in this work. The diffraction analysis (XRD) on powders confirmed the presence of LiCoPO4 as major crystalline phase and Li4P2O7 and Co2P as secondary phases. The morphological investigation of the composites shows a layer of crystalline spongy-like material on the surface of the GCF for t = 0 h and of acicular crystallites with different dimensions (5–50 μm) for t ≥ 0.1 h. The voltammetric curves (cyclic voltammogramms) show mean values of reduction potential above 5.0 V independently of the annealing time. The LCP-GCF composites deliver a discharge-specific capacity of 76mAh g−1 (t = 0 h) and of 102mAh g−1 (t = 0.1 h) at a discharge rate of C/10 and room temperature. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity as a function of the annealing time

Investigation on graphitic carbon foams – LiNiyPO4 (y = 0.8–1.0) composites

Graphitic carbon foams coated with olivine-structured lithium nickel phosphate (LiNiyPO4) (y = 0.8–1.0) as possible cathode materials for 5 V applications are investigated. The composites are prepared by soaking the foams into solutions containing lithium, nickel ions and phosphates, treated in flowing air then in flowing nitrogen. The structural, morphological and electrochemical properties are strongly dependent upon the Ni-content. The X-ray diffractograms, performed on powders prepared under very similar conditions, showed the formation of LiNiPO4 phase with Li4P2O7 and Li2Ni3(P2O7)2. The morphological investigation revealed a dramatic change of the layer by decreasing the Ni-content. The voltammetric curves show values of the mean peak maxima in the anodic region between 5.1 and 5.2 V and in the cathodic region between 4.88 for (y = 1.0) and ∼5.18 V for (y = 0.9 and 0.8) respectively. The specific capacity of the composites (at the first cycle, a discharge rate of C/10 and room temperature) increases by decreasing the nickel content into the cathode material reaching a maximum of 122 mAh g−1 for y = 0.8

Investigation of the LiCo1−xMgxPO4 (0⩽x⩽0.1) system

LiCo1−xMgxPO4 (0 ⩽ x ⩽ 0.1) compounds are prepared by Pechini assisted sol–gel method coupled with the 2-steps annealing process (T = 300 °C for 5 min in flowing air, then at T = 730 °C for t = 12 h in flowing nitrogen). The XRD patterns show LiCoPO4 as major crystalline phase, Co2P and Co2P2O7 as secondary phases independently of the Mg-content. The morphology of the powders consists of a spongy-like structure with plate grains and coarse particles separated on the surface. The CV curves show a very good electrochemical reversibility with very close values of the mean peak maxima in the cathodic region, 4.4 V for x ⩽ 0.05 and 4.6 V for x = 0.1 respectively. The electrochemical measurements, at a discharge rate of C/10 at room temperature, show the increase of the discharge specific capacity from 61 mA h g−1 for x = 0.0–88 mA h g−1 for x = 0.025, then the decrease to 36 mA h g−1 for x = 0.1. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity at low Mg-ions content into the LiCoPO4 system (x = 0.025)