The interfacial origin of performance improvement and fade of high-voltage cathodes of LiNi 0.5 Co 0.2 Mn 0.3 O 2 for high-energy lithium-ion batteries has been investigated. Performance improvement was achieved through interfacial stabilization using 5 wt % methyl (2,2,2-trifluoroethyl) carbonate (FEMC) of fluorinated linear carbonate as a new electrolyte additive. Cycling with the FEMC additive at 3.0−4.6 V versus Li/Li + results in the formation of a stable solid electrolyte interface (SEI) layer and effective passivation of cathode surface, leading to improved cycling performance delivering enhanced discharge capacities to 205−182 mAhg −1 and capacity retention of 84% over 50 cycles. The SEI layer notably includes plenty of metal fluorides and −CF-containing species formed by additive decomposition. On the contrary, the origin of performance fade in electrolyte only was ineffective surface passivation and dissolution of metal elements, which leads to oxygen loss, surface structural degradation and crack formation at the LiNi 0.5 Co 0.2 Mn 0.3 O 2 particles. The data provide a basic understanding of the interfacial stabilization mechanism on high-voltage layered oxide cathodes.

No abstract

No abstract

The discharge capacities of spinel-type Li 1.1 Mn 1.9 O 4 /graphite cells charged in electrolytes with solid electrolyte interphase ͑SEI͒-forming additives are investigated after being stored at 60°C. The presence of Mn deposits on the anode surface, which is responsible for the capacity fading of cells, is clearly shown by means of open-circuit voltage, ex situ X-ray diffraction, and energy-dispersive spectrometry measurements. Unlike fluoroethylene carbonate, using vinylene carbonate as an SEI former leads to a noticeable improvement in the discharge capacity retention of cells that were stored for 20 days at 60°C.Lithium-ion ͑Li-ion͒ batteries have been used as reliable power sources for portable electronic devices. 1 Furthermore, Li-ion batteries are very attractive for applications in electric vehicles, hybrid electric vehicles, and plug-in hybrid electric vehicles owing to their high energy density and long lifetime. A high energy density in batteries can be achieved by increasing the discharge capacity of the cathode or by augmenting the working potential of the cathode materials. 2 Lithium manganese oxides ͑LiMn 2 O 4 ͒ with a spinel structure have been extensively studied for high energy and high power batteries to replace lithium cobalt oxides ͑LiCoO 2 ͒ as cathode materials. LiMn 2 O 4 has the potential to create batteries that are low cost, eco-friendly, have a prolonged lifecycle, and are safe to operate. 3,4 The capacity fading mechanisms of LiMn 2 O 4 are complex, especially at elevated temperatures, and the capacity fading of batteries with spinel LiMn 2 O 4 cannot be explained solely via the loss of cathode materials. Dissolved Mn ions undergo reduction on the anode and thereby lead to self-discharge of the lithiated graphite anode. Even very small amounts of manganese in an electrolyte can affect the calendar life of Li-ion batteries for large-scale power sources. Therefore, it is necessary to restrain the manganese dissolution to attain highly reliable batteries. Recently, it has been established that the partial substitution of manganese ions with transitionmetal ions, such as Co, Cr, or Ni, enhances the structural stability and electrochemical performance of lithium manganese oxides with a spinel structure. 5 Surface coatings with lithium cobalt oxide and other oxides seem to improve the performance of spinel lithium manganese oxides at elevated temperatures. 6,7 It was reported that a considerable degree of Mn dissolution into the electrolyte occurs in the presence of HF that is formed by the hydrolysis of LiPF 6 salts and deposits on the anode surface. [8][9][10] In the present study, we aim to understand the influence of Mn dissolution from a delithiated lithium manganese oxide cathode on the capacity retention behavior of fully charged cells that have been stored at 60°C. We also report intriguing data on the roles of SEIforming additives that could mitigate severe self-discharge in a lithiated graphite anode caused by Mn deposits. ExperimentalAn electrolyte solution composed of a commerc...

We investigated electrochemical performance of natural graphite surface-treated with aluminum compared to that of untreated graphite. Aluminum triethoxide was used as the treatment source. In the treatment process, the drying temperature has critical influence on electrochemical performance of the treated samples. The surface property of treated samples was investigated by scanning electron microscopy and Raman spectroscopy. The E 2g vibration mode of the treated sample was sharpened and shifted upward, whereas no remarkable changes were found in A 1g mode. The electrochemical performance improved markedly with Al treatment. The impedance measurement shows that the Al treated sample had much smaller charge-transfer resistance during cycling.Rechargeable lithium-ion batteries, using a carbon material as anode and transition metal oxide, such as LiCoO 2 , LiMn 2 O 4 , or LiNiO 2 , as cathode, have been developed. Recently, there has been a lot of research to improve battery performance, usually carried out on various types of carbonaceous material ranging from graphite to disordered carbon by control of various properties such as structure, 1-3 surface modification. 4-6 Among the several types of carbonaceous materials, natural or synthetic graphitic carbons are commonly found in most commercial products in the market today due to their merits such as flat and low working voltage with respect to lithium metal and relatively high coulombic efficiency. Specifically, natural graphite can be thought of as a potential material for anodes in lithium-ion batteries due to cost considerations. 7 However, it is known that it is difficult to control the key parameters of natural graphite that affect their characteristics for use as anodes because carbon materials have large variations in their electrical properties. Among the various parameters of natural graphite, surface property is one of the critical factors that affect electrochemical performance, such as reversible specific capacity, cycle life, and rate capability. 7 In this paper, we report on an investigation of the influence of surface and/or structure modification of natural graphite by introducing aluminum compound for electrochemical performance of anodes in lithium-ion batteries. ExperimentalAluminum treated samples were prepared by aluminum triethoxide (Al͑OC 2 H 5 ͒ 3 ), Soekawa Chemicals͒ treatment on NG2 ͑Kansai chemicals͒. The NG2 graphite was soaked in ethanol solution containing 10 wt % aluminum triethoxide, followed by ultrasonic treatment for 3 h, filtration, and drying at various temperatures for 1 day to remove residual alcohol. Untreated samples were also prepared by alcohol soaking without Al triethoxide, ultrasonic treatment, and heat-treatment for comparison with Al-treated one. The infrared ͑IR͒ spectra of the samples were measured with a Jasco FT/IR 350 by KBr method. An X-ray diffractometry ͑XRD, Rigaku RINT2500͒ with Cu K␣ radiation was used to measure Bragg reflections from untreated and treated NG2. Raman scattering measurements were carried...

No abstract

No abstract

The development of high‐energy and high‐power density sodium‐ion batteries is a great challenge for modern electrochemistry. The main hurdle to wide acceptance of sodium‐ion batteries lies in identifying and developing suitable new electrode materials. This study presents a composition‐graded cathode with average composition Na[Ni0.61Co0.12Mn0.27]O2, which exhibits excellent performance and stability. In addition to the concentration gradients of the transition metal ions, the cathode is composed of spoke‐like nanorods assembled into a spherical superstructure. Individual nanorod particles also possess strong crystallographic texture with respect to the center of the spherical particle. Such morphology allows the spoke‐like nanorods to assemble into a compact structure that minimizes its porosity and maximizes its mechanical strength while facilitating Na+‐ion transport into the particle interior. Microcompression tests have explicitly verified the mechanical robustness of the composition‐graded cathode and single particle electrochemical measurements have demonstrated the electrochemical stability during Na+‐ion insertion and extraction at high rates. These structural and morphological features contribute to the delivery of high discharge capacities of 160 mAh (g oxide)−1 at 15 mA g−1 (0.1 C rate) and 130 mAh g−1 at 1500 mA g−1 (10 C rate). The work is a pronounced step forward in the development of new Na ion insertion cathodes with a concentration gradient.