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Ni-rich LiNi0.8Co0.15Al0.05O2 materials have been successfully applied in electric vehicles due to the merits of high energy density which can meet the requirements for driving range. Nevertheless, the electrochemical performances of Ni-rich materials are limited by their structural instability. Herein, LiNi0.8Co0.15Al0.05O2 materials with the concentration-gradient structure of a Ni-rich core and a Co-rich surface were synthesized. The electrochemical results indicate that surface-concentration gradient LiNi0.8Co0.15Al0.05O2 provides improved electrochemical performance. It not only displays an initial Coulomb efficiency of 82.4%, and a capacity retention of 80.37% after 200 cycles at 25 °C, but also shows a capacity retention of 77.76% after 150 cycles at a high temperature of 55 °C. These excellent performances can be attributed to adjusting the distribution of Ni on the surface of the LiNi0.8Co0.15Al0.05O2 material, which inhibits the interfacial reaction between the material surface and electrolyte, lowers the consumption of active Li+ and decreases the interfacial film impedance. Moreover, less Ni content on the material surface is beneficial for reducing the formation of a NiO rock salt phase during the charging process and inhibits the surface structural evolution. The proposed method and detected mechanism will provide guidance for the design of cathode materials and their practical industrial applications. [ABSTRACT FROM AUTHOR]

The development of high energy density material is of great importance and urgency for new generation of energy storage system. However, electrolyte formula for high voltage system remains a challenge. The use of various functional additives gives rise to the complexity of electrolyte system and hinders completely understanding of the action mechanism of additives. Herein, we report the adaptability and mechanism of a single additive LiPO 2 F 2 added in the conventional LiPF 6 -based electrolyte system. The resulting conclusion displays a notable improvement in the cycling stability for 5 V-class cathode LiNi 0.5 Mn 1.5 O 4 , the capacity retention increase from 85.76% to 95.92%. It is comforting that the rate performance is not reduced due to the increase in cycle stability, and it also shows good advantages in terms of high rate and reversibility. Meanwhile, detailed analysis about interface mechanism for LiPO 2 F 2 by the surface testing (SEM, TEM and XPS) give the direct characterizations. Common ion effect of the decomposition product Li 3 PO 4 from additive is probed from the above characterization and combined with DFT calculations and some clever experiments to prove the positive effect of additives. The findings obtained from this work may provide a useful guidance for the research on electrolyte formulation for high voltage system. Unlabelled Image • LiPO 2 F 2 as film-formed additive for high voltage system • Li 3 PO 4 produced by LiPO 2 F 2 on the surface of cathode plays a key role in performance improvement by common ion effect. • Cycling performance for LNMO has been improved. [ABSTRACT FROM AUTHOR]

The development of high energy density and power density battery is of increasing importance for new generation energy storage system. However, interface instability between cathode and electrolyte remains a challenge for taking advantage of battery consistency. The use of commercial LiPF 6 -based electrolyte still has the limitations in optimizing interface stability to reduce material performance degradation. Here, self-developed synthetic lithium difluorobis (oxalato) phosphate (LiDFBOP) additive acts as "interface modifier" is adopted in the traditional electrolyte system. The resulting optimized electrolyte formulation exhibits improved electrochemical properties and self-discharge inhibition at high temperatures. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and density functional theory (DFT) calculation is applied to detect the LiDFBOP effect mechanism and distribution of main components of the interface film. It can be demonstrated that the participation of LiDFBOP can lead to a change in the composition of the interface film, which increases the number of components that facilitate the transport of lithium ions. The analytical means for additive effect obtained from this work offer a new opportunity to make an in-depth analysis of film components between cathode and electrolyte. Image 1 • LiDFBOP as a novel additive is firstly synthesized and characterized. • LiDFBOP as film reconstructor can optimize the performance of LNMO/Li cells. • CEI film composition distribution is proven by the TOF-SIMS. • The effect mechanism of LiDFBOP is verified by the DFT calculation in detail. [ABSTRACT FROM AUTHOR]

• The elements of Li, Ni, Co and Mn in Li-rich Mn-based cathode materials were replacing with Al. • Al-doped materials display different electrochemical performances. • The relationship between electrochemical characteristics and structure evolution has been systematically studied. Layered Li-rich Mn-based cathode materials have attracted immense interest for using in lithium-ion batteries, owing to their high energy density. However, the severe degradation of cycle and rate performances has impeded the actual commercial application. Herein, Al was selected as doping element to substitute for the metal elements of Li, Ni, Co and Mn in Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 material to promote electrochemical performances and optimize element proportion. Results indicate that when replacing Li with Al, it displays outstanding initial coulombic efficiency of 80.06%. Besides, Al-substitution for Co shows excellent rate performance of 147.3 mAh g−1 at 5.0 C. Particularly, the replacement of Mn not only shows the highest capacity and voltage retention within the potential range from 2.0 to 4.8 V, but also presents superior capacity retention up to the potential of 5.0 V. Unfortunately, the substitution of Ni displays the worst balanced electrochemical performance among Al-doped materials, which shows lower voltage retention than that of pristine. The reasons why Al-substitution for various cations displays difference on electrochemical performance were discussed from the perspective of migration, dissolution and valence reduction of transition metal ions to the structure evolution in detail. The proposed method and detected action mechanisms can provide guidance on how to optimize materials structure and composition for cathode materials in lithium-ion batteries to obtain electrode materials with excellent comprehensive electrochemical performance. [Display omitted] [ABSTRACT FROM AUTHOR]

A non-carbonaceous titanium-based materials of Na 2 Ti 3 O 7 have been considered as an attractive anode material for sodium ion battery (SIBs), due to its low charge potential and high energy density. However, the selection of preferred sodium salts in liquid electrolyte is still a challenge to improve battery performance. Herein, the compatibility of Na 2 Ti 3 O 7 @C anode material with sodium perchlorate (NaClO 4)-based and sodium trifluoromethyl sulfonate (NaCF 3 SO 3)-based electrolytes are studied, respectively. The results show that solid electrolyte interphase (SEI) film formed by NaCF 3 SO 3 -based electrolyte is thin, compact and uniform, which can effectively reduce the transmission energy barrier of Na+. Different from that, the SEI film derived in NaClO 4 -based electrolyte contains more Na 2 CO 3 and NaF, caused by the continuous decomposition of NaClO 4 salt in carbonate solvent. It makes the SEI film thicker and the interface impedance larger, which results in the decline of battery cycle performance. In addition, more sulfur-containing compounds with good sodium conductivity and stability are generated due to the decomposed of NaCF 3 SO 3 salt in carbonate solvent, which improves interfacial transport performance of materials, and inhibits the increase of the SEI film thickness and thus improves the cycling and rate performance of batteries. This study provides a reference method for designing advanced SIBs. [Display omitted] • NaCF 3 SO 3 improves the initial coulomb efficiency of the material. • NaClO 4 promotes the formation of a thick but soft SEI film containing more Na 2 CO 3. • A thin but hard SEI film derived NaCF 3 SO 3 contains more stable inorganic species. • NaCF 3 SO 3 -based electrolyte is more conducive to performance promotion of Na 2 Ti 3 O 7 @C. • Direct visualization information of the formation of SEI film is provided. [ABSTRACT FROM AUTHOR]