Search

Summary: Although the high‐capacity Si/graphite anode serves to advance the energy density of lithium‐ion batteries, the volume change remains the main disfigurement of Si/graphite anode. Many studies show that crosslinked structure binders tend to play a good inhibitory effect on volume expansion. In this work, a three‐dimensionally covalently cross‐linked and flexible polyimides (C–PI–OH) is successfully synthesized and applied as silicon/graphite anode, which is composed through a tri‐monomer co‐polycondensation and crosslinking process. The as‐formed free carboxylic acid groups and amide groups in C–PI–OH are efficient in structural stability, so the electrode bound by C–PI–OH exhibits the highest peeling strength than C–PI and polyvinylidene fluoride. The flexible network of the C–PI–OH binder is competent for accommodating the volume expansion and contraction of silicon particles during the deintercalation of lithium ion, which helps in the wholeness of solid electrolyte interface film and electrodes, and effectively boosting the cycle stability of the Si/graphite anode. [ABSTRACT FROM AUTHOR]

The use of inexpensive graphite oxide (GO) as a carbon source, instead of the expensive reduced graphene oxide (rGO), is essential to prepare metal oxide/rGO composites. In this work, we investigated the in situ reaction of GO and FeCl3 to produce Fe2O3/rGO composites as anode materials for high‐energy lithium‐ion batteries (LIBs). In this reaction, iron ions combined with the oxygen‐containing functional groups of GO, which subsequently grew into Fe2O3 nanoparticles, whereas the GO transformed into rGO under hydrothermal conditions. In the composite Fe2O3−rGOx samples, intergranular gaps in the Fe2O3 sub‐micron particles evidently increased the contact between the Fe2O3 active material and the electrolyte, which improved the Li‐ion conductivity and electrochemical performance of the Fe2O3−rGOx composites. The Fe2O3−rGO2 sample showed the best cyclic performance and delivered the highest capacity of all samples. The initial discharge and charge capacities of Fe2O3−rGO2 were 1086.3 and 722.4 mAh g−1, respectively. After 100 cycles, the discharge specific capacity of Fe2O3−rGO2 was 653.2 mAh g−1 and the coulombic efficiency was 98.4 %. We found that an appropriate weight ratio and composite morphology of Fe2O3−rGOx were important in influencing the electrochemical properties of the composite anode materials for high‐energy LIBs. [ABSTRACT FROM AUTHOR]

Summary: The heterostructural construction of metal disulfide/oxide is essential in the electrochemical performance as anode material for lithium‐ and sodium‐ion batteries (LIBs and SIBs). In this work, an integrated composite of molybdenum disulfide (MoS2) and hexagonal molybdenum dioxide (MoO2) together enwrapped in reduced graphene oxide (rGO) is synthesized under hydrothermal condition. In the pelletizing MoS2‐MoO2/rGO composite, rGO as substrate effectively prevents the restacking and pulverization of MoS2‐MoO2 during a long cycling process. Meanwhile, the synergistic effect among the MoS2, MoO2, and rGO components are responsible for abundant active sites and shorten ionic transport channels. When evaluating as anode material for LIB, MoS2‐MoO2/rGO sample presents excellent cyclic performance and still delivers a high capacity of 1062.3 mA h g−1 after 120 cycles at 0.2 A g−1; evaluating in a SIB at 0.04 A g−1, it presents excellent cyclic performance and delivers 430 mA h g−1 at the 80th cycle. The heterostructural composite MoS2‐MoO2/rGO is one of the candidate anode materials for high‐performance LIB and SIB. [ABSTRACT FROM AUTHOR]

Abstract To limit the pulverization of tin-based anode materials during lithiation/delithiation, submicron tin oxide/tin particles are fixed on core/sheath carbon nanofiber/spongy carbon via hydrothermal and carbothermal reduction treatment in this work. During carbothermal reduction, SnO 2 nanosheets are converted to spherical Sn submicron particles and simultaneously the hollow spongy carbon is produced and still enwrap on carbon nanofiber. The as-produced flexible film is used for a binder-free anode for lithium ion batteries, without the polymer binder and conductive carbon. At 0.1, 0.5, 1 and 2 A g−1, the composite electrode respectively displays a discharging capacity of 1393.0, 738.2, 583.6 and 382.6 mAh g−1. Moreover, it delivers specific capacity of 726.9 mAh g−1 and coulombic efficiency of 99.45% after 300 cycles at 0.1 A g−1. The comparison sample of carbon nanofiber/SnO x film without the presence of spongy carbon displays much lower rate performance and worse cyclic performance. The integrated structure of carbon nanofiber/SnO x /spongy carbon results in the remarkable Li-storage performance, in which the carbon nanofiber and spongy carbon synergistically provide conductive channel and buffer zone to hinder the pulverization and peeling of SnO x particles during charging-discharging processes. Graphical abstract Image 1 Highlights • Submicron SnO 2 particles fixed on core/sheath carbon nanofibers/spongy carbon. • CNF/SnO x /SC flexible film used as a binder free anode material. • SnO 2 nanoflakes coated by spongy carbon can be reduced to Sn submicron particles. • Integrated CNF/SnO x /SC provides conductive channel and buffers volume change. [ABSTRACT FROM AUTHOR]

Abstract: Three‐dimensional porous SnO2/rGO xerogels with superior cycling performance in lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs) are fabricated through a freeze‐drying‐assisted method. SnO2 nanoparticles (5 nm in diameter) are homogeneously attached to the surface of graphene sheets without self‐aggregation. The heterostructured SnO2/rGO xerogel possesses numerous micron‐sized pores that can efficiently buffer the volumetric change of SnO2 during the charge/discharge process and provide multidimensional channels, improving the conductivity between active materials and electrolyte. The SnO2/rGO xerogel exhibits excellent electrochemical performance, both in LIBs and SIBs, owing to its particular porous structure. For LIBs, it delivers a high initial discharge capacity of 1670.5 mAh g−1 in the first cycle and remains at 1139.4 mAh g−1 after 166 cycles at a current density of 0.1 A g−1. The SnO2/rGO xerogel also delivers a high discharge capacity of 189.4 mAh g−1 without capacity loss over 266 cycles at a current density of 0.5 A g−1 for SIBs. The SnO2/rGO xerogel can be used as an electrode material in both LIBs and SIBs, and can maintain an excellent rate performance and cyclic performance, owing to the abundant porosity and high conductivity. [ABSTRACT FROM AUTHOR]

Spinel LiMn2O4 is one of the most important cathode materials but it still suffers from rapid capacity degradation during electrochemical cycling. Beside surface coating to improve the electrochemical performances, controlling the bulk morphology of LiMn2O4 (LMO) is another effective strategy. In this work, porous LiMn2O4 microspheres composed of numerous primary nanoparticles are synthesized by micro-emulsion and co-precipitation methods. The porous structure and the primary nanoparticles size of LiMn2O4 are effected by the concentration of micro-emulsion and the precursor of Mn2+. The well-established porous LiMn2O4 microspheres with abundant ionic channels and good contact with electrolyte endow the spinel a remarkable electrochemical performance. After 300 cycles, 0.50 M-LMO sample presents excellent reversible capacity of 112.8 mAh g−1 at 0.5 C rate. After 1000 cycles, 0.50 M-LMO sample presents the highest capacity of 97.9 mAh g−1 and remains 54.2 mAh g−1 at the current rate of 10 C. The porous spherical structure of cathode materials is essential to improve the rate performance due to the good contact between the active material and electrolyte. [ABSTRACT FROM AUTHOR]

In this paper, a novel adhesive prepared by blending lithium-ion functionalized epoxy resin (ionized oligomer) with poly(vinylidenedifluoride) (PVdF) is used to fabricate the cathode electrode of LiCoO2. The properties of the blending adhesive are studied by Fourier transform infrared spectroscopy, differential scanning calorimeter, and thermogravimetric analysis, and the morphology and performance of the composite cathodes are characterized by using X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy, electrochemical impedance spectroscopy, and galvanostatic charge-discharge. With the blended ionized oligomer, the crystallinity behavior of PVdF is decreased effectively, which will be beneficial to the movement of conducting ions. An appropriate amount of ionized oligomer effectively improves the conductivity and charge-transfer capability of the cathode material. When the amount of ionized oligomer to the PVdF binder is 10 wt%, the LiCoO2-based composite cathode delivers the highest charge−discharge capacity (178 mAh g−1) and the capacity retention is up to 82.2 % after 100 cycles. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report the sphere-like C/CuO and CuO nanocrystals that have been fast prepared by the microwave-assisted hydrothermal method in the presence of green additive d-glucose. The rapid formation mechanism of the C/CuO and CuO nanocrystals and how the d-glucose worked in the microwave-assisted hydrothermal system were discussed in details. The crystal phase, morphology and electrochemical performance were characterized by means of X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) and electrochemical testing. The XRD patterns indicated that the CuO nanocrystals are pure with monoclinic structure and TEM images showed that the size of the samples could be tunable by adjusting the ratio of d-glucose and metal salt. Finally, a possible growth mechanism for the C/CuO spheres and CuO nanocrystals was proposed and discussed. The electrochemical performance of the products may be influenced by the size and uniformity of the nanocrystals. [Copyright &y& Elsevier]

Abstract: Olivine structure LiMnPO4 has been considered as one of the very promising electrodes for lithium-ion batteries because of their low cost, low toxicity and high voltage plateau compared with LiFePO4. In order to improve the electrochemical performance a key challenge in the field of lithium-ion battery, is to explore and invent suitable synthetic route to control the size and morphology of LiMnPO4. Here a detailed study exploring the novel route of microwave-hydrothermal (MH) synthesis for successfully obtaining LiMnPO4 crystals within few minutes is reported and the reaction process discussed in detail. Variation of the synthetic parameters show that a decrease in reactant concentration could lead to LiMnPO4 nano-platelets orientated in the ac plane with a very high electrochemical performance. The effect of the starting precursor (like, Mn) concentration as a means to tailor LiMnPO4 electrochemical performance is discussed. The effect of alteration of size, morphology, lattice parameters and crystal structure induced by addition of additives like citric acid (H3cit) and sodium dodecyl benzene sulfonate (SDBS) is further described and an example of the first reversible discharge of a product treated with H3cit obtained by MH route as high as 89.0mAh/g, is shown. The general investigation demonstrates that there is a relationship among microwave irradiation condition, crystal structure, morphology and electrochemical performance that can be exploited for the design of next generation lithium batteries. [Copyright &y& Elsevier]

Three dimensional networks, herein carbon coated SnO 2 micron-sized particles are fixed in carbon nanofibers (CNF/SnO 2 @C), is fabricated and synthesized by using hydrothermal method and carbonization. The weight ratio of SnO 2 reaches to 50% of CNF/SnO 2 @C, meanwhile, CNF/SnO 2 @C remains its flexibility. CNF/SnO 2 @C film is directly used as a binder-free anode for lithium ion batteries without conductive additive and polymer binder. The discharge capacities of CNF/SnO 2 @C are 1286 mAh g −1 at 0.05 A g −1 and 397 mAh g −1 at 1 A g −1 , respectively. The buffering effect of CNFs is studied by using ex-situ SEM in the cycled electrodes operated at various lithiation states. The particles size of SnO 2 @C sample increase to 4 μm after 20 charge/discharge cycles, and a serious aggregation of particles occurs in the cycled SnO 2 @C electrode which is in coincidence with its rapidly faded capacity. The particles of CNF/SnO 2 @C sample also present the increased size from the original size of 2 μm to the lithiated size of 4 μm but they are still fixed in CNFs network without any aggregation. The improved specific capacity, cyclic stability and rate performance of CNF/SnO 2 @C are attributed to the structural synergy of CNFs and SnO2 particles, because CNFs as flexible substrate provides excellent conductive channel improving the rate capability and effective network buffering the volume change to promote the cyclic performance. [ABSTRACT FROM AUTHOR]

A series of composites manganese oxide/carbon with one-dimensional structure are synthesized using electrospinning. The phase composition, morphology and electrochemical performance of MnO x /carbon are studied, which affected by the manganese concentration in precursor and subsequent carbonization conditions. The manufacture of MnO x /carbon is composed of two steps including thermal stabilization (at 250 °C in air) and carbonization (at 700 °C in nitrogen). The main functional groups of samples are well identified by FT-IR spectra. The sample Mn33_3h with the lowest manganese content presents the construction structure which amorphous and/or nanosized MnO x with smaller crystal size are grown and enwrapped in carbon fiber during carbonization. Mn33_3h presents the initial charge and discharge capacities of 1054.1 and 665.6 mAh g−1, and the discharge capacity at the 50th cycle remains 99.7% of that at the 2nd cycle. Beside the well rate capability at the range of current densities from 20 to 1000 mA g−1, Mn33_3h presents very good recovery ability after high rate cycling at 1000 mA g−1. The advantages of this composite structure as well as its high capacity make manganese oxide a very attractive candidate as an anode material for the next generation of rechargeable lithium ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: Monoclinic Li3V2(PO4)3 can be rapidly synthesized at 750°C for 5min (MW5m) by using temperature-controlled microwave solid-state synthesis method (TCMS). The carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage 3.0–4.3, MW5m presents a charge capacity 132mAhg−1, almost equivalent to the reversible cycling of two lithium ions per Li3V2(PO4)3 formula unit (133mAhg−1), and discharge capacity 126.4mAhg−1. In the cut-off voltage 3.0–4.8V, MW5m shows an initial discharge capacity of 183.4mAhg−1, near to the theoretical discharge capacity. In the cycle performance, the capacity fade of Li3V2(PO4)3 is dependent on the cut-off voltage and the preparation method. [Copyright &y& Elsevier]

Abstract Li 1.147 K 0.026 Mn 0.582 Ni 0.25 O 2 (LKMNO) sample is successfully prepared by doping K+ ions into Li slab without changing the original structure of Li 1.167 Mn 0.575 Ni 0.25 O 2 (LMNO). LKMNO sample delivers the capacities of 160.2 and 135.1 mAh g−1 at 1 and 5 C rates, respectively, but LMNO sample only delivers 135.1 and 0 mAh g−1. After 100 cycles at 1 C rate, LMNO and LKMNO samples respectively remain 67.4% and 93.0% of their initial capacities. The effects of K+ doping on the relationship between the charging-discharging process and phase change are detailed studied by the incremental capacity curves (d Q/ d V) at the various cycles. K+ doping in LKMNO sample plays an essential role in rate performance and cyclic performance, because it effectively hinders the formation of spinel structure and stabilizes the host layered structure. Considering the irreversible extraction of Li and O from the Li 2 MnO 3 region occurred beyond 4.6 V, after the charging/discharging are collected for 1–5 cycles at 2.5–4.9 V and 6–300 cycles at 2.5–4.6 V, LKMNO sample further reveals a remarkable improvement in cycling performance. In the full cell state (pouch cell), the discharge capacity of LKMNO is 194.6 and 115.4 mAh g−1 at 0.1 and 1 C rates, respectively, which are much higher than 175.5 and 79.7 mAh g−1 of LMNO sample. The capacity retention of LMNO and LKMNO samples is respective 48.8% and 74.9% of their initial capacity after 100 cycles. Graphical abstract Image 1 Highlights • Li 1.147 K 0.026 Mn 0.582 Ni 0.25 O 2 is successfully prepared by doping K+ into Li slab. • K+ doping results in Mn3+ state and is essential in rate and cyclic performance. • After 100 cycle LMNO and LKMNO remain 67.4% and 93.0% of their initial capacities. • K+ doping hinders the formation spinel structure and stabilizes the host structure. • In full cell LKMNO delivers two times capacity than LMNO at 1 C rate. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The α-Fe 2 O 3 grains were grafted onto the TiO 2 /CNFs via the vapor-solid reaction. • The TiO 2 /CNFs reserved void space to suppress the disintegration of the Fe 2 O 3. • The 3D network provide interstitial sites and enhanced pathways for Li+ and e−. Abstract α-Fe 2 O 3 grains grafted onto TiO 2 /carbon nanofibers (CNFs) for use as anode materials in lithium-ion batteries have been successfully fabricated by electrospinning and vapor-solid reaction (VSR). Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N 2 adsorption-desorption isotherms reveal that the ultrafine α-Fe 2 O 3 nanoparticles were formed on the TiO 2 /CNFs and have uniform dispersion along the fiber direction. The VSR approach could retard nucleation, thus making TiO 2 /CNFs with small Fe 2 O 3 grains grafting (approximately 5 nm in diameter). The TiO 2 /CNFs are capable of buffering the large volume variation of α-Fe 2 O 3 during cycling and preventing electrode pulverization and aggregation, as well as providing sufficiently large interstitial space within the crystallographic structure to host Li ions. The electrochemical properties of the composite electrodes were tested by galvanostatic cycling at both constant and variable current rates. The composite delivers both good rate capability under an uprated current density of 1000 mA g−1 and especially enhanced cycle stability (∼600 mA h g−1 after 200 cycles at a current density of 1000 mA g−1). The super electrochemical performance is attributed to a synergetic effect between α-Fe 2 O 3 and TiO 2 -CNFs as well as the three- dimensional (3D) network, which contributes to greatly enhanced diffusion kinetics and structural stability for lithium-ion batteries. This VSR approach can be extended to other hierarchical metal oxide nanostructures for favorable applications in electrochemical devices. [ABSTRACT FROM AUTHOR]

Tin-based materials are considered to be next-generation anode materials for lithium-ion batteries (LIBs) due to their high theoretical capacity and safety, but their large volume expansion results in rapid capacity fading. In this work, the heterostructure of Sn|SnO 2 submicron particles supported by carbon fibers and amorphous carbon layers (CF/Sn|SnO 2 @C) is successfully synthesized by hydrothermal and thermal treatments. Sn|SnO 2 submicron particles are uniformly grown on CF and encased in the CF network. Herein, CF together with a layer of amorphous carbon not only buffers the volume change of Sn|SnO 2 to prevent its pulverization and dissolution but also improves the electric and lithium ionic transportation capabilities during the lithiation/delithiation cycle. The CF/Sn|SnO 2 @C film can directly act as a binder-free anode for LIBs, exhibits a stable capacity of 657.6 mAh g −1 at a current density of 0.1 A g −1 after 50 cycles and presents better rate capacities than the Sn|SnO 2 @C comparison sample. Taking advantage of the stabilization and conductive channels of CF, this work demonstrates potential applications in the preparation of CF-based, binder-free anodes for LIBs in which metal oxide submicron particles can be effectively supported by a CF network. [ABSTRACT FROM AUTHOR]

A novel heterostructure of NiO/Ni 3 S 2 nanoflake is synthesized and composited with carbon nanofibers (CNF) membrane. NiO/Ni 3 S 2 nanoflakes are homogeneously dispersed in CNF network, herein, NiO/Ni 3 S 2 like leaf and CNF like branch. Carbon nanofibers network efficiently prevents the pulverization and buffers the volume changes of NiO/Ni 3 S 2 , meanwhile, NiO/Ni 3 S 2 nanoflakes through the conductive channels of carbon nanofibers own improved Li + diffusion ability and structural stability. The capacity of NiO/Ni 3 S 2 /CNF reaches to 519.2 mA g −1 after 200 cycles at the current density of 0.5 A g −1 while NiO/Ni 3 S 2 fades to 71 mAh g −1 after 40 cycles. Owing to the synergetic structure, the resultant binder-free electrode NiO/Ni 3 S 2 /carbon nanofibers shows an excellent reversible lithium storage capability. [ABSTRACT FROM AUTHOR]

Li 1.24 Ni 0.12 Co 0.12 Mn 0.56 O 2 (LNCM) with high specific capacity is a potential cathode for commercial lithium-ion batteries (LIBs). To improve the high-rate capacity and cyclic stability, LNCM sample is successfully coated by minor AlF 3 . The crystal structure and electrochemical properties of the bare and coated samples are investigated by X-ray diffractometry (XRD), scanning and transmission electron microscopy (SEM, TEM), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), and charge/discharge measurements. The coating layer AlF 3 efficiently plays a positive role in enhancing rate performance and cyclic stability of LNCM. At 0.5 A g −1 , the specific discharge capacity of LNCM@2%AlF 3 is 149 mAh g −1 much higher than 35 mAh g −1 in bare LNCM. At 20 mA g −1 , the specific discharge capacity of LNCM@2%AlF 3 is 223 mAh g −1 at the 60th cycle in comparison with 203 mAh g −1 in bare LNCM. Moreover, a proper AlF 3 coating layer efficiently ensures the stability of LNCM cathode operated at higher temperature. LNCM@2%AlF 3 operated at 55 °C remains 219 mAh g −1 at the 50th cycle, much higher than bare LNCM only remains 99 mAh g −1 at the 40th cycle. [ABSTRACT FROM AUTHOR]

In recent years, enormous effort have been made in recycling spent lithium-ion batteries (LIBs), but more efficient and energy efficient methods still need to be found. In this work, we propose a new recycling process which can directly use recycled metals as raw materials to re-synthesize LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode material based on co-precipitation method. The influence of temperature on the physical and electrochemical properties of the regenerated material has been studied by changing sintering temperature. The as-produced regenerated cathode materials gain the electrochemical performance as well as the commercial LiNi 0.5 Co 0.2 Mn 0.3 O 2. Cop-830 ℃ obtained at sintering temperature of 830 ℃ still delivers 149.2 mAh g−1 after 100 cycles at 0.2 C rate, which is 92.4% of its initial capacity. It confirms that the optimized sintering temperature is essential for the regeneration of spent ternary cathode materials in potential application. • Recycling process is successfully processed directly use recycled metals. • LiNi 0.5 Co 0.2 Mn 0.3 O 2 was regenerated from spent LIBs by co-precipitation method. • Electrochemical properties of regenerated materials reach to commercial materials. • Cop-830 ℃ delivers 149.2 mAh g−1 after 100 cycles at 0.2 C, 92.4% of initial capacity. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) contain a variety of toxic inorganic and organic compounds, and the spent cathode materials are high quality resources of Ni, Co, Mn, and Li elements. In this case, how to efficiently deal with spent materials has become an urgent problem. In this work, the regeneration of spent ternary materials via molten salt solid-liquid method and traditional solid-solid method are studied comparatively. Ordered and uniform crystals in MS-NCM are successfully grown in liquid medium of molten salts. The regenerated TS-NCM by traditional sintering method still presents inhomogeneous larger and smaller crystals. Moreover, only regeneration by molten salt method effectively removes F-contained impurity on the surface of spent materials, and the Ni3+ and Mn3+ on the crystal surface of MS-NCM are close to the values in commercial sample (Com-NCM). After 100 cycles at 0.2 C rate, MS-NCM and TS-NCM respectively deliver 149.1 mA h g−1 and 123.2 mA h g−1, maintaining 98.1% and 84.4% of their initial capacity. MS-NCM presenting better electrochemical performance than TS-NCM is attributed to the efficient regeneration of the spent cathode material in liquid medium of molten salts. [Display omitted] • Spent NCM regeneration via solid-liquid better than traditional via solid-solid. • Uniform NCM crystals successfully re-grown in liquid medium of molten salts. • Regeneration in molten salts effectively supplement Li+ and remove F-impurity. • MS-NCM delivers much higher capacity than TS-NCM after 100 cycle. [ABSTRACT FROM AUTHOR]

• Micron single crystals of LiNi 0.8 Co 0.1 Mn 0.1 O 2 were prepared by molten salt method. • SC-NCM has lower cationic mixing accompanying with ordered growth of micron crystal. • Ni(III) in SC-NCM is majority benefiting for cyclic stability. • After 300 cycles at 5C rate SC-NCM remains 80.7 mAh g−1 and retention 62.0%. • Micron single crystals on electrochemical property benefit for structure stability. In this work, Ni-rich layered micron-sized LiNi 0.8 Co 0.1 Mn 0.1 O 2 (SC-NCM) single crystals were prepared by wet ball-milling and molten-salt methods. Through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectrometry (XPS), the differences between SC-NCM and a commercial polycrystalline micron-sized NCM material (M-NCM) were compared. An extended sintering process for SC-NCM plays a role in decreasing cationic mixing accompanied by the ordered growth of single crystals. The SC-NCM sample presents homogeneous micron-sized crystals. The Ni3+ content in SC-NCM constitutes 90.45% of the total Ni content, while the Ni3+ in M-NCM constitutes only 68.49%. The existence of Ni2+ in ternary cathode materials is harmful to electrochemical stability and cyclic stability. The initial specific discharge capacity of SC-NCM (168 mAh g−1) is lower than that of M-NCM (187 mAh g−1); however, M-NCM shows a rapid decline in capacities and voltage plateaus from the 1st to 180th cycle. After 300 cycles at a 5 C rate, M-NCM remains only 42 mAh g−1 with a capacity retention rate of only 25.6% in comparison with SC-NCM with a remaining capacity of 80.7 mAh g−1 and a capacity retention of 62.0%. The effect of micron-sized single crystals on electrochemical properties during redox reactions is negative in terms of conductivity but positive in terms of structural stability. [ABSTRACT FROM AUTHOR]

Abstract: To substitute minor Mn2+ by the transition metal ion M=Mg2+, V3+, Fe2+, Co2+, or Gd3+, LiMn0.95M0.05PO4 samples are synthesized by a solid-state reaction route. The interpretation of doping effects is complicated by the interrelations between doping microstructure and morphology, because the crystal structure would be affected by the doped elements. The lattice structure and deviation of Li–O bond lengths of the doped LiMnPO4 are refined by XRD refinement. All the samples present a couple of oxidation and reduction peaks in cyclic voltammetry, corresponding to a redox Mn3+/Mn2+ reaction coupled with the extraction/reinsertion process of Li+ in LiMnPO4 structure. During charge/discharge process, the electron flowing and Li+ cation diffusion in the various doped LiMnPO4 samples should be different thermodynamic and kinetic process. For further studying which step in thermodynamic and kinetic process would affect or control the electrochemical performance, the initial charge/discharge capacities and cycleability of doped LiMnPO4 samples are obtained under different voltage range (from 2.7 to the upper cut-off voltage 4.4, 4.6 and 4.8V, respectively) and different environment temperatures (0, 25, and 50°C). At relative higher measuring temperature, the discharge capacity of Co-doped LiMnPO4 shows 151.9mAhg−1. [Copyright &y& Elsevier]

Lithium-rich cathode materials have the potential for applications in high energy lithium-ion batteries, but they suffer from a low rate performance and an inferior cycling stability. In this work, Li 1.167- x K x Mn 0.583 Ni 0·25 O 2 (x = 0, 0.025, 0.05 and 0.075) samples are synthesized and characterized. In addition, K+ doping results in small perturbations in the crystal structure of Li 1.167- x K x Mn 0.583 Ni 0·25 O 2 , such as the Li–O bond lengths, lattice parameters and the oxidation states of manganese, which effectively improves the lithium diffusion ability and hinders the detrimental interphase growth of the spinel phase during cycling. In a half-cell, Li 1·117 K 0·05 Mn 0·583 Ni 0·25 O 2 (LK2MNO) with an optimized doping quantity of K+ delivers the best capacities of 152.0 mAh g−1 after 100 cycles at a 1C rate and 82.9 mAh g−1 after 300 cycles at a 10C rate, in comparison with Li 1·167 Mn 0·583 Ni 0·25 O 2 , which has a capacity of only 126.0 and 33.3 mAh g−1. In the full-cell with graphite as the negative electrode, LK2MNO delivers an initial capacity of 249.9 mAh g−1 at a 0.1C rate and retains 90.8% of its initial capacity after 100 cycles. The surface chemical states of the positive electrode and negative electrodes after 100 cycles is studied by ex situ SEM and XPS measurements, and the results reveal that an appropriate K+ doping amount effectively hinders the dissolution of Mn2+ from the cathode material and decreases the decomposition of electrolytes to some degree. K+ doping in Mn-based lithium-rich cathode materials improves the lithium diffusion ability and hinders the detrimental interphase growth of the spinel phase during cycling. In full cell, the LK2MNO sample delivers an initial capacity of 249.9 mAh g−1 at a 0.1C rate and retains 90.8% of its initial capacity after 100 cycles. The surface chemical state of the positive and negative electrodes after 100 cycles reveal that K+ doping effectively suppresses side reactions and electrolyte decomposition. Image 1 • K+ doping results in small perturbations in Li 1.167- x K x Mn 0.583 Ni 0·25 O 2 structure. • Potassium doping decreases the detrimental interphase growth of spinel phase during cycling. • Expanding interlayer spacing by K+ provide fast conductive channel for Li+ diffusion. • LK2MNO delivers 249.9 mAh g−1 and remains 90.8% of initial capacity after 100 cycles. • K+ doping suppresses side reactions and electrolyte decomposition during cycling. [ABSTRACT FROM AUTHOR]