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The Li2MoO3 (LMO) material is one promising cathode material for lithium-ion batteries due to its high specific capacity and absence of oxygen release. However, its surface instability in air and poor conductivity have limited its application. To solve these problems, the Ru element has been successfully introduced into the LMO lattice with the aid of the molten salt method. XRD and TEM characterization showed that the introduction of Ru does not change the crystal structure but expands the crystal plane spacing of the {001} facets, which is further evidenced by density functional theory (DFT) calculations. XPS and EDS tests indicated that the introduction of Ru inhibits the oxidation of Mo species and leads to a more uniform distribution of the material. In addition, DFT calculations revealed that covalent interactions are formed between Mo4d/Ru4d and O2p orbitals, leading to a significant reduction of the band gap. Therefore, Ru-doped samples exhibit good electrochemical performances. The initial discharge capacity of an LMRO-2 sample reaches 299.1 mA h g−1 at a 1C rate, and the capacity remains at 125.2 mA h g−1 after 100 cycles. In comparison, the initial discharge capacity of pure phase sample LMO is only 250.5 mA h g−1 under the same conditions, and the capacity remains only at 76.5 mA h g−1 after 100 cycles. The present results confirmed that Ru doping is an effective strategy to improve the performance of the LMO cathode material. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Pristine LiNi 0.5 Mn 1.5 O 4 and FePO 4 -coated one with Fd-3m space groups were prepared by a sol-gel method. The structure and performance were studied by X-ray diffraction (XRD) rietveld refinement, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS) mapping, electrochemical impedance spectroscopy (EIS) and charge-discharge tests, respectively. The lattice parameters of all samples almost remain the same from the Rietveld refinement, revealing that the crystallographic structure has no obvious difference between pristine LiNi 0.5 Mn 1.5 O 4 and FePO 4 -coated one. All materials show similar morphologies with uniform particle distribution with small particle size, and FePO 4 coating does not affect the morphology of LiNi 0.5 Mn 1.5 O 4 material. EDS mapping and HRTEM show that FePO 4 may be successfully wrapped around the surfaces of LiNi 0.5 Mn 1.5 O 4 particles, and provides an effective coating layer between the electrolyte and the surface of LiNi 0.5 Mn 1.5 O 4 particles. FePO 4 (1 wt%)-coated LiNi 0.5 Mn 1.5 O 4 cathode shows the highest discharge capacity at high rate (2 C) among all samples. After 80 cycles, the reversible discharge capacity of FePO 4 (1 wt%) coated LiNi 0.5 Mn 1.5 O 4 is 117 mAh g−1, but the pristine one only has 50 mAh g−1. FePO 4 coating is an effective and controllable way to stabilize the LiNi 0.5 Mn 1.5 O 4 /electrolyte interface, and avoids the direct contact between LiNi 0.5 Mn 1.5 O 4 powders and electrolyte, then suppresses the side reactions and enhances the electrochemical performance of the LiNi 0.5 Mn 1.5 O 4. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The electrochemical property of LNMO@LLTO cathode is first reported. • Prominent rate capability of LNMO@LLTO is demonstrated. • The mechanism of performance improvement is analyzed in detail. Abstract Pristine LiNi 0.5 Mn 1.5 O 4 (LNMO) and LNMO@LLTO (Li 0.33 La 0.56 TiO 3) composites were synthesized by a sol-gel process. The lattice constant of LNMO increases with the increasing coated content of LLTO. All samples show irregular morphologies, and the particle size distributes uniformly between 200 and 500 nm. The inherent characteristic of Li 0.33 La 0.56 TiO 3 with a large ionic conductivity decreases the interfacial charge transfer impedances, leading to an enhanced migration rate of Li-ions in the composite. As a cathode of LIBs, LNMO@LLTO (3 wt%) exhibits a large reversible capacity and a remarkable rate capability. Therefore, Li 0.33 La 0.56 TiO 3 modification can be considered as an effective strategy to improve the rate capability of LNMO. [ABSTRACT FROM AUTHOR]

Well-crystallized and high-performance x Li 2 MnO 3 ·(1- x )LiMn 1/3 Co 1/3 Ni 1/3 O 2 cathode materials over a wide compositional range (0.1 ≤ x ≤ 0.5) were prepared by a facile co-precipitation strategy. All samples show small and uniform particle dimensions in the range of 200-500 nm. 0.3Li 2 MnO 3 ·0.7LiMn 1/3 Co 1/3 Ni 1/3 O 2 (LMNC3) delivers the highest discharge capacities of 321.1 mA h g −1 at 0.1C, 305.2 mA h g −1 at 0.2 C, 243.2 mA h g −1 at 0.5C, 205.9 mA h g −1 at 1C, 182.1 mA h g −1 at 2C, and 133.7 mA h g −1 at 5C, respectively. LMNC3 also exhibits an excellent fast charge-discharge performance, and even at a charge-discharge rate of 2C in the 100th cycle its capacity still remains 128.2 mAh g −1 . The improved performance of LMNC3 can be ascribed to the improvement of electrochemical reversibility, lithium ion diffusion and ionic conductivity. First-principles calculation based on density function theory reveals that the strong covalent bonds formed between Mn-3d and O-2p orbits and stable Li 2 MnO 3 -enriched layer are helpful for stabilizing the LiMn 1/3 Co 1/3 Ni 1/3 O 2 structure. The same strategy adopted in this work could be helpful to develop other Li-rich cathodes with long cycle life and high rate performance. [ABSTRACT FROM AUTHOR]

Well-defined LiNi 0.5 Mn 1.5 O 4 powder has been synthesized by ethylene glycol (EG)-assisted oxalic acid co-precipitation method. The structure and physicochemical properties of this as-prepared powder were investigated by powder X-ray diffraction (XRD), Raman spectra (RS), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge test in detail. XRD shows impurity phase of Li y Ni 1-y O due to the oxygen loss reaction at high temperatures. SEM indicates that LiNi 0.5 Mn 1.5 O 4 synthesized by EG-assisted method has a uniform and narrow size distribution under 1 μm. RS confirms that both samples have Fd-3 m space group. EIS and CV test exhibit that LiNi 0.5 Mn 1.5 O 4 electrode synthesized by EG-assisted method has lower potential polarization, smaller charge transfer resistance, higher reversibility and larger lithium ion diffusion coefficient than the one obtained by ammonium hydroxide co-precipitation method. Galvanostatic charge–discharge test reveals that LiNi 0.5 Mn 1.5 O 4 synthesized by EG-assisted method shows higher discharge capacity than that the one synthesized by ammonium hydroxide co-precipitation method at each rate. [ABSTRACT FROM AUTHOR]

Abstract: Li4Ti5O12 (LTO)-coated 5V spinel LiMn1.5Ni0.5O4 as cathode was prepared by the sol–gel method followed by high-temperature calcinations. The structural and electrochemical properties of these cathodes were investigated using differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and charge–discharge studies. TG–DTA shows that LiMn1.5Ni0.5O4 spinel forms at about 400°C. XRD reveals that a substitutional compound LiMn2−x−y Ni x Ti y O4 can be formed when the coated content of LTO exceeds 3wt%. SEM exhibits that the coated LiMn1.5Ni0.5O4 is covered with small particles that consist mainly of LTO. CV and dQ/dV versus voltage curves demonstrate that the modified material exhibits remarkably enhanced electrochemical reversibility and stability. The charge–discharge test indicates that 3wt% LTO-coated LiMn1.5Ni0.5O4 has excellent fast charge–discharge performances. These results reveal that LTO-coated layer protects the surface of the active materials from HF in the electrolyte during electrochemical cycling. As a result, the surface-modification of LiMn1.5Ni0.5O4 with LTO should be an effective way to improve the fast charge–discharge properties. [Copyright &y& Elsevier]

Abstract: The Li4Ti5O12 (LTO)-coated LiCoO2 powders treated at different temperatures (t =500, 600, 700 and 900°C) and coated contents (x =0, 3%, 5%, 10% and 15%) were prepared. The effects of treated temperatures on structure and performance of LiCoO2 coated by LTO particles have been investigated by X-ray diffraction (XRD) and the galvanostatic charge–discharge test at the high upper voltage limit of 4.5V. 3wt.% and 5wt.% LTO-coated materials expose the absence of secondary phase peaks in the range of the diffraction patterns below 700°C, and distinct additional peaks start appearing when the treated temperature arrives at 900°C. The diffraction patterns of the 15wt.% LTO-coated LiCoO2 shift toward higher angles compared to the other coated and bare LiCoO2. The 3wt.% LTO-coated LiCoO2 cathodes treated at 500, 700 and 900°C exhibit discharge capacities of 157, 162 and 140mAhg−1, respectively, versus capacities of 82mAhg−1 for the uncoated cathodes after 40 cycles. The LTO coatings are shown to suppress the capacity fade by reducing cell polarization. [Copyright &y& Elsevier]

Abstract: The electronic property and structural stability of LiMn2O4 and LiNi0.5Mn1.5O4 with Fd m space group are investigated by density functional theory (DFT) plane-wave pseudopotential method. The calculated values of Mn(Ni)–O bond lengths are found to be consistent with the reported experimental values. Due to the Ni doping, the significant shortening of Mn(Ni)–O bond strengthens the structural stability of spinel. The electronic properties of spinel show that the bonding between O and metal (Mn and Ni) is also strengthened due to the Ni doping, and then it improves the structural stability of LiNi0.5Mn1.5O4. Ni-doped spinel has a lower formation enthalpy than that of the pristine, indicating that the Ni doping improves the structural stability of spinel. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Li4Ti5O12 (LTO) coating amount on the electrochemical cycling behavior of the LiCoO2 cathode was investigated at the high upper voltage limit of 4.5V. Li4Ti5O12 (≤5wt.%) is not incorporated into the host structure and leads to formation of uniform coating. The cycling performance of LiCoO2 cathode is related with the amount of Li4Ti5O12 coating. The initial capacity of the LTO-coated LiCoO2 decreased with increasing Li4Ti5O12 coating amount but showed enhanced cycling properties, compared to those of pristine material. The 3wt.% LTO-coated LiCoO2 has the best electrochemical performance, showing capacity retention of 97.3% between 2.5V and 4.3V and 85.1% between 2.5V and 4.5V after 40 cycles. The coulomb efficiency shows that the surface coating of Li4Ti5O12 is beneficial to the reversible intercalation/de-intercalation of Li+. LTO-coated LiCoO2 provides good prospects for practical application of lithium secondary batteries free from safety issues. [Copyright &y& Elsevier]

[Display omitted] • Zinc storage mechanism of V oxides-based compounds is systematically summarized. • Strategy developing high-performance V oxides-based compounds is proposed. • An insight into the future research direction of V oxides-based compounds is highlighted. Aqueous rechargeable Zn-ion batteries (AZIBs) have regarded as promising secondary chemical battery system because of the excellent safety, low cost and environmental friendliness. Nonetheless, it is still a great challenge to exploit suitable cathode materials for the insertion of zinc ions. The vanadium oxides-based materials are regarded as hopeful cathode materials of AZIBs because of their various coordination numbers and oxidation states. Especially, the hydrated, monovalent (divalent)-cations co-preinserted vanadium oxides show more excellent electrochemical performance because of the enlarged interlayer space. In this review, a comprehensive overview of the energy storage mechanisms and research development of various efficient ways to improve electrochemical performance for vanadium oxides-based compounds is presented. Finally, some insights into the future developments, challenges, and prospects of vanadium oxides-based compounds for AZIBs are proposed. This review illustrates electrochemical reaction mechanism of vanadium oxides-based compounds for AZIBs, and benefits the discovery of new AZIBs cathode materials, gives a novel viewpoint to shed light on the future innovation in vanadium oxides-based cathode materials, then facilitates the fast development and large-scale applications of AZIBs. The article will provide useful guidance for future design and construction of high-performance cathode materials for AZIBs. [ABSTRACT FROM AUTHOR]

Abstract: LiMn2O4 and LiNi0.5Mn1.5O4 spinel cathode materials powder was successfully synthesized by an ultrasonic-assisted co-precipitation (UACP) method. The geometry structures of LiMn2O4 and LiNi0.5Mn1.5O4 are successful optimized and the corresponding electronic structures are then calculated by density functional theory (DFT) plane-wave pseudopotential method. The initial discharge capacity of LiMn2O4 and LiNi0.5Mn1.5O4 are 130.9 and 130.5 mAh·g−1, respectively. The calculated average voltages of Li x Mn2O4 and Li x Ni0.5Mn1.5O4 at the range of 0≤ x ≤1 are 4.28 and 4.66 V, and the errors are 4.39% and 0.74% compared with electrochemical experiment value, respectively. The increase of voltage after doping is related with the different filling of electrons in M–O6 octahedron framework after the intercalation/deintercalation of Li+, and lithium element exists in spinel materials in form of ions. [Copyright &y& Elsevier]

Abstract: Spinel LiNi0.4Mn1.6O4 has been successfully synthesized by ultrasonic-assisted co-precipitation (UACP) method. The structure and physicochemical properties of this as-prepared powder compared with the LiNi0.4Mn1.6O4 synthesized by co-precipitation method were investigated by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge test in detail. XRD and SEM show that all samples have high phase purity, and ultrasonic process plays an important role in controlling morphology; FT-IR reveals that the Mn(III)–O stretching band at 511cm−1 has a red shift to 503cm−1, and the Mn(IV)–O stretching band at 612cm−1 has a blue shift to 622cm−1 because of the doped Ni. CV confirms that the LiNi0.4Mn1.6O4 sample (UACP) has bigger area of the reduction peaks than that of sample synthesized by co-precipitation method, indicating that the former has higher discharge capacity than that of the latter. Galvanostatic charge–discharge test indicates that the initial discharge capacities for the LiNi0.4Mn1.6O4 (UACP) at C/5 and 1C are 129 and 116mAhg−1, respectively. After 100 cycles, their capacity retentions are 94.6% and 85.3%, respectively. EIS indicates that LiNi0.4Mn1.6O4 samples synthesized by UACP method have smaller charge transfer resistance than that of samples synthesized by co-precipitation method corresponding to the extraction of Li+ ions. [Copyright &y& Elsevier]

Abstract: Sub-micro spinel LiNi0.5−x Mn1.5+x O4 (x <0.1) cathode materials powder was successfully synthesized by the ultrasonic-assisted co-precipitation (UACP) method. The structure and electrochemical performance of this as-prepared powder were characterized by powder XRD, SEM, XPS, CV and the galvanostatic charge–discharge test in detail. XRD shows that there is a small Li y Ni1−y O impurity peak placed close to the (400) line of the spinel LiNi0.5−x Mn1.5+x O4, and the powders are well crystallized. XPS exhibits that the Mn oxidation state is between +3 and +4, and Ni oxidation state is +2 in LiNi0.5−x Mn1.5+x O4. SEM shows that the prepared powders (UACP) have the uniform and narrow size distribution which is less than 200nm. Galvanostatic charge–discharge test indicates that the initial discharge capacities for the LiNi0.5−x Mn1.5+x O4 (UACP) at C/3, 1C and 2C, are 130.2, 119.0 and 110.0mAhg−1, respectively. After 100 cycles, their capacity retentions are 99.8%, 88.2%, and 73.5%, respectively. LiNi0.5−x Mn1.5+x O4 (UACP) at C/3 discharge rate exhibits superior capacity retention upon cycling, and it also shows well high current discharge performance. CV curve implies that LiNi0.5−x Mn1.5+x O4 (x <0.1) spinel synthesized by ultrasonic-assisted co-precipitation method has both reversibility and cycle capability because of the ultrasonic-catalysis. [Copyright &y& Elsevier]

Layered oxide cathode materials have good structural stability and high capacity, making them ideal cathode materials of Na-ion batteries (SIBs). Nonetheless, the irreversible phase transitions and metal dissolution often result in poor cycling stability. Here, a simple strategy was developed to Na 2 MoO 4 and MoO 3 coated Na 0.67 Fe 0.15 Cu 0.1 Mn 0.65 Ni 0.1 O 2 (NFCMN-M) as cathode material of SIBs with ultrahigh cycling stability caused by the enhanced kinetic. The formed Na 2 MoO 4 layer on the surface of Na 0.67 Fe 0.15 Cu 0.1 Mn 0.65 Ni 0.1 O 2 (NFCMN) particles supplies a good conductive connection, and inhibits side effects between cathode material and electrolyte. Thanks to the unique component, the as-prepared NFCMN-M shows a good rate performance with a reversible discharge capacity of 132.4, 112.6, 102.3, 87.1 and 79.3 mAh g−1 at 0.1, 0.5, 1, 3 and 5C, respectively. The NFCMN-M also delivers an initial capacity of 73.7 mAh g−1 at 10C and an ultrahigh cycling stability with a capacity retention rate of about 80 % after 1000 cycles. The result confirms that the Na 2 MoO 4 modification is a direct and effective strategy to improve the capacity and enhance cycling stability of NFCMN at high charge-discharge rates. [ABSTRACT FROM AUTHOR]

To improve the rate capability and cycle performance of the LiMnPO 4 cathode, carbon-coated LiMn 1- x Fe x PO 4 (0 ≤ x ≤ 0.5) nanocomposites have been successfully prepared by hydrothermal process. The carbon-coating does not affect the morphology of LiMn 1- x Fe x PO 4 (0 ≤ x ≤ 0.5), but restrains the aggregation of particles, and an obvious carbon film with a thickness of about 2.5 nm can be observed on the surface of LiMn 1- x Fe x PO 4. Fe doping has an important influence on the morphology of LiMnPO 4 , and carbon-coated LiMn 0·5 Fe 0·5 PO 4 obviously shows a nanorod morphology with a length of 100–200 nm. Carbon-coated LiMn 0·5 Fe 0·5 PO 4 shows excellent rate capability, and delivers specific capacities of about 156.4, 151, 147.6, 145.7 and 137.3 mAh g−1 at 0.05, 0.1, 0.2, 0.5 and 1 C, respectively. However, carbon-coated LiMnPO 4 only delivers specific capacities of about 109.5, 100, 82.4, 79 and 65.8 mAh g−1 at corresponding current densities. The carbon-coated LiMn 0·5 Fe 0·5 PO 4 also shows a large initial specific capacity of 134.5 mAh g−1 at 5 C rate with outstanding capacity retention of 84.6% even after 100 cycles. The enhanced rate capability and cycling stability of carbon-coated LiMn 0·5 Fe 0·5 PO 4 at high rate are attributed to the decreased charge transfer resistance, decreased electrode polarization, enhanced reversibility of extraction and insertion of Li-ions, and increased Li-ion diffusion coefficient. DFT calculation shows that Fe–O bond is stronger than Mn–O bond, and it can be expected that the thermodynamic stability of LiFe 0·5 Mn 0·5 O 4 will be improved obviously in comparison with LiMnPO 4 , which well explains the better cycling stability of LiFe 0·5 Mn 0·5 O 4 than LiMnPO 4 observed experimentally. Image 1 • The doping contents of affect the morphology of LiMnPO 4. • Prominent rate capability of LiMn 0·5 Fe 0·5 PO 4 /C nanorod is demonstrated. • The mechanism of performance improvement is analyzed by DFT. [ABSTRACT FROM AUTHOR]

[Display omitted] Li-rich Mn-based oxides (LRMOs) are considered as one of the most-promising cathode materials for next generation Li-ion batteries (LIBs) because of their high energy density. Nevertheless, the intrinsic shortcomings, such as the low first coulomb efficiency, severe capacity/voltage fade, and poor rate performance seriously limit its commercial application in the future. In this work, we construct successfully g-C 3 N 4 coating layer to modify Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 (LMNC) via a facile solution. The g-C 3 N 4 layer can alleviate the side-reaction between electrolyte and LMNC materials, and improve electronic conduction of LMNC. In addition, the g-C 3 N 4 layer can suppress the collapse of structure and improve cyclic stability of LMNC materials. Consequently, g-C 3 N 4 (4 wt%)-coated LMNC sample shows the highest initial coulomb efficiency (78.5%), the highest capacity retention ratio (78.8%) and the slightest voltage decay (0.48 V) after 300 loops. Besides, it also can provide high reversible capacity of about 300 and 93 mAh g−1 at 0.1 and 10C, respectively. This work proposes a novel approach to achieve next-generation high-energy density cathode materials, and g-C 3 N 4 (4 wt%)-coated LMNC shows an enormous potential as the cathode materials for next generation LIBs with excellent performance. [ABSTRACT FROM AUTHOR]

[Display omitted] Lithium-rich manganese-based cathode has made a subject of intense scrutiny for scientists and application researchers due to their exceptional thermal stability, high specific capacity, high operating voltage, and cost-effectiveness. However, the inclusion of cobalt, as a crucial component in lithium-rich manganese-based cathode materials, has become a cause for concern due to its limited availability and non-renewable nature, which eventually limits the growth of the battery industry and increase costs. Considering the poor stability of cobalt-free cathode, this work proposes a coating strategy of LiF through a simple high-temperature melting method. Directly coating LiF on Li 1.2 Ni 0.2 Mn 0.6 O 2 surface is found to be an effective way to protect the cathode material, decrease metal solubility, and inhibit irreversible phase transition processes, thus leading to an improved electrochemical performance. As a result, the battery employing LiF coated Li 1.2 Ni 0.2 Mn 0.6 O 2 cathode can be stabilized over 280 cycles and maintain a capacity of 110 mAh g−1 at 1C. What's more, the mechanisms of ion insertion/extraction behavior and ion migration process are also studied systematically. This study will open the avenue to develop a high-energy battery system with cobalt-free cathode. [ABSTRACT FROM AUTHOR]

In this work, the Prussian-blue type FeFe(CN) 6 (Fe-PBA)/Ti 3 C 2 T x hybrids (Fe-PBA-CT) with improved reversible capacity and high stable cycling stability are synthesized by a hydrolytic process. The Fe–PBAs cubic nanoparticles effectively promote electrode/electrolyte contact, accelerate electron transfer and ion diffusion. The Ti 3 C 2 T x MXenes conductive networks can not only facilitate the transmission and diffusion of electrons/ions, but also provide additional Li+ ions storage sites to increase the specific capacity, thereby improving the rate performance and reversible capacity. Benefiting from the synergistic effect of nano cubic Fe-PBA and layered Ti 3 C 2 T x MXenes, compared with pristine Fe-PBA, the Fe-PBA-CT2 cathode with moderate content of Ti 3 C 2 T x MXenes delivers a superior discharge capacity of 145.9 mAh g−1 at 0.1 C, remarkable rate performance and excellent cycling stability without capacity fading after 900 cycles at 1 C. The ex-situ X-ray diffraction test proves that the structure change of Fe-PBA-CT is highly reversible process during cycling. The as-prepared Fe-PBA-CT exhibits a promising potential as a cathode material for the next generation lithium-ion batteries with stable cycling stability. [ABSTRACT FROM AUTHOR]

Abstract: The impact of lithium extraction on the structural stabilities, electronic structures, bonding characteristics, and electrochemical performances of LiFePO4 compound was investigated by first-principles technique. The results demonstrated that the partition scheme of electrons not only affects the calculated atomic charges but also the magnetic properties. In FePO4 and LiFePO4 compounds, all Fe ions take high spin arrangements and have large magnetic moments (MMs), while the MMs of other ions are very small. The magnetisms of Li x FePO4 compounds are mainly originated form Fe ions. It was found that the changes in d band electrons of the transition metals do play an important role in determining the voltage of a battery (versus Li/Li+). Furthermore, the variations in d band electrons also provide us a method to control the density of states (DOS) and carrier concentration at the Fermi energy. Our calculations confirmed that the substitution of Fe by Co and Ni ions leads to a voltage increase by about 0.70V and 1.23V respectively. According to the bond populations, it can be identified that strong covalent bonds are formed between O and P ions. The P–O bonds are much stronger than Fe–O ones. The partial DOSs further revealed that the covalent bonds in Li x FePO4 are derived from the orbital overlaps between O2s,2p and P3s,3p states, and the overlap between Fe3d and O2p states. Such covalent bonds are of particularly importance for the excellent thermodynamic stabilities of the two-ends structures of Li x FePO4. [Copyright &y& Elsevier]

The NASICON structure of Na 3 V 2 (PO 4) 2 F 3 (NVPF) separates the valence electrons between the polyanion group and V and regulates the redox coupling energy. As a result, NVPF exhibits a high operating voltage in sodium-ion batteries. However, NVPF cathode material has poor specific capacity and low-rate performance. It is necessary to improve the electrochemical performance by increasing the electronic conductivity and accelerating the ion diffusion rate. Through morphology control, more active sites and ion channels can be provided to enhance rate performance and cycle stability. However, there are few reviews on how to control the morphology of NVPF. Therefore, this paper starts with the factors affecting the morphology of NVPF. The effects of pH value, surfactant, and external additives on its morphology were systematically summarized. On this basis, reasonable strategies, including morphology design, preparation method, structure control, surface modification, and defect engineering, are summarized. This paper provides theoretical support for the development of high-voltage NVPF. It provides inspiration for creating NVPF cathode materials with high specific capacity and high cycle performance. • The effects of various factors on the morphology of Na 3 V 2 (PO 4) 2 F 3 were systematically summarized. • The electrochemical properties of Na 3 V 2 (PO 4) 2 F 3 coated with different carbon sources were summarized. • The low-pressure platform caused by fluorine loss and its fluorine supplement measures are explained. • The effects of binders and electrolyte additives on Na 3 V 2 (PO 4) 2 F 3. [ABSTRACT FROM AUTHOR]

• V2O5-coated LNMO shows excellent cycling stability. • V2O5-coated LNMO exhibits outstanding rate capability. • V2O5-coated LNMO indicates high reversible capacity at high rate. LiNi 0.5 Mn 1.5 O 4 (LNMO) and V 2 O 5 -modified LNMO materials with P 4 3 32 structure were prepared by ethanol assisted co-precipitation process. The discharge capacities of V 2 O 5 -coated LiNi 0.5 Mn 1.5 O 4 is 131.4, 122, 111.1 93.8 and 52.1 mAh g−1 at 0.2, 0.5, 1, 2 and 5 C charge-discharge rates, respectively. The discharge capacities of pristine LNMO are only 125.7, 107.3, 86.2, 69.7 and 37.6 mAh g−1 at homologous rates. The V 2 O 5 modification can be considered as an efficient way to enhance the rate capability of LNMO. The improved rate capability of V 2 O 5 -coated LNMO material could be ascribed to the enhanced lithium-ions diffusion coefficient and reduced charge-transfer reaction resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • NFCMT-0.05 material possesses a capacity retention of 83.5% after 400 cycles at 5C. • NFCMT-0.05 keeps the P2 phase structure during the sodiation/desodiation process. • NFCMT-0.05 exhibits the reversible anionic redox reaction during cycling. • DFT calculation proves the doping of Ti promotes the valence transition of Fe and Mn. P2-type layered oxides with low Na+ diffusion barriers have emerged as promising cathode materials for sodium-ion batteries (SIBs) due to excellent cycle stability and rate performance. Among them, Co/Ni-free Fe-Mn-Cu based cathode materials have gained significant attention owing to their abundance, low cost, and environmentally friendless. However, their practical application has been hindered by irreversible phase changes during the charging/discharging process, leading to rapid capacity decay. To address this issue, the inactive element (Titanium) is introduced in Na 0.70 Fe 0.20 Cu 0.20 Mn 0.60 O 2 oxides to mitigate the detrimental phase transitions and enhance electrochemical performance by facilitating anionic redox reactions. The resulting Na 0.70 Fe 0.20 Cu 0.20 Mn 0.55 Ti 0.05 O 2 (NFCMT-0.05) cathode material exhibits a high initial discharge specific capacity of 186 mAh/g at 0.1C and superior cycling stability, with a capacity retention of 83.5% after 400 cycles at 5C between 2.0 and 4.3 V. Furthermore, the NFCMT-0.05 maintains P2 phase structure throughout the entire sodiation/desodiation process, and the reversible oxygen-related redox reaction provides additional discharge capacity for the Fe-Mn-based cathode above 4.1 V. The NFCMT-0.05 also demonstrates fast Na+ ion transfer kinetics and excellent rate performance, delivering a discharge capacity at 5C that is 60% of that at 0.1C. The DFT calculation confirms that the introduction of titanium effectively reduces the volume change and suppresses the relative slip of adjacent TMO 6 layers. As a result, Ti-doping is instrumental in improving the cycle stability of NFCMT. This work offers a low-cost strategy for constructing high-performance cathode materials for SIBs. offering promising prospects for the development of efficient and affordable energy storage systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na 1.06 Fe[Fe(CN) 6 ]·2.8H 2 O/Na 2 WO 4 materials with stable cycle stability are fabricated for Li-ion batteries for the first time. • The introduction of Na 2 WO 4 enhances the electrochemical property of Na 1.06 Fe[Fe(CN) 6 ]·2.8H 2 O. • Na 1.06 Fe[Fe(CN) 6 ]·2.8H 2 O/Na 2 WO 4 material shows a potential application prospect. Prussian blue analogues have been considered as one of hopeful cathode materials of Li-ion batteries (LIBs) because of their tunable composition, low cost and simple synthesis method, but the high volume variation and electrical resistance during cycling limit the wide application. In this work, Na 1.06 Fe[Fe(CN) 6 ]·2.8H 2 O/Na 2 WO 4 (PBA/NW) composites with high performance are successfully synthesized by a hydrothermal route following through a simple solution dispersion approach. The Na 2 WO 4 coating will not alter the structure and morphology of PBA sample. Na 2 WO 4 coating improves the structure stability and Li+ insertion/extraction reversibility, and decreases the charge transfer resistance, then promotes the transfer of Li+. The PBA-NW2 indicates an outstanding reversible discharge capacity of 134.9 mAh g−1 at 1C after 1000 cycles, but the pure PBA only performs a discharge capacity of 108 mAh g−1. In addition, PBA-NW2 also indicates superior rate property with discharge capacity of 150.3, 145.1, 140.0, 132.5, 132.32, 105.3, 91.9 mAh g−1 at 0.1, 0.3, 0.5, 1, 2, 5 and 10C, respectively. This work offers a facile and easy synthesis method to construct high-performance Prussian blue analogues cathode material for low-cost LIBs. [ABSTRACT FROM AUTHOR]

Rechargeable aqueous Zn–MnO 2 batteries have been developed rapidly in decades because of the low cost, rich resources, low toxicity, and high working potential. Unfortunately, MnO 2 -based cathode materials also suffer from poor conductivity, Mn dissolution, sluggish ion diffusion dynamics and bad structure stability, resulting in low reversible capacity and inferior cyclability. Especially, the formation of irreversible inert phase on the surface of electrode can inhibits the further electrochemical reactions between MnO 2 and electrolyte, and result in the failure of Zn–MnO 2 battery. A comprehensive understanding of formation mechanism for the irreversible inert phases will act a vital role in developing high-performance Zn–MnO 2 battery. This review mainly concentrates on recent progress of the formation mechanism and solutions of irreversible inert phases of Zn–MnO 2 battery. A comprehensive optimization strategy of alleviating the generation of irreversible inert phase to boost the electrochemical property of MnO 2 -based materials is put forward. This review clarifies the formation mechanism of irreversible inert phase in the MnO 2 -based material for aqueous Zn–MnO 2 battery, and put forward the development prospects of MnO 2 -based cathode materials for AZIBs. This provides new perspectives for the fabrication of MnO 2 -based cathode materials in the future, thus accelerating the extensive development and commercial application of aqueous Zn–MnO 2 battery. [Display omitted] • The alleviation strategies of the formation of inert phase of MnO 2 -based cathode are proposed for the first time. • The formation mechanism of irreversible inert phase in the MnO 2 -based material is clarified. • This review provides a specific viewpoint for the construction of aqueous high-performance Zn–MnO 2 battery. [ABSTRACT FROM AUTHOR]

[Display omitted] Benefiting from the low cost, high safety and environmentally friendly characteristics, aqueous second zinc ion batteries (AZIBs) have attracted wide attention. The electrochemical performance of the AZIBs is highly influenced by cathode materials. Mn-based compounds are deemed as promising cathode materials for AZIBs because of their various crystal structures and three-dimensional spatial frameworks. However, the diversity in crystal structure and chemical constituent for Mn-based compounds lead to a distinction of energy storage mechanisms, which engenders tremendous discrepancy in electrochemical properties. Herein, a state-of-the-art review of the rational construction of high-performance Mn-based cathodes of AZIBs is presented. Firstly, the energy storage mechanisms of Mn-based cathodes are systematically clarified. Accordingly, the reasonable strategies including morphology design, surface modification, defect engineering, structure modulation are comprehensively summarized. At last, the challenges, future developments, and prospects of Mn-based materials for AZIBs are prospected. This review provides an important understanding for the design and optimization of high-performance Mn-based cathodes materials, which can be expected to shed light on the future development of stable Mn-based cathodes toward high-performance AZIBs. [ABSTRACT FROM AUTHOR]

Prussian blue analogue material is regarded as an ideal cathode candidate for Li-ion batteries due to its open 3D frame structure and various transition metals with different valence states. However, poor electronic conductivity and structural collapse severely limit its application in the electrochemical field. In this work, Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O electrode materials with stepwise hollow inverted pyramid morphology are prepared by simple hydrothermal method. The inverted pyramid Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O maintains the stability of the crystal structure and slows down the volume expansion during the Li + insertion-extraction process. Benefiting from the unique structure and composition, the discharge specific capacities of the optimal Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O electrode (FeHCF-2) are 153.7, 126.28, 119.4 and 113.4, 107.61, 102.52 and 92.46 mAh·g−1 at 0.1, 0.3, 0.5, 1, 2, 5 and 10 C, respectively. The first discharge capacity of FeHCF-2 electrode at 1 C is 111.88 mAh·g−1, and the discharge capacity of FeHCF-2 electrode is 115.04 mAh·g−1 after 1000 cycles, indicating that FeHCF-2 electrode has ultrastable cycle stability. Therefore, designing the hollow inverted pyramid morphology can be regarded as an available way to enhance the electrochemical activity of Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O for advanced lithium-ion batteries, and effective design strategies can be used for the modification of other cathode materials for Li-ion batteries. [Display omitted] • The hollow inverted pyramid Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O with ultrastable cycle stability are constructed for Li-ion batteries. • The hollow inverted pyramid Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O improves the electrochemical property of Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O. • The hollow inverted pyramid Na 1.13 Fe[Fe(CN)] 6 ·3.22H 2 O electrode material shows a potential application prospect. [ABSTRACT FROM AUTHOR]

As cathode materials of sodium-ion batteries (SIBs), O3-type NaTMO 2 (TM = transition metal) have attracted wide interest. However, the irreversible structural change during the cycling and the unsatisfactory rate performance hinder their practical application. In this work, we designed sodium-deficient O3 phase-Na 0.75 Fe 0.5- x Cu x Mn 0.5 O 2 as the cathode materials of SIBs by simple sol-gel method to improve the electrochemical performance. The suitable copper ion doping can stabilize crystal structure, deliver higher discharge capacity, and restrain the nonreversible phase transition from O3 to P3. The Na 0.75 Fe 0.25 Cu 0.25 Mn 0.5 O 2 can provide a reversible capacity of 100 mAh g−1 with a capacity retention of 91% between 2.5 and 4.1 V at 0.1 C. The sodium storage mechanism and phase transition process of Na 0.75 Fe 0.25 Cu 0.25 Mn 0.5 O 2 were revealed by the ex-situ XRD and XPS. When charging to 3.2V, the phase change from single-phase O3 to biphase P3/O3 is found. After a complete cycle, the biphase P3/O3 regains O3 phase, demonstrating the phase transition of Na 0.75 Fe 0.25 Cu 0.25 Mn 0.5 O 2 is completely reversible, which is mainly based on the solid-solution reaction during the whole electrochemical reaction process. Meanwhile, the Mössbauer spectroscopy also displays the iron atoms in two different coordination environments when charged to 4.1 V, indicating a coexistence of P3 and O3 phases. This sodium deficient cathode material possesses advantages of high capacity from the O3 phase and the excellent stability from the P2 phase simultaneously. This work provides a new idea for the design of cathode materials for SIBs. [Display omitted] • Sodium-deficient O3 phase-Na 0. 7 5 Fe 0.5- x Cu x Mn 0.5 O 2 are constructed for the first time. • The Na storage mechanism of Na 0. 7 5 Fe 0.5- x Cu x Mn 0.5 O 2 is revealed by ex-situ XRD. • Na 0. 7 5 Fe 0.25 Cu 0.25 Mn 0.5 O 2 with excellent cycling stability and low cost shows a potential application prospect. [ABSTRACT FROM AUTHOR]

Based on the Mn 0.806 Co 0.194 CO 3 precursors, Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 micro-cube (MC-LMNC) was prepared. The as-prepared sample is hollow and possesses a shell of about 200 nm, which is assembled by a series of nano particles (∼50 nm). X-ray diffraction and Raman spectroscopy confirmed that the materials obtained are well crystalline and have a good layered structure. The electron microscopy showed that the micro-cubes disperse uniformly and have a hierarchical structure. In comparison to the sample obtained by a sol-gel method (SG-LMNC), LNMC micro-cube has a much better electrochemical performance. The average discharge capacities for SG-LMNC sample are 276.6, 220.1, 155.8, 97.9, 66.7, and 40.3 mAh g−1 at a 0.1, 0.2, 0.5, 1.0, 3.0, and 5.0 C respectively, while those for MC-LMNC are 302.5, 241.2, 190.5, 145.4, 103.8, and 70.6 mAh g−1 at the same rates. EIS measurements confirmed that the diffusion coefficients for SG-LMNC and MC-LMNC are 1.13 × 10−16 and 1.61 × 10−16 cm2 s−1. The origin of the performance differences can be attributed to the different morphology, surface area, and pore size of the two samples, which has been verified by the BET analysis. • A Li-rich material with a special micro-cubic morphology was firstly synthesized. • The effect of morphology on the electrochemical properties was revealed. • Hollow and hierarchical structure is helpful for the improvement of rate capability. [ABSTRACT FROM AUTHOR]