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In this paper, we reported on a comparison of LiVPO4F to Li4Ti5O12 as anode materials for lithium-ion batteries. Combined with powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, galvanostatic discharge/charge tests and in situ X-ray diffraction technologies, we explore and compare the insertion/extraction mechanisms of LiVPO4F based on the V3+/V2+/V+ redox couples and Li4Ti5O12 based on the Ti4+/Ti3+ redox couple cycled in 1.0-3.0 V and 0.0-3.0 V. The electrochemical results indicate that both LiVPO4F and Li4Ti5O12 are solid electrolyte interphase free materials in 1.0-3.0 V. The insertion/extraction mechanisms of LiVPO4F and Li4Ti5O12 are similar with each other in 1.0-3.0 V as proved by in situ X-ray diffraction. It also demonstrates that both samples possess stable structure in 0.0-3.0 V. Additionally, the electrochemical performance tests of LiVPO4F and Li4Ti5O12 indicate that both samples cycled in 0.0-3.0 V exhibit much higher capacities than those cycled in 1.0-3.0 V but display worse cycle performance. The rate performance of Li4Ti5O12 far exceeds that of LiVPO4F in the same electrochemical potential window. In particular, the capacity retention of Li4Ti5O12 cycled in 1.0-3.0 V is as high as 98.2% after 20 cycles. By contrast, Li4Ti5O12 is expected to be a candidate anode material considering its high working potential, structural zero-strain property, and excellent cycle stability and rate performance.

Abstract: The time domain transients of batteries comprised of LiFePO4 cathode material exhibit large nonlinearity with the increasing discharging rates. Hence, the calculated overpotential transients match the experimental determined well only when the discharging current is low enough. The results of electrochemical impedance spectra at different OCV level indicate that the change of the parameters of equivalent circuit or even the circuit architecture are probably responsible for the large discrepancy between the predicted and the measured transient profiles. By taking the change of equivalent circuit model at high discharging current into consideration, we successfully simulate the time domain transients of polarization within the entire discharging current range. Also with the help of circuit analysis, the contribution of the ohmic resistance, charge transfer impedance and solid-state diffusion impedance to total polarization has been differentiated as a function of discharging time. [Copyright &y& Elsevier]

Layered LiNiCoMnO was synthesized by a citric acid assisted solid-state method. The structure and electrochemical properties of the LiNiCoMnO materials were investigated. XRD analysis indicated the as-synthesized LiNiCoMnO was with the layered α-NaFeO structure. The discharge capacity was about 154 m·Ahg at 0·1 °C rate in the range of 2·0-4·5 V. The kinetics of the LiNiCoMnO materials was investigated by the galvanostatic intermittent titration technique (GITT) method. The lithium ion diffusion coefficient of the LiNiCoMnO was determined in the range of 10 − 10cm· s as a function of voltage of 3·7−4·5 V. [ABSTRACT FROM AUTHOR]

Abstract: Lithium-ion battery cathode material Li1+ x V3O8 is synthesized by a citric acid/tartaric acid assisted sol–gel method and sintered at 350 °C, 450 °C and 550 °C for 3 h for the formation of Li1+ x V3O8 phase. The synthesized samples were fully characterized by FTIR, TG/DTA, XRD, SEM, EIS and charge–discharge tests. Li1+ x V3O8 material synthesized by tartaric acid assisted route and sintered at 450 °C for 3 h shows best electro-chemical performance. It shows a high initial capacity of 249 mAh g−1 and still reserves a discharge capacity of 260 mAh g−1 after 50 cycles. Moreover, in the case of tartaric assisted products, no capacity decadence is observed in 50 cycles. XRD together with TG/DTA measurements reveal that compared with citric acid assisted products, the adoption of tartaric acid as chelating agent effectively lowers the crystallization temperature of amorphous Li1+x V3O8. Therefore, precursors obtained by tartaric acid route calcinated at 450 °C for 3 h exhibit lower crystallinity and smaller grain size, which contributes to the better electrochemical performance of the cathode electrodes. From EIS measurements, the bulk resistance is reduced, which favors the intercalation and de-intercalation of lithium ions while cycling. [Copyright &y& Elsevier]

Abstract: A series of LiNi0.5Co0.5− x Ti x O2 (0⩽ x ⩽0.5) are prepared by a tartaric acid-assisted sol–gel technique. The phase formation process is observed by TG–DTA. It is found that the target product appears at a temperature higher than 400°C and completes to phase formation at 700°C. The crystal structure and morphology are characterized by XRD, SEM and Raman spectroscopy. XRD patterns show that the as-prepared sample transforms from hexagonal structure into cubic structure with the increase of Ti content in LiNi0.5Co0.5− x Ti x O2. Raman spectra also demonstrate the successive substitution of Ti for Co in the structure with band blue-shift phenomenon. SEM images confirm that the as-prepared sample exhibits narrow and regular particles with the size between 0.5 and 1.5μm. The apparent particle size of sample starts to decrease with x ⩽0.1, and the gradually increases by introducing Ti dopant with higher content (x ⩾0.15). The electrochemical behavior of the sample displays different characteristics after Ti substitution. It is found that the initial working potential increases with the increase of Ti doping content. As a result, the initial lithium storage capacity for trace Ti-doped sample is higher than that delivered by the pristine one. The decrease of reversible capacity for high degree Ti-doped sample is ascribed to the electrochemical inactivity of the cubic compound in the sample. Therefore, trace Ti doping is beneficial to achieve promising cathode material for lithium-ion batteries. [Copyright &y& Elsevier]

A series of Nasicon-type solid electrolytes Li1+2x+2y Al x Zn y Ti2−x−y Si x P3−x O12 was synthesized by conventional solid state ceramic route. X-ray diffraction and Rietveld whole pattern refinement were applied to investigate the phase, structure and the unit cell parameters of those solid electrolytes. EIS complex impedance method was carried out to study the Li+ conductivity. The results showed that Li1+2x+2y Al x Zn y Ti2−x−y Si x P3−x O12 with x=0.1 y=0.5 presents highest ionic conductivity 7.2×10−5 Scm−1 at ambient temperature and 2.0×10−3 Scm−1 at 473K. The activation energy of Li+ migration was calculated to be ca. 20kJmol−1. The influence of Zn2+ element on the structure and Li+ mobility was preliminary explained. [ABSTRACT FROM AUTHOR]

The perovskite type oxide Ca 1-x Li x MnO 3-δ (x = 0, 0.02, 0.05, 0.1, 0.2) was prepared by a simple citric acid assisted sol-gel method and was investigated as a possible lithium ion anode material. XRD confirmed that up to 10% calcium element in the CaMnO 3 lattice can be replaced by lithium without the obvious corruption of lattice symmetry or the appearance of the secondary phase. Although pure CaMnO 3 exhibited poor electro-chemical performance, the introduction of lithium has greatly improved the electrochemical performance of Ca 1-x Li x MnO 3-δ . Without carbon coating, the specific capacity of Ca 0.95 Li 0.05 MnO 3-δ within the initial 10 cycles were maintained at ca. 480 mA h g −1 , and after 50 cycles of rate capability testing it was estimated to be around 350 mA h g −1 . The rate capability was also improved significantly. The detailed structural analysis of lithium doping CaMnO 3 revealed that this improvement in the electro-chemical performance mostly likely originated from the extra lithium diffusion path between two 8c sites mediated by the 36 f oxygen vacancy in between. Further EIS and CV tests demonstrated that the lithium doping reduced the charge transfer resistance effectively and increased the lithium ion diffusion coefficient accordingly. Although the performance of lithium doping CaMnO 3 was still inferior to the frequently investigated anode material like Si series or metal oxide series, the further improvement of the material was still possible by further modification of perovskite CaMnO 3 . [ABSTRACT FROM AUTHOR]

Isostructural LiMTiO 4 (M = Mn, Fe, Co) have been successfully synthesized by a facile sol-gel route and evaluated their possibility as an anode materials for lithium ion batteries (LIBs). All the samples exhibit high operating potential plateaus (>1.7 V vs. Li + /Li), which can prevent the formation of the solid electrolyte interphase (SEI) film on the electrode surface effectively. In addition, electrochemical investigations show that LiCoTiO 4 has a superior cycling performance, better rate capability, lower charge transfer resistance and higher lithium-ion diffusion coefficient than those of LiMnTiO 4 and LiFeTiO 4 . These electrochemical results indicate that LiCoTiO 4 is the most promising lithium storage material among all the examined spinel-type LiMTiO 4 samples. [ABSTRACT FROM AUTHOR]

In this paper, carbon coated Li 5 Cr 9 Ti 4 O 24 is prepared by using cystine as carbon source, which results in the formation of carbon co-doped with nitrogen/sulfur (CNS) coating layer after pyrolysis. Compared with carbon free Li 5 Cr 9 Ti 4 O 24 , the resulting Li 5 Cr 9 Ti 4 O 24 @CNS exhibits enhanced lithium storage capability. Cycled at 500 mA g −1 , it can be found that carbon free Li 5 Cr 9 Ti 4 O 24 can only deliver the reversible capacity of 97.8 mAh g −1 with capacity retention of 80.7% after 200 cycles. In contrast, Li 5 Cr 9 Ti 4 O 24 @CNS can maintain the reversible lithium storage capacity of 111.4 mAh g −1 with capacity retention of 91.9% after 200 cycles. This improvement is attributed to the introduction of nitrogen/sulfur dual-doped carbon coating layer, which significantly enhances the electronic/ionic conductivity and reduces the charge-transfer resistance of Li 5 Cr 9 Ti 4 O 24 . Hence, Li 5 Cr 9 Ti 4 O 24 @CNS may be a promising anode candidate for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

In this work, a novel lithium storage material Li 5 Cr 9 Ti 4 O 24 is reported as anode material for rechargeable lithium-ion batteries. We prepare Li 5 Cr 9 Ti 4 O 24 by two different routes, sol-gel method and solid state reaction. Li 5 Cr 9 Ti 4 O 24 nanocrystalline can be achieved by sol-gel method, while solid state reaction delivers micro-sized product. Electrochemical results show that Li 5 Cr 9 Ti 4 O 24 nanocrystalline exhibits reduced charge transfer resistance, decreased redox polarization and improved lithium-ion diffusion coefficient compared with micro-sized product. As a result, Li 5 Cr 9 Ti 4 O 24 nanocrystalline shows excellent lithium storage capability with 100% capacity retention after 200 cycles. Cycled at 600 mA g −1 , it still can deliver a charge specific capacity of 110.3 mAh g −1 . In contrast, micro-sized Li 5 Cr 9 Ti 4 O 24 only reveals the reversible capacity of 66.8 mAh g −1 at the same current density. In addition, Li 5 Cr 9 Ti 4 O 24 nanocrystalline also shows outstanding structural stability for repeated lithium storage. In-situ structural observation reveals that the entire volume expansion of Li 5 Cr 9 Ti 4 O 24 is only 0.62% during the charge/discharge process, which is similar with the zero-strain Li 4 Ti 5 O 12 . Therefore, Li 5 Cr 9 Ti 4 O 24 nanocrystalline can be used as high performance anode material for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

A series of Li 3− x Na x V 2 (PO 4 ) 3 /C (0≤ x ≤3) materials are successfully prepared by a simple solid-state reaction method and used for the first time as anode materials for Na-ion batteries. Powder X-ray diffraction (XRD) results show that the phase structures of Li 3− x Na x V 2 (PO 4 ) 3 /C evolve along with the change of Li/Na atomic ratio (0≤x≤3). With increasing x in Li 3− x Na x V 2 (PO 4 ) 3 /C from 0.0 to 3.0, the main phase in as-prepared sample transforms from monoclinic Li 3 V 2 (PO 4 ) 3 to rhombohedral Li 3 V 2 (PO 4 ) 3 , and finally to rhombohedral Na 3 V 2 (PO 4 ) 3 , which results in different sodium storage behavior and performance between Li 3− x Na x V 2 (PO 4 ) 3 /C (0≤ x ≤3) materials. Electrochemical results show that Li 3− x Na x V 2 (PO 4 ) 3 /C ( x =0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0) can deliver the initial charge capacities of 21.1, 35.9, 33.8, 41.7, 43.3, 43.9 and 47.7 mAh g −1 at a current density of 10 mA g −1 , respectively. After 45 cycles, the reversible capacities can be kept at 16.9, 45.1, 32.6, 44.6, 43.7, 37.8 and 27.3 mAh g −1 for Li 3 V 2 (PO 4 ) 3 /C, Li 2.5 Na 0.5 V 2 (PO 4 ) 3 /C, Li 2 NaV 2 (PO 4 ) 3 /C, Li 1.5 Na 1.5 V 2 (PO 4 ) 3 /C, LiNa 2 V 2 (PO 4 ) 3 /C, Li 0.5 Na 2.5 V 2 (PO 4 ) 3 /C and Na 3 V 2 (PO 4 ) 3 /C, respectively. Furthermore, the structural reversibility of Li 3− x Na x V 2 (PO 4 ) 3 /C ( x =1.0, 2.0, and 3.0) is also observed by in-situ XRD observation during sodiation/de-sodiation process. All these observed evidences indicate that only some of Li 3− x Na x V 2 (PO 4 ) 3 /C (0≤ x ≤3) can be used as possible sodium storage materials. [ABSTRACT FROM AUTHOR]

The overlithiation and delithiation behaviors of sol-gel formed LiNi 0.75 Co 0.25 O 2 are investigated in this work. As an insertion host material, LiNi 0.75 Co 0.25 O 2 is cycled in a broad working potential range of 1.35–4.3 V. It shows two lithiation platforms at 1.75/3.6 V and only one reverse delithiation platform at 3.7 V. The long lithiation platform at 1.75 V is attributed to the overlithiation behavior of LiNi 0.75 Co 0.25 O 2 . Although overlithiation reaction takes place below 2.0 V, LiNi 0.75 Co 0.25 O 2 can maintain electrochemical reversibility during the initial 20 cycles. To study the overlithiation/delithiation process, the structural evolution of LiNi 0.75 Co 0.25 O 2 is thoroughly observed by in-situ X-ray diffraction method. It can be found that the electrochemical reaction between LiNi 0.75 Co 0.25 O 2 and Li in 1.35–4.3 V is a reversible process, which is associated with a single-phase transition process above 3.0 V and a two-phase transformation below 2.0 V. This result not only demonstrates the high structural and electrochemical reversibility of LiNi 0.75 Co 0.25 O 2 in 1.35–4.3 V, but also proves the improved structural stability of LiNi 0.75 Co 0.25 O 2 via partial replacement of Ni by Co in layered LiNiO 2 . [ABSTRACT FROM AUTHOR]

Co 3+ substituted lithium rich cathode material 0.5Li 2 MnO 3 ·0.5LiNi 0.5 Mn 0.5 O 2 , Li(Li 0.3 Ni 0.2 Mn 0.5 Co 0.1 )O 2 , was prepared at strictly controlled pH level realized by a carefully designed feeding system. The as prepared cathode material showed lamellar morphology with clearly shown edges. Less cation mixing and higher hexagonal ordering were observed indicating intact layered structure and good electrochemical performances. The first charge delivered a total capacity of ca. 328 mAh g −1 and the subsequent discharge sent a capacity of 238 mAh g −1 back. Except for the initial several cycles, the fading of the discharge capacity was limited. A discharge capacity of 166 mAh g −1 was still reserved after 50 cycles. The rate performance was also improved. The last cycle of each current density, namely 0.1 C, 0.2 C, 0.5 C, 1 C and 2 C, delivered a capacity of ca. 226 mAh g −1 , ca. 191 mAh g −1 , ca. 160 mAh g −1 , ca. 135 mAh g −1 and ca. 110 mAh g −1 , respectively. When the current density was back to 0.1 C, ca. 80% of the initial discharge capacity, nearly 200 mAh g −1 , was regained. [ABSTRACT FROM AUTHOR]

Na 2 Li 2 Ti 6 O 14 is synthesized by a simple solid state method between 500 and 900 °C. It is found that pure Na 2 Li 2 Ti 6 O 14 is only formed at 800 °C or above. The tap density of as-prepared Na 2 Li 2 Ti 6 O 14 is about 1.52 g cm −3 . Particle morphology analysis shows that the size of Na 2 Li 2 Ti 6 O 14 gradually increases with the increase of sintering temperature. Calcined at 900 °C, Na 2 Li 2 Ti 6 O 14 shows slight particle aggregation and melting. As a result, Na 2 Li 2 Ti 6 O 14 formed at 800 °C reveals higher electrochemical activity than the sample obtained at 900 °C. Therefore, the suitable preparation temperature for Na 2 Li 2 Ti 6 O 14 by solid state reaction is 800 °C. Charge–discharge results show that Na 2 Li 2 Ti 6 O 14 prepared at 800 °C can deliver a reversible capacity of 89.9 mAh g −1 at 100 mA g −1 , 81.3 mAh g −1 at 200 mA g −1 , 75.2 mAh g −1 at 300 mA g −1 , 69.6 mAh g −1 at 400 mA g −1 and 65.5 mAh g −1 at 500 mA g −1 . Besides, the lithium storage mechanism in Na 2 Li 2 Ti 6 O 14 is also studied by various in-situ and ex-situ methods, which prove that the structural evolution is highly reversible for Na 2 Li 2 Ti 6 O 14 during lithiation/delithiation process. [ABSTRACT FROM AUTHOR]

Three Li 3-x Na x V 2 (PO 4 ) 3 (x=0.5, 1.5 and 2.0) samples are synthesized by a traditional solid-state reaction method in this work. Their phase composition, surface morphology and electrochemical property are described and compared by using various physical/chemical methods. Phase analysis results reveal that Li 2.5 Na 0.5 V 2 (PO 4 ) 3 consists of monoclinic Li 3 V 2 (PO 4 ) 3 , rhombohedral Li 3 V 2 (PO 4 ) 3 and rhombohedral Na 3 V 2 (PO 4 ) 3. While, both Li 1.5 Na 1.5 V 2 (PO 4 ) 3 and LiNa 2 V 2 (PO 4 ) 3 are the two-phase mixture consisted of rhombohedral Li 3 V 2 (PO 4 ) 3 and rhombohedral Na 3 V 2 (PO 4 ) 3 . Electrochemical testing results reveal that LiNa 2 V 2 (PO 4 ) 3 and Li 1.5 Na 1.5 V 2 (PO 4 ) 3 can deliver the initial discharge capacities of 101.4 mAh g −1 and 108.6 mAh g −1 with a long potential plateau at 3.69 V, respectively. In contrast, Li 2.5 Na 0.5 V 2 (PO 4 ) 3 presents an initial discharge capacity of 111.7 mAh g −1 with four potential plateaus. High lithium ion diffusion coefficient in Li 2.5 Na 0.5 V 2 (PO 4 ) 3 indicates that the existence of monoclinic Li 3 V 2 (PO 4 ) 3 phase can improve the ionic conductivity and then be responsible for good electrochemical performance. Besides, in-situ X-ray diffraction observation of LiNa 2 V 2 (PO 4 ) 3 demonstrates that the phase transition is not fully reversible but quasi-reversible during the lithiation-delithiation process. The partial irreversibility of structural evolution for LiNa 2 V 2 (PO 4 ) 3 induces the capacity loss upon repeated cycles. [ABSTRACT FROM AUTHOR]

In this work, triclinic structured LiVPO 4 F is prepared by a simple two-step carbothermal reduction method and subsequently exposed to water under different storage conditions. The impact of exposure on the structure, morphology and electrochemical performance of LiVPO 4 F is investigated in detail. It is found that the effect of exposure at room temperature (20 °C) is slight. In contrast, exposure at 80 °C has great effect on the structure and electrochemical properties of LiVPO 4 F. Li, P and V dissolution into aqueous solution at 80 °C results in the formation of a yellowish solution. Electrochemical tests show that LiVPO 4 F samples aged in water at 80 °C for 3 and 5 days show poorer electrochemical properties than the pristine sample. LiVPO 4 F aged in water at 80 °C for 15 days exhibits higher initial reversible capacity compared with the pristine sample. However, it deteriorates rapidly in the following cycles due to the moisture-sensitive surface, which induces the formation of thick Li 2 CO 3 /Li 3 PO 4 film on the surface and leads to a high charge transfer resistance and the degradation of electrochemical performance. [ABSTRACT FROM AUTHOR]

A series of Li 3− x Na x V 2 (PO 4 ) 3 /C (0≤x≤3) is successfully synthesized through a simple solid-state reaction method. The structures of these lithium sodium vanadium phosphate compounds are investigated by the X-ray diffraction. It can be found that Li 3− x Na x V 2 (PO 4 ) 3 /C is composed of one monoclinic phase with 0≤x≤0.2, two monoclinic phases with 0.2

A series of Li 2 BaTi 6 O 14 samples are synthesized by a traditional solid-state method by calcining at different temperatures from 800 to 1000 °C. Structural analysis and electrochemical evaluation suggest that the optimum calcining temperature for Li 2 BaTi 6 O 14 is 950 °C. The Li 2 BaTi 6 O 14 calcined at 950 °C exhibits a high purity phase with an excellent reversible capacity of 145.7 mAh g −1 for the first cycle at a current density of 50 mA g −1 . After 50 cycles, the reversible capacity can be maintained at 137.7 mAh g −1 , with the capacity retention of 94.51%. Moreover, this sample also shows outstanding rate property with a high reversible capacity of 118 mAh g −1 at 300 mA g −1 . The excellent electrochemical performance is attributed to the stable lithium storage host structure, decreased electrochemical resistance and improved lithium-ion diffusion coefficient. In-situ and ex-situ structure analysis shows that the electrochemical reaction of Li 2 BaTi 6 O 14 with Li is a highly reversible lithiation–delithiation process. Therefore, Li 2 BaTi 6 O 14 may be a promising alternative anode material for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

In this work, a series of Li 2+ x Na 2− x Ti 6 O 14 (0≤ x ≤0.20) are synthesized by a simple solid-state reaction method. All the as-prepared samples are high purity titanates and well crystallized with a particle size distribution in the range of 0.3–0.5 μm. Electrochemical analysis shows that Li 2.05 Na 1.95 Ti 6 O 14 displays a higher working potential platform at 1.33 V than that about 1.28 V of other Li 2+ x Na 2− x Ti 6 O 14 ( x =0.00, 0.10, 0.15 and 0.20) samples. Charge/discharge results show that Li 2.05 Na 1.95 Ti 6 O 14 presents higher charge capacities of 302.9 mA h g −1 for the first cycle than other four samples. After 50 cycles, Li 2.05 Na 1.95 Ti 6 O 14 still delivers a reversible charge capacity of 277.6 mA h g −1 , but Li 2+ x Na 2− x Ti 6 O 14 ( x =0.00, 0.10, 0.15 and 0.20) samples only present the charge capacities of 211.8, 232.1, 183.9 and 231.9 mA h g −1 , respectively. Furthermore, Li 2.05 Na 1.95 Ti 6 O 14 also provides a remarkable rate performance with the charge capacities of 241.2 mA h g −1 at 200 mA g −1 , 228.2 mA h g −1 at 300 mA g −1 and 217.4 mA h g −1 at 400 mA g −1 . In contrast, pristine Li 2 Na 2 Ti 6 O 14 only delivers the lithium storage capacities of 207.0 mA h g −1 at 200 mA g −1 , 194.5 mA h g −1 at 300 mA g −1 and 187.7 mA h g −1 at 400 mA g −1 . All these improved electrochemical properties of Li 2.05 Na 1.95 Ti 6 O 14 are attributed to the lowest polarization and the highest lithium ion diffusion coefficient among all the five samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] Li4Ti5O12@C is prepared by a facile carbon coating strategy. [•] Amorphous carbon coating layer shows a thickness of 4–6nm. [•] Li4Ti5O12@C delivers a capacity of 160.6mAhg−1 at 20mAg−1 in 1.0–2.0V. [•] Li4Ti5O12@C displays a capacity of 205.1mAhg−1 at 1500mAg−1 in 0.0–2.0V. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a series of LiVPO4F-based samples are prepared through sintering LiVPO4F at different temperatures under air. Experimental results show that the pristine sample is oxidized to a new compound Li1 −x VPO4F1 −y O z (0

Abstract: Spherical LiNi0.5Co0.3Mn0.2O2 samples with the particle size distribution between 10 and 20 μm are prepared by a hydroxide co-precipitation method and subsequent high temperature solid state calcination. Electrochemical results show that the reversible lithium storage capacities of spherical LiNi0.5Co0.3Mn0.2O2 cathode after 20 cycles are 121.5, 154.2 and 99.3 mAh g−1 in 2.0–4.3 V, 2.0–4.6 V and 2.0–4.9 V, respectively. The structural evolutions of layered materials in different working potential ranges are carefully studied by homemade in-situ X-ray diffraction techniques. It is found that the formation of hexagonal phase H3 is the main source resulting in poor electrochemical properties, where the hexagonal phase H2 to hexagonal phase H3 transition occurs at about 4.7 V in the charge process. As a result, it is expected that the suppression of hexagonal phase H3 can achieve a long-term cyclability and high reversible capacity for LiNi0.5Co0.3Mn0.2O2. Therefore, spherical LiNi0.5Co0.3Mn0.2O2 cathode shows the highest reversible lithium storage capacity of 154.2 mAh g−1 in 2.0–4.6 V after 20 cycles among all the three electrochemical working windows. [Copyright &y& Elsevier]

Abstract: Time domain transients to current step of multiple current densities were calculated to evaluate the polarization and fractional contribution of lithium rich cathode material Li[Li0.2Ni0.2Mn0.6]O2 based on the equivalent circuit determined from the electrochemical impedance spectrum. The calculated data matched the experimental profiles well. The contributions of the individual circuit elements, like charge transfer reaction, lithium transportation across the SEI film and solid-state lithium diffusion process, were successfully differentiated and the importance of each element was fully assessed. The results told us that they should be equally paid attention to and minimized by the optimized preparation method and cell design. [Copyright &y& Elsevier]