Eliminating the irreversible capacity loss of high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode by blending with other lithium insertion hosts

The large irreversible capacity loss generally encountered with the high capacity layered oxide solid solutions between layered Li[Li_1/3Mn_2/3]O₂ and LiMO₂ (M = Mn, Ni, and Co) has been reduced by blending layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂, which is a solid solution between Li[Li_1/3Mn_2/3]O₂ and Li[Mn_1/3Ni_1/3Co_1/3]O₂, with spinel Li₄Mn₅O₁₂ or LiV₃O₈. The irreversible capacity loss decreases from 68 to 0 mAh g⁻¹ as the Li₄Mn₅O₁₂ content increases to 30 wt.% in the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-Li₄Mn₅O₁₂ composite and the LiV₃O₈ content increases to 18 wt.% in the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-LiV₃O₈ composite. The decrease in irreversible capacity loss is due to the ability of Li₄Mn₅O₁₂ or LiV₃O₈ to insert the extracted lithium that could not be inserted back into the layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ during the first cycle. The Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂-LiV₃O₈ composite with ∼18 wt.% LiV₃O₈ exhibits a high capacity of ∼280 mAh g⁻¹ with little or no irreversible capacity loss and good cyclability.     

LiNi1/3Co1/3Mn1/3O2/polypyrrole composites as cathode materials for high-performance lithium-ion batteries

Polypyrrole is successfully introduced to enhance the reaction stability and ionic conductivity of LiNi_1/3Co_1/3Mn_1/3O₂ material through an ultrasound dispersion method and applied as cathode materials for lithium-ion batteries. This polymer can significantly advance the electrochemical properties. Expectedly, the 8 wt.% LiNi_1/3Co_1/3Mn_1/3O₂/polypyrrole composite has lower mixing degree of Li⁺/Ni²⁺, higher c/a value, which delivers the first discharge capacity of 199.2 mAh g⁻¹, which abate to 121.3 mAh g⁻¹ in the 300th cycle at 0.2 C between 2.5 and 4.5 V. Even at 3 C, it continues to reveal a reversible capacity of 86.4 mAh g⁻¹ after 100 cycles. All the consequences implied that the 8 wt.% LiNi_1/3Co_1/3Mn_1/3O₂/polypyrrole verified a minor charge transfer resistance and better Li⁺ diffusion ability, hence establishing preferable rate and cycling performance compared with the primordial LiNi_1/3Co_1/3Mn_1/3O₂.     

Improving rate capability and decelerating voltage decay of Li-rich layered oxide cathodes by chromium doping

In order to improve the rate capability and mitigate the voltage decay of lithium rich layered oxides, chromium doped cathode materials Li_1.2[Mn_0.54Ni_0.13Co_0.13]_1?xCr_xO₂ (x = 0,0.003,0.005,0.007) is synthesized via co-precipitation method followed by calcination. As a result, Cr-doped samples present shortened voltage platform at 4.5 V, indicating that the escape of lattice oxygen is suppressed by Cr doping. Among all samples, Li_1.2[Mn_0.54Ni_0.13Co_0.13]_1?xCr_xO₂ (x = 0.005) sample shows the greatest rate capability (119.3 mAh g^?1 at 10 C) and the minimum voltage drop (0.6167 V) after 200 cycles at 1.0 C. The reasons for the improved electrochemical performance are the enhanced structural stability, the stronger CrO bond than MnO band and the decreased metal–oxygen covalency induced by Cr doping.     

Wet-chemistry synthesis of Li4Ti5O12 as anode materials rendering high-rate Li-ion storage

Compared with traditional anode materials, spinel-structured Li₄Ti₅O₁₂ (LTO) with “zero-strain” characteristic offers better cycling stability. In this work, by a wet-chemistry synthesis method, LTO anode materials have been successfully synthesized by using CH₃COOLi·2H₂O and C₁₆H₃₆O₄Ti as raw materials. The results show that sintering conditions significantly affect purity, uniformity of particle sizes, and electrochemical properties of as-prepared LTO materials. The optimized LTO product calcined at 650°C for 20 hours demonstrates small particle sizes and excellent electrochemical performances. It delivers an initial discharge capacity of 242.3 mAh g⁻¹ and remains at 117.4 mAh g⁻¹ over 500 cycles at the current density of 60 mA g⁻¹ in the voltage range of 1.0 to 3.0 V. When current density is increased to 1200 mA g⁻¹, its discharge capacity reaches 115.6 mAh g⁻¹ at the first cycle and remains at 64.6 mAh g⁻¹ after 2500 cycles. The excellent electrochemical performances of LTO can be attributed to the introduction of rutile TiO₂ phase and small particle sizes, which increases electrical conductivity and electrode kinetics of LTO. Therefore, as-synthesized LTO in this study can be regarded as a promising anode candidate material for lithium-ion batteries.     

Preparation and characterization of layered LiMn1/3Ni1/3Co1/3O2 as a cathode material by an oxalate co-precipitation method

The layered LiMn_1/3Ni_1/3Co_1/3O₂ cathode materials were synthesized by an oxalate co-precipitation method using different starting materials of LiOH, LiNO₃, [Mn_1/3Ni_1/3Co_1/3]C₂O₄·2H₂O and [Mn_1/3Ni_1/3Co_1/3]₃O₄. The morphology, structural and electrochemical behavior were characterized by means of SEM, X-ray diffraction analysis and electrochemical charge–discharge test. The cathode material synthesized by using LiNO₃ and [Mn_1/3Ni_1/3Co_1/3]C₂O₄·2H₂O showed higher structural integrity and higher reversible capacity of 178.6 mAh g⁻¹ in the voltage range 3.0–4.5 V versus Li with constant current density of 40 mA g⁻¹ as well as lower irreversible capacity loss of 12.9% at initial cycle. The rate capability of the cathode was strongly influenced by particle size and specific surface area.     

Synthesis and electrochemical performance of the high voltage cathode material Li[Li0.2Mn0.56Ni0.16Co0.08]O2 with improved rate capability

The high voltage layered Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode material, which is a solid solution between Li₂MnO₃ and LiMn_0.4Ni_0.4Co_0.2O₂, has been synthesized by co-precipitation method followed by high temperature annealing at 900 °C. XRD and SEM characterizations proved that the as prepared powder is constituted of small and homogenous particles (100-300 nm), which are seen to enhance the material rate capability. After the initial decay, no obvious capacity fading was observed when cycling the material at different rates. Steady-state reversible capacities of 220 mAh g⁻¹ at 0.2C, 190 mAh g⁻¹ at 1C, 155 mAh g⁻¹ at 5C and 110 mAh g⁻¹ at 20C were achieved in long-term cycle tests within the voltage cutoff limits of 2.5 and 4.8 V at 20 °C.     

Complexing of NixMny sulfides microspheres via a facile solvothermal approach as advanced electrode materials with excellent charge storage performances

Mixed metal sulfides with high specific capacitances and superior rate capabilities can meet the need of new materials for technological advancement of energy storage systems. We demonstrate in this study a facile fabrication of microspheres-like Ni_xMn_y sulfides with different molar ratios of metallic salts through a one-step solvothermal route. The hierarchical Ni_xMn_y sulfides-based compounds feature spherical architectures with relatively rough surfaces and assembled from ultrasmall and self-aggregated nanoprimary crystals. Especially, the Ni_xMn_y sulfide (x/y = 1:1) presents an excellent battery-like performance with a high specific capacitance (219.4 mAh g⁻¹ at current density of 1 A g⁻¹) and a good rate capability (123 mAh g⁻¹ at 50 A g⁻¹), benefiting from the greatly improved faradaic redox processes boosted by the synergistic effect of Ni and Mn electroactive components and as well as fast mass transfer. Furthermore, the as-fabricated asymmetric supercapacitor based on Ni_xMn_y sulfide (x/y = 1:1) presents a maximum energy density of 34 W h kg⁻¹ at a power density of 868.1 W kg⁻¹ with both superior rate and long-term cycling stabilities. In view of low cost and improved electrochemical performance, such integrated compound proposes a new and feasible pathway as a potential electrode configuration for energy storage devices.     

Electrochemical stability of core–shell structure electrode for high voltage cycling as positive electrode for lithium ion batteries

The core–shell type cathode material Li[(Ni_0.8Co_0.1Mn_0.1)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ (CS) for Li-ion battery was synthesized via co-precipitation method. The electrochemical and thermal properties of the core–shell structured Li[(Ni_0.8Co_0.1Mn_0.1)_0.8(Ni_0.5Mn_0.5)_0.2]O₂ were compared with those of the average composition of core–shell Li[Ni_0.74Co_0.08Mn_0.18]O₂ (ACCS) and the mixture of the core Li[Ni_0.8Co_0.1Mn_0.1]O₂ and the shell Li[Ni_0.5Mn_0.5]O₂ material (MCS). The CS shows the enhanced electrochemical properties in a high voltage range (4.5 V and 4.6 V) as well as the typical cut-off voltage range (4.3 V). The capacity retentions of CS, core, and ACCS material were 94.2% (176.9 mAh g⁻¹), 86.6% (172 mAh g⁻¹), and 88.4% (169.3 mAh g⁻¹) after 120 cycles, respectively.     

Electrochemical properties of iodine-containing lithium manganese oxide spinel

Iodine-containing, cation-deficient, lithium manganese oxides (ICCD-LMO) are prepared by reaction of MnO₂ with LiI. The MnO₂ is completely transformed into spinel-structured compounds with a nominal composition of Li_1−δMn_2−2δO₄I_x. A sample prepared at 800 °C, viz. Li_0.99Mn_1.98O₄I_0.02, exhibits an initial discharge capacity of 113 mA h g⁻¹ with good cycleability and rate capability in the 4-V region. Iodine-containing, lithium-rich lithium manganese oxides (ICLR-LMO) are also prepared by reaction of LiMn₂O₄ with LiI, which results in a nominal composition of Li_1+xMn_2−xO₄I_x. Li_1.01Mn_1.99O₄I_0.02 shows a discharge capacity of 124 mA h g⁻¹ on the first cycle and 119 mA h g⁻¹ a on the 20th cycle. Both results indicate that a small amount of iodine species helps to maintain cycle performance.     

Storage and cycling performance of Cr-modified spinel at elevated temperatures

The influences of partial substitution of Mn in LiMn₂O₄ with Cr³⁺ and Li⁺ on their charge/discharge profiles were quite different: Cr³⁺ affected it only in the high-voltage region, while Li⁺ showed in the both high and low voltage regions. Either Cr³⁺ or Li⁺ doping significantly improved the storage and cycling performance of spinel LiMn₂O₄ at the elevated temperature, specially both doped spinel. Li_1.02Cr_0.1Mn₂O₄ shows very low rate of capacity rention, 0.1% per cycle, and maintained a steady discharge capacity of 114 mAh/g, 95% of the initial discharge capacity over 50 cycles at 50°C. The chemical analysis and X-ray diffraction measurement indicate that the capacity losses of LiMn₂O₄ is mainly due to the dissolution of Mn into electrolyte, further transformation to lithium-rich spinel Li_1+xMn₂O₄. The improvements in their electrochemical profiles for the Cr³⁺ and Li⁺ modified spinel is attributed to that the partial substitution of Mn stabilize its structure, thus minimizing the dissolution of Mn into electrolyte, as well as maintaining its original morphologies.     

An application of lithium cobalt nickel manganese oxide to high-power and high-energy density lithium-ion batteries

Evolved gas analysis (EGA) by mass spectroscopy (MS) was carried out for the pyrolysis of Li_1−xCo_1/3Ni_1/3Mn_1/3O₂ (185 mAh g⁻¹ of charge capacity) and the results were compared with that of Li_1−xCoO₂ (140 mAh g⁻¹). Electrochemically prepared Li_1−xCo_1/3Ni_1/3Mn_1/3O₂ clearly shows that O₂ evolution begins at much higher temperature than Li_1−xCoO₂, suggesting that Li_1−xCo_1/3Ni_1/3Mn_1/3O₂ is superior to LiCoO₂ with respect to thermal stability. High-temperature XRD measurements of charged LiCo_1/3Ni_1/3Mn_1/3O₂-electrodes at 4.45 V were also carried out and shown that the decomposition product by heating was identified as a cubic spinel consisting of cobalt, nickel, and manganese. This indicates that phase change from a layered to spinel-framework structure plays a crucial role in the suppression of oxygen evolution from the solid matrix. In order to show practicability of the new material, lithium-ion batteries with graphite-negative electrodes are fabricated and examined in the R18650-hardware. The new lithium-ion batteries show high rate discharge performances, excellent cycle life, and safety together with high-energy density.     

PVP-assisted synthesis of hollow Ni0.75Zn0.25Fe2O4 nanospheres for lithium-ion batteries

Hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres with a diameter of about 250–300 nm and thickness of 30–40 nm have been successfully fabricated through a PVP (polyvinylpyrrolidone)-assisted hydrothermal strategy. PVP plays an important role in the formation of hollow structure and a plausible formation mechanism of hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres is also proposed in this paper. The as-fabricated hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres display a good dispersibility and high specific surface area of 34.7 m² g⁻¹. Hollow Ni_0.75Zn_0.25Fe₂O₄ nanospheres also demonstrate satisfactory cycle life and rate performance when evaluated as a lithium ion battery negative electrode. Namely, after 120 cycles, the discharge specific capacity is 1321.3 mAh g⁻¹ at 200 mA g⁻¹, and the capacity retention rate is as high as 99.2%. Furthermore, the average discharge capacities are 1482.5, 1451.5, 1330.9, 1232.3, 1031.2 and 944.8 mAh g⁻¹ under the current densities of 100, 200, 500, 1000, 2000 and 4000 mA g⁻¹, respectively. The promising electrochemical performance of the hollow Ni_0.75Zn_0.25Fe₂O₄ nanosphere could be attributed to the unique hollow structure of nanospheres, which offers a higher specific surface area and shorten transmission pathways of electrons and ions, buffering the volume expansion during the Li⁺ insertion/desorption process.     

Synthesis and characterization of high tap-density layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ was prepared by mixing uniform co-precipitated spherical metal hydroxide (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with 7% excess LiOH followed by heat-treatment. The tap-density of the powder obtained was 2.38 g cm⁻³, and it was characterized using X-ray diffraction (XRD), particle size distribution measurement, scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and galvanostatic charge–discharge tests. The XRD studies showed that the material had a well-ordered layered structure with small amount of cation mixing. It can be seen from the EDS results that the transition metals (Ni, Co and Mn) in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are uniformly distributed. Initial charge and discharge capacity of 185.08 and 166.99 mAh g⁻¹ was obtained between 3 and 4.3 V at a current density of 16 mA g⁻¹, and the capacity of 154.14 mAh g⁻¹ was retained at the end of 30 charge–discharge cycles with the capacity retention of 93%.     

Effect of micro-patterning on electrochemical performances of Ni-rich LiNi0·91Co0·06Mn0·03O2 cathode for superior of LIBs

Micro-patterned Ni-rich LiNi_0·91Co_0·06Mn_0·03O₂ cathode is successfully fabricated at little expense for superior electrochemical performances. The micro-patterned Ni-rich LiNi_0·91Co_0·06Mn_0·03O₂ cathode delivers high discharge capacity of 211.5 mAh g⁻¹, extraordinary rate performance of 81.3% even at high C-rate of 4.0 C, stable cycle performance of 77.3% after 80 cycles. It is attributed to that the micro-patterning enhance the lithium ion and electron diffusion via expansion of electrochemically active sites with maintaining structural stability. Consequently, it can be concluded that micro-patterning shows great promise in excellent electrochemical performances for next-generation lithium ion batteries.     

Effects of synthesis conditions on the structural and electrochemical properties of layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via the hydroxide co-precipitation method LIB SCITECH

The uniform layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material for lithium ion batteries was prepared by using (Ni_1/3Co_1/3Mn_1/3)(OH)₂ synthesized by a liquid phase co-precipitation method as precursor. The effects of calcination temperature and time on the structural and electrochemical properties of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ were systemically studied. XRD results revealed that the optimal prepared conditions of the layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ were 850 °C for 18 h. Electrochemical measurement showed that the sample prepared under the above conditions has the highest initial discharge capacity of 162.1 mAh g⁻¹ and the smallest irreversible capacity loss of 9.2% as well as stable cycling performance at a constant current density of 16 mA g⁻¹ between 3 and 4.3 V versus Li at room temperature.     

On the LiNi0.2Mn0.2Co0.6O2 positive electrode material

Layered LiNi_0.2Mn_0.2Co_0.6O₂ phase, belonging to a solid solution between LiNi_1/2Mn_1/2O₂ and LiCoO₂ most commercialized cathodes, was prepared via the combustion method at 900 °C for a short time (1 h). Structural, electrochemical and magnetic properties of this material were investigated. Rietveld analysis of the XRD pattern shows this compound as having the α-NaFeO₂ type structure (S.G. R-3m; a = 2.8399(2) ?; c = 14.165(1) ?) with almost none of the well-known Li/Ni cation disorder. SQUID measurements clearly indicate that the studied compound consists of Ni²⁺, Co³⁺ and Mn⁴⁺ ions in the crystal structure. X-ray analysis of the chemically delithiated Li_xNi_0.2Mn_0.2Co_0.6O₂ phases reveals that the rhombohedral symmetry was maintained during Li-extraction, confirmed by the monotonous variation of the potential-composition curve of the Li//Li_xNi_0.2Mn_0.2Co_0.6O₂ cell. LiNi_0.2Mn_0.2Co_0.6O₂ cathode has a discharge capacity of ∼160 mAh g⁻¹ in the voltage range 2.7-4.3 V corresponding to the extraction/insertion of 0.6 lithium ion with very low polarization. It exhibits a stable capacity on cycling and good rate capability in the rate range 0.2-2 C. The almost 2D structure of this cathode material, its good electrochemical performances and its relatively low cost comparing to LiCoO₂, make this material very promising for applications.     

Influence of lithium content on high rate cycleability of layered Li1+xNi0.30Co0.30Mn0.40O2 cathodes for high power lithium-ion batteries

Layered Li_1+xNi_0.30Co_0.30Mn_0.40O₂ (x = 0, 0.05, 0.10, 0.15) materials have been synthesized using citric acid assisted sol-gel method. The materials with excess lithium showed distinct differences in the structure and the charge and discharge characteristics. The rate capability tests were performed and compared on Li_1+xNi_0.30Co_0.30Mn_0.40O₂ (x = 0, 0.05, 0.10, 0.15) cathode materials. Among these materials, Li_1.10Ni_0.30Co_0.30Mn_0.40O₂ cathode demonstrated higher discharge capacity than that of the other cathodes. Upon extended cycling at 1C and 8C, Li_1.10Ni_0.30Co_0.30Mn_0.40O₂ showed better capacity retention when compared to other materials with different lithium content. Li_1.10Ni_0.30Co_0.30Mn_0.40O₂ exhibited 93 and 90% capacity retention where as Li_1.05Ni_0.30Co_0.30Mn_0.40O₂, Li_1.15Ni_0.30Co_0.30Mn_0.40O₂, and Li_1.00Ni_0.30Co_0.30Mn_0.40O₂ exhibited only 84, 71, and 63% (at 1C), and 79, 66 and 40% (at 10C) capacity retention, respectively, after 40 cycles. The enhanced high rate cycleability of Li_1.10Ni_0.30Co_0.30Mn_0.40O₂ cathode is attributed to the improved structural stability due to the formation of appropriate amount of Li₂MnO₃-like domains in the transition metal layer and decreased Li/Ni disorder (i.e., Ni content in the Li layer).     

Structure change of orthorhombic LiMnO2 cathodes during electrochemical cycle for rechargeable lithium battery

Abstract

The research confirms that the irreversible transformation to spinel-like structure during orthorhombic LiMnO₂ cycle is a gradual phase transformation process. A model for the structure change of orthorhombic LiMnO₂ during the electrochemical cycle is presented. The model successfully clarified the fact that the 4 V voltage plateau does not exist for the first discharge. Because the LiMnO₂ has 124 mAh g^–1 of the first charge capacity, there are many Li ions containing the octahedral sites. The tetrahedral sites left by Mn ions migrating would be occupied by lithium ions containing the octahedral sites with further cycle, which make the 4 V voltage plateau developing. According to the model suggestion, the different variants of spinel Li_xMn₂O₄ will develop the nanodomain.     

Characterization of LiCoO2 coated Li1.05Ni0.35Co0.25Mn0.4O2 cathode material for lithium secondary cells

In this study, nano-crystalline LiCoO₂ was coated onto the surface of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ powders via sol–gel method. The influence of the coating on the electrochemical behavior of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ is discussed. The surface morphology was characterized by transmission electron microscopy (TEM). Nano-crystallized LiCoO₂ was clearly observed on the surfaces of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂. The phase and structural changes of the cathode materials before and after coating were revealed by X-ray diffraction spectroscopy (XRD). It was found that LiCoO₂ coated Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ cathode material exhibited distinct surface morphology and lattice constants. Cyclic voltammetry (2.8–4.6 V versus Li/Li⁺) shows that the characteristic voltage transitions on cycling exhibited by the uncoated material are suppressed by the 7 wt.% LiCoO₂ coating. This behavior implies that LiCoO₂ inhibits structural change of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ or reaction with the electrolyte on cycling. In addition, the LiCoO₂ coating on Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ significantly improves the rate capability over the range 0.1–4.0C. Comparative data for the coated and uncoated materials are presented and discussed.     

Effect of Mg-doping on the electrochemical performance of LiNi0.84Co0.11Mn0.05O2 cathode for lithium ion batteries

Mg-doped LiNi_0.84Co_0.11Mn_0.05O₂ cathode material is synthesized from introducing Mg by high temperature solid state method. X-ray diffraction analysis confirms the formation of ordered α-NaFeO₂ rock-salt like structure with R-3m symmetry. Rietveld refinement results confirm the expansion in ɑ and c lattice parameters as the amount of Mg increases. All the Mg-doped samples show significant improvement in structure stability and electrochemical properties, such as capacity retention and rate capability. The 1 wt% Mg-doped LiNi_0.84Co_0.11Mn_0.05O₂ delivers the high discharge capacity of 196.7 mAh g⁻¹ (0.1 C) and maintains the capacity retention of 85.95% after 80 cycles indicating outstanding cycling performance. Furthermore, at high cut-off voltage the Mg-doped samples exhibit superior electrochemical performance than the un-doped sample. Cyclic voltammetry results show that the addition of Mg has suppressed the phase transition between H2+H3.