Electrochemical Performance Of LiNi0 Research Articles

Effect of Amorphous LiPON Coating on Electrochemical Performance of LiNi0.8Mn0.1Co0.1O2 (NMC811) in All Solid-State Batteries

High nickel layered oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) was coated with a nanometer layer coating of a lithium ion conducting solid electrolyte, lithium phosphorus oxynitride (LiPON) by using RF-magnetron sputtering. The cells with LiPON coated NMC811 exhibit much improved cycling performance compared to the cells with pristine NMC811 with 64.1% and 42.6% capacity retention respectively over 100 cycles in an all solid-state battery. The LiPON layer provides interfacial stability at high voltages, suppresses the growth of impedance with cycling and improves the rate capability. Thicker coatings show a negative impact on the performance owing to the increase in electronic resistance with increasing thickness of the LiPON layer. The dQ/dV analysis, electrochemical impedance spectroscopy (EIS), and the overpotential study during galvanostatic cycling were conducted to elucidate the improvement of the cycling stability and enhancement of Li+ transport through LiPON layers surrounding NMC811.

Enhanced Structural Stability and Electrochemical Performance of LiNi0.6Co0.2Mn0.2O2 Cathode Materials by Ga Doping.

Structural instability during cycling is an important factor affecting the electrochemical performance of nickel-rich ternary cathode materials for Li-ion batteries. In this work, enhanced structural stability and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials are achieved by Ga doping. Compared with the pristine electrode, Li[Ni0.6Co0.2Mn0.2]0.98Ga0.02O2 electrode exhibits remarkably improved electrochemical performance and thermal safety. At 0.5C rate, the discharge capacity increases from 169.3 mAh g−1 to 177 mAh g−1, and the capacity retention also rises from 82.8% to 89.8% after 50 cycles. In the charged state of 4.3 V, its exothermic temperature increases from 245.13 °C to more than 271.24 °C, and the total exothermic heat decreases from 561.7 to 225.6 J·g−1. Both AC impedance spectroscopy and in situ XRD analysis confirmed that Ga doping can improve the stability of the electrode/electrolyte interface structure and bulk structure during cycling, which helps to improve the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode material.

Enhanced Electrochemical Performance of Nickel-Rich Cathode Materials by Surface Modification with Al2O3–ZrO2 for Lithium Ion Batteries

Al2O3–ZrO2 was coated on the surface of nickel-rich cathode materials by the sol–gel method to improve its electrochemical performance. The nanometer-thick Al2O3–ZrO2 coating layer refrains the side reaction between the electrolyte and the electrode, thus preventing the collapse of LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 layered structure and protecting the stability of the material. The electrochemical test shows that LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 coated with Al2O3–ZrO2 has good cycle and rate performance. Under the cut-off voltage of 2.8–4.5[Formula: see text]V, LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 coated with Al2O3–ZrO2 delivered an initial capacity which was 166.7[Formula: see text]mAh[Formula: see text]g[Formula: see text]at 1C (200[Formula: see text]mAh[Formula: see text]g[Formula: see text] rate, and the capacity retention rate was 77.7% after 200 cycles. The pristine LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 delivered an initial capacity which was 166.4[Formula: see text]mAh[Formula: see text]g[Formula: see text] at 1C rate, and the capacity retention rate was 51.7% after 200 cycles. The EIS and CV provided the enhanced electrochemical performance of LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 coated with Al2O3–ZrO2 which was due to accelerating Li[Formula: see text] diffusion of nickel-rich materials and electrolytes.

Enhancing the stabilities and electrochemical performances of LiNi0.5Co0.2Mn0.3O2 cathode material by simultaneous LiAlO2 coating and Al doping

Superior environmental and thermal stabilities and well-defined electrochemical performances of lithium nickel cobalt manganese oxide cathode materials are needed for next-generation high-performance and safe lithium-ion batteries, to which appropriate modification means have been proven to be crucial for enhancing the properties for these materials. Herein, we develop a facile in-situ approach to co-modify LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode material with simultaneous lithium aluminum oxide (LiAlO2) coating and Al doping. Without any additional steps and reagents, the co-modification begins during the preparation of the hydroxide precursor of NCM523 and ends upon the calcination of the cathode material. Combining the synergistic effects from LiAlO2 coating and Al doping, the resultant Al-modified NCM523 possesses a robust protective layer as well as a well-ordered layered structure with enlarged lattice spacing, restrained cation mixing, and concentration-gradient-distributed Ni, thus exhibiting significantly enhanced environmental and thermal stabilities and electrochemical performances over its pristine counterpart. At a high active material content of 94.0 wt.% and a high mass loading of 19.5 mg cm−2 for the testing electrode, the optimized Al-modified NCM523 shows a high discharge capacity (168.4 mAh g−1 at 0.1 C), a high rate capability (capacity retains 67.8% at 3.0 C vs. 0.1 C), and a long cycle life (capacity retains 62.3% after charge / discharge at 0.5 C for 120 cycles). Reasonably, the unique in-situ co-modification approach developed in the present work can be applied for other NCMs with simultaneous LiAlO2 coating and Al doping. More broadly, apart from Al, this approach may be further extended to utilize other modification chemistries to co-modify NCMs and other cathode materials in situ for enhancing their stabilities and electrochemical performances.

Effects of Al doping on the electrochemical performances of LiNi0.83Co0.12Mn0.05O2 prepared by coprecipitation

The Ni-rich LiNi0.83Co0.12Mn0.05O2 (NCM83) cathode materials have drawn intensive attention due to the high energy density and low cost. However, Ni-rich LiNi1-x-yCoxMnyO2 still has the fatal weakness of poor cycle stability, limiting its further wide application. Bulk doping is an effective means to enhance the cycle stability, yet the electrochemical performances are very sensitive to the doping quantity. Here a facile method of co-precipitation is adopted to coat (Ni0.4Co0.2Mn0.4)1-xAlx(OH)2+x on precursor particles of NCM83. Al ions diffuse evenly in the NCM83 particles after sintering. The cells are operated at a high cut-off voltage of 4.5 V. The discharge capacity of NCM83 is 187.8 mAh g−1, and decays fast with cycles. The doped sample even exhibits a higher discharge capacity of 195 mAh g−1, and the capacity retention is improved to 83.8% after 200 cycles.

Improving electrochemical performances of LiNi0.5Mn1.5O4 by Fe2O3 coating with Prussian blue as precursor

LiNi0.5Mn1.5O4 (LNMO) cathodes always suffer from severe capacity fading because of the oxidization of electrolyte and the dissolution of transition metal. Surface modification has been widely recognized as one of the most effective approaches. Herein, a uniform Fe2O3 layer was coated on LNMO via a simple solid-state method with Prussian blue as precursor. The SEM, TEM, XPS, and XRD results show that the Fe2O3 layer was effectively coated on the surface of LNMO. Fe2O3 layer not only increased the specific capacity of Li/LNMO@Fe2O3–0.65% (more than 120 mAh g−1, 2 C) but also improved the capacity retention (more than 90% after 300 cycles at 25 °C). While those of LNMO are about 94 mAh g−1 and 74%, respectively. These are owing to the successful suppression of side reactions and the dissolution of Mn and Ni. Therefore, this long-term cycling coated material is a promising candidate for high-energy lithium-ion batteries.

Effect of Calcining Temperatures on the Electrochemical Performances of LiNi0.5Co0.2Mn0.3O2 Cathode Material for Lithium Ion Batteries

Effect of Calcining Temperatures on the Electrochemical Performances of LiNi0.5Co0.2Mn0.3O2 Cathode Material for Lithium Ion Batteries

An effective strategy to control thickness of Al2O3 coating layer on nickel-rich cathode materials

Controllable uniformity and thickness of the coating layer of oxides on the nickel-rich materials are extremely crucial for optimization of the performance of the materials, due to the poor electronic and ionic conductivity of oxides. In this work, an efficient coating approach is developed based on organic/water two-phase system. The Al 2 O 3 -coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 with uniform and controlled thickness of the coating layer can be prepared by adjusting the amount of water used in the organic/water mixture, where aluminum isopropoxide is hydrolyzed in water phase on the surface of the LiNi 0.8 Co 0.1 Mn 0.1 O 2 spheres. It is demonstrated that the electrochemical performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 strongly correlates to the thickness of the Al 2 O 3 coating layer. With optimized thickness of the coating layer, the Al 2 O 3 -coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 can deliver a good initial discharge capacity of 191.3 mAh g −1 , although the coated Al 2 O 3 is electrochemically inactive. Importantly, a capacity retention of 95.42% can be achieved for the Al 2 O 3 -coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 upon 200 cycles at 1C, superior to that of 82.73% for the pristine counterpart. Those are ascribed to the protection effect of the coating layer to LiNi 0.8 Co 0.1 Mn 0.1 O 2 , to alleviate the side reactions at the electrode/electrolyte interface. • Al 2 O 3 coating layer can be prepared in two phase system via hydrolysis of AIP. • Thickness of Al 2 O 3 coating layer can be controlled by regulating the water amount. • Electrochemical performance of NCM811 depends on the thickness of coating layer.

Effect of Lithium Bis(oxalato) Borate Additive on Electrochemical Performances of 5V Class Cathodes at 60°C

Spinel LiNi0.5Mn1.5O4 material is one of the promising cathode materials for high energy density of lithium-ion batteries because of its high voltage, acceptable stability, and good cycling performance. However, these 5V class cathode has been noticed to be unwanted interfacial reaction with electrolyte at the high voltage. In this study, the positive impact of an electrolyte additive LiBOB on electrochemical performances of LiNi0.5Mn1.5O4 cathodes at 60°C will be discussed. In addition the oxidative decomposition of electrolytes at the cathode surface was investigated at various charged states by means of X-ray photoelectron spectroscopy(XPS) and scanning electron microscope(SEM).

Effect of Cr3+ doping on morphology evolution and electrochemical performance of LiNi0·5Mn1·5O4 material for Li-ion battery

In consideration of higher bonding strength with oxygen and no Jahn-Teller effect, Cr3+ ions were substituted for equal amount of Ni2+ and Mn4+ ions to obtain series of LiNi0.5-x/2CrxMn1.5-x/2O4 (x = 0, 0.025, 0.05, 0.1, 0.2) materials, which were prepared via a combined coprecipitation-hydrothermal method followed by a two-step calcination process. The effects of different Cr3+ doping contents on the structure, morphology and electrochemical performance were systematically investigated. The results show that Cr3+ doping increases Ni/Mn disordering while reduces Mn3+ content, which can balance rate capability and cycling stability. What’s more, Cr3+ doping reduces the primary particle size and secondary agglomeration degree. More significantly, the morphology evolution of primary particles with Cr3+ doping content is very impressive. At x ≤ 0.05, the {110} and {311} planes with higher surface energies appear in turn, while at x = 0.1 and 0.2, {311} surface disappears, {100} and {110} surfaces decrease and {111} surface increases gradually. Electrochemical results show that LiNi0·475Cr0·05Mn1·475O4 material exhibits the optimal rate and cycling performances, which can be attributed to the elimination of LixNi1-xO impurity, higher Ni/Mn disordering, lower Mn3+ content, appropriate particle size with more uniform distribution, higher structural stability resulting from the introduction of Cr–O bond and no Jahn-Teller effect of Cr3+ ions, as well as lower proportion of {111} surface and higher proportion of {100}, {110} and {311} surfaces.

Mechanism of Stability Enhancement for Adiponitrile High Voltage Electrolyte System Referring to Addition of Fluoroethylene Carbonate.

In order to improve the stability of high voltage electrolyte for 5 V-level LiNi0.5Mn1.5O4 cathode material, adiponitrile (ADN) with high oxidation stability was selected as the main solvent, meanwhile, 2% fluoroethylene carbonate (FEC) as the additive with good film forming effect was also used. And then, the effect of 2 mol L−1 LiBF4-GBL/ADN+2% FEC on the electrochemical performance of LiNi0.5Mn1.5O4 was explored at room temperature. The electrolyte system containing FEC can improve the cycle stability of the battery. At 1 C rate, the cycle capacity retention rate can reach 83% after 100 cycles, while the capacity retention rate of the electrolyte system without FEC and the ordinary commercial electrolyte system is only 77 and 68%, respectively. Besides, the rate performance of the battery with the addition of FEC also shows excellent performance, however, this kind of advantage is not obvious under the conditon of large rate. In addition, under the conditon of the synergistic effect between adiponitrile and fluoroethylene carbonate, the high-voltage electrolyte exhibits the good compatibility and lithium reversibility in the full cell with Li4Ti5O12 as the negative electrode.

Synergistic effect of Ce4+ modification on the electrochemical performance of LiNi0·6Co0·2Mn0·2O2 cathode materials at high cut-off voltage

Ni-rich layered LiNi0·6Co0·2Mn0·2O2 materials have recently drawn much attention for their high specific capacity. However, they still suffer from the cycling instability arising from Li+/Ni2+ ions mixing in crystal structure and harmful side reactions with electrolyte, especially charged at high cut-off voltage to achieve higher energy density. In this study, the Li(Ni0·6Co0·2Mn0.2)O2 (NCM622) cathode materials were prepared by sol-gel method, and Ce4+ modification was utilized to improve cycling stability and rate performance. Through XRD refinement, XPS, SEM and TEM characterization, it was found that in the case of 0.5 at% level, Ce4+ ions not only entered into the crystal lattice to replace transition metal ions, but also produced CeO2 coating on the surface of NCM622 particles. The results of electrochemical performance showed that after 100 cycles at 1 C rate, the capacity retention of NCM-0.5 sample increased by 11.03% compared to pristine sample. Besides, in the case of 5 C, the capacity of NCM-0.5 sample reached to 114.92 mAh·g−1, much higher than that of NCM-0 (91.92 mAh·g−1). The findings indicate that it is the synergistic effect of Ce4+ that endows NCM622 excellent cycling stability and rate performance at high cut-off voltage.

Improving the rate performance of LiNi0.5Mn0.5O2 material at high voltages by Cu-doping

A series of LiNi0.5-xCuxMn0.5O2 (0 ≤ x ≤ 0.05) samples were synthesized through a combination of co-precipitation (CP) and solid-state reaction. The synthesized cathode materials were systematically investigated by X-ray diffraction (XRD), Rietveld refinement, inductively coupled plasma (ICP) spectroscopy, X-ray photoelectron spectroscopy (XPS), and charge-discharge tests. The structural measurements indicated that Cu2+ was successfully doped into the structure of the LiNi0.5Mn0.5O2 material. The results of the electrochemical measurements suggest that the electrochemical performances of LiNi0.5Mn0.5O2 can be obviously improved by Cu -doping, and the best doping amount is 1 mol%. Specifically, the capacity retention of a 1 mol% Cu-doped sample is 18% higher than that of pure LiNi0.5Mn0.5O2 in the range of 2.5~4.6 V at 0.2 C. Most importantly, the cycle stability of LiNi0.5Mn0.5O2 at high currents can also be improved by Cu-doping. We found that Cu-doping can lower the Li/Ni cation mixing, enlarge the migration channels of lithium ions, reduce migration resistance, and retard polarization, and in turn, it can improve the electrochemical properties of LiNi0.5Mn0.5O2.

Preparation and electrochemical performance of LiNi0.5Mn1.5O4 spinels with different particle sizes and surface orientations as cathode materials for lithium-ion battery

LiNi0.5Mn1.5O4 hierarchical microspheres composed of primary particles with different sizes and surface orientations are synthesized by high-temperature calcination based on different Ni–Mn oxides pre-sintered at different temperatures. The effects of pre-sintering temperature on the microstructure, morphology, and electrochemical properties of materials are investigated. The results show that pre-sintering temperature has a significant effect on the composition of Ni–Mn oxides, whereas all LiNi0.5Mn1.5O4 products have phase-pure spinel structure. SEM shows that pre-sintering temperature exerts a great influence on the primary particles’ size and surface orientations. With pre-sintering temperature increasing, primary particle size increases gradually, and particle morphology changes from octahedron with {111} surface to truncated polyhedron with extra {100} and/or {110} surfaces. Electrochemical properties are investigated in LiNi0.5Mn1.5O4/Li half-cell and LiNi0.5Mn1.5O4/Li4Ti5O12 full-cell. It is found that the particle size and surface orientation have great influence on the electrochemical performance of LiNi0.5Mn1.5O4. Among them, the LiNi0.5Mn1.5O4 sample synthesized with Ni–Mn oxide pre-sintered at 600 °C shows better rate and cycling performances. This can be ascribed to the synergistic effect of exposed {111} surface and smaller primary particle size, which improves interfacial stability and reduces Li+ ion diffusion distance. The particle size and surface orientation can be tailored to meet different applications of LiNi0.5Mn1.5O4 material.

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

Mg-doped LiNi0.84Co0.11Mn0.05O2 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 LiNi0.84Co0.11Mn0.05O2 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.

Effects of Co doping sites on the electrochemical performance of LiNi0.5Mn1.5O4 as a cathode material

Using a co-precipitation approach, we introduce Co into LiNi0.5Mn1.5O4 to prepare a series of Co-doped cathode materials in which the Co substitutes partial Ni and Mn. We then systematically study the effects of Co doping at these various sites. The structural and electrochemical properties are investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller analysis, galvanostatic charge–discharge tests, and electrochemical impedance spectroscopy. The Co-doped samples experience a slight capacity loss, but their cycling stability and rate properties are significantly improved. When Ni and Mn are simultaneously substituted, the capacities at 0.1 C and 2.0 C of a battery using this doped material as the cathode stay at 99.7% and 96.8%, respectively, after 80 cycles, which is much better than the results for a battery with undoped material as the cathode.

Effects of Graphene Nanosheets with Different Lateral Sizes as Conductive Additives on the Electrochemical Performance of LiNi0.5Co0.2Mn0.3O2 Cathode Materials for Li Ion Batteries.

In this study, we focus on lateral size effects of graphene nanosheets as conductive additives for LiNi0.5Co0.2Mn0.3O2 (NCM) cathode materials for Li-ion batteries. We used two different lateral sizes of graphene, 13 (GN-13) and 28 µm (GN-28). It can be found that the larger sheet sizes of graphene nanosheets give a poorer rate capability. The electrochemical measurements indicate that GN-13 delivers an average capacity of 189.8 mAh/g at 0.1 C and 114.2 mAh/g at 2 C and GN-28 exhibits an average capacity of 179.4 mAh/g at 0.1 C and only 6 mAh/g at 2 C. Moreover, according to the results of alternating current (AC) impedance, it can be found that the GN-28 sample has much higher resistance than that of GN-13. The reason might be attributed to that GN-28 has a longer diffusion distance of ion transfer and the mismatch of particle size between NCM and GN-28. The corresponding characterization might provide important reference for Li-ion battery applications.

Effects of gradient concentration on the microstructure and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials

Nickel(Ni)-rich layered materials have attracted considerable interests as promising cathode materials for lithium ion batteries (LIBs) owing to their higher capacities and lower cost. Nevertheless, Mn-rich cathode materials usually suffer from poor cyclability caused by the unavoidable side-reactions between Ni4+ ions on the surface and electrolytes. The design of gradient concentration (GC) particles with Ni-rich inside and Mn-rich outside is proved to be an efficient way to address the issue. Herein, a series of LiNi0.6Co0.2Mn0.2O2 (LNCM622) materials with different GCs (the atomic ratio of Ni/Mn decreasing from the core to the outer layer) have been successfully synthesized via rationally designed co-precipitation process. Experimental results demonstrate that the GC of LNCM622 materials plays an important role in their microstructure and electrochemical properties. The as-prepared GC3.5 cathode material with optimal GC can provide a shorter pathway for lithium-ion diffusion and stabilize the near-surface region, and finally achieve excellent electrochemical performances, delivering a discharge capacity over 176 mAh·g−1 at 0.2 C rate and exhibiting capacity retention up to 94% after 100 cycles at 1 C. The rationally-designed co-precipitation process for fabricating the Ni-rich layered cathode materials with gradient composition lays a solid foundation for the preparation of high-performance cathode materials for LIBs.

Effect of calcination time on the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathode materials

The layered Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode materials were synthesized by a solid-state method at different calcination times. The structure, morphological and electrochemical performance of the synthesized materials were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and galvanostatic charge-discharge tests. The results indicate that the sample prepared at 20h delivers higher rate capacities of 184.8, 182.8, 171.2, 158.3, 142.8, and 116.4 mAh g−1 at rates of 0.1C 0.2C, 0.5C, 1C, 2C, and 5C, respectively. And the sample prepared at 16h exhibits better cycle stability than others.

Boosting Electrochemical Performances of High-Voltage NCA/LTO Cells by Cathode Electrolyte Interface Nano Film Formation in Ionic Liquid Electrolyte

LiTFSI/EMITFSI ionic liquid was applied in this study as an electrolyte to enhance electrochemical performances of LiNi0.8 Co0.15 Al0.05 O2 /Li4 Ti5 O12 (NCA/LTO) batteries at a high charging cutoff voltage of 3.2 V. Li-EMITFSI electrolyte generated extremely stable and uniform cathode electrolyte interface (CEI) nano film on the cathode surface. This CEI film not only inhibited the continuous decomposition of electrolyte, but also stabilized the high operating voltage of NCA/LTO batteries, resulting in enhanced discharge gravimetric specific capacity (Cg) and cyclic stability of NCA/LTO batteries. With Li-EMITFSI electrolyte, the NCA/LTO batteries achieved higher C g of 172 mAhg –1 at 0.1 C and good capacity retention of 75% over 50 cycles at 1.4 ~ 3.2 V, compared to traditional commercial electrolytes.