Pristine NCM Research Articles

Enhancing the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 by surface modification with homemade high-purity hexagonal phase tungsten oxide nanoparticles

Nickel-rich layered oxides with high energy density and acceptable cost are considered as one of the most ideal cathode materials for power batteries. However, its large-scale production and application still face the challenge in terms of rapid capacity fading and poor structural stability, which has prompted research into surface coating materials/technologies within both academic and industrial fields. In this work, A feasible and environmental friendly fabrication method of high-purity hexagonal phase tungsten oxide (h-WO3) nanoparticles as surface modification of LiNi0.8Co0.1Mn0.1O2(NCM) is proposed.The results indicate that NCM modified with h-WO3 has lower Li+/Ni2+ mixing rate, superior rate performance, and better cycling stability than the pristine NCM. Although tungsten oxide is widely used as surface modification due to its excellent physical and chemical properties, but its crystal type has not been considered, and there is little research on the theoretical explanation of h-WO3 modification.This work reveals the working mechanism of h-WO3 from the perspective of interface and crystal type, which can provide meaningful reference for obtaining nickel-rich layered oxides with excellent electrochemical properties.

Synthesizing core–shell Ni-rich LiNixCoyMnzO2 from spent Li-ion battery leachate

As the global electric vehicle market continues to grow, the recycling of Li-ion battery (LIB) becomes more important worldwide and the resynthesis of cathode materials would be the most value-added recycling approach taking into account limited metal resources. Although resynthesized homogenous LiNixCoyMnzO2 (NCM) from spent LIB leachate shows comparable battery performance to pristine NCM from virgin materials, there is general concern in its cycling performance. Here, we synthesize core–shell (CS) Ni-rich NCM, which consists of Ni-rich NCM as the core and NCM derived from the original or purified leachate of spent LIBs as the shell. Resynthesized CS Ni-rich NCM exhibits improved rate capability resulting from expanded interslab thickness in the NCM structure. CS Ni-rich NCM from purified LIB leachate shows improvement in cycling performance and thermal stability. It specifically delivers a capacity retention of 86.6% at a high temperature after 80 cycles compared to that (75.0%) of pristine CS Ni-rich NCM. These improvements are caused by a relatively high Mg content on the shell and the widespread distribution of Al through the CS structure. CS Ni-rich NCM derived from spent LIB leachate provides a new alternative approach to conventional LIB recycling methods, which would utilize efficiently limited metal resources for the sustainable LIB production.

Design of double layer cathode electrode for improving the safety and stability of lithium-ion batteries

LiNi0.8Co0.1Mn0.1O2 (NCM) is a widely used cathode material for lithium-ion batteries (LIBs). However, the poor cycle performance and safety issue remains a huge challenge for its practical applications. Here we show a simple double layer strategy to improve the electrochemical characteristics and safety performance. NCM was coated by LiFePO4 (LFP), a safe cathode material with long cycle stability, exhibited more excellent cycling stability and similar rate properties at room temperature (called NCM/LFP). Under 45 ℃, the NCM/LFP (6:1)||graphite pouch cell shows excellent 83% capacity retention after 600 cycles at 1C, which compared to the sharp attenuation of pristine NCM. Furthermore, NCM/LFP (6:1)||graphite cell could pass the nail penetration tests and the thermal runaway temperature (TTR) delayed by 193℃, which proved the double layer design has better safety performance. The current work might pave an avenue for cathode materials, as a sustainable solution to high energy density LIBs for applications.

Surface engineering of P2-type cathode material targeting long-cycling and high-rate sodium-ion batteries

The widespread interest in layered P2-type Mn-based cathode materials for sodium-ion batteries (SIBs) stems from their cost-effectiveness and abundant resources. However, the inferior cycle stability and mediocre rate performance impede their further development in practical applications. Herein, we devised a wet chemical precipitation method to deposit an amorphous aluminum phosphate (AlPO4, denoted as AP) protective layer onto the surface of P2-type Na0.55Ni0.1Co0.1Mn0.8O2 (NCM@AP). The resulting NCM@5AP electrode, with a 5 wt% coating, exhibits extended cycle life (capacity retention of 78.4% after 200 cycles at 100 mA g−1) and superior rate performance (98 mA h g−1 at 500 mA g−1) compared to pristine NCM. Moreover, our investigation provides comprehensive insights into the phase stability and active Na+ ion kinetics in the NCM@5AP composite electrode, shedding light on the underlying mechanisms responsible for the enhanced performance observed in the coated electrode.

Synergetic effect of trimetallic double hydroxide nanospikes embraced N-doped graphene nanosheets as electrode material for supercapacitors

In the energy storage sector, layered double hydroxides (LDHs) are coming to the forefront as a promising option for electrode materials. However, LDHs suffer from insufficient intrinsic conductivity and agglomeration during formation which restrict their wide applications. In this context, a two-step hydrothermal technique is employed to synthesize NiCoMn hydroxide (NCM)/N-doped graphene (NG). Initially, NG is produced through hydrothermal treatment utilizing urea to serve as both a reduction and doping source. Subsequently, a straightforward hydrothermal technique is utilized to cultivate NCM onto the surface of NG nanosheets. The electrochemical properties of NCM-NG composite with different compositions of NG have been analyzed, resulting in capacitance increment on account of increased conductivity and large number of active sites upon incorporation of NG as compared to pristine NCM. Moreover, NG nanosheets inhibit the agglomeration of NCM nanospikes. Amongst different compositions, NCM-NG-2 nanohybrid secured the highest specific capacitance (Cs) of 783.5 F/g at 0.25 A/g. The Asymmetric supercapacitor device assembled with NCM-NG-2 (anode) and activated carbon (AC) (cathode) exhibits the Cs of 114.5 F/g at 0.5 A/g. The optimized specific energy (Es) of 31.8 Wh/kg and specific power (Ps) of 473.4 W/kg with remarkable retention of 101.9 % up to 15,000 continuous cycles, indicating a higher potential of the NCM-NG-2 electrode in energy storage applications. These findings open new avenues for developing highly productive multi-material electrodes for utilization in energy storage systems.

Reconstruction of solvation structure at the cathode-electrolyte interface via partial de-solvation in a metal-organic framework

The formation of cathode-electrolyte interphase (CEI) is closely related to the solvation structure in direct contact with the cathode. The de-solvated solvent molecules are subject to the attack of highly catalytic transition metal ions in the cathode materials (such as Ni-rich LiNi0.8Co0.1Mn0.1O2, Ni-rich NCM), especially at high voltage or high temperature, leading to the poor CEI structure that accelerates the deterioration of rechargeable batteries. Considerable strategies have been proposed to solve this issue. Herein, we have constructed a porous Mg-MOF buffer layer on the surface of Ni-rich NCM, which not only greatly reduces the contact between solvent molecules and cathodes to alleviate the extensive interface reactions, but also promote the de-solvation of Li+ solvation structure through strong affinity between solvents and Mg2+. The partially de-solvated structure induces the anion to participate in the solvation structure and contributes to the formation of a uniform LiF-rich CEI with superior mechanical integrity and chemical stability. Therefore, the NCM with Mg-MOF buffer layer exhibits improved cycling stability at both elevated temperature of 45 °C and high voltage of 4.5 V with lithium as anode. Moreover, the modified NCM/graphite full cells also deliver ultra-stable rechargeable capability with a remarkable capacity retention of 87.3% over 1000 cycles as compared to the only 21.7% of pristine NCM based cells.

Fluorides coated Ni-rich cathode materials with enhanced surficial chemical stability for advanced lithium-ion battery

Ni-rich cathode materials (LiNixCoyMnzO2 denoted as NCM, where x ≥ 0.8 and x + y + z = 1) with high energy density are considered as next-generation promising cathodes for lithium-ion batteries (LIBs). However, the high surface chemical sensitivity against CO2 and H2O in air triggers serious surface degradation. Meanwhile, the notorious surficial residual lithium compounds are often prone to react with polyvinylidene fluoride (PVDF) binder, resulting in slurry gelation, and further deteriorating electrochemical performance. Herein, a facile solvothermal strategy is proposed to construct thin and uniform fluoride coating layers on NCM surface (NCM-F) via in-situ reacting trifluoroethanol with residual lithium compounds. This fluoride protective layer not only significantly suppresses the surface deterioration by inhibiting Li+/H+ exchange, but also avoids the side reactions between NCM and electrolyte. As a result, NCM-F with low pH value of 11.2 exhibits highly chemical stability against ambient air, excellent processing performance and superior cyclic stability. More importantly, even after 4 weeks air aging, NCM-F demonstrates high initial capacity and low electrode polarization compared to pristine NCM (P-NCM). This work not only opens up new perspectives on surface modification of NCM cathodes, but also provides guidance on improving air stability for other functional materials.

Boron & nitrogen synergistically enhance the performance of LiNi0.6Co0.1Mn0.3O2

Nickel-rich ternary material faces up with the performance degradation problem associated with its poor structural stability and interfacial side reactions with the electrolyte. Herein, boron and nitrogen co-modified LiNi0.6Co0.1Mn0.3O2 material was synthesized, aiming at studying the effect on the crystal structure, electronic conductivity and the electrochemical performance. It is interesting to find out that the rate performance and the cycle stability of the B&N co-modified materials are greatly associated with the ratio of B/N. The optimal sample NCM/B4N4 has initial specific discharge capacity 198.4 mAh g−1, the retention of 81.3% after 200 cycles (1 C) as well as the electronic conductivity of 5.00 × 10−4 S/cm, against the pristine NCM (194.0 mAh g−1, 56.7%, 1.22 ×10−4 S/cm). Moreover, the discharge capacity of the modified sample is improved obviously at high rate (5 C). TEM and XPS show that boron and nitrogen were successfully doped into the surface of the materials. Compared the PXRD patterns after 300 cycles and in situ XRD tests, it is found that the boron and nitrogen co-modification can inhibit the irreversible phase transition. DFT calculations disclose that Li layer thickness of the B&N co-doped sample is larger than that in individual B doped sample and the pristine material. GITT test confirms the higher lithium ions diffusion rate of NCM/B4N4. This work suggests that Nitrogen-doping can improve the electronic conductivity of Boron-doped material, consequently facilitating the Li ion diffusion of nickel-rich cathode materials.

Enhanced microstructure stability of LiNi0.8Co0.1Mn0.1O2 cathode with negative thermal expansion shell for long-life battery

With high specific energy density, Ni-rich layered LiNi0.8Co0.1Mn0.1O2 (NCM) material has become one promising cathode candidate for advanced lithium-ion batteries (LIBs). However, severe capacity fading induced by microstructure degradation and deteriorated interfacial Li+ transportation upon repeated cycling makes the commercial application of NCM cathode in dilemma. To address these issues, LiAlSiO4 (LASO), one unique negative thermal expansion (NTE) composite with high ionic conductivity, is utilized as a coating layer to improve the electrochemical performances of NCM material. Various characterizations demonstrate that LASO modification can endow NCM cathode with significantly enhanced long-term cyclability, through reinforcing the reversibility of phase transition and restraining lattice expansion, as well as depressing microcrack generation during repeated delithiation-lithiation processes. The electrochemical results indicate that LASO-modified NCM cathode can deliver an excellent rate capability of 136 mAh g−1 at a high current rate of 10 C (1800 mA g−1), larger than that of the pristine cathode (118 mAh g−1), especially higher capacity retention of 85.4% concerning the pristine NCM cathode (65.7%) over 500 cycles under 0.2 C. This work provides a feasible strategy to ameliorate the interfacial Li+ diffusion and suppress the microstructure degradation of NCM material during long-term cycling, which can effectively promote the practical application of Ni-rich cathode in high-performance LIBs.

Fundamental Understanding of the Effect of a Polyaniline Coating Layer on Cation Mixing and Chemical States of LiNi0.9Co0.085Mn0.015O2 for Li-Ion Batteries

A high nickel content of the cathode usually results in a large discharge capacity but causes structural collapse. Ni2+ ions move to the Li layer when Li+ ions are deintercalated during discharge, resulting in irreversible phase transition, cation mixing, dissolution of transition metal ions, and side reactions. A protective barrier is essential for maintaining the layered structures of cathode materials, even after several charge/discharge cycles of Li-ion batteries. Polyaniline (PANi) is an organic coating material with high conductivity and flexibility. PANi-coated cathodes have been widely reported for improving electrochemical performances. However, it is insufficient to prove the correlation between the PANi coating layer and structural stability through further analysis after an electrochemical test. Therefore, we focused on the structural stability and chemical states of the PANi-coated cathode after a cycle test by observing the morphology, lattice patterns, and chemical states of the surface. PANi-coated LiNi0.9Co0.085Mn0.015O2 (NCM; PANi@NCM) exhibited an initial discharge capacity of 221 mAh g–1 and a capacity retention of 81% after 50 cycles at 45 °C, which corresponded to an improved performance compared to pristine NCM. The cycled PANi@NCM showed an identical morphology to that of the cathode before the test. The R3̅m layered structure of PANi@NCM was maintained even after 50 cycles, as confirmed by transmission electron microscopy analysis with fast Fourier transform patterns and high-angle annular dark-field images. In addition, PANi@NCM maintains a thinner passivation layer (8 nm) compared with that of pristine NCM (27 nm). According to the X-ray photoelectron spectroscopy results, the surface chemical state of PANi@NCM showed that side reactions between the cathode and the electrolyte were suppressed during the cycle test. Therefore, it is demonstrated that the PANi coating layer prevents cation mixing and side reactions.

Tri-functionalized Li2B4O7 coated LiNi0.5Co0.2Mn0.3O2 for boosted performance lithium-ion batteries

Building stable interfacial structure is regarded as an effective strategy to enhance structure stability and facilitate Li+ migration. Herein, LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode materials are surface-modified with amorphous Li2B4O7 (LBO) Li+-conductor with high relative permittivity. Comparing to pristine NCM, surface-modified electrodes exhibit a significant improvement in capacity retention and rate capability, delivering a reversible capacity of 163.4 mAh·g−1 and 87.6 % capacity retention over 100 cycles at 1 C. Besides the protection from HF-attack, enlarged crystal lattice volume by boron-doping and Li+-conductor characteristic of Li2B4O7 is beneficial for Li+-ion diffusion in NCM523 and reduces charge transfer resistance. In addition, the reduced work function induced by Li2B4O7-coating is helpful for the suppression of the electrolyte oxidation, the enhanced rate capability and improved cyclic stability in terms of interfacial stability. Moreover, dielectric polarization field induced by high-permittivity Li2B4O7 at NCM523-Li2B4O7-electrolyte triple-phase interface would synergistically facilitate Li-ion migration across electric double-layer. Our work would provide a new insight into the enhanced performance of cathode material surface-modified by Li+-conductor with large relative permittivity.

Stabilization of high-voltage layered oxide cathode by multi-electron rare earth oxide

High-voltage medium-nickel low-cobalt lithium layered oxide materials have been recognized as a kind of promising cathodes to further promote the energy density of lithium-ion batteries (LIBs) due to their relatively high capacity, low cost, and improved safety. However, the high voltage induced bulk structure degradation and interfacial environment deterioration limit the performance liberation of this kind of cathodes. Here, an ultrathin and uniform Sm2O3 rare earth oxide functional coating has been introduced to enhance the lithium storage performance of LiNi0.6Co0.05Mn0.35O2 (NCM) cathode. On the one hand, this multi-electron Sm2O3 function coating could increase the activation energy of surface lattice oxygen loss, improving the electrode–electrolyte interface stability; on the other hand, it delays the phase transition temperature and weakens the harmful H3 phase transition of NCM, improving its thermal stability as well as minimizing the mechanical degradation. These beneficial effects endowed by the Sm2O3 coating imply that it could behave as both a physical passivation layer and a charge compensation payer. As a result, the 2%-Sm2O3@NCM delivers a higher capacity retention rate (97.3% vs 75.0% after 150 cycles) and a superior rate capacity (117 mAh g−1vs 52 mAh g−1 at 5C) than the pristine NCM, making high-voltage lithium layered oxide one step closer to being a viable cathode.

Study on the Structural Degradation of the Polyaniline(PANi) Coated LiNi0.90Co0.85Mn0.15o Particles

The nickel content of the layered lithium transition metal oxide cathodes is proportional to the discharge capacity of energy storage systems. Ni2+ ion, the oxidation state of Ni, moves to the Li sites when Li+ ion is deintercalated during discharge process due to the similar size of ion (Ni2+: 0.069 nm, Li+: 0.076 nm). The spatial transition of Ni2+ ion causes gradual cation mixing and structure degradation of cathode, resulting in the failure of the battery. Also, thick cathode-electrolyte interphase (CEI) is formed on the cathode surface because of the transition metal dissolution, the degradation of electrolyte, and the residual gas such as H2O and CO2.Coating technology is one of the strategies for the physical protection of the cathode surface and the control of CEI layer thickness. Polyaniline(PANi) is a conductive polymer with stable oxidation state. PANi can enhance the electrochemical property and structural stability as a protective layer. In this study, we synthesized PANi material by the oxidative polymereization and coated NCM with the synthesized PANi by sonication method.The PANi-coated NCM(PANi@NCM) has uniform coating layer with 5 nm thickness. PANi@NCM exhibits an initial discharge capacity of 208 mAhg-1 and a capacity retention of 81% after 50 cycles at 45 oC in Figure 1(a) and (b). After the cycling test, pristine and coated cathodes were disassembled for the comparison of the microstructure. Pristine NCM only shows the structural transition from layered structure to structure in the XRD pattern of Figure 1(c). Cross-sectional SEM image of the pristine NCM after cycling test shows micro and macro cracks are distributed from the bulk to the surface of the cathode as shown in Figure 1(d). On the other side, cracks are barely observed on the PANi@NCM particles in Figure 1(e). The layered structure of PANi@NCM is maintained even after cycling test, which are confirmed by TEM analysis with FFT patterns and HAADF images. Figure (f) and (g) show the FFT pattern of the two cathode surfaces after cycling test. Mixed phase is observed on the pristine cathode surface, while the layered structure is maintained on the PANi@NCM surface. Also, the PANi@NCM maintains a thinner passivation layer compared with that of the pristine NCM (6 nm vs 35 nm). In conclusion, the PANi coating layer prevents the degradation of structure and the formation of thick CEI layer. The structural stability enhances the electrochemical performance. Figure 1

Enhanced Structural Stability and Capacity Retention of Ni-Rich LiNi0.91Co0.06Mn0.03O2 Cathode Material By Dual Doping and Coating for Libs

Nickel-rich layered cathode material has been received a lot of attention due to their superior cycle-ability, high energy density and improved safety. However, there are some issues which are needed to be resolved to ensure the long term application. The hostile attack of electrolyte with the charged cathode electrode results in the growth of thick solid electrolyte interphase (SEI) at the expense of Li+ consumption and increase in interfacial resistance. In addition, de/intercalation of Li+ leads to the continuous contraction and expansion of lattice structure that leads to the crack formation in the active material particles during extended cycling.In this work, a facile technique has been adopted to resolve the mentioned problems. In this study, Li3BO3 has been coated on the NCM surface to protect the active material against the continuous attack of electrolyte and boron is doped to enhance the structural stability of LiNi0.91Co0.06Mn0.03O2 NCM cathode material. The samples were characterized by XPS, XRD, SEM and TEM and the electrochemical properties were measured by assembling the coin cells. The XRD results confirm the shifting of (003) diffraction peak towards low angle which validates the boron doping in the crystal structure. The presence of B1s is confirmed on the surface of modified NCM by XPS analysis. The FETEM images shows a uniform and distinct coating layer of 12 nm on the surface of 0.05 wt% coated NCM. The 0.05 wt% NCM samples offers the highest discharge capacity of 215.3 mAh g-1 at 0.1C and capacity retention of 81.6% at 0.5C (1C = 202 mA g-1) after 100 cycles. The reason behind enhanced cycling is the high bond dissociation energy of B−O (ΔHf298 = 402 kJ mol−1) than Ni–O (ΔHf298 = 391.6 kJ mol−1), Co–O (ΔHf298 = 368 kJ mol−1) and even Mn–O (ΔHf298 = 402 kJ mol−1). Even at 2C cycling, LBO-0.05 NCM sample demonstrated a capacity retention of 79.4% after 100 cycles while pristine shows only 67.3%. The modified samples displayed superior rate performance as compare to pristine NCM, especially at high current density. The cyclic voltammetry and EIS results are in-line with the cycling data. The presence of B3+ doping in host structure and Li3BO3 coating on the NCM surface results in the superior electrochemical performance of modified NCM.

Surface engineering for high stable lithium-rich manganese-based cathode materials

Lithium-rich manganese-based material shows great potential as the high specific cathode materials due to its low cost, environmental friendliness, high operating voltage and simple preparation process. However, the poor capacity retention and cycling performance caused by its unstable structure during cycling restrict the commercialization. In this work, Li1.2Ni0.16Mn0.56Co0.08O2 was synthesized utilizing a Co-precipitation method and different amount of La(PO3)3 (La(PO3)3 = 2 wt%, 4 wt% and 6 wt%) was selected as the coating layer to resolve the above issues. During the calcination process, La(PO3)3 reacts with impurities such as LiOH and Li2CO3 on the lithium-rich surface to reduce the residual lithium on the surface, thus improving the interfacial stability, slowing down the corrosion of the electrolyte, and finally enhancing its electrochemical performance. The cathode materials coated with 4% of La(PO3)3 showed the best electrochemical performance in terms of capacity retention and cycling performance compared to the pristine NCM. The high initial discharge capacity of 214.21 mAh/g and capacity retention of 94.2% after 100 cycles at 0.1 C can be obtained. This work provides an effective strategy to protect the cathode from corrosion and will promote its further practical applications in high specific Li-ion batteries.

Lanthanum Oxyfluoride modifications boost the electrochemical performance of Nickel-rich cathode

Lanthanum oxyfluoride (LaOF) materials have appreciable higher conductivity, favorable thermal and chemical stability, herein the LaOF coating layer was synthesized on the cathode LiNi0.8Co0.1Mn0.1O2 through one-step solid-phase method, to study the effect of LaOF modification of the electrochemical performance. The modified sample 0.4LaOF-NCM exhibits the initial discharge capacity of 182.8 mAh·g−1 and the retention of 87.8% after 300 cycles at 1C and 2.8–4.3 V (half-cell, room temperature); meanwhile, its full cell has the capacity of 179.8 mAh·g−1 and the retention of 83.5% after 300 cycles, superior to the pristine NCM (175.8 mAh·g−1 and 79%, full cell). Through analyses of XRD, SEM, HRTEM and XPS test results, it indicates that the LaOF amorphous coating layer on the surface of the NCM material can inhibit the side reactions between the cathode and the electrolyte during the cycling, and consequently improve the cycling stability. After 100th cycles, the Li+ diffusion rate during the delithiation and lithiation process is 1.63 × 10−10 and 1.02 × 10−10 cm2 s−1 for the pristine NCM, whereas for the 0.4LaOF-NCM the Li+ diffusion rate is respectively 2.08 × 10−10 and 1.45 × 10−10 cm2 s−1, which are more than 1.3 times faster than those of the pristine NCM. It is suggested that such LaOF modification would have promising applications to improve the performance of LIB.

Surface Reconstruction of Ni‐Rich Layered Cathodes: In Situ Doping versus Ex Situ Doping

The structural instability and sluggish Li+ diffusion kinetic of the nickel‐rich LiNixCoyMn1−x−yO2 (NCM) cathode still hinder its further commercialization for lithium‐ion batteries. Doping heteroatoms are widely studied as an effective strategy to maintain structural and thermal stability for improving the capacity retention of NCM during cycling. Herein this work, in situ Zn2+‐doped NCM (in situ Zn‐NCM) is successfully designed by atomic layer deposition (ALD) combined with annealing. In comparison to ex situ Zn2+‐doped NCM (ex situ Zn‐NCM), in situ Zn‐NCM can better enhance the layered structure stability and reduce the generation of surface defects due to that it has lower migration energy barrier and more uniform distribution of heteroatoms. As a result, at a high cutoff voltage of 4.5 V, in situ Zn‐NCM with the obvious advantages of lower cation mixing, better phase transition stability, as well as more efficient charge transfer displays higher reversible capacity (i.e., 203.2 mAh g−1 at 50 mA g−1) and initial Coulombic efficiency (85%) compared to ex situ Zn‐NCM and the pristine NCM. Therefore, in situ doping is a novel and universal strategy to enhance battery performance of high‐energy‐density NCM cathodes for lithium‐ion batteries.

Hydrophobic surface coating against chemical environmental instability for Ni-rich layered oxide cathode materials

Ni-rich layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM) as a most promising cathode material for Li-ion batteries suffers easily from the deterioration of electrochemical performance during storage because of the chemical environmental instability. Herein, a simple and scalable strategy is reported to overcome these issues by a hydrophobic coating with dihexadecyl phosphate (DHP) on NCM particle surface, which is composed of an outer-layer hydrophobic alkyl surface and an inner-layer phosphate-based coating with O=POLi covalent bonds. The former layer can alleviate the absorption of H2O/CO2 on the particle surface in the humid environment, and the later can improve Li+ transportation coefficient during charge–discharge process. As a result, profiting from these two synergistic effects, the DHP-coated NCM shows excellent rate performance and cycling stability, particularly, after 14 days of exposure to air, the DHP-coated NCM delivers the initial capacity of 168.7 mAh g−1 at 2 C rate, but only 134.7 mAh g−1 for the pristine NCM. This work provides an effective approach to improve the environmental stability in Ni-rich layered oxide cathodes.

Realizing ultrahigh-voltage performance of single-crystalline LiNi0.55Co0.15Mn0.3O2 cathode materials by simultaneous Zr-doping and B2O3-coating

Improving the high-voltage stability of cathode materials is a new strategy to enhance the energy density of lithium-ion batteries (LIBs) in recent years. However, as a traditional cathode material, the low reversible capacity at high cut-off voltages (≥ 4.3 V) greatly restricts the application of LiCoO2. Herein, we have rationally synthesized a novel single-crystalline LiNi0.55Co0.15Mn0.3O2 cathode material (Z-NCM@B) by using the synergistic effect of Zr-doping and B2O3-coating. Excitedly, the modified Z-NCM@B cathode material shows improved high-voltage stability and excellent long-term cycling performance. Furthermore, it is revealed that the stronger ZrO bond formed by Zr4+ dopant can stabilize the crystal structure and promote the migration of Li+ in the cathode materials. Meanwhile, the uniform B2O3 coating layer effectively suppresses the material corrosion by electrolyte and reduces the loss of transition metal ions during the charge/discharge cycle process. As anticipated, the Z2-NCM@B2 || graphite pouch-type full cell exhibits an advanced capacity retention of 96.9% over 250 cycles at an operating voltage of 4.2 V, while the capacity retention of the pristine NCM is only 88%. Besides, the Z2-NCM@B2 coin-cell retains a discharge capacity of 145.2 mA h g−1 at 1 C with a satisfactory capacity retention of 79.2% after 100 cycles within a broad voltage range between 2.95 and 4.7 V, which is much superior than that for the pristine NCM (130.9 mA h g−1, 70.9%). This synergistic modification strategy offers a reference for the practical application of NCM cathode materials with high-voltage stability and long-term cycling performance in LIBs.

Sodium doping derived electromagnetic center of lithium layered oxide cathode materials with enhanced lithium storage

High-voltage high-nickel low-cobalt lithium layered oxide cathode materials show great application prospects for lithium-ion batteries because of their low cost and high capacity. Unfortunately, the deterioration of the bulk structure and electrode-electrolyte interface will significantly deteriorate the cycle life and thermal stability of the battery as the nickel content and voltage increase. Here we introduce the 2 mol% Na-doped Li0.98Na0.02Ni0.6Co0.05Mn0.35O2 (NCM-Na) high-nickel low-cobalt cathode. Na ion plays the role of an electromagnetic center and effectively inhibits the harmful phase transitions and Li+/Ni2+ mixing, thereby greatly improving the lithium storage performance of the cathode material. NCM-Na delivers a higher capacity retention rate (93.3% vs. 83.2%) after 100 cycles and a superior rate capacity (121 mAh g−1 vs. 93 mAh g−1) at 3C current density compared to the pristine NCM under 4.5 V high voltage. And the improved lithium diffusion kinetics, bulk layered structure stability, electrode-electrolyte interface stability, and thermal stability are also confirmed through the relevant in/ex-situ characterization and theoretical calculation simulation. These beneficial effects also make the designed graphite anode high voltage full battery exhibit excellent electrochemical performance. This work provides a valuable strategic guideline for the use of high-voltage high-nickel low-cobalt cathodes in lithium-ion batteries.