Cathode Electrolyte Interphase Layer Research Articles

Robust interfacial engineering construction to alleviate polysulfide shuttling in metal sulfide electrodes for achieving Fast-charge High-capacity lithium storages

Robust cathode/electrolyte interphase (CEI) layer exhibits much importance in capacity retention. However, metal sulfide electrodes with unstable CEI layers suffer from fast capacity fading and poor Coulombic efficiency caused by notorious polysulfide shuttling effect. Herein, different from nanoparticle engineering, the morphology and state of CEI interface engineering are modulated via introducing highly active lithium bisfluorosulfonylimide (LiFSI) in the ether-based electrolyte. The presence and evolution of the uniform and robust LiF-Li3N-rich CEI layer in preventing polysulfide shuttling are fully understood by electrochemical measurements, interface-sensitive sum frequency generation spectroscopy, X-ray spectroscopies and electron microscopy. With the aid of the time-of-flight secondary-ion mass spectrometry, the three-dimensional architecture of CEI is re-depicted, showing the uniform coverage and thus inhibiting the polysulfide shuttling. As a result, the so-fabricated metal sulfide electrodes with continuous CEI layer exhibit much higher rate capacity and significantly-improved Coulombic efficiency than the controlled electrode samples. Even cycled at a high-power density of 6700 W kg−1 (5 C), the FeS2 electrode remains a high initial capacity (512 mA h g−1) and long lifespan up to 1000 cycles, depicting a blue-script of constructing robust CEI on the electrode for achieving the fast-charge electrodes.

Cationic Covalent Organic Framework with Ultralow HOMO Energy Used as Scaffolds for 5.2 V Solid Polycarbonate Electrolytes.

Solid polymer electrolytes (SPEs) have become promising candidate to replace common liquid electrolyte due to highly improved security. However, the practical use of SPEs is still restricted by their decomposition and breakage at the electrode interfacial layer especially at high voltage. Herein, a new cationic covalent organic framework (COF) is designed and synthesized as a reinforced skeleton to resist the constant oxidative decomposition of solid polycarbonate electrolyte, which can stabilize cathode electrolyte interphase layer to develop long‐term cycle solid lithium metal battery. The ultralow HOMO energy (−12.55 eV according to density functional theory (DFT) calculations), reflecting its oxidation resistance at positive potential, would be responsible for the high decomposition voltage of 5.2 V versus Li+/Li of solid polycarbonate electrolyte. Furthermore, the smooth surface of interfacial layer and inhibited decomposition reaction at cathode side is confirmed in solid LiCoO2 cell, which realizes high initial capacity up to 160.3 mAh g−1 at 0.1 C and greatly improved stability in 4.5 V class solid polymer lithium metal battery with high capacity retention over 200 cycles. This new type of high‐voltage resistant solid polymer electrolyte promotes the realization of high‐voltage cathode materials and higher energy density lithium metal battery.

Boosting high voltage cycling of LiCoO2 cathode via triisopropanolamine cyclic borate electrolyte additive

Energy density of lithium-ion batteries (LIBs) can be promoted by raising the charge cutoff voltage, which faces the challenges of accelerated structural and interfacial degradation. Introducing a functional electrolyte additive is considered as an effective approach by forming a robust and protective cathode electrolyte interphase (CEI). Herein, triisopropanolamine cyclic borate (TPCB) additive is probed for the first time as an electrolyte additive to significantly enhance the interfacial stability of LiCoO2 (LCO) cathode at high charge cutoff voltages (≥4.6 V). With optimized 0.5% TPCB in electrolyte, a thin (about 8 nm) and dense CEI layer, containing C–N, B–O/B–F species and less LiF, is generated to suppress the decomposition of electrolyte at high voltages and alleviate structure damage of LCO during long-term cycling. As a result, the LCO cathode in the TPCB-modified electrolyte displays remarkably enhanced capacity retention of 82.2% after 200 cycles at 1C at high charge cut-off 4.6 V, exceeding that of 63.2% in the Base electrolyte.

Dictating the interfacial stability of nickel-rich LiNi0.90Co0.05Mn0.05O2 via a diazacyclo electrolyte additive – 2-Fluoropyrazine

Nickel-rich (Ni-rich) cathode materials, LiNixCoyMnzO2 (NCM, x ≥ 0.9, x + y + z = 1) hold great promise for developing high energy density lithium ion batteries especially for vehicle electrification. However, the practical application of Ni-rich cathode materials is still suffered from fast structural and interfacial degradation, and the resulted capacity decay. In this study, a diazacyclo type electrolyte additive, 2-fluoropyrazine (2-FP), was explored for the first time to boost the interfacial stabilization of single crystal LiNi0.90Co0.05Mn0.05O2 (NCM90) cathode. The capacity retention of the NCM90 is evidently promoted from 72.3% to 82.1% after 200 cycles at 1C (180 mA g−1) when adding 0.2% 2-FP into the electrolyte. The improvement of the electrochemical performance is ascribed to the generation of a compact and homogeneous cathode electrolyte interphase (CEI) film through ring-opening electrochemical polymerization of 2-FP upon the NCM90 electrode particles. This enhanced CEI layer benefits the suppression of the decomposition of LiPF6 electrolyte and the dissolution of the transition metals (Co and Mn), thus preventing the detrimental side reactions between the NCM90 electrode and the electrolyte.

Enabling the High-Voltage Operation of Layered Ternary Oxide Cathodes via Thermally Tailored Interphase.

Layered ternary oxides LiNix Mny Coz O2 are promising cathode candidates for high-energy lithium-ion batteries (LIBs), but they usually suffer from the severe interfacial parasitic reactions at voltages above 4.3V versus Li+ /Li, which greatly limit their practical capacities. Herein, using LiNi1/3 Mn1/3 Co1/3 O2 (NMC111) as the model system, a novel high-temperature pre-cycling strategy is proposed to realize its stable cycling in 3.0-4.5V by constructing a robust cathode/electrolyte interphase (CEI). Specifically, performing the first five cycles of NMC111 at 55°C helps to yield a uniform CEI layer enriched with fluorine-containing species, Li2 CO3 and poly(CO3 ), which greatly suppresses the detrimental side reactions during extended cycling at 25°C, endowing the cell with a capacity retention of 92.3% at 1C after 300 cycles, far surpassing 62.0% for the control sample without the thermally tailored CEI. This work highlights the critical role of temperature on manipulating the interfacial properties of cathode materials, opening a new avenue for developing high-voltage cathodes for Li-ion batteries.

Insight into Superior Electrochemical Performance of 4.5 V High-Voltage LiCoO2 Using a Robust Polyacrylonitrile Binder

The polyvinylidene fluoride (PVdF) binder is the classic binder for cathodes because of its excellent electrochemical stability and superior adhesion property. However, PVdF is very expensive and sensitive to moisture. Therefore, pursuit of a cost-effective binder is highly desirable, especially for high-voltage cathode application. Polyacrylonitrile (PAN) possesses strong polar C≡N groups, endowing it with oxidation resistance and strong binding properties. Herein, the PAN binder was systematically investigated for the electrochemical performance of the 4.5 V high-voltage LiCoO2 (HV-LCO) electrode. The results showed that the HV-LCO-PAN electrode delivered superior rate capability and cycling stability to the corresponding HV-LCO-PVdF. The PAN binder was highly tolerant of moisture and was capable of forming uniform coating on the cathode materials. Moreover, the PAN binder had ultrahigh mechanical modulus (8.01 GPa) and hardness (381.45 MPa) in a liquid electrolyte, thereby improving cycling stability and rate capability. X-ray photoelectron spectroscopy analysis further demonstrated that PAN formed uniform coating on the surface of LiCoO2 and played a role of an artificial cathode–electrolyte interphase layer, suppressing decomposition of the liquid electrolyte under high cutoff voltage.

Optimizing the Electrolyte Systems for Na3 (VO1-x PO4 )2 F1+2x (0≤x≤1) Cathode and Understanding their Interfacial Chemistries Towards High-Rate Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have been regarded as promising alternative to lithium-ion batteries (LIBs) due to the abundance of sodium resource and cost-effectiveness of electrode manufacture. Na3 (VO1-x PO4 )2 F1+2x (0≤x≤1, NVPF1+2x ) polyanionic material, a potential high-energy-density cathode, has shown superior electrochemical performances for advanced SIBs due to its high working voltage (>3.9 V). Electrolyte composition, which plays an indispensable and critical role in determining the cycle stability and the electrode/electrolyte interfacial properties, is of great significance to possess good compatibility with electrode materials, especially the NVPF1+2x cathode. Here, different electrolyte systems, including commonly used 1.0 m NaPF6 /diglyme (NP-005), 1.0 m NaPF6 /propylene carbonate (PC)/5.0 % fluoroethylene carbonate (FEC) (NP-009), 1.0 m NaClO4 /ethylene carbonate-dimethyl carbonate (EC-DMC; 1 : 1 v/v)/5.0 % FEC (NC-019), and 1.0 m NaClO4 /PC (NC-013), were systematically investigated and compared for NVPF1+2x cathode. NVPF1+2x electrode with NP-009 electrolyte showed a superior cycle stability and rate capability at 1-10 C (1 C=130 mA g-1 ) than that of NC-019 and NC-013, while NVPF1+2x electrode with NP-005 electrolyte showed the best high-rate capability at 20-50 C. The cathode/electrolyte interphase (CEI), post-mortem electrode morphology, and electrochemical kinetic characteristics of NVPF1+2x electrode with different electrolytes were profoundly investigated and compared. It demonstrated that NVPF1+2x electrode with NP-005 exhibited a thin, efficient, and NaF-rich CEI layer with less polarization, smaller interfacial resistance, and faster Na+ diffusion than that of NC-019 and NC-013 since they suffered from a thick, overgrown CEI layer due to the consecutive decomposition of FEC, NaClO4 , and/or linear DMC, resulting in inferior electrochemical performance. This work provides new insights for the battery community to gain more comprehensive understanding about the compatibility and interfacial chemistry between different electrolyte systems and various electrode surfaces.

Fluorination-Enhanced Surface Stability of Disordered Rocksalt Cathodes.

Cation-disordered rocksalt (DRX) oxides are a promising new class of high-energy-density cathode materials for next-generation Li-ion batteries. However, their capacity fade presents a major challenge. Partial fluorine (F) substitution into the oxygen (O) lattice appears to be an effective strategy for improving the cycling stability, but the underlying atomistic mechanism remains elusive. Here, using a combination of advanced transmission electron microscopy based imaging and spectroscopy techniques, the structural and chemical evolution upon cycling of Mn-based DRX cathodes with an increasing F content (Li-Mn-Nb-O-Fx , x= 0, 0.05, 0.2) are probed. The atomic origin behind the beneficial effect of high-level fluorination for enhancing the surface stability of the DRX is revealed. It is discovered that, due to the reduced O redox activity while with increasing F concentration, F in the DRX lattice mitigates the formation of an O-deficient surface layer upon cycling. For low F-substituted DRX, the O loss near the surface results in the formation of an amorphous cathode-electrolyte interphase layer and nanoscale voids after extended cycling. Increased F concentration in the DRX lattice minimizes both O loss and the interfacial reactions between DRX and the liquid electrolyte, enhancing the surface stability of DRX. These results provide guidance on the development of next-generation cathode materials through anion substitution.

AlF3-Al2O3 ALD Thin-Film-Coated Li1.2Mn0.54Co0.13Ni0.13O2 Particles for Lithium-Ion Batteries: Long-Term Protection.

Improving the performance of existing cathode materials of lithium-ion batteries (LIBs) through surface modification has been proven to be an effective way to improve the performance of LIBs. However, it is a challenge to use a traditional method to prepare an effective coating film, which meets the requirements of uniformity, continuity, electrochemical stability, and strong mechanical properties. In this study, an ultrathin AlF3-Al2O3 film was coated on the surface of Li1.2Mn0.54Co0.13Ni0.13O2 (LRNMC) particles by atomic layer deposition (ALD) in a fluidized bed reactor. A cathode electrolyte interphase layer mainly composed of inorganic components was formed on the surface of AlF3-Al2O3-coated LRNMC during the charge/discharge cycling process, which led to the enhancement of capacity and cycling stability. In addition, the coating layer significantly increased the shelf life of the cathode particles. For LRNMC particles with one cycle of Al2O3 ALD and one cycle of AlF3 ALD coatings, there was no obvious degradation of electrochemical performance after being stored for more than 1 year, indicating long-term protection of ALD films for LIB cathode particles.

A hybrid dual-salt polymer electrolyte for sodium metal batteries with stable room temperature cycling performance

Sodium metal batteries (NMBs) are among the most promising alternatives to lithium-ion batteries. However, the thermal instability, potential leakage, and dendrite growth typical of NMBs with organic liquid electrolytes still pose severe limitations to this technology. These challenges can be overcome by replacing the organic liquid electrolytes with solids or gels. In this study, a hybrid dual-salt polymer electrolyte (DSPE), comprising sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and sodium difluoro(oxalate)borate (NaDFOB) salts is reported. The two salts work synergistically: NaTFSI enhances ionic conductivity and thermal stability, while NaDFOB extends the electrochemical window and inhibits the corrosion of the Al current collectors caused by NaTFSI. Furthermore, the DSPE with a NaDFOB/NaTFSI optimized molar ratio of 20% delivers a high ionic conductivity of 0.31 mS cm−1 at 23 °C. At this temperature, the NMB with a Na3V2(PO4)3@carbon positive electrode has excellent cycling performance (104.0 mAh g − 1 at 1 C with 92.4% capacity retention over 300 cycles) and rate capability (93.5 mAh g − 1 at 5 C). X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterizations, together with ab initio calculations reveal that stable battery performance is linked to the formation of a NaxBOyFz-containing protective cathode-electrolyte interphase layer. Leveraging the synergistic combination of two salts, this new DSPE formulation opens a new path for next-generation, high-performance NMBs.

Resolving Chemical and Spatial Heterogeneities at Complex Electrochemical Interfaces in Li-Ion Batteries

The high specific capacities of Ni-rich transition-metal oxides have garnered immense interest for improving the energy density of Li-ion batteries (LIBs). Despite the potential of these materials, Ni-rich cathodes suffer from interfacial instabilities that lead to crystallographic rearrangement of the active material surface as well as the formation of a cathode electrolyte interphase (CEI) layer on the composite surface during electrochemical cycling. While changes in crystallographic structure can be detected with diffraction-based methods, probing the chemistry of the disordered, heterogeneous CEI layer is challenging. In this work, we use a combination of ex situ solid-state nuclear magnetic resonance (SSNMR) spectroscopy and X-ray photoemission electron microscopy (XPEEM) to provide chemical and spatial information, on the nanometer length scale, on the CEI deposited on LiNi0.8Mn0.1Co0.1O2 (NMC811) composite cathode films. XPEEM elemental maps offer insight into the lateral arrangement of the electrolyte decomposition products that comprise the CEI and paramagnetic interactions (assessed with electron paramagnetic resonance (EPR) and relaxation measurements) in 13C SSNMR provide information on the radial arrangement of the CEI from the NMC811 particles outward. Using this approach, we find that LiF, Li2CO3, and carboxy-containing structures are directly appended to NMC811 active particles, whereas soluble species detected during in situ 1H and 19F solution NMR experiments (e.g., alkyl carbonates, HF, and vinyl compounds) are randomly deposited on the composite surface. We show that the combined approach of ex situ SSNMR and XPEEM, in conjunction with in situ solution NMR, allows spatially resolved, molecular-level characterization of paramagnetic surfaces and new insights into electrolyte oxidation mechanisms in porous electrode films.

A novel trimethylsilyl 2-(fluorosulfonyl)difluoroacetate additive for stabilizing the Ni-rich LiNi0.9Co0.05Mn0.05O2/electrolyte interface

A stabilized cathode electrolyte interphase (CEI) formed on the cathode electrode by virtue of effective electrolyte additives is crucial for prolonging the lifespan of lithium-ion battery adopting high energy density Ni-rich cathode materials. Here, we report a novel multifunctional additive trimethylsilyl 2-(fluorosulfonyl)difluoroacetate (TMSFS) for LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NCM90). By adding 0.5% TMSFS, the NCM90 electrode shows an enhanced capacity retention of 85.1% at 1C up to 200 cycles, superior over that of 73.1% for baseline electrolyte. The improvement on cycling performance can be also achieved at harsh testing conditions (e.g., 60 °C and even a high voltage of 4.4 V), along with fast electrode kinetics in the presence of TMSFS. It's demonstrated that TMSFS additive could scavenge the undesired H 2 O, PF 5 and HF species in electrolyte, alleviating the subsequent damages to both cathode-electrolyte interface and NCM90 cathode structure. More importantly, a compact, inorganics-enriched CEI layer formed in TMSFS-added electrolyte is further revealed, rationalizing the impressive improvement in electrochemical performance. Furthremore, we also prove the effectiveness of TMSFS additive for graphite||NCM90 full cells. • A novel electrolyte additive TMSFS for NCM90 cathode. • Scavenging the undesired H 2 O, PF 5 and HF species in electrolyte. • A compact inorganics-enriched CEI layer formed in TMSFS-added electrolyte. • Faster kinetics and improved cycling stability enabled by TMSFS additive.

Organic–Inorganic Hybridization Engineering of Polyperylenediimide Cathodes for Efficient Potassium Storage

AbstractPolyperylenediimide (PDI) is always subject to its modest conductivities, limited reversible active sites and inferior stability for potassium storage. To address these issues, herein, we firstly propose an organic–inorganic hybrid (PDI@Fe‐Sn@N‐Ti3C2Tx), where Fe/Sn single atoms are bound to the N‐doped MXenes (N‐Ti3C2Tx) via the unsaturated Fe/Sn–N3 bonds, and functionalized with PDI via d–π hybridization, forming a high conjugated δ skeleton. The resulted hybrid cathode endowed with enhanced electronic/ionic conductivities, lowered dissociation barriers of multiple redox centers and a stable cathode electrolyte interphase layer displays a 14‐electron involved high‐rate capacities and long cycle life. Moreover, it shows competitive performance in full cells even under different folding states and low operating temperatures.

Organic–Inorganic Hybridization Engineering of Polyperylenediimide Cathodes for Efficient Potassium Storage

Polyperylenediimide (PDI) is always subject to its modest conductivities, limited reversible active sites and inferior stability for potassium storage. To address these issues, herein, we firstly propose an organic-inorganic hybrid (PDI@Fe-Sn@N-Ti3 C2 Tx ), where Fe/Sn single atoms are bound to the N-doped MXenes (N-Ti3 C2 Tx ) via the unsaturated Fe/Sn-N3 bonds, and functionalized with PDI via d-π hybridization, forming a high conjugated δ skeleton. The resulted hybrid cathode endowed with enhanced electronic/ionic conductivities, lowered dissociation barriers of multiple redox centers and a stable cathode electrolyte interphase layer displays a 14-electron involved high-rate capacities and long cycle life. Moreover, it shows competitive performance in full cells even under different folding states and low operating temperatures.

Electrolytes Polymerization‐Induced Cathode‐Electrolyte‐Interphase for High Voltage Lithium‐Ion Batteries

AbstractLithium‐ion batteries (LIBs) based on LiNixCoyMn1‐x‐yO2 (NCM) cathode materials have been widely commercialized, because of their high energy density, favorable rate performance, and relatively low cost. However, with increased Ni content to further increase their energy density, their cycling stability deteriorates dramatically and thus fails to meet the commercial application requirements. The artificial cathode‐electrolyte‐interphase (CEI) is a promising approach to solve this problem. Here, a robust CEI is fabricated through in situ polymerization of ethylene carbonate induced by aluminum isopropoxide (AIP). By adding 1 wt.% AIP in a commercial electrolyte, the capacity retention of LiNi0.8Co0.1Mn0.1O2||Li cell at 1 C rate has been significantly increased from 80.8% to 97.8% with a highly reversible capacity of 176 mA h g−1 after 200 cycles. AIP can be also used as an additive during the slurry‐making process, enabling a reversible capacity of 170 mA h g−1 for LiCoO2 after 200 cycles even at a high charge cut‐off voltage of 4.6 V. It is confirmed that the in situ formed CEI layer can prevent the cathodes from cracking and reduce the irreversible phase transformation.

Effects of a Sodium Phosphate Electrolyte Additive on Elevated Temperature Performance of Spinel Lithium Manganese Oxide Cathodes.

LiMn2O4 (LMO) spinel cathode materials suffer from severe degradation at elevated temperatures because of Mn dissolution. In this research, monobasic sodium phosphate (NaH2PO4, P2) is examined as an electrolyte additive to mitigate Mn dissolution; thus, the thermal stability of the LMO cathode material is improved. The P2 additive considerably improves the cyclability and storage performances of LMO/graphite and LMO/LMO symmetric cells at 60 °C. We explain that P2 suppresses the hydrofluoric acid content in the electrolyte and forms a protective cathode electrolyte interphase layer, which mitigates the Mn dissolution behavior of the LMO cathode material. Considering its beneficial role, the P2 additive is a useful additive for spinel LMO cathodes that suffer from severe Mn dissolution.

High-voltage and high-safety nickel-rich layered cathode enabled by a self-reconstructive cathode/electrolyte interphase layer

To achieve widespread adoption of Ni-rich layered oxides in commercial applications, it is highly necessary to address their cyclic stabilities and safety aspects under prolonged and harsh operating conditions, which will aggravate the simultaneous degradation of the Ni-rich cathode and electrolyte due to the more serious interfacial side reactions between them. Herein, a self-reconstructive cathode/electrolyte interphase (CEI) layer with good interfacial stability was designed and constructed for Ni-rich cathode, through the incorporation of dendritic mesoporous silica (DMS) with rich surface silicon-hydroxyl groups as a multifunctional electrolyte additive. The DMS shows the ability to reconstruct the CEI layer in real time, i.e., endowing the CEI layer with defluorination function, spontaneously formed LiPO2F2, and in-situ formed anti-fluorination protective layer with enhanced electron and Li+ diffusion. As expected, the sample with a self-reconstructive CEI layer exhibits significantly superior cyclic stability compared to the pristine one under extended cut-off voltage (4.5 V) or elevated temperature (55°C). Notably, the flame-retardant effect of DMS additive can also contribute towards the thermal stability of the electrolyte and electrode, which will effectively improve the safety aspect of the battery. Thus, this work provides new insights into reducing undesired self-reinforced failure process in Ni-rich cathode and reconstructing a self-healing CEI layer for high-safety, high-voltage lithium-ion batteries.

Artificial cathode electrolyte interphase by functional additives toward long-life sodium-ion batteries

Although Na0.67Fe0.5Mn0.5O2 has attracted tremendous attentions as a cathode material for sodium-ion batteries (NIBs), undesirable side reactions at the interphase between the electrode and electrolyte have limited its wide utilization. An effective way to prevent the side reaction is to artificially induce a mechanically robust and chemically stable cathode electrolyte interphase (CEI). In this paper, functional additives of NaF and Na2CO3 were used to artificially form a thick and stable CEI layer, and their effects were deeply investigated. It was demonstrated that the functional additives in electrolytes could be partially decomposed during a charge process, then it could play a key role in forming a thick and stable interphase directly on the cathode surface. The newly formed CEI layer could sup- press the dissolution of transition metals into the electrolyte and prevent the deterioration of the solid interphase layer. As a result, the additives successfully prevent the capacity fading problem of Na0.67Fe0.5Mn0.5O2 during electrochemical cycling, which results in the improved cyclability compared to the bare Na0.67Fe0.5Mn0.5O2. We believe that the addition of functional additive is a simple and cost-effective way to artificially form a stable CEI layer on a cathode, therefore, this approach is expected to be widely applicable to other electrode materials that suffer from the unstable interfaces.

Regulation of an Inner Helmholtz Plane by hierarchical porous biomass activated carbon for stable cathode electrolyte interphase films

The formation of a cathode electrolyte interphase (CEI) layer and the transportation of ions at the electrode/electrolyte interface in batteries rely on the structure of the charge distribution in the Inner Helmholtz Plane (IHP) in the electrical double layer. Herein, a novel hierarchical porous activated carbon (AC) additive with a powerful electrical double layer capacity that is used in cathodes for lithium-ion batteries (LIBs) is developed using low-cost and abundant persimmon branches as the raw material. The AC additives strengthen the IHP on the cathode surface and induce the formation of Li2CO3, which is one of the main components in the CEI layer on the surface of cathode materials. Moreover, after AC was used as an additive in the cathode, the discharge capacity increased from 49 mAh g−1 to 92 mAh g−1. Cycling tests reveal that the additive reduces the capacity loss after extended cycling at a high current density.

Synthesis and electrochemical properties of Na0:67Mn0:75Ni0:25O2 in carbonate-based electrolytes

In this work, a single phase of P2-Na0:67Mn0:75Ni0:25O2 (NaMNO) material was successfully synthesized via a coprecipitation method with the size varying from 2 to 4 mm. According to the atomic absorption spectroscopy (AAS), all the metallic elements were uniformly distributed in the bulk material with the desired ratio Mn¸Ni = 3¸1. The electrochemical properties of P2-NaNMO were investigated in carbonate-based electrolytes using 1M NaClO4 or 1M NaPF6. Among these electrolytes, this cathode exhibited the best electrochemical performance with initial capacity up to 205.7 mAh/g and capacity retention reaches 63.2% during 60 cycles when using 1M NaClO4/PC + 2% (v/v) VC. Indeed, vinylene carbonate (VC) additive plays an important role in improving the performance of NaMNO cathode through the formation of a stable cathode electrolyte interphase layer (CEI). Electrochemical impedance spectroscopy (EIS) was performed to demonstrate CEI layer formation indicated by the elevation of the electrode surface film and double layer impedance in the initial cycle. During cycling, galvanostatic intermittent titration technique (GITT) helps to calculate the Na+ ion diffusion coefficient, which was increased clearly at the working voltages of Mn3+/Mn4+ and Ni3+/Ni4+ redox couples.