Na‐Ion Batteries for Large Scale Applications: A Review on Anode Materials and Solid Electrolyte Interphase Formation

The urgent need for optimizing the available energy through smart grids and efficient large‐scale energy storage systems is pushing the construction and deployment of Li‐ion batteries in the MW range which, in the long term, are expected to hit the GW dimension while demanding over 1000 ton of positive active material per system. This amount of Li‐based material is equivalent to almost 1% of current Li consumption and can strongly influence the evolution of the lithium supply and cost. Given this uncertainty, it becomes mandatory to develop an energy storage technology that depends on almost infinite and widespread resources: Na‐ion batteries are the best technology for large‐scale applications. With small working cells in the market that cannot compete in cost ($/W h) with commercial Li‐ion batteries, the consolidation of Na‐ion batteries mainly depends on increasing their energy density and stability, the negative electrodes being at the heart of these two requirements. Promising Na‐based negative electrodes for large‐scale battery applications are reviewed, along with the study of the solid electrolyte interphase formed in the anode surface, which is at the origin of most of the stability problems.     

KTi2(PO4)3 with Large Ion Diffusion Channel for High‐Efficiency Sodium Storage

To accommodate the decreasing lithium resource and ensure continuous development of energy storage industry, sodium‐based batteries are widely studied to inherit the next generation of energy storage devices. In this work, a novel Na super ionic conductor type KTi₂(PO₄)₃/carbon nanocomposite is designed and fabricated as sodium storage electrode materials, which exhibits considerable reversible capacity (104 mAh g^?1 under the rate of 1 C with flat voltage plateaus at ≈2.1 V), high‐rate cycling stability (74.2% capacity retention after 5000 cycles at 20 C), and ultrahigh rate capability (76 mAh g^?1 at 100 C) in sodium ion batteries. Besides, the maximum ability for sodium storage is deeply excavated by further investigations about different voltage windows in half and full sodium ion cells. Meanwhile, as cathode material in sodium‐magnesium hybrid batteries, the KTi₂(PO₄)₃/carbon nanocomposite also displays good electrochemical performances (63 mAh g^?1 at the 230th cycle under the voltage window of 1.0–1.9 V). The results demonstrate that the KTi₂(PO₄)₃/carbon nanocomposite is a promising electrode material for sodium ion storage, and lay theoretical foundations for the development of new type of batteries.     

A Hybrid Mg2+/Li+ Battery Based on Interlayer‐Expanded MoS2/Graphene Cathode

The hybrid Mg²⁺/Li⁺ battery (MLIB) is a very promising energy storage technology that combines the advantage of the Li and Mg electrochemistry. However, previous research has shown that the battery performance is limited due to the strong dependence on the Li content in the dual Mg²⁺/Li⁺ electrolyte. This limitation can be circumvented by significantly improving the diffusion kinetics of Mg²⁺ in the electrode, so that both Li⁺ and Mg²⁺ ions can be utilized as charge carriers. Herein, a free‐standing interlayer expanded MoS₂/graphene composite (E‐MG) is demonstrated as a cathode for MLIB. The key advantage of this cathode is to enable the efficient intercalation of both Mg²⁺ and Li⁺. The E‐MG electrode displays a reversible capacity of ≈300 mA h g^?1 at 20 mA g^?1 in an MLIB cell, corresponding to a specific energy density up to ≈316.9 W h kg^?1, which is comparable to that of the state‐of‐the‐art Li‐ion batteries (LIBs) and has no dendrite formation. The composite electrode is stable against cycling with a coulombic efficiency close to 100% at 500 mA g^?1. This new electrode design represents a significant step forward for building a safe and high‐density electrochemical energy storage system.     

A Postspinel Anode Enabling Sodium‐Ion Ultralong Cycling and Superfast Transport via 1D Channels

Sodium‐ion batteries are intensively investigated for large‐scale energy storage due to the favorable sodium availability. However, the anode materials have encountered numerous problems, such as insufficient cycling performance, dissatisfactory capacity, and low safety. Here, a novel post‐spinel anode material, i.e., single‐crystalline NaVSnO₄, is presented with the confined 1D channels and the shortest diffusion path. This material delivers an ultra long cycling life (84% capacity retention after 10 000 cycles), a high discharging capacity (163 mA h g^?1), and a safe average potential of 0.84 V. Results indicate that the post‐spinel structure is well maintained over 10 000 cycles, surprisingly, with 0.9% volume change, the Sn⁴⁺/Sn²⁺ based redox enables two sodium ions for reversible release and uptake, and the diffusion coefficient of sodium ions is characterized by 1.26 × 10^?11 cm² s^?1. The findings of this study provide a new insight into design of new frameworks with polyelectronic transfers for full performance electrode materials of sodium‐ion batteries.     

Mechanism of Na‐Ion Storage in Hard Carbon Anodes Revealed by Heteroatom Doping

Hard carbon is the leading candidate anode for commercialization of Na‐ion batteries. Hard carbon has a unique local atomic structure, which is composed of nanodomains of layered rumpled sheets that have short‐range local order resembling graphene within each layer, but complete disorder along the c‐axis between layers. A primary challenge holding back the development of Na‐ion batteries is that a complete understanding of the structure–capacity correlations of Na‐ion storage in hard carbon has remained elusive. This article presents two key discoveries: first, the characteristics of hard carbons structure can be modified systematically by heteroatom doping, and second, that these structural changes greatly affect Na‐ion storage properties, which reveals the mechanisms for Na storage in hard carbon. Specifically, via P or S doping, the interlayer spacing is dilated, which extends the low‐voltage plateau capacity, while increasing the defect concentrations with P or B doping leads to higher sloping sodiation capacity. The combined experimental studies and first principles calculations reveal that it is the Na‐ion‐defect binding that corresponds to the sloping capacity, while the Na intercalation between graphenic layers causes the low‐potential plateau capacity. The understanding suggests a new design principle of hard carbon anode: more reversibly binding defects and dilated turbostratic domains, given that the specific surface area is maintained low.     

Ultrafine MoO2‐Carbon Microstructures Enable Ultralong‐Life Power‐Type Sodium Ion Storage by Enhanced Pseudocapacitance

The achievement of the superior rate capability and cycling stability is always the pursuit of sodium‐ion batteries (SIBs). However, it is mainly restricted by the sluggish reaction kinetics and large volume change of SIBs during the discharge/charge process. This study reports a facile and scalable strategy to fabricate hierarchical architectures where TiO₂ nanotube clusters are coated with the composites of ultrafine MoO₂ nanoparticles embedded in carbon matrix (TiO₂@MoO₂‐C), and demonstrates the superior electrochemical performance as the anode material for SIBs. The ultrafine MoO₂ nanoparticles and the unique nanorod structure of TiO₂@MoO₂‐C help to decrease the Na⁺ diffusion length and to accommodate the accompanying volume expansion. The good integration of MoO₂ nanoparticles into carbon matrix and the cable core role of TiO₂ nanotube clusters enable the rapid electron transfer during discharge/charge process. Benefiting from these structure merits, the as‐made TiO₂@MoO₂‐C can deliver an excellent cycling stability up to 10 000 cycles even at a high current density of 10 A g^?1. Additionally, it exhibits superior rate capacities of 110 and 76 mA h g^?1 at high current densities of 10 and 20 A g^?1, respectively, which is mainly attributed to the high capacitance contribution.     

Large‐Sized Few‐Layer Graphene Enables an Ultrafast and Long‐Life Aluminum‐Ion Battery

To develop high‐power and high‐energy batteries with a long life remains a great challenge, even combining the benefits of metal (fast kinetics and high capacity) and carbon materials (robust structure). Among them, Al‐ion batteries based on aluminum anode and graphite carbon cathode have gained lots of interests as one of the most promising technologies. Here, it is demonstrated that the size of graphitic material in ab plane and c direction plays an important role in anion intercalation chemistry. Sharply decreasing the size of vertical dimension (c direction) strongly facilitates the kinetics and charge transfer of anions (de)intercalation. On the other hand, increasing the size of horizontal dimension (ab plane) contributes to improving the flexibility of graphitic materials, which results in raising the cycling stability. Meanwhile, chloroaluminate anions are reversibly intercalated into the interlayer of graphite materials, leading to the staging behaviors. In the end, an ultrafast Al‐ion battery with exceptional long life is achieved based on large‐sized few‐layer graphene as a cathode and aluminum metal as an anode.     

Electrospun NaVPO4F/C Nanofibers as Self‐Standing Cathode Material for Ultralong Cycle Life Na‐Ion Batteries

NaVPO₄F has received a great deal of attention as cathode material for Na‐ion batteries due to its high theoretical capacity (143 mA h g^?1), high voltage platform, and structural stability. Novel NaVPO₄F/C nanofibers are successfully prepared via a feasible electrospinning method and subsequent heat treatment as self‐standing cathode for Na‐ion batteries. Based on the morphological and microstructural characterization, it can be seen that the NaVPO₄F/C nanofibers are smooth and continuous with NaVPO₄F nanoparticles (≈6 nm) embedded in porous carbon matrix. For Na‐storage, this electrode exhibits extraordinary electrochemical performance: a high capacity (126.3 mA h g^?1 at 1 C), a superior rate capability (61.2 mA h g^?1 at 50 C), and ultralong cyclability (96.5% capacity retention after 1000 cycles at 2 C). 1D NaVPO₄F/C nanofibers that interlink into 3D conductive network improve the conductivity of NaVPO₄F, and effectively restrain the aggregation of NaVPO₄F particles during charge/discharge process, leading to the high performance.     

Multiscale Morphological and Electrical Characterization of Charge Transport Limitations to the Power Performance of Positive Electrode Blends for Lithium‐Ion Batteries

In this work, exhaustive characterizations of 3D geometries of LiNi_1/3Mn_1/3Co_1/3O₂ (NMC), LiFePO₄ (LFP), and NMC/LFP blended electrodes are undertaken for rational interpretation of their measured electrical properties and electrochemical performance. X‐ray tomography and focused ion beam in combination with scanning electron microscopy tomography are used for a multiscale analysis of electrodes 3D geometries. Their multiscale electrical properties are measured by using broadband dielectric spectroscopy. Finally, discharge rate performance are measured and analyzed by simple, yet efficient methods. It allows us to discriminate between electronic and ionic wirings as the performance limiting factors, depending on the discharge rate. This approach is a unique exhaustive analysis of the experimental relationships between the electrochemical behavior, the transport properties within the electrode, and its 3D geometry.