In spite of the excellent electrochemical performance in lithiumion batteries (LIBs), transition-metal compounds usually show inferior capacity and cyclability in sodium-ion batteries (SIBs), implying different reaction schemes between these two types of systems. Herein, coupling operando magnetometry with electrochemical measurement, we peformed a comprehensive investigation on the intrinsic relationship between the ion-embedding mechanisms and the electrochemical properties of the typical FeS 2 /Na (Li) cells. Operando magnetometry together with ex-situ transmission electron microscopy (TEM) measurement reveal that only part of FeS 2 is involved in the conversion reaction process, while the unreactive parts form "inactive cores" that lead to the low capacity. Through quantification with Langevin fitting, we further show that the size of the iron grains produced by the conversion reaction are much smaller in SIBs than that in LIBs, which may lead to more serious pulverization, thereby resulting in worse cycle performance. The underlying reason for the above two above phenomena in SIBs is the sluggish kinetics caused by the larger Na-ion radius. Our work paves a new way for the investigation of novel SIB materials with high capacity and long durability.

In article number 2207353, Chen Ge, Qiang Li, and co-workers propose a space-charge mechanism, through decoupling the transport of ions and electrons, to achieve magnetoelectric coupling in ferromagnetic-metal films. This method combines the advantages of both carrier doping and chemical reaction mechanisms, which allows for an efficient modulation with both large-magnitude and robust endurance.

ensures the excellent performance of spin-based devices at room temperature. [5][6][7] Taking advantage of the intrinsic coupling of electricity and magnetism, multiferroics and magnetoelectrics favor a modulation via exchange interaction with metals. [3,[8][9][10] However, there is currently a dearth of technologically viable multiferroics that exhibit strong magnetoelectric (ME) coupling at room temperature. [11,12] A broader available option, high dielectric gates (MgO, HfO 2 , AlO x , etc.) are typically used to manipulate charge-related magnetism in ultra-thin FM-metal systems, such as Co/HfO 2 , [13] FeCo/MgO and Fe/MgO junctions. [14][15][16] This charge doping method can change the density of the itinerant electrons in a ferromagnet, thus further manipulating magnetocrystalline anisotropy. [17][18][19] Although this allows for an ultra-fast modulation with a lifespan beyond 10 4 cycles, the volatile and small magnitude of modulation limit its application. [12,[19][20][21] The quest for realizing a modulation of magnetism in metals, where a low power-consumption is accompanied with a large-amplitude modulation, high reversibility, fast switching speed and room temperature, has been continuously explored (some representative works are summarized in Table S1, Supporting Information).The pursuit of enormous manipulation effects (e.g., magnetiza tion, magnetic phase) has encouraged the emergence Ferromagnetic metals show great prospects in ultralow-power-consumption spintronic devices, due to their high Curie temperature and robust magnetization. However, there is still a lack of reliable solutions for giant and reversible voltage control of magnetism in ferromagnetic metal films. Here, a novel space-charge approach is proposed which allows for achieving a modulation of 30.3 emu/g under 1.3 V in Co/TiO 2 multilayer granular films. The robust endurance with more than 5000 cycles is demonstrated. Similar phenomena exist in Ni/TiO 2 and Fe/TiO 2 multilayer granular films, which shows its universality. The magnetic change of 107% in Ni/TiO 2 underlines its potential in a voltage-driven ON-OFF magnetism. Such giant and reversible voltage control of magnetism can be ascribed to space-charge effect at the ferromagnetic metals/TiO 2 interfaces, in which spin-polarized electrons are injected into the ferromagnetic metal layer with the adsorption of lithium-ions on the TiO 2 surface. These results open the door for a promising method to modulate the magnetization in ferromagnetic metals, paving the way toward the development of ionic-magnetic-electric coupled applications.

The performance of electrode materials depends intensively on the lithium (Li)-ion storage mechanisms correlating ultimately with the Coulombic efficiency, reversible capacity, and morphology variation of electrode material upon cycling. Transition metal nitrides anode materials have exhibited high-energy density and superior rate capability; however, the intrinsic mechanism is largely unexplored and still unclear. Here, a typical 3D porous Fe 2 N micro-coral anode is prepared and, an intercalation-conversion-heterogeneity hybrid Li-ion storage mechanism that is beyond the conventional intercalation or conversion reaction is revealed through various characterization techniques and thermodynamic analysis. Interestingly, using advanced in situ magnetometry, the ratio (ca. 24.4%) of the part where conversion reaction occurs to the entire Fe 2 N can further be quantified. By rationally constructing a Li-ion capacitor comprising 3D porous Fe 2 N micro-corals anode and commercial AC cathode, the hybrid full device delivers a high energy-density (157 Wh kg −1 ) and high power-density (20 000 W kg −1 ), as well as outstanding cycling stability (93.5% capacitance retention after 5000 cycles). This research provides an original and insightful method to confirm the reaction mechanism of material related to transition metals and a fundamental basis for emerging fast charging electrode materials to be efficiently explored for a next-generation battery.

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