Lithium/fluorinated carbon (Li/CF x ) primary batteries have essential applications in consumer electronics and medical and high-power military devices. However, their application is limited due to the difficulty in achieving simultaneous high power density and high energy density in the CF x cathode. The tradeoff between conductivity and fluorine content is the decisive factor. Herein, by rational design, 3D porous fluorinated graphene microspheres (FGS-x) with both high conductivity and a high F/ C ratio are successfully synthesized for the first time. FGS-x possesses an F/C ratio as high as 1.03, a nanosheet structure with hierarchical pores, abundant CC bonds, few inactive C−F 2 bonds, and electrochemically active C−F bonds. The beneficial features that can increase discharge capacity, shorten the diffusion length for both ions and electrons, enhance the Li + intercalation kinetics, and accommodate the volume change are demonstrated. The Li/FGS-1.03 coin cell delivers an unprecedented power density of 71,180.9 W/kg at an ultrahigh rate of 50 C (43.25 A/g), coupled with a high energy density of 830.7 Wh/kg. Remarkably, the Li/FGS-1.03 pouch cell exhibits a record cell-level power density of 12,451.2 W/kg at 20 C. The in-depth investigation by the ex situ method on structural evolution at different discharge depths reveals that the excellent performance benefits from the structural stability and the uniform formation of LiF. The FGS-1.03 cathode also has excellent performance in extreme operating temperatures (0 to 100 °C) and high active material mass loading (4.3 mg/cm 2 ). These results indicate that the engineered fluorinated graphene developed here has great potential in applications requiring both high power density and high energy density.
Accomplishing acid-stable water oxidation is a critical matter for achieving both long-lasting water-splitting devices and other fuel-forming electro- and photocatalytic processes. Because water oxidation releases protons into the local electrolytic environment, it becomes increasingly acidic during device operation, which leads to corrosion of the photoactive component and hence loss in device performance and lifetime. In this work, we show that thin films of manganese-modified titania, (Ti,Mn)O , topped with an iridium catalyst, can be used in a coating stabilization scheme for acid-stable water oxidation. We achieved a device lifetime of more than 100 h in pH = 0 acid. We successfully grew (Ti,Mn)O coatings with uniform elemental distributions over a wide range of manganese compositions using atomic layer deposition (ALD), and using X-ray photoelectron spectroscopy, we show that (Ti,Mn)O films grown in this manner give rise to closer-to-valence-band Fermi levels, which can be further tuned with annealing. In contrast to the normally n-type or intrinsic TiO coatings, annealed (Ti,Mn)O films can make direct charge transfer to a Fe(CN) redox couple dissolved in aqueous electrolytes. Using the Fe(CN) redox, we further demonstrated anodic charge transfer through the (Ti,Mn)O films to high work function metals, such as iridium and gold, which is not previously possible with ALD-grown TiO. We correlated changes in the crystallinity (amorphous to rutile TiO) and oxidation state (2+ to 3+) of the annealed (Ti,Mn)O films to their hole conductivity and electrochemical stability in acid. Finally, by combining (Ti,Mn)O coatings with iridium, an acid-stable water-oxidation anode, using acid-sensitive conductive fluorine-doped tin oxides, was achieved.
Sodium and potassium are considered to be the most promising anode candidates due to their easy availability, low‐cost and similar chemical properties to lithium. Here, novel 3D accordion‐like fluorinated graphite nanosheets (FGNSs) are reported as cathodes for sodium primary batteries (SPBs) and potassium primary batteries (PPBs). The FGNSs‐x cathode exhibits unprecedented power and energy density due to the impressive 3D structure, high F/C ratio (1.0), and more surface CC bonds (7.14%). The FGNSs‐1.0 exhibits very high specific capacities of 831.3 and 834.1 mAh g−1 for SPBs and PPBs, respectively, close to the theoretical capacity. Besides, the maximum energy density of FGNSs‐1.0 in SPBs and PPBs are 1960.5 and 2144.6 Wh kg−1, respectively. The maximum power density for Na/CFx and K/CFx batteries could reach up to 7076.8 and 6227.4 W kg−1, respectively. The electrochemical performance of FGNSs‐1.0 at extreme temperatures (−30 to 100 °C), long storage time (60 days), high mass loading (3.6 mg cm−2), and pouch‐type cell is also evaluated for the first time. Surprisingly, FGNSs‐1.0 has outstanding performance in these projects. Therefore, the new‐type Na/CFx and K/CFx primary battery systems developed here have broad application prospects in high‐energy applications that require high‐power, low‐cost, and normal use under extreme conditions.
High interfacial impedance is a major obstacle in the application of solidstate Li metal batteries (SSLMBs). Understanding the atomic-scale structure of the interfaces in SSLMBs is thus critical to their practical implementations. However, due to the beam sensitivity of battery materials, such information is not accessible by conventional electron microscopy (EM). Herein, by using cryogenic-EM (cryo-EM), the atomic-scale structures of interfaces in garnet electrolyte based SSLMBs are revealed. A LiF-rich interlayer exhibiting intimate contacts with both Li and LLZTO is shown, thus rendering uniform Li + transport across the interface in turn inhibiting Li dendrite growth. Consequently, the Li symmetric cell based on the LiF-rich interlayer exhibits a high critical current density of 3.2 mA cm −2 and a long lifespan over 1800 cycles at 1 mA cm −2 . Moreover, a full cell with a LiNi 0.88 Co 0.1 Al 0.02 O 2 cathode at a high mass loading ≈12 mg cm −2 reached over 400 cycles at 1.2 mA cm −2 , which represents a major progress in the performance of the garnet-type SSLMBs. This study provides atomic-scale understanding of interfaces in SSLMBs and an effective strategy to design dendrite-free SSLMBs for practical applications.
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