Lithium-ion batteries (LIBs) are highvoltage, high-energy, and high-power density energy storage devices with long cycle life, therefore intensively applied in full and hybrid electric vehicles, portable electronic devices (computers, mobile phones, and tablet), and renewable (solar and wind) sector. [1,2] Typically, LIBs for such applications with estimated lifetime of around 3-10 years generate a vast amount of waste at their end-of-life. [3,4] It is estimated that over 11 million tonnes of spent LIBs will be discarded through to 2030, and only less than 5% of them are being recycled. [4] Moreover, due to rapidly increasing demand of LIBs, the price of crucial element resources (Li, Ni, and Co) is also significantly increasing. In contrast, the health and environmental concerns may arise in the event of large, accumulated quantities of cobalt and lithium metals, which typically constitutes up to 20 and 7 wt%, respectively, of LIB cathodes, as well as toxic and flammable electrolytes (e.g., lithium hexafluorophosphate, LiPF 6 ). [3][4][5] Therefore, efficient recovery of such raw materials in spent LIBs is extremely crucial.At present, LIBs are recycled commercially using well-known processes such as pyrometallurgy, hydrometallurgy, and direct recycling. [4] However, these processes do not extract the maximum value from their feedstock. For instance, pyrometallurgy, or smelting operate at very high temperature (over 1100 C), which eliminates several materials (carbon anode, plastic separator, and electrolyte solvents) through vaporization (electrolyte), combustion, and melting. The final product is a mixed alloy of cobalt, nickel, and copper. The concept of direct recycling is simple: keep the cathode crystal structure intact. The definition of direct recycling is the recovery, regeneration, and reuse of battery components directly without breaking down the chemical structure. It has also been called direct cathode recycling and cathode-to-cathode recycling. By recovering cathode material, several energy-intensive and costly processing steps can be avoided. Not only does recovery of more materials offer potential additional revenues, but also costs and other impacts from waste treatment can be avoided. Advantages include low temperatures and low energy consumption, and the avoidance of most impacts from virgin material production.

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The rapid growth of lithium‐ion batteries (LIBs) in many markets from portable electronics to large scale electric vehicles makes it increasingly urgent to address recycling of strategic materials from used batteries. Herein, we report the excellent electrochemical performance of recycled graphite (REG) from spent LIBs, which was successfully employed as an anode in potassium‐ion batteries (KIBs). The graphite‐anode not only delivers highly reversible capacity of 361.4 mAh g−1 (at 0.1 C) but also demonstrates good long‐term cycling stability. The phase evolution of electrochemically potassium intercalated/deintercalated REG electrodes is elucidated using in‐situ X‐ray diffraction. The well‐preserved structure of the recycled graphite makes it ideal host for reversible intercalation and de‐intercalation of K‐ions. Furthermore, a potassium‐hybrid capacitor was fabricated by coupling the recycled graphite with textile waste‐derived activated carbon as cathode material. The cell demonstrates considerable energy density of 84.5 Wh kg−1 and power density of 400 W kg−1, respectively. Apart from the great electrochemical performances, the low‐cost, abundant, and sustainable recycled graphite in this work will help to address the challenges in Li‐ion battery recycling and show the prospects of next‐generation battery system development.

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energy storage capabilities. A range of energy sources, including piezoelectric, pyroelectric, triboelectric, have been recently emphasized for energy harvesting from natural processes. [3][4][5][6] Typically, energy harvesting and storage systems can be integrated either extrinsically using electrical circuitries, or intrinsically via engineering the device structure with functionalized materials. [3,7] However, extrinsically integrated devices have high manufacturing cost due to the need of complex power management systems (rectifier), which reduces integration density. [8,9] Therefore, it is highly desirable to improve the integration level and minimize unnecessary energy loss in the external circuits between energy harvesting and storage devices.Recently, rectification free piezoelectric supercapacitors (PSCs) as an integrated device have been developed, which not only maintains the integration density of the devices but also provides continuous energy supply. The operation principle of PSC is based on the incorporation of piezoelectric materials in place of separators commonly used in supercapacitors and then harvesting the energy internally instead of relying on external power supply. In general, PSC is constructed using two electrodes, piezoelectric-separator and gel-electrolyte [10] where piezoelectric separator converts ubiquitously irregular and low-frequency mechanical vibration into electricity and simultaneously stores at the supercapacitive electrodes. Polyvinylidene fluoride (PVDF) film is commonly used in PSCs due to their excellent piezoelectric and mechanical properties. [11,12] The interfacial energy conversion efficiency of bare PVDF (electrically nonpolarized) in PSC, however, is poor and difficult to translate for real-time operation of electronic devices. [13] Among various approaches used to improve the performance, the PVDF matrix with fillers is an efficient and effective method. [13][14][15][16][17][18] For instance, Song et al. developed a rectification free, PVDF-based PSC. Simple carbon cloth was used as the electrode, with a gel electrolyte composed of PVA and H 2 SO 4 . The device achieved an aerial capacitance of 357.6 F m -2 , energy density of 0.049 mWh cm −2 and the power density 0.44 mW cm −2 . Kartiken et al. [19] embedded siloxene in to PVDF nanofibers to influence the structure and induce the β phase of PVDF, improving energy generation performance relative to bare PVDF. The fabricated device of the siloxene based supercapacitor achieved an areal capacitance of 28.98 mF cm -2The expected widespread use of wearable and other low-power healthcare devices has triggered great interest in piezoelectric materials as a promising energy harvester. However, traditional piezoelectric materials suffer from poor interfacial energy transfer when used in self-charging power cells. Herein, piezoelectric supercapacitors (PSCs) are engineered using MXene-incorporated polymeric piezo separator and MXene (Ti 3 C 2 T x ) multilayered sheets as electrodes. The MXene-blended polymer film showed ...