first lithiation cycle leads to n-doping of the TzG polymer by N 1s signal shifting to higher binding energy (Figure ), analogous to lithiated graphite, and, hence, to an increase of its conductivity above and beyond the effect achieved by the conducting additive in TzG/Si/CB@Cu. We subjected the TzG/Si@Cu electrode to de-/lithiation cycling at C/8 in a half-cell set-up recording specific capacity (Figure ). In the first lithiation cycle, we observe the formation of the SEI at a comparatively low CE value of ~70%, meaning that the surface of Si NPs is readily accessible for lithium and for the electrolyte via the pore channels of the TzG polymer. Similar Coulombic efficiencies have been reported for nanosized silicon particles with a large external surface area. Microsized silicon particles with a smaller ratio of exposed surfaces show higher initial CE values but suffer from limited discharge capacities and poor cycling performance. In the third cycle, the CE rises above 97% and steadily improves up to 99.5% which means that SEI formation is completed early on. The specific capacity observed during the first lithiation exceeds the theoretical value for fully lithiated silicon (3579 mA h g -1 ) due to the formation of the SEI. Starting with the second cycle, no excess capacity is recorded and, hence, the newly formed SEI does not contribute to the measured discharge capacity. The recorded specific lithiation capacity in the second cycle is ~3500 mA h g -1 , and it remains at a record high in subsequent cycles (e.g. ~3450 mA h g -1 in the fifth cycle). In comparison, the TzG/Si/CB@Cu electrode prepared together with carbon black does not perform better than the additive-free electrode (Figure ). Taking the specific lithiation capacity in the second cycle as a baseline, TzG/Si@Cu retains 81.0% of its specific capacity after 50 cycles (2862 mA h g -1 ) and 69.1% after 100 cycles (2443 mA h g -1 ) Conversions of these values to areal and volumetric capacities can be found in Figure . For comparison, we prepared two electrodes using conventional binders and CB additive, PVdF/Si/CB@Cu and PAA/Si/CB@Cu (Figure ). These conventional formulations allow a total Si mass loading of up to 60% without compromising the performance of the electrode, compared to 75% of Si in the TzG/Si@Cu system. Overall, the specific capacity and retention Table . Relative molar concentrations of elements as determined by peak integration using X-ray photoelectron spectroscopy (XPS) data recorded at 1486.6 eV for TzG/Si@Cu electrodes at various stages of de-/lithiation cycled at a constant current of 0.32 mA cm -2 (i.e. C/8 for the capacity of Si, within 0.01-1. of TzG/Si@Cu anodes exceeds that of the best-performing multicomponent systems with and without conductivity-enhancing additives that are reported to date (Table ). We tuned massloading of TzG/Si@Cu electrodes that lead to similar excellent performance (Supplementary information Table , Section S2.6, Figure -S19). For example, we were able to increase the Si mass-loading of the electrode beyond 1 mg cm -2 by a two rounds of polymerisation on top of a TzG/Si@Cu electrode in the presence of small quantities of Cu(OAc)2 as an additional source of Cu(II) species (Supplementary Information Section S1.6, Table ). The obtained electrodes show a stable cycling performance and comparably high capacities as electrodes obtained in a onestep growth process (Figure ). TzG is a thermally stable polymer with a decomposition onset above 400 °C under air. Hence, we tested the performance of the TzG/Si@Cu half-cell after a heat treatment of 80 °C for 6 h, above temperatures experienced by Li-ion batteries in some industrial and military settings. The overall performance of the TzG/Si@Cu half-cell after the thermal-stress test remains at ~3000 mA h g -1 in the second cycle comparable to the performance of untreated electrodes. The difference in overall capacity and in capacity retention can be attributed to partial decomposition of LiPF6 during the extended heat treatment (Figure ). As a proof of concept, we assembled a full cell using TzG/Si@Cu as the anode (Si areal mass-loading of 0.291 mg cm - 2 , specific capacity 3579 mA h g -1 ) and the commercially available standard NCM811 as the cathode (areal mass-loading of 6.502 mg cm -2 , specific capacity ~170 mA h g -1 ) (Figure ). The NCM811 cathode was selected over three commercial options (NCM532, NCM622, and NCA) as the one with the highest specific capacity and most stable cycling performance. Even though the specific capacities of our anode and the commercial standard NCM811 cathode are mismatched, the fullcell assembly shows an acceptable initial CE of 79% that stabilises at >98% after the fourth cycle. Overall, the full-cell has a capacity of 3234 mA h g -1 in the third cycle and a capacity retention of 68.2% over 30 cycles (Figure and 3d, Supplementary information Section S2.7, Figure ). We believe that full-cell assemblies with better coulombic efficiencies can be achieved using cathodes that (i) match the high capacity of our anode better, and (ii) have similar diffusion kinetics.