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Roll-to-roll prelithiation of lithium-ion battery anodes by transfer printing

Roll-to-roll prelithiation of lithium-ion battery anodes by transfer printing
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For further investigation of the prelithiation reaction, a series of preGr (30 preGr, 100 preGr, 200 preGr and 300 preGr) anodes with different amounts of electrodeposited lithium were prepared through the method mentioned above and assembled in C2025 cells. After a static stage of 24 h, the graphite layer of the preGr anode underwent a complete reaction with active lithium with the intervention of electrolyte to form lithium–graphite intercalation compounds (Li–GICs) with different compositions (Supplementary Fig. 7). Compared with pristine Gr anodes, these preGr anodes exhibit gradual colour variation from black to gold, indicating the formation of golden LiC6 compounds in the 200 preGr anode and 300 preGr anode (Fig. 2a).

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Fig. 2: Characterizations of preGr electrodes.

a, Photographs of Gr, 30 preGr, 100 preGr, 200 preGr and 300 prGr electrodes. b, XRD patterns of Gr, 30 preGr, 100 preGr, 200 preGr and 300 prGr electrodes. c, Raman spectra of Gr, 30 preGr, 100 preGr, 200 preGr and 300 prGr electrodes. d, Voltage profiles of the Gr and 30 preGr electrodes. The open-circuit voltage (OCV) of these cells is presented. e, Delithiation test of the 30 preGr electrode and the capacity comparison with deposited lithium. f, CV curves of Gr and 30 preGr anodes.

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Moreover, X-ray diffraction (XRD) patterns and Raman spectra were provided for further understanding the chemical changes occurring in these preGr anodes (Fig. 2b,c). With the augment of active lithium, several new peaks are detected, reflecting the evolution of Li–GICs27,28,29. Peaks at 26.4°, 25.3° and 24.0° are recognized as {002} peak of graphite, {002} peak of LiC12 and {001} peak of LiC6, respectively. Moreover, peaks at 2θ = 25.7° and 2θ = 26.2° are correlated with the appearance of Li–GICs with low levels of lithium insertion29. Clearly, after the prelithiation reaction, 30 preGr consists of a mixture of graphite and Li–GICs with low levels of lithium insertion27. With the increased active lithium in preGr electrodes, LiC12 begins to emerge in 100 preGr and 200 preGr. Finally, Li–GICs in the 300 preGr anode are all made up of LiC6. The lithium intercalation process in the preGr electrodes was also verified by Raman spectroscopy (Fig. 2c). For the 30 preGr and 100 preGr anodes, the G-band line gradually shifts up from the original graphite line and sharpens, representing low levels of Li insertion30. For the 200 preGr electrode, two new lines appear at both sides of the original graphite lines, which are assigned to the appearance of LiC12 (ref. 30). Finally, the original G-band line gets completely vanished for 300 preGr anodes, revealing the entire lithiation of graphite30. Supplementary Fig. 8 displays the X-ray photoelectron spectroscopy (XPS) results of Gr and 30 preGr electrodes after prelithiation reaction. Evidently, an increase in 30 preGr O 1s branches occurs compared to Gr, indicating the formation of oxygen-containing SEI compounds on the surface. After prelithiation, a new peak at 288.8 eV correlated with lithium carbonate or lithium alkyl carbonates (O−C=O) in C 1s spectra confirms the SEI formation, and similarly, a new peak at 684.8 eV in F 1s spectra is assigned to lithium fluoride31. In the case of Li 1s spectra, the new peak at 55.5 eV is likely to merge from subpeaks correlated with lithium fluoride, lithium carbonate, lithium alkyl carbonates and Li–GIC compounds.

Noteworthy, proper prelithiation followed by the method proposed in this study can fully recover the lithium loss in the first cycle. Without prelithiation, an artificial graphite anode displays a relatively low ICE of 83.13% in Gr||Li half cells (Fig. 2d) with a lithium loss of 69.7 mAh g−1 in the first charge–discharge cycle. In contrast, in a 30 preGr||Li half cell, the ICE increases up to 99.99% and a decrease of open-circuit voltage (OCV) from 2.427 to 0.3702 V is observed (Fig. 2d). For further investigation, a delithiation test of 30 preGr anode was carried out in a preGr||Li half cell (Fig. 2e), and 30 preGr anode exhibits a delithiation capacity of 22.94 mAh g−1 and the capacity of electrodeposited lithium is 111.6 mAh g−1. It indicates that not only SEI compounds, but also certain amounts of Li–GICs are formed after the prelithiation reaction in 30 preGr. The voltage profiles of Gr||Li half cells show an obvious voltage platform of SEI formation at about 1.0 V in the first cycle compared with that in the second (Supplementary Fig. 9).

More details are presented by analysing cyclic voltammetry (CV) curves of Gr and 30 preGr anodes (Fig. 2f). The two anodes share a similar pattern, that is, a reduction slope from 0.5 to 0 V and a single oxidation peak at about 0.35 V. However, the Gr anodes own another reduction peak at about 1.0 V due to the SEI formation at the surface of electrodes. Furthermore, a larger increase at the oxidation peak in subsequent scans reveals a worse reversibility compared to the 30 preGr anode. Thus, beneficially, a higher Coulombic efficiency in the first five cycles is achieved in Gr||Li half cells by using the 30 preGr electrode, indicating the formation of an SEI with higher cycling efficiency (Supplementary Fig. 10). Supplementary Fig. 11 illustrates the differential capacity (dQ/dV) plots of Gr and 30 preGr electrodes at the first lithiation process. The peaks appearing at 0.20, 0.11 and 0.07 V are correlated with different lithiation stages. Compared with the Gr electrode, the 30 preGr electrode exhibits a weaker peak at 0.20 V, indicating the insertion of lithium ions. Moreover, a peak of Gr anode is detected at 1.0 V, which is supposed to be corresponding to the SEI formation.

With the gradual increase of lithium loading, the OCVs of these cells sharply decline and the ICEs steadily increase (Fig. 3a). The lithium-loading capacity of each preGr anode can be carefully controlled by electrodeposition parameters, and notably, preGr anodes with the same lithium loading maintain good consistency in different batches (Fig. 3b). In a full cell, excessive lithium-ion compensation results in harmful lithium plating on the anode surface, leading to unfavourable weak battery performance and potential safety hazards. Consequently, the stable and controllable lithium-ion compensation ability of preGr anodes designed in this study is of great importance for prelithiated electrodes. Electrochemical impedance spectroscopy (EIS) was used to monitor the evolution of SEI of Gr and 30 preGr half cells during cycles (Fig. 3c and Supplementary Fig. 12). R0 represents the ohmic conductor; RCC represents the conduction behaviour between electrodes and current collector; and RSEI represents the influences of SEI32. Clearly, the results indicate that the 30 preGr anode has a lower RSEI during cycling. The above-mentioned phenomenon demonstrates that 30 preGr electrodes own a better SEI for lithiation reaction during the first cycles.

Fig. 3: Electrochemistry features of preGr and preSi/C electrodes.
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a, Voltage profiles of the Gr, 10 preGr, 20 preGr, 30 preGr and 40 preGr electrodes. b, Comparisons of the OCVs and ICEs of multiple graphite electrodes with different lithiation capacities. c, Equivalent circuits of the Gr and 30 preGr half cells after 1, 10 and 100 cycles. d, Galvanostatic cycling of Gr and 30 preGr half cells. For these cells, 1C = 372 mAh g−1. e, Rate capacity of Gr and 30 preGr half cells at various current rates. f, Cross-sectional SEM image of 25 preSi/C anodes. g, Voltage profiles of the Si/C and 25 preSi/C electrodes. h, Galvanostatic cycling of Si/C and 25 preSi/C half cells. For these cells, 1C = 450 mAh g−1.

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The cycling performance of the Gr and the 30 preGr electrodes is displayed in Fig. 3d. For achieving better performance of these cells, they were first activated at 0.1C (1C = 372 mAh g−1) for ten cycles and then run at 0.5C for 140 cycles. The initial delithiation capacities of 30 preGr and Gr electrodes are 317.7 and 304.4 mAh g−1, respectively, at the first cycle of 0.5C, and after 140 cycles, the capacity changes to 341.4 and 333.4 mAh g−1, respectively. The capacity retentions of these electrodes are 107% and 110%, respectively. After prelithiation, the 30 preGr anode exhibits no drawback in cycling stability compared to Gr anodes. Figure 3e further evaluates the rate capabilities of the Gr and the 30 preGr anodes at current rates of 0.1C, 0.2C, 0.5C and 1C. During the test, the 30 preGr electrodes reveal gradually decreasing capacities of 348.3, 338.3, 320.7 and 266.7 mAh g−1, respectively, and show a better rate capability compared to the Gr anode at all rates.

Notably, the transfer-printing process is also an ideal choice for the prelithiation of other active anode materials. Commercial Si/C material with a capacity of about 450 mAh g−1 was used as an example (Supplementary Fig. 13). Prelithiated Si/C (preSi/C) anodes with a lithium-loading equivalent of 25% of the Si/C capacity (25 preSi/C anodes) were fabricated. Figure 3f shows the cross-sectional SEM image of the 25 preSi/C anodes, which share a similar three-tier structure with preGr anodes. Without prelithiation, the Si/C anode displays an ICE of 85.37% in half cells (Fig. 3g). For cells with the 25 preSi/C anodes, the ICE increases up to 99.05% with a decrease of OCV from 2.351 to 0.2995 V (Fig. 3g). Supplementary Fig. 14a,b shows the CV and EIS features of Si/C and 25 preSi/C electrodes. Further testing shows the absence of obvious capacity fading in 25 preSi/C anode half cells during a long cycling test (Fig. 3h). The successful prelithiation of artificial graphite materials and Si/C materials demonstrates the wide applicability as an anode prelithiation method for LIBs.

NCM and LFP full cells were produced for practical evaluation of the preGr and preSi/C anodes with an NP ratio of 1.1. Compared with the Gr||NCM full cell, the ICE of the 30 preGr||NCM cell improves from 83.10% to 89.39% and a higher reversible capacity of 153.3 mAh g−1 at 0.1C (1C = 200 mAh g−1) is delivered (Fig. 4a and Supplementary Fig. 15). The 30 preGr||NCM cell achieves a discharge capacity retention of 79.6% and a capacity advantage of about 10 mAh g−1 after 595 cycles at 0.5C (Fig. 4b). At a high rate of 1.5C, the 30 preGr||NCM cell achieves a discharge capacity retention of 76.1% and a capacity advantage of about 30 mAh g−1 after 1,000 cycles (Supplementary Fig. 16). Full cells with anodes of 20 preGr and 40 preGr and full cells with NP ratio of 1.0 and 1.2 are also assembled and compared (Supplementary Figs. 17 and 18). In these comparisons, the 30 preGr cell exhibited both energy density and safety advantages. For the LFP cathode, the ICE of the 30 preGr||LFP cell improves from 79.91% to 95.88% and a higher reversible capacity of 153.4 mAh g−1 at 0.1C (1C = 170 mAh g−1) is delivered (Fig. 4c and Supplementary Fig. 19). The 30 preGr||LFP cell achieves a discharge capacity retention of 99.8% and a capacity advantage of about 28 mAh g−1 after 195 cycles at 0.5C (Fig. 4d). The energy densities of the 30 preGr||NCM and the 30 preGr||LFP cell improve from 363.8 to 380.2 Wh kg−1 and 264.7 to 329.6 Wh kg−1, respectively (Fig. 4e). The higher improvements of energy densities (28 mAh g−1 compared to 11 mAh g−1) and ICE (6% compared to 16%) in LFP full cells originate from the high ICE of LFP half cells (Supplementary Fig. 20). Comparative analysis indicates that the ICEs of LFP and NCM half cells are measured as 90.17% and 96.86% (Supplementary Figs. 21 and 22). In the 25 preSi/C||NCM full cell, the ICE increases from 83.04% to 89.21%, and the reversible capacity increases to 149.8 mAh g−1 at 0.05 C (1C = 200 mAh g−1) (Fig. 4f). The 25 preSi/C||NCM cell achieves a discharge capacity retention of 95.1% and a capacity advantage of about 23 mAh g−1 after 98 cycles at 0.1C (Fig. 4g). The energy density of the 25 preSiC||NCM cell also improves from 375.8 to 401.5 Wh kg−1 (Fig. 4h).

Fig. 4: ICE improvements and cycling stabilities of prelithiated full cells.
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a, Voltage profiles of the Gr||NCM and 30 preGr||NCM full cells. b, Galvanostatic cycling of the Gr||NCM and 30 preGr||NCM full cells. For these cells, 1C = 200 mAh g−1 based on cathodes. c, Voltage profiles of the Gr||LFP and 30 preGr||LFP full cells. d, Galvanostatic cycling of the Gr||LFP and 30 preGr||LFP full cells. For these cells, 1C = 170 mAh g−1 based on cathodes. e, Comparisons of the energy densities of the NCM and LFP full cells. f, Voltage profiles of the Si/C||NCM and 25 preSi/C||NCM full cells. g, Galvanostatic cycling of the Si/C||NCM and 25 preSi/C||NCM full cells. For these cells, 1C = 200 mAh g−1 based on cathodes. h, Comparisons of the ICEs and energy densities of Si/C||NCM and 25 preSi/C||NCM full cells.

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