Publication date: Jul 21, 2021
High nickel content in LiNixCoyMnzO2 (NCM, x ≥ 0.8, x + y + z = 1) layered cathode material allows high energy density in lithium-ion batteries (LIBs). However, Ni-rich NCM cathodes suffer from performance degradation, mechanical and structural instability upon prolonged cell cycling. Although the use of single-crystal Ni-rich NCM can mitigate these drawbacks, the ion-diffusion in large single-crystal particles hamper its rate capability. Herein, we report a strategy to construct an in situ Li1.4Y0.4Ti1.6(PO4)3 (LYTP) ion/electron conductive network which interconnects single-crystal LiNi0.88Co0.09Mn0.03O2 (SC-NCM88) particles. The LYTP network facilitates the lithium-ion transport between SC-NCM88 particles, mitigates mechanical instability and prevents detrimental crystalline phase transformation. When used in combination with a Li metal anode, the LYTP-containing SC-NCM88-based cathode enables a coin cell capacity of 130 mAh g-1 after 500 cycles at 5 C rate in the 2.75-4.4 V range at 25 °C. Tests in Li-ion pouch cell configuration (i.e., graphite used as negative electrode active material) demonstrate capacity retention of 85% after 1000 cycles at 0.5 C in the 2.75-4.4 V range at 25 °C for the LYTP-containing SC-NCM88-based positive electrode.
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Figure 1.png
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1.5 MiB | Figure 1. LYTP@SC-NCM88 preparation process. Schematic illustration of the synthesis method for LYTP modified SC-NCM88 cathode. |
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344.4 KiB | Figure 2. Representative morphology images of LYTP@SC-NCM88. (a) Overall and (b) cross-sectional morphologies derived from SEM images. (c) Cross-section EPMA image of 1% LYTP@SC-NCM88 with the corresponding selected area LYTP mapping results of Ni, Co, Mn, Ti, and P elements. (d) TEM, (e) HRTEM, and (f) STEM elemental mappings of Ni, Co, Mn, Y, and Ti for 1% LYTP@SC-NCM88. |
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829.1 KiB | Figure 3. Raw data of conductivity and structure characterization of LYTP@SC-NCM88. The comparison of (a) electron conductivity and (b) Li-ion conductivity between pristine SC-NCM88 and 1% LYTP@SC-NCM88. (c) The XRD Rietveld refinement of 1% LYTP@SC-NCM88. |
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2.4 MiB | Figure 4. Raw data of electrochemical performance for coin-type half cells. Cycling stability of pristine SC-NCM88 and 1% LYTP@SC-NCM88 against a lithium metal anode at 0.5 C under testing temperature of (a) 25 oC and (b) 55 oC. Charge/discharge curves for (c) SC-NCM88 and (d) 1% LYTP@SC-NCM88 from 1st to 100th cycle at 55 oC. (e) Cycling capability at various current densities and (f) long-term cycling stability at 5C for SC-NCM88 and 1% LYTP@SC-NCM88. All cells were cycled in 2.75-4.4V. |
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95.2 KiB | Figure 5. Raw data of electrochemical evaluation for pouch-type full cells. (a) Cycling performances and (b, c) corresponding dQ/dV curves of the pristine SC-NCM88 and the 1% LYTP@SC-NCM88 against a graphite anode from the 1st cycle to the 1000th cycle. (d) Cycling performance and (e) energy density for the pristine SC-NCM88 and the 1% LYTP@SC-NCM88 at an elevated temperature of 45 oC. All cells were cycled in the voltage range of 2.75-4.4 V. |
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2.9 MiB | Figure 6. Raw data of phase transitions Investigation during cycling. Operando XRD characterization of the full contour plots and selected line patterns for (a, c) SC-NCM88 and (b, d) 1% LYTP@SC-NCM88 cathodes during the initial cycle in the voltage range of 2.75-4.6 V. (e) The variation of the c-axis parameter during charging for pristine SC-NCM88 and 1% LYTP@SC-NCM88. |
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504.8 KiB | Figure 7. Density functional theory calculation. Raw data of the total and partial density of states plots for (a) pristine SC-NCM88 and (b) 1% LYTP@SC-NCM88. |
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348.9 KiB | Figure 8. Raw data of surface chemistry compositions of cycled cathodes. TOF-SIMS depth profiles of the near-surface chemical composition for (a) C2HO-, (b) POF2-, (c) C2F-, (d) PO3-, (e) NiF3-, (f) CoF3-, (g) MnF3- and (h) 6LiF2-. XPS spectra of (i) C 1s, (j) O 1s, (k) F 1s and (l) P 2p elements for the pristine SC-NCM88 and 1% LYTP@SC-NCM88 cathodes after 200 cycles from 2.7V to 4.4 V. |
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622.6 KiB | Figure 9. Intraparticle structural evolution after long-term cycling. Post-mortem HRTEM and magnified HRTEM at selected area images for (a, a1, a2) pristine SC-NCM88 and (b, b1, b2) 1% LYTP@SC-NCM88 after 200 cycles. Cross-sectional SEM images of (c) pristine SC-NCM88 and (g) 1% LYTP@SC-NCM88. Low-magnification HAADF-STEM image of FIB-cross section for the surface region and magnified HAADF-STEM images taken from the corresponding surface areas for (d-f) pristine SC-NCM88 and (h-j) 1%LYTP@SC-NCM |
2021.116 (version v1) [This version] | Jul 21, 2021 | DOI10.24435/materialscloud:ga-f0 |