{ "sample": "04-jpowsour-2016-multi-issue", "threshold": 0.35, "cache_status": { "exists": true, "usable": true, "reason": "cache_page_count_ok", "expected_pdf_pages": 10, "cached_docling_pages": 8, "cached_docling_max_page": 10, "formula_enrichment_enabled": false, "formula_enrichment_scale": 3.0, "formula_nodes": 1, "recognized_formula_nodes": 0 }, "candidate_blocks": [ { "page": 1, "page_count": 10, "bbox": [ 197.23, 511.66, 552.99, 614.48 ], "text": "Li-rich layered oxides have been regarded as valuable cathode materials for high energy density lithium-ion batteries. However, high initial irreversible capacity, bad rate capability, as well as serious capacity fading and voltage decay hinder their commercial application. In this paper, a nano CoF2 protective layer is coated on the surface of Li1.2Ni0.2Mn0.6O2 via a facial wet chemistry method. A high initial discharge capacity of 264.4 mAh g\u00031 is obtained for 0.5% CoF2-coated sample and 259.1 mAh g\u00031 for 1% CoF2-coated sample owing to the suppression of irreversible release of O2 and the contribution of electrochemical conversion of CoF2/LiF. Furthermore, 1% CoF2-coated sample exhibits the excellent rate capability of 167.5 mAh g\u00031 at 5 C rate, the superior cycling stability with the capacity retention of 241.0 mAh g\u00031 and the ameliorative voltage drop of 0.312 V at 0.1C after 100 cycles. The enhanced rate performance as well as stability of capacity and voltage can be attributed to the nano coatings which inhibit the electrolyte-electrode side reaction, enhance the electrochemical kinetics and mitigate structure transition from layered to spinel phase.", "category": "front_summary", "coverage": 1.0, "words": 199 }, { "page": 5, "page_count": 10, "bbox": [ 301.83, 672.97, 552.96, 744.68 ], "text": "exhibit two distinguished voltage regions during the first charge process. The sloping curve below 4.5 V is attributed to the lithium extraction from LiNi0.5Mn0.5O2 with hexagonal layered structure along with the oxidation of Ni2þ/Ni3þ/Ni4þ, and the plateau above 4.5 V is ascribed to the lithium extraction as well as the release of O2 from monoclinic Li2MO3 accompanying with the activation of Li2MO3, which generates oxygen-ion vacancy and induces lithium-", "category": "scientific_body", "coverage": 0.0, "words": 76 }, { "page": 6, "page_count": 10, "bbox": [ 42.52, 411.54, 293.7, 598.24 ], "text": "ion vacancy in TM layers during initial discharge procedure resulting in a large irreversible capacity loss [31,42,43], corresponding sche- matic view of extraction/insertion of Liþ during initial charge- discharge process in LNMO active materials shown in Fig. 5(c). Fig. 5(b) presents the CV profiles of all the samples for the initial cycle. The oxidation peaks of Ni2þ/Ni3þ/Ni4þ at about 3.875e4.0 V as well as the peaks of the release of O2 at about 4.75 V can be observed clearly for all the samples during initial charge process, while the peak intensity of the release of O2 weakens gradually as the increase of CoF2 coating amount in consequence of effective suppression of the loss of O2 by nano-coating layer. And the reduction peaks of Ni4þ/ Ni3þ/Ni2þ at approximately 3.75 V as well as the weak reduction peaks corresponding to Mn4þ/Mn3þ couple at about 3.25 V during initial discharge process are observed. Besides, the intensity of reduction peaks of Mn4þ/Mn3þ wanes with increasing the amount of CoF2 coating as a result of the reduction of MnO2 with electro- chemical activity after the activation of Li2MnO3, consistent with the change tendency of the release of O2.", "category": "scientific_body", "coverage": 0.266, "words": 207 }, { "page": 6, "page_count": 10, "bbox": [ 311.53, 463.81, 562.59, 618.22 ], "text": "3.2.2. Cyclic performance and rate capability Fig. 6(a) shows the cycling stability of all the cathode materials measured at 0.1C in the voltage range of 2.0e4.8 V. CF-0.1, CF-0.5 and CF-1.0 exhibit the discharge capacity of 207.2 mAh g\u00031, 225.3 mAh g\u00031 and 241.0 mAh g\u00031 with the capacity retention of 81.5%, 85.2% and 93.0% after 100 cycles, respectively, while much lower discharge capacity of 153.7 mAh g\u00031 and capacity retention of 63.0% for bare LNMO is obtained at 0.1C. The reason for this superior cyclic stability, which generally enhances as the content of CoF2 nano-coating increases, involves two aspects. One reason can be the subdued interfacial reaction and the reduction of TM dissolution benefiting from the protection of coating layer. The other reason is the reduction of Liþ irreversible dissolution and TM migration owing to less amount of O2 release, which suppresses the phase transformation from layer to spinel structure upon cycling.", "category": "scientific_body", "coverage": 0.625, "words": 180 }, { "page": 6, "page_count": 10, "bbox": [ 42.52, 599.82, 293.6, 628.71 ], "text": "As shown in Fig. 5(a), all the samples deliver similar initial charge capacity, while CF-0.1, CF-0.5 and CF-1.0 samples exhibit higher initial discharge capacities of 254.3 mAh g\u00031, 264.4 mAh g\u00031", "category": "scientific_body", "coverage": 0.184, "words": 42 }, { "page": 6, "page_count": 10, "bbox": [ 42.52, 627.65, 293.6, 724.18 ], "text": "and 259.1 mAh g\u00031 as well as larger first coulombic efficiencies of 82.1%, 86.2% and 84.4% than bare LNMO (244.0 mAh$g\u00031 and 75.5%), respectively, which mainly attributed to the suppression of side reaction between electrolyte and active material at high po- tential by CoF2 protective layer, less electrolyte oxidation resulting from less oxygen removal, proved by CV results (Fig. 5(b)), and additional capacity provided by reduction reaction of CoF2 during initial discharge process, the electrochemical conversion reactions of CoF2 shown as follows:", "category": "scientific_body", "coverage": 0.807, "words": 92 }, { "page": 6, "page_count": 10, "bbox": [ 311.53, 620.74, 562.59, 743.79 ], "text": "Voltage decay resulting from the layer-spinel structure conver- sion, which gives rise to serious decrease in energy density upon cycling, is one of the major issues for Li-rich cathode materials [44,45]. The discharge voltage stability curves of all the samples upon cycling shown in Fig. 6(b), are employed to evaluate the voltage decay. The LNMO cathode material suffers from the serious voltage fading with a large voltage drop of 0.675 V at 0.1C after 100 cycles, while the values of voltage drop for CF-0.1, CF-0.5 and CF-1.0 are 0.542 V, 0.482 V and 0.312 V, respectively. Obviously, the voltage fading rate efficiently slowed down as the increase of CoF2 coating content, which can be attributed to the weak electrode/ electrolyte interfacial reaction and the enhancement of structural", "category": "scientific_body", "coverage": 0.971, "words": 142 }, { "page": 7, "page_count": 10, "bbox": [ 301.83, 557.98, 552.9, 691.46 ], "text": "the one hand, the relatively thicker coating layer not only sup- presses excessively the release of O2 but also prevents the extrac- tion/insertion of Liþ in layered structure, resulting in low capacity. On the other hand, the low reduction potential of 2.854 V for CoF2/ LiF can reduce the operating voltage of CF-2.0. Moreover, CF-2.0 exhibits the improved stability with the capacity retention of 93.6% and the value of voltage drop of 0.299 V after 100 cycles as shown in Fig. S1(inset a and b), which is close to the results of CF- 1.0. However, CF-2.0 delivers the much lower energy density of 694.6 Wh kg\u00031 than CF-0.5 and CF-1.0 owing to its low capacity and voltage. Thus, CF-1.0 reaches the optimal integrated performance between high capacity, high operating voltage and outstanding cycling stability.", "category": "scientific_body", "coverage": 0.23, "words": 152 }, { "page": 7, "page_count": 10, "bbox": [ 32.83, 673.06, 283.9, 743.79 ], "text": "In order to investigate the capacity and voltage stability for the sample whose CoF2 coating content is higher than 1.0 wt%, Fig. S1 in supplementary materials presents the operation voltages versus specific capacities of 2.0 wt% CoF2-coated sample (CF-2.0) and other four samples after 1st cycle and 100th cycle, respectively. The initial discharge capacity of 236.0 mAh g\u00031 and operating potential of 3.444 V for CF-2.0, lower than other four samples, are obtained. On", "category": "scientific_body", "coverage": 0.136, "words": 85 }, { "page": 8, "page_count": 10, "bbox": [ 42.52, 576.83, 293.58, 670.54 ], "text": "5 C, CF-1.0 exhibits the highest capacity of 167.5 mAh g\u00031, yet that of LNMO is only 120.1 mAh g\u00031. Moreover, when the current density is back to 0.1 C, the discharge capacity returns to 98.7% of its initial value for CF-1.0, implying good reversibility and structural stability after high-rate measurements. The primary reason for the signifi- cantly improved rate capability of CF-1.0 is that the introduction of CoF2 nano-coating layer, which accelerates the electrons transport and Liþ diffusion, and inhibits the interfacial reaction between electrolyte and active materials.", "category": "scientific_body", "coverage": 0.03, "words": 103 }, { "page": 8, "page_count": 10, "bbox": [ 311.53, 578.81, 562.59, 745.1 ], "text": "fitted with the equivalent circuits in the inset. Fig. 7(a) presents the EIS curves of the cells at open circuit potential before cycling. The intercept on the x-axis at the highest frequency is related to ohmic resistance of the electrolyte (Rs), the diameter of the semicircle represents charge-transfer resistance (Rct), and the slope line at the low frequency is assigned to the Warburg impedance (Zw) exhib- iting the diffusion of Liþ in the electrode material. It can be obvi- ously seen that a significant decrease in the Rct with the increase of CoF2 coating amount except for the similar values of Rs and Zw, exhibiting better electrochemical kinetics on the electrode/elec- trolyte interface for CF-1.0. The EIS spectra at the charged potential of 4.3 V after 100 cycles at 0.1 C, with a high-frequency semicircle ascribed to the resistance (Rf) of the solid electrolyte interface (SEI) and a medium-frequency corresponding to charge-transfer resis- tance (Rct), are presented in Fig. 7(b). As expected, CF-1.0 appears the lowest values of Rf and Rct, indicating that the formation and", "category": "scientific_body", "coverage": 0.005, "words": 187 }, { "page": 9, "page_count": 10, "bbox": [ 32.82, 589.24, 283.96, 649.62 ], "text": "growth of the unacceptable SEI film as well as the interfacial re- action have been mitigated by CoF2 coating layer. Thus, the improvement of electrochemical kinetics, the suppression of the formation of SEI film and side reaction between electrolyte and electrode, are responsible for the outstanding stability of capacity and rate capability of CF-1.0.", "category": "scientific_body", "coverage": 0.02, "words": 55 }, { "page": 9, "page_count": 10, "bbox": [ 32.82, 693.98, 283.92, 743.79 ], "text": "To disclose the reasons for improving the capacity fading and voltage decay upon cycling of CoF2-coated samples, LNMO and CF- 1.0 after several cycles were observed using TEM. Fig. 8 (b1 and b2) presents TEM image and corresponding SAED pattern of LNMO after 50 cycles at 0.1 C between 2.0 and 4.8 V. Two types of", "category": "scientific_body", "coverage": 0.018, "words": 61 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 66.34, 293.64, 157.98 ], "text": "particle in Fig. 8(c2), indicating complete structure transition after 100 cycles. However, the thin SEI film mixed with CoF2 coating layer can be observed in Fig. 8(d1) for CF-1.0 after 100 cycles owing to the inhibition of the release of oxygen during initial several cycles, meanwhile it still remain in the rhombohedral layered phase, which is in good agreement with the best stability of capacity and operating voltage. Therefore, the phase transition from layered to spinel can be delayed effectively by CoF2 nano-coating layer upon cycling.", "category": "scientific_body", "coverage": 0.011, "words": 91 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 191.85, 293.64, 295.29 ], "text": "In this paper, a nano protective layer of CoF2, in situ synthesized by means of a common wet chemistry technology, was coated on LNMO. The results of SEM, TEM, EDS and XPS demonstrate that CoF2 coating, belong to cubic structure, distributes homogeneously on the surface of LNMO, and the cell tests reveal that electro- chemical performances are enhanced obviously for CoF2-coated samples. CF-0.5 delivers the highest initial discharge capacity of 264.4 mAh g\u00031 and coulombic efficiency of 86.2%, benefiting from the electrochemical conversion reaction based on CoF2/LiF, as well as the reduction in the amount of irreversible O2 release and the Liþ", "category": "scientific_body", "coverage": 0.057, "words": 110 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 296.45, 293.62, 492.7 ], "text": "vacancies proved by the CV measurements. In addition, the higher first discharge capacity of 259.1 mAh g\u00031 compared to bare LNMO of 244.0 mAh g\u00031, the excellent cycling stability with the capacity retention rate of 93.0% after 100 cycles at 0.1 C, the improved rate performance with the capacity of 167.5 mAh g\u00031 even at 5 C, and the restraining operating voltage decay with the drop of 0.312 V after 100 cycles at 0.1 C are obtained for CF-1.0 sample. The outstanding electrochemical performances are ascribed to the CoF2 nano-coating in protection electrode material from deterioration in the electrolyte, the enhancement of kinetics electrochemical involving better electron transfer and Liþ diffusion, and the inhi- bition of layered-spinel phase transition initiated from particle edge and spread into inner bulk by means of minimizing the migration of TM ions into Li layers. Therefore, the novel design of CoF2 nano-coating not only provides a tactic to surmount the de- fects of LNMO and displays the superior comprehensive effect on improving electrochemical performance among the coatings in published data, but also illuminates in depth the mechanism of capacity fading and voltage decay upon cycling.", "category": "scientific_body", "coverage": 0.04, "words": 203 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 526.57, 293.66, 565.94 ], "text": "This work was supported by National Natural Science Founda- tion of China (Grant no. E51504196), the China Postdoctoral Science Foundation (no. 2012M521760) and the Fundamental Research Funds for the Central Universities (no. xjj2014052).", "category": "back_matter", "coverage": 0.0, "words": 32 } ], "low_coverage_blocks": [ { "page": 5, "page_count": 10, "bbox": [ 301.83, 672.97, 552.96, 744.68 ], "text": "exhibit two distinguished voltage regions during the first charge process. The sloping curve below 4.5 V is attributed to the lithium extraction from LiNi0.5Mn0.5O2 with hexagonal layered structure along with the oxidation of Ni2þ/Ni3þ/Ni4þ, and the plateau above 4.5 V is ascribed to the lithium extraction as well as the release of O2 from monoclinic Li2MO3 accompanying with the activation of Li2MO3, which generates oxygen-ion vacancy and induces lithium-", "category": "scientific_body", "coverage": 0.0, "words": 76 }, { "page": 6, "page_count": 10, "bbox": [ 42.52, 411.54, 293.7, 598.24 ], "text": "ion vacancy in TM layers during initial discharge procedure resulting in a large irreversible capacity loss [31,42,43], corresponding sche- matic view of extraction/insertion of Liþ during initial charge- discharge process in LNMO active materials shown in Fig. 5(c). Fig. 5(b) presents the CV profiles of all the samples for the initial cycle. The oxidation peaks of Ni2þ/Ni3þ/Ni4þ at about 3.875e4.0 V as well as the peaks of the release of O2 at about 4.75 V can be observed clearly for all the samples during initial charge process, while the peak intensity of the release of O2 weakens gradually as the increase of CoF2 coating amount in consequence of effective suppression of the loss of O2 by nano-coating layer. And the reduction peaks of Ni4þ/ Ni3þ/Ni2þ at approximately 3.75 V as well as the weak reduction peaks corresponding to Mn4þ/Mn3þ couple at about 3.25 V during initial discharge process are observed. Besides, the intensity of reduction peaks of Mn4þ/Mn3þ wanes with increasing the amount of CoF2 coating as a result of the reduction of MnO2 with electro- chemical activity after the activation of Li2MnO3, consistent with the change tendency of the release of O2.", "category": "scientific_body", "coverage": 0.266, "words": 207 }, { "page": 6, "page_count": 10, "bbox": [ 42.52, 599.82, 293.6, 628.71 ], "text": "As shown in Fig. 5(a), all the samples deliver similar initial charge capacity, while CF-0.1, CF-0.5 and CF-1.0 samples exhibit higher initial discharge capacities of 254.3 mAh g\u00031, 264.4 mAh g\u00031", "category": "scientific_body", "coverage": 0.184, "words": 42 }, { "page": 7, "page_count": 10, "bbox": [ 301.83, 557.98, 552.9, 691.46 ], "text": "the one hand, the relatively thicker coating layer not only sup- presses excessively the release of O2 but also prevents the extrac- tion/insertion of Liþ in layered structure, resulting in low capacity. On the other hand, the low reduction potential of 2.854 V for CoF2/ LiF can reduce the operating voltage of CF-2.0. Moreover, CF-2.0 exhibits the improved stability with the capacity retention of 93.6% and the value of voltage drop of 0.299 V after 100 cycles as shown in Fig. S1(inset a and b), which is close to the results of CF- 1.0. However, CF-2.0 delivers the much lower energy density of 694.6 Wh kg\u00031 than CF-0.5 and CF-1.0 owing to its low capacity and voltage. Thus, CF-1.0 reaches the optimal integrated performance between high capacity, high operating voltage and outstanding cycling stability.", "category": "scientific_body", "coverage": 0.23, "words": 152 }, { "page": 7, "page_count": 10, "bbox": [ 32.83, 673.06, 283.9, 743.79 ], "text": "In order to investigate the capacity and voltage stability for the sample whose CoF2 coating content is higher than 1.0 wt%, Fig. S1 in supplementary materials presents the operation voltages versus specific capacities of 2.0 wt% CoF2-coated sample (CF-2.0) and other four samples after 1st cycle and 100th cycle, respectively. The initial discharge capacity of 236.0 mAh g\u00031 and operating potential of 3.444 V for CF-2.0, lower than other four samples, are obtained. On", "category": "scientific_body", "coverage": 0.136, "words": 85 }, { "page": 8, "page_count": 10, "bbox": [ 42.52, 576.83, 293.58, 670.54 ], "text": "5 C, CF-1.0 exhibits the highest capacity of 167.5 mAh g\u00031, yet that of LNMO is only 120.1 mAh g\u00031. Moreover, when the current density is back to 0.1 C, the discharge capacity returns to 98.7% of its initial value for CF-1.0, implying good reversibility and structural stability after high-rate measurements. The primary reason for the signifi- cantly improved rate capability of CF-1.0 is that the introduction of CoF2 nano-coating layer, which accelerates the electrons transport and Liþ diffusion, and inhibits the interfacial reaction between electrolyte and active materials.", "category": "scientific_body", "coverage": 0.03, "words": 103 }, { "page": 8, "page_count": 10, "bbox": [ 311.53, 578.81, 562.59, 745.1 ], "text": "fitted with the equivalent circuits in the inset. Fig. 7(a) presents the EIS curves of the cells at open circuit potential before cycling. The intercept on the x-axis at the highest frequency is related to ohmic resistance of the electrolyte (Rs), the diameter of the semicircle represents charge-transfer resistance (Rct), and the slope line at the low frequency is assigned to the Warburg impedance (Zw) exhib- iting the diffusion of Liþ in the electrode material. It can be obvi- ously seen that a significant decrease in the Rct with the increase of CoF2 coating amount except for the similar values of Rs and Zw, exhibiting better electrochemical kinetics on the electrode/elec- trolyte interface for CF-1.0. The EIS spectra at the charged potential of 4.3 V after 100 cycles at 0.1 C, with a high-frequency semicircle ascribed to the resistance (Rf) of the solid electrolyte interface (SEI) and a medium-frequency corresponding to charge-transfer resis- tance (Rct), are presented in Fig. 7(b). As expected, CF-1.0 appears the lowest values of Rf and Rct, indicating that the formation and", "category": "scientific_body", "coverage": 0.005, "words": 187 }, { "page": 9, "page_count": 10, "bbox": [ 32.82, 589.24, 283.96, 649.62 ], "text": "growth of the unacceptable SEI film as well as the interfacial re- action have been mitigated by CoF2 coating layer. Thus, the improvement of electrochemical kinetics, the suppression of the formation of SEI film and side reaction between electrolyte and electrode, are responsible for the outstanding stability of capacity and rate capability of CF-1.0.", "category": "scientific_body", "coverage": 0.02, "words": 55 }, { "page": 9, "page_count": 10, "bbox": [ 32.82, 693.98, 283.92, 743.79 ], "text": "To disclose the reasons for improving the capacity fading and voltage decay upon cycling of CoF2-coated samples, LNMO and CF- 1.0 after several cycles were observed using TEM. Fig. 8 (b1 and b2) presents TEM image and corresponding SAED pattern of LNMO after 50 cycles at 0.1 C between 2.0 and 4.8 V. Two types of", "category": "scientific_body", "coverage": 0.018, "words": 61 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 66.34, 293.64, 157.98 ], "text": "particle in Fig. 8(c2), indicating complete structure transition after 100 cycles. However, the thin SEI film mixed with CoF2 coating layer can be observed in Fig. 8(d1) for CF-1.0 after 100 cycles owing to the inhibition of the release of oxygen during initial several cycles, meanwhile it still remain in the rhombohedral layered phase, which is in good agreement with the best stability of capacity and operating voltage. Therefore, the phase transition from layered to spinel can be delayed effectively by CoF2 nano-coating layer upon cycling.", "category": "scientific_body", "coverage": 0.011, "words": 91 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 191.85, 293.64, 295.29 ], "text": "In this paper, a nano protective layer of CoF2, in situ synthesized by means of a common wet chemistry technology, was coated on LNMO. The results of SEM, TEM, EDS and XPS demonstrate that CoF2 coating, belong to cubic structure, distributes homogeneously on the surface of LNMO, and the cell tests reveal that electro- chemical performances are enhanced obviously for CoF2-coated samples. CF-0.5 delivers the highest initial discharge capacity of 264.4 mAh g\u00031 and coulombic efficiency of 86.2%, benefiting from the electrochemical conversion reaction based on CoF2/LiF, as well as the reduction in the amount of irreversible O2 release and the Liþ", "category": "scientific_body", "coverage": 0.057, "words": 110 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 296.45, 293.62, 492.7 ], "text": "vacancies proved by the CV measurements. In addition, the higher first discharge capacity of 259.1 mAh g\u00031 compared to bare LNMO of 244.0 mAh g\u00031, the excellent cycling stability with the capacity retention rate of 93.0% after 100 cycles at 0.1 C, the improved rate performance with the capacity of 167.5 mAh g\u00031 even at 5 C, and the restraining operating voltage decay with the drop of 0.312 V after 100 cycles at 0.1 C are obtained for CF-1.0 sample. The outstanding electrochemical performances are ascribed to the CoF2 nano-coating in protection electrode material from deterioration in the electrolyte, the enhancement of kinetics electrochemical involving better electron transfer and Liþ diffusion, and the inhi- bition of layered-spinel phase transition initiated from particle edge and spread into inner bulk by means of minimizing the migration of TM ions into Li layers. Therefore, the novel design of CoF2 nano-coating not only provides a tactic to surmount the de- fects of LNMO and displays the superior comprehensive effect on improving electrochemical performance among the coatings in published data, but also illuminates in depth the mechanism of capacity fading and voltage decay upon cycling.", "category": "scientific_body", "coverage": 0.04, "words": 203 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 526.57, 293.66, 565.94 ], "text": "This work was supported by National Natural Science Founda- tion of China (Grant no. E51504196), the China Postdoctoral Science Foundation (no. 2012M521760) and the Fundamental Research Funds for the Central Universities (no. xjj2014052).", "category": "back_matter", "coverage": 0.0, "words": 32 } ], "high_risk_body_missing_blocks": [ { "page": 5, "page_count": 10, "bbox": [ 301.83, 672.97, 552.96, 744.68 ], "text": "exhibit two distinguished voltage regions during the first charge process. The sloping curve below 4.5 V is attributed to the lithium extraction from LiNi0.5Mn0.5O2 with hexagonal layered structure along with the oxidation of Ni2þ/Ni3þ/Ni4þ, and the plateau above 4.5 V is ascribed to the lithium extraction as well as the release of O2 from monoclinic Li2MO3 accompanying with the activation of Li2MO3, which generates oxygen-ion vacancy and induces lithium-", "category": "scientific_body", "coverage": 0.0, "words": 76 }, { "page": 6, "page_count": 10, "bbox": [ 42.52, 411.54, 293.7, 598.24 ], "text": "ion vacancy in TM layers during initial discharge procedure resulting in a large irreversible capacity loss [31,42,43], corresponding sche- matic view of extraction/insertion of Liþ during initial charge- discharge process in LNMO active materials shown in Fig. 5(c). Fig. 5(b) presents the CV profiles of all the samples for the initial cycle. The oxidation peaks of Ni2þ/Ni3þ/Ni4þ at about 3.875e4.0 V as well as the peaks of the release of O2 at about 4.75 V can be observed clearly for all the samples during initial charge process, while the peak intensity of the release of O2 weakens gradually as the increase of CoF2 coating amount in consequence of effective suppression of the loss of O2 by nano-coating layer. And the reduction peaks of Ni4þ/ Ni3þ/Ni2þ at approximately 3.75 V as well as the weak reduction peaks corresponding to Mn4þ/Mn3þ couple at about 3.25 V during initial discharge process are observed. Besides, the intensity of reduction peaks of Mn4þ/Mn3þ wanes with increasing the amount of CoF2 coating as a result of the reduction of MnO2 with electro- chemical activity after the activation of Li2MnO3, consistent with the change tendency of the release of O2.", "category": "scientific_body", "coverage": 0.266, "words": 207 }, { "page": 6, "page_count": 10, "bbox": [ 42.52, 599.82, 293.6, 628.71 ], "text": "As shown in Fig. 5(a), all the samples deliver similar initial charge capacity, while CF-0.1, CF-0.5 and CF-1.0 samples exhibit higher initial discharge capacities of 254.3 mAh g\u00031, 264.4 mAh g\u00031", "category": "scientific_body", "coverage": 0.184, "words": 42 }, { "page": 7, "page_count": 10, "bbox": [ 301.83, 557.98, 552.9, 691.46 ], "text": "the one hand, the relatively thicker coating layer not only sup- presses excessively the release of O2 but also prevents the extrac- tion/insertion of Liþ in layered structure, resulting in low capacity. On the other hand, the low reduction potential of 2.854 V for CoF2/ LiF can reduce the operating voltage of CF-2.0. Moreover, CF-2.0 exhibits the improved stability with the capacity retention of 93.6% and the value of voltage drop of 0.299 V after 100 cycles as shown in Fig. S1(inset a and b), which is close to the results of CF- 1.0. However, CF-2.0 delivers the much lower energy density of 694.6 Wh kg\u00031 than CF-0.5 and CF-1.0 owing to its low capacity and voltage. Thus, CF-1.0 reaches the optimal integrated performance between high capacity, high operating voltage and outstanding cycling stability.", "category": "scientific_body", "coverage": 0.23, "words": 152 }, { "page": 7, "page_count": 10, "bbox": [ 32.83, 673.06, 283.9, 743.79 ], "text": "In order to investigate the capacity and voltage stability for the sample whose CoF2 coating content is higher than 1.0 wt%, Fig. S1 in supplementary materials presents the operation voltages versus specific capacities of 2.0 wt% CoF2-coated sample (CF-2.0) and other four samples after 1st cycle and 100th cycle, respectively. The initial discharge capacity of 236.0 mAh g\u00031 and operating potential of 3.444 V for CF-2.0, lower than other four samples, are obtained. On", "category": "scientific_body", "coverage": 0.136, "words": 85 }, { "page": 8, "page_count": 10, "bbox": [ 42.52, 576.83, 293.58, 670.54 ], "text": "5 C, CF-1.0 exhibits the highest capacity of 167.5 mAh g\u00031, yet that of LNMO is only 120.1 mAh g\u00031. Moreover, when the current density is back to 0.1 C, the discharge capacity returns to 98.7% of its initial value for CF-1.0, implying good reversibility and structural stability after high-rate measurements. The primary reason for the signifi- cantly improved rate capability of CF-1.0 is that the introduction of CoF2 nano-coating layer, which accelerates the electrons transport and Liþ diffusion, and inhibits the interfacial reaction between electrolyte and active materials.", "category": "scientific_body", "coverage": 0.03, "words": 103 }, { "page": 8, "page_count": 10, "bbox": [ 311.53, 578.81, 562.59, 745.1 ], "text": "fitted with the equivalent circuits in the inset. Fig. 7(a) presents the EIS curves of the cells at open circuit potential before cycling. The intercept on the x-axis at the highest frequency is related to ohmic resistance of the electrolyte (Rs), the diameter of the semicircle represents charge-transfer resistance (Rct), and the slope line at the low frequency is assigned to the Warburg impedance (Zw) exhib- iting the diffusion of Liþ in the electrode material. It can be obvi- ously seen that a significant decrease in the Rct with the increase of CoF2 coating amount except for the similar values of Rs and Zw, exhibiting better electrochemical kinetics on the electrode/elec- trolyte interface for CF-1.0. The EIS spectra at the charged potential of 4.3 V after 100 cycles at 0.1 C, with a high-frequency semicircle ascribed to the resistance (Rf) of the solid electrolyte interface (SEI) and a medium-frequency corresponding to charge-transfer resis- tance (Rct), are presented in Fig. 7(b). As expected, CF-1.0 appears the lowest values of Rf and Rct, indicating that the formation and", "category": "scientific_body", "coverage": 0.005, "words": 187 }, { "page": 9, "page_count": 10, "bbox": [ 32.82, 589.24, 283.96, 649.62 ], "text": "growth of the unacceptable SEI film as well as the interfacial re- action have been mitigated by CoF2 coating layer. Thus, the improvement of electrochemical kinetics, the suppression of the formation of SEI film and side reaction between electrolyte and electrode, are responsible for the outstanding stability of capacity and rate capability of CF-1.0.", "category": "scientific_body", "coverage": 0.02, "words": 55 }, { "page": 9, "page_count": 10, "bbox": [ 32.82, 693.98, 283.92, 743.79 ], "text": "To disclose the reasons for improving the capacity fading and voltage decay upon cycling of CoF2-coated samples, LNMO and CF- 1.0 after several cycles were observed using TEM. Fig. 8 (b1 and b2) presents TEM image and corresponding SAED pattern of LNMO after 50 cycles at 0.1 C between 2.0 and 4.8 V. Two types of", "category": "scientific_body", "coverage": 0.018, "words": 61 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 66.34, 293.64, 157.98 ], "text": "particle in Fig. 8(c2), indicating complete structure transition after 100 cycles. However, the thin SEI film mixed with CoF2 coating layer can be observed in Fig. 8(d1) for CF-1.0 after 100 cycles owing to the inhibition of the release of oxygen during initial several cycles, meanwhile it still remain in the rhombohedral layered phase, which is in good agreement with the best stability of capacity and operating voltage. Therefore, the phase transition from layered to spinel can be delayed effectively by CoF2 nano-coating layer upon cycling.", "category": "scientific_body", "coverage": 0.011, "words": 91 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 191.85, 293.64, 295.29 ], "text": "In this paper, a nano protective layer of CoF2, in situ synthesized by means of a common wet chemistry technology, was coated on LNMO. The results of SEM, TEM, EDS and XPS demonstrate that CoF2 coating, belong to cubic structure, distributes homogeneously on the surface of LNMO, and the cell tests reveal that electro- chemical performances are enhanced obviously for CoF2-coated samples. CF-0.5 delivers the highest initial discharge capacity of 264.4 mAh g\u00031 and coulombic efficiency of 86.2%, benefiting from the electrochemical conversion reaction based on CoF2/LiF, as well as the reduction in the amount of irreversible O2 release and the Liþ", "category": "scientific_body", "coverage": 0.057, "words": 110 }, { "page": 10, "page_count": 10, "bbox": [ 42.52, 296.45, 293.62, 492.7 ], "text": "vacancies proved by the CV measurements. In addition, the higher first discharge capacity of 259.1 mAh g\u00031 compared to bare LNMO of 244.0 mAh g\u00031, the excellent cycling stability with the capacity retention rate of 93.0% after 100 cycles at 0.1 C, the improved rate performance with the capacity of 167.5 mAh g\u00031 even at 5 C, and the restraining operating voltage decay with the drop of 0.312 V after 100 cycles at 0.1 C are obtained for CF-1.0 sample. The outstanding electrochemical performances are ascribed to the CoF2 nano-coating in protection electrode material from deterioration in the electrolyte, the enhancement of kinetics electrochemical involving better electron transfer and Liþ diffusion, and the inhi- bition of layered-spinel phase transition initiated from particle edge and spread into inner bulk by means of minimizing the migration of TM ions into Li layers. Therefore, the novel design of CoF2 nano-coating not only provides a tactic to surmount the de- fects of LNMO and displays the superior comprehensive effect on improving electrochemical performance among the coatings in published data, but also illuminates in depth the mechanism of capacity fading and voltage decay upon cycling.", "category": "scientific_body", "coverage": 0.04, "words": 203 } ], "front_summary_missing_blocks": [], "back_matter_low_overlap_blocks": [ { "page": 10, "page_count": 10, "bbox": [ 42.52, 526.57, 293.66, 565.94 ], "text": "This work was supported by National Natural Science Founda- tion of China (Grant no. E51504196), the China Postdoctoral Science Foundation (no. 2012M521760) and the Fundamental Research Funds for the Central Universities (no. xjj2014052).", "category": "back_matter", "coverage": 0.0, "words": 32 } ] }