Enhanced Overdischarge Stability of LiCoO₂by a Solution Deposited AlPO₄Coating

Abstract

Enhancing the stability of lithium ion cathode active materials to over-insertion of lithium can improve overdischarge tolerance in cells that have excess reversible lithium compared to the stoichiometric cathode capacity. In the present work, a solution deposited coating of AlPO 4 on LiCoO 2 , known to stabilize overcharge, is applied to test its effect on the overdischarge (or over-insertion) tolerance of LiCoO 2 . Cathode testing versus lithium metal is performed with constant current charge to 140 mAh/g LiCoO 2 , constant current discharge to 3.0 V vs. Li/Li + and 7 mAh/g LiCoO 2 lithium over-insertion at fixed resistive load. Results show that the AlPO 4 coating maintains >99% of the discharge energy (compared to 96% for the as-received LiCoO 2 ) after 10 cycles. X-ray diffraction analysis of the relative intensity of {003} peak of the R3M space group indicates that after repeated lithium over-insertion, the AlPO 4 coating suppresses irreversible cation exchange between Li and Co ions in the octahedral layers of LiCoO 2 . Thus, AlPO 4 surface coatings can prevent crystal structure changes detrimental to charge/discharge performance in LiCoO 2 caused by over-insertion of lithium ions. Overdischarge of conventional lithium ion cells can lead to reduced cell performance, cell failure, or safety concerns.1,2 The primary mechanism of overdischarge damage in a conventional lithium ion cell is dissolution of the anode copper current collector, which can lead to internal shorting and capacity loss.3-8 Dissolution of the copper current collector occurs during overdischarge because of the high electrochemical potential that the anode experiences in conventional cells (>3.0 V vs. Li/Li + ). 3,6,9,10 Such a high anode potential during overdischarge ultimately results from loss of reversible lithium to the formation of the solid electrolyte interphase (SEI) during the initial cycling of a cell.9,11 Thus, efforts to protect cells from overdischarge have generally focused on prevention of copper dissolution. 3,6,8,[12][13][14] In advanced lithium ion cells, adding reversible lithium (via high loss cathode materials, anode pre-lithiation, etc.) is utilized to improve general cell performance, 15-17 eliminate the need for formation cycling, 18 manage high first cycle irreversible loss in the anode, 19 and prevent dissolution of the anode copper current collector during overdischarge 3 or near zero volt storage. 9,20 The resulting cell may have excess reversible lithium compared to the normal operation cathode insertion capacity. For such a cell, in an overdischarge scenario, the anode potential will not increase to a high enough value (e.g. >3.1 V vs. Li/Li + ) for copper dissolution to occur. Rather, the cathode potential will decrease to less than its normal range, and the cathode can be over-inserted with lithium at a potential less than its normal operating voltage. 9This over-insertion of lithium can lead to degradation of the cathode performance.9 As such, in advanced lithium ion cells with added reversible lithium, d...

New Organic Complex for Lithium Layered Oxide Modification: Ultrathin Coating, High-Voltage, and Safety Performances

“…[28][29][30][31][32][33][34][35][36][37][38] To date, the metal phosphates have become an efficient coating layer to improve the NCM performance because of their great anti-corrosive feature to the acidic compound (e.g., HF) in the electrolyte. 39,40 In addition, the metal phosphates are more robust than metal oxides 41,42 (i.e., the higher binding energy of "M-OP" than that of "M-O"), 43 and also much easier to handle than fluorides. 44,45 However, there is only one soultion-based precipitation method developed in the past two decades, [46][47][48][49][50] where a uniform and ultrathin coating is still a great challenge.…”

“…A thick, rough and/or scattered coating layer was always caused by the aforementioned precipitation method, where the metal phosphate suspension (e.g., AlPO 4 ) was prepared first by the precipitation of metal nitrate and (NH 4 ) 2 HPO 4 , and then used as precursors to coat the NCM. 39,43 As a result, an irregular dispersion and aggregation of metal phosphate on NCM were induced due to the inhomogeneous suspension and the high surface tension of aqueous solution. Unfortunately, this situation is hard to be improved at present, because the metal hydroxide may be formed on the alkaline surface of NCM if the metal phosphate was not precipitated first.…”

“…To date, metal phosphates have become an efficient coating layer to improve the NCM performance because of their great anticorrosive feature to the acidic compound (e.g., HF) in the electrolyte. , In addition, metal phosphates are more robust than metal oxides , (i.e., the higher binding energy of “M–OP” than that of “M–O”) and also much easier to handle than fluorides. , However, there has been only one soultion-based precipitation method developed in the past 2 decades, − where a uniform and ultrathin coating is still a great challenge. A thick, rough, and/or scattered coating layer was always caused by the aforementioned precipitation method, where the metal phosphate suspension (e.g., AlPO 4 ) was prepared first by the precipitation of metal nitrate and (NH 4 ) 2 HPO 4 and then used as a precursor to coat the NCM. , As a result, irregular dispersion and aggregation of metal phosphate on NCM were induced due to the inhomogeneous suspension and the high surface tension of aqueous solution. Unfortunately, this situation is hard to improve at present because the metal hydroxide may be formed on the alkaline surface of NCM if the metal phosphate is not precipitated first.…”

High‐Voltage Layered Ternary Oxide Cathode Materials: Failure Mechanisms and Modification Methods†

“…The (NH 4 ) 3 AlF 6 coating on the LiNi 1/3 Co 1/3 Mn 1/3 O 2 particles plays a key role in stabilizing the interface between the cathode and the electrolyte, thus the cycle performance at high voltage (3.0—4.8 V) of LiNi 1/3 Co 1/3 Mn 1/3 O 2 coated with (NH 4 ) 3 AlF 6 was consequently improved (Figure 8i). Besides, metal phosphates also have become an efficient coating layer because of their great anticorrosive feature to the acidic compound ( e.g ., HF) in the electrolyte, [ 128 ] and metal phosphates are more robust than metal oxides [ 129 ] ( i.e ., the higher binding energy of “M−OP” than that of “M−O”) [ 130 ] and also much easier to handle than fluorides. [ 131 ] Liu et al .…”

Advances in Cathode Nanomaterials for Lithium-Ion Batteries

“…In order to improve the overcharge of the LiCoO2 (discharge energy of 96 %) a coating with AlPO4 was used and the over-insertion tolerance maintains to over 99 % of the discharge energy after 10 cycles. Also, the AlPO4 coating prevents crystal structure changes and suppresses irreversible cation Li and Co exchange in the octahedral layers of the LiCoO2 during the over-insertion of Li + ions (Crompton et al 2017).…”