Transition metal oxide containing solid-solution lithium, and non-aqueous electrolyte secondary battery using transition metal oxide containing solid-solution lithium as positive electrode
A transition metal oxide containing solid-solution lithium that realizes high initial discharge capacity and capacity retention is represented by the compositional formula: Li 1.5 [Ni a M b Mn c [Li] d ]O 3 , wherein M represents at least one kind of element selected from the group consisting of silicon, phosphorus and metal elements (excluding Ni, Mn and Li), a, b, c and d satisfy specific relationships, and n is the valence of M. The oxide has a layered structure site and a site which changes to a spinel structure by performing a charge or a charge-discharge in a predetermined electric potential range, and a spinel structure change ratio k in a range of 0.25≤k<1.0 when the spinel structure change ratio is assumed to be 1 in a case where Li 2 MnO 3 of the layered structure in the transition metal oxide containing solid-solution lithium completely changes to LiMn 2 O 4 of the spinel structure.
1. A method for producing a non-aqueous electrolyte secondary battery using a transition metal oxide containing solid-solution lithium as a positive electrode, wherein
the transition metal oxide containing solid-solution lithium is represented by the compositional formula (1):
Li 1.5 [Ni a M b Mn c [Li] d ]O 3 (1)
wherein Li represents lithium, Ni represents nickel, M represents at least one kind of element selected from the group consisting of silicon, phosphorus and metal elements (but excluding Ni, Mn and Li), Mn represents manganese, O represents oxygen, a, b, c and d satisfy the relationships of 0<a<1.4, 0<b≤0.2, 0<c<1.4, 0.1<d≤0.4, a+b+c+d=1.5 and 1.1≤[a+b+c]<1.4, and n, which is the valence of M, is in a range of 3.5≤n≤6 (when M consists of two or more elements, n is the average value of the valence of each element),
wherein the transition metal oxide containing solid-solution lithium has a layered structure site and a site which changes to a spinel structure, the method comprising:
electrochemically pretreating the transition metal oxide by preforming a first charge-discharge in which a maximum potential of the battery in a predetermined electric potential range is 4.3 V or higher and less than 4.8 V, wherein the electrochemically pretreating further comprises resting between a charge and a discharge for a predetermined time that is not less than ten minutes; and
charge-discharge treating by performing a second charge-discharge in which the maximum potential of the battery in the predetermined electric potential range is 4.8 V to convert to a lithium metal counter electrode, the electrochemically pretreating and the charge-discharge treating resulting in the layered structure site and the spinel structure site, whereby
a spinel structure change ratio k of the transition metal oxide containing solid-solution lithium is in a range of 0.25≤k<1.0 when the spinel structure change ratio is assumed to be 1 in a case where Li 2 MnO 3 of the layered structure in the transition metal oxide containing solid-solution lithium completely changes to LiMn 2 O 4 of the spinel structure.
2. The method according to claim 1 , wherein the n, which is the valence of M, is in a range of 4≤n≤6, and the spinel structure change ratio k is in a range of 0.5≤k≤0.9.
3. The method according to claim 2 , wherein the n, which is the valence of M, is in a range of 4≤n≤5, and the spinel structure change ratio k is in a range of 0.6≤k≤0.9.
4. The method according to claim 1 , wherein the first charge-discharge is repeatedly performed at the maximum potential.
5. The method according to claim 1 , wherein both a charge and a discharge during electrochemically pretreating are performed in a range of 0.01 to 0.5 C in a constant current charge-discharge mode.
6. The method according to claim 1 , wherein the charge-discharge treating is performed in a constant current and constant voltage charge-constant current discharge mode.