According to one embodiment, a separator is provided. The separator includes a composite membrane. The composite membrane includes a substrate layer, a first composite layer, and a second composite layer. The first composite layer is located on one surface of the substrate layer. The second composite layer is located on the other surface of the substrate layer. The composite membrane has a coefficient of air permeability of 1×10.sup.−14 m.sup.2 or less. The first composite layer has a first surface and a second surface. The first surface is in contact with the substrate layer. The second surface is located on an opposite side to the first surface. Denseness of a portion including the first surface is lower than denseness of a portion including the second surface in the first composite layer.

The invention provides for a high occupancy or heavy-duty vehicle with a battery propulsion power source, which may include lithium titanate batteries. The vehicle may be all-battery or may be a hybrid, and may have a composite body. The vehicle battery system may be housed within the floor of the vehicle and may have different groupings and arrangements.

The invention provides for a high occupancy or heavy-duty vehicle with a battery propulsion power source, which may include lithium titanate batteries. The vehicle may be all-battery or may be a hybrid, and may have a composite body. The vehicle battery system may be housed within the floor of the vehicle and may have different groupings and arrangements.

Various embodiments of the present disclosure describe energy storage devices. In one example, an energy storage device includes an anode having a plurality of active material particles, a cathode having a transition metal oxide material, and an electrolyte including a room temperature ionic liquid to couple the anode to the cathode. Each of the plurality of anode active material particles have a particle size of between about one micrometer and about fifty micrometers. One or more of the plurality of anode active material particles are enclosed by and in contact with a membrane coating permeable to lithium ions.

Various embodiments of the present disclosure describe energy storage devices. In one example, an energy storage device includes an anode having a plurality of active material particles, a cathode having a transition metal oxide material, and an electrolyte including a room temperature ionic liquid to couple the anode to the cathode. Each of the plurality of anode active material particles have a particle size of between about one micrometer and about fifty micrometers. One or more of the plurality of anode active material particles are enclosed by and in contact with a membrane coating permeable to lithium ions.

There are provided an assembled battery and a battery pack having excellent cycle characteristics with respect to high rate charging and discharging. An assembled battery according to an embodiment includes at least one first single cell and at least one second single cell that are connected in series. The first single cell includes a positive electrode containing an active material represented by the general formula LiMO.sub.2 (M includes at least one element selected from the group consisting of Ni, Co, and Mn) and a negative electrode including a titanium-containing oxide. The second single cell includes a positive electrode containing an active material represented by the general formula LiM′PO.sub.4 (M′ includes at least one element selected from the group consisting of Fe, Mn, Co, and Ni) and a negative electrode including a titanium-containing oxide. The ratio of a charging resistance of the second single cell to a charging resistance of the first single cell is 1 or more and 1.5 or less if an open circuit voltage when the at least one first single cell and the at least one second single cell are connected in series is 4.5 V.

There are provided an assembled battery and a battery pack having excellent cycle characteristics with respect to high rate charging and discharging. An assembled battery according to an embodiment includes at least one first single cell and at least one second single cell that are connected in series. The first single cell includes a positive electrode containing an active material represented by the general formula LiMO.sub.2 (M includes at least one element selected from the group consisting of Ni, Co, and Mn) and a negative electrode including a titanium-containing oxide. The second single cell includes a positive electrode containing an active material represented by the general formula LiM′PO.sub.4 (M′ includes at least one element selected from the group consisting of Fe, Mn, Co, and Ni) and a negative electrode including a titanium-containing oxide. The ratio of a charging resistance of the second single cell to a charging resistance of the first single cell is 1 or more and 1.5 or less if an open circuit voltage when the at least one first single cell and the at least one second single cell are connected in series is 4.5 V.

A nonaqueous electrolyte secondary battery includes a positive electrode, a nonaqueous electrolytic solution, and a negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer which is formed on the negative electrode current collector. The negative electrode active material layer has a first region and a second region. The first region is a region formed on a surface of the negative electrode current collector and contains lithium titanium composite oxide as a major component. The second region is a region including a surface of the negative electrode active material layer and contains lithium titanium composite oxide as a major component and further contains silicon oxide.

A nonaqueous electrolyte secondary battery includes a positive electrode, a nonaqueous electrolytic solution, and a negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer which is formed on the negative electrode current collector. The negative electrode active material layer has a first region and a second region. The first region is a region formed on a surface of the negative electrode current collector and contains lithium titanium composite oxide as a major component. The second region is a region including a surface of the negative electrode active material layer and contains lithium titanium composite oxide as a major component and further contains silicon oxide.

The present disclosure relates to a lithium secondary battery using lithium titanium oxide (LTO) as a negative electrode active material. More specifically, the present disclosure relates to a secondary battery having improved input and output characteristics through the optimization of the pore ratio of the LTO. The lithium secondary battery including the lithium titanium oxide negative electrode active material according to the present disclosure provides an effect of significantly improved output density through the maximization of reaction active sites with electrolyte due to a porous structure.