Non-aqueous electrolyte secondary battery

Abstract

The invention is to provide a means for achieving adequate charge / discharge cycle characteristics in a non-aqueous electrolyte secondary battery having large capacity and a large area even when a mixture of a high-capacity Si material and a carbon material that swells little is used as a negative electrode active material. A non-aqueous electrolyte secondary battery in which the value of the ratioof the battery volume (the product of the thickness of the battery and the projected area of the battery including a battery exterior body) with respect to the rated capacity is 10 cm<3> / Ah or less and the rated capacity is 3 Ah or more, said non-aqueous electrolyte secondary battery comprising a power generation element that includes: a positive electrode in which a positive electrode active material layer including a positive electrode active material is formed on the surface of a positive electrode current collector; a negative electrode in which a negative electrode active material layerincluding a negative electrode active material is formed on the surface of a negative electrode current collector; and a separator. The non-aqueous electrolyte secondary battery is characterized in that: the negative electrode active material layer contains a negative electrode active material represented by formula (1) alpha (Si material) and beta (carbon material) (in the formula, the Si material is one or more substances selected from the group consisting of Si-containing alloys and SiOx (x represents the number of oxygen atoms satisfying the valence of Si) that is a mixture of amorphous SiO2 particles and Si particles, the carbon material is one or more substances selected from the group consisting of graphite, hardly graphitizable carbon, and amorphous carbon, alpha and beta representthe mass% of the individual components in the negative electrode active material layer, 80 <= alpha + beta <= 98, 0.1 <= alpha <= 40, and 58 <= beta <= 97.9); and when a plurality of discretionary locations within the plane of the negative electrode active material layer are selected and the area ratios (%) of the Si material and the carbon material in the area of the field of view in each of images of a cross section of the negative electrode active material layer are denoted respectively as S (%) and (100-S) (%), the difference between the maximum value and the minimum value of S is within5%.

Description

technical field [0001] The present invention relates to a nonaqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery of the present invention is used, for example, as a driving power source and an auxiliary power source for engines of vehicles such as electric vehicles, fuel cell vehicles, and hybrid electric vehicles. Background technique [0002] In recent years, in order to cope with global warming, it is required to reduce the amount of carbon dioxide. Therefore, non-aqueous electrolyte secondary batteries with a small environmental load are being used not only in mobile devices, but also in power sources for electric vehicles such as hybrid electric vehicles (HEV), electric vehicles (EV), and fuel cell vehicles. A lithium-ion secondary battery intended to be used in an electric vehicle is required to have a large capacity, a large area, and a high capacity. [0003] Conventionally, carbon materials such as graphite, which are advantageous ...

AI Technical Summary

Problems solved by technology

However, in negative electrode active materials using carbon materials such as graphite, charge and discharge are performed by the storage / release of lithium ions into graphite crystals, so there is a disadvantage that LiC, which is the largest lithium-introducing compound, cannot be obtained. 6 The obtained charge and discharge capacity has a theoretical capacity of 372mAh / g or more

[0005] However, the expansion and contraction of the negative electrode during charging and discharging of a lithium-ion secondary battery using a material alloyed with Li, especially a Si material, in the negative electrode is large.

For example, the volume expansion when absorbing Li ions is about 1.2 times in graphite materials, and when Si and Li are alloyed in Si materials, the transition from an amorphous state to a crystalline state causes a large volume change of about 4 times, Therefore, there is a problem of reducing the cycle life of the electrode

In addition, in the case of the Si negative electrode active material, capacity and cycle durability are in a trade-off relationship, and there is a problem that it is difficult to realize high capacity and improve high cycle durability.

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