Nonaqueous electrolyte battery

Abstract

A non-aqueous battery with improved volume energy density and enhanced load characteristics is made available even when using olivine-type lithium phosphate as a positive electrode active material. The non-aqueous electrolyte battery of the present invention is provided with a positive electrode (1) containing lithium iron phosphate as a positive electrode active material, a negative electrode (2), and a non-aqueous electrolyte (4). In the positive electrode (1), a positive electrode active material-containing layer that is made of the positive electrode active material, a conductive agent, and a binder agent is formed on a positive electrode current collector. The positive electrode current collector has a thickness of less than 20 mum and its surface that is in contact with the positive electrode active material-containing layer has a mean surface roughness Ra of greater than 0.026 mum.

Description

technical field [0001] The present invention relates to a nonaqueous electrolyte battery comprising a positive electrode containing lithium iron phosphate as a positive electrode active material, a negative electrode, and a nonaqueous electrolyte, and particularly relates to improvement of a positive electrode current collector with improved adhesion to the positive electrode active material. Background technique [0002] In recent years, mobile information terminals such as mobile phones, personal computers, and PDAs have been rapidly reduced in size and weight, and further increases in capacity are required for batteries serving as driving power sources. Nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used as driving power sources for mobile information terminals as described above because of their high energy density and high capacity. [0003] The non-aqueous electrolyte secondary battery generally uses lithium cobalta...

AI Technical Summary

Problems solved by technology

On the other hand, since olivine-type lithium phosphate has low adhesion to the metal foil as the positive electrode current collector, even if a binder is mixed, there is a problem of peeling off from the positive electrode current collector.

[0013] In this case, although it can be considered to reduce the thickness of the positive electrode mixture layer to suppress the method of peeling off the positive electrode active material from the positive electrode current collector, when the thickness of the positive electrode mixture layer is reduced, the positive electrode current collector will be in the positive electrode. The proportion of the thickness increases, so there is a problem that the volumetric energy density of the positive electrode decreases

In addition, since olivine-type lithium phosphate is different from the previously used LiCoO 2 , LiNiO 2 , Li x Ni 1-y co y o 2 , LiMn 2 o 4 and LiNi 1 / 3 co 1 / 3 mn 1 / 3 o 2 The resistance of the equal ratio is large, so in the case of charging and discharging with a large current, the voltage of the battery drops, and there is a problem that it is impossible to obtain a sufficient charge and discharge capacity.

[0014] In order to solve this problem, studies have been made on coating the surface of olivine-type lithium phosphate with carbon to improve electrical conductivity, but it cannot be said that it is ideal enough.

In addition, when in order not to peel off the positive electrode active material from the positive electrode current collector, and after the coating of the positive electrode mixture is not sufficiently rolled, not only the volumetric energy density is reduced, but also the positive electrode active material, the conductive agent, the positive electrode current collector, etc. The contact area of ​​the body is reduced, which becomes the cause of the reduction of load characteristics

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