Lithium ion secondary battery and method for manufacturing lithium ion secondary battery

A method for manufacturing a lithium ion secondary battery comprising:

• a negative electrode sheet including a negative current collector sheet and a negative active material layer formed on the negative current collector sheet, the negative material layer containing negative active material particles;
• and
• a positive electrode sheet facing the negative electrode sheet through separators interposed therebetween,
• wherein the negative active material particles includes at least first particles made of graphite and second particles made of amorphous carbon,
• the negative active material layer is configured so that:
• a ratio of an amount of the first particles to a total amount of the negative active material particles contained in a portion of the negative active material layer on a side close to the negative current collector sheet in a layer thickness direction is higher than a ratio of an amount of the first particles to a total amount of the negative active material particles contained in the negative active material layer, and
• a ratio of an amount of the second particles to a total amount of the negative active material particles contained in a portion of the negative active material layer on a side close to a surface in the layer thickness direction is higher than a ratio of an amount of the second particles to a total amount of the negative active material particles contained in the negative active material layer,
• the negative active material layer is formed of a plurality of layers laminated in the layer thickness direction,
• the layers including a first layer located on a side closest to the negative current collector sheet and a second layer located on a side closest to the surface,
• the negative active material particles of the first layer are composed of the first particles,
• the negative active material particles of the second layer are composed of the second particles, and
• the first layer has a density of 1.2 to 1.6 g/cm3,
• wherein the method includes:
• a lamination coating step of applying active material paste containing the negative active material particles on the negative current collector sheet more than once to form a laminated coating film;
• and
• a drying step of drying the laminated coating film, and
• the lamination coating step uses active material pastes prepared so that the pastes to be coated for more upper layers have a higher or equal ratio of the second particles and a lower or equal ratio of the first particles relative to a total amount of the negative active material particles contained in own paste.

A method for manufacturing a lithium ion secondary battery comprising:

• a negative electrode sheet including a negative current collector sheet and a negative active material layer formed on the negative current collector sheet, the negative material layer containing negative active material particles;
• and
• a positive electrode sheet facing the negative electrode sheet through separators interposed therebetween,
• wherein the negative active material particles includes at least first particles made of graphite and second particles made of amorphous carbon,
• the negative active material layer is configured so that:
• a ratio of an amount of the first particles to a total amount of the negative active material particles contained in a portion of the negative active material layer on a side close to the negative current collector sheet in a layer thickness direction is higher than a ratio of an amount of the first particles to a total amount of the negative active material particles contained in the negative active material layer, and
• a ratio of an amount of the second particles to a total amount of the negative active material particles contained in a portion of the negative active material layer on a side close to a surface in the layer thickness direction is higher than a ratio of an amount of the second particles to a total amount of the negative active material particles contained in the negative active material layer,
• the negative active material layer is formed of a plurality of layers laminated in the layer thickness direction,
• the layers including a first layer located on a side closest to the negative current collector sheet and a second layer located on a side closest to the surface,
• the negative active material particles of the first layer are composed of the first particles,
• the negative active material particles of the second layer are composed of the second particles, and
• the first layer has a density of 1.2 to 1.6 g/cm3,
• wherein the method includes:
• a coating step of applying active material paste containing the negative active material particles on the negative current collector sheet or on a lower-layer negative active material layer made of already coated and dried active material paste;
• and
• a drying step of drying the coated paste,
• the coating step and the drying step being alternately repeated, and
• the coating step uses the active material pastes prepared so that the pastes to be coated at later stages have a higher or equal ratio of the second particles and a lower or equal ratio of the first particles relative to a total amount of the negative active material particles contained in own paste.