NOVELTY - Lithium ion battery comprises: positive and negative electrodes that are capable of occluding and emitting lithium ions; separator (7) disposed between positive electrode and negative electrode; and electrolytic solution, where the negative electrode includes negative-electrode active material and polymer, a surface of negative-electrode active material is entirely or partially coated with polymer, and the polymer includes polyethylene glycol boric acid ester that can be obtained by polymerizing a substituted aliphatic polycarbonate (I) or substituted polymerizable boron compound (II).    USE - The lithium ion battery is useful as: a power supply for a hybrid vehicle and industrial equipments including electric power tools and fork lifts; and a backup power supply for an electric control system of a vehicle.    ADVANTAGE - The lithium ion battery exhibits: a capacity retention rate of higher than 75.6% for 30 days of a storage date; initial direct-current resistance of lower than 65 m Omega (claimed); and improved output characteristics at room temperature without deteriorating high-temperature storage characteristics at greater than or equal to 50 degrees C.    DETAILED DESCRIPTION - Lithium ion battery comprises: a positive electrode that is capable of occluding and emitting lithium ions; a negative electrode that is capable of occluding and emitting lithium ions; a separator (7) that is disposed between the positive electrode and the negative electrode; and an electrolytic solution, where the negative electrode includes a negative-electrode active material and a polymer, a surface of the negative-electrode active material is entirely or partially coated with the polymer, and the polymer includes polyethylene glycol boric acid ester that can be obtained by polymerizing a substituted aliphatic polycarbonate of formula (-(R1-O-C(=O)-O-)n-) (I) or a substituted polymerizable boron compound of formula (Z1-(R)p-O-B(O-(R)q-Z2)-(O-(R)r-Z3)) (II).    n = more than 10 to less than 10000, preferably more than 100 to less than 1000;    Z1, Z2, Z3 = organic groups having an acryloyl or methacryloyl, or 1-10C hydrocarbyl, where at least one of Z1-Z3 are organic groups having acryloyl or methacryloyl;    R = at least two types of 1-6C oxyalkylene; either    p, q, r = average addition number of moles of the oxyalkylene, which is larger than 0 to less than 4; or    p+q+r = greater than or equal to 3; and    R1 = 2-7C hydrocarbyl, preferably 2-3C hydrocarbyl.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a wound-type battery.    Positive-electrode collector (1)    Negative-electrode collector (3)    Separator (7)    Negative-electrode lead (9)    Positive-electrode lead (10)