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Si alloy negative electrode active material for electric device

a negative electrode and active material technology, applied in the direction of non-metal conductors, cell components, conductors, etc., can solve the problems of large expansion-shrinkage in charge-discharge in the negative electrode, difficult to achieve capacity and energy density, and difficult to achieve a charge-discharge capacity of 372 mah/g or more, etc., to achieve the effect of preventing amorphous crystal phase transition, reducing the capacity of the negative electrode, and reducing the amorphous

Active Publication Date: 2014-09-02
NISSAN MOTOR CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0014]According to a negative electrode active material for electric device of the present invention, an effect of suppressing amorphous-crystal phase transition and improving a cycle life is attained when an alloy having the above-specified composition formula contains a first additive element Zn within the above-specified range when Si and Li are alloyed with each other. Further, in the case of alloying Si and Li with each other, an effect that a capacity of an electrode is not reduced even though a concentration of the first additive element is increased is attained when the alloy having the above-specified composition formula contains a second additive element Al within the above-specified range. As a result of these combined effects, the negative electrode active material containing the alloy having the above composition formula obtains advantageous effects such as high initial capacity and high capacity / high cycle durability.

Problems solved by technology

However, since the charge-discharge is performed by occlusion / release of lithium ions into / from a graphite crystal with the carbon / graphite negative electrode material, there is a drawback that it is difficult to attain a charge-discharge capacity of 372 mAh / g or more which is the theoretical capacity obtainable from LiC6 which is the largest-amount-lithium intercalation compound.
Therefore, it is difficult to attain capacity and energy density which are satisfactory for the practical use in vehicles with the use of the carbon / graphite negative electrode material.
However, in the lithium ion secondary battery using the material alloyed with Li for the negative electrode, expansion-shrinkage in charge-discharge is large in the negative electrode.
For example, a volumetric expansion of a graphite material in the case of occluding Li ions is about 1.2 times, while the Si material has a problem of reducing a cycle life of an electrode due to a large volumetric change (about 4 times) which is caused by transition from an amorphous state to a crystal state in the alloying between Si and Li.
Also, since a capacity and cycle durability have a trade-off relationship in the case of the Si negative electrode active material, there has been a problem that it is difficult to improve high cycle durability while maintaining a high capacity.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

Samples 1 to 48

[0131]1. Production of Cell for Evaluation

[0132](1) Production of Electrode for Evaluation

[0133]As electrodes for evaluation, thin film alloys obtained by sputtering and having various alloy compositions were used.

[0134]More specifically, as a sputtering apparatus, an independently controllable ternary DC magnetron sputtering apparatus (manufactured by Yamato-Kiki Industrial Co., Ltd.; combinatorial sputter coating apparatus; gun-sample distance: about 100 mm) was used. The thin film alloys (Samples 1 to 48) of various alloy compositions were obtained under the following sputtering conditions, target specs, and electrode sample specs.

[0135](i) More specifically, the sputtering conditions areas follows.

[0136]1) Base pressure: up to 7×10−6 Pa

[0137]2) Sputtering gas: Ar (99.9999% or more)

[0138]3) Sputtering gas introduction amount: 10 sccm

[0139]4) Sputtering pressure: 30 mTorr

[0140]5) DC power source: Si (185 W), Zn (30 to 90 W), Al (30 to 180 W)

[0141]6) Pre-sputtering t...

example 2

[0186]The initial cycle of each of the cells for evaluation (CR2032 type coin cells) using the electrodes for evaluation of Samples 14 and 42 was conducted under the same charge-discharge conditions as those of Example 1. A dQ / dV curve relative to a voltage (V) during discharge of the initial cycle is shown in FIG. 9.

[0187]As an interpretation of dQ / dV of Sample 14 based on FIG. 9, it was confirmed that crystallization of the Li—Si alloy was suppressed by adding the elements (Zn and Al) in addition to Si since the curve was gentle due to a reduction in number of downwardly projecting peaks in a region of low potential (0.4 V or less). Also, it was confirmed that decomposition of electrolyte solution was suppressed (near about 0.4 V). As used herein, Q represents a cell capacity (discharge capacity).

[0188]More specifically, the downwardly projecting sharp peak indicates a change caused by decomposition of the electrolyte solution in the vicinity of 0.4 V of Sample 42 (pure Si metal t...

example 3

[0190]A cell for evaluation (CR2032 type coin cell) using the electrode for evaluation of Sample 14 was subjected to the initial to 50th cycles under the charge-discharge conditions same as those of Example 1. The charge-discharge curves from the initial cycle to the 50th cycle are shown in FIG. 10. The charging in FIG. 10 indicates states of the charging curves in the cycles caused by the Li reaction (lithiation) in the electrode for evaluation of Sample 14. The discharging indicates states of the discharging curves of the cycles caused by Li release (delithiation).

[0191]In FIG. 10, the dense curve in each of the cycles indicates the suppressed cycle deterioration. The small kink (turn or twist) indicates that the amorphous state is maintained. Further, the small capacity difference between the charging and the discharging indicates the good charge-discharge efficiency.

[0192]From the above-described test results, it is possible to assume (estimate) the mechanism (functional mechani...

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Abstract

A negative electrode active material for an electric device, including an alloy having a composition formula SixZnyAlz, where x++y=100 , 26≦x≦47, 18≦y≦44, and 22≦z≦46 are satisfied.

Description

TECHNICAL FIELD[0001]The present invention relates to a Si alloy negative electrode active material for electric device and an electric device using the Si alloy negative electrode active material for electric device. The Si alloy negative electrode active material for electric device and the electric device using the same of the present invention are usable as a secondary battery, a capacitor, or the like for a driving power source or an auxiliary power source of a motor of a vehicle such as an electric vehicle, a fuel cell vehicle, and a hybrid electric vehicle.BACKGROUND ART[0002]In recent years, in order to address atmospheric pollution and global warming, there has been a strong demand for reduction of a carbon dioxide amount. In the automobile industry, there are high expectations that the reduction of carbon dioxide amount can be attained by introduction of an electric vehicle (EV) and a hybrid electric vehicle (HEV), and an electric device such as a secondary battery for dri...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): H01M4/134C22C18/00H01M4/42H01M4/38C22C21/02H01M4/46C22C30/06C22C21/10H01M4/1395H01M4/04
CPCC22C18/00H01M4/1395H01M4/42H01M4/134Y02E60/12H01M4/386C22C21/02H01M4/463C22C30/06C22C21/10H01M4/0426
Inventor WATANABE, MANABUTANAKA, OSAMUMIYAMOTO, TAKASHI
Owner NISSAN MOTOR CO LTD
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