JP2014167909A - Negative electrode active material for electricity storage device and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode active material for an electricity storage device with improved cycle characteristic without reducing discharge capacity and initial charge and discharge efficiency.SOLUTION: A negative electrode active material for electricity storage device contains metal Si and an oxide component. The oxide component contains oxide of at least one element selected from P, Si, and B, and oxide of Li.

Description

  The present invention relates to a negative electrode active material for an electricity storage device used for portable electronic devices, electric vehicles, electric tools, backup emergency power supplies, and the like, and a method for producing the same.

  In recent years, with the widespread use of portable electronic devices, electric vehicles, and the like, there is an increasing demand for higher capacity and smaller size of power storage devices such as lithium ion secondary batteries. If the capacity of the electricity storage device is increased, it will be easy to reduce the size of the battery. Therefore, there is an urgent need to develop the capacity of the electricity storage device.

For example, high potential type LiCoO ₂ , LiCo _1-x Ni _x O ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like are widely used as the positive electrode active material for lithium ion secondary batteries. On the other hand, a carbon material is generally used for the negative electrode active material. These materials function as an electrode active material that reversibly occludes and releases lithium ions by charging and discharging, and a so-called rocking chair type secondary battery that is electrochemically connected by a non-aqueous electrolyte or a solid electrolyte. Configure. For example, a binder or a conductive auxiliary agent is added to these electrode active materials, and the electrode active material is used as an electrode by applying it to the surface of a metal foil or the like that serves as a current collector.

  Examples of the carbon material used for the negative electrode active material include graphitic carbon material, pitch coke, fibrous carbon, and soft carbon. However, since the theoretical capacity of the carbon material is about 372 mAh / g, there is a problem that it is difficult to increase the capacity of the battery.

  As a negative electrode active material capable of inserting and extracting lithium ions and having a higher capacity density than a negative electrode active material made of a carbon material, a negative electrode active material containing Si or Sn exists. However, the negative electrode active material containing Si and Sn has a remarkably large volume change due to the insertion and release reaction of lithium ions during charge and discharge, and therefore the structure of the negative electrode active material deteriorates and cracks when repeatedly charged and discharged. It tends to occur. As cracks progress, in some cases, cavities are formed in the negative electrode active material and may be pulverized. As a result, since the electron conduction network is divided, there has been a problem of a decrease in discharge capacity (cycle characteristics) after repeated charge and discharge.

  Thus, in Patent Document 1, a negative electrode active material containing SiO as a negative electrode active material capable of inserting and extracting lithium ions and having excellent cycle characteristics as compared with a negative electrode active material containing Si or Sn. Has been proposed.

WO2006 / 011290

  Although the negative electrode active material made of SiO has improved cycle characteristics, there is a problem that the discharge capacity and the initial charge / discharge efficiency (ratio of the discharge capacity to the initial charge capacity) are lowered.

  The present invention has been made in view of the above circumstances, and provides a negative electrode active material for an electricity storage device having improved cycle characteristics and a method for producing the same without reducing discharge capacity and initial charge / discharge efficiency. With the goal.

  The negative electrode active material for an electricity storage device of the present invention contains metal Si and an oxide component, and the oxide component contains an oxide of at least one element selected from P, Si and B, and an oxide of Li. It is characterized by.

  The negative electrode active material for an electricity storage device of the present invention preferably has a structure in which the surface of the metal Si is coated with the oxide component.

  The negative electrode active material for an electricity storage device of the present invention preferably contains a carbon component.

  It is preferable that the negative electrode active material for electrical storage devices of this invention contains 10-80% of metal Si, 20-90% of oxide components, and 0-20% of carbon components by mass%.

  The method for producing a negative electrode active material for an electricity storage device of the present invention includes a step of mechanically milling a mixed raw material containing metal Si and an oxide raw material, wherein the oxide raw material is at least one selected from P, Si and B It contains an oxide raw material of an element and an oxide raw material of Li.

  The mechanical milling process is preferably performed in a non-oxidizing atmosphere.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode active material for electrical storage devices which improved the cycling characteristics is obtained, without reducing discharge capacity and first time charge / discharge efficiency.

  The negative electrode active material for an electricity storage device of the present invention contains metal Si and an oxide component, and the oxide component contains an oxide of at least one element selected from P, Si and B, and an oxide of Li. It is characterized by. By adopting the above configuration, the surface of the metal Si serving as the lithium ion storage / release site is coated with an oxide component, or the oxide component is dispersed between the metal Si. It becomes possible to relieve / suppress the volume change of the metal Si accompanying this. As a result, good cycle characteristics and high discharge capacity can be maintained without reducing the high discharge capacity.

  Furthermore, since the oxide component has the above-described configuration, part of lithium ions occluded in the metal Si is difficult to be absorbed by the oxide component in the first charge. When lithium ions are absorbed by the oxide component, the lithium ions remain in the oxide component without being released in the subsequent discharge. As a result, the initial discharge capacity is reduced by the amount of electricity corresponding to the lithium ions absorbed by the oxide component with respect to the initial charge capacity, and the initial charge / discharge efficiency is reduced. In particular, it is preferable that the oxide component contains P since the lithium ion conductivity of the oxide component is excellent and the discharge capacity and rapid charge / discharge characteristics are excellent. If the oxide component is not included, the volume change of the metal Si accompanying the insertion and extraction of lithium ions during charge / discharge cannot be relaxed, and the cycle characteristics are likely to deteriorate. Further, if the oxide component does not contain an oxide of at least one element selected from P, Si and B, the volume change of metal Si associated with insertion and extraction of lithium ions during charge and discharge cannot be reduced, and the cycle The characteristic tends to deteriorate. On the other hand, if the oxide component does not contain Li, the amount of lithium ions stored in the oxide component increases, and the initial charge / discharge efficiency tends to decrease.

The oxide component is a mole percent oxide _equivalent, Li 2 O 5 to _85%, preferably a _{P 2 O 5 + SiO 2 +} B 2 O 3 15~95%. The reason why each component is limited in this way will be described below.

Li 2 _O is an effect to suppress the lithium ion occlusion of the oxide components. The content of Li ₂ O is preferably 5 to 85%, more preferably 15 to 80%, and still more preferably 25 to 77%. When the Li 2 _O content is too small, the increases lithium ion storage amount of the oxide components, initial charge and discharge efficiency tends to be lowered. On the other hand, when the content of Li 2 _O is too large, the oxide becomes water resistance is likely to decrease in the component, the cycle characteristics tend to be lowered.

Since P ₂ O ₅ , SiO ₂ , and B ₂ O ₃ are all network-forming oxides, it becomes possible to relax the volume change of the metal Si that accompanies occlusion and release of lithium ions during charge and discharge. It has the effect of improving the characteristics. The total amount of these contents is preferably 15 to 95%, more preferably 20 to 85%, and still more preferably 23 to 75%. If the total amount of these contents is too small, the volume change of the metal Si accompanying the occlusion and release of lithium ions during charge / discharge cannot be alleviated, and the cycle characteristics tend to deteriorate. On the other hand, when the total amount of these contents is too large, the amount of lithium ions absorbed into the oxide component increases, and the initial charge / discharge efficiency tends to decrease.

P ₂ O ₅ is a component that improves the lithium ion conductivity of the oxide component. The content of P ₂ O ₅ is preferably 0 to 70%, more preferably 15 to 60%, and still more preferably 20 to 55%. When the content of P ₂ O ₅ is too large, the oxide becomes water resistance is likely to decrease in the component, the cycle characteristics tend to be lowered.

Incidentally, the content of SiO ₂ is 0 to 75%, more preferably from 0% to 70%, more preferably from 0 to 67%. The content of B ₂ O ₃ is preferably 0 to 75%, more preferably 0 to 70%, and still more preferably 0 to 67%.

  The oxide component may be either crystalline or amorphous, and both may coexist.

The crystals are Li ₃ PO ₄ , Li ₄ P ₂ O ₇ , LiPO ₃ , Li ₄ SiO ₄ , Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ , Li ₆ B ₂ O ₆ , Li ₆ B ₄ O ₉ , At least one selected from Li ₂ B ₄ O ₇ and Li ₂ B ₂ O ₄ is preferable. Among these, Li ₃ PO ₄ , Li ₄ SiO ₄ and Li ₆ B ₂ O ₆ having excellent lithium ion conductivity are more preferable, Li ₃ PO ₄ and Li ₄ SiO ₄ are more preferable, and Li ₃ PO ₄ is particularly preferable.

  The metal Si includes not only a metal made of Si alone but also an alloy containing Si metal.

  The negative electrode active material for an electricity storage device of the present invention preferably contains a carbon component. By including a carbon component having excellent electron conductivity, the discharge capacity of the negative electrode active material tends to increase.

  The carbon component is composed of conductive carbon black such as acetylene black and ketjen black, carbon powder such as graphite, carbon fiber, and the like. Of these, acetylene black having a high electron conductivity is preferable.

  The negative electrode active material for an electricity storage device of the present invention preferably contains 10 to 80% by mass of metal Si 10 to 80%, oxide component 20 to 90%, carbon component 0 to 20%, metal Si 25 to 70%, oxidized It is more preferable to contain 29-74% of physical components and 1-10% of carbon components. With the above configuration, the cycle characteristics can be improved without reducing the discharge capacity and the initial charge / discharge efficiency.

  The shape of the negative electrode active material for an electricity storage device of the present invention is not particularly limited, but is preferably a powder.

  When the shape of the negative electrode active material for an electricity storage device of the present invention is powder, the average particle size is preferably 0.1 to 20 μm, more preferably 0.2 to 15 μm, and 0.3 to 10 μm. More preferably, it is particularly preferably 0.5 to 5 μm. The maximum particle size is preferably 150 μm or less, more preferably 100 μm or less, further preferably 75 μm or less, and particularly preferably 55 μm or less. If the average particle size or maximum particle size is too large, the volume change of the negative electrode active material associated with insertion and extraction of lithium ions during charge / discharge cannot be mitigated, and it will be easy to peel off from the current collector, resulting in a significant decrease in cycle characteristics. Tend to. On the other hand, if the average particle size is too small, the powder is in a poorly dispersed state when formed into a paste, and it tends to be difficult to produce a uniform electrode. In addition, since the specific surface area becomes too large and the negative electrode active material powder is difficult to disperse when producing a paste for forming an electrode, a large amount of binder and solvent are required. Furthermore, it is inferior to the applicability of the electrode forming paste, and it becomes difficult to form a negative electrode having a uniform thickness.

  Here, the average particle size and the maximum particle size are D50 (50% volume cumulative diameter) and D90 (90% volume cumulative diameter), respectively, in terms of the median diameter of primary particles, and were measured by a laser diffraction particle size distribution analyzer. Value.

  The method for producing a negative electrode active material for an electricity storage device of the present invention includes a step of mechanically milling a mixed raw material containing metal Si and an oxide raw material, wherein the oxide raw material is at least one selected from P, Si and B It contains an oxide raw material of an element and an oxide raw material of Li.

  By carrying out the mechanical milling treatment, high impact energy can be given to the mixed raw material. Due to the high impact energy, it becomes easy for the surface of the metal Si serving as a lithium ion occlusion / release site to be coated with an oxide component or to be dispersed between the metal Si.

  For the mechanical milling process, a general pulverizer such as a mortar, a rake machine, a ball mill, an attritor, a vibration ball mill, a satellite ball mill, a planetary ball mill, a jet mill, or a bead mill can be used. In particular, it is preferable to use a planetary ball mill. The planetary ball mill can efficiently generate very high impact energy by rotating the platform while the pot rotates.

  Furthermore, the mixed raw material preferably contains a carbon raw material. By containing the carbon raw material, as described above, the discharge capacity of the negative electrode active material is increased, and the formation of aggregates can be prevented when mechanically milling the mixed raw material containing the metal Si and the oxide raw material. This makes it possible to produce the negative electrode active material in a shorter time.

  The mechanical milling treatment is preferably performed in a non-oxidizing atmosphere. By setting it as a non-oxidizing atmosphere, the oxidation of metal Si can be suppressed. The non-oxidizing atmosphere includes a reducing atmosphere and an inert atmosphere.

In order to obtain a reducing atmosphere, it is preferable to supply a reducing gas during the mechanical milling process. The composition of the reducing gas, by _volume%, N 2 90 to _99.5%, it is preferable to use a mixed gas containing _{H 2 0.5~10%, N 2 92~99} %, H 2 1 More preferably, a mixed gas containing ˜4% is used.

  In order to obtain an inert atmosphere, it is preferable to supply an inert gas during the mechanical milling process. As the inert gas, it is preferable to use any of nitrogen, argon, and helium.

  A negative electrode material for an electricity storage device can be obtained by adding a binder or a conductive additive to the negative electrode active material for an electricity storage device of the present invention.

  Examples of the binder include cellulose derivatives such as carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, ethylcellulose, hydroxymethylcellulose, and water-soluble polymers such as polyvinyl alcohol; thermosetting polyimide, phenolic resin, epoxy resin, urea Examples thereof include thermosetting resins such as resins, melamine resins, unsaturated polyester resins, and polyurethanes; polyvinylidene fluoride.

  Examples of the conductive assistant include conductive carbon black such as acetylene black and ketjen black, carbon powder such as graphite, and carbon fiber.

  The negative electrode material for an electricity storage device can be used as an anode for an electricity storage device by applying it to the surface of a metal foil or the like that serves as a current collector.

  In addition, after charging / discharging the electrical storage device produced using the negative electrode active material of this invention, metal lithium, lithium oxide (an oxide, such as a silicic acid, phosphoric acid, boric acid, and a lithium atom are contained in a negative electrode active material. Oxide (including complexed lithium composite oxide), Si metal, Si-Li alloy, and the like may be included.

  The negative electrode active material of the present invention is not only a lithium ion secondary battery, but also other nonaqueous secondary batteries, and further, a negative electrode active material for lithium ion secondary batteries and a positive electrode active material for nonaqueous electric double layer capacitors. It can also be applied to a hybrid capacitor combined with a substance.

  A lithium ion capacitor, which is a hybrid capacitor, is one type of asymmetric capacitor that has different charge / discharge principles for a positive electrode and a negative electrode. The lithium ion capacitor has a structure in which a negative electrode for a lithium ion secondary battery and a positive electrode for an electric double layer capacitor are combined. Here, the positive electrode forms an electric double layer on the surface and is charged / discharged by utilizing a physical action (electrostatic action), whereas the negative electrode has a lithium ion chemistry similar to the lithium ion secondary battery described above. Charge and discharge by reaction (occlusion and release).

  For the positive electrode of the lithium ion capacitor, a positive electrode active material made of carbonaceous powder having a high specific surface area such as activated carbon, polyacene, or mesophase carbon is used. On the other hand, the negative electrode active material of the present invention can be used for the negative electrode.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to this Example.

(1) Production of negative electrode active material The negative electrode active materials of Examples 1 to 7 and Comparative Example 1 are mixed raw materials composed of metal Si, an oxide raw material, and acetylene black which is a carbon raw material, as shown in Tables 1 and 2. the weighed such that the weight%, placed in a _ZrO 2 1 kg of the mixed raw material 30g and φ5mm in 500 mL ZrO ₂ pots, a planetary ball mill: using (device name Fritch Co. P6), under Ar atmosphere, It produced by carrying out the mechano-milling process for 40 hours (Examples 1-4 and Comparative Example 1) or 20 hours (Examples 5-7) with the revolution speed of 370 rpm.

  The negative electrode active material of Comparative Example 2 was SiO powder.

  The structure of the obtained negative electrode active material was identified by powder X-ray diffraction measurement. The results are shown in Table 1.

(2) Production of negative electrode The obtained negative electrode active material, conductive additive and binder were weighed to a mass ratio of 80: 5: 15, dispersed in dehydrated N-methylpyrrolidone, and then rotated. -It stirred sufficiently with the revolution mixer and was made into the slurry. Here, conductive carbon black (SuperC65, manufactured by Timcal) was used as the conductive auxiliary agent, and thermosetting polyimide resin was used as the binder.

  Next, using a doctor blade with a gap of 75 μm, the obtained slurry was coated on a 20 μm thick copper foil as a negative electrode current collector, vacuum-dried with a dryer at 70 ° C., and then between a pair of rotating rollers. An electrode sheet was obtained by pressing through. This electrode sheet was punched to a diameter of 11 mm with an electrode punching machine and dried under reduced pressure at a temperature of 200 ° C. for 8 hours to obtain a circular working electrode (a negative electrode for a non-aqueous secondary battery).

(3) Production of test battery Next, the obtained negative electrode was placed on the lower lid of the coin cell with the copper foil surface facing down, and dried on the top at 70 ° C. under reduced pressure for 8 hours. A test battery was manufactured by laminating a separator made of a membrane (Cellguard # 2400 manufactured by Hoechst Celanese) and metallic lithium as a counter electrode. As the electrolytic solution, 1M LiPF ₆ solution / EC: DEC = 1: 1 (EC = ethylene carbonate, DEC = diethyl carbonate) was used. The test battery was assembled in an environment with a dew point temperature of −40 ° C. or lower.

(4) Charge / Discharge Test The amount of electricity charged to the negative electrode active material of unit mass by performing CC (constant current) charge (lithium ion occlusion in the negative electrode active material) from 1 V to 0 V at 30 ° C. (Charge capacity) was determined. Next, CC discharge (lithium ion release from the negative electrode active material) was performed from 0 V to 1 V, and the amount of electricity (discharge capacity) discharged from the negative electrode active material of unit mass was obtained. The C rate was 0.5C. Table 2 shows the results of the charge / discharge characteristics. The initial charge / discharge efficiency is the ratio of the initial discharge capacity to the initial charge capacity, and the discharge capacity maintenance ratio is the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity.

  In Examples 1 to 7, the initial discharge capacity is 817 mAh / g or more, the initial charge / discharge efficiency is 61% or more, the discharge capacity maintenance rate is 51% or more, the capacity is high, the initial charge / discharge efficiency is excellent, and the cycle performance is also good. Met. On the other hand, in Comparative Examples 1 and 2, the discharge capacity retention rate was as high as 79% or more, but the initial discharge capacity was 586 mAh / g or less, and the initial charge / discharge efficiency was as low as 46% or less.

  The negative electrode active material for power storage devices of the present invention is suitable as a negative electrode active material for power storage devices used for portable electronic devices, electric vehicles, electric tools, backup emergency power supplies, and the like.

Claims (6)

  A negative electrode active material for an electricity storage device, comprising metal Si and an oxide component, wherein the oxide component includes an oxide of at least one element selected from P, Si and B, and an oxide of Li.   The negative electrode active material for an electricity storage device according to claim 1, wherein the surface of the metal Si has a structure coated with the oxide component.   The negative electrode active material for an electricity storage device according to claim 1, comprising a carbon component.   The negative electrode active material for an electricity storage device according to any one of claims 1 to 3, comprising 10 to 80% of metal Si, 20 to 90% of an oxide component, and 0 to 20% of a carbon component in mass%.   Including a step of mechanical milling a mixed raw material including metal Si and an oxide raw material, wherein the oxide raw material includes an oxide raw material of at least one element selected from P, Si and B, and an oxide raw material of Li The manufacturing method of the negative electrode active material for electrical storage devices characterized by the above-mentioned. The method for producing a negative electrode active material for an electricity storage device according to claim 5, wherein the mechanical milling treatment is performed in a non-oxidizing atmosphere.