JP2005353330A - Nonaqueous electrolyte electrochemical cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte electrochemical cell of 3V level with large discharge capacity, excellent in safety and cycle property. <P>SOLUTION: In the nonaqueous electrolyte electrochemical cell provided with a cathode, an anode, and a nonaqueous electrolyte, the cathode contains a cathode activator of 5V level, the anode contains an anode activator composed of at least one kind of element chosen from nickel, cobalt and manganese. In the case that the anode activator contains nickel and manganese, and the number of molecules of the nickel and manganese are denoted as α, β respectively, the molar ratio α/β is not less than 1. Further, in the case that the anode activator additionally contains lithium, and the ratio of the number of lithium molecules to that of nickel and cobalt in the activator is denoted as γ, the relation; 0.9≤γ≤1 is fulfilled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a 3V class non-aqueous electrolyte electrochemical cell.

  In recent years, with the development of portable electronic devices such as mobile phones and video cameras, electric tools, HEV, EV, and the like, development of high-performance batteries has been desired. Lithium batteries using lithium transition metal composite oxide for the positive electrode and graphite and amorphous carbon for the negative electrode are widely put into practical use as non-aqueous electrolyte batteries with high operating voltage and high energy density. In order to obtain a non-aqueous electrolyte secondary battery with higher energy density, there are a method of increasing the specific capacity (capacity per unit weight) of the active material and a method of increasing the voltage.

Therefore, for example, in Patent Document 1, a lithium / nickel / manganese composite oxide, which is a 5V class positive electrode active material that exhibits a flat charge / discharge potential in a potential range of about 5 V (vs. Li ^/ Li ⁺ ) based on a lithium reference electrode A product (LiNi _0.5 Mn _1.5 O ₄ ) has been proposed. However, as described in Patent Document 2, in a battery including a positive electrode including the lithium / nickel / manganese composite oxide and a negative electrode including graphite, the voltage is high (the positive electrode side has a noble potential, On the negative electrode side, there is a problem that the electrolyte solution is decomposed to generate gas and the battery not only swells but also the battery performance deteriorates, making it difficult to put it to practical use.

  Here, “5V class” means a battery in which the flat portion (plateau portion) of the discharge voltage shows about 5V. The designations “5V class”, “4V class”, and “3V class” are, for example, JP 2001-43859 A, JP 2001-52737 A, JP 2001-185148 A, and JP 2001-256966 A. As described in publications and the like, it is a term generally used to indicate the discharge voltage of a non-aqueous secondary battery.

On the other hand, it is speculated that the demand for 3V class non-aqueous electrolyte secondary batteries will increase in the future from the viewpoint of the development of ICs that operate at a low voltage of 3 V or less and the safety of the batteries. Commonly known positive electrode active materials for 3V class non-aqueous electrolyte secondary batteries include MnO ₂ and V ₂ O ₅ . Since these active materials do not contain lithium, metallic lithium or a lithium alloy must be used for the counter electrode. On the other hand, although a layered lithium manganese composite oxide (LiMnO ₂ ), which is a 3V class active material, has been attracting attention, it becomes easy to spinel with charge / discharge, resulting in a two-stage discharge. Further, all of the above 3V class positive electrode active materials had poor cycle performance.

On the other hand, Patent Documents 3 to 5 and Non-Patent Documents 1 to 3 report that transition metal oxides can also be used for the negative electrode active material. Patent Document 3 discloses a technique using iron oxide (FeO, Fe ₂ O ₃ , Fe ₃ O _4, etc.) or cobalt oxide (CoO, Co ₂ O ₃ , Co ₃ O _4, etc.) as a negative electrode active material. .

In Patent Document 4, as a negative electrode active material, various transition metal oxides containing or not containing lithium, for example, Li _x M _q V _1-q O _j (where M is a transition metal, x is 0. 17 ≦ x ≦ 11.25, 0 ≦ q ≦ 0.7, 1.3 ≦ j ≦ 4.1) and a production technique thereof are disclosed.

  Patent Document 5 discloses a technique of inserting lithium ions electrochemically with the particle size of the transition metal oxide negative electrode active material, the firing conditions, and electrochemically.

Non-Patent Document 1 discloses characteristics and reaction mechanisms of transition metal oxides such as CoO, Co ₃ O ₄ , NiO, FeO, and Cu ₂ O as negative electrode active materials. These transition metal oxides showed a discharge capacity of 700 mAh / g or more, and it was confirmed that Li ₂ O was produced and nano-sized transition metals were present during charging. It has also been reported that the cycle performance of cobalt oxide was good.

  Non-Patent Document 2 reports a technique for producing lithium-containing transition metal oxides and sulfides by a mechanical milling method, and the maximum initial discharge capacity of the obtained mixture is 600 mAh / g or more. Was inferior.

  Non-Patent Document 3 reports negative electrode active materials composed of lithium-containing Ni, Co, and Mn ternary transition metal oxides, and these transition metal oxides exhibit a discharge capacity of about 700 mAh / g.

These transition metal negative electrode active materials have a large discharge capacity, and show an average discharge potential of 1 to 2.0 V (vs. Li / Li ⁺ ). However, these documents did not disclose or suggest the application of the transition metal oxide to the negative electrode active material of the 3V class non-aqueous electrolyte battery and improvement of safety.

JP 2002-42814 A JP-A-11-219722 Japanese Patent Laid-Open No. 03-291862 Japanese Patent No. 3242751 Japanese Patent Laid-Open No. 07-14581 P. Poizot, S.M. Laruelle, S.M. Grugeon, L .; Dupont, and J.M. M.M. Tarascon, Nature, 407, 496-499 (2000) M.M. Dolle, P.M. Poizot, L.M. Dupont, and J.M. M.M. Tarascon, Electrochemical and Solid-state Letters, 5, A70-A73 (2002) Liu, Yasuda, Yamachi, 44th Battery Conference Proceedings, P114, 3A18 (2003)

  The safety of a conventional 5V class non-aqueous electrolyte secondary battery using a 5V class positive electrode active material is low, and the charge / discharge cycle performance of the conventional 3V class non-aqueous electrolyte secondary battery is insufficient. Accordingly, an object of the present invention is to provide a novel 3V class non-aqueous electrolyte electrochemical cell having a large discharge capacity and excellent both safety and cycle performance.

  As a result of our earnest research, by using a 5V class positive electrode active material for the positive electrode and a negative electrode active material made of an oxide of at least one element selected from the group consisting of nickel, cobalt and manganese for the negative electrode, It has been found that a novel 3V non-aqueous electrolyte electrochemical cell excellent in both safety and cycle performance can be obtained.

  The invention of claim 1 is a non-aqueous electrochemical cell comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a 5V class positive electrode active material, and the negative electrode is selected from the group consisting of nickel, cobalt and manganese. It contains a negative electrode active material made of an oxide of one kind of element.

  According to a second aspect of the present invention, in the nonaqueous electrolyte electrochemical cell, when the negative electrode active material contains nickel and manganese, and the molar numbers of the nickel and manganese are α and β, respectively, the molar ratio α / β is 1. It is the above.

  The invention according to claim 3 is the nonaqueous electrolyte electrochemical cell, wherein the negative electrode active material further contains lithium, and the ratio of the number of moles of lithium to the total number of moles of nickel, cobalt and manganese in the negative electrode active material is γ In this case, 0.9 ≦ γ ≦ 1.

  The invention of claim 4 is characterized in that, in the non-aqueous electrolyte electrochemical cell, a low crystalline carbon layer is formed on the surface of the negative electrode active material.

  By using a negative electrode active material composed of an oxide of at least one element selected from the group consisting of nickel, cobalt and manganese as a positive electrode and a negative electrode as in the present invention, an excellent discharge potential, A 3V class non-aqueous electrolyte electrochemical cell exhibiting a large discharge capacity and excellent cycle performance is obtained.

  According to claim 2, since a resource-rich oxide containing nickel and manganese is used for the negative electrode active material, a low-cost nonaqueous electrolyte electrochemical cell can be obtained, and the molar ratio of Ni and Mn By specifying, a 3V class non-aqueous electrochemical cell with improved cycle performance can be obtained.

  According to the third aspect of the present invention, a 3V class non-aqueous electrolyte electrochemical cell having a low negative electrode irreversible capacity, excellent cycle performance and high energy density can be obtained.

  According to the fourth aspect of the present invention, poor current collection performance due to expansion / contraction or pulverization of the negative electrode active material can be avoided, and a 3V class non-aqueous electrolyte electrochemical cell having excellent high rate discharge performance and cycle performance can be obtained. .

The nonaqueous electrolyte electrochemical cell of the present invention has a small amount of Mn _{2-YaO 4-δ} selected from the group consisting of a 5V class active material as the positive electrode active material and nickel, cobalt and manganese as the negative electrode active material (where 0 <X ≦ 1. An oxide of at least one element is used.In the present invention, the “5V class active material” means about 5 V (vs. Li) based on a lithium reference electrode. / Li ⁺ ) ≦ Y ≦ 0.55, 0 ≦ δ ≦ 0.4), and is a positive electrode active material exhibiting a flat charge / discharge potential in a potential range, and “non-aqueous electrolyte electrochemical cell” It means a lithium secondary battery or an electrochemical capacitor.

As the 5V class active material used for the positive electrode, a lithium / nickel / manganese spinel composite oxide or an olivine material can be used. Lithium / nickel / manganese spinel composite oxide may be LiCoPO ₄ , LiVOPO ₄ or the like as the general formula Li _{X + a} Ni _Y 0, 0 ≦ a ≦ 0.1, 0.45 olivine material.

  Such a combination of a positive electrode active material and a negative electrode active material can solve problems such as battery swelling, cycle deterioration, and safety that are peculiar to conventional batteries using a 5 V class positive electrode active material. . By using an oxide of at least one element selected from the group consisting of nickel, cobalt and manganese as the negative electrode active material, an electrochemical cell having a large discharge capacity and a continuously changing discharge potential can be obtained. . In particular, since the negative electrode active material used in the present invention continuously changes in discharge potential, an electrochemical cell having excellent pulse discharge and a large output can be obtained.

  Further, in order to obtain a non-aqueous electrolyte electrochemical cell that is cheaper and has excellent cycle performance, the negative electrode active material contains Ni and Mn, and the mole numbers of Ni and Mn are α and β, respectively. The ratio α / β is preferably 1 or more. This is because when the molar ratio α / β is 1 or more, not only the discharge capacity is large but also the cycle performance is excellent.

  As the negative electrode active material satisfying this condition, a mixture or solid solution of nickel oxide and manganese oxide can be used, but in order to obtain continuous potential change characteristics and excellent cycle performance, Ni and By using a solid solution in which Mn is mixed at the atomic level, an electrochemical cell having better cycle performance can be obtained.

  In addition, when a composite oxide obtained by heating an oxyhydroxide containing Ni and Mn at a temperature of 250 ° C. or higher and 800 ° C. or lower is used, the performance improvement effect of the active material appears more remarkably. The reason is that adsorbed water and crystal water are removed from the active material by heat treatment, and as a result, cycle performance is significantly improved.

  Moreover, you may contain lithium in the oxide used for the negative electrode active material of this invention. The lithium content is preferably 0.9 ≦ γ ≦ 1, where γ is the ratio of the number of moles of lithium to the total number of moles of nickel, cobalt, and manganese in the negative electrode active material.

Because, if γ is smaller than 0.9, the irreversible capacity is large and it is difficult to obtain a high-energy cell, and if γ is larger than 1, the active material is unstable in the air, which is inactive. This is because Li ₂ O and Li ₂ CO ₃ are generated.

  Furthermore, it is preferable that a low crystalline carbon layer is formed on the surface of the oxide particles used in the negative electrode active material of the present invention. By forming low crystalline carbon on the surface of the negative electrode active material particles, it not only suppresses the growth of the coating on the surface of the negative electrode active material particles, but also suppresses poor current collection due to expansion / contraction or pulverization of the active material. You can also. Note that “a low crystalline carbon layer is formed on the oxide surface” means that the oxide particle surface is coated with the low crystalline carbon layer or the oxide particle surface is coated with the low crystalline carbon layer. And a case where a low crystalline carbon layer is provided on the surface of the electrode.

  As a method for forming a carbon material on the surface of the negative electrode active material particles, benzene, toluene, xylene, methane, propane, butane, ethylene, or acetylene is decomposed in a gas phase using a carbon source, and the surface of the particles is chemically formed. It can be produced by a CVD method for vapor deposition, a method for baking after mixing with a thermoplastic resin such as pitch, tar or furfuryl alcohol, or a method using a mechanochemical reaction.

  Among these manufacturing methods, the CVD method is desirable. The reason is that according to the CVD method, low crystalline carbon can be formed on the surface of the negative electrode active material particles more uniformly and inexpensively, and the high-performance of a 3V class non-aqueous electrolyte electrochemical cell using this can be obtained. This is because improvement in rate discharge performance and cycle performance is expected.

  Further, as a method for producing an oxide used for the negative electrode active material of the present invention, an oxyhydroxide, preferably an oxyhydroxide having an average oxidation number of transition metal contained in the starting material, of less than 3 is used as a starting material. By oxidizing the transition metal until the average oxidation number becomes 3 or more, the effect of the present invention can be further extracted. When oxidized until the average oxidation number becomes 3 or more, a stable transition metal oxide is obtained. Otherwise, there is a danger that the oxide of the transition metal will phase separate.

  A coprecipitation method is preferred as a production method for mixing Ni, Co, and Mn contained in the oxide used for the negative electrode active material of the present invention at an atomic level. In the coprecipitation method, a hydroxide containing Ni, Co or Mn as a starting material is dispersed in an alkaline solution, oxidized with an oxidizing agent at a temperature of 40 to 60 ° C., and the precipitate is filtered and dried to obtain oxywater. An oxide can be obtained.

  In this coprecipitation method, when a hydroxide containing Ni, Co or Mn is dispersed in an LiOH aqueous solution and oxidized with an oxidizing agent at a temperature of 75 to 85 ° C., a part of protons contained in the oxyhydroxide is obtained. An oxyhydroxide containing Ni, Co or Mn exchanged with lithium ions is obtained.

  In the coprecipitation method, it is desirable to oxidize with an oxidizing agent while protecting with Mn or argon gas in order to prevent Mn from being easily oxidized to tetravalent. This not only provides an oxyhydroxide in which Ni, Co, and Mn are mixed at the atomic level, but also avoids the formation of “inert carbonates”.

Here, the “inert carbonate” refers to Li ₂ CO ₃ or a carbonate of Ni, Co, or Mn. Since these carbonates are insulative and have poor electrochemical activity, the characteristics of the electrochemical cell deteriorate when they are contained in the negative electrode active material.

  As the negative electrode active material of the present invention, an oxide containing at least one element selected from the group consisting of Ni, Co, and Mn obtained by the above production method may be used as it is. However, the irreversible capacity accompanying the reductive decomposition of the oxide immediately after production and the generation of the surface film is large, and as a result, it becomes difficult to obtain an electrochemical cell having a large energy density. Therefore, as described above, lithium may be introduced into the oxide as the negative electrode active material by an ion exchange reaction, but the ion exchange reaction is not effective in reducing the irreversible capacity.

Therefore, in order to reduce the irreversible capacity of the oxide negative electrode active material, suppress the growth of the surface film, or promote the amorphization, the transition metal oxide is partially reduced or completely reduced by an electrochemical or chemical method ( It is desirable to reduce the potential to 0.5 V (vs. Li ^/ Li ⁺ ) or less) and introduce a required amount of lithium. Furthermore, the above completely reduced oxide may be further oxidized by an electrochemical or chemical method. When the oxide as the negative electrode active material is oxidized by an electrochemical method, it is preferable to use a method of oxidizing to a potential of 3.5 V or less with respect to lithium.

  When the oxide used in the negative electrode active material of the present invention is electrochemically reduced in an organic electrolyte containing lithium ions, lithium can be introduced into the negative electrode, and the irreversible capacity can be reduced when a battery is produced. Can do. Furthermore, when the reduced compound is oxidized again, an amorphous compound having a small initial irreversible capacity is obtained. In addition, the method for producing an amorphized or nanosized transition metal oxide exemplified here is an electrochemical method, but it can also be reduced by an organic complex of Li, and a chemical method for extracting lithium with an organic solvent. good.

Furthermore, an electrode as a negative electrode active material is short-circuited in an electrolytic solution, or an electrode is prepared together with a lithium-containing transition metal nitride such as a lithium alloy powder or Li _2.5 Co _0.5 N powder, When brought into contact with the organic electrolyte, a local battery reaction occurs and a lithium-containing oxide can be produced. Further, a lithium-containing oxide can be prepared by bringing an oxide as a negative electrode active material into contact with an organic solution of lithium, for example, an organic solution such as butyl lithium for reaction.

  When the lithium-containing oxide thus obtained is further discharged (oxidation) using the electrochemical method as described above, for example, when the lithium-containing oxide contains Ni and Mn, the lithium-containing oxide is contained. To obtain a nanoparticle mixture that is not detectable by XRD analysis because the ratio of the number of moles of Li to the total number of moles of Ni and Mn contained in the oxide is 1 or less and the crystallite is smaller than the wavelength of X-rays Can do. The quantitative determination of lithium, manganese, nickel and other metal elements was performed by ICP analysis.

The oxide as the negative electrode active material used in the present invention includes those produced from the above oxyhydroxide, for example, CoO, Co ₃ O ₄ , Co ₂ O ₃ , NiO, MnO, MnO ₂ , Mn ₂ O. ₃ , Mn ₃ O _{4 and the} like. Further, as the negative electrode active material, these two or more kinds of oxides may be mixed and used, but a solid solution in which two or more elements are mixed at the atomic level is more desirable. Further, these oxides may contain typical nonmetallic elements such as N, P, F, Cl, Br, I, and S.

  Further, the oxide as the negative electrode active material used in the present invention can be from crystalline to amorphous, but amorphous is preferred for high rate discharge. The shape of these oxides may be powder, membrane, fiber, or porous body.

  As the conductive material of the negative electrode active material of the present invention, fine powders such as Cu, Ni, Ti, and Co can be used, but carbon materials such as acetylene black, amorphous carbon, graphite powder, carbon nanotube, and carbon nanophone are more. desirable. In order to mix the conductive material and the oxide as the negative electrode active material well, a mechanical milling method is desirable as a mixing method.

  Cu, Ni, Ti, Al, stainless steel, etc. can be used as the current collector material for the negative electrode. Examples of the form include a three-dimensional structure such as a sheet, a mesh, and a foam.

  As the positive electrode material used in the 3V class electrochemical cell of the present invention, it is necessary to use a 5V class active material. As the 5V class active material, lithium / nickel / manganese spinel composite oxide and olivine material can be used. From the viewpoint of cycle performance and discharge capacity, spinel type lithium / nickel / manganese spinel composite oxide Is preferred.

General formula Li _{X + a} Ni _Y Mn _2- YaO _4-δ (where 0 <X ≦ 1.0, 0 ≦ a ≦ 0.1, 0.45 lithium / nickel / manganese spinel composite oxide Specifically, for example, it can be synthesized by a solid phase method in which a compound serving as a lithium source, a manganese source, and a nickel source is mixed and calcined, or by a sol-gel method as disclosed in JP-T-2000-515672. Can also be synthesized.

  Examples of the lithium source include lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, lithium acetate, lithium bromide, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, and lithium oxalate. Lithium phosphate, lithium pyruvate, lithium sulfate, lithium oxide and the like.

  Examples of the manganese source include manganese dioxide, manganese oxide, manganese hydroxide, manganese carbonate, manganese nitrate, manganese sulfate, and manganese oxalate. Among these, manganese dioxide is particularly preferable.

  Furthermore, examples of the nickel source include nickel nitrate, nickel carbonate, and nickel oxide.

When the Mn site of LiMn ₂ O ₄ is replaced with Ni and the molar ratio Ni / Mn becomes 1/3, a positive electrode active material in which the high potential side discharge potential flat region exhibits a high potential of 4.5 V or more can be obtained. it can. Further, by replacing the Mn site of LiMn ₂ O ₄ with Li, the discharge potential flat portion in the 4V region can be reduced.

In addition, the general formula Li _{X + a} Ni _Y Mn _2- YaO _4-δ (where 0 <X ≦ 1.0, 0 ≦ a ≦ 0.1, 0.45 ≦ Y ≦ 0.55, 0 ≦ δ) In the lithium / nickel / manganese spinel composite oxide represented by .ltoreq.0.4), X indicating the proportion of Li changes by charge / discharge and becomes 1 at the time of full charge. On the other hand, if overdischarge occurs, the crystal structure of the lithium / nickel / manganese spinel composite oxide becomes unstable. Therefore, 0 <X ≦ 1.0 is preferable.

  a is the ratio of Li substituted at the Mn site. When a part of Mn is replaced with Li, the valence of Mn increases and the discharge potential flat portion in the 4V region becomes smaller. If a exceeds 0.1, the discharge capacity decreases, which is not preferable. Therefore, 0 ≦ a ≦ 0.1 is preferable.

  Y is the ratio of Ni substituted at the Mn site. If Y is less than 0.45, the flat portion of the discharge potential in the 5V region is not preferable. On the other hand, if Y exceeds 0.55, the valence of Ni ions changes from divalent to trivalent, so the discharge capacity in the 5V region decreases. Therefore, 0.45 ≦ Y ≦ 0.55 is preferable.

  Δ represents an oxygen vacancy in the crystal structure. As this increases by δ, the valence of Mn decreases and the potential flat portion in the 4V region increases. On the other hand, if δ exceeds 0.4, oxygen constituting the frame of the spinel structure is insufficient, so that the spinel structure may not be maintained, which is not preferable. Therefore, 0 ≦ δ ≦ 0.4 is preferable.

In addition, Li _{X + a} Ni _Y Mn _2- YaO _4-δ (where 0 <X ≦ 1.0, 0 ≦ a ≦ 0.1, 0.45 ≦ Y ≦ 0.55, 0 ≦ As long as δ ≦ 0.4) is included, other positive electrode active materials may be included.

  In the lithium-nickel-manganese spinel composite oxide, the lattice constant and the site occupancy of each atom are determined by Rietveld analysis of the diffraction pattern obtained by the powder X-ray diffraction method (see, for example, The Rietveld Method, ed. Young, Oxford University Press, Oxford (1993)). Rietveld analysis is a method for refining parameters related to crystal structure by fitting a powder diffraction pattern using X-rays and neutrons and a diffraction pattern calculated based on an assumed structural model.

  The non-aqueous electrolyte used in the non-aqueous electrolyte electrochemical cell of the present invention may be a non-aqueous electrolyte, a polymer electrolyte, a room temperature molten salt or ionic liquid, or a solid electrolyte.

  Solvents used for the non-aqueous electrolyte include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane. And polar solvents such as 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane and methyl acetate, and mixed solvents thereof.

Moreover, as a solute of the nonaqueous electrolytic solution, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiSCN, LiCF ₃ CO ₂ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF _2). Illustrative are salts such as CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (COCF ₂ CF ₃ ) ₂ or mixtures thereof.

  Furthermore, it is desirable to add various additives to the electrolyte. Examples of additives include vinylene carbonate and derivatives thereof, benzenes such as biphenyl and cyclohexylbenzene, sulfurs such as propane sultone, ethylene sulfide, hydrogen fluoride, triazole-based cyclic compounds, fluorine-containing esters, tetraethylammonium Fluoride hydrogen fluoride complexes or derivatives thereof, phosphazenes and derivatives thereof, amide group-containing compounds, imino group-containing compounds, or at least one selected from the group consisting of nitrogen-containing compounds.

  Hereinafter, the nonaqueous electrolyte secondary battery including the negative electrode active material and the positive electrode active material of the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples.

  Furthermore, considering the capacity balance between the positive and negative electrodes of the complete cell, the amount of charged electricity (including the irreversible capacity) was made the same. The discharge capacity of the cell is the value obtained by dividing the discharge capacity of each cycle by the total weight of the positive electrode mixture or negative electrode mixture (solid content = active material + conductive material + binder), that is, the positive electrode mixture or The discharge capacity per unit weight of the negative electrode mixture was evaluated.

[Examples 1 to 3 and Comparative Examples 1 and 2]
[Example 1]
Using _Ni 0.75 _{Mn 0.25} O _1.36 as the negative electrode active material. The method for synthesizing the negative electrode active material and the method for producing the negative electrode plate are as follows.

The ion-exchanged water was heated to 50 ° C., to replace the dissolved oxygen in _{N 2,} further _{N 2} is _Ni 0.75 _Mn 0.25 of Ni / Mn molar ratio 3/1 to the reaction pot being purged (OH) ₂ was dispersed, 1.2 equivalents of NaClO was added, and the mixture was stirred for 4 hours while maintaining 50 ° C. to be oxidized. Subsequently, the mixture was filtered with suction, washed three times with de-O ₂ deionized water, further dried at 60 ° C. for 12 hours, and then fired in air at 250 ° C. for 2 hours and 600 ° C. for 10 hours. There was thus obtained the negative electrode active material _Ni 0.75 _{Mn 0.25} O _1.36.

This negative electrode active material was pulverized and classified, and those having a particle size of 5 μm to 15 μm were used for the electrodes. The negative electrode active material 80 wt%, acetylene black 10 wt% as a conductive material, and polyvinylidene fluoride (PVdF) N-methyl-2-pyrrolidone (NMP) solution (PVdF solid content 10 wt%) as a binder were dried. After mixing in a room to make a paste, and applying as a current collector to one side of a 14 μm thick electrolytic copper foil so that the solid content is 2.3 mg / cm ² , it is vacuum dried at 150 ° C., Roll press was performed to produce a negative electrode plate having a thickness of 33 μm and a size of 30 mm × 40 mm. This was welded with a Ni lead having a width of 4 mm by an ultrasonic welding method to obtain a negative electrode plate A1.

The positive electrode plate was produced as follows. 90 wt% of spinel type lithium / manganese / nickel composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) as a positive electrode active material, ₄ wt% of acetylene black as a conductive agent, and 6 wt% of PVdF as a binder Mixing was performed, and NMP was appropriately added and dispersed to prepare a slurry. This slurry was uniformly applied to one side of an aluminum positive electrode current collector having a thickness of 20 μm, and the weight of the solid content was adjusted to 14.6 mg / cm ² . After drying, this was compression molded with a roll press. Further, a positive electrode plate having a thickness of 95 μm and a size of 30 mm × 40 mm was produced. An Al lead having a width of 4 mm was welded thereto by an ultrasonic welding method to obtain a positive electrode plate P1.

The positive electrode plate P1 and the negative electrode plate A1 are used one by one, and the positive electrode plate mixture layer and the negative electrode plate mixture layer face each other through a 22 μm thick polyethylene separator, and are fixed with PPS tape. Was an element. Further, this element was inserted into an envelope-type laminate case (size: 7 cm × 5 cm), and the lead side was thermally welded. Subsequently, 0.5 ml of a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate containing 1.0 M LiPF ₆ was injected under reduced pressure. Further, the opening end surface of the envelope-type laminate case opposite to the lead side was welded under reduced pressure. Thus, the electrochemical cell E1 of Example 1 was obtained.

[Example 2]
A positive electrode plate P2 was produced in the same manner as in Example 1 except that LiCoPO ₄ was used as the positive electrode active material. The electrochemical cell E2 of Example 2 was obtained in the same manner as in Example 1 by combining the positive electrode plate P2 and the negative electrode plate A1.

[Example 3]
A positive electrode plate P3 was produced in the same manner as in Example 1 except that LiVOPO ₄ was used as the positive electrode active material. The electrochemical cell E3 of Example 3 was obtained in the same manner as in Example 1 by combining the positive electrode plate P3 and the negative electrode plate A1.

[Comparative Example 1]
A positive electrode plate P4 was produced in the same manner as in Example 1 except that LiCoO ₂ was used as the positive electrode active material. The electrochemical cell X1 of Comparative Example 1 was obtained in the same manner as in Example 1 by combining the positive electrode plate P4 and the negative electrode plate A1.

[Comparative Example 2]
A negative electrode plate N1 was produced in the same manner as in Example 1 except that natural graphite was used as the negative electrode active material and the coating weight was 7.1 mg / cm ² . The electrochemical cell X2 of Comparative Example 2 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate N1.

  The electrochemical cells E1, E2, E3, X1, and X2 thus obtained were evaluated. Charging performed at a constant current of 3 mA up to 4.3 V and discharging performed at a similar current up to 1.7 V were repeated to obtain charge / discharge characteristics.

  The charge / discharge curve in the second cycle of the electrochemical cell E1 of Example 1 is shown in FIG. 1, and the charge / discharge curve in the second cycle of the electrochemical cell X1 of Comparative Example 1 is shown in FIG. 1 and 2, the charge / discharge current is 3 mA, the capacity on the horizontal axis indicates the capacity per unit weight of the negative electrode active material, symbols ● and ▲ indicate charge curves, and symbols ◯ and Δ indicate discharge curves. The contents of each electrochemical cell are shown in Table 1, and the measurement results are shown in Table 2. In addition, “capacity maintenance ratio” in Table 1 means the ratio (%) of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle.

  As can be seen from the results of Tables 1 and 2, the cell X1 of Comparative Example 1 has a low average discharge voltage of about 2V, and the cell X2 of Comparative Example 2 has a high average discharge voltage of about 4.5V. The retention rate was 50% or less, and cell swelling was observed.

  Compared to the cells of Comparative Examples 1 and 2, the cells E1 to E3 of Examples 1 to 3 have a large discharge capacity at the first cycle, an average discharge voltage of about 3 V, and a capacity retention rate of 85% or more. No cell swelling was observed. Thus, it was found that the electrochemical cell of the present invention is excellent in both discharge capacity and cycle performance.

On the other hand, the lithium nickel manganese spinel oxide positive electrode active material, in conventional cell X2 in which the graphite negative active material, a large cell swelling was observed, and the main component of gas has been found to be H _2. The cause is currently unknown.

[Examples 4 to 9]
[Example 4]
A negative electrode plate A2 was produced in the same manner as in Example 1 except that NiO was used as the negative electrode active material. The electrochemical cell E4 of Example 4 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate A2.

[Example 5]
A negative electrode plate A3 was produced in the same manner as in Example 1 except that CoO was used as the negative electrode active material. The electrochemical cell E5 of Example 5 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate A3.

[Example 6]
A negative electrode plate A4 was produced in the same manner as in Example 1 except that Mn ₂ O ₃ was used as the negative electrode active material. The electrochemical cell E6 of Example 6 was obtained in the same manner as Example 1 by combining the positive electrode plate P1 and the negative electrode plate A4.

[Example 7]
A negative electrode plate A5 was produced in the same manner as in Example 1 except that Ni _0.75 Co _0.25 O _1.1 was used as the negative electrode active material. The electrochemical cell E7 of Example 7 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate A5.

[Example 8]
A negative electrode plate A6 was produced in the same manner as in Example 1 except that Mn _0.50 Co _0.50 O _1.59 was used as the negative electrode active material. The electrochemical cell E8 of Example 8 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate A6.

[Example 9]
A negative electrode plate A7 was produced in the same manner as in Example 1 except that Ni _1/3 Mn _1/3 Co _1/3 O _1.29 was used as the negative electrode active material. The electrochemical cell E9 of Example 9 was obtained in the same manner as Example 1 by combining the positive electrode plate P1 and the negative electrode plate A7.

  The thus obtained electrochemical cells E4 to E9 were evaluated. Charging performed at a constant current of 3 mA up to 4.3 V and discharging performed at a similar current up to 1.7 V were repeated to determine the charge / discharge characteristics.

  The contents of the electrochemical cells of Examples 4 to 9 are shown in Table 3, and the measurement results are shown in Table 4. The “capacity maintenance ratio” in Table 4 was the same as in Table 2. Table 3 and Table 4 also show the results of the cell E1 of Example 1 for comparison. Further, in all the electrochemical cells of Examples 4 to 9, no cell swelling was observed.

  From the results in Table 3 and Table 4, except for Example 6, as long as the negative electrode active material is an oxide of at least one element selected from the group consisting of nickel, cobalt and manganese, 1 of nickel, cobalt and manganese In either case, the oxide consisting of only the seed, the oxide containing two kinds, or the oxide containing all three kinds, the discharge capacity at the first cycle is 90 mAh / g or more, the average discharge voltage is about 3 V, the capacity It was found that an electrochemical cell having excellent characteristics with a maintenance rate exceeding 80% can be obtained.

Further, in the cell E6 using Mn ₂ O ₃ as the negative electrode active material of Example 6, the average voltage was high, but the discharge capacity and the capacity retention rate were slightly small.

[Examples 10 to 13]
[Example 10]
According to the same manufacturing method as in Example 1, when the negative electrode active material is an oxide containing nickel and manganese and the composition is expressed by Ni _α Mn _β O _m , α = 0.95, β = 0.05, manganese A negative electrode active material having a molar ratio of nickel to (α / β) = 19 was prepared, and a negative electrode plate A8 using the negative electrode active material was prepared. The electrochemical cell E10 of Example 10 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate A8.

[Example 11]
When the negative electrode active material is an oxide containing nickel and manganese and the composition is expressed as Ni _α Mn _β O _m by the same production method as in Example 1, α = 0.85, β = 0.15, manganese A negative electrode active material in which the molar ratio of nickel to (α / β) = 5.7 was produced, and a negative electrode plate A9 using this was produced. The electrochemical cell E11 of Example 11 was obtained in the same manner as Example 1 by combining the positive electrode plate P1 and the negative electrode plate A9.

[Example 12]
When the negative electrode active material is an oxide containing nickel and manganese and the composition is expressed as Ni _α Mn _β O _m by the same production method as in Example 1, α = 0.50, β = 0.50, manganese A negative electrode active material having a molar ratio of nickel to (α / β) = 1 was prepared, and a negative electrode plate A10 using the negative electrode active material was prepared. The electrochemical cell E12 of Example 12 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate A10.

[Example 13]
When the negative electrode active material is an oxide containing nickel and manganese and the composition is expressed as Ni _α Mn _β O _m by the same manufacturing method as in Example 1, α = 0.45, β = 0.55, manganese A negative electrode active material having a molar ratio of nickel to (α / β) = 0.81 was produced, and a negative electrode plate A11 was produced using this. The electrochemical cell E13 of Example 13 was obtained in the same manner as in Example 1 by combining the positive electrode plate P1 and the negative electrode plate A11.

  The electrochemical cells E10 to E13 thus obtained were evaluated. Charging performed up to 4.3 V at a constant current of 3 mA and discharging performed up to 1.7 V at the same current density were repeated to obtain charge / discharge characteristics.

  The contents of the electrochemical cells of Examples 10 to 13 are shown in Table 5, and the measurement results are shown in Table 6. The “capacity maintenance ratio” in Table 6 was the same as in Table 2. Tables 5 and 6 also show the results of the cell E1 of Example 1 for comparison. In all of the electrochemical cells of Examples 10 to 13, no cell swelling was observed.

  From the results in Tables 5 and 6, the discharge capacity and the capacity retention rate were slightly reduced in the cell E13 of Example 13 in which the value of α / β was smaller than 1. In the cells E1, E10 to E13 according to the present invention, it is found that the cell voltage increases as the content of Mn in the negative electrode active material increases (as the value of α / β decreases). It was. This is because manganese oxide undergoes a redox reaction at a relatively low potential.

  Furthermore, in the cells of Examples 1 and 10 to 13, since no cell swelling was observed, there was almost no gas generation due to the decomposition of the electrolyte, and the cell of the present invention was more than the conventional cell using the 5V class positive electrode active material. I found it safe.

When the cells E1, E10 to E13 of the present invention were compared, the cell E1 showed the most excellent cell discharge specific capacity and cycle.
[Examples 14 to 16]
[Example 14]
The negative electrode active material A1 particles obtained in Example 1 (Ni _0.75 Mn _0.25 O _1.36 having a particle size of 5 μm to 15 μm) were subjected to CVD treatment at 720 ° C. using acetylene gas as a carbon source, and the negative electrode Acetylene black was formed on the surface of the active material A1 particles. As a result of performing TG measurement on the obtained composite particles of A1 particles and acetylene black, the mass content of carbon was 4.6 wt%.

Using this composite particle as a negative electrode active material, a negative electrode plate A12 was prepared with the same procedure and composition as in Example 1, and the weight of the solid content was 2 in order to make the net carrying amount of the active material the same as that of Example 1. 4 mg / cm ² . Furthermore, the electrochemical cell E14 of Example 14 was produced using the positive electrode plate P1 similarly to Example 1.

[Example 15]
By mixing the negative electrode active material A1 particles obtained in Example 1 with pitch and then firing at 800 ° C., low crystalline carbon is formed on the surface of the negative electrode active material A1 particles to obtain a negative electrode active material, Using this, a negative electrode plate A13 was produced in the same procedure and composition as in Example 1, and an electrochemical cell E15 of Example 15 was produced in the same manner as in Example 14 using the positive electrode plate P1.

[Example 16]
After the negative electrode active material A1 particles obtained in Example 1 were mixed with acetylene black, a low crystalline carbon was formed on the surface of the negative electrode active material A1 particles by a mechanochemical reaction to obtain a negative electrode active material. A negative electrode plate A14 was prepared by the same procedure and composition as in Example 14, and an electrochemical cell E16 of Example 16 was produced in the same manner as in Example 14 using the positive electrode plate P1.

  In Examples 14 to 16, since the carbon formed on the surface of the negative electrode active material A1 particles is all heated at a temperature of 800 ° C. or lower, graphitization does not occur, and these carbons are low crystalline. It is clear that it is a sexual carbon.

  About the electrochemical cells E14-E16 of Examples 14-16, the same measurement as Example 1 was performed. The contents of the electrochemical cells of Examples 14 to 16 are shown in Table 7, and the measurement results are shown in Table 8. In all of the electrochemical cells of Examples 14 to 16, no cell swelling was observed. In Tables 7 and 8, the results of the cell E1 of Example 1 are also shown for comparison.

When the first cycle discharge capacity and cycle performance of the cells E14 to E16 of Examples 14 to 16 were compared with the cell E1 of Example 1, the discharge capacity was slightly reduced, but the cycle performance was greatly improved. Therefore, it has been found that forming low crystalline carbon on the surface of the negative electrode active material is an extremely effective means for improving the cycle performance of the negative electrode. Moreover, cell E1 of Examples 14-16
Among 4-E16, the cycle performance of the cell E14 of Example 14 was the best. Accordingly, it was found that the CVD method is the most suitable method for forming low crystalline carbon on the surface of the negative electrode active material particles.

  Although only the negative electrode active material containing nickel and manganese is exemplified here, it has been separately confirmed that this CVD coating method is also effective for other negative electrode active materials of the present invention.

[Examples 17 to 22]
[Example 17]
Using the negative electrode active material used in Example 1, a negative electrode plate A15 was produced with the same paste composition as in Example 1 and a solid content coating weight of 1.59 mg / cm ² . In combination with the negative electrode plate A4 and the positive electrode plate P1, an electrochemical cell E17 of Example 17 was produced.

[Example 18]
Using the negative electrode plate A15 prepared in Example 17, a triode cell having a metal lithium electrode as a reference electrode was prepared, and in this triode cell, an electric amount of 200 mAh / g was applied to the negative electrode plate. A15 was reduced. The obtained negative electrode plate was designated as A16, and combined with the positive electrode plate P1, an electrochemical cell E18 of Example 18 was produced. Note that γ = 0.59 in the active material Li _γ Ni _0.75 Mn _0.25 O _1.36 included in the negative electrode plate A16.

[Example 19]
In the tripolar cell, a negative electrode plate A17 was produced in the same manner as in Example 18 except that the negative electrode plate A15 was reduced by energizing 304 mAh / g, and combined with the positive electrode plate P1. Nineteen electrochemical cells E19 were produced. Note that γ = 0.9 in the active material Li _γ Ni _0.75 Mn _0.25 O _1.36 included in the negative electrode plate A17.

[Example 20]
In the tripolar cell, a negative electrode plate A18 was prepared in the same manner as in Example 18 except that the negative electrode plate A15 was reduced by energizing 323.4 mAh / g, and combined with the positive electrode plate P1. An electrochemical cell E20 of Example 20 was produced. In the active material Li _γ Ni _0.75 Mn _0.25 O _1.36 contained in the negative electrode plate A18, γ = 1.0.

[Example 21]
In the tripolar cell, a negative electrode plate A19 was produced in the same manner as in Example 18 except that the negative electrode plate A15 was reduced by energizing an electric quantity of 500 mAh / g, and combined with the positive electrode plate P1. 21 electrochemical cells E21 were produced. Note that γ = 1.48 in the active material Li _γ Ni _0.75 Mn _0.25 O _1.36 contained in the negative electrode plate A19.

[Example 22]
In a three-electrode cell, a negative electrode plate A20 was produced in the same manner as in Example 18 except that the negative electrode plate 15 was reduced to 0.5 V on a lithium basis at a constant current of 3 mA and subsequently discharged to 3 V. In combination with the positive electrode plate P1, an electrochemical cell E22 of Example 22 was produced. Note that γ = 0.96 in the active material Li _γ Ni _0.75 Mn _0.25 O _1.36 contained in the negative electrode plate A20.

The contents of cells E40 to E45 of Examples 17 to 22 are shown in Table 9, and the measurement results are shown in Table 10. In Table 9, when the negative electrode active material is represented by Li _γ Ni _0.75 Mn _0.25 O _1.36 , γ represents the ratio of the number of moles of lithium to the total number of moles of nickel and manganese. In all of the electrochemical cells of Examples 17 to 22, no cell swelling was observed.

  As can be seen from the results of Table 9 and Table 10, Examples 18 to 22 using the negative electrodes A16 to A20 that have undergone an electrochemical reduction process, as compared with the cell E17 of Example 17 that uses the negative electrode A15 that has not undergone the reduction treatment. The specific discharge capacities of the cells E18 to E22 were large.

  In particular, it was found that the cells of Examples 19, 20 and 22 using a negative electrode active material having a γ value of 0.9 or more and 1 or less showed a large specific discharge capacity and an excellent cycle performance. . Among these, the cell E22 of Example 22 using the negative electrode active material A20 produced through an electrochemical reduction and oxidation process has the best cycle performance, and the ideal positive and negative electrodes are in a discharged state. It has been found that a cell can be fabricated.

The figure which shows the charging / discharging curve of the 2nd cycle of the electrochemical cell E1 of Example 1. FIG. The figure which shows the charging / discharging curve of the 2nd cycle of the electrochemical cell X1 of the comparative example 1. FIG.

Claims (4)

In a non-aqueous electrochemical cell comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, the positive electrode contains a 5V class positive electrode active material, and the negative electrode is an oxide of at least one element selected from the group consisting of nickel, cobalt and manganese A non-aqueous electrolyte electrochemical cell comprising a negative electrode active material comprising: 2. The nonaqueous electrolyte according to claim 1, wherein the negative electrode active material contains nickel and manganese, and the molar ratio α / β is 1 or more when the number of moles of nickel and manganese is α and β, respectively. Electrochemical cell. The negative electrode active material further contains lithium, and 0.9 ≦ γ ≦ 1 when the ratio of the number of moles of lithium to the total number of moles of nickel, cobalt, and manganese in the negative electrode active material is γ. The nonaqueous electrolyte electrochemical cell according to claim 1 or 2. 4. The nonaqueous electrolyte electrochemical cell according to claim 1, wherein a low crystalline carbon layer is formed on the surface of the negative electrode active material.

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