JP6549444B2 - Method of producing active material particles, active material powder material and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a method for producing active material particles for lithium ion secondary batteries, and an active material powder material composed of the active material particles.

  A lithium ion secondary battery is known which has positive and negative electrodes having a material (active material) capable of reversibly absorbing and desorbing lithium (Li), and which charges and discharges by lithium ions moving between the electrodes. ing. The lithium ion secondary battery is preferably used as a power source for vehicle mounting or as a power source for personal computers, portable terminals and the like.

As a representative example of an active material used for an electrode (typically, a positive electrode) of a lithium ion secondary battery, a composite oxide containing lithium and a transition metal element can be mentioned. For example, as a positive electrode active material, lithium cobalt complex oxide (LiCoO ₂ ), lithium nickel complex oxide (LiNiO ₂ ), lithium nickel cobalt manganese complex oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) Composite oxides having a layered structure such as are preferably used.

  Moreover, as a lithium ion secondary battery, JP-A-2011-119092 (Patent Document 1) has an active material particle having a perforated hollow structure (hollow portion, and a through hole connecting the hollow portion and the outside) A secondary battery using active material particles) is disclosed. Here, the active material particles are mixed in the form of a paste in a solvent (for example, N-methylpyrrolidone (NMP)) at a predetermined composition with the conductive material particles and the binder. Then, the paste is applied to a current collector, dried, and pressed to a predetermined thickness. As a result, a sheet-like electrode in which an active material layer containing hollow active material particles is applied to a current collector is obtained. When hollow active material particles are used, the electrolytic solution permeates not only around the active material particles but also through the through holes in the hollow portion (inside the active material particles) in the active material layer. Therefore, in the battery reaction, the release and storage of lithium ions are smoothly performed by the active material particles. As a result, the rise in resistance of the secondary battery can be suppressed to a low level, and the performance of high rate discharge and quick charge is improved.

JP, 2011-119092, A

  By the way, when forming an active material layer, the paste which mixed the active material particle with the solvent is apply | coated to a collector, and it dries. By the drying step, the solvent in the paste coating is volatilized to form an active material layer. According to the knowledge of the present inventor, the solvent may remain in the active material layer even after the drying step. In particular, when the number of the through holes is large among the hollow active material particles described above and the opening width is large, the solvent enters the inside (hollow part). Therefore, the solvent is less likely to be volatilized in the drying step, and the solvent is likely to remain in the active material particles. If the solvent remains in the active material particles, there is a possibility that the required output can not be exhibited in the low temperature range.

  Therefore, it is an object of the present invention to provide an active material powder material for a lithium ion secondary battery, which exhibits a performance suitable for increasing the output of the battery. Another object of the present invention is to provide a method of producing such active material particles.

  According to the present invention, there is provided a method of producing an active material particle having a perforated hollow structure. The active material particles have secondary particles in which a plurality of primary particles of lithium transition metal oxide are gathered, and a hollow portion formed inside the secondary particles. The secondary particle is formed with a through hole penetrating from the outside to the hollow portion. The active material particles can be suitably used as a constituent material of a lithium ion secondary battery. The above active material particle production method is a step of supplying ammonium ions to an aqueous solution (typically aqueous solution) of a transition metal compound to precipitate particles of a transition metal hydroxide from the aqueous solution (raw material hydroxide formation Process). Here, the aqueous solution contains a transition metal element constituting the lithium transition metal oxide. Moreover, the process (mixing process) of mixing the said transition metal hydroxide and a lithium compound, and preparing an unbaked mixture is included. The method further includes the step of firing the mixture in a temperature range of 700 ° C. to 1000 ° C. to obtain active material particles (baking step). And it is characterized by baking in a pressure atmosphere of 600MPa-900MPa in at least one copy of the above-mentioned calcination process.

  According to this manufacturing method, by baking while pressurizing in a pressure atmosphere of 600 MPa to 900 MPa, the opening width of the through holes of the active material particles can be suppressed to be small. Therefore, the solvent used at the time of electrode production does not easily enter the hollow portion through the through holes, and the residual solvent in the active material particles can be suppressed even after drying. Therefore, according to this configuration, an optimal lithium ion secondary battery in which the solvent remains in the active material particles can be suppressed. Such a secondary battery may be excellent in, for example, low temperature output performance.

  In a preferable embodiment of the manufacturing method disclosed herein, the pressure baking process includes an atmospheric pressure baking process of baking the mixture under an atmospheric pressure atmosphere, and a baked product obtained by the atmospheric pressure baking process at 600 MPa to And a pressure baking process of baking while pressurizing under a pressure atmosphere of 900 MPa. By carrying out pressure firing according to such a multistage pressure firing schedule, hollow active material particles having desired properties can be stably produced.

  Further, according to the present invention, as another aspect for achieving the above object, an active material powder material for a lithium ion secondary battery is provided. The active material particles constituting the active material powder material have secondary particles in which a plurality of primary particles of lithium transition metal oxide are collected, and a hollow portion formed inside the secondary particles. And the through-hole penetrated to the said hollow part from the exterior is formed in the said secondary particle. Here, the powder material has the following characteristics: when solidified by immersing and solidifying the powder material in a liquid epoxy resin adjusted to a viscosity of 4500 mPa · s (B-type viscometer, rotation speed 10 to 100 rpm), Resin filling number ratio X (%) determined from the total number A of active material particles appearing in the SEM image of the cut surface and the number B of active material particles in which the hollow portion is filled with the epoxy resin X = (100 × B / A) has 1 ≦ X ≦ 17.

  In the active material powder material having such a configuration, the opening width of the through holes of the active material particles making up the powder material is suppressed to a small value, and the solvent used at the time of electrode preparation hardly remains in the active material particles. Therefore, such active material particles may be used as an electrode (for example, a positive electrode) of a lithium ion secondary battery to provide a battery that stably exhibits higher performance. For example, a lithium ion secondary battery excellent in low temperature output performance can be constructed.

  In a preferable embodiment of the active material powder material disclosed herein, the resin filling number ratio X is 3 ≦ X ≦ 8. When the resin filling number ratio X is in the range, a lithium ion secondary battery having more excellent low temperature output performance can be realized.

  According to the present invention, there is also provided a lithium ion secondary battery using any of the active material powder materials disclosed herein. Such a lithium ion secondary battery typically comprises a positive electrode, a negative electrode and a non-aqueous electrolyte. And at least one of the positive electrode and the negative electrode (preferably the positive electrode) is a hollow active material-containing electrode having any one of the active material particles disclosed herein. The lithium ion secondary battery having such a configuration may have a small amount of residual solvent in the active material particles and may be excellent in low temperature output performance.

It is a figure which shows typically the active material particle used for one Embodiment. It is a figure which shows the manufacture flow of the active material particle which concerns on one Embodiment. It is a figure showing typically the battery composition concerning one embodiment. It is a figure for demonstrating the winding electrode body which concerns on one Embodiment. It is a graph which shows the relationship between the resin filling number ratio and the amount of residual solvents. It is a graph showing the relationship between the resin filling number ratio and the low temperature output

  Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Each drawing is drawn schematically and does not necessarily reflect the real thing. The matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be understood as the design matters of those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in the present specification and common technical knowledge in the field.

  In the present specification, the term "lithium ion secondary battery" refers to a secondary battery in which charge and discharge are realized by using lithium ions as electrolyte ions and transferring charges associated with lithium ions between positive and negative electrodes.

  The active material particles disclosed herein and the active material powder material composed of the active material particles can be applied to various lithium ion secondary batteries configured such that the particles can function as an electrode active material. Application to a lithium ion secondary battery provided with a liquid non-aqueous electrolyte (i.e. non-aqueous electrolyte) is particularly preferred. The above-mentioned active material particles can be used as a positive electrode active material or a negative electrode active material depending on the combination with the active material of the counter electrode. Among these, utilization as a positive electrode active material is more preferable.

  Hereinafter, the present invention will be described in more detail by way of example mainly applied to a positive electrode active material of a lithium ion secondary battery, but the scope of the present invention is not intended to be limited.

<Material of active material particles>
The material of the active material particles disclosed herein may be various lithium transition metal oxides capable of reversibly absorbing and desorbing lithium ions. For example, it may be a lithium transition metal oxide having a layered structure, a lithium transition metal oxide having a spinel structure, or the like used for a positive electrode of a general lithium ion secondary battery. As a preferable example of a lithium transition metal oxide having a layered crystal structure, a nickel-containing lithium composite oxide containing at least nickel as a constituent element can be mentioned. Such a nickel-containing lithium composite oxide may contain one or more metal elements other than Li and Ni (ie, a transition metal element other than lithium and nickel and / or a main metal element). For example, a nickel-containing lithium composite oxide containing nickel, cobalt and manganese as constituent elements may be used. Among these transition metal elements, a nickel-containing lithium composite oxide is preferable in which the main component is Ni, or Ni, Co, and Mn are contained in substantially the same proportion.

  Furthermore, in addition to these transition metal elements, one or more other elements may be contained as additional constituent elements (additional elements). Such additional elements include Group 1 (alkali metals such as sodium), Group 2 (alkaline earth metals such as magnesium and calcium), Group 4 (transition metals such as titanium and zirconium), Group 6 of the periodic table. Any of transition metals such as chromium and tungsten, group 8 (transition metals such as iron), group 13 (metals such as boron which is a metalloid element or metals such as aluminum) and group 17 (halogen such as fluorine) Can be included. As a typical example, Zr, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B and F are exemplified. In particular, a compound containing W and / or Zr as an additive element is preferable. By including W and / or Zr as an additive element, good battery performance can be exhibited more stably. These additional constituent elements may be added in a proportion of 20 mol% or less, preferably 10 mol% or less, of the constituent transition metal elements of nickel, cobalt and manganese.

As a preferable composition of the active material particles disclosed herein, the following general formula (I):
Li _{1 + m} Ni _p Co _q Mn _r M ¹ _s O ₂ (I);
The layered Ni containing Li oxide represented by these is illustrated. Here, in the above formula (I), M ¹ is ^one or two selected from the group consisting of W, Zr, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B and F. It may be more than. m may be a number satisfying 0 ≦ m ≦ 0.2 (preferably 0.05 ≦ m ≦ 0.2). p may be a number satisfying 0.1 ≦ p ≦ 0.9 (preferably 0.1 <p <0.9). q may be a number satisfying 0 ≦ q ≦ 0.5 (preferably 0.1 <q <0.4). r may be a number satisfying 0 ≦ r ≦ 0.5 (preferably 0.1 <r <0.4). s may be a number satisfying 0 ≦ s ≦ 0.2 (preferably 0 ≦ s ≦ 0.02, more preferably 0 <s ≦ 0.01). Here, typically, p + q + r + s = 1. In one aspect, 0 ≦ s <p. s may be substantially zero (ie, an oxide substantially free of M ¹ ).

  Preferred examples of the Ni-containing Li oxide include oxides containing at least Co and Mn (LiNiCoMn oxide). For example, LiNiCoMn oxide in which 0 <q ≦ 0.5 and 0 <r ≦ 0.5 in the above-mentioned formula (I) is preferable. The first element of Ni, Co and Mn (element contained most in atomic number conversion) may be any of Ni, Co and Mn. In a preferred embodiment, the first element is Ni. In another preferred embodiment, the content of Ni, Co and Mn is approximately the same in atomic number conversion.

  The active material particle 10 disclosed herein has a hollow structure having a secondary particle 12 and a hollow portion 14 formed inside the secondary particle 12 as shown in FIG. This is a perforated hollow active material particle 10 in which a through hole 16 penetrating to the hollow portion 14 is formed. The secondary particles 12 have a form in which primary particles 18 of a lithium transition metal oxide (preferably, a layered structure oxide, for example, a layered Ni-containing Li oxide) as described above are gathered.

  Further, the active material particles 10 are produced by being fired while being pressurized in a high pressure atmosphere of 600 MPa to 900 MPa in a pressurized firing step described later. Therefore, the number of the through holes 16 may be smaller and the opening width h may be narrower than the conventional perforated hollow active material particles not subjected to the pressure firing process.

<Opening width h of through hole>
In a preferred embodiment of the active material particles 10 disclosed herein, the average opening width h of the through holes 16 is 10 nm or more (preferably 20 nm or more). Here, the opening width h of the through hole 16 is a difference length in the narrowest portion of the path of the through hole 16 from the outside of the active material particle 10 to the hollow portion 14. The electrolytic solution can sufficiently enter the hollow portion 14 from the outside through the through holes 16 when the opening width h of the through holes 16 is 10 nm or more on average. Thereby, the effect of improving the battery performance of the lithium ion secondary battery can be more appropriately exhibited. The average aperture width h is preferably about 50 nm or more, and more preferably about 80 nm or more. On the other hand, when the average opening width h is too large, the solvent used at the time of electrode production (typically, when applying a paste obtained by mixing active material particles in a solvent onto a current collector and drying) is hollow through the through holes 16 Get into 14 Therefore, the solvent may remain in the active material particles 10 even after drying, and the battery performance (particularly, low temperature output performance) may be reduced. From the viewpoint of suppressing the remaining of the solvent, the average opening width h of the through holes 16 is preferably about 200 nm or less, more preferably 170 nm or less, and still more preferably 130 nm or less.

<Number of through holes>
The number of through holes 16 in the active material particle 10 is preferably about 20 or less (for example, 1 to 20) as an average per particle, and about 1 to 10 (for example, 1 to 3) It is more preferable that it is typically 1-2. If the average number of through holes is too large, the solvent used at the time of electrode production is likely to enter the hollow portion 14 through the through holes 16. Therefore, the solvent may remain in the active material particles 10 and the battery performance (particularly, low temperature output performance) may be reduced. According to the active material particles 10 having the preferable average number of through holes disclosed herein, the battery performance improvement effect (for example, the internal resistance is reduced by having the perforated hollow structure while suppressing the solvent remaining in the active material particles 10) Effect can be exhibited well and stably.

  The through hole 16 is preferably formed to connect the outside of the active material particle 10 and the hollow portion 14 in a relatively short path. In a preferred embodiment, 50% by number or more (more preferably 70% by number or more, for example 80% by number or more, or 90% by number) of the through holes 16 appearing in the cross section of the active material particles 10 may be obtained. Penetrates the outer shell of the active material particle 10 (that is, the portion separating the outer portion from the hollow portion 14) so that the hollow portion 14 can be linearly connected to the outside of the active material particle 10 through the through hole 16 . The through hole 16 having such a path shape is preferable because the electrolytic solution can easily enter and exit the hollow portion 14 through the through hole 16 because the flow path resistance is small. It is preferable that 50% by number or more (more preferably 75% by number or more, for example 90% by number or more) of through holes having a path shape penetrating the outer shell of the active material particle 10 almost perpendicularly and reaching the hollow portion 14. Active material particles 10 having an average of 1 to 20 (for example, 1 to 10) of such through holes 16 per particle are preferable.

  The characteristic values such as the average opening width h, the average number of through holes, and the path shape of the through holes are grasped, for example, by observing the cross section of the active material particles with an SEM (Scanning Electron Microscope: scanning electron microscope) be able to. For example, a sample obtained by solidifying active material particles or a material containing the active material particles (active material powder material) with a suitable resin (preferably a thermosetting resin) is cut at an appropriate cross section, and the cut surface thereof is gradually added. It is good to perform SEM observation while shaving. Alternatively, since the orientation (posture) of the active material particles can be generally assumed to be generally random in the above sample, the SEM observation results in a single cross section or a relatively small number of cross sections of about 2 to 10 places are statistically determined. The characteristic value can also be calculated by processing.

  In a typical aspect of the active material particles 10 disclosed herein, primary particles 18 constituting the secondary particles 12 are sintered to one another. Such active material particles 10 can be highly shape-maintaining (can be less likely to be broken; for example, may be reflected in high average hardness, high compressive strength, etc.). Therefore, according to such an active material particle 10, good battery performance can be exhibited more stably.

  In a preferred embodiment, in the portion surrounding the hollow portion 14 (i.e., the outer shell) of the secondary particles 12, excluding the portion of the through hole 16, the primary particles 18 constituting the secondary particles 12 are densely sintered There is. For example, in the SEM observation, it is preferable to sinter so that no gaps are substantially present at the grain boundaries of the primary particles 18. Such active material particles 10 are preferable because they can be particularly high in shape retention. In addition, according to the porous hollow active material particle 10 in which the primary particles 18 are sintered densely as described above (typically, at least dense enough to prevent passage of a general electrolytic solution), The places where the electrolyte can flow between the outside and the hollow portion 14 are limited to the places where the through holes 16 are present. This can be one factor in which the performance improvement effect of the lithium ion secondary battery is exhibited by the active material particles 10 disclosed herein.

<Average particle size>
The average particle size of the primary particles 18 constituting the active material particles 10 disclosed herein may be in the range of about 0.1 μm to 0.6 μm. Preferably, the primary particles 18 have an average particle size of about 0.2 μm to 0.5 μm. The average particle size of the primary particles can be determined by methods known in the art, such as surface SEM measurement of the active material. Moreover, it is preferable that the average particle diameter of the secondary particles 12 (here, the median diameter (D50) is referred to hereinafter. The same applies) is approximately 2 μm to 25 μm. According to the active material particles 10 having such a configuration, good battery performance can be exhibited more stably. From the viewpoint of improving the battery performance, the average particle diameter of the secondary particles 12 is more preferably approximately 3 μm or more. Also, from the viewpoint of the productivity of the active material particles, the average particle size is preferably about 25 μm or less, and more preferably about 15 μm or less (eg, about 10 μm or less). In a preferred embodiment, the average particle size of the secondary particles 12 is about 3 μm to 10 μm. The average particle diameter of the secondary particles 12 can be determined by a method known in the art, for example, measurement based on a laser diffraction scattering method.

<Method of manufacturing active material particles>
The perforated hollow active material particles disclosed herein can be produced through a raw material hydroxide production step S10, a mixing step S20 and a firing step S30 as shown in FIG. Specifically, the hydroxide of the transition metal is precipitated under appropriate conditions from an aqueous solution containing the transition metal element contained in the lithium transition metal oxide constituting the active material particles, and the transition metal hydroxide It can be produced by a method of mixing and calcining lithium and a lithium compound. Hereinafter, one embodiment of the method for producing an active material particle will be described in detail by taking as an example the case of producing a perforated hollow active material particle composed of a layered structure of LiNiCoMn oxide, but the application target of the production method is It is not intended that the present invention be limited to the perforated hollow active material particles.

<Raw material hydroxide production process S10>
The method for producing active material particles disclosed herein comprises the step of supplying ammonium ions (NH ₄ ⁺ ) to an aqueous solution of a transition metal compound to precipitate particles of transition metal hydroxide from the aqueous solution (raw material hydroxide Product generation step S10). Raw material water suitable for forming the perforated hollow active material particles disclosed herein by supplying NH ₄ ⁺ to an aqueous solution of transition metal compound and depositing particles of transition metal hydroxide from the aqueous solution Oxide particles (precursors) can be produced.

  The solvent (aqueous solvent) constituting the aqueous solution is typically water, and may be a mixed solvent containing water as a main component. As solvents other than water which comprises this mixed solvent, the organic solvents (lower alcohol etc.) which can be mixed uniformly with water are suitable. The aqueous solution of the transition metal compound (hereinafter also referred to as "transition metal solution") constitutes the lithium transition metal oxide according to the composition of the lithium transition metal oxide constituting the active material particles which is the production object. It contains transition metal elements (here, Ni, Co and Mn). For example, a transition metal solution containing one or more compounds capable of supplying Ni ions, Co ions and Mn ions in an aqueous solvent is used. As a compound to be a metal ion source of Ni, Co and Mn, a sulfate, nitrate, chloride or the like of the metal can be appropriately adopted. For example, a transition metal solution having a composition in which nickel sulfate, cobalt sulfate and manganese sulfate are dissolved in an aqueous solvent (preferably water) can be preferably used.

The NH ₄ ⁺ may be supplied to the transition metal solution, for example, in the form of an aqueous solution (typically, an aqueous solution) containing NH ₄ ⁺ , by supplying ammonia gas directly to the transition metal solution. These supply methods may be used in combination. An aqueous solution containing NH ₄ ⁺ can be prepared, for example, by dissolving a compound (ammonium hydroxide, ammonium nitrate, ammonia gas, etc.) that can be an NH ₄ ⁺ source in an aqueous solvent. In this embodiment, NH ₄ ⁺ is supplied in the form of an aqueous ammonium hydroxide solution (ie aqueous ammonia).

In a preferred embodiment, the raw material hydroxide production step has a pH of 12 or more (typically, pH 12 or more and 14 or less, for example, pH 12.2 or more and 13 or less) and an NH ₄ ⁺ concentration of 25 g / L or less (typically 3 to 3). The method may comprise the step of precipitating the transition metal hydroxide from the transition metal solution under the conditions of 25 g / L) (nucleation step). The pH and the NH ₄ ⁺ concentration can be adjusted by appropriately balancing the amounts of the ammonia water and the alkali agent (compound having an ability to make the solution alkaline). As the alkali agent, for example, sodium hydroxide, potassium hydroxide and the like can be used, typically in the form of an aqueous solution. An aqueous sodium hydroxide solution is used in this embodiment. In the present specification, the value of pH refers to a pH value based on a liquid temperature of 25 ° C.

In a preferred embodiment, the raw material hydroxide production step further comprises: a nucleus (typically in the form of particles) of the transition metal hydroxide precipitated in the nucleation step, having a pH of less than 12 (typically, 10 or more). Grow at 12 or less, preferably pH 10 or more and 11.8 or less, for example, pH 11 or more and 11.8 or less and NH ₄ ⁺ concentration of 1 g / L or more, preferably 3 g / L or more (typically 3 to 25 g / L) It may include a stage (particle growth stage). Usually, the pH of the particle growth stage is 0.1 or more (typically 0.3 or more, preferably 0.5 or more, for example, about 0.5 to 1.5 or so) lower than the pH of the nucleation stage. It is appropriate to do.

The pH and NH ₄ ⁺ concentration can be adjusted in the same manner as the nucleation stage. This particle growth step is performed to satisfy the above pH and NH ₄ ⁺ concentration (preferably, the NH ₄ ⁺ concentration is 15 g / L or less (eg, 1 to 15 g / L, typically 3 to 15 g / L at the above pH) L), more preferably 10 g / L or less (e.g., in the range of 1 to 10 g / L, typically 3 to 10 g / L), transition metal hydroxide (here, Ni, Co and Mn) Of the composite hydroxide), and the raw material hydroxide particles more suitable for the formation of the perforated hollow active material particles disclosed herein (in other words, the fired product of the perforated hollow structure is formed more Raw material hydroxide particles) can be generated. The NH ₄ ⁺ concentration in the particle growth stage may be 7 g / L or less (eg, 1 to 7 g / L, more preferably 3 to 7 g / L). NH ₄ ⁺ concentration in the particle growth step, for example, may be a substantially the same level as NH ₄ ⁺ concentration in the nucleation stage may be lower than NH ₄ ⁺ concentration in the nucleation stage. Note that the deposition rate of the transition metal hydroxide is, for example, the transition metal ion contained in the liquid phase of the reaction liquid relative to the total number of moles of transition metal ions contained in the transition metal solution supplied to the reaction liquid. It can be grasped by examining the transition of the total number of moles (total ion concentration).

  In each of the nucleation step and the particle growth step, the temperature of the reaction solution is preferably controlled to be a substantially constant temperature (for example, a predetermined temperature ± 1 ° C.) in the range of approximately 30 ° C. to 60 ° C. The temperature of the reaction solution may be made the same in the nucleation step and the particle growth step. In addition, the atmosphere in the reaction solution and the reaction vessel is preferably maintained at a non-oxidizing atmosphere throughout the nucleation step and the particle growth step. In addition, the total number of moles of Ni ions, Co ions and Mn ions (total ion concentration) contained in the reaction solution should be, for example, about 0.5 to 2.5 mol / L throughout the nucleation step and the particle growth step. And preferably about 1.0 to 2.2 mol / L. The transition metal solution may be replenished (typically continuously supplied) in accordance with the deposition rate of the transition metal hydroxide so that the ion concentration is maintained. The amounts of Ni ions, Co ions and Mn ions contained in the reaction solution correspond to the composition of the active material particles as a target (that is, the molar ratio of Ni, Co, Mn in the LiNiCoMn oxide constituting the active material particles). It is preferable to set it as the quantitative ratio which

<Mixing step S20>
In this embodiment, the transition metal hydroxide particles thus produced (here, composite hydroxide particles containing Ni, Co and Mn) are separated from the reaction liquid, washed and dried. Then, the transition metal hydroxide particles and the lithium compound are mixed in a desired amount ratio to prepare an unfired mixture (mixing step S20). In this mixing step, typically, the amount ratio corresponding to the composition of the target active material particles (that is, the molar ratio of Li, Ni, Co, Mn in the LiNiCoMn oxide constituting the active material particles), The lithium compound and transition metal hydroxide particles are mixed.

  As the lithium compound, a lithium compound which can be dissolved by heating to form an oxide, such as lithium carbonate, lithium hydroxide, lithium nitrate, or a mixture thereof can be preferably used. From the viewpoint of ease of handling and quality stability, lithium carbonate or lithium hydroxide is preferably used, and the use of lithium carbonate is particularly preferred.

  The mixing step S20 can be performed using a general mixer. For example, a shaker mixer, a juliary mixer, a ribbon mixer, a lodige mixer, a V blender and the like can be preferably used. In addition, it is preferable that the mixing process be performed such that the transition metal hydroxide particles and the lithium compound are sufficiently mixed to such an extent that the shape of the transition metal hydroxide particles is not broken.

<Firing Step S30>
After mixing the lithium compound and the transition metal hydroxide particles as described above, the active material particles are obtained by firing and firing in a temperature range of 700 ° C. to 1000 ° C. (firing step S30). The active material particle manufacturing method disclosed here is characterized by baking in a high pressure atmosphere of 600 MPa to 900 MPa in at least a part of the baking step S30. That is, by firing at a firing temperature of 700 ° C. to 1000 ° C., the sintering reaction of the primary particles 18 of the lithium transition metal oxide (here, LiNiCoMn oxide) proceeds, and a plurality of the primary particles 18 aggregate. Active material particles 10 having particles 12, hollow portions 14 and through holes 16 may be formed. In addition, by performing the firing process under pressure (for example, keeping the inside of the firing furnace in a high pressure atmosphere), the gap between the primary particles 18 is reduced, and the opening width h of the through holes 16 is appropriately narrow. Material particles 10 can be obtained. The firing step S30 is typically performed in an oxidizing atmosphere.

  In the firing step S30, it is preferable to apply sufficient pressure so as to appropriately reduce the opening width h of the through holes. For example, the atmospheric pressure in the firing step may be set in the range of 600 MPa to 900 MPa. Thereby, the gaps between the primary particles 18 are reduced, and the perforated hollow active material particles 10 having a relatively narrow opening width h of the through holes 16 can be manufactured. It is more preferable that the pressure be 650 MPa or more, preferably 700 MPa or more (e.g. 700 MPa to 850 MPa), typically 750 MPa or more (e.g. 750 MPa to 800 MPa).

  The firing temperature (maximum firing temperature) in the firing step S30 is 700 ° C. to 1000 ° C. For example, the firing temperature is preferably 800 ° C. or higher (preferably 800 ° C. to 1000 ° C., for example, 800 ° C. to 900 ° C.). According to the firing temperature in this range, the sintering reaction of primary particles of lithium transition metal oxide (preferably Ni-containing Li oxide, in this case LiNiCoMn oxide) can be appropriately advanced. In addition, by appropriately advancing the sintering reaction of the primary particles, it is possible to obtain the perforated hollow active material particles 10 in which the number of through holes and the opening width h are appropriately reduced.

  In a preferred embodiment, the firing step S30 is obtained by atmospheric pressure firing treatment S32 in which the mixture is fired at a temperature of 700 ° C. or more and 1000 ° C. or less under an atmospheric pressure (about 0.1 MPa) atmosphere, and the atmospheric pressure firing treatment S32 thereof. And a pressure baking process S34 of baking at a temperature of 700 ° C. or more and 1000 ° C. or less while pressurizing the baked product in a high pressure atmosphere of 600 MPa to 900 MPa. By performing the pressure firing according to such a multistage pressure firing schedule, it is possible to more stably form the perforated hollow active material particle 10 in which the opening width h of the through hole is appropriately reduced. The atmospheric pressure calcination treatment S32 and the pressurization calcination treatment S34 may be continued (for example, after the mixture is calcined in an atmospheric pressure atmosphere, subsequently pressurized to a high pressure atmosphere and calcined), or, atmospheric pressure atmosphere After firing, the material may be cooled (for example, cooled to room temperature), crushed and sieved, if necessary, and then subjected to pressure baking treatment S34.

  The baking time (baking time at the maximum baking temperature) of the atmospheric pressure baking treatment S32 may be approximately 1 hour to 20 hours (preferably 3 hours to 20 hours, particularly preferably 10 hours to 20 hours). The sintering reaction of primary particles of lithium transition metal oxide (preferably, Ni-containing Li oxide, in this case, LiNiCoMn oxide) can be appropriately progressed within the range of such a baking time. The firing time (the firing time at the highest firing temperature) of the pressure firing process S34 may be approximately 1 hour to 20 hours (preferably 1 hour to 15 hours, and particularly preferably 3 hours to 10 hours). If it is in the range of such baking time, the perforated hollow active material particle 10 in which the opening width h of the through hole is appropriately reduced can be formed.

  Active material particles can be obtained by pulverizing the lithium transition metal oxide (LiNiCoMnW oxide) obtained by the above-mentioned firing step S30, preferably by means of a mill, etc. after cooling, and appropriately classifying it. In this manner, it is possible to obtain a perforated hollow structure active material particle 10 having the secondary particle 12, the hollow portion 14 and the through hole 16.

  Active material particles 10 having a perforated hollow structure disclosed herein are manufactured by firing in a temperature range of 700 ° C. to 1000 ° C. while being pressurized in a pressure atmosphere of 600 MPa to 900 MPa, as shown in FIGS. 1 and 2. It is done. Therefore, in the obtained perforated hollow active material particles 10, the opening width h of the through holes 16 is relatively narrow, and the filling rate of the liquid epoxy resin may tend to decrease. Typically, when the active material powder material composed of the active material particles is solidified by immersion in a liquid epoxy resin adjusted to a viscosity of 4500 mPa · s (B-type viscometer, rotation speed 10 to 100 rpm), Resin filling number ratio X (%) determined from the total number A of active material particles 10 appearing in the SEM image of the cut surface of the solidified product and the number B of active material particles 10 in which the hollow portion 14 is filled with the epoxy resin = (100 x B / A) is generally 17% or less (e.g. 1% to 17%), preferably 10% or less (e.g. 1% to 10%), more preferably 8% or less (e.g. 3% to 8%) Can be In the active material powder material (active material particles) having the resin-filled number ratio X within such a range, the opening width h of the through hole 16 is appropriately narrow, and the solvent used at the time of electrode preparation hardly enters the hollow portion 14. Therefore, it is possible to construct an optimal lithium ion secondary battery in which the remaining of the solvent in the active material particles 10 is suppressed.

  As described above, the active material particles 10 obtained by the manufacturing method of the present embodiment have a narrow opening width h of the through holes 16 as described above, and the solvent used at the time of electrode production hardly remains. It can be preferably used as a component of various forms of lithium ion secondary battery or a component (active material) of an electrode incorporated in the lithium ion secondary battery. A lithium ion secondary battery can be constructed using the same process as the conventional one, except that the active material particles 10 disclosed herein are used.

Hereinafter, an embodiment of a lithium ion secondary battery constructed using the active material particles 10 manufactured by applying the above-described method will be described with reference to schematic diagrams shown in FIGS. 3 and 4. FIG. 3 is a cross-sectional view of a lithium ion secondary battery 100 according to an embodiment of the present invention. FIG. 4 is a view showing an electrode assembly 40 incorporated in the lithium ion secondary battery 100. The lithium ion secondary battery 100 uses, as a positive electrode active material, perforated hollow active material particles manufactured by applying the above-described method.

  A lithium ion secondary battery 100 according to an embodiment of the present invention is configured in a flat rectangular battery case (i.e., an outer container) 20 as shown in FIG. 3. In the lithium ion secondary battery 100, as shown in FIGS. 3 and 4, the flat wound electrode body 40 is accommodated in the battery case 20 together with the liquid electrolyte (electrolyte solution) 80.

  The battery case 20 has a box-shaped (that is, a bottomed rectangular parallelepiped) case body 21 having an opening at one end (corresponding to the upper end of the battery 100 in a normal use state), and is attached to the opening It is comprised from the cover body (sealing plate) 22 which consists of a rectangular-shaped plate member which block | closes an opening part. The material of the battery case 20 may be the same as that used in a conventional lithium ion secondary battery, and is not particularly limited. A battery case 20 mainly composed of a lightweight, thermally conductive metal material is preferable, and aluminum or the like is exemplified as such a metal material.

  As shown in FIG. 3, the lid 22 is formed with a positive electrode terminal 23 and a negative electrode terminal 24 for external connection. Between the two terminals 23 and 24 of the lid 22, a thin-walled safety valve 30 configured to release the internal pressure when the internal pressure of the battery case 20 rises above a predetermined level, and a liquid injection port 32 are formed. It is done. In addition, in FIG. 3, the said liquid injection port 32 is sealed by the sealing material 33 after liquid injection.

<Wound electrode body>
As shown in FIG. 4, the wound electrode body 40 has a total of two sheets of a long sheet-like positive electrode (positive electrode sheet 50) and a long sheet-like negative electrode (negative electrode sheet 60) similar to the positive electrode sheet 50. And a long sheet-like separator (separators 72 and 74).

<Positive electrode sheet>
The positive electrode sheet 50 includes a strip-shaped positive electrode current collector 52 and a positive electrode active material layer 53. For the positive electrode current collector 52, for example, a metal foil suitable for the positive electrode can be suitably used. In this embodiment, an aluminum foil is used as the positive electrode current collector 52. An uncoated portion 51 is set along the edge on one side in the width direction of the positive electrode current collector 52. In the illustrated example, the positive electrode active material layer 53 is held on both sides of the positive electrode current collector 52 except for the uncoated portion 51 set in the positive electrode current collector 52. The positive electrode active material layer 53 contains positive electrode active material particles, a conductive material, and a binder. As the positive electrode active material particles, perforated hollow active material particles manufactured by applying the method described above are used. Examples of the conductive material include carbon blacks such as acetylene black (AB) and ketjen black, and powdery carbon materials such as other (graphite and the like). Examples of the binder include polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC) and the like.

  When forming the positive electrode active material layer 53, the positive electrode active material layer forming paste (the positive electrode active material (porous hollow active material particles), the conductive material and the binder are dispersed in an appropriate solvent and kneaded. Prepare slurry or ink, the same shall apply hereinafter. As the solvent, those used for conventional paste materials of this type can be used without particular limitation, and both aqueous solvents and non-aqueous solvents can be used. For example, non-aqueous solvents such as N-methyl pyrrolidone (NMP), pyrrolidone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, dimethylformamide, dimethyl acetamide, etc., or a combination of two or more of these may be used. Alternatively, it may be water or an aqueous solvent mainly containing water. As solvents other than water which comprises this aqueous solvent, 1 type, or 2 or more types of organic solvents (a lower alcohol, a lower ketone, etc.) which can be mixed uniformly with water can be selected suitably, and can be used. The solid fraction (NV) of the paste is not particularly limited, but from the viewpoint of drying efficiency etc., usually 40% by mass or more (eg 40% by mass to 95% by mass) is suitable, preferably 55 % By mass (e.g. 55% by mass to 90% by mass), more preferably 60% by mass or more (e.g. 60% by mass to 85% by mass). An appropriate amount of this paste is applied onto a positive electrode current collector and dried to prepare a positive electrode for a lithium ion secondary battery. The operation of applying the paste can be performed using a suitable coating device such as, for example, a gravure coater, a slit coater, a die coater, a comma coater, or a dip coater. The above-mentioned drying can also be performed by a conventional general means (for example, heat drying or vacuum drying). The drying temperature is not particularly limited, but may be approximately 100 ° C. to 200 ° C. (eg, 120 ° C. to 180 ° C.). As described above, in the active material particles (positive electrode active material) disclosed herein, the opening width h of the through holes is appropriately narrow, and the solvent does not easily enter the hollow portion. Therefore, even after drying, the above-mentioned solvent does not easily remain in the active material particles (as a result, the positive electrode active material layer), and a higher performance positive electrode can be manufactured.

  In a preferred embodiment, the content of the solvent contained in the positive electrode active material layer is 90 ppm or less (eg, 10 ppm to 90 ppm), preferably 80 ppm or less, more preferably 60 ppm or less based on the total solid content of the positive electrode active material layer. (E.g. 40 ppm to 60 ppm). Within the range of such solvent content, it is possible to construct an optimum lithium ion secondary battery in which the output performance in the low temperature range is further improved.

<Negative sheet>
As shown in FIG. 4, the negative electrode sheet 60 includes a strip-like negative electrode current collector 62 and a negative electrode active material layer 63. For the negative electrode current collector 62, for example, a metal foil suitable for the negative electrode can be suitably used. In this embodiment, a strip-shaped copper foil is used for the negative electrode current collector 62. An uncoated portion 61 is set along the edge on one side in the width direction of the negative electrode current collector 62. The negative electrode active material layer 63 is held on both sides of the negative electrode current collector 62 except for the uncoated portion 61 set in the negative electrode current collector 62. The negative electrode active material layer 63 contains a negative electrode active material, a conductive material, and a binder. Examples of the negative electrode active material include powdery carbon materials made of graphite and the like. As a binder, the thing similar to the positive electrode mentioned above can be used. Then, as in the case of the positive electrode, the powdery material is dispersed in an appropriate solvent and kneaded to prepare a negative electrode active material layer-forming paste. An appropriate amount of this paste is applied onto a negative electrode current collector and dried to prepare a negative electrode for a lithium ion secondary battery.

<Separator>
The separators 72 and 74 are members for separating the positive electrode sheet 50 and the negative electrode sheet 60, as shown in FIG. In this example, the separators 72 and 74 are formed of a band-like sheet material having a predetermined width and having a plurality of minute holes. For the separators 72 and 74, for example, a separator having a single layer structure made of a porous polyolefin resin or a separator having a laminated structure can be used. In addition, a layer of insulating particles may be further formed on the surface of the sheet material made of such a resin. Here, as particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene) It may consist of. In this example, as shown in FIG. 6, the width b1 of the negative electrode active material layer 63 is slightly wider than the width a1 of the positive electrode active material layer 53. Furthermore, the widths c1 and c2 of the separators 72 and 74 are slightly wider than the width b1 of the negative electrode active material layer 63 (c1, c2>b1> a1).

<< Installation of winding electrode body >>
In this embodiment, as shown in FIG. 4, the wound electrode body 40 is flatly pressed and bent in one direction orthogonal to the winding axis WL. In the example shown in FIG. 4, the uncoated portion 51 of the positive electrode current collector 52 and the uncoated portion 61 of the negative electrode current collector 62 are spirally exposed on both sides of the separators 72 and 74. In this embodiment, as shown in FIG. 3, the middle portion of the uncoated portion 51 is gathered and welded to the current collecting tabs 25, 26 of the electrode terminals (internal terminals) arranged inside the battery case 20. Be done. Reference numerals 25a and 26a in FIG. 3 indicate the welds.

  Then, the wound electrode body 40 is accommodated in the main body 21 from the upper end opening of the case main body 21, and the opening is sealed by welding with the lid 22 or the like. Further, the electrolytic solution 80 is disposed (injected) in the case main body 21 from the liquid injection port 32.

<Electrolyte (non-aqueous electrolyte)>
As the electrolyte solution (non-aqueous electrolyte solution) 80, the same non-aqueous electrolyte solution conventionally used for lithium ion secondary batteries can be used without particular limitation. Such non-aqueous electrolytes typically have a composition in which a suitable non-aqueous solvent contains a supporting salt. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane and the like. One or two or more selected from the group can be used. Further, as the supporting salt, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiN (CF 3 SO 2) 2, LiC (CF 3 SO 2) _3, etc. Lithium salts can be used. As an example, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (for example, volume ratio 3: 4: 3) containing LiPF ₆ at a concentration of about 1 mol / L is not used. A water electrolyte is mentioned.

  Thereafter, the liquid injection port 32 is sealed by the sealing material 33, and the assembly of the lithium ion secondary battery 100 according to the present embodiment is completed. The sealing process of the case 20 and the placement (injection) process of the electrolytic solution may be the same as the method performed in the manufacture of a conventional lithium ion secondary battery, and do not characterize the present invention. Thus, the construction of the lithium ion secondary battery 100 according to the present embodiment is completed.

  In the lithium ion secondary battery 100 constructed in this manner, the opening width of the through holes of the perforated hollow active material particles (positive electrode active material) is appropriately narrowed as described above, and the residual solvent in the positive electrode is preferably suppressed. Therefore, the battery may exhibit excellent battery performance. For example, by constructing a lithium ion secondary battery using the above-described perforated hollow active material particles, at least one of excellent low-temperature input-output characteristics, excellent low SOC region input-output characteristics, and excellent cycle characteristics A lithium ion secondary battery satisfying (preferably all) can be provided.

  In the following test examples, a lithium ion secondary battery for test was constructed using the porous hollow structure active material particles disclosed herein, and its performance was evaluated.

(Test Example 1)
<Production of Active Material Particles Having a Holed Hollow Structure>
Ion exchange water is placed in a reaction tank set with an overflow pipe and set at a temperature in the tank of 40 ° C., nitrogen gas is circulated while stirring, and the ion exchange water is replaced with nitrogen and oxygen gas in the reaction tank ( O ₂₎ was adjusted to a non-oxidizing atmosphere at a concentration of 2.0%. Next, a 25% aqueous sodium hydroxide solution and a 25% aqueous ammonia were added such that the pH measured on the basis of a liquid temperature of 25 ° C. was 12.0 and the NH ₄ ⁺ concentration in the liquid was 15 g / L.

The reaction solution is adjusted to pH 12.4 by supplying each sulfate of nickel, cobalt and manganese, a mixed aqueous solution of a zirconium compound and a tungsten compound, a 25% aqueous NaOH solution and a 25% aqueous ammonia into the above reaction vessel at a constant rate. 5, NiCoMnZrW composite hydroxide was crystallized from the reaction solution while controlling to an NH ₄ ⁺ concentration of 5 g / L (nucleation step).

At 2 minutes and 30 seconds after the start of the supply of the mixed aqueous solution, the supply of 25% aqueous NaOH solution was stopped. The mixed aqueous solution and 25% aqueous ammonia were continuously supplied at a constant rate. After the pH of the reaction solution dropped to 11.6, the supply of 25% aqueous NaOH solution was resumed. Then, while controlling the reaction liquid pH11.6 and the _NH ^{4 +} concentration 5 g / L, the mixed aqueous solution, 25% operation for supplying aqueous NaOH and 25% aqueous ammonia for 4 hours continuously by the NiCoMnZrW composite hydroxide particles Were grown (particle growth stage). The product was then removed from the reaction vessel, washed with water and dried. Thus, a composite of the composition represented by (Ni _0.33 Co _0.33 Mn _0.33 ) _0.993 Zr _0.002 W _0.005 (OH) _{2 + α} (where _α in the formula is 0 ≦ α ≦ 0.5) Hydroxide particles were obtained (raw material hydroxide production step).

The composite hydroxide particles were subjected to heat treatment at 150 ° C. for 12 hours in the air atmosphere. Next, Li ₂ CO ₃ as a lithium source and the above composite hydroxide particles are represented by the number of moles of lithium (Li) and the total number of moles of Ni, Co, Mn, Zr and W constituting the above composite hydroxide ( M _all) the ratio of (Li / M _all ratio) was mixed such that about 1.14 (mixing step). The firing step was performed on this mixture. Specifically, the mixture was fired for 20 hours (atmospheric pressure firing treatment) under the atmospheric pressure atmosphere on the condition that the highest firing temperature is set within the range of 700 ° C. to 1000 ° C. Furthermore, the baked product which passed through atmospheric pressure baking processing was baked for 20 hours on the conditions from which the highest baking temperature is set within the range of 700 degreeC-1000 degreeC in pressure atmosphere of 600 Mpa-900 Mpa (pressure baking processing). Thus, a perforated hollow active material particle sample having a composition represented by Li _1.14 (Ni _0.33 Co _0.33 Mn _0.33 ) _0.993 Zr _0.002 W _0.005 O ₂ was obtained.

Examples 1 to 9
More specifically, the pressure atmosphere is made different between 600 MPa and 900 MPa by adjusting the conditions of the pressure atmosphere and the maximum firing temperature in the above-mentioned active material particle sample preparation process, and the maximum The porous hollow active material particles of Examples 1 to 9 shown in Table 1 were produced by changing the firing temperature between 700 ° C. and 1000 ° C.

<Comparative Examples 1 to 4>
In the above-mentioned active material particle sample production process, perforated hollow active material particles were produced without performing a pressure firing process. Specifically, after the above mixing step, the mixture of Li ₂ CO ₃ and the composite hydroxide particles is subjected to atmospheric pressure atmosphere in a range of 700 ° C. to 1000 ° C. for 20 hours under the condition that the maximum firing temperature is set. By firing, the perforated hollow active material particles of Comparative Examples 1 to 4 shown in Table 1 were produced.

<Resin filling number ratio>
The resin filling number ratio of the perforated hollow active material particle sample of each example was measured. The measurement of the resin filling number ratio was performed as follows. That is, a liquid low viscosity epoxy resin (Specifix-20, manufactured by Marumoto Struers Co., Ltd.) and a curing agent (Specifix-20, manufactured by Marumoto Struas Ltd.) are mixed at a volume ratio of 7: 1. The viscosity of the liquid epoxy resin was adjusted to 4500 mPa · s (B-type viscometer, 25 ° C., rotation speed 10 to 100 rpm) by standing for 90 minutes. To 5 ml of the epoxy resin after the viscosity adjustment, 0.02 g of the powder of each of the perforated hollow active material particle samples was charged, and stirred and dispersed. Thereafter, the epoxy resin was allowed to cure completely for 8 hours or more. The cured product was cut at an appropriate cross section, and the cut surface was polished and smoothed. Then, after noble metal (Au, Pt or Pd) is vapor-deposited on the smoothed cut surface and metal coated, the total number A of active material particles appearing in the image obtained by SEM observation and the epoxy resin fill the hollow portion The number B of active material particles was counted. Here, the reflection electron image (concave / convex mode; magnification 1000 times) by SEM of the same field of view is observed, and particles having no unevenness in the hollow portion are “active material particles in which the hollow portion is filled with epoxy resin”, unevenness in the hollow portion Some particles were counted as "active material particles whose hollow portion is not filled with epoxy resin". Then, the resin filling number ratio X (%) was calculated by (B / A) × 100. The results are shown in Table 1.

  In addition, the powder of each active material particle sample was solidified with a resin, cut at an appropriate cross section, and the cut surface was observed with an SEM to calculate the average opening width h of the active material particle sample. The results are shown in Table 1. As shown in Table 1, in the porous hollow active material particle production process, an embodiment was carried out under a pressure atmosphere of 600 MPa to 900 MPa while performing a pressure baking process of baking in a temperature range of 700 ° C. to 1000 ° C. In the active material particles 1 to 9, the resin filling number ratio and the opening width h both tended to decrease as compared with the active material particles of Comparative Examples 1 to 4 in which the pressure firing process was not performed.

  A positive electrode sheet and a test lithium ion secondary battery were constructed using the perforated hollow active material particle samples of each example, and the performance evaluation was performed. Here, positive electrode sheets of a plurality of samples different only in the positive electrode active material particles and a lithium ion secondary battery for test were constructed, and their performance was compared and examined.

<Positive electrode sheet>
The perforated hollow active material particle sample obtained above, AB (conductive material), and PVDF (binder) are mixed with NMP (solvent) so that the mass ratio of these materials is 90: 8: 2. It mixed, and prepared the paste for positive electrode active material layer formation. The positive electrode active material layer is formed on both sides of the positive electrode current collector by applying the positive electrode active material layer forming paste in a strip on both sides of a long 15 μm thick aluminum foil (positive electrode current collector) and drying. The provided positive electrode sheet was produced. After drying, the content (ppm) of NMP remaining in the positive electrode active material layer was measured. The content of the NMP was grasped by quantitative analysis using a gas chromatograph. Specifically, after cutting out the positive electrode active material layer to a predetermined size, NMP was extracted with a solvent such as diethyl carbonate (DEC), and the content of NMP was measured by gas chromatograph using decane as a standard substance. The results are shown in FIG. FIG. 5 is a graph showing the relationship between the resin filling number ratio and the amount of residual solvent.

  As shown in FIG. 5, the amount of residual NMP in the positive electrode active material layer showed a decreasing tendency as the resin filling number ratio decreased. As the resin filling number ratio of the active material particles is smaller, NMP is less likely to enter the hollow portion, so it is considered that the NMP remaining in the hollow portion after drying decreases and the amount of NMP remaining in the positive electrode active material layer decreases.

<Negative sheet>
The negative electrode sheet was produced as follows. Natural graphite powder as a negative electrode active material, SBR, and CMC are dispersed in water such that the mass ratio of these materials is 98.6: 0.7: 0.7 to form a negative electrode active material layer The paste was prepared. The negative electrode active material layer is provided on both sides of the negative electrode current collector by applying and drying this negative electrode active material layer forming paste on both sides of a long copper foil (negative electrode current collector) having a thickness of 10 μm. A negative electrode sheet was produced.

<Lithium ion secondary battery>
The positive electrode sheet and the negative electrode sheet are laminated via two separators (having a single layer structure made of porous polyethylene) and wound, and the wound body is squashed and wound from the side direction A flat wound electrode body was produced. The wound electrode body was housed together with the non-aqueous electrolyte in a box-shaped battery container, and the opening of the battery container was sealed airtight. As the non-aqueous electrolytic solution, a mixed solvent containing EC, EMC, and DMC in a volume ratio of 3: 3: 4 and containing LiPF ₆ as a supporting salt at a concentration of about 1 mol / liter was used. Thus, a lithium ion secondary battery was assembled. Thereafter, initial charge / discharge treatment (conditioning) was performed by a conventional method to obtain a test lithium ion secondary battery. The test lithium ion secondary battery has a rated capacity of about 4 Ah.

<Output characteristics at -30 ° C, SOC 25% charge condition>
The output characteristics of each test lithium ion secondary battery at -30 ° C. and 25% SOC were measured. The output characteristics were measured by the following procedure.
Procedure 1: Adjust SOC to 25% with constant current charge of 3.0 V to 1 C in a temperature environment of normal temperature (here, 25 ° C.), and then charge with constant voltage for 1 hour.
Procedure 2: The battery adjusted to the SOC 25% is left to stand in a constant temperature bath at -30 ° C for 6 hours.
Procedure 3: After procedure 2, discharge at constant watt (W) from SOC 25% in a temperature environment of -30 ° C. At this time, the number of seconds from when the discharge starts to when the voltage reaches 2.0 V is measured.
Step 4: Repeat the above steps 1 to 3 while changing the constant wattage discharge voltage of step 3 under the conditions of 80 W to 200 W. Here, the constant wattage discharge voltage in step 3 is increased to 200 W while the constant wattage discharge voltage in step 3 is increased by 10 W at a first time of 80 W, a second time of 90 W, a third time of 100 W, and so on. Repeat the above steps 1 to 3 until
Step 5: With the number of seconds up to 2.0 V measured under the condition of constant wattage in Step 4 above taken on the horizontal axis and the W at that time taken on the vertical axis, output W at 2 seconds from the approximate curve Calculated as a characteristic.
This output characteristic shows an output that the test lithium ion secondary battery can exhibit even when the battery is left in a very low temperature environment of -30.degree. C. for a predetermined time with a low charge amount of about 25% of SOC. Therefore, the above output characteristic indicates that the higher the value of W, the more stable the high output can be obtained even in the low SOC and low temperature state. The results are shown in Table 1 and FIG. FIG. 6 is a graph showing the relationship between the resin filling number ratio and the low temperature output.

  As shown in Table 1, in the porous hollow active material particle production process, an embodiment was carried out under a pressure atmosphere of 600 MPa to 900 MPa while performing a pressure baking process of baking in a temperature range of 700 ° C. to 1000 ° C. The batteries 1 to 9 were smaller in low temperature output and superior in output performance in a low temperature range, as compared with the batteries of Comparative Examples 1 to 4 in which the pressure baking process was not performed. From this result, low-temperature output performance can be achieved by performing a pressure firing process in which the firing is performed in a temperature range of 700 ° C. to 1000 ° C. while pressurizing under a pressure atmosphere of 600 MPa to 900 MPa in the process of producing perforated hollow active material particles. It has been confirmed that it improves. Further, as shown in FIG. 6 and Table 1, the low temperature output showed a tendency to increase as the resin filling number ratio of the perforated hollow active material particles became smaller. In the case of the battery tested here, a high low temperature output of 100 W or more could be achieved by setting the resin filling number ratio to 1% to 17%. In particular, by setting the resin filling number ratio to 3% to 8%, an extremely high low temperature output of 128 W or more could be achieved. From the viewpoint of improving the output characteristics in the low temperature range, it is appropriate to set the resin filling number ratio of the perforated hollow active material powder to 1% to 17%, preferably 3% to 8%.

Although the present invention has been described in detail above, the above embodiment is merely an example, and the invention disclosed herein includes various modifications and alterations of the specific example described above.
For example, in the above-described embodiment, in the firing step, the pressure firing process is performed after the atmospheric pressure firing process, but the invention is not limited thereto. For example, atmospheric pressure firing may be omitted. That is, the mixture of the transition metal hydroxide and the lithium compound may be fired in a high pressure atmosphere of 600 MPa to 900 MPa from the initial stage of firing. Even in such a case, the above-described effects can be obtained.

  As described above, the lithium ion secondary battery provided by the technology disclosed herein can stably exhibit high output even in a low temperature range (for example, at a temperature of -10 ° C. or less), and thus various uses It can be used as a lithium ion secondary battery for For example, it can be suitably used as a power source for a motor (motor) mounted on a vehicle such as a car. Such lithium ion secondary batteries may be used in the form of an assembled battery in which a plurality of them are connected in series and / or in parallel. Therefore, according to the technology disclosed herein, a vehicle (typically a car, particularly a hybrid car, an electric car, a fuel cell car) equipped with such a lithium ion secondary battery (which may be in the form of an assembled battery) as a power source. An automobile equipped with such an electric motor can be provided.

DESCRIPTION OF SYMBOLS 10 Active material particle 12 Secondary particle 14 Hollow part 16 Through-hole 18 Primary particle 100 Lithium ion secondary battery

Claims (2)

The secondary particle has a secondary particle in which a plurality of primary particles of lithium transition metal oxide are gathered, and a hollow portion formed inside the secondary particle, and a through hole penetrating from the outside to the hollow portion is formed in the secondary particle A method for producing a perforated hollow structure active material particle for a lithium ion secondary battery, comprising:
A raw material hydroxide producing step of supplying ammonium ions to an aqueous solution of a transition metal compound containing a transition metal element constituting the lithium transition metal oxide to precipitate particles of the transition metal hydroxide from the aqueous solution;
Mixing the transition metal hydroxide and the lithium compound to prepare an unfired mixture; and
A firing step of firing the mixture in a temperature range of 700 ° C. to 1000 ° C. to obtain active material particles;
To include
A method for producing active material particles, comprising firing in a pressure atmosphere of 600 MPa to 900 MPa in at least a part of the firing step. The firing step is
Atmospheric pressure calcination processing which bakes the said mixture under atmospheric pressure atmosphere,
The manufacturing method of Claim 1 including the pressure-ized baking process which bakes the baked products obtained by the said atmospheric-pressure-baking process under the pressure atmosphere of 600 Mpa-900 Mpa, pressurizing.

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