JP6095626B2 - High density and high voltage stable cathode materials for secondary batteries - Google Patents

Description

  The present invention relates to high density and high voltage stable cathode materials for secondary batteries.

Until recently, LiCoO ₂ was selected as the primary cathode material. This combines a relatively high capacitance, a high packing density, and good electrochemical performance with a relatively simple manufacturing. In recent years, however, two major trends have been observed in lithium secondary batteries for portable applications. Lithium, nickel, manganese, cobalt oxide (LMNCO) has replaced LiCoO ₂ in middle-end and low-end uses, eg 2.2-2.6 Ah cylindrical batteries, and has high voltage stability and high A special LiCoO ₂ engineered for density is used in “high-end” uses, such as 3.0 Ah cylindrical batteries used in laptops.

A typical example of replacement in middle-end use and low-end use is a 2.2-2.4 Ah cylindrical battery, which is LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , or LiCoO ₂ and LiNi _0.5 Mn _0.3 Co _0.2 O. Cathode material such as a mixture with ₂ is used. LMNCO materials are much cheaper considering the cost of the metal (Ni and Mn are much cheaper than Co), but are more difficult to manufacture on a large scale. LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is has a volumetric energy density similar to that of LiCoO ₂ (represented by mAh / cm ^3), but to obtain an electrode having a similar low porosity and LiCoO ₂ Is difficult. Therefore, the substantially achievable volumetric energy density (ie, the capacity achieved in a fixed volume of a fixed battery design) remains a little low.

Another trend is the introduction of special “high-end” LiCoO ₂ , which has a higher density and higher charging voltage, typically 4.5V or 4.6V when mounted on a coin cell. When mounted on Li metal and full cells, 4.35V and 4.4V vs. graphite are possible, establishing its strong position in more demanding high-end uses. This is due to two main reasons: (1) high packing density, thereby making it possible to produce thicker, less porous electrodes, and (2) special “high-end” LiCoO ₂ based cathodes Higher voltage charging and cycling is possible, which increases the average battery voltage and also significantly increases the reversible and rate capacities. Thus, there is clearly a need for a high capacity LiCoO ₂ based cathode that has a high rate capacity and can be stably cycled in a real battery at a high voltage.

Several approaches have been proposed in the prior art. In order to achieve high voltage stability, the high-end LiCoO ₂ material is usually coated (eg with Al ₂ O ₃ ) or otherwise chemically modified (eg by providing a fluorinated surface) Has been. The problem is that the coated high density LiCoO ₂ often has a low reversible capacity, so that part of the energy density acquisition by high voltage charging is consumed by the low specific capacity. This effect can be observed in aluminum oxide and LiF protective coatings, but similar effects are observed for other coating approaches (ZrO ₂ , AlPO ₃ ,...).

Further investigation of the literature shows that no coating may be required to achieve high voltage stability. For example, Non-Patent Document 1 teaches that freshly manufactured LiCoO ₂ exhibits a stable cycle at 4.5 V when tested in a coin cell with a Li metal anode. Such an approach may be correct with coin batteries, but this effect cannot be reproduced with batteries that are actually on the market. These results are now confirmed by the fact that a few years after this publication, special treatments have been performed and impure LiCoO ₂ is commercially available for high voltage applications.

Chen & Dahn (Electrochem. Solid-State Lett. Vol. 7, No. 1, pages A11-A14 (2004))

  There are currently no known other strategies that lead to high voltage performance. The object of the present invention is to provide a novel cathode material with high density and high voltage performance and high rate capacity for secondary batteries for high end use.

Viewed from a first aspect, the present invention is a lithium metal oxide powder for use as a cathode material in a rechargeable battery, the powder being 10 ⁻ when compressed at 25 ° C. and 63.7 MPa. ^The powder has a conductivity of less than ⁵ S / cm, and the powder has a discharge rate of C / 10 at 25 ° C., 3.0 to 4.5 Vvs. Lithium metal oxide powders having a reversible electrode capacity of at least 180 mAh / g when used as an active material in a cathode cycled with Li ⁺ / Li can be provided. In certain embodiments, the conductivity is less than 10 ⁻⁶ S / cm, alternatively less than 10 ⁻⁷ S / cm. In other embodiments, the powder has a reversible electrode capacity of at least 180 mAh / g at a C / 5 discharge rate at 25 ° C., or at least 180 mAh / g at a discharge rate of 1 C at 25 ° C. In one embodiment, the lithium metal oxide powder contains at least 50 mol% Co, or at least 70 mol% Co, or at least 90 mol% Co.

In another embodiment, the lithium metal oxide powder has a compression density of at least 3.5 g / cm ³ . In another embodiment, the pressed density is at least 3.7 g / cm ^3, or at least 3.8 g / cm ^3. The compression density is measured by applying 1.58 ton / cm ² to the as-obtained powder.

  The conductivity is measured by applying a pressure of 63.7 MPa. In the detailed description and claims, a value of 63 MPa is also mentioned as an approximate numerical value when a pressure of 63.7 MPa is actually applied.

Viewed from a second aspect, the present invention is a lithium metal oxide powder for use as a cathode material in a rechargeable battery, said powder being compressed at 25 ° C. at 63.7 MPa. ^-5 having a conductivity of less than ⁵ S / cm, and the powder has a discharge rate of 0.5 C at 25 ° C and 3.0 to 4.6 V vs. Provided is a lithium metal oxide powder having a reversible electrode capacity of at least 200 mAh / g and an energy loss rate of less than 60% when used as an active material in a cathode cycled with Li ⁺ / Li can do. In certain embodiments, the conductivity is less than 10 ⁻⁶ S / cm, alternatively less than 10 ⁻⁷ S / cm. In certain embodiments, the powder is 3.0-4.6 Vvs. At a discharge rate of 0.5 C at 25 ° C. When used as an active material in cathodes cycled with Li ⁺ / Li, it has an energy loss rate below 40% or below 30%. In another embodiment, the powder has a reversible electrode capacity of at least 200 mAh / g and the same energy loss rate at a discharge rate of 1 C at 25 ° C. In one embodiment, the lithium metal oxide powder contains at least 50 mol% Co, or at least 70 mol% Co, or alternatively at least 90 mol% Co.

The lithium metal oxide powders of the two embodiments described above may consist of a core and a shell, in which case less than 1 × 10 ⁻⁶ S / cm and preferably 1 × 10 ⁻⁷ S / cm. Less than or alternatively less than 1 × 10 ⁻⁸ S / cm, and the conductivity of the shell of the lithium metal oxide powder is lower than the conductivity of the core. In one embodiment, at least 98 mol% of the metal in the lithium metal oxide powder consists of the elements Li, Mn, Ni and Co, or consists of the elements Li, Mn, Fe, Ni, Co and Ti. Either. In another embodiment, at least 98 mol% of the metal in both the shell and the core consists of the elements Li, Mn, Ni and Co, or consists of the elements Li, Mn, Fe, Ni, Co and Ti. One of them.

The lithium metal oxide powders of the two embodiments have the general formula xLiCoO _2. (1-x) MO _y , where 0.1 <x <1, 0.5 <y ≦ 2, and M is Li And M ′, M ′ = Ni _a Mn _b Ti _c , 0 ≦ c ≦ 0.1, a> b, and a + b + c = 1]. In one embodiment, 0.9 <x <1, which facilitates obtaining a uniformly sintered material and results in a low conductivity end product.

Viewed from a third aspect, the present invention is a lithium metal oxide powder for use as a cathode material in a rechargeable battery, wherein the powder is 10 when compressed at 25 ° C. at 63.7 MPa. Less than ⁻⁵ S / cm, and preferably less than 10 ⁻⁶ S / cm, and the powder has a 10C rate performance (0.1C rate) of at least 90%, preferably at least 95%. Discharge capacity measured at 10C rate, expressed in%), and 3.0 to 4.4 Vvs. Lithium metal oxide powders can be provided having an energy loss rate of less than 10% and advantageously less than 7% when used as an active material in a cathode cycled with Li ⁺ / Li. In one embodiment, the lithium metal oxide powder has a conductivity of less than 10 ⁻⁵ S / cm, and advantageously less than 10 ⁻⁶ S / cm, or 10 when compressed at 63.7 MPa at 25 ° C. ^-7 may have a conductivity of less than ⁷ S / cm and the powder has a 20C rate performance (discharge capacity measured at 20C rate versus 0.1C rate, preferably at least 85%, preferably at least 90%) %) And 3.0-4.4 Vvs. When used as an active material in a cathode cycled with Li ⁺ / Li, it exhibits an energy loss rate of less than 10% and advantageously less than 7%. This powder is 3.0-4.4 Vvs. A cycle at the Li ⁺ / Li 20C rate may have an average discharge voltage of greater than 3.7V, preferably greater than 3.75V, and most advantageously greater than 3.77V. In one embodiment, the powder has the general formula xLiCoO _2. (1-x) M _y O _z , where 0.1 <x <1, 0.5 <z / y ≦ 2, and M is 'consists, where, M' li and M is _{= Ni a Mn b Co c Ti} d Mg e, is a + b + c + d + e = 1, a + b> 0.5, and c ≧ 0, d ≧ 0, e ≧ 0 ] May be included. In one embodiment, 0.9 <x <1, which facilitates obtaining a uniformly sintered material and results in a low conductivity end product.

Viewed from a fourth aspect, the present invention is a method for producing a lithium metal oxide powder comprising the following steps:
LiCoO ₂ powder;
Mixture with any of Li-Ni-Mn-Co oxide or Ni-Mn-Co containing powder and Li containing compound, preferably lithium carbonate, greater than 90% by weight and preferably at least 95% by weight Preparing a mixture containing 1% LiCoO ₂ powder, and sintering the mixture at a temperature T of at least 910 ° C., and preferably at least 950 ° C., for a time t of 1 to 48 hours. In this case, the amount of Li-containing compound in the mixture is less than 10 ⁻⁵ S / cm, preferably less than 10 ⁻⁶ S / cm, and most preferably when compressed at 63.7 MPa at 25 ° C. It is possible to provide a production method of selecting so as to obtain an insulating lithium metal oxide powder having a conductivity of 10 ⁻⁷ S / cm.

In one embodiment, the LiCoO ₂ powder further contains one or more of Al, Mg and Ti, and a doped Co precursor, such as any one of Al, Mg and Ti or Contains Co (OH) ₂ or Co ₃ O ₄ doped with multiple species, and a Li precursor, such as Li ₂ CO ₃ . The content of one or more of Al, Mg and Ti is 0.1 to 1 mol%, or 0.25 to 1 mol%.

In another embodiment, the mixture comprises the pure LiCoO ₂ powder or doped LiCoO ₂ powder, and Ni—Mn—Co hydroxide, Ni—Mn—Co oxyhydroxide, Ni—Mn—Co carbonate. It consists of any one or more of a salt and Ni-Mn-Co oxycarbonate.

In another embodiment of the method, the amount of Li-containing compound, such as lithium carbonate, is selected such that the Li / M ratio is less than 0.1 mol / mol, where the Li / M molar ratio is , LiCoO ₂ and MOOH (M = Ni, Mn and Co) overall transition metal content versus Li addition (depending on Li-containing compound), which in the finally obtained lithium metal oxide powder Corresponds to the transition metal content. This may be less than 0.05 mol / mol, or less than 0.02 mol / mol. In another embodiment, the Li / M ratio is zero.

  In the claims, d50 is defined as 50% of the volume of a powder consisting of particles having a size less than or equal to the d50 value, where d50 is the dry average value and wetness by a suitable known method such as laser diffraction. Measured as an average value.

a) LCO-1, and b) SEM image at 2000x magnification of Example 1a Graph of energy loss rate (open circles) and capacity loss rate (black circles) at 4.5V as a function of conductivity on a logarithmic scale a) SEM image of LCO-3 at 2000x magnification and b) Example 2d at 2000x and 5000x (bottom) magnification a) LCO-2, Examples 2a, 2b and 2c, and b) Energy loss rate at 4.5 V (open circles) as a function of conductivity on the logarithmic scale of Examples 2d, 2e and 2f and Capacity loss rate (black circle) graph Testing in the full battery of Example 3 at a) 4.35V and b) 4.40V. The discharge capacity (mAh / g) was plotted against the number of cycles (#). 4. Test with a standard LiCoO ₂ complete battery at 35V. Discharge capacity plotted against cycle number Relationship between high voltage stability and conductivity of LiCoO ₂ coated with alumina a) SEM image of LCO-5 at 2000x magnification, b) Example 5a at 2000x and 5000x magnification, and c) Comparative Example 5 at 2000x and 5000x magnification. Graph of volume fraction as a function of particle size for Examples 5a (open circles) and 5b (black circles) Coin cell test: first charge-discharge obtained for LiF-coated LiCoO ₂ between 4.3 V and 3.0 V at C / 10 rate (1C = 160 mAh / g) at 25 ° C. Voltage profile obtained in cycle, heated at different temperatures Development of 20C rate performance of Examples 10a-10d and LCO-10 as a function of conductivity Relationship between conductivity and energy loss rate at 1C at 4.5V for Examples 10a, 10c and 10d vs. LCO-10

DETAILED DESCRIPTION The present invention discloses a strategy for obtaining a LiCoO ₂ based cathode with high voltage stability and high rate performance. The resulting LiCoO ₂ based cathode material has a high density and is capable of stable cycling at high voltage in an actual cell. The key to this strategy is to achieve very low conductivity, which is an order of magnitude lower than that reported for other current cathode materials.

It is widely accepted that sufficient conductivity is required when targeting high performance cathode performance. A typical example is the use of carbon coated particulate LiFePO ₄ . Without carbon coating, capacity and rate performance is very poor. In the case of LiFePO ₄ , a typical target for the conductivity of the compressed cathode powder is 10 ⁻³ to 10 ⁻² S / cm. Other cathode materials also have a relatively high conductivity.

The conductivity of the different reference materials was measured using pellets compressed at a pressure of 63.7 MPa at room temperature. A typical electrolyte ionic conductivity is 10 mS / cm (10 ⁻² S / cm), so a cathode with similar or higher conductivity can be defined as “highly conductive”. When the conductivity is large up to about 1% of this value (10 ⁻⁴ S / cm), it is defined as “low conductivity”. A cathode can be defined as “insulating” if its conductivity is less than 0.1% (10 ⁻⁵ S / cm). It is generally accepted that the cathode must have at least low conductivity and that it will not work with an insulating cathode.

High Ni materials, such as LiNi _0.8 Co _0.15 Al _0.05 O ₂ , for example, have about 3.47 × 10 ⁻² S / cm and LMNCO (LiNi _0.5 Mn _0.3 Co _0.2 O ₂ ) has about 2.21 × 10 ^{−. The} famous “111” (Li _{1 + x} M _1-x O ₂ , M = Ni _1/3 Co _1/3 Mn _1/3 , and x≈0.05) with ³ S / cm is about 2.03 × 10 ⁻⁴ S / cm. Commercially available LiCoO ₂ has a relatively low conductivity in the range of 10 ⁻² to 10 ⁻³ S / cm. A conductivity of about 10 ⁻⁵ S / cm is measured for all of these cathode materials. Therefore, none of these cathodes are insulating.

  Cathode materials according to the present invention are “insulating” using the above definitions. They have a conductivity that is at least 2-3 orders of magnitude lower than the conductivity of the currently known, least conductive cathode materials. The low conductivity is believed to be the main reason for the high voltage stability of the new insulating cathode material. It is surprising that such an insulating cathode provides excellent electrochemical performance, that is, large discharge capacity and rate performance. This is because it is generally considered that a certain conductivity is required for the diffusion of Li cations in the solid cathode and at the interface between the electrolyte and the cathode.

When a LiCoO ₂ based cathode is charged at high voltage (ie, the cathode is significantly non-intercalated), a Li _x CoO ₂ composition is obtained in which the majority of Co is tetravalent. Trivalent Li _x CoO ₂ is a very strong oxidant and is highly reactive. The electrolyte is not thermodynamically stable when in contact with such oxidizing surfaces. Reaction with the electrolyte (which is a reducing agent) is energetically advantageous. Even at low temperatures (during the normal cycle of a LiCoO ₂ cathode at high voltage), this reaction proceeds slowly but constantly. The reaction product covers the cathode surface, the electrolyte is decomposed, and both effects continuously degrade the electrochemical performance of the cell, observing a significant increase in resistance due to capacity loss and polarization.

The situation for high voltage charging cathodes is not very different from the situation of well-studied carbon anodes. The electrolyte is not stable under reducing conditions during Li intercalation with a potential of approximately zero V (vs. Li / Li ⁺ ). The electrolyte is therefore decomposed and reduced. However, in this case, the decomposition product of the electrolyte forms a so-called SEI (Solid Electrolyte Interface) together with lithium. SEI is an ionic conductor, but is known to be an electronic insulator. Thus, SEI still allows Li to be transported across the surface between the solid and the electrolyte, which further prevents electrolyte reduction. The important point is that the reduction of the electrolyte requires the local presence of Li cations and electrons simultaneously. Li cations are present in the electrolyte and electrons are in the carbon bulk. However, if the SEI physically separates the electrons in the carbon from the Li cations in the electrolyte as an electronic insulator, no further reduction of the electrolyte is possible.

  This mechanism is well known and attempts have been made to apply a similar mechanism to the cathode. Many studies have focused on electrolyte additives that decompose on the cathode surface to form cathode SEI. However, the search for electrode additives in contact with highly oxidized (ie delithiated) cathodes to form SEI at high voltages has been unsuccessful or only partially successful. Absent.

  Obviously, an electronically insulating cathode material will solve this problem. If an electronically insulating cathode material can be successfully cycled, high voltage stability can be expected. This is because electrolyte oxidation requires electrons to be supplied to the cathode. In general, however, it has been speculated that such insulated cathodes may not have good electrochemical performance.

The present invention
It is based on the discovery that 1) insulating cathodes can have high voltage stability, and 2) it is nevertheless possible to make insulating cathodes that exhibit very good electrochemical performance.

  Thus, examples of cathode compact powders, as disclosed below, exhibit very low electrical conductivity, which is a substantially good insulator. Surprisingly, however, this cathode exhibits good electrochemical performance. In addition, measurements have shown that the bulk of the cathode particles is conductive while the surface is insulating.

In one embodiment, to achieve good performance, the lithium metal oxide powder particles may have the following properties:
1) Core-shell structure, where the shell is electronically insulating and the core is electronically conductive,
2) An insulating shell that does not completely cover the entire core, generally much greater than 50% and less than 100%, and 3) a shell composed primarily of transition metals.

WO 2008-092568 discloses a method for producing LiCoO ₂ coated with Mn islands. In an example of one method embodiment of the present invention, LiCoO ₂ powder coated with such Mn islands is produced, but to achieve minimal conductivity, the Li: metal ratio Subtle adjustments are necessary. First, a LiCoO ₂ precursor is mixed with a transition metal source, such as a mixed hydroxide MOOH (M = Mn—Ni—O), and a Li source, such as Li ₂ CO ₃ . The ratio of transition metal in LiCoO _{2 to} metal in MOOH is, for example, 0.95: 0.05 to 0.8: 0.2. After the firing step, LiCoO ₂ covered with islands is obtained. A typical firing temperature is 1000 ° C. The resulting island is rich in manganese, while manganese is not found in the LiCoO ₂ bulk. The amount of Li added to this formulation is determined by the conductivity of the final fired specimen. This can be established by simply measuring how much Li should be added as Li ₂ CO ₃ in order to achieve the lowest possible conductivity, and will be described in detail in the examples below. In one embodiment, no Li ₂ CO ₃ is added.

A further important aspect of the present invention is that the inner core of the particle has a higher conductivity than the outer region. In a typical embodiment of the invention, the outer side is enriched with manganese than the inner region. High electrochemical performance was observed despite the outer side of the LiCoO ₂ particles being covered by a non-conductive shell.

  One example of a cathode configuration of the present invention is as follows: The relatively conductive core is often but not 100% covered by an insulating shell. Furthermore, the insulating shell may be made of a transition metal oxide having a metal composition of at least 95% cobalt, manganese and nickel.

  However, the presence of the core-shell structure is only one embodiment of the invention, which is observed particularly in powders having a wide average particle size of at least 10 μm, or at least 20 μm. The method described in the claims gives the lowest possible conductivity, irrespective of the structure obtained. By changing the mixing ratio of Li: metal, cathodes having different conductivity can be obtained. The Li: metal ratio according to one embodiment is the ratio that results in minimal conductivity. A high voltage stable cathode is a cathode material that has minimal conductivity as a function of Li: metal ratio.

  The invention is illustrated in detail by different examples as described below.

Example 1:
This example shows that cycle stability improves as conductivity decreases. Improved stability and reduced conductivity is achieved by optimizing the Li: metal ratio.

Production of LCO-1: A preparation of Co (OH) ₂ doped with 0.25 mol% titanium and 0.5 mol% magnesium is produced as a precursor of LiCoO _{2 in} the pilot line. LiCoO ₂ doped with titanium and magnesium (designated LCO-1) is obtained by mixing the precursor and Li ₂ CO ₃ using standard high temperature solid phase synthesis and has an average particle size of 25 μm. can get.

Production of LCO-1 covered by islands: cathode powder material is a transition metal mixed with 95 wt% titanium and magnesium doped LiCoO ₂ (denoted LCO-1) and 5 wt% MOOH It is produced by mixing oxyhydroxide (M = Ni _0.55 Mn _0.30 Co _0.15 ) and a specified amount of Li ₂ CO ₃ or Li ₂ CO ₃ without using them. Examples 1a, 1b and 1c are prepared as described in Table 1 and mixed thoroughly to produce a uniform feed mixture. This mixture is charged into an alumina crucible and heated at 1000 ° C. for 8 hours under constant air flow. After cooling, the resulting powder is sieved, characterized by 4-probe DC conductivity, and mounted on a coin cell for further electrochemical characterization.

Table 2 summarizes the conductivity and electrochemical performance of Examples 1a, 1b and 1c and LCO-1 at an applied pressure of 63 MPa. SEM images of LCO-1 and Example 1a are shown in FIG. The form of these two products is very different. While LCO-1 has a smooth surface and has non-agglomerated particles, Example 1a has a coating of particulate islands on the surface of LiCoO ₂ particles.

  The relationship between conductivity and cycle stability at 4.5V is shown in FIG. The conductivity of the coated specimens (ie Examples 1a-1c) is 3-4 orders of magnitude lower than that of the uncoated LCO-1. The electrochemical properties of LCO-1, such as discharge capacity, rate performance, capacity loss and energy loss rate, are very poor. Examples 1a-1c characterize the dramatic improvement in these properties in comparison to LCO-1. For Examples 1a-1c, the conductivity is increased by the addition of lithium. At the same time, both capacity loss and energy loss are improved. The reduction in resistance correlates well with the improved stability at 4.5V for both coated and uncoated specimens.

  Examples 1a, b and c are insulative and are examples of embodiments of the present invention.

In this example and in all the following examples, the electrochemical performance was tested in a coin cell, using a Li sheet as a counter electrode in a lithium hexafluoride (LiPF ₆ ) type electrode at 25 ° C. The active material loading is in the range of 10-12 mg / cm ² . The battery is charged at 4.3V and discharged at 3.0V to measure rate performance and capacity. High voltage discharge capacity and capacity retention in extended cycles are measured at a charge voltage of 4.5V or 4.6V (Examples 3-4 and 9).

  A specific capacity of 160 mAh / g is selected for the determination of the discharge rate. For example, for a discharge at 2C, a specific current of 320 mA / g is used.

  This is a summary of the tests used in all coin cells and full cells in this description.

  The following definitions are used for data analysis (Q: capacity, D: discharge, C: charge).

  The discharge capacity QD1 is measured during the first cycle in the range of 4.3-3.0V at 0.1C.

  The irreversible capacity Qirr is (QC1-QD1) / QC1 (%).

  Rate performance: QD at 0.2, 0.5, 1, 2, 3C vs. QD at 0.1C, respectively.

  Loss rate per 100 cycles (0.1 C), capacity: (1-QD31 / QD7) × 100/23.

  Loss rate per 100 cycles (1.0 C), capacity: (1-QD32 / QD8) × 100/23.

  Energy loss rate: Discharge energy (capacity × average discharge voltage) is used instead of the discharge capacity QD.

Example 2:
This example shows that the cycle stability of LiCoO ₂ coated with islands is much higher than that of uncoated LiCoO ₂ , in which case its conductivity is about 5 orders of magnitude lower at the same time. This example provides clear evidence that the cycle stability of LiCoO ₂ coated with islands increases with decreasing intrinsic conductivity.

Production of LCO-2: As a precursor for LiCoO ₂ , 1 mol% magnesium doped Co (OH) ₂ is produced in a pilot line. Magnesium-doped LiCoO ₂ (denoted LCO-2) is obtained by mixing the precursor and Li ₂ CO ₃ by standard high temperature solid phase synthesis to achieve an average particle size of 25 μm.

Production of LCO-3: 1 mol% magnesium doped cobalt tetroxide (Co ₃ O ₄ ) powder is used as a precursor of LiCoO ₂ (commercial product of Umicore, Korea). Magnesium-doped LiCoO ₂ (designated LCO-3) is obtained by mixing the precursor and Li ₂ O ₃ by standard high temperature solid phase synthesis, achieving an average particle size of 25 μm.

Production of LCO-2 and LCO-3 covered by islands: Cathode powder material was mixed with transition metal oxyhydroxide (M) mixed with 95 wt% LCO-2 or LCO-3 and 5 wt% MOOH = Ni _0.55 Mn _0.30 Co _0.15 ) and a specified amount of Li ₂ CO ₃ . Examples 2a, 2b and 2c were obtained from LCO-2, and Examples 2d, 2e and 2f were from LCO-3 according to the precursor content described in Table 1 and a homogeneous feed mixture In order to manufacture, it is manufactured by mixing thoroughly.

The mixture is placed in an alumina crucible and heated at 1000 ° C. for 8 hours under constant air flow. After cooling, the resulting powder is sieved and characterized using 4-probe DC conductivity and mounted in a coin cell for further electrochemical characterization. Table 4 summarizes the conductivity under an applied voltage of 63 MPa and the electrochemical performance of Examples 2a-2f and LCO-2 and LCO-3 (the test protocol is as described in Example 1). . SEM images of LCO-3 and Example 2d are shown in FIG. 3 (similar results have been obtained for the LCO-2 series). The two product forms are significantly different: LCO-3 has non-agglomerated particles with a smooth surface, while Example 2d is in the form of particles on the surface of LiCoO ₂ particles. The islands show the coating.

  The relationship between conductivity and cycle stability at 4.5V is illustrated in FIG. The conductivity of the specimens coated with islands (ie Examples 2a-2f) is 5 to 6 orders of magnitude lower than that of uncoated LCO-2 and LCO-3. The electrochemical properties of LCO-2 and LCO-3, such as discharge capacity, rate performance, capacity loss and energy loss rate, are very poor. Examples 2a-2f characterize the dramatic improvement in these properties compared to LCO-2 and LCO-3. For Examples 2a-2c and 2d-2f, the conductivity increases with the addition of lithium. At the same time, both capacity loss and energy loss rate are compromised. The reduction in resistance correlates well with an improvement in stability at 4.5V for both coated and uncoated specimens. Examples 2a-f are insulating and are examples of embodiments of the present invention.

Example 3:
This example shows that LiCoO ₂ coated with islands and having electrical insulating properties has better cycle stability in a complete battery.

Preparation of Example 3 (Ex3): Ex3 is prepared by sintering a 95: 5 molar ratio mixture of LCO-3 and MOOH (M = Ni _0.55 Mn _0.30 Co _0.15 ) and adding the appropriate lithium carbonate. Manufactured on a pilot production line and a conductivity of less than 5 × 10 ⁻⁸ S / cm is achieved. The average particle size of Ex3 is 25 μm. In this case, the conductivity under an applied pressure of 63 MPa is measured as 3.94 × 10 ⁻⁸ S / cm. The performance of the Ex3 coin cell at 4.5V and 4.6V is listed in Table 5a and shows excellent electrochemical performance.

The compression density is measured by applying 1.58 ton / cm ² to the obtained powder. The compression density of Ex3 is 3.82 g / cm ³ .

Ex3 is tested at 25 ° C. in a Li-ion polymer battery (LiPB) with a 10 μm polyethylene separator in a lithium hexafluoride (LiPF ₆ ) type electrode and a graphite type anode as a counter electrode. After formation, the LiPB cell is cycled 500 times between 4.35 V (or 4.40 V) and 3.0 V and the capacity retention during the extended cycle is measured. A specific capacity of 800 mAh is inferred with respect to determining charge and discharge rates. Charging was performed using a 40 mA cutoff current at 1 C rate in CC / CV mode, and discharging was performed at 1 C up to 3 V in CC mode.

The loss of discharge capacity in the Ex3 cycle at high voltage (4.35V) and very high voltage (4.4V) is described in FIGS. 5a and 5b, respectively. The life performance of Ex3 is compared to standard LiCoO ₂ (Umicore's mass produced product with an average particle size of 17 μm) and the data is shown in FIG. The conductivity of this standard LiCoO ₂ is 9.0 × 10 ⁻² S / cm.

Tests on full batteries confirm that Ex3 has better cycle stability compared to standard LiCoO ₂ with low conductivity. At the end of the 500 cycles, Ex3 has characterized a reversible capacity of 85% of the original performance of both 4.35V and 4.40V, with 200 for the standard LiCoO _{2 at} 4.35V. It decreased to 85% at an early point after the cycle.

Example 4: LiCoO ₂ coated with Al ₂ O ₃
This example again shows that cycle stability improves as conductivity decreases. An improvement in stability can be achieved by coating. However, a sufficiently low conductivity value is not achieved, and the reversible capacity is compromised as the low value is approached.

The LiCoO ₂ precursor (LCO-4) is 1 mol% Mg-doped LiCoO ₂ (a mass produced product of Umicore). This has potato-type particles with a d50 of a particle size distribution of about 17 μm. Three specimens are prepared from the LiCoO ₂ precursor by the mass production coating method disclosed in EP 10008563, a co-pending application. By this coating method, fine Al ₂ O ₃ powder is adhered to the surface, and then the Al ₂ O ₃ powder and the surface of LiCoO ₂ (LCO-4) are reacted by a mild heat treatment exceeding 500 ° C.

  The three specimens (Comparative Example 4a, Comparative Example 4b, Comparative Example 4c) have different levels of Al coating. Comparative Example 4a contains 0.05% by mass of Al, Comparative Example 4b contains 0.1% by mass, and Comparative Example 4c contains 0.2% by mass. The conductivity results are listed in Table 5b. The aluminum coated specimen has a lower conductivity than the uncoated LCO-4, and for the coated specimen, the conductivity decreases continuously with the thickness of the Al coating.

Electrochemical performance (capacity, rate, cycle stability at 4.5V) is tested in a coin cell. The uncoated specimen has very poor stability. The coated specimen has a very good stability and Table 6 shows the results. The discharge capacity is 4.5-3.0 V, which is obtained from cycle 7 of the cycle schedule given earlier. A clear improvement in cycle stability is observed with increasing coating level, regardless of the cycle stability measurement method. At the same time, however, the electrochemical performance (capacity, rate) is impaired as the Al ₂ O ₃ coating thickness increases.

FIG. 7 summarizes the results of capacity as a function of conductivity and cycle stability at 4.5V. In the upper drawing, both capacitance (triangle) and energy (black circle) losses are plotted against conductivity. In the lower drawing, the discharge capacity is plotted against conductivity. It is clearly observed that better high voltage stability at 4.5V has been obtained with respect to the decrease in conductivity. However, at the same time, the reversible capacity is impaired. Thus, in the case of alumina coated LiCoO ₂ , further improvement in cycle stability due to reduced conductivity is difficult without losing electrochemical performance. Furthermore, the electrochemical properties at 4.6V are very low compared to Example 3 regardless of the level of aluminum coating.

Example 5:
This example shows that LiCoO ₂ coated with islands has an electronic insulating shell, resulting in better cycle stability and an electronically conductive core.

The specimen of Example 5a has a mass ratio of 95: 5, a mass-produced product having an average particle size of 23 μm, 1 mol% magnesium-doped LiCoO ₂ (denoted LCO-5), and MOOH (M = Ni Sintered with _0.55 Mn _0.30 Co _0.15 ) and added with appropriate lithium carbonate to achieve a conductivity of less than 1 × 10 ⁻⁷ S / cm. The compression density of Ex5a is 3.87 g / cm ³ .

  Preparation of Comparative Example 5b: Example 5a 30 g and 1 cm diameter zirconium ball 400 g were placed in a 1 L bottle and shaken for 12 hours using a Turbula mixer. The produced powder is recovered as it is and used in subsequent tests.

The SEM images of LCO-5 and Example 5a and Comparative Example 5b are shown in FIG. 8 (each shown at two different magnifications). The product forms are very different. While LCO-5 has a smooth surface and non-agglomerated particles, Example 5a shows the coating of LiCoO ₂ particles with particulate islands. The SEM image of Comparative Example 5b clearly shows that the particles covered by the islands are destroyed by the ball rolling process. The particle size distribution measured using laser diffractometry in the dry media of Examples 5a and 5b is set forth in FIG. The particle size distribution of the test specimens processed by the ball mill shows that the average particle size decreases dramatically from 23 μm to 10 μm, and an increase in the fine particle fraction is clearly confirmed. Ball milling clearly destroys the particles, resulting in substantial exposure of the core material. This core material has a conductivity comparable to that of untreated LCO-5. Thus, the core of Example 5a has a conductivity of> 1 × 10 ⁻³ S / cm, while the shell has a conductivity of less than 1 × 10 ⁻⁷ S / cm. It is shown. The PSD also shows that there are a small amount of large particles due to the gentle agglomeration of the relatively sticky powder.

The conductivity of Example 5a at 25 ° C. and an applied pressure of 63 MPa was measured as 7.13 × 10 ⁻⁸ S / cm, which is 6 orders of magnitude less than that of uncoated LCO-5. The ball milled Comparative Example 5b is characterized by an increase in conductivity by 5 orders of magnitude compared to 5a. This result proves that the core has higher conductivity than the shell.

  Table 7 shows the test performance and conductivity of Example 5a, Comparative Example 5b, and LCO-5 with a coin battery. As shown in Examples 1 and 2 above, the capacity and energy loss rate of Example 5a (between 3.0-4.5V) is not coated, but at the same time the conductivity is reduced. This is a significant improvement compared to LCO-5. The electrochemical performance of the specimen of Comparative Example 5b is substantially impaired, which is considered to be due to the disappearance of the electronic insulating shell structure.

Comparative Example 6:
This example shows that prior art transition metal based oxide cathode materials cannot achieve low conductivity and good high voltage stability at the same time. The conductivity and electrochemical performance of several commercial products (Umicore (Korea)) are summarized in Table 8. These materials have the general composition Li _{1 + x} M _1-x O ₂ (x≈0.05, M = Ni _0.5 Mn _0.3 Co _0.2 for Comparative Example 6a, M = Ni ₁ // for Comparative Example 6b. ₃ Mn _1/3 Co _1/3 and Comparative Example 6c have M = Ni _0.8 Co _0.15 Al _0.05 ). In general, the conductivity of LiCoO ₂ is very sensitive to its lithium stoichiometry and is accepted to increase with lithium excess. Levasseur's paper # 2457 (Bodeaux University, 2001) shows that there is a two-digit difference in conductivity at room temperature between LiCoO ₂ with a stoichiometric excess of lithium and a stoichiometric one. It has been reported to exist. M.M. Menetrier, D.M. Carlier, M.C. Brangero and C.I. Delmas, Electrochemical and Solid-State Letters, 11 (11) A179-A182 (2008), reports a method for producing complex high stoichiometric LiCoO ₂ . The production of this high stoichiometric LiCoO ₂ specimen is reproduced and used to produce Comparative Example 6d.

Furthermore, the compression density was measured. This is because high compression density is important for cathode applications in high end use batteries. The compression density of Comparative Examples 6a-6d is at least 0.4 g / cm ³ lower than the example embodiment of the present invention, making these materials unsuitable for high end use batteries. The volume energy density achievable in practice (meaning the capacity achieved in a fixed volume of a fixed battery design) still remains slightly lower. Furthermore, these cathode materials are characterized by a conductivity of more than 10 ⁻⁵ S / cm. This is at least 2-3 orders of magnitude greater than the conductivity of the example cathode material of some embodiments of the invention.

Reference example 7:
This example shows that known transition metal based oxides can have a conductivity lower than 10 ^-5 S / cm and can support the presence of an electrically insulating transition metal based shell. is there.

Commercial MnOOH (Chuo Denki Kogyo Co., REX7a a display), (labeled Cosmo Chemical KA300, REX7b) commercially available TiO _2, a commercially available _{Fe 2 O 3 (Yukari Pure Chemicls} Co., REX7c a display), and commercially available Measure the conductivity of Co ₃ O ₄ (labeled Umicore, REX7d). The results are listed in Table 9.

All these materials are characterized by a conductivity of less than 10 ⁻⁵ S / cm. These conductivities are in the same range as those of the electronically insulating cathode material of the present invention and provide an example of a transition metal based shell having electrical insulation.

Comparative Example 8:
This example shows that insulating cathode materials with good performance are very difficult or impossible to achieve with inorganic coatings that are not based on transition metals. LiF is a suitable example for inorganic metal coatings of non-transition metals. A dense and fully coated LiF surface can be achieved by a PVDF-based manufacturing path. Details of the mechanism are described in the co-pending application PCT / EP2010 / 006352. Even a coating layer that is too thin to significantly reduce conductivity prevents Li diffusion. The electrically insulating shell needs to have sufficient ionic conductivity. If the shell is not based on a transition metal (LiF coating), the ionic conductivity is too low and the cathode does not work well.

LiF coated LiCoO ₂ is produced by the following method: A production specimen of lithium cobalt oxide material is used as the cathode precursor. Its composition is 1 mol% Mg-doped LiCoO ₂ with an average particle size of 17 μm. 1000 g of this precursor powder and 10 g (1% by weight) of PVDF powder are carefully mixed using a Henschel type mixer. Similarly, another specimen is produced using a third amount of PVDF (0.3% by weight). The final specimen (150 g) is produced by heat treatment in air. During a 9 hour heat treatment at 300 ° C. and 350 ° C., initially the PDVF melts and completely wets the surface. Subsequently, the decomposition of PVDF proceeds, and fluorine reacts with lithium to form a dense LiF layer. 1 wt% PVDF corresponds to about 3 mol% LiF.

  The LiF layer is fully developed at 300 ° C. (Comparative Example 8b). The coin cell test shows very low performance. The capacity is very small and extreme polarization is observed. These results are not the results of the inferior coin battery preparation (the two batteries show the same result) but have been reproduced several times using different specimens. When much less PVDF is used (0.3% by weight), full capacity is achieved, but the specimen still shows extreme polarization (Comparative Example 8d). However, the coating layer is too thin or too weak to achieve low conductivity. The inferior cycle data can be compared with a test specimen produced at 150 ° C. (using 1% by weight of PVDF: Comparative Example 8a), in which case PVDF melts but does not react, thus forming LiF. And as a result, much higher capacity and rate performance is achieved. Table 10 summarizes the data, and FIG. 10 compares the first charge / discharge (C / 10 rate). Similar results are obtained with other inorganic transition metal-free coatings. Clearly, the LiF inorganic layer is completely closed so that Li cannot penetrate across the solid interface of the electrolyte. This situation is quite different in the embodiments of the present invention, where the insulating shell has a high ionic conductivity, which is evidenced by a large rate performance.

Example 9
This example shows that LiCoO ₂ doped with magnesium and aluminum coated with islands and having electronic insulating properties has excellent cycle stability in coin cells.

Example 9 (Ex9) Preparation 1 mol% magnesium and 1 mol% aluminum doped cobalt tetroxide (Co ₃ O ₄ ) powder is used as a precursor for LiCoO ₂ (from Umicore, Korea) Commercial products). Magnesium and aluminum doped LiCoO ₂ (designated LCO-6) is obtained by mixing the precursor and Li ₂ CO ₃ using standard high temperature solid phase synthesis and has an average particle size of 20 μm. Achieved. Ex9 is produced in a pilot line by sintering LCO-6 and MOOH (M = Ni _0.55 Mn _0.30 Co _0.15 ) in a 95: 5 molar ratio and adding appropriate lithium carbonate. Conductivity of less than 10 ^-8 S / cm is achieved. The average particle size of Ex9 is 20 μm. In this case, the conductivity under an applied voltage of 63 MPa is measured as 4.40 × 10 ⁻⁸ S / cm. The performance of the Ex9 coin cell is listed in Table 11 and exhibits excellent electrochemical properties.

The compression density is measured by applying 1.58 ton / cm ² to the obtained powder. The compression density is high, 3.82 g / cm ³ , and this high value, together with good electrochemical performance, indicates that these cathodes are excellent candidates for high end use batteries.

Example 10: High Rate Performance Material It is accepted that a high rate performance material should be a combination of high electronic and ionic conductivity. The latter is usually achieved by reducing the particle size and increasing the specific surface area (BET) of the particle to facilitate lithium diffusion within the particle. However, the increase in specific surface area is not desirable because it promotes oxidation of the electrolyte and creates safety problems, further limiting its practical application.

This example demonstrates the rate performance and high voltage stability of co-sintered LiCoO ₂ , characterized by a smaller particle size than the previous example, and increases when conductivity is reduced, At the same time, the BET value may be 1 m ² / g and in this case 0.4 m ² / g. The enhanced performance of co-sintered LiCoO ₂ is achieved by controlling the lithium stoichiometry.

Production of LCO-10: LiCoO ₂ (denoted LCO-10) is obtained by mixing Co ₃ O ₄ and Li ₂ CO ₃ using standard high temperature solid phase synthesis, with a 6.1 μm Average particle size is achieved.

Preparation of Example 10: The final cathode powder material was a transition metal oxyhydroxide (M = Ni _0.55 ) mixed with 95.3% by weight LiCoO ₂ (LCO-10) and 4.70% by weight MOOH. Mn _0.30 Co _0.15 ) and a predefined amount of Li ₂ CO ₃ . Examples 10a, 10b, 10c and 10d are prepared according to the description in Table 12 and are mixed well to produce a uniform feed mixture. This mixture is charged into an alumina crucible and heated at 1000 ° C. for 8 hours under constant air flow. After cooling, the resulting powder is classified to achieve a final average particle size of 6.6 μm. The powder properties were measured and are listed in Table 13.

The cathode material was further mounted on a coin cell for electrochemical characterization. The active material loading of the cathode electrode is about 4 mg / cm ² . In this example, and below, 10C and 20C rate performance was measured at 4.4V using a specific capacity of 160 mAh / g to determine the discharge rate current. The parameters for these tests are listed below:

  The following definitions are used for data analysis: Q: capacity, D: discharge, C: charge, and the numbers after it are the numbers indicating the number of cycles.

The initial discharge capacity DQ1 is measured during the first cycle in the range of 4.4V to 3.0V at 0.1C,
The rate performance is DQi / DQ1 × 100, where the rate is 1C for i = 2, 5C for i = 3, 10C for i = 4, 15C for i = 5, and i = 6 is 20C,
The irreversible capacity Qirr (%) is (CQ1-DQ1) / CQ1 × 100.
-Capacity loss rate at 1C per 100 cycles Qfad. Is (1−DQ56 / DQ7) × 2, and energy loss rate: instead of the discharge capacity QD, discharge energy (capacity × average discharge voltage) is used.

  Table 14 summarizes the rate performance of Examples 10a-10d and LCO-10 at 4.4V. Evaluation of the rate performance of Examples 10a-10d as a function of conductivity and 20C for LCO-10 is shown in FIG.

  It is clearly observed that better 10C and 20C rate performance is obtained with respect to reduced conductivity. The average discharge voltage at 20C of Examples 10a to 10d is significantly increased by at least 0.1 V compared to LCO-10. Materials that characterize the 10C and 20C rate capacity increases and the 20C average discharge voltage increase are highly desirable. This is because they produce higher electrical energy (Wh / g) and, when combined with high compression density, produce higher volumetric energy (Wh / L). Such materials as illustrated in Examples 10a-10d are suitable candidates for applications requiring high power, such as electric vehicles and electric tools.

  The high voltage performance of Examples 10a, 10c, and 10d, and LCO-10 is shown in Table 15.

  The relationship between conductivity and the energy loss rate at 4.5V at 1C is shown in FIG. The conductivity of Examples 10a-10d is 3-4 orders of magnitude less than that of LCO-10 in the initial state. The high voltage 1C rate performance, capacity loss and energy loss rate of Examples 10a-10d are dramatically improved compared to LCO-10. For Examples 10a-10d, the conductivity increases with the addition of lithium. At the same time, both capacity loss and energy loss rate are compromised. The reduction in resistance correlates well with the 4.5V stability improvement and rate performance. Examples 10a, b, c and d are insulating materials and are examples of embodiments of the present invention.

Example 11: High Rate Performance Material This example shows that the rate performance and high voltage stability of co-sintered LiCoO ₂ has reduced conductivity and at the same time a BET value below 1 m ² / g and in this case It shows an increase when it is lower than 0.4 m ² / g. The enhanced performance of Example 11 is achieved by controlling the lithium stoichiometry.

Preparation of Example 11: The cathode powder material was a transition metal oxyhydroxide (M = Ni _0.55 Mn _0.30 Co) mixed with 95.3% by mass LiCoO ₂ (LCO-10) and 4.70% by mass MOOH. Manufactured by mixing with _0.15 ). The addition of lithium carbonate is determined to achieve a conductivity of less than 10 ^-7 S / cm. 50 kg of the mixture is thoroughly mixed to form a uniform formulation, charged into an alumina crucible, and then heated at 1000 ° C. for 8 hours under constant air flow. After cooling, the resulting powder is classified to achieve a final average particle size of 6.6 μm. The compression density of Example 11 is 3.4 g / cm ³ . The properties of the powder were measured and listed in Table 16.

  The cathode material was further mounted in a coin cell and subjected to electrochemical characterization. Table 17 summarizes the rate performance of Example 11 and LCO-10 at 4.4V.

  It is clearly observed that better 10C and 20C rate performance is obtained with respect to reduced conductivity. The average discharge voltage at 20C of Example 11 is significantly increased by at least 0.16V compared to LCO-10.

  The high voltage performance of 4.6V and 4.5V of Example 11 is shown in Table 18. The conductivity of Example 11 is 3-4 orders of magnitude lower than the initial LCO-10. The high voltage 1C rate performance, capacity loss and energy loss rate of Example 11 are dramatically improved compared to LCO-10.

  The reduction in resistance of Example 11 correlates well with the 4.6V and 4.5V stability improvements and the 10C and 20C rate performance increases. Example 11 is an insulating cathode material and provides an example of an embodiment of the present invention.

  Although the foregoing has shown and described specific embodiments and / or details of the invention, the application of the principles of the invention has been illustrated and described as more fully described in the claims. Or any other method known to those skilled in the art (including any and all equivalents) and should be understood from such principles to be used in accordance with the principles of the present invention. It does not leave.

Claims (12)

Lithium metal oxide powder for use as a cathode material in a rechargeable battery, wherein the lithium metal oxide has the general formula xLiCoO _2. (1-x) M _y O _{z wherein} 0.1 < x <a 1,0.5 <z / y ≦ 2, and M is 'made, M' Li and M = Ni _a Mn _b Co a _{c Ti d Mg e, a +} b + c + d + e = 1, a + b> 0. 5 and c ≧ 0, d ≧ 0, e> 0], and the powder further comprises Mg or Mg and Al and / or Ti as dopants . When used as an active material in a cathode that is cycled at 3.0 to 4.5 V vs. Li ⁺ / Li at a C / 10 discharge rate at 25 ° C. And a reversible electrode capacity of at least 180 mAh / g, and the powder has a conductivity of less than 10 ⁻⁵ S / cm when compressed at 63.7 MPa at 25 ° C., and The powder comprises a core and a shell, wherein the core has a conductivity greater than 1 × 10 ⁻³ S / cm and the shell has a conductivity less than 1 × 10 ⁻⁶ S / cm, The powder contains LiCoO ₂ particles with Mn and Ni, the particles have multiple islands enriched in Mn and Ni on their surface, the islands being higher than in the bulk of the particles. And the island has at least 5 mol% Mn Containing lithium metal oxide powder. The lithium metal oxide powder according to claim 1, wherein the islands enriched with Mn and Ni have a thickness of at least 100 nm and cover less than 70% of the surface of the LiCoO ₂ particles with Mn and Ni. . 3. The lithium metal oxide powder according to claim 1, wherein the Mn concentration in the island is at least 4 mol% higher than the Mn concentration in the bulk of the LiCoO ₂ particles having Mn and Ni. Lithium according to any one of claims 1 to 3, wherein the Ni concentration in the Mn and Ni-enriched island is at least 2 mol% higher than the Ni concentration in the bulk of the LiCoO ₂ particles with Mn and Ni. Metal oxide powder. Lithium metal oxide powder according to any one of claims 1 to 4, wherein the LiCoO ₂ particles with Mn and Ni contain at least 3 mol% of both Ni and Mn. 6. The lithium metal oxide powder according to claim 1, wherein the particle size distribution of LiCoO ₂ particles having Mn and Ni has a d50 greater than 10 μm.   The lithium metal oxidation according to any one of claims 1 to 6, which contains less than 1 mol% of one or more dopants selected from the group consisting of Be, B, Ca, Zr, S, F and P. Powder. Having a compression density of at least 3.5 g / cm ^3, the lithium metal oxide powder of any one of claims 1 to 7. The lithium metal oxide powder according to any one of claims 1 to 8, which has a compression density of at least 3.7 g / cm ³ .   An electrochemical cell having a cathode containing the lithium metal oxide powder according to any one of claims 1 to 9 as an active material.   Use of a lithium metal oxide powder according to any one of claims 1 to 9 in the form of a mixture as cathode material in a rechargeable battery, the mixture further comprising a conductive additive. Use of the lithium metal oxide powder according to any one of claims 1 to 9.   12. Use according to claim 11, wherein the mixture contains at least 1% by weight of a conductive additive.