Cathode materials for secondary batteries
A cathode active material includes a composition expressed as: Li 1+β (Ni x Mn y Co z ) M1 α (Ni x′ Mn y′ Co z′ ) M2 1-α O 2 ; or Na 1+β (Ni x Mn y Co z ) M1 α (Ni x′ Mn y′ Co z′ ) M2 1-α O 2 ; where: M1 represents a core composition comprising of Ni, Mn, and/or Co or a combination of at two of thereof; M2 represents a surface composition having at least 50% Co, and, optionally Ni and/or Mn; the structure of M2 may be a composite structure and includes a rock-salt or disordered rock-salt phase; 0.5≤α<1, 0≤x≤1, 0≤y≤0.5, 0≤z≤1, 0≤x′≤0.5, 0≤y′≤0.5, 0.5≤z′≤1, and −0.1≤β≤0.1; the sum of x, y and z is 0.9-1.1, and the sum of x′, y′ and z′ is 0.9-1.1.
1. A cathode active material comprising:
a core portion comprising: Li 1+β (Ni x Mn y Co z ) M1 O 2 ; and
a surface portion comprising Li 1+β′ (Ni x′ Mn y′ Co z′ ) M2 O 2 ; or
a core portion comprising Na 1+β (Ni x Mn y Co z ) M1 O 2 ; and
a surface portion comprising Na 1+β′ (Ni x′ Mn y′ Co z′ ) M2 O 2 ;
wherein:
the cathode active material comprises particles having a generally spherical morphology and a vector radius defined from a core of each particle to the surface of each particle;
the surface composition comprises at least 50% Co;
the structure of M2 comprises a disordered rock-salt phase;
0≤x≤1, 0≤y≤0.5, 0≤z≤0.4, 0≤x′≤0.5, 0≤y′≤0.5, 0.5≤z′≤1, −0.1≤β<0.1 and −0.1≤β′<0.1;
the sum of x, y and z is 0.9-1.1, and the sum of x′, y′ and z′ is 0.9-1.1;
the Ni concentration continuously decreases along the vector radius of each particle;
the Mn concentration continuously decreases along the vector radius of each particle; and
the Co concentration continuously increases along the vector radius of each particle.
2. The cathode active material of claim 1 , wherein 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4, 0≤x′≤0.5, 0≤y′≤0.5, and 0.6≤z′≤1.
3. The cathode active material of claim 1 , wherein M2 comprises from about 60 mol % to about 90 mol % Co.
4. The cathode material of claim 1 , wherein the composite structure of M1 is a layered structure and/or a spinel structure nearer a central portion of the particle.
5. The cathode active material of claim 1 , wherein a concentration of any metals changes by one or more slopes.
6. The cathode active material of claim 1 further comprising a dopant cation.
7. The cathode active material of claim 1 further comprising a surface coating on the particle.
8. The cathode active material of claim 7 , wherein the surface coating comprises a metal oxide, a metal fluoride, a metal phosphate, a conductive carbon coating, a conductive polymer, or a combination of any two or more thereof.
9. A cathode active material comprising:
a core portion comprising: Li 1+β (Ni x Mn y Co z ) M1 O 2 ; and
a surface portion comprising Li 1+β′ (Ni x′ Mn y′ Co z′ ) M2 O 2 ; or
a core portion comprising Na 1+β (Ni x Mn y Co z ) M1 O 2 ; and
a surface portion comprising Na 1+β′ (Ni x′ Mn y′ Co z′ ) M2 O 2 ;
wherein:
the cathode active material comprises particles having a generally spherical morphology and a vector radius defined from a core of each particle to the surface of each particle;
the surface composition comprises from about 60% Co to about 90 mol % Co;
the structure of M2 comprises a disordered rock-salt phase;
0≤x≤1, 0≤y≤0.5, 0≤z≤0.4, 0≤x′≤0.5, 0≤y′≤0.5, 0.5≤z′≤1, −0.1≤β<0.1 and 0<β′<0.1;
the sum of x, y and z is 0.9-1.1, and the sum of x′, y′ and z′ is 0.9-1.1;
the Ni concentration continuously decreases along the vector radius of each particle;
the Mn concentration continuously decreases along the vector radius of each particle; and
the Co concentration continuously increases along the vector radius of each particle.
10. The cathode active material of claim 8 , wherein the surface coating comprises a conductive polymer comprising poly(3,4-ethylenedioxythiophene).